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Monday, December 3, 2012

Circulation on the Ebb Shoal at New River Inlet, NC

The effects of waves, winds, and tides on the spatially variable circulation (Fig. 1) on an ebb shoal offshore of New River Inlet, NC will be examined with observations collected in April and May 2012. Measurements of currents, waves, tides, and sea levels were obtained at 32 locations in the inlet and ebb shoal channels (2- to 10-m water depths) and across and offshore of the ebb shoal (1- to 5-m water depths). Maximum tidal flows in the inlet channel (onshore of the mouth) were +/- 1.5 m/s. In contrast, tidal flows 500 m offshore of the inlet mouth at the end of a channel recently dredged across the ebb shoal were stronger during ebbs (-1.5 m/s) than during floods (+0.5 m/s). Significant wave heights in 9-m water depth ranged from 0.5 to 2.5 m and wind speeds observed near the inlet mouth ranged from 0 to 14 m/s. Preliminary results suggest wave- and wind-forcing had a significant affect on the flows on the ebb shoal, especially during slack tides. The importance of setup gradients, wave-driven radiation stresses, and wind stresses to the circulation will be discussed.
Speaker: Britt Raubenheimer
Time: 8:15 a.m.
Location: 3024 Moscone West


The dendroclimatology of Common Era volcanic eruptions

Nearly all reconstructions of the large-scale temperature history of the Common Era rely on tree-ring proxies. Estimates of past climate variability and the sensitivity of the ocean-atmosphere system to changes in radiative forcing are likewise informed by these reconstructions. In concert with ice cores, tree-rings provide one of the primary means for identifying the timing of (often poorly observed) volcanic eruptions and the ensuing climate response. Here, we use a validated and parameterized forward model of tree-ring formation to simulate suites of actual tree-ring observations and explore the sensitivity of the data-model intercomparison to the amplitude of the environmental forcing, the covariance of the climate response and the proxy network, the seasonality of forcing and response, and to investigate the likelihood of systematic amplitude or chronological bias in the tree-ring proxies.
Speaker: Kevin Anchukaitis
Time: 8:15 a.m.
Location: 2010 Moscone West


Inferences on melting and mantle heterogeneity through analyses of olivine-hosted melt inclusions from the Eastern Volcanic Zone, Gakkel Ridge

Here we combine volatile (CO2, H2O, Cl, Fl, and S), major, and trace element concentrations from 66 olivine-hosted melt inclusions with petrologic models of mantle melting to explore mantle source heterogeneity and melting dynamics beneath the Eastern Volcanic Zone (EVZ) of the ultraslow-spreading Gakkel Ridge. The EVZ is the easternmost segment of the Gakkel Ridge and it is volcanically active compared to the adjacent Sparsely Magmatic Zone. Naturally glassy melt inclusions hosted in olivine phenocrysts from lavas erupted at four locations along the length of the EVZ (31°E, 39°E, 57°E and 72°E) were analyzed. Melt inclusion analyses suggest that there are systematic variations in the mantle composition from the eastern end (at 72°E) to the western end (31°E, near the Sparsely Magmatic Zone) of the EVZ. Water contents increase from an average of 0.16 ± 0.01 wt % at 72°E to an average of 0.40 ± 0.03 wt % at 31°E. Highly incompatible trace elements (e.g., Ba, U, and Nb) increase from east to west, while the middle and heavy rare earth elements remain constant or decrease along the ridge axis. Ratios of light to heavy rare earth elements in the easternmost melt inclusions are relatively constant (at 72°E La/Yb ratios range from 1.41 to 1.68) compared to compositions observed at 31°E (La/Yb from 1.80 to 3.14).

To determine the source of the geochemical variability observed along the EVZ, we model mantle melting in one and two component systems, where melting occurs in either the spinel field only or the garnet and spinel fields. Possible mantle sources that were investigated include depleted MORB mantle, depleted mantle peridotite, metasomatised mantle, and/or pyroxenite veins. Melt inclusion compositions from all four locations are depleted in heavy rare earth elements (e.g., Dy, Y, and Yb) compared to normal MORB, consistent with mantle melting beginning in the garnet stability field. However, variable degrees of melting of a single mantle composition cannot produce the range of trace element and H2O concentrations observed along the EVZ, regardless of the depth extent of melting. The observed geochemical variations can be explained by melting from the garnet to spinel field of a mantle source composed of two components (including DMM and a metasomatised component enriched in fluid mobile elements, but depleted in middle and heavy rare earth elements), where the proportion of the metasomatised component in the mantle increases towards the Sparsely Magmatic Zone. Furthermore, the increase in overall geochemical variability along the ridge axis suggests that melt focusing and homogenization in the mantle is less efficient near the volcanically starved Sparsely Magmatic Zone.
Speaker: V. Dorsey Wanless
Time: 8:45 a.m.
Location: 308 Moscone South


High-Resolution Radiocarbon Chronology Of Ooids By Gas Ion Source Accelerator Mass Spectrometry

The National Ocean Sciences Accelerator Mass Spectrometry (NOSAMS) facility at the Woods Hole Oceanographic Institution has developed a gas-accepting microwave-plasma gas ion source for the analysis of 14C in a continuously flowing stream of CO2. In addition to the demonstrated rapid analysis of bulk carbonates, the instrument can assist in 14C-based reaction analyses that elucidate coarse isotopic spectra of complex mixtures. We employed the gas ion source AMS with a novel reactor and fraction collector to obtain 14C chronologies as a function of particle radius in ooidic carbonate sediments from Highborne Cay, Bahamas and Shark Bay, Australia via progressive acidification. The method revealed disrupted 14C chronologies with ooid lifespans on the order of millennia that i) complicate the interpretation of bulk measurements and ii) may provide an independent constraint on marine reservoir ages.
Speaker: Steven R. Beaupre
Time: 9:30 a.m.
Location: 303 Moscone South


Detachment Fault Initiation and Control by Partially Molten Zones in the Lower Ocean Crust

The close association of oxide gabbro and deformation in interleaved ferrogabbro and olivine gabbro at Atlantis Bank on the SW Indian Ridge explains the formation of this enormous single-domed gabbroic oceanic core complex. ODP Holes 735B and 1105A show that the stratigraphy is defined by 100’s of zones of intense deformation and strain localization in the upper 500-m where various melts percolated including late-stage iron-titanium rich melts. The latter created highly deformed oxide-rich gabbro zones at scales from millimeters to over 100 meters. Mapping by ROV, over-the-side rock drilling, dredging, and submersible shows that this stratigraphy exists uniformly over the bank. Deep drilling and sampling up the headwalls of major landslips cutting into the core complex show that the fault zone was imbricate, likely reflecting relocation of the active slip plane due to cyclic intrusion in the lower crust.

The detachment originated as a high-angle fault on the rift valley wall that propagated into a zone of partially molten gabbro beneath the sheeted dikes. This zone then pinned the footwall block, creating a plutonic growth fault along which gabbro intruded beneath the ridge axis was continuously uplifted and exposed on the Antarctic plate for ~3.9 myr. The overlying basaltic carapace spread more slowly to the north on the African Plate. Textural evidence, particularly that provided by iron-titanium oxides, shows that melts migrated along complex shear zones in which several creep mechanisms operated, ranging from crystal plastic dislocation creep, diffusion creep, grain boundary sliding, and brittle deformation. More than one of these mechanisms may have occurred concurrently. Subsequently, these zones localized later solid-state creep, often producing texturally complex rocks where separation of the timing and duration of different creep mechanisms is difficult to unravel. As uplift of the plutonic section progressed, the footwall passed through the zone of diking beneath the rift valley, and as a consequence numerous inliers of the dike gabbro transition are found exposed across the gabbro massif.

Olivine gabbros that underwent localized deformation and shearing were strongly affected both by crystallization of abundant oxides and new more sodic plagioclase and iron-rich pyroxene, and by local re-equilibration of existing calcic plagioclase and pyroxene with the invading iron-titanium rich melt. This was likely accompanied by dissolution of existing olivine and crystallization of secondary igneous clinopyroxene. Brown amphibole after clinopyroxene and plagioclase also formed, with some amphibole rimming relict olivine. The latter processes makes it hard to differentiate between ferrogabbros that crystallized directly from a melt, and those produced by hybridization of pre-existing olivine gabbro by migrating melts in the shear zone.

Dredge samples collected at numerous localities at oceanic transforms along the SW Indian, American-Antarctic, and Mid-Atlantic Ridge with similar fabrics show that the relationship between oxide gabbros and deformation is widely associated with the exposure of plutonic rocks at oceanic core complexes. Atlantis Bank therefore provides the general case for the formation of the numerous large gabbro massifs exposed on the ocean floor at all slow and ultraslow spreading ridges.
Speaker: Henry J. Dick
Time: 9:45 a.m.
Location: 308 Moscone South


SPURS Overview: Salinity Processes Upper Ocean Regional Study First Results (Invited)

A multi-national study of the surface salinity maximum of the North Atlantic was initiated in 2012. We are seeking answers to basic questions about how the salinity maximum is maintained. The Salinity maximum occurs in a region where evaporation is large and precipitation small, where winds drive convergent surface flow and eddy kinetic energy is low. We are attempting to ascertain the relative roles of lateral and vertical mixing in dissipating the high salinities built up by surface water loss. The field program utilizes a suite of autonomous gliders, floats, drifters and moorings as well as ship operations. Real-time model runs incorporate satellite and in-situ data and provide guidance to the shipboard sampling. Results from the first cruise in September-October 2012 will be presented.
Speaker: Raymond W. Schmitt
Time: 10:35 a.m.
Location: 2022-2024 Moscone West


Constraints on the pattern of melt migration beneath mid-ocean ridges based on the major and trace element chemistry of erupted lavas and melt inclusions

We combine the predictions of coupled petrologic-geodynamic models with observations of crustal thickness and the major and trace element chemistry of erupted lavas and melt inclusions to place constraints on the pattern of melting and melt migration beneath mid-ocean ridges. This new approach, which allows us to characterize the 3-D shape and extent of the melt extraction region, indicates that a large fraction of the melt generated beneath ridges remains trapped in the mantle. Mantle flow and axial temperature structure are calculated assuming a visco-plastic, temperature-dependent rheology that simulates brittle weakening within the lithosphere. Melting is calculated based on a modified version of the Kinzler & Grove [1992] melting model, which incorporates the pressure dependence of the melting reaction, variable melt productivity, and explicit treatment of trace element partitioning. Once melts are produced, they are assumed to rise vertically through the mantle until they encounter a permeability barrier (e.g., top of the melting region, base of the lithosphere, cpx-out reaction zone) at which point they migrate laterally “uphill” along this boundary until they are extracted at the ridge axis. The volume and composition of the aggregate melt that eventually reaches the ridge axis is a function of the mantle potential temperature, spreading rate, mantle composition, and pattern of melt migration. A key unknown parameter is the length scale over which melts migrate laterally once they encounter a permeability barrier. This length scale is important because melts generated at the edges of the melting region have lower average degrees of melting, which can strongly influence the aggregate melt composition, but will have a minimal effect on total crustal thickness. By contrast, differences in spreading rate, mantle temperature, and mantle composition will influence both melt chemistry and crustal thickness. To isolate the influence of the length scale of melt migration, we calculate melt composition and crustal thickness over a spectrum of spreading environments for which high quality crustal thickness and lava and melt inclusion data exist. Comparing our predictions with the complimentary geophysical and geochemical data we find that most ridges require efficient pooling of melts over a relatively restricted region beneath the axis. This implies that although melting occurs over a wide region beneath the ridge axis, up to 20–30% of the total melt volume is not extracted, and will eventually refreeze and refertilize the lithosphere.
Speaker: Mark D. Behn
Time: 11:20 a.m.
Location: 308 Moscone South


Mantle hydration at the Middle America Trench: Constraints from seismic anisotropy

We present measurements of seismic anisotropy that constrain the amount of water fluxing into the mantle at the Middle America Trench based on active-source seismic data collected during the 2008 TicoCava experiment offshore Nicaragua. Water carried to depth by subducting oceanic lithosphere is the primary source of mantle hydration, an essential component of many arc- and global-scale processes. The upper mantle is often assumed to be efficiently dehydrated by melting at ridges, but recent seismic-reflection images of bending-induced normal faults extending into the upper mantle and reduced upper-mantle seismic velocities under the outer rise near trenches have been interpreted as evidence that the subducting mantle is pervasively hydrated via serpentinization by seawater penetrating through the crust along plate-bending-induced faults. This seawater may fill cracks in the upper mantle with free water; react strongly with olivine in upper mantle peridotite, filling cracks and fault zones with serpentinite; and/or diffuse between fault zones, pervasively serpentinizing the upper mantle.

The seismic velocity of serpentinized rocks is much slower than that of unaltered mantle rocks, and much of the support for the hypothesis that subducting mantle is commonly hydrated near the outer-rise comes from isotropic seismic velocity analyses that assume observed slow velocity anomalies can be entirely attributed to the presence of serpentine. However, the outer-rise normal faults themselves, as well as inherited, strain-induced lattice-preferred orientation (LPO) of mineral grains in the upper mantle can produce azimuthally dependent seismic wave speeds that are up to ~0.5 km/s slower in one direction than in another, an effect comparable to the change in velocity due to ~20% pervasive serpentinization.

To include the effects of serpentinization in estimates of the extent and distribution of serpentinization at the Middle American outer rise and trench, we are measuring the azimuthal dependence of seismic wave speed in crustal and upper mantle refraction phases (i.e., Pg and Pn) from the TicoCava experiment. This experiment involved airgun shots fired along a range of azimuths and recorded by an array of 30 ocean-bottom seismometers deployed at offsets of up to ~200 km. We are using a “delay-time” approach in which the difference between travel times calculated for a best-fit isotropic velocity model and observed travel-times are calculated as a function of source-receiver azimuth, with travel-times corrected for non-mantle travel paths and for source/receiver offset. A comparison of the patterns and amplitudes of azimuthally-dependent delay times between lithosphere seaward of the outer rise and directly beneath the outer rise will constrain the orientation and source (e.g., LPO or cracking) of anisotropy, enabling the effects of cracks and LPO to be separated from the effect of pervasive serpentinization, and thus providing a more accurate estimate of the amount of water entering the mantle at subduction zones than one based on isotropic analyses.
Speaker: Nathaniel C. Miller
Time: 2:10 p.m.
Location: 308 Moscone South


U.S. 2013 National Climate Assessment of Oceans and Marine Resources (Invited)

We will discuss the key findings from the Oceans and Marine Resources chapter of the U.S. 2013 National Climate Assessment. As a nation, we depend on the ocean for seafood, recreation and tourism, cultural heritage, transportation of goods, and increasingly, energy and other critical resources. The U.S. ocean Exclusive Economic Zone extends 200 nautical miles seaward from the coast, spanning an area about 1.7 times the land area of the continental United States and encompassing waters along the U.S. east, west and Gulf coasts, around Alaska and Hawaii, and including the U.S. territories in the Pacific and Caribbean. This vast region is host to a rich diversity of marine plants and animals and a wide range of ecosystems from tropical coral reefs to sea-ice covered, polar waters in the Arctic. We will highlight the current state of knowledge on changing ocean climate conditions, such as warming, sea-ice retreat and ocean acidification, and how these may be impacting valuable marine ecosystems and the array of resources and services we derive from the sea now and into the future. We will also touch on the interaction of climate change impacts with other human factors including pollution and over-fishing.
Speaker: Scott C. Doney
Time: 3:10 p.m.
Location: 3002 Moscone West


