2011 Research Highlights
The Physical Oceanography Department, in association with the Geology and Geophysics and Marine Chemistry and Geochemistry Departