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Monday, February 24, 2014

Intersection Of Nutrient Limitation Biomes In The Equatorial Pacific Ocean As Detected By Quantitation Of Proteomic Biomarkers
The extent marine primary productivity is largely controlled by the scarcity of nutrients and micronutrients, yet our understanding of the extent of these limitations is informed by indirect surveys of nutrient fields and modeling studies. Direct observations of nutrient limitation have sparse geographical and depth coverage due to experimental difficulty and limited ship time. Using recent improvements in proteomic mass spectrometry technologies and stable isotope labeled peptide standards, we measured cyanobacterial (primarily Prochlorococcus) nutrient biomarkers for iron, nitrogen, and phosphate across an ocean section in the Central Pacific Ocean. These biomarkers reveal transitions between the nitrogen-limited waters of the subtropical gyre to the iron-limited waters of the equatorial Pacific, broadly consistent with modeling studies. There was also significant structure in a phosphate stress biomarker suggestive of phosphate co-stress in these regions. Urea transporters were found in higher abundance in the North Pacific Gyre region demonstrating the ecological importance of organic nitrogen chemical species to the microbial loop. Iron limitation continues into the South Pacific gyre, consistent with estimates of aeolian deposition. Together these results provide evidence for the expression of multiple biochemical adaptations nutrient scarcity across these biomes, and demonstrate that cyanobacterial populations in some locations were stressed for multiple nutrients simultaneously.
Speaker: Max Saito
Time: 8:30 a.m.
Location: 319 AB

Carbon Flux From Bio-Optical Profiling Floats: A Side-By-Side Comparison To Neutrally-Buoyant Sediment Traps
A mechanistic understanding of the ocean biological pump is limited by lack of carbon flux observations from the upper kilometer of the ocean. Development of autonomous sensors for particulate carbon flux could transformatively expand the number of available measurements. Transmissometers on autonomous profiling floats serve this purpose qualitatively as “optical sediment traps”; here we calibrate them against traditional sediment traps. We co-deployed transmissometer-equipped, neutrally-buoyant sediment traps (NBSTs) and bio-optical profiling floats during a series of 4 monthly cruises at the Bermuda Atlantic Timeseries Study (BATS) site. We compare the resulting, direct particulate carbon fluxes (from NBST samples) to simultaneously-observed, proxy measurements of particulate carbon flux (from transmissometers used as “optical sediment traps”). The resulting data set provides a preliminary calibration of the autonomous, optical carbon flux proxy. It also illustrates high spatiotemporal resolution variability in particulate carbon flux at BATS.
Speaker: Meg Estapa
Time: 9:00 a.m.
Location: 317 AB

Insights Into Carbon Cycling Along Line-P From Integration Of Microbial Metabolomics And Dissolved Organic Matter Composition
Dissolved organic matter (DOM) in marine systems is an important component of the global carbon cycle whose molecular-level composition is determined by a combination of abiotic and biotic factors related to sources, sinks and transformations. Here we examine the DOM composition along Line P in the eastern Pacific Ocean, collected during the interdisciplinary GeoMICS cruise in May 2012. We employ three mass spectrometric techniques designed to detect, identify and quantify known and unknown compounds within organic matter mixtures. We explore the shifts in DOM composition and cellular metabolites from the coast to the open ocean as well as down the depth profile at selected locations. We further explore the sources of DOM through comparison with culture-based investigations of metabolites exuded by phytoplankton and heterotrophic bacteria. Using multivariate statistical tools, we observe significant changes in compound distributions along horizontal and depth gradients. We explore the role microbes may play in these changes through integration of our three complementary datasets. These data provide important chemical contexts for an emerging systems-biology view of the ocean.
Speaker: Elizabeth B. Kujawinski
Time: 9:00 a.m.
Location: 319 AB

Submarine Groundwater Discharge As A Source Of Radioactivity To The Ocean From The Fukushima Nuclear Power Plant
The tsunami-damaged Fukushima Nuclear Power Plant (FNPP) remains to this day a source radioactivity to the ocean. This is evidenced by time-series cesium (Cs)- 134 and -137 activities that have remained elevated over ~two years and exceed background values in the coastal ocean off Japan. Though most of the Fukushima atmospheric fallout was believed to be over the ocean, fallout over land led to Cs enrichment in river runoff and contamination of surficial aquifers. Furthermore, groundwater is infiltrating the NPP reactor buildings at several hundred tons/day and being transformed into highly contaminated radioactive wastewater. While some of this wastewater is being stored in tanks for further treatment, TEPCO has acknowledged ongoing direct radionuclide inputs to the local aquifer with the potential for transport to the coastal ocean via submarine groundwater discharge (SGD). We present results from a May 2013 survey of the coastal waters and surficial aquifer surrounding the FNPP where we measured naturally occurring radium isotopes in order to quantify SGD for this region. SGD fluxes for the key radionuclides of concern (Cs isotopes, 90-Sr) will be presented in the context of other known sources of FNPP discharge.
Speaker: Matthew Charette
Time: 10:45 a.m.
Location: 314

Mixing Length And Horizontal Diffusion From Argo Observations In The Pacific Ocean
Horizontal stirring and diffusion result in fluctuations of temperature and salinity along isopycnals, which are readily observed by the Argo float array from the surface to 1000 m depth. This first analysis of smaller-scale spice fluctuations in Argo observations focuses on the Pacific Ocean and fluctuations at scales less than one month and 300 km. The geographic pattern of spice fluctuations compares favorably with the large-scale along-isopycnal spice gradient available to stir, so a mixing length framework for estimating horizontal diffusivity is appropriate for the majority of the Pacific Ocean. Mixing length estimates are largest in western boundary current regions and smallest in subpolar regions and bands about the equator, consistent with recent theoretical predictions. Combined with velocity fluctuations derived from satellite altimetry, horizontal diffusivity is estimated from the surface to 1000 m depth. Variations with depth and geographic location in along-isopycnal salinity fluctuations, mixing length, and horizontal diffusivity show how horizontal stirring varies with location, depth, mean velocity and tracer fields, and other relevant features of the ocean.
Speaker: Sylvia Cole
Time: 10:45 a.m.
Location: 315

Investigation Of Microbial Adherence And Virulence Factors Associated With Open-Ocean Derived Plastic Marine Debris: Vibrio Bacteria As A Model System
Plastic Marine Debris (PMD) persists much longer than any natural floating substrate and provides an attachment surface for thin layers of life (termed the Plastisphere). Our previous amplicon sequencing surveys of 16S rRNA genes have shown that Bacteria of the genus Vibrio can comprise a major portion of the Plastisphere – at times nearly 25% of the bacterial community. We adapted a 96-well plate format biofilm quantification assay to survey over 50 Vibrio spp. cultivars for attachment ability to various plastic resins. Some vibrios demonstrated cell density-dependent attachment and/or a preference for plastic resin type. Strikingly, ‘super-colonizer’ vibrios were discovered to form measureable biofilms on plastic in a matter of minutes. In general, biofilm formation phenotypes clustered within Heat Shock Protein 60 (HSP 60) gene phylogenies. We generated a metagenomic dataset of a Vibrio-dominated PMD sample and analyzed it for key adherence and virulence genes. Characterizing Vibrio attachment to plastic will provide a model for PMD colonization and clues to the ecological function of this prevalent group of Plastisphere inhabitants.
Speaker: Tracy Mincer
Time: 11:00 a.m.
Location: 316 B

Observational Evidence For Fukushima Radionuclide Signals In The North Pacific Two Years After The Release
Contaminated waters from the Fukushima nuclear power plant were discharged directly into the North Pacific Ocean in March 2011. Although the coastal current system in this region and the time scale of water exchange with the open ocean is not well understood, both observational evidence and numerical model simulations indicate relatively rapid advection of contaminants eastward into the highly energetic mixed water region in the confluence of the Kuroshio and Oyashio currents. In this investigation, we use radionuclides of Fukushima origin as a tracer to understand the North Pacific circulation and mixing process 2 years after the release. Depth profiles from the March-May 2013 30N Climate Variability and Predictability and Carbon (CLIVAR) repeat transect and recently collected coastal cruise hydrography data are examined to track the radionuclide penetration into the subsurface ocean and the subduction pathways along isopycnal surfaces.
Speaker: Sachiko Yoshida
Time: 11:00 a.m.
Location: 314

Submesoscale Biological Hotspots: Insights From A High Resolution Towed Oxygen Profiler And From Surface O2/Ar Ratios
Kilometer-scale records of rates of net community production have shown order of magnitude variations in distances as short as several kilometers. Analysis of satellite records of chlorophyll reveal strong submesoscale variability in the surface ocean. It has been hypothesized that frontal convergence and divergence zones can stimulate phytoplankton productivity and export production. Here, we present data from an undulating, towed video plankton recorder (VPR-II) in the tropical Atlantic. The VPR-II collected profiles of oxygen, fluorescence, temperature and salinity in the upper 140 m of the water column at a spatial resolution of <2 km. The data revealed remarkable "hotspots" in biological productivity, i.e. locations in time and space where intense submesoscale upwelling led to elevated fluorescence but decreased oxygen due to upwelled oxygen debt. We statistically characterized the distribution of these hotspots and formulated a conceptual model outlining their possible generation and decline. Simultaneous measurements of O2/Ar in the mixed layer from a shipboard mass spectrometer quantified rates of surface net community production. We thus linked the subsurface biological hotspots to surface expression of changes in rates of biological productivity.
Speaker: Rachel Stanley
Time: 11:15 a.m
Location: 313 A