Glacial and Deglacial Radiocarbon in the Drake Passage

Changes in the dynamics of the Southern Ocean are thought to be important for glacial-interglacial atmospheric CO2 change. Radiocarbon is a sensitive tracer of past circulation and carbon cycle changes because it is produced in the atmosphere, enters the ocean through air-sea gas exchange at the surface, and then decays away as it is isolated from the atmosphere. We present thirty new radiocarbon measurements of U-Th dated deep-sea corals from the Drake Passage and combine them with forty previously published deep-sea coral radiocarbon measurements from this region (1). These corals have ages between 9.9 and 27.2 thousand years ago, and were dredged from water depths ranging between 328 and 1710 m. The increased temporal resolution provided from these newly dated corals is used to pinpoint the timing and examine the potential causes of millennial scale variations in Southern Ocean Δ14C during the glacial and deglacial periods. Our data show changes in Southern Ocean stratification and ventilation that are likely to influence atmospheric CO2 levels.
Speaker: Andrea Burke        
Time: 5:00 p.m.
Location: 2008 Moscone West


On a path towards long-term sampling following the Deepwater Horizon: Initial insights (Invited)

During the past two decades in the United States, few areas contaminated from an oil spill have been revisited on the time scales from months to years. The lack of sampling is a missed opportunity to shine light on long-term processes, evaluate recovery, identify compounds most likely to persist, and apply new chemical and biological techniques. To address this issue, my laboratory has begun a land-based effort to collect oiled samples from the Gulf of Mexico beaches from the Deepwater Horizon disaster. Each sample is archived, analyzed, and available for others via an online repository. Detailed analysis of many of these samples has already been fruitful on determining the fate of the spilled oil, which will be discussed. This meeting is an ideal time to discuss strategies for long-term sampling and archiving. With support from the Gulf Research Initiative for the next nine years, the opportunities to use these samples will be frequent.
Speaker: Christopher M. Reddy
Time: 5:45 p.m.
Location: 2003 Moscone West


Coral barium incorporation: implications for proxy applications

Coral Ba/Ca ratios have been proposed as proxies for various environmental variables including sediment loading, upwelling and groundwater input. Two assumptions that underpin the application of Ba/Ca ratios as an environmental proxy is 2) that corals take up Ba/Ca in concentrations proportional to seawater concentrations and 1) that the specified forcing mechanism influences seawater [Ba]. Here we present data from laboratory experiments that demonstrates corals reared in a range of seawater [Ba] linearly incorporate this signature in their skeletal Ba/Ca ratios. Observed coral Ba/Ca perturbations above baseline typically range from 5-15 μmol/mol which is ~100-500% increase over baseline. Other factors known to influence coral Ba/Ca include the temperature dependence on the partition coefficient and mass fraction aragonite precipitated by the coral which may be linked to calcification rate. In our experiments, calcification rate increased with temperature, thus the observed coral partition coefficient is the net effect of temperature (Ba/Ca increase at lower temperature) and calcification rate (Ba/Ca increase at higher temperature). We observed that the partition coefficient for reared coral Ba/Ca increased 20% 27.7 to 22.5 C, much less than observed Ba/Ca perturbations. Thus we predict that seawater [Ba] drives coral Ba/Ca signals in many locations. We present a model framework to calculate the expected contribution from sediment input, upwelling and groundwater discharge that is needed to produce this signature in corals growing in receiving waters. Finally we apply this model to a coral record from the Yucatan Peninsula, Mexico, recording groundwater discharge to the coastal ocean.
Speaker: Meagan E. Gonneea
Time: 5:30 p.m.
Location: 2004 Moscone West


Tuesday, December 4, 2012

Stochastic Closures for Finite Amplitude Internal Waves (Invited)

The theoretical paradigm of a self-consistent theory for the interaction of finite amplitude oceanic internal waves and its evolution from the resonant, infinitesimal amplitude limit are considered. The two limits are investigated using ray tracing techniques, analytic approximations to kinetic equations, and solutions for moments of a diffusive approximation to the resonant kinetic equation. We focus here on high frequency internal waves interacting with larger vertical and horizontal scale waves having inertial frequency. Tracing high frequency waves in one and two inertial wave backgrounds demonstrates that the infinitesimal amplitude and finite amplitude limits are phenomenologically distinct: the finite amplitude state is characterized by the coalescing of the two small scale members of the triad and a transition to a bound wave phenomena. This coalescence marks the transition to a strongly nonlinear parameter regime.

Tracing high frequency waves in a stochastic background of inertial oscillations provides estimates of the evolution of the time mean and variance of wavenumber and intrinsic frequency. These estimates are compared to the evolution of the first and second moments of a diffusive approximation of the kinetic equation. In the finite but weakly nonlinear regime we find a diffusive characterization. In the strongly nonlinear limit we find an advective characterization.

We next turn to the Finescale Paramterization of Polzin (2004, J. Phys. Oceanogr.), which has been used to successfully predict observations of turbulent dissipation. The Finescale Parameterization is an advective closure, and we demonstrate how it can be derived from resonant formula, which is a diffusive characterization. We conclude by considering application to the atmospheric internal wavefield.
Speaker: Kurt L. Polzin        
Time: 8:15 a.m.
Location: 3002 Moscone West


On the global distribution of hydrothermal vent fields: One decade later

Since the last global compilation one decade ago, the known number of active submarine hydrothermal vent fields has almost doubled. At the end of 2009, a total of 518 active vent fields was catalogued, with about half (245) visually confirmed and others (273) inferred active at the seafloor. About half (52%) of these vent fields are at mid-ocean ridges (MORs), 25% at volcanic arcs, 21% at back-arc spreading centers (BASCs), and 2% at intra-plate volcanoes and other settings. One third are in high seas, and the nations with the most known active vent fields within EEZs are Tonga, USA, Japan, and New Zealand. The increase in known vent fields reflects a number of factors, including increased national and commercial interests in seafloor hydrothermal deposits as mineral resources. Here, we have comprehensively documented the percentage of strike length at MORs and BASCs that has been systematically explored for hydrothermal activity. As of the end of 2009, almost 30% of the ~60,000 km of MORs had been surveyed at least with spaced vertical profiles to detect hydrothermal plumes. A majority of the vents discovered at MORs in the past decade occurred at segments with < 60 mm/yr full spreading rate. Discoveries at ultra-slow MORs in the past decade included the deepest known vent (Beebe at Mid-Cayman Rise) and high-temperature black smoker vents (e.g., Dragon at SWIR and Loki’s Castle at Mohns Ridge), and the highest temperature vent was measured at the slow-spreading S MAR (Turtle Pits). Using a previously published equation for the linear relationship between the number of active vent fields per 100 km strike length (F_s) vs. weighted-average full spreading rate (u_s), we predicted 676 vent fields remaining to be discovered at MORs. Even accounting for the lower F_s at slower spreading rates, almost half of the vents that are predicted remaining to be discovered at MORs are at ultra-slow to slow spreading rates (< 40 mm/yr) and about 1/3 at intermediate rates (40-80 mm/yr). MOR regions that are little explored tend to be at high latitudes, such as the ultra-slow to slow spreading Arctic MORs (e.g., Kolbeinsey and Mohns Ridges), the ultra-slow American-Antarctic Ridge, and the intermediate spreading Pacific-Antarctic Ridge. Although a greater percentage of the ~11,000 km of BASCs has been surveyed for hydrothermal activity, the discoveries at BASCs in the past decade were mainly at segments with intermediate to fast spreading rates. Using the same equation for F_s vs. u_s, we predicted 71 vent fields remaining to be discovered at BASCs, and most are likely to be found at ultra-slow and slow spreading segments (e.g., Andaman Basin, and central to northern Mariana Trough). With 2/3 of our overall predicted total vent fields at spreading ridges remaining to be discovered, we expect that the next decade of exploration will continue to yield new discoveries, leading to new insights into biogeography of vent fauna and the global impacts of fluxes of heat and materials from vents into our oceans.
http://www.interridge.org/irvents/maps
Speaker: Stace E. Beaulieu
Time: 10:20 a.m.
Location: 3022 Moscone West


Hydrothermal Activity on the Mid-Cayman Rise: ROV Jason sampling and site characterization at the Von Damm and Piccard hydrothermal fields

In January 2012 our multi-national and multi-disciplinary team conducted a series of 10 ROV Jason dives to conduct first detailed and systematic sampling of the Mid Cayman Rise hydrothermal systems at the Von Damm and Piccard hydrothermal fields. At Von Damm, hydrothermal venting is focused at and around a large conical structure that is approximately 120 m in diameter and rises at least 80m from the surrounding, largely sedimented seafloor. Clear fluids emitted from multiple sites around the flanks of the mound fall in the temperature range 110-130°C and fall on a common mixing line with hotter (>200°C) clear fluids emitted from an 8m tall spire at the summit which show clear evidence of ultramafic influence. Outcrop close to the vent-site is rare and the cone itself appear to consist of clay minerals derived from highly altered host rock. The dominant fauna at the summit of Von Damm are a new species of chemosynthetic shrimp but elsewhere the site also hosts two distinct species of chemosynthetic tube worm as well as at least one species of gastropod. The adjacent Piccard site, at ~5000m depth comprises 7 distinct sulfide mounds, 3 of which are currently active: Beebe Vents, Beebe Woods and Beebe Sea. Beebe Vents consists of 5 vigorous black smoker chimneys with maximum temperatures in the range 400-403°C while at Beebe Woods a more highly colonized thicket of up to 8m tall chimneys includes predominantly beehive diffusers with rare black smokers emitting fluids up to 353°C. Beebe Sea a diffuse site emitting fluids at 38°C Tmax, is the largest of the currently active mounds and immediately abuts a tall (8m) rift that strikes NE-SW bisecting the host Axial Volcanic Ridge. The fauna at Piccard are less diverse than at Von Damm and, predominantly, comprise the same species of MCR shrimp, a distinct gastropod species and abundant anemones.
Speaker: Christopher R. German
Time: 10:50 a.m.
Location: 3022 Moscone West


Hydration of mantle olivine under variable water and oxygen fugacity conditions: a combined SIMS and FTIR study

Trace concentrations of H+ dissolved in peridotite strongly affect both its rheology and solidus. Olivine comprises ~70% of a peridotite mode and is capable of incorporating substantial H+ at upper mantle conditions. Recently, Grant et al. (2007) conducted olivine hydration experiments to determine the influence of oxygen fugacity on H+ incorporation. FTIR analyses of their run products show that absorption bands at 3325 and 3355 cm-1 (Group II bands of Bai and Kohlstedt (1993)) are sensitive to oxygen fugacity and, therefore, likely correspond to Fe3+-bearing point defects. New olivine hydration experiments were conducted to quantify H+ concentration changes associated with these defects. SIMS was used to quantify the H+ concentration and FTIR analyses were used to monitor changes in point defect populations. Our results agree with those of Grant et al. (2007) that Group II absorption bands are sensitive to fO2, but SIMS analyses indicate that changing oxygen fugacity from Fe-Fe1-XO to Ni-NiO at constant P, T and olivine composition only increases the concentration of H+ by ~50%.

Olivine hydration experiments were conducted at 1.0, 1.5, or 2.0 GPa and 1200 °C using a piston cylinder device. Oxygen fugacity was controlled at the Fe-Fe1-XO, Fe1-XO-Fe3O4, or Ni-NiO buffer. Mixed H2O-CO2 experiments were used to resolve the influence of P from that of H2O fugacity. Starting materials, fabricated from large single crystals of San Carlos olivine (Fo88-91), were pressure-sealed in either a Fe0 or Ni0 capsule. The H+ concentration of run products were measured using a Cameca 6F ion microprobe and the protocols of Koga et al. (2003). Total infrared absorption spectra were determined by a combined polarized absorption spectra taken at three orthogonal orientation, roughly parallel to crystallographic orientation. Spectra were taken on single crystal olivines shaped as parallelapipeds with several 100s of micron thicknesses.

Results from our experiments confirm that H2O fugacity is the dominant influence on the solubility of H+ in mantle olivine. Increasing the fugacity of oxygen produces a modest increase in H+ solubility despite a significant increase in Group II absorption bands. Increasing pressure or Al3+ produce modest decreases. The negative dependence on Al3+ concentration is thought to reflect changing SiO2 activity. The solubility of H+ is insensitive to the Fe/Mg ratio of the olivine over the compositional range explored in our experiments.
Speaker: Glenn A. Gaetani
Time: 11:05 a.m.
Location: 2022-2024 Moscone West


Investigating dust input to the Red Sea using barium in corals

Seasonal wind jets frequently develop through gaps in the coastal mountains that line the margins of the Red Sea (Jiang et al., 2009 Geophys. Res. Lett.). The most prominent of these wind jets is an eastward blowing jet that is funneled through the Tokar Gap on the Sudanese coast. This wind jet, which is related to the northward migration of the Inter-Tropical Convergence Zone (ITCZ) and nocturnal drainage airflow, develops almost daily from mid-June to mid-September. The Tokar region of Sudan is an arid alluvial delta of the Baraka River, and is one of the primary dust sources in the Middle East. Large dust plumes originating from the Tokar Gap can be observed over the Red Sea using satellite imagery. These dust events can last several days and occur frequently during the summer season.

We investigated past variability in the dust input to the Red Sea using Ba/Ca in corals. We have drilled cores through massive Porites corals from the eastern margin of the Red Sea. These corals grow ~1-1.5 cm/yr, and some of the cores contain continuous growth for the past 250-300 years. Coral Ba/Ca has been previously used to examine sediment flux from rivers (e.g., McCulloch et al., 2003 Nature; Fleitmann et al., 2007 Geophys. Res. Lett.; Prouty et al., 2010 Mar. Poll. Bull.). These studies were based on the observation that dissolved barium adsorbed onto river-borne suspended particles is released as they encounter increased salinities in estuaries (e.g. Coffey et al., 1997 Estuarine Coastal and Shelf Science). We propose that wind-borne Tokar delta sediments transport barium to the eastern Red Sea, providing Ba to the coral sites either through desorption upon encountering seawater similar to river-borne sediments, or through direct settling of particles onto coral colonies, or both. We test these hypotheses and examine how Red Sea coral Ba/Ca has changed over the past 250 years.

Coral Ba/Ca was measured at biweekly resolution at two sites for the past 15 years. Ba/Ca displays a seasonal cycle that is negatively correlated with sea surface temperature and positively correlated with coral Sr/Ca. The seasonal cycle is consistent with the previously suggested temperature dependence on the incorporation of barium into coralline aragonite. Superimposed on the seasonal cycle are distinct peaks, which are likely caused by wind jet dust events. To investigate long-term variability in dust input, we have measured coral Ba/Ca at annual to biannual resolution at both sites for the past 250 years. We removed the influence of temperature on Ba/Ca using coral Sr/Ca; providing a record of residual Ba/Ca in the coral skeleton. Our results reveal a long-term increase in residual Ba/Ca, suggesting an increase in dust input to the Red Sea over the past 250 years. We discuss these results and their implications for changes in the SW Asian summer monsoon system since the Little Ice Age.
Speaker: Sean P. Bryan
Time: 11:05 a.m.
Location: 2008 Moscone West


How Not to Write for Peer-Reviewed Publications: Talking to Everyone Else

In an era when pressing societal issues demand scientific knowledge, science deniers and deriders are increasing, science education is deteriorating, and science in traditional media is diminishing. Scientists are challenged more than ever to explain their work beyond their peers, but they are not encouraged nor trained to do this. Rather, they can be isolated from society at large and trained to communicate in a prescribe style that the public often finds incomprehensible or can’t relate to. We created a voluntary course for graduate students in the MIT/WHOI Joint Program in Oceanography to encourage young scientists to venture beyond their laboratories and add much-needed clear and accurate scientific information to critical issues under public debate. The course is team-taught by a scientist with extensive experience dealing with the media, policymakers, legislators, and benefactors, and a journalist with decades of experience writing about science and working with scientists. Together, we expose students to the cultures, perspectives, motivations, and timelines of various stakeholders with whom they may communicate. With guests that include graphic designers, web gurus, and working journalists, the students learn editorial processes and skills to enhance effective communication with non-scientists, including the use of graphics, illustrations, photography and multimedia. Each student is also connected with a mentor: a working science journalist who volunteers personal attention throughout the student’s process of writing an article explaining their research. (e.g. Dick Kerr of /Science/ and Peter Spotts of /The Christian Science Monitor/). In short, the course helps students become comfortable and facile outside the ivory tower.
Speaker: Christopher M. Reddy
Time: 11:10 a.m.
Location: 3004 Moscone West