On 'Q' And The Localness Of Internal Tide Dissipation
The fraction 'Q' of internal wave energy locally dissipated near its source appears in several parameterizations of internal tide-driven mixing over rough topography. The effects of bottom scattering and nonlinear interactions on q are considered for the case of spatially variable topography. Isolated low-mode sources such as the Hawaiian ridge can have very low Q, consistent with previous estimates. Over extended features such as the mid Atlantic ridge, it is shown that Q is scale dependent, and a significantly larger fraction of the internal tide than the previously estimated Q ≈ 30% can be trapped within a few mode-1 wavelengths of its generation site. Total dissipation of internal tide energy can also be significantly larger than dissipation associated with the locally generated tide, leading to erroneously large estimates of Q. Alternatives for characterizing the localness of internal tide dissipation are discussed.
Speaker: Stephen Jayne
Time: 11:30 a.m.
Location: 316 C

The Kuroshio Current, Internal Waves And Turbulence In The Luzon Strait
The waters of the Luzon Strait are among the most energetic environments in the global ocean. Tidal currents, strong stratification and steep ridge topography give rise to enormous internal waves. In addition, the Kuroshio Current often drives strong flow through the area. Not surprisingly, this environment supports exceptional turbulent energy levels. Here, we present the first full-depth, direct measurements of turbulence along the Lan-Yu Ridge of the Luzon Straits over a spring-neap cycle of tidal forcing. Our findings suggest that the Kuroshio Current plays several important roles in the internal wave physics of the Luzon Strait: 1) the Kuroshio is the primary process setting the stratification at the site, 2) The Kuroshio modulates the total barotropic velocity responsible for wave generation, and 3) the shear associated with the Kuroshio serves as a catalyst for instabilities that drive turbulence occurring at mid-depth. The turbulent mixing at mid-depth occurs in the stratification maximum of the Kuroshio layer, providing water-mass conversion of consequence to the entire Pacific Basin.
Speaker: Louis St. Laurent
Time: 2:00 p.m.
Location: 316 C

Physical Aggregation Of Buoyant Trichodesmium Spp. Colonies Through Eddy/Wind Interaction: Observations And Modeling
Abundances and distributions of Trichodesmium colonies of raft, puff, and bowtie morphologies were observed by Video Plankton Recorder in Fall 2010 and Spring 2011 in the southwestern North Atlantic. Raft abundances peaked highest in the water column, with consistent near-surface maxima. Patches of elevated near-surface raft abundance often coincided with cyclonic eddies, in contrast to the association of Trichodesmium colonies with anticyclones previously observed farther north in the subtropical North Atlantic. Physical aggregation through Ekman flux convergence is proposed as a mechanism producing elevated Trichodesmium raft abundances in cyclones. This mechanism is evaluated through simulations of a buoyant tracer, representing Trichodesmium rafts, in cyclones and anticyclones with and without eddy-wind interaction. Simulations confirm the potential of the eddy/wind interaction to produce abundance
Speaker: Elise Olson
Time: 2:30 p.m.
Location: 313 B

An Undercurrent Of Change: Assessing Potential Natural Mitigation Of Ocean Warming At The U.S. Pacific Remote Islands Marine National Monument
Upwelling across the tropical Pacific is projected to weaken in accordance with that of atmospheric overturning, enhancing the warming and nutrient decline relative to other regions in response to anthropogenic forcing. MPAs may not provide refuge from the anticipated rate of large-scale changes, which could exceed the capacity of ecosystems and commercial interests that depend on them to adapt. Here we build on Karnauskas and Cohen (2012) to assess the potential for anthropogenic changes in ocean circulation to mitigate warming across the U.S. Pacific Remote Islands by combining in situ data with climate models. Applied to future projections from IPCC AR5 global climate models, our results for Jarvis Island suggests that between 5-15% of the regional warming will be mitigated by a strengthening Equatorial Undercurrent (EUC), or up to 35% if observed EUC trends can be extrapolated. At Baker and Howland, the mitigation effect is smaller. The potential mitigation at these islands is apparently smaller than at the Gilbert Islands (7-45%). Whether observed trends or model projections prevail will likely decide the fate of marine ecosystems in the tropical Pacific.
Speaker: Kristopher Karnauskas
Time: 2:45 p.m.
Location: 317 AB

Sediment Transport In A Tidal River And Estuary During Extreme Discharge Events
Tropical Storms Irene and Lee in 2011 produced intense precipitation and flooding in the U.S. Northeast, including the Hudson River watershed. Sediment input to the Hudson River was approximately 2.7 Mt, about 5 times the long-term annual average. Rather than the common assumption that sediment is predominantly trapped in the estuary, observations and model results indicate that ~2/3 of the new sediment remained trapped in the tidal freshwater river more than 1 month after the storms, and only about 1/5 of the new sediment reaching the saline estuary. Seaward transport during the periods of elevated discharge carried only a small fraction of the new sediment through the freshwater portion of the tidal river, and seaward fluxes decreased substantially upon the return to predominantly tidal forcing. High sediment concentrations were observed in the estuary, but the model results suggest this was predominantly due to remobilization of bed sediment. Spatially localized deposits of new and remobilized sediment were consistent with longer term depositional records. The results indicate that tidal rivers can intercept (at least temporarily) delivery of terrigenous sediment to the marine environment during major flow events.
Speaker: David Ralston
Time: 3:30 p.m.
Location: 312

The Role Of Basin-Scale Climate Variability In The Demise Of The Caribbean Reefs
Coral cover across the Caribbean declined by 80% since the 1970’s. Growth rates of the dominant reef-building coral species, measured in 3-D CAT scan images of skeletal cores, have declined in concert, by as much as 50% over the corresponding time period. Extending the coral records back in time reveals multi-decadal oscillations in growth that correlate strongly with the Atlantic Multidecadal Oscillation (AMO), a basin-wide mode of SST variability linked to shifts in marine productivity and fisheries. Culture experiments and field data show that skeletal extension is driven by coral tissue thickness, an index of coral nutrition. Using output from the MOM3 physical model coupled to the TOPAZ biogeochemical model we explored changes in mixed layer depth, nutrients and productivity, and their influence on coral growth across the Caribbean since 1954. We find a consistently strong, positive correlation between surface nitrate concentrations and coral growth across the 7 Caribbean sites studied. Our results suggest that basin-scale changes in ocean circulation, driven by large scale, low frequency modes of climate variability played a major role in the demise of Caribbean reefs.
Speaker: Anne Cohen
Time: 3:45 p.m.
Location: 317 AB

Imprint Of The Nitrogen Cycle On Deep Subsurface Autotrophy
While the role of water column microbial communities in the global nitrogen cycle has been the focus of intense study for many decades, nitrogen cycling within the deep biosphere remains virtually unexplored. Here we present a glimpse into the subsurface nitrogen cycle from the perspective of the nitrate dual isotopic composition of porewaters underlying the North Pond site on the seafloor of the oligotrophic North Atlantic. Large inventories of porewater nitrate far exceed concentrations found in bottom waters and persist across large depths where oxygen drops below detection. Coupled nitrogen and oxygen isotopic composition suggests pervasive overlap of nitrification and denitrification across a wide range of oxygen concentrations. Results of a steady-state box model suggest that while rates of nitrification exceed denitrification by up to a factor of 10 in the upper 20m, rates of nitrification and denitrification are more similar deeper into zones of anoxic sediments. The subsurface biosphere of North Pond appears dominated by an autotrophic nitrogen cycle, which may account for more than 20% of total oxygen consumption and a large fraction of subsurface carbon fixation.
Speaker: Scott Wankel
Time: 3:45 p.m.
Location: 301 AB

Tuesday, February 25, 2014

Central Equatorial Pacific Records Of Equatorial Undercurrent Variability
Where the Pacific Equatorial Undercurrent (EUC) encounters coral reef islands, topographic upwelling forces cool, nutrient-rich water to the surface. GCMs project a strengthening of the EUC over this century, enhanced upwelling and mitigation, at least in part, of surface ocean warming for a handful of equatorial coral reef systems [Karnauskas and Cohen, 2012]. A recent analysis of the Simple Ocean Data Assimilation (SODA) product detected a 47% increase in EUC’s core velocity since 1871 [Drenkard and Karnauskas, 2013]. However, the quality of instrumental data used in the SODA reanalysis decreases back through time. Proxy records that provide an independent record of EUC strength can be used to confirm the apparent increase in EUC strength. Upwelling of EUC water on the west side of Jarvis Island creates a cross-island temperature difference that is strongly correlated with EUC velocity. We exploit existing 10-yr records of in situ temperature to evaluate the ability of coral-based proxy records, generated for each side of Jarvis Island, to capture the cross-island temperature difference and enable reconstruction of past EUC velocity.
Speaker: Alice Alpert
Time: 8:30 a.m.
Location: 313 B

Using Metabolomics To Characterize Organic Matter From Marine Phytoplankton
The fixation of inorganic carbon into organic carbon by autotrophic microbes is a central component of the global carbon cycle. Recent advances in mass spectrometry have allowed the characterization of organic compounds (‘metabolites’) produced by these organisms. However, significant computational challenges remain in (1) the identification of individual organic compounds and (2) efficient analysis across multiple experiments. In the present project, we established a database designed to collate metabolites from different experiments. We populated the database with metabolites from culture experiments conducted with Thalassiosira pseudonana and queried the database to define metabolites which warranted additional investigation. This combination of computational developments and laboratory experiments will improve our ability to identify metabolites from marine microorganisms. More importantly, our results will allow us track the impact of phytoplankton on dissolved organic matter in aquatic systems.
Speaker: Krista Longnecker
Time: 9:45 a.m.
Location: 317 AB