Geochemistry of Hydrothermal Fluids from the Ultra-Slow Spreading Mid-Cayman Rise

The Mid-Cayman Rise is an ultra-slow spreading ridge in the western Caribbean, and with an axial rift valley floor at a depth of 4500-6500 m, represents one of the deepest sections of ridge crest worldwide. High temperature vent fluids were collected in January 2012 from the newly discovered Von Damm and Piccard fields using gas-tight samplers deployed from the ROV Jason. Fluids were analyzed for abundances of volatile and non-volatile aqueous species to assess the chemical environments inhabited by vent communities, and constrain fluid-rock reactions and magmatic processes in subsurface environments. Measured vent temperatures varied from 21 to 226°C at Von Damm and 45 to 398°C at Piccard. Water depths at Von Damm and Piccard are 2300 and 4960 m, respectively, corresponding to seafloor pressures of 230 and 496 bar.

Vent fluids from Von Damm are slightly acidic with measured pH (25°C) from 5 to 6. Aqueous H2 and CH4 approach 20 and 3 mmol/kg, respectively. Concentrations are strikingly similar to other vent systems hosted in ultramafic rocks suggesting extensive interaction with olivine-rich rock. Aqueous SiO2 as high as 8 mmol/kg along with K enrichments relative to seawater provide additional evidence for extensive fluid-rock interaction. Dissolved CO2 was only slightly enriched relative to seawater (<1mmol/kg) suggesting a limited contribution of magmatic volatiles to these fluids. Endmember Cl concentrations are enriched relative to seawater by ~20% and hydration of ultramafic crust during serpentinization is likely responsible. Owing to the relatively low temperature of these fluids and near neutral pH, dissolved metal concentrations were substantially lower than abundances typically observed in acidic fluids from higher temperature basalt- and ultramafic-hosted systems.

High temperature fluids were collected from two areas of venting at the Piccard Site (Beebe and Beebe Woods) hosted in basaltic crust. Measured pH (25°C) approached 3, substantially more acidic than the lower temperature Von Damm vent fluids. Consistent with fluids from other basalt-hosted hydrothermal systems, end-member CH4 concentrations were less than 150 µmol/kg. Endmember dissolved H2 concentrations, however, were substantially higher than typical basalt-hosted hydrothermal systems, with values as high as 20 mmol/kg. The extraordinarily reducing nature of these fluids may reflect fluid-rock reactions occurring at temperatures in excess of those attained at other basalt-hosted systems due to the higher pressures of subseafloor reaction zones at Piccard. Evidence for relatively high pressure and temperature reactions zones at Piccard is provided by endmember Cl concentrations that are ~30 % depleted relative to seawater, which implies subseafloor phase separation. Phase separation of Piccard fluids at seafloor pressures would occur at a temperature of 481°C, with substantially higher temperatures required in higher pressure subseafloor environments. Relative to the Von Damm fluids, endmember fluids at Piccard show greater enrichments in SiO2 and K. The Piccard fluids also show substantially higher concentrations of dissolved metals and H2S, consistent with their lower pH and higher temperature. Dissolved CO2 concentrations as high as 26 mmol/kg provides evidence for a contribution of mantle-derived volatiles to Piccard vent fluid chemistry.
Speaker: Jeffrey Seewald
Time: 11:35 a.m.
Location: 3022 Moscone West


Abundance of volatile and organic species in intermediate temperature fluids from the Von Damm and Piccard deep sea hydrothermal fields, Mid-Cayman Rise

Two recently discovered submarine hydrothermal systems at the ultra-slow spreading Mid-Cayman Rise provide a unique opportunity to investigate how mixing and cooling influence hydrothermal fluid chemistry at the deepest-yet discovered, basalt-hosted Piccard vent field (4960m) and at the Von Damm vent field (2300m), postulated to be ultramafic-hosted. Vent fluids were collected in January 2012 during R/V Atlantis cruise AT18-16 with gas-tight samplers deployed by the ROV Jason II, allowing the characterization and quantification of redox-reactive volatile species and organic compounds. Von Damm vent fluids ranged in temperature from 21 to 226°C, whereas Piccard fluids ranged from 45 to 398°C. A key feature of these systems is the variety of fluids that were actively venting from the seafloor at 100 to 200°C, substantially cooler than the hottest fluids observed at either site. The lower temperatures reflect subsurface seawater mixing and/or conductive heat loss. Fluids venting within this temperature range have rarely been sampled at other systems, and the Cayman fluids thus present an excellent opportunity to study the effect of cooling and mixing processes on enriched volatile species such as H2, H2S, CO2 and CH4. Three dominant processes are thought to affect volatile and organic species in intermediate temperature fluids. These include microbial consumption or production, thermal alteration of biomass, and abiotic reactions. The effect of these processes on fluid compositions carries implications for carbon utilization and metabolic activity of modern microbial populations hosted within hydrothermal mineral deposits and ascending plumes, carbon cycling within hydrothermal systems, and net geochemical fluxes to the ocean.

Endmember CO2 concentrations at Von Damm range from slightly enriched relative to seawater in the highest temperature fluids, to measurably depleted in the cooler fluids. Such CO2 depletions have not been previously observed in other acidic vent fluids, and imply the presence of a CO2 sink. Von Damm fluid CO2/CH4 ratios are relatively constant at 1.0 to 1.5 (mol/mol) in the higher temperature fluids, and are low compared with CO2/CH4 ratios of 200 to 250 (mol/mol) in the higher temperature Piccard fluids. All vent fluids at Von Damm are enriched in CH4 and longer-chain n-alkanes. Von Damm fluid H2 and H2S abundances are consistent with those at Rainbow and other ultramafic-influenced systems. At the Von Damm vent field, H2 shows non-conservative behavior in intermediate fluids at temperatures ≤114 °C. Such behavior is consistent with previous studies, which attributed non-conservative H2 behavior in ~30 °C vent fluids to microbial consumption (e.g. Von Damm and Lilley, 2004). Similar activity may be occurring at Von Damm. At Piccard, H2 shows non-conservative mixing behavior at temperatures ≤149 °C. H2 depletion at Piccard occurs at higher temperatures than at Von Damm, in excess of the currently known limit for life at 122 °C (Takei et al., 2008), suggesting that abiotic as well as microbial processes may be affecting H2 abundance. Methylated organic compounds, including methanethiol and methanol, were also observed in vent fluids at Piccard and Von Damm, and further organic compound analyses are ongoing.
Speaker: Jill M. McDermott
Time: 11:50 a.m.
Location: 3022 Moscone West


Modeling the distribution of Radium-228 to derive mixing rates in the North Atlantic

Radium, conservative in seawater and a marker of seawater-lithosphere interaction, can be used to measure mixing rates in a variety of ocean settings including the main thermocline and in proximity to the coastal ocean. The half-life of radium-228 (≈6 y) is appropriate for estimating diapycnal and cross-basin mixing rates; the multi-year half-life of the tracer providing information on approximately a decadal time-scale. Profiles of 228Ra were collected between Mauritania and the Cape Verde Islands as part of the 2010 US North Atlantic GEOTRACES cruise. The application of a 1-D vertical diffusivity model generates 228Ra-derived vertical mixing rates within the main thermocline in the range of 0.33-0.88 cm2 s-1, with a trend of increased mixing as one moves westward away from the west African coastline. Although these mixing rates are higher than other published values, they agree within an order of magnitude. However, they should be viewed cautiously given the known influence of lateral mixing. The 6-year half-life is long enough such that lateral, as well as vertical transport processes are likely to have a significant influence on the shape of vertical 228Ra profiles. Here, we will present a progression from a 1-D vertical model, on to a more informative 2-D vertical and horizontal model, and finally investigate the application of a 3-D model for the region sampled. Mixing rates calculated using the various approaches will be compared, and then placed in the context of how they can be used to estimated geochemical fluxes of other trace elements.
Speaker: Paul J. Morris
Time: 11:50 a.m.
Location: 3005 Moscone West

Ocean Salinity Variance and the Global Water Cycle (Invited)

Ocean salinity variance is increasing and appears to be an indicator of rapid change in the global water cycle. While the small terrestrial water cycle does not reveal distinct trends, in part due to strong manipulation by civilization, the much larger oceanic water cycle seems to have an excellent proxy for its intensity in the contrasts in sea surface salinity (SSS). Change in the water cycle is arguably the most important challenge facing mankind. But how well do we understand the oceanic response? Does the ocean amplify SSS change to make it a hyper-sensitive indicator of change in the global water cycle? An overview of the research challenges to the oceanographic community for understanding the dominant component of the global water cycle is provided.
Speaker: Raymond W. Schmitt
Time: 4:00 p.m.
Location: 3005 Moscone West


Total Dissolved Cobalt and Labile Cobalt in the North Atlantic (Invited)

This study presents the total and labile dissolved cobalt distributions from the North Atlantic GEOTRACES Zonal Transect expeditions of the fall of 2010 and 2011. Labile cobalt was detected in much of the water column below the euphotic zone, suggesting that strong cobalt binding ligands were not present in excess of the total cobalt concentration. Near complete complexation of cobalt was observed in surface waters, and linear relationships were observed when both total and labile cobalt were compared to phosphate in surface waters, indicative of a strong biological influence on cobalt cycling. Decoupling of cobalt and macronutrients in the surface waters was observed approaching the North American coast, and a relationship between cobalt and salinity was observed, suggesting that coastal inputs may dominate the distributions of cobalt there. In deep waters, both total and labile cobalt were generally lower in concentration than at intermediate depths, which is evidence of scavenging processes removing cobalt from the water column. Elevated concentrations of labile and total cobalt were observed in samples taken within the TAG hydrothermal plume, and a reverse relationship between cobalt and oxygen was observed in the western basin OMZ.
Speaker: Mak A. Saito
Time: 4:30 p.m.
Location: 3011 Moscone West


Distal transport of hydrothermal iron in the deep Eastern South Pacific Ocean

While dust deposition and transport from continental margin sediments are usually thought to be the main inputs of iron to the surface ocean dissolved Fe (dFe) pool, Fe input to the deep ocean has been attributed mostly to remineralization of sinking biogenic particles. Hydrothermal vents are known to emit large amounts of Fe to the deep ocean, but most of this Fe precipitates near the ridge crest, so it is not clear that vents supply a significant amount of dFe to the deep ocean. Several recent studies have seen dFe maxima in the deep ocean near ridge crests and attributed this dFe to hydrothermal activity (Boyle & Jenkins, 2008; Klunder et al. 2011; Wu et al. 2011; Klunder et al. 2012; Noble et al. 2012). Hydrothermally-derived Fe is believed to be maintained in the dissolved phase by a combination of binding by organic ligands (Bennett et al. 2008; Sander & Koschinsky, 2012) and a nanoparticle/colloidal contribution to the dFe class (Yucel et al. 2011). Modeling efforts using the distribution of excess He-3 in deep waters arising from hydrothermal activity have predicted that deep ocean dFe may be much higher than currently believed, especially in the southern hemisphere (Tagliabue et al. 2010).

In this presentation, we show the first deep ocean dFe data from two stations in the Eastern South Pacific Ocean (Station 7 at 26.3degS, 104degW and Station 4 at 23.5degS, 88.8degW). He-3 and dissolved manganese (dMn) distributions at these stations imply that hydrothermal activity is a significant source of dFe to the deep ocean in this region. Maximum deep dFe concentrations at 2250m reach 1.5 nmol/kg at Station 7 and are still 0.86 nmol/kg at Station 4, thousands of kilometers from presumed East Pacific Rise hydrothermal sources. Excess He-3 and dFe are correlated in the plume maximum by comparison of the measured dFe with nearby WOCE He-3 stations spatially interpolated on isopycnals. We observe a slope of 1.1-2.0 x 10^6 mol Fe/mol He-3, similar to but somewhat larger than Southwest Pacific measurements of 9.0 x 10^5 (Boyle & Jenkins, 2008). However, this slope is not applicable to the entire water column at these Southeast Pacific sites, as biological activity elevates dFe in the upper 1000m, and scavenging or water mass changes reduce dFe below the plume, while He-3 remains unaffected in both cases. This dFe/He-3 variability with depth contrasts with a constant dFe/He-3 with depth measured by Boyle & Jenkins in the Southwest Pacific below ~1000 m depth (Boyle & Jenkins, 2008). Thus, while it is clear from this study that hydrothermal activity is a source of dFe to the deep ocean and global ocean Fe inventory, dFe can also be affected by biology and scavenging, unlike He-3, especially with increasing distance from the vent source.
Speaker: Jessica N. Fitzsimmons
Time: 5:15 p.m.
Location: 3011 Moscone West


Wednesday, December 5, 2012

A statistical context for TEX86 (Invited)

The TEX86 proxy has become a widely used technique in paleoceanography since its inception in 2002. It has been particularly useful for deep-time applications where other techniques of estimating past sea-surface temperatures (SSTs) are not always available, but some of the results of these studies -- including very high estimations of southern high latitude SSTs during the early Eocene -- have raised questions regarding the viability of this organic paleothermometer. This talk re-examines the fundamental statistical basis of the TEX86 proxy, including the functional forms that represent the relative abundances of the GDGT lipids, the implications of spatial autocorrelation in the calibration dataset, and the choice of regression models. While improving the predictive capability of TEX86 ultimately rests on developing a better understanding of Thaumarchaeotal ecology and community effects, some progress can be made by employing alternative statistical approaches.
Speaker: Jessica E. Tierney
Time: 8:15 a.m.
Location: 2010 Moscone West


Weaker Walker Circulation during the Last Glacial Maximum due to reduced sea level

The Last Glacial Maximum (LGM) -- a target climate interval for both proxy and model investigations -- provides an opportunity to test mechanisms that drive tropical climate change. Here, we present the first multi-proxy, multi-model synthesis of Indo-Pacific Warm Pool (IPWP) hydroclimate during the LGM. We collect precipitation and salinity proxy data and compare them to an ensemble of nine model simulations conducted as part of PMIP2 and PMIP3, employing a new semi-quantitative approach: the Cohen's κ statistic for categorical data comparison. We find that both the terrestrial and marine proxies -- which derive from completely independent archives -- record a coherent pattern of change that only one out of the nine models simulates correctly. This pattern is diagnostic of a mechanism involving the ascending branch of Walker circulation in the IPWP, and reflects the response of tropical circulation to the exposure of the Sunda Shelf due to lowered sea level. Our results implicate sea level as a first-order driver of tropical hydroclimate on glacial-interglacial timescales, and furthermore emphasize that changes in the tropical water cycle during the glacial times cannot be simply understood as a response to the "wet-get-drier" mechanism, which is the inverse of the "wet-get-wetter" mechanism for global warming. Our finding that the models simulate diverse responses to the Sunda Shelf exposure -- most of which do not agree with the proxies -- has major implications for our ability to simulate tropical climates both past and future.
Speaker: Jessica E. Tierney
Time: 2:55 p.m.
Location: 2008 Moscone West


Global transfer of terrestrial organic carbon to the Ocean: an erosional control (Invited)