Are Modeled Rates Of Photoproduction Of Co From Cdom And Its Microbial Oxidation Overestimated By Two-Fold? Constraints From Three In-Situ Incubation Methods
CO cycle models take the rates of its microbial oxidation (major sink) as equaling outgassing-corrected night time CO loss rates. However, larger or smaller rates seem plausible: some bacteria are light-inhibited; those that are not can access higher daytime CO concentrations. In-situ incubations using 14-CO (Limnol. Oceanogr., 50(4), 2005, 1205-1212) found daytime rates ~10x below night rates, with interesting implications for the modeling, microbiology, photoproduction, and oceanic CO cycle. 14-CO night rates were also 3-4x lower than those measured in situ at night. (Limnol. Oceanogr., 53(2), 2008, 835–850), which seem reliable in summer (cv 15%). Concurrent in-situ incubations of cyanide-poisoned vs. unpoisoned water in daylight imply higher rates, but are complicated by a new-found, significant role for particulate CO photoproduction. A novel new method also supports higher rates, utilizing differences in day-long CO column burden increases, despite identical photoproductions, in unamended samples with the dawn CO burden either present or removed by air purging. Additionally, optical modeling of in situ incubation data yields apparent quantum yield spectra and depth-dependences for various sample types.
Speaker: Oliver C. Zafiriou            
Time: 2:15 p.m.
Location: 317 AB

Microbial Eukaryotic Community Structure And Dynamics In A Seasonally Anoxic Fjord, Saanich Inlet
Marine oxygen minimum zones (OMZs) are widespread regions of low dissolved oxygen concentration found throughout the global ocean. Changes in ocean temperature and circulation patterns compounded by human activities are leading to oxygen minimum zone expansion with concomitant alteration in nutrient and climate active trace gas cycling. Here we present a high-resolution study of the responses of microbial eukaryotes to oxygen-deficiency based on analysis of small subunit ribosomal RNA gene pyrotags amplified from water samples collected monthly for a year at sixteen depths in Saanich Inlet, a seasonally anoxic fjord on the coast of Vancouver Island British Columbia. Multivariate statistical analysis of the pyrotag data identifies distinct shifts in taxonomic composition occurring over the annual stratification cycle, captures bloom dynamics, and reveals patterns of redox-driven niche specialization relevant to nutrient and climate active trace gas cycling extensible to expanding coastal and open ocean OMZs.
Speaker: Virginia P. Edgcomb
Time: 2:45 p.m.
Location: 313 A

Ocean Circulation Between Artists, Scientists And The Public
"Synergy" was a project in eastern Massachusetts that engaged 8 pairs of artists and ocean scientists in collaborative acts of creation around themes of ocean acidification, climate change, and marine pollution. All of the scientists offered source material to the artists, and some of them had a hand in making the artwork. The resulting works of art were inspired by ocean science, and ranged from 12-foot-tall paintings to a woven amusement park sculpture to a rosette of several hundred acid-worn eggshells. All the pieces were installed in a 4-month exhibit at Boston's Museum of Science. In addition, we created short video portraits of each artist/scientist pair to show at the museum and online. The artists and scientists interacted with one another over 9 months, and many of the pairs built meaningful and productive relationships that extended beyond the exhibition. The resulting installation offered a set of strong aesthetic hooks to inspire a lay audience to think about our ocean and the problems it faces in a bold and memorable way.
http://synergyexhibit.org/
Speaker: Ari Shapiro
Time: 3:00 p.m.
Location: 318 AB

Using Spherical Displays To Inspire Students And Public Audiences To Learn About Deep Ocean Processes And Exploration
Spherical display systems, also known as digital globes, are new technologies that, in person or online, can inspire students and public audiences to learn about earth system processes. We will present a collaboration between the Woods Hole Oceanographic Institution and the Ocean Explorium in New Bedford, hosting a Magic Planet and Science On a Sphere® (SOS), respectively. To educate and excite young learners and their chaperones about exploration in the deep ocean and the geophysical and biological processes found there, we are creating content for spherical display systems using global datasets and imagery from deep-sea vehicles. We will share the collaborative process by which we developed two educational pieces, “Life without Sunlight” and “Smoke and Fire Underwater” – each focusing on a different set of Earth Science Literacy and Ocean Literacy Principles. Each educational piece is matched to a hands-on, K-12 field trip program at the Ocean Explorium, and a teacher professional development component. We will show how we are evaluating both the level of excitement generated by interacting with our materials and the knowledge gained within these literacy principles.
http://www.divediscover.whoi.edu/sos
Speaker: Stace Beaulieu
Time: 3:15 p.m.
Location: 304 AB

Wednesday, February 26, 2014

Moored Observations Of The North Icelandic Jet Upstream Of Denmark Strait
The North Icelandic Jet (NIJ) was discovered only a decade ago and constitutes a new and significant export pathway for dense water from the Nordic Seas through the Denmark Strait. Observations to date, however, have been limited to synoptic sections taken across the current, mostly in summertime. This has meant that although the current has been established as a robust feature (transporting about half of the overflow waters to the sill) little is known about its variability or dynamics. To this end, we present data from a year-long mooring deployment across the NIJ which includes extensive hydrographic and velocity measurements from vertical profiling instruments. We demonstrate that the current is present in all seasons of the year and transports a significant quantity of the densest Denmark Strait Overflow water toward the sill. The current displays marked variability on sub-weekly scales, which is related to its location on the continental slope as well as the presence of the nearby East Greenland Current. The causes of this high-frequency variability are explored, including the roles of topographic waves and hydraulic control of the overflow plume.
Speaker: Ben Harden
Time: 8:30 a.m.
Location: 312

Evidence Of Direct Exchange Of Low Salinity Intermediate Waters Across The Iceland-Faroe Front In Winter
A previously undocumented equatorward flux of anomalously fresh water across the Iceland-Faroe Front (IFF) and Ridge (IFR) is observed in three years of wintertime autonomous glider observations (10,100 total profiles). A low salinity water mass of Nordic Seas origin subducts along isopycnals from the surface at the IFF to ~600 m depth south of the IFR crest. The exchange is seen in early winter (Dec., Jan.) subsequent to extreme convective mixing (up to 600 m) on the Atlantic side of the IFF. Isopycnal and diapycnal mixing with the Subpolar Mode Water present south of the IFR modifies the subducted water mass substantially. Cross frontal exchanges are additionally illustrated by the patchy northward advection of low oxygen intermediate waters from the Iceland Basin permanent pycnocline. We investigate possible frontal mechanisms driving subduction of the low salinity water at the IFF, and relate these mechanisms to the seasonality of the observed signal.
Speaker: Nick Beaird
Time: 9:00 a.m.
Location: 312

Evolution Of Water Masses In Barrow Canyon During Summer/Fall: First Results From The Dbo International Transects 2010-13
Barrow Canyon, in the northeast Chukchi Sea, is a major conduit by which Pacific-origin waters enter the Arctic basin. Starting in 2010, as part of the Distributed Biological Observatory (DBO) program, hydrographic transects across the canyon have been occupied by international ships of opportunity. To date there have been 28 occupations during the months of June-October from 2010-2013, providing an unprecedented high-resolution view of the Pacific-origin water flowing through the canyon. In this study we use the temperature and salinity data to characterize the evolution of hydrographic properties in the canyon from summer to early fall. The relative timing of the summer and winter water masses in the canyon is quantified, as are their characteristics and spatial distributions. The role of wind forcing is investigated using atmospheric data from the nearby Pt Barrow weather station. Clear patterns emerge in the hydrography of the canyon, including the seasonal appearance of the Alaskan Coastal Current and evidence of a slow pathway of winter water entering the western side of the canyon as the summer season progresses. Using the three years of data the interannual variability is assessed, and the causes of the year-to-year variations are explored.
Speaker: Carolina Nobre
Time: 9:15 a.m.
Location: 316 A

Iron Supply And Demand In An Antarctic Shelf Ecosystem
With an annual primary production of ~20 Tg C yr^-1, the Ross Sea continental shelf sustains a rich marine ecosystem and provides a significant regional sink for atmospheric carbon dioxide. This phytoplankton production occurs mainly during the October-March period, within a polynya that opens to a maximum area of ~4 x 10^5 km^2. During this short growing season, surface macronutrient concentrations remain relatively high, and availability of dissolved iron (dFe), which can be drawn down to low concentrations (~0.1 nM) by mid-November, is thought to exert the major control on phytoplankton growth. Here we combine new data on the distribution of dFe throughout the water column, high-resolution model simulations of ice melt and regional circulation, and satellite-based estimates of primary production to quantify iron supply and demand over the Ross Sea continental shelf. Our analysis suggests that the largest sources of dFe to the euphotic zone are wintertime mixing and melting sea ice, with a lesser input from intrusions of circumpolar deep water, and a small amount from melting glacial ice. Together these sources are in approximate balance with the dFe demand inferred from satellite-based productivity algorithms, although both supply and demand estimates have large uncertainties.
Speaker: Dennis McGillicuddy
Time: 9:15 a.m.
Location: 316 B

Observations Of Turbulence During Upper Ocean Stable Stratification
The turbulent characteristics of the upper few meters of the ocean have not been well measured. Novel instrumentation has recently allowed us to explore the turbulent characteristics of the near-surface layer. In particular, we have examined the microstructure properties of the stably stratified boundary layer during diurnal warming. During recent field campaigns, Slocum gliders with Rockland Scientific MicroRiders were deployed for roughly 30 total days collecting microstructure data (shear and temperature) of unprecedented quality in the surface layer of the ocean. Over the 30 days, there were 16 days with observable warming of over 0.25°C and 9 days with warming over 0.5°C. During these events, we find concentrated levels of dissipation within the stable layer, even during periods of very weak winds. We observed enhanced TKE dissipation signals 102-104 greater than expected values in the upper few meters of the ocean during days with warming greater than 0.25°C. In this talk we will investigate possible causes and effects of the observed interplay between turbulence and near-surface diurnal warming.
Speaker: AlecBogdanoff
Time: 9:15 a.m.
Location: 316 C

Transformation Of Atlantic Water In The Lofoten Basin From 2 Years Of Moored Data
The Lofoten Basin of the Nordic Seas is increasingly being recognized as an important component of the Atlantic Meridional Overturning Circulation. Large wintertime buoyancy loss and an energetic eddy field contribute to densification of warm Atlantic waters as they flow poleward. Despite this importance, details of the water mass transformation and transport within the region of closed topographic contours remain unclear. Using hydrographic and velocity data from a mooring deployed in the center of the Lofoten Basin from June 2010 to September 2012, we detail the mechanisms responsible for the seasonal cycle of convection and restratification in the basin. In particular, we focus on the influence of eddies and the role they play in the seasonal cycle.
Speaker: Clark Richards
Time: 9:45 a.m.
Location: 312

ROLE OF SHELFBREAK UPWELLING ON PRIMARY PRODUCTIVITY IN THE BEAUFORT AND CHUKCHI SEAS
There has been a significant increase in the productivity of phytoplankton in recent decades in the Pacific sector of the Arctic Ocean. At the same time, easterly winds have strengthened in the region. Here we investigate the ability of shelfbreak upwelling to trigger phytoplankton blooms via upward nitrate flux from the halocline, using a combination of in-situ mooring and shipboard data, atmospheric reanalysis fields, and simplified numerical simulations. An upwelling proxy is derived which indicates that the number and strength of upwelling events along the north slope of Alaska have increased over the last two decades. This is largely dictated by the behavior of the two atmospheric centers of action, the Beaufort High and Aleutian Low. Vertical velocities during the upwelling events flux nitrate into the euphotic zone which can account for new production on par with carbon fixed during the summer growing season in the absence of storms. A particular event in June 2011 on the Chukchi slope was associated with some of the highest chlorophyll values ever observed in the global ocean. A numerical simulation of this event reveals the physical mechanisms responsible for the shelfbreak upwelling, consistent with concurrent observations.
Speaker: Robert Pickart
Time: 10:45 a.m.
Location: 316 A

Estuarine And Coastal Shellfish And Polycyclic Aromatic Hydrocarbons: More Comprehensive Risk Assessments Needed
Polycyclic aromatic hydrocarbons (PAH) are organic chemicals of environmental concern that enter estuarine and coastal waters as a result of natural processes and human activities. PAH from oil spills and chronic releases of PAH from human sources accumulate in higher concentrations in estuarine sediments and shellfish in urban harbor areas, or nearby, compared to rural areas. Several of the PAH in shellfish can be measured quantitatively and regulatory agencies have calculated or estimated risk factors for human health for consumption of shellfish tissue containing these PAH. However, there are many more PAH in these tissues for which we do not yet make quantitative measurements and for which risk factors are not calculated. This is known by environmental organic chemists but often ignored in risk assessments and in related statements to the public. The challenge of a complex situation is there: for the scientific arena, for the science-policy-management arena, and for communication of a complex situation to the public. A response is needed to rectify this situation.
Speaker: John Farrington
Time: 11:15 a.m.
Location: 319 AB

Some New Perspectives On Frontal Air-Sea Exchange Over The Gulf Stream In Climode
The separated Gulf Stream (GS) is one of the ocean ‘hot spots’ for heat and water loss to the atmosphere. Under this area of enhanced surface exchange, the ocean responds by altering its stratification and forming a water mass with deep winter mixed layers of up to 500m thickness. In the North Atlantic Ocean, this subtropical mode water is called Eighteen Degree Water (EDW). Data indicate that frontal processes are important in EDW formation: much like atmospheric convection can be affected by atmospheric frontal dynamics that does not exist in a simple 1-D atmospheric boundary layer response to heating from below. The locus of strong air-sea exchange is closely tied to the GS north and south ‘wall’ positions, which can vary on time scales of months to years. Here we estimate the fraction of EDW formed in the GS front due to both diabatic cooling and wind-driven Ekman transport and compare these to estimates of the total EDW production during wintertime (JFM) from some recent climatologies. In a CLIMODE case study aboard the R/V Knorr from the night of 16 March 2007, we observe a rapid transition of the Atmospheric Boundary Layer (ABL) as it passes from colder shelf/slope water over the warm core of the GS. Besides a rapid growth in ABL thickness by ca. 1 km, we observe a wavelike signature in the free troposphere above the boundary layer resembling mountain lee waves. In both of these CLIMODE topics, we build upon recent work carried out by others.
Speaker: Terry Joyce
Time: 11:15 a.m.
Location: 311

A Simple Model For The Halocline And Circulation Of Atlantic Water In The Arctic Ocean
Idealized eddy-resolving numerical models and an analytic three-layer model are used to develop ideas about what controls the halocline and circulation of Atlantic Water in the Arctic Ocean. The analytic model provides theoretical estimates of the halocline depth, stratification, freshwater content, and transport in the Atlantic Water boundary current. The theory compares well with a series of numerical model calculations in which mixing and environmental parameters are varied, thus lending credibility to the dynamics of the analytic model. In these models, lateral eddy fluxes from the boundary and vertical diffusion in the interior are important drivers of the halocline and the circulation of Atlantic Water in the Arctic Ocean.
Speaker: Michael Spall
Time: 11:30 a.m.
Location: 312

A Meridional Cobalt Section From The Equatorial Pacific
Cobalt is an important micronutrient to cyanobacteria and bottle incubations have indicated the potential for cobalt co-limitation of these organisms. Dissolved cobalt was measured from samples obtained from the Metzyme cruise (October 2011) along a southward transect from Hawaii to Samoa, showing hemispheric differences in both surface and deep-water cobalt concentration. North of the equator, euphotic zone cobalt reached 10-20 pM, supported by high cobalt stores in the underlying low oxygen regions. In the South Pacific, surface cobalt approached the ~3 pM detection limit of the cathodic stripping voltammetry method. Themocline cobalt was also low, overlapping with negative Si* values that trace Antarctic mode and intermediate waters, suggesting that polar phytoplankton metal uptake renders these waters cobalt poor. Given the low surface concentrations in the South Pacific, lack of a mid-water remineralization peak, and small atmospheric input, it is possible that cyanobacteria in the South Pacific basin may experience cobalt-related stress.
Speaker: Nicholas Hawco
Time: 11:45 a.m.
Location: 317 AB

Role Of Submarine Canyons On Phytoplankton Dynamics Along The Western Antartic Peninsula
The Western Antarctic Peninsula (WAP) is experiencing dramatic climate change, with regional and local effects on ecosystems as maritime conditions propagate poleward and interact with local physics and topography. At local scales, limited profiles and glider surveys suggest that submarine canyons may act as conduits for warmer upper circumpolar deep water, reduce seasonal ice concentrations and provide a reservoir of macro and micronutrients. To assess the canyon hypothesis in space and time, four canyons were identified along a latitudinal gradient using high resolution bathymetry. Dynamics above canyons and adjacent shelves were compared using satellite-derived SST, sea-ice and ocean color variables, including phytoplankton biomass (chl-a) and diatom abundance derived from remote sensing reflectance. Canyons exhibited higher SST and reduced ice coverage relative to adjacent shelves. In situ and satellite-derived pigment patterns indicate increased dominance by diatoms over canyons, as well as increased overall phytoplankton biomass, particularly during high ice years. Canyons along the WAP may support a phytoplankton community primed for export production, but interannual variability in sea ice concentration and duration may result in shifts in bloom timing and magnitude.
Speaker: Maria Kavanaugh
Time: 12:15 p.m.
Location: 316 B

Zooplankton Of The Chukchi And Northern Bering Seas In Late Fall/Early Winter 2011
Understanding of winter biological conditions in the Arctic is severely limited. In November-December 2011 we conducted a cruise on the USCGC Healy to the Chukchi and Bering Seas to describe the hydrography and associated zooplankton distributions and to identify the overwintering habitat and activity of Calanus spp. and euphausiids. Distinct groups of zooplankton associated with specific water mass types were observed. Advection of water and zooplankton from the Bering Sea was a prominent feature structuring the spatial distributions of Chukchi Sea zooplankton types and abundances. Zooplankton communities along the Chukchi shelf-break were distinct in species and, for Calanus glacialis/marshallae, life stage composition. Both Calanus glacialis/marshallae and euphausiids appeared to be active and feeding, with Calanus glacialis/marshallae not in diapause but rather continuing to develop. The smaller copepods Pseudocalanus spp.Acartia longiremus, and Oithona similis were recently reproductively active, evidenced by the presence of naupliar stages. Based on estimates of metabolically required lipid expenditures and observed lipid stores, Calanus glacialis/marshallae may not successfully overwinter on the shallow Chukchi Shelf unless their activity levels are further depressed as the overwintering season progresses.
Speaker: Carin Ashjian
Time: 2:00 p.m.
Location: 316 A