Riverine export of organic carbon (OC) to the ocean fundamentally affects the atmospheric C inventory over a wide range of timescales. Over geological timescales, the balance between biospheric OC sequestration and rock-derived (petrogenic) C oxidation sets the magnitude of atmospheric C sequestration. Over shorter timescales, variations of the rate of exchange between C reservoirs, such as soils and marine sediment, modulate atmospheric carbon dioxide levels. Heretofore, the respective fluxes of biospheric and petrogenic C have been poorly constrained and the mechanisms controlling OC export have remained elusive, impeding our ability to make quantitative predictions of OC fluxes under forcing scenarios. Here, we present petrogenic and biospheric OC flux estimates for a set of river systems representative of the natural variability in catchment properties. We show that the efficiency of both petrogenic and biospheric OC export is positively related to suspended sediment yield, revealing a global control of OC export by physical erosion. Using a global compilation of gauged suspended sediment flux, we propose new estimates of global biospheric and petrogenic OC fluxes of 165 and 55 Mt/yr, respectively, showing that petrogenic C accounts for ca. 25% of the global riverine transfer of OC to the ocean. Biospheric OC export is to the first order controlled by the capacity of rivers to mobilize and transport OC, and rather insensitive to primary production. We conclude that the primary drivers of terrestrial OC cycling are climate and tectonics over short and long timescales, respectively.
Speaker: Valier Galy
Time: 4:45 p.m.
Location: 2004 Moscone West


Thursday, December 6, 2012

A statistical context for TEX86 (Invited)

The TEX86 proxy has become a widely used technique in paleoceanography since its inception in 2002. It has been particularly useful for deep-time applications where other techniques of estimating past sea-surface temperatures (SSTs) are not always available, but some of the results of these studies -- including very high estimations of southern high latitude SSTs during the early Eocene -- have raised questions regarding the viability of this organic paleothermometer. This talk re-examines the fundamental statistical basis of the TEX86 proxy, including the functional forms that represent the relative abundances of the GDGT lipids, the implications of spatial autocorrelation in the calibration dataset, and the choice of regression models. While improving the predictive capability of TEX86 ultimately rests on developing a better understanding of Thaumarchaeotal ecology and community effects, some progress can be made by employing alternative statistical approaches.
Speaker: Jessica E. Tierney
Time: 8:15 a.m.
Location: 2010 Moscone West


Weaker Walker Circulation during the Last Glacial Maximum due to reduced sea level

The Last Glacial Maximum (LGM) -- a target climate interval for both proxy and model investigations -- provides an opportunity to test mechanisms that drive tropical climate change. Here, we present the first multi-proxy, multi-model synthesis of Indo-Pacific Warm Pool (IPWP) hydroclimate during the LGM. We collect precipitation and salinity proxy data and compare them to an ensemble of nine model simulations conducted as part of PMIP2 and PMIP3, employing a new semi-quantitative approach: the Cohen's κ statistic for categorical data comparison. We find that both the terrestrial and marine proxies -- which derive from completely independent archives -- record a coherent pattern of change that only one out of the nine models simulates correctly. This pattern is diagnostic of a mechanism involving the ascending branch of Walker circulation in the IPWP, and reflects the response of tropical circulation to the exposure of the Sunda Shelf due to lowered sea level. Our results implicate sea level as a first-order driver of tropical hydroclimate on glacial-interglacial timescales, and furthermore emphasize that changes in the tropical water cycle during the glacial times cannot be simply understood as a response to the "wet-get-drier" mechanism, which is the inverse of the "wet-get-wetter" mechanism for global warming. Our finding that the models simulate diverse responses to the Sunda Shelf exposure -- most of which do not agree with the proxies -- has major implications for our ability to simulate tropical climates both past and future.
Speaker: Jessica E. Tierney
Time: 2:55 p.m.
Location: 2008 Moscone West


Global transfer of terrestrial organic carbon to the Ocean: an erosional control (Invited)

Riverine export of organic carbon (OC) to the ocean fundamentally affects the atmospheric C inventory over a wide range of timescales. Over geological timescales, the balance between biospheric OC sequestration and rock-derived (petrogenic) C oxidation sets the magnitude of atmospheric C sequestration. Over shorter timescales, variations of the rate of exchange between C reservoirs, such as soils and marine sediment, modulate atmospheric carbon dioxide levels. Heretofore, the respective fluxes of biospheric and petrogenic C have been poorly constrained and the mechanisms controlling OC export have remained elusive, impeding our ability to make quantitative predictions of OC fluxes under forcing scenarios. Here, we present petrogenic and biospheric OC flux estimates for a set of river systems representative of the natural variability in catchment properties. We show that the efficiency of both petrogenic and biospheric OC export is positively related to suspended sediment yield, revealing a global control of OC export by physical erosion. Using a global compilation of gauged suspended sediment flux, we propose new estimates of global biospheric and petrogenic OC fluxes of 165 and 55 Mt/yr, respectively, showing that petrogenic C accounts for ca. 25% of the global riverine transfer of OC to the ocean. Biospheric OC export is to the first order controlled by the capacity of rivers to mobilize and transport OC, and rather insensitive to primary production. We conclude that the primary drivers of terrestrial OC cycling are climate and tectonics over short and long timescales, respectively.
Speaker: Valier Galy
Time: 4:45 p.m.
Location: 2004 Moscone West


Friday, December 7, 2012

Pacific Circulation and the Resilience of its Equatorial Reefs (Invited)

High rates of calcification by tropical reef-building corals are paramount to the maintenance of healthy reefs. Investigations of the impact of ocean acidification in both laboratory and field studies demonstrate unequivocally the dependence of coral and coral reef calcification on the carbonate ion concentration of seawater, a dependence predicted by fundamental laws of physical chemistry. Nevertheless, results from a new generation of experiments that exploit the biology of coral calcification, suggest that effects of ocean acidification can - in some instances - be mitigated with simultaneous manipulation of multiple factors. These laboratory results imply that coral reefs in regions projected to experience changes in, for example, nutrient delivery, light and flow, in addition to pH and carbonate ion concentration, may be more resilient (or vulnerable) to the effects of ocean acidification alone. If demonstrated to be true, these observations have profound implications for the conservation and management of coral reefs in the 21st century. We quantified spatial and temporal variability in rates of calcification of a dominant Indo-Pacific reef building coral across sites where changes in ocean circulation patterns drive variability in multiple physical, chemical and biological parameters. Such changes are occurring against a background of variability and trends in carbonate system chemistry. Our field data provide support for hypotheses based on laboratory observations, and show that impacts of ocean acidification on coral calcification can be partially and in some cases, fully, offset by simultaneous changes in multiple factors. Our results imply that projected changes in oceanic and atmospheric circulation patterns, driven by global warming, must be considered when predicting coral reef resilience, or vulnerability, to 21st century ocean acidification.            
Speaker: Anne L. Cohen  
Time: 9:30 a.m.
Location: 3005 Moscone West


Multiproxy reconstruction of tropical Pacific Holocene temperature gradients and water column structure

The El Niño-Southern Oscillation (ENSO) is the most prominent mode of tropical Pacific climate variability and has the potential to significantly impact the climate of the Indo-Pacific region and globally1. In the past, the mean state of the Pacific Ocean has, at times, resembled El Niño or La Niña conditions2. Although the dynamical relationships responsible for these changes have been studied through paleoproxy reconstructions and climate modeling, many questions remain. Recent paleoproxy based studies of tropical Pacific hydrology and surface temperature variability have hypothesized that observed climatological changes over the Holocene are directly linked to ENSO and/or mean state variability, complementing studies that dynamically relate centennial scale ENSO variability to mean state changes3-8. These studies have suggested that mid Holocene ENSO variability was low and the mean state was more “La Niña” like3-6. In the late Holocene, paleoproxy data has been interpreted as indicating an increase in ENSO variability with a more moderate mean ocean state3-6. However, alternative explanations could exist. Here, we test the hypothesis that observed climatological changes in the eastern tropical Pacific are related to mean state or ENSO variability during the Holocene.