Evidence For Climate And Regime-Shift Impacts On An Upper-Level Consumer On Georges Bank
Georges Bank has historically been one of the most important and productive ecosystems in the world, yet our understanding of how climate and environmental change have impacted its upper trophic levels is limited. To examine decadal-scale influences on Georges Bank haddock, a 79-yr archive of scales (1931-2009) was analyzed for carbon and nitrogen stable isotopes. Haddock δ15N values (largely related to trophic level) generally declined up until 1990, but increased thereafter. These patterns corresponded to available diet data, but also haddock condition levels and population sizes, indicating haddock feed at a higher trophic level when preferred prey is less available and intraspecific competition is high. Population sizes (and δ15N) were significantly correlated with the AMO, the Gulf Stream index, and salinity. Additionally, a significant shift (decrease) in δ13C values occurred in 1990, also coincident with the well-documented regime shift that occurred in the region. These results indicate that ecosystem-level changes on Georges Bank have cascaded to upper level consumers, evidenced by signals related to both diet and the base of the food web.
Speaker: Joel Llopiz
Time: 2:30 p.m.
Location: 313 B

Sea-Surface Salinity Dynamics In The Freshwater Regime
Evidence from Aquarius and SMOS suggests that the spatial distribution of sea surface salinity (SSS) in low-salinity basins has different characteristics. For instance, in the Bering Sea of the subpolar North Pacific Ocean, a SSS front is visible along the shelf break and slope that confines much of the fresh waters to the shallow shelf region. In the Bay of Bengal of the eastern tropical Indian Ocean, the fresh surface layer extends beyond the shelf break all the way into the interior basin. The far eastern tropical Pacific freshwater pool is dictated not only by precipitation but also by oceanic processes. Questions arise as to why the low-salinity distribution can be steered by seafloor topography in one basin but not in the others, and what are relative contributions of freshwater forcing versus ocean dynamic processes to observed SSS variability. An improved understanding of these questions is prerequisite for understanding where and how ocean salinity can be used as a rain gauge for the global water cycle. This study will provide some answers to these questions.
Speaker: Lisan Yu
Time: 2:30 p.m.
Location: 323 ABC

Constraining Microbial Communities To Micro-Niches Within The Coral Holobiont
Corals harbor a rich diversity of bacteria and a less-understood diversity of archaea within their mucus, tissue and skeletal micro-environments. Most of our understanding of coral-microbial diversity is based on homogenates of biomass from these different environments, and we lack insight into how the physical and biochemical parameters of these discrete micro-niches influence the establishment and diversity of microbial associates. Using a novel separation method, we are characterizing the microbial diversity and composition of the mucus and tissue environments of reef-building corals from diverse reef environments of in the Florida Keys and Micronesian Islands. Sequencing of bacterial and archaeal SSU rRNA gene amplicons is being performed with the Illumina MiSeq platform, and the depth of this data will provide a thorough examination of how coral micro-niches influence the associated microbial community, and if the micro-niches harbor similar microbial associates across coral species. Ultimately, constraining microbial diversity and composition to micro-niches within the coral holobiont will aid our understanding of how microorganisms may be interacting with corals and the surrounding seawater environment.
Speaker: Amy Apprill
Time: 2:45 p.m.
Location: 304 AB

Thursday, February 27, 2014

Small-Scale Mixing And Stable/Unstable Mixed Layers In The Spurs Region
We evaluate the upper ocean stability structure and its effect on mixing processes during several regimes occurring during the SPURS experiment using a combination of modeling and measurements from buoy and glider measurements. We focus on the density ratio changes with depth from the surface to the upper thermocline, subject to the influence of mixing processes. The stabilizing effects of freshwater from rain as contrasted to conditions of high solar radiation and low winds will be shown, with observations providing surprising new insights into upper ocean mixing in these regimes. Previous observations of freshwater lenses have demonstrated a maximum of dissipation near the bottom of the stable layer; our observations provide a first demonstration of a similar maximum near the bottom of the solar heating-induced stable layer. The effects of high evaporation rates on the density ratio and possible effects of double-diffusive instabilities will also be explored, and capabilities and limitations of current mixing models will be demonstrated. Our findings suggest that parameterizations of near-surface mixing rates during stable stratification and low-wind conditions require considerable revision, in the direction of larger diffusivities.
Speaker: Carol Anne Clayson        
Time: 8:45 a.m.
Location: 323 ABC

Near-Surface Vertical Structure In Temperature And Salinity In The Spurs Study Area
Vertical variability in temperature and salinity in the upper few meters of the ocean is examined using year-long datasets from 3 Wave Glider autonomous surface vehicles and short missions under low-wind conditions by Iver 2 EcoMapper autonomous underwater vehicles. Each Wave Glider carried SeaBird GPCTDs at depths of 25 cm and 6.5 m. In addition, one Wave Glider was outfitted with 12 temperature loggers at intermediate depths for the latter half of the deployment. The measurements were made in the SPURS study area near 25 N, 38 W, approximately at the center of the North Atlantic surface salinity maximum. Diurnal and seasonal variability of near-surface vertical gradients in T and S is characterized in relation to wind speed and insolation. Extreme cases of temperature stratification are documented, reaching 3.5 deg C in the upper meter, and nearly 5 deg in the upper 6.5 m.
Speaker: Benjamin Hodges
Time: 8:15 a.m.
Location: 323 ABC

New Direct Estimates Of Iceland-Scotland Overflow Water Transport Through The Charlie-Gibbs Fracture Zone
Recent two-year time series from eight moorings provide the first long-term simultaneous observations of the hydrographic properties and transport of Iceland-Scotland Overflow Water (ISOW) entering the western North Atlantic through the Charlie-Gibbs Fracture Zone. Using the isohaline 34.94 to define the ISOW layer, the two year mean and standard deviation of ISOW transport was -1.7 ± 1.5 Sv, compared to -2.4 ± 3.0 Sv reported by Saunders for a 13-month period in 1988-1989 using the same isohaline. Differences in the two estimates could reflect the difficulty of defining the long-term mean in the presence of strong transport variability on multiple time scales: ten 13-month mean transport estimates from the two-year record range from -2.0 to -1.4 Sv. Furthermore, the temperature/salinity time series indicate large fluctuations in ISOW layer thickness: for example, thickness over the northern rift valley had a mean value of about 1400 m and ranged from 400 to 2100 m (compared to Saunders’ fixed value of 2200 m at this site). Another factor being considered is the possible change in salinity of ISOW over the intervening years.
Speaker: Amy Bower
Time: 8:30 a.m.
Location: 314

Impact Of Subpolar North Atlantic Warming On Greenland’s Glaciers
Increasing evidence suggests that warming of the subpolar North Atlantic, over the last decade, triggered the recent acceleration of glaciers in western and southeastern Greenland leading to a doubling of the ice sheet’s contribution to sea-level rise. The mechanism invoked is increased submarine melting at the glaciers’ margins due to warming ocean waters. Yet linking changes in submarine melting of glaciers to subpolar gyre variability is far from trivial given the wide range of processes and scales involved: cross-shelf exchange, fjord circulation and meltwater plume dynamics. Using synoptic and moored data collected in one major southeast Greenland fjord and nearby shelf region, along with Argo data from the subpolar gyre, we present evidence that, and discuss the mechanisms through which, the large-scale ocean variability affects the waters in the vicinity of the glaciers and, potentially, the submarine melt rate.
Speaker: Fiamma Straneo
Time: 8:45 a.m.
Location: 314

Strain-Specific Response Of Marine Synechococcus To Iron Limitation
Availability of iron (Fe) limits primary productivity in vast areas of the ocean, and phytoplankton have evolved a suite of responses to cope with Fe stress. Marine Synechococcus are ubiquitous phytoplankton that inhabit waters with a range of Fe levels. To characterize the Fe-stress responses in genetically distinct Synechococcus strains from different ocean provinces, we compared the growth, photophysiology, and proteomic response of one coastal (WH8020) and one oceanic (WH8102) strain of Synechococcus to Fe-limited growth. In both strains photosynthetic efficiency was strongly related to Fe concentration, as was the cellular abundance of major photosynthetic proteins. However, distinct responses and different thresholds were observed to iron limitation in each strain. The oceanic strain WH8102 showed a consistent Fe limitation threshold based on photophyiology and protein abundance. In contrast, several distinct thresholds were observed in coastal strain WH8020, suggesting a more sophisticated strategy for conserving and partitioning Fe within the cell. The difference in response to Fe stress has implications for strain competitiveness and may be one factor underlying the biogeographical distribution of Synechococcus strains throughout the world's oceans.
Speaker: Kate Mackey        
Time: 9:15 a.m.
Location: 313 C

A Preliminary Evaluation Of Upper-Ocean Heat And Salt Budgets During The Spurs Campaign
The Salinity Processes Upper-ocean Regional Study (SPURS) was a field campaign focused on understanding the physical processes acting to maintain the climatological sea surface salinity (SSS) maximum in the subtropical North Atlantic. An upper-ocean salinity budget provides a useful framework for guiding progress toward that goal. The SPURS measurement program included a heavily instrumented air-sea interaction mooring, which allows accurate estimates of the surface fluxes, and a dense array of measurements from moorings, Argo floats, and gliders. These data will be used to estimate terms in the upper-ocean salinity and heat budgets during the year-long SPURS campaign, with the goal of gaining insight into the physical processes important to the evolution and maintenance of the SSS maximum. Here we report preliminary air-sea flux estimates and the evolution of upper ocean heat and freshwater content from the air-sea interaction mooring.
Speaker: Tom Farrar
Time: 9:15 a.m.
Location: 323 ABC

Noble Gas Constraints On Bubble-Mediated Air-Sea Gas Flux In A Global Ocean Model
Noble and inert gases (Ne, Ar, Kr, Xe and N2) are useful tracers of air-sea exchange processes due to their largely conservative behavior and range of physical properties. We attribute observed saturation anomalies to physical processes including bubble-mediated fluxes and the ocean solubility pump. Bubble fluxes drive lighter, more soluble gases towards supersaturation, while the combination of cooling and ventilation of the overturning circulation drives heavier, more soluble gases towards undersaturation due to the temperature dependence of gas solubility. By applying a global database of inert gas tracer observations to the circulation field from the Estimating the Circulation & Climate of the Ocean (ECCO) one-degree ocean model, we inversely constrain the contribution of each process to gas disequilibrium. The inverse solution provides a wind speed dependent parameterization for a two end-member model of bubble-mediated gas flux. Simulated saturation of heavy noble gases in the abyssal ocean was more negative than observations suggesting that ventilation in the Southern Ocean was deficient in the model.
Speaker: David Nicholson 
Time: 9:30 a.m.
Location: 312

Mean Salt Balance Of The North Atlantic Salinity Maximum
The North Atlantic Salinity Maximum is the world’s saltiest open ocean S-max and was the focus of the recent SPURS process study. It is formed by an excess of evaporation over precipitation and the wind-driven convergence of the subtropical gyre. Such salty areas are getting saltier with global warming (a record high SSS was observed in SPURS) and it is imperative to determine the relative roles of surface fluxes and oceanic processes in such trends. One approach to understanding the mean salinity balance in the ocean is to define a control volume by the 37.0 isohaline, across which all mean advective terms cancel. This is a “sock-shaped” closed surface around the S-max, with the “toe” trending to the southwest at depth. Using estimates of the net surface water flux (E-P) at the surface, it is possible to apportion the salt flux between lateral and vertical mixing processes. Direct measurements of the vertical mixing rate in the thermocline from the SPURS field program allow us to constrain the lateral mixing rate at the 1 degree scale of the water mass climatology.
Speaker: Ray Schmitt         
Time: 9:45 a.m.
Location: 323 ABC

Fukushima And Ocean Radioactivity
The triple disaster of the March 11, 2011 earthquake, tsunami, and subsequent radiation releases at Fukushima Dai-ichi were unprecedented events for the ocean and society. In this tutorial, the radioactive releases from Fukushima are compared to natural and prior human sources. Total Cs-137 releases from Fukushima are most likely in the 15-30 peta Bequerel range, with an equal amount of Cs-134. This is smaller than 1960’s fallout, but of similar magnitude to the Sellafield UK reprocessing site, and greater than what reached the ocean from Chernobyl. The fate of Cs is largely determined by its soluble nature in seawater, though uptake in sediments does occur via Cs’ association with both detrital particles and biological uptake and sedimentation. Cesium’s continued supply from the rivers and ongoing leakages suggests that coastal sediments may remain contaminated for decades to come. This may be one reason why benthic fish near Fukushima remain elevated in Cs causing ongoing public concern. Fukushima cesium will be detectable along the US coast in late 2013 to 2014, but at levels below those considered of human health concern.
http://www.whoi.edu/CMER
Speaker: Ken Buesseler
Time: 2:30 p.m.
Location: 310 Theater

A Buoy-Based Sensor Technology For Simultaneous, In-Situ Measurements Of Seawater Ph And Total Dissolved Inorganic Carbon
A buoy-based in-situ sensor has been recently developed for simultaneous measurements of seawater pH and total dissolved inorganic carbon (DIC) in subsurface marine environments. The sensor is among the first to achieve high-frequency, simultaneous measurements of two CO2 system parameters with sufficient accuracy for use in carbon and ocean acidification studies. Such a capability allows the seawater CO2 system to be fully characterized in high resolution with relatively small errors. The pH and DIC measurements are based on improved spectrophotometric methodologies. The measurement cycles are under 10 minutes, which are among the fastest of its kind. The DIC channel has also incorporated in-situ calibration capability using Certified Reference Material. The sensor has been deployed in the productive coastal water off the Woods Hole Oceanographic Institution for more than a month, and has obtained high quality data. Measurement precisions for pH and DIC are ±0.001 pH units and ±3 µmol/kg, respectively. Field accuracies are estimated to be ±0.002 pH units for pH and ±5 µmol/kg for DIC. The sensor package also provides connectivity to an in-situ O2 optode or a CTD.
Speaker: Zhaohui 'Aleck' Wang    
Time: 2:30 p.m.
Location: 313 A

On The Effect Of The East/Japan Sea Sst Variability On The North Pacific Atmospheric Circulation
The East/Japan Sea (EJS) is a semi-enclosed marginal sea located in the vicinity of the North Pacific storm track, where two dominant patterns of winter SST variability are characterized as the basin-wide warming/cooling and the northeast/southwest dipole structures. Processes leading to local and remote atmospheric circulation response to these SST anomalies are investigated using a hemispheric Weather Research and Forecast (WRF) model with multiple two-way nesting capabilities. The atmospheric circulation in direct contact with anomalous diabatic forcing exhibits a linear and symmetric response with respect to sign, pattern and magnitude of SST anomalies, suggesting the importance of fine-scale structure of the EJS SSTs to predictability of the regional atmospheric conditions. The remote circulation response, in contrast, is strongly nonlinear in that an intraseasonal equivalent barotropic ridge emerges as a common equilibrium response in the Gulf of Alaska irrespective of the polarity of EJS SST anomalies. This downstream blocking high response is accompanied by the enhanced synoptic transient eddy activity east of Japan, which maintains the anomalous blocking anticyclone via transient eddy vorticity flux convergence. A strong nonlinearity in remote response implies that the details of the EJS SST anomalies may not be critical. The overall results clearly demonstrate a remarkably far-reaching impact of the EJS SSTs on the downstream North Pacific atmospheric circulation.
Speaker: Hyodae Seo         
Time: 2:45 p.m.
Location: 301 AB

DIAGNOSING OVERTURNING AND WATER MASS TRANSFORMATION IN THE LABRADOR SEA FROM ARGO FLOATS
We examine the horizontal and overturning circulations of the Labrador Sea using Argo float profiles and trajectories. Argo floats have sampled the Labrador Sea from 2003 to 2013, a period of relatively weak wintertime deep convection relative to earlier periods. A composite geostrophic velocity section across the mouth of the Labrador Sea, constructed from ten years of Argo potential density profiles and referenced to float trajectories at 1000 m, balances mass to within 1 Sv. This velocity section is used to calculate the horizontal and overturning circulations and the water mass transformation. Using Argo, we track the seasonal and spatial patterns in the downstream transformation of waters in the boundary current. These recent observations are compared to previous circulation estimates that used different data sources, as well as to PALACE float observations from 1994 to 1999.
Speaker: James Holte         
Time: 3:00 p.m.
Location: 314

Friday, February 28, 2014

Assessing The Role Of Spatial Variability In Exchange Across The Inner Shelf: Results From A High Resolution Hf Radar System
This study seeks to quantify the spatial variability present over the inner part of the continental shelf at scales of 100s of meters to 10s of kilometers, and its contribution to the total exchange present. Recent observations of the coastal ocean south of Martha's Vineyard, MA have documented startling examples of spatially variable flows, due in part to tidal dynamics and/or buoyancy-driven currents, which drive focused lateral exchange with the potential to surpass that due to the frequently examined along-shelf uniform response to upwelling or downwelling. While evidence of additional transport due to major capes or headlands, bathymetric irregularities, or non-uniform wind fields has been found in most coastal areas, the relative impact of these sources of variability on exchange and dispersion across the shelf have not been quantified. Two years of surface current observations from a high resolution HF radar system, resolving the inner shelf south of Martha's Vineyard, MA with spatial resolutions approaching 400 m, are used to quantify the temporal and spatial scales of variability present. Linked to satellite-based SST gradients and in situ observations of the depth-dependent transport, these data provide an initial estimate of the role of spatial variability on exchange, including the effects of small-scale and/or transient features, that will be tested in upcoming field work.
Speaker: Anthony Kirincich
Time: 8:00 a.m.
Location: 304 AB

Retrospectively Investigating White Shark Diets In The Northwest Atlantic Ocean Via Amino Acid D15n Analysis
White sharks (Carcharodon carcharias) are iconic, apex predators found seasonally in Massachusetts’ waters. Understanding their trophic position is key because as apex predators, they are likely to have a disproportionate influence on food web structure. Anecdotal evidence points to a recent diet shift, as nearshore shark sightings and reports of attacks on gray seals have increased dramatically in the last decade, concurrent with the rebound of the seal population following the passage of the Marine Mammal Protection Act in 1972. To examine this potential diet shift, we sampled shark tissues, including vertebrae, which are constructed of distinct layers laid down sequentially over an individual’s lifetime, and which preserve a chemical record of environmental exposure. We conducted bulk δ15N and δ13C, and amino acid δ15N analyses on muscle tissue, blood, and bomb Δ14C age-estimated vertebral white shark samples and compared them to data from possible prey items. This work provides a historical to present day look at potential changes Atlantic white shark feeding ecology and trophic position.
Speaker: Li Ling Hamady
Time: 8:45 a.m.
Location: 318 AB

Lightweight, Flexible Approaches For Disseminating High-Volume, Active Datasets
In a large underwater image analysis project we are using lightweight, "repository-less" approaches to sharing data that enable near real-time access to data and metadata. In close collaboration with working science teams, we have developed a "local data resolver" that uses a combination of rule-based approaches to interrogate and regularize complex, ad-hoc filesystem hierarchies in order to provide global identification for digital objects at fine granularity, and template-based approaches to producing on-demand metadata representations rather than managing metadata separately in a repository. Our approach enables distributed computing without requiring expensive and time-consuming staging and preparation of datasets. This mode of access not only makes observational data amenable to semantic harvesting immediately upon generation, but also greatly improves remote access to live datasets, allowing distribution of processing jobs across a wide variety of computing platforms without recourse to specialized high performance computing APIs or packaging processing code as workflows. The approach we have taken lends itself to exploratory processing as well as to routine processing, and is being used in production for an underwater observatory and a benthic survey program.
Speaker: Joe Futrelle
Time: 8:45 a.m.
Location: 317 AB