We focus our study on two sets of cores from the equatorial Pacific, with one located in the Indo-Pacific Warm Pool (BJ803-119 GGC, 117MC, sedimentation rates ~29 cm/kyr) and the other just off the Galapagos in the heart of the Eastern Cold Tongue (KNR195-5 43 GGC, 42MC, sedimentation rates ~20cm/kyr). The western site lies in the region predicted by models to show the greatest variations in temperature and water column structure in response to mean state changes, while the eastern site lies in the area most prone to changes due to ENSO variability7. Together, these sites allow us the best chance to robustly reconstruct ENSO and mean state related changes. We use a multiproxy approach and consider records from organic (sterol abundances) and inorganic proxies (Mg/Ca and δ18O of 3 planktonic foraminiferal species, % G. bulloides) to reconstruct zonal tropical Pacific (sub)surface temperature and stratification gradients over the Holocene. A benefit of using this approach is that it enables us to combine the strengths of each individual proxy to derive more robust records. We will compare our records with published paleoproxy and model studies in the Pacific and Indo-Pacific regions. Armed with this information, we aim to better understand mean state changes in the tropical Pacific over the Holocene.
Speaker: Jennifer A. Arbuszewski
Time: 9:00 a.m.
Location: 2010 Moscone West


Sea level anomalies influence coastal groundwater dynamics and discharge

Within coastal aquifers there are two interacting water masses. The fresh water lens (terrestrial groundwater) is supplied by inland recharge and overlies a salt wedge (marine groundwater), with dispersive mixing occurring at the interface. The extent of mixing within coastal aquifers and surface water exchange is driven by an elevation gradient between the aquifer and sea level, with temporal variability on the scale of months to years (i.e. greater than tidal) thought to be controlled by terrestrial groundwater levels. We monitored the position of the mixing zone in the coastal aquifer of Waquoit Bay, MA, USA, for 4 years and observed that an increase in hydraulic gradient led to an overall seaward movement of the interface, resulting in low salinity conditions, while a decrease in head led to landward movement of the interface and high salinity groundwater at this location. Our results indicate that seasonal scale variability in sea level, not groundwater level, is the dominant variable driving the hydraulic gradient, which in turn modulates discharge from unconfined coastal aquifers. To explore the potential impact of sea level revealed by the coastal aquifer salinity time series on groundwater flow to the ocean, we constructed a simulation model of groundwater flow and salt transport in an unconfined coastal aquifer using the USGS code SEAWAT. Model simulations driven with observed coastal groundwater and sea level demonstrate increased mixing between marine and terrestrial groundwater compared to those assuming a static sea level. In addition, the coastal aquifer time series demonstrated a direct response to the 2009-2010 El Nino event, which elevated sea level on the US eastern seaboard for over a year. Thus the physical and chemical behavior of coastal aquifers appears to be sensitive to external climate forcing.
Speaker: Matthew A. Charette
Time: 12:05 p.m.
Location: 3020 Moscone West


Being There & Getting Back Again: Half a Century of Deep Ocean Research & Discovery with the Human Occupied Vehicle “Alvin” (Invited)

In 2013, Alvin returns to service after significant observational and operational upgrades supported by the NSF, NAVSEA & NOAA. Here we review highlights of the first half-century of deep submergence science conducted by Alvin, describe some of the most significant improvements for the new submarine and discuss the importance of these new capabilities for 21st century ocean science and education.

Alvin has a long history of scientific exploration, discovery and intervention at the deep seafloor: in pursuit of hypothesis-driven research and in response to human impacts. One of Alvin’s earliest achievements, at the height of the Cold War, was to help locate & recover an H-bomb in the Mediterranean, while the last dives completed, just ahead of the current refit, were to investigate the impacts of the Deep Water Horizon oil spill. Alvin has excelled in supporting a range of Earth & Life Science programs including, in the late 1970s, first direct observations and sampling of deep-sea hydrothermal vents and the unusual fauna supported by microbial chemosynthesis. The 1980s saw expansion of Alvin’s dive areas to newly discovered hot-springs in the Atlantic & NE Pacific, Alvin's first dives to the wreck of RMS Titanic and its longest excursions away from WHOI yet, via Loihi Seamount (Hawaii) to the Mariana Trench. The 1990s saw Alvin’s first event-response dives to sites where volcanic eruptions had just occurred at the East Pacific Rise & Juan de Fuca Ridge while the 2000s saw Alvin discover novel off-axis venting at Lost City. Observations from these dives fundamentally changed our views of volcanic and microbial processes within young ocean crust and even the origins of life! In parallel, new deep submergence capabilities, including manipulative experiments & sensor development, relied heavily on testing using Alvin. Recently, new work has focused on ocean margins where fluid flow from the seafloor results in the release of hydrocarbons and other chemical species that can sustain chemosynthetic seep ecosystems comparable to, and sometimes sharing species with, hot vents. What will Alvin’s next 50 years discover?

During 2011-12, Alvin has undergone a transformation, including a larger personnel sphere with more & larger viewports to provide improved overlapping fields of view for the pilot & observers. The new Alvin will be certified for operations to 4500m depth initially, but the new sphere will be 6500m-rated and planned future upgrades will ultimately allow the vehicle to dive that deep, enabling human access to 98% of the global ocean floor. This will allow the study of processes and dynamics of Earth’s largest ecosystem (the abyssal plains) as well as margin and ridge environments and the overlying water column. Meantime, the current upgrades to Alvin already include a suite of scientific enhancements including new HD video & still imaging, sophisticated data acquisition systems for seafloor observations and mapping, a new work platform with greater payload capacity and improved observer ergonomics.

The new Alvin is poised to play important roles in core Earth and Life science programs and to serve large-scale programs such as the Ocean Observatory Initiative (OOI) and the International Ocean Discovery Program (IODP). It will continue to attract, engage and inspire a new generation of scientists & students to explore and study the largest ecosystem on Earth, just as it has done throughout its first half century.
Speaker: Christopher R. German
Time: 3:10 p.m.
Location: 3011 Moscone West


Partnerships Drive Informatics Solutions for Biological Imaging at Ocean Observatories (Invited)

In the big-data, era informatics-oriented partnerships are needed to achieve improved scientific results and understanding. Our teams’ experience shows that formal methodologies to build interdisciplinary partnerships enable us to efficiently produce needed technological innovation. One-on-one partnerships between individual research scientists and informaticists provide a crucial building block for supporting larger, nested partnerships. We present one such partnership as an example.

As ocean observatories mature, they produce data at a pace that threatens to overwhelm the capacity of individual researchers to manage and analyze it. Our multi-disciplinary team has addressed these challenges in the context of a study involving very large numbers (~1 billion) of images collected by Imaging FlowCytobot, an automated submersible flow cytometer that continuously images plankton at up to 10hz. These data provide novel insights into coastal ecosystem dynamics, including characterization of biological responses to environmental change and early warning of harmful algal blooms.

In contrast with the traditional focus on technology adoption, we have instead emphasized building partnerships between oceanographers and computer scientists. In these partnerships we identify use cases, design solutions, develop prototypes, and refine them until they meet oceanographers’ science needs. In doing so we have found that rapid and significant advances do not always require technological innovations, but rather effective communication, focus on science outcomes, and an iterative design and evaluation process. In this work we have adopted a methodology developed in the Tetherless World Constellation at Rensselaer Polytechnic Institute, a framework that has been used for several data-intensive earth science applications.

The prototype system produced for Imaging FlowCytobot data provides simple and ubiquitous access to observational data and products via web services and includes a data dashboard (http://ifcb-data.whoi.edu/) that enables near-real-time browsing of images. Data can now be reprocessed with improved algorithms in a fraction of the time (weeks now, instead of years). Public web services replace researchers’ need to gain access to internal networks or custom software. Links to image data can now be cited in publications and other documentation, emailed, posted to social networks, etc. A key strategy has been to enable these new capabilities without disrupting existing, working systems (e.g., no requirement to reformat existing data or rewrite analysis codes). The new data system is currently in use by multiple researchers deploying Imaging FlowCytobots and providing input that is informing continued development.
Speaker: Heidi M. Sosik       
Time: 4:00 p.m.
Location: 2020 Moscone West

Last updated: December 18, 2012