Why We Need A Semantic Web Framework For Marine Ecosystem Indicators
Ecosystem-based management of Large Marine Ecosystems (LMEs) involves the sharing of data and information products among a diverse set of stakeholders - from environmental and fisheries scientists to policy makers and the public. Tracing a synthesized data product back to its original data sources is important for verification, understanding, and comparing with similar data products or indicators monitored by different stakeholder groups. Our collaborative use case develops a software framework for the bi-annual Ecosystem Status Report (ESR) for the U.S. Northeast Shelf LME. The ESR provides data and information products for ecosystem drivers and pressures, such as climate forcing and fisheries indicators, and ecosystem status including primary production. Here we present the use of the W3C provenance (PROV) Linked Data standard for data products in the ESR. Furthermore we recommend linking to domain-specific ontologies to give meaning to the source datasets and derived products. Semantically enabling not only the provenance but also the data products will yield a better understanding of the connected web of relationships between marine ecosystem and ocean health assessments conducted by different stakeholder groups.
Speaker: Stace Beaulieu
Time: 9:00 a.m.
Location: 317 AB

Turbulence In The Cold Wake Of A Typhoon
We present observations of a cold wake formed during the passage of Typhoon Fanapi in the Philippine Sea. Fanapi formed in the western North Pacific Ocean, and subsequently traveled westward and came ashore in Tawain as a category-3 storm on September 19, 2010. Following its landfall, a cruise abroad the R/V Revelle was undertaken to study the structure, evolution, and decay of the cold wake as part of the Impact of Typhoons on the Pacific (ITOP) program. The wake was 3 days old when it was initially sampled, and was crossed on 3 occasions over 4 successive days. We found elevated levels of turbulence linger in the wake up to one week after its generation. The enhancement was specifically in the deep part of the wake, around 100-meters depth. At shallower depths, turbulence levels appeared reduced relative to the areas on either side of the wake, apparently due to the suppression of turbulence caused by the increased near-surface stratification. Within the wake itself, turbulence levels were enhanced to the right of the wake’s center, consistent with the asymmetry in forcing.
Speaker: StevenJayne
Time: 9:00 a.m.
Location: 315

The Buoyancy Gain Part Of Amoc
The densest waters in the Atlantic undergo diapycnal transformation into warmer, lighter density classes. The Dynamics of Abyssal Mixing and Interior Transports Experiment (DynAMITE) conducted an investigation of the processes underlying this upward transfer of mass and buoyancy gain — the Abyssal Upwelling Cell (AUC) — which is important to closing budgets of mass, heat and tracers in the AMOC. Combining a moored array down Bermuda Rise with a microstructure survey, DynAMITE mapped the structure of vertical diffusivities, and revealed a vigorous lateral circulation (order 10 Sv) through the basin interior between 20°- 38°N. These deep flows are primarily driven by turbulent mixing and vortex stretching along the MAR and deep Gulf Stream. Upwelling sets the deep layers in motion, boosting the DWBC flows by 10-15 Sv near Cape Hatteras. Mixing weakens the stratification resulting in two massive reservoirs of low potential vorticity waters – an abyssal analog to water masses formed by convective processes and buoyancy loss at high latitudes. The AUC accounts for the seeming disconnect between AMOC variability measured at mid-latitudes (Line W, Labrador Sea) and the tropics (RAPID, MOVE).
Speaker: Ruth Curry
Time: 9:30 a.m.
Location: 312

Submesoscale Subduction Of Particulate Organic Carbon, Oxygen And Spice
Traditionally, export of carbon is ascribed to the sinking flux of particulate organic carbon (POC). However, glider-based observations from the 2008 North Atlantic Bloom study (NAB08) show numerous intrusions of elevated POC, oxygen and spice (T-S anomalies) at 100-400 m depth, suggesting a local, advective transfer of water from the surface. High-resolution modeling reveals that these three-dimensional intrusions descend from the surface mixed layer as coherent, filamentous features originating predominantly along the edges of eddies. By examining simultaneous observations from a cluster of three gliders circuiting an anticyclonic eddy over 30 days we resolve the local isopycnal slopes on scales of 2-40 km, and estimate the downward POC transport and remineralization rates on the subducted water. We find that the eddy-driven flux of POC at 100 m depth is comparable to particle sinking fluxes, but is unlikely to extend past the depth of the deepest winter mixed layer. These high resolution observations and modeling results implicate a carbon export associated with submesoscale eddies and fronts that is unresolved in global carbon cycle models.
Speaker: Melissa Omand
Time: 9:30 a.m.
Location: 316 A

Studying Late Fall Occurrence Of Baleen Whales In The Central Gulf Of Maine Using Autonomous Vehicles And Real-Time Passive Acoustic Detections
Recent surveys have identified a region in the central Gulf of Maine that is used extensively by baleen whales from November to January, but its remote location and frequent stormy conditions make traditional shipboard habitat studies difficult. To overcome these challenges, we deployed profiling floats and Slocum gliders equipped with digital passive acoustic monitoring (DMON) instruments in the region during late fall 2009 and 2012 to monitor the distribution of calling baleen whales. In 2012, the DMON was programmed to also detect and classify baleen whale calls and report them in near real time to shore-side researchers via Iridium satellite. In both years, the calls of fin, humpback, and right whales were recorded on all platforms over the 3-4 week deployments. Despite poor weather in 2012, the real-time detection data allowed scientists on the R/V Endeavor to quickly locate whales and conduct proximate in-situ oceanographic and zooplankton sampling during a 9-day cruise, which suggested Calanus finmarchicus and euphausiids were the primary prey for baleen whales. Ongoing analysis is focusing on glider-observed oceanographic conditions that influence the distribution of the whales.
Speaker: Mark Baumgartner
Time: 9:45 a.m.
Location: 316 B

Tracer Dispersion In The Mid-Depth Gulf Of Mexico
Dispersion of a tracer, released on an isopycnal surface near 1100 m depth over the continental slope in the Gulf of Mexico, was studied with a field experiment, with numerical simulations, and with a dynamical systems approach. The diapycnal diffusivity along the slope was enhanced (> 10-4 m2/s), along the slope, as has been found in other regions. Stirring of the tracer proceeded rapidly, compared with the open ocean, although lateral variations of the tracer column integral were still large at the end of one year, when the tracer was spread over approximately half the Gulf. The zero-crossing of the spatial autocorrelation function of the column integral grew from ~4 km one week after release, to ~100 km at 4 months, and to ~200 km at 12 months. The overall pattern of the tracer distribution, and its statistics, will be compared with numerical simulations and with a persistence pattern of Lagrangian Coherent Structures. The results promise to advance simulations of the dispersal of nutrients and pollutants in the Gulf, both of which are important to the mid-depth ecosystem.
Speaker: Jim Ledwell
Time: 10:30 a.m.
Location: 316 A

Eutrophication Affects Carbon Exchange Between Benthic Microalgae And Bacteria In Salt Marsh Tidal Creeks
Benthic microalgae (BMA) are important primary producers in shallow estuaries. A portion of carbon fixed by BMA can be rapidly transferred to heterotrophic bacteria and then respired, buried, or consumed by animals. Coastal eutrophication may increase BMA production and bacterial carbon demand, thereby affecting carbon cycling and fate. To measure the rate and efficiency of carbon transfer from BMA to bacteria under different nutrient conditions, I conducted seasonal stable isotope probing experiments with sediment cores from two salt marsh tidal creeks that are part of the TIDE long-term nutrient enrichment experiment within the Plum Island Ecosystem-LTER (MA, USA). One creek is fertilized while the second creek has low, ambient nutrient concentrations. 13C-labeled sodium bicarbonate was added to water overlying experimental cores and traced into BMA and bacteria using compound specific isotope analysis of phospholipid fatty acids. The label was rapidly incorporated into microalgal fatty acids (<4 hr.) and transferred to heterotrophic bacteria. This process was faster and more extensive in sediment microbes from the nutrient enriched creek. Thus, nutrient loading may increase rates of carbon cycling by sediment microbial communities.
Speaker: Amanda Spivak
Time: 10:30 a.m.
Location: 318 AB

Laboratory Experiments Investigating The Influence Of Multiple Subglacial Discharges On Submarine Melting Of Greenland’s Glaciers
Idealized laboratory experiments investigate the ice-ocean boundary dynamics near a vertical ‘glacier’ (i.e. no floating ice tongue) in a two-layer stratified fluid, similar to Sermilik Fjord where Helheim Glacier terminates. In summer, the discharge of surface runoff at the base of the glacier (subglacial discharge) causes the circulation near the glacier to be much more vigorous and is associated with a larger melt rate than in winter. In the laboratory, the effect of multiple subglacial discharges is simulated by introducing fresh water at melting temperatures from two sources at the base of the ice block representing the glacier. Two buoyant plumes of cold melt water and subglacial discharge water entrain ambient waters, rise vertically and interact. The results suggest that the distance between the two subglacial discharges influences the amount of submarine melting and the final location of the melt water within the interior of the water column. Hence, the distribution and number of sources of subglacial discharge may play an important role in glacial melt rates and the fiord stratification and circulation. Support was given by NSF project OCE-113008.
Speaker: Claudia Cenedese
Time: 11:15 a.m.
Location: 301 AB

Influence Of Individual Phytoplankton Cells And Their Physiology On Particle Export In The South Atlantic Ocean
Sinking particles were collected in the South Atlantic Ocean along a transect from Uruguay to Barbados to assess the contribution and influence of different phytoplankton types on organic matter export from the surface ocean. Sediment traps deployed at 19 locations collected bulk sinking material and individual particles in polyacrylamide gel. The identity of individual particles was determined by microscopy of the polyacrylamide gels. In general, aggregates dominated the sinking particles, followed by zooplankton fecal pellets, and together they likely contributed most to measured organic carbon and nitrogen export. Although not numerically dominant, a surprising number of individual phytoplankton cells were collected in the polyacrylamide gel, including both diatoms and coccolithophores. Relative abundance of diatoms compared to coccolithophores increased dramatically across the basin. At one location individual diatoms even dominated the total particle flux. The centric diatom, Coscinodiscus spp., was isolated from this station and cultured in low nitrate, phosphate, or silicic acid to examine their sinking speeds. Ongoing work will determine whether physiological state could explain the direct export of individual cells and their variable contribution to total particle flux.
Speaker: Colleen Durkin
Time: 11:45 a.m.
Location: 323 ABC

Local Scales Of Larval Dispersal
Over the past 15 years, new techniques such as natural and artificial geochemical tags and DNA markers have provided emerging evidence that self-recruitment rates back to natal reefs and natal islands may be considerable for some marine species. This pattern of high local recruitment has been identified for species that are known to have metapopulation dynamics with regional exchange across sites more than 50-100km away, including reef fish with pelagic larval durations that exceed a week and sites where larger scale oceanographic transport has been observed. Here we analyze island-scale recruitment patterns of one such species, the Orange clownfish, Amphiprion percula, obtained from parentage analyses in three different years around Kimbe Island, Papua New Guinea. Comparing the observed natal-to-settlement events to all possible anemone-to-anemone connections reveals that there is bias towards shorter dispersal distances at the local scale in all years despite potentially variable oceanographic conditions. Around island connectivity also appears to be a regular occurrence, with exchange of larvae across some of the more distant anemones.
Speaker: Julie Kellner
Time: 12:15 p.m.
Location: 313 C

The Oceans And The Global Water Cycle
The global water cycle is often misrepresented to the public, with an over-emphasis on land hydrology. In fact it is predominately an ocean-atmosphere phenomena; the sum of all river flows is less than ten percent of the global evaporation from the ocean. Most of the rain falling out on land has come from the ocean, which can be used to improve rainfall predictions. The patterns of mid-latitude evaporation and low and high latitude precipitation produce distinct flows in the ocean due to mass and angular momentum conservation as well as characteristic salinity patterns and allow estimation of the global meridional latent heat flux. Trends in ocean salinity are such that salty areas are getting saltier, and fresh areas getting fresher, which suggests a strong intensification of the water cycle with global warming at rates well above those derived from climate models. With new salinity sensing technology, both in-situ and remote, and new field programs such as SPURS, we hope to better ascertain the water cycle intensification rate and its future impact on terrestrial rainfall.
Speaker: Ray Schmitt
Time: 2:00 p.m.
Location: 310 Theater

Observations Of Bedforms, Near Bed Flow And Turbulence, And Sediment Transport In The Columbia River Mouth
In spring of 2013, field measurements in the Columbia River mouth were conducted in order to study sediment transport processes in highly energetic conditions with near surface tidal currents of up to 3 m/s and wave heights up to 5m. Sensors on the instrumented frames included bedform imaging sonars, an upward-aimed ADCP, a downward-aimed pulse coherent Doppler profiler, ADVs and acoustic backscatter profilers. The measured bedforms had wavelengths from 1 m (H= 20 cm) during neap tides to 6 m (H= 70 cm) during spring tides. Migration directions reversed on each half tidal cycle with maximum rates of 1.5 m/hr. The migration rates will be compared to commonly used bedload models with forcing from both predicted and measured bed stress. Turbulence measurements from the ADVs and profiler will be examined relative to the changing bed geometry. The turbulence and sediment transport measurements also aid interpreting shipboard survey measurements of the dynamics of the fresh water plume lift-off, which occurred in the vicinity of the instrumentation. (Geyer and Traykovski, this session)
Speaker: Peter Traykovski
Time: 2:00 p.m.
Location: 311

A Research Coordination Network For Motivating Interdisciplinary Research
Ocean researchers must work across disciplines to provide policy makers with clear and understandable assessments of the state of the ocean. With advances in technology, not only in observation, but also communication and computer science, we are in a new era where we can answer questions asked over the last 100 years at the time and space scales that are relevant. A National Science Foundation-funded Research Coordination Network (RCN) is addressing approaches for improving interdisciplinary research capabilities in the ocean sciences. To this end, task groups engage in half year studies with a new task begun nominally quarterly. The immediate product of each task is a report but the ultimate goal is a better way to make earth observations available to society as knowledge and understanding for improved policy and decision-making. This presentation will examine the steps forward in stimulating interdisciplinary research through data exchange and better addressing the gaps in communication and approaches that are still common across the ocean sciences.
Speaker: Albert Williams
Time: 2:00 p.m.
Location: 316 B

Local And Remote Forcing Of The Atlantic Meridional Overturning Circulation (Amoc) Transport Along The Rapid-Mocha Line (26.5n)
Observations made by mooring array along the UK-US RAPID-MOCHA Line along 26.5N show substantial variability of the AMOC transport on seasonal to interannual time scales. This variability is well simulated by a two-layer and wind-driven model. The model is used to examine both local and remote forcing mechanisms. It was found that the seasonal variability of the AMOC transport along the RAPID Line is strongly forced by wind-stress curl in the Subpolar N. Atlantic through the connection is through Kelvin and topographic Rossby waves. The major weakening of the AMOC in 2010 was also strongly influenced by wind-stress in the subpolar basin. The amplitudes and phases of both seasonal and interannual variations of the AMOC transport are significantly altered if the subpolar forcing is blocked. Topography, especially the mid-ocean ridge, plays an important role in setting remote forcing pathways across the latitudes.
Speaker: Jiayan Yang
Time: 2:15 p.m.
Location: 312

Wave Energy Injection To Depth By Fronts
Recent high-resolution in-situ observations suggest that inertia-gravity waves play a major role in transferring energy from the ocean surface to depth (e.g. Klymak and Moum, 2007; Nagai et al., 2009; Whitt and Thomas, 2013). Wind-generated inertial motions are modified by their interaction with the flow field at ocean fronts, generating wave packets that propagate downward along isopycnals. Our aim is to describe the wave energy penetration to depth as a function of the lateral buoyancy gradient, the front depth, and the vertical variation of the stratification. We explore this three-parameter space with a non-hydrostatic process study ocean model forced by a wind impulse. Shallow submesoscale fronts trigger highly energetic wave packets within the upper 300m. In contrast, a deep mesoscale front with a less intense, lateral buoyancy gradient develops weaker wave packets that penetrate to depths of 1000m. The superposition of submesoscale and mesoscale fronts occurring in many of the ocean’s semi-permanent frontal zones, results in an increase of wave energy transfer to depth within the front. Finally, several alternate pathways for the loss of the near-inertial wave energy are explored.
Speaker: Mariona Claret
Time: 2:30 p.m.
Location: 316

How Well Would The Modern-Day Circulation Be Resolved If We Were Limited To Paleoceanographic-Like Observational Sampling?
Paleoceanographic observations have been used to suggest plausible stories about how the ocean has changed in the past, but the main types of data are limited to the fluid envelope: the seafloor, oceanic margins and islands, and the sea surface. Furthermore, the total number of paleoceanographic observations for a well-dated timeslice like the Last Glacial Maximum might approach a thousand or so. On the other hand, we have millions of modern-day observations, yet various regions are still inadequately sampled for many purposes. To test the limitations of paleoceanographic observations due to their sparsity, an inverse method is applied to modern-day tracer observations that have been sub-sampled at paleoceanographic resolution. From this limited set of observations, what features of the modern-day circulation are recoverable? The method is based on a high-resolution box model recently used to diagnose the water-mass decomposition and transit time distributions of the global ocean from temperature, salinity, nutrients, oxygen, and various isotopes including radiocarbon. As tracer observations of much of the modern-day ocean have been recently obtained by WOCE, the experiment is designed such that the true answer is fairly well known, and thus an accurate diagnosis of the success or failure of the reconstruction method is possible. The modern-day oceanographic features that are well recovered give guidance to the parts of the past ocean that we can reasonably expect to resolve.
Speaker: Geoffrey Gebbie
Time: 3:45 p.m.
Location: 317 AB

Tide-Induced Mixing And Frontogenesis At The Columbia River Mouth
The Columbia River estuary exhibits a rapid transition from highly stratified to mixed conditions during strong ebbs, due to intense, tidally induced shears that produce gradient Richardson numbers as low as 0.1. A strong salinity front is generated at the seaward limit of the mixing zone, which marks the “lift-off” of the Columbia River plume. The position of the lift-off front always corresponds to a lateral constriction, but it occurs at different locations depending on the strength of the ebb tides and river outflow. Under moderate outflow conditions the front is located 5 km upstream of the mouth at the constriction formed by the transverse “A Jetty”, and during maximum outflow conditions (peak river flow and solstice spring tides) the front forms at the mouth. Mixing induced by tidal boundary layer shears leads to buoyancy fluxes of 2x10-5 m2 s-3 during peak spring tides. However, significantly higher buoyancy fluxes occur in the intensely sheared pycnocline of the lift-off front.
Speaker: Rocky Geyer
Time: 3:45 p.m.
Location: 301 AB

Last updated: February 19, 2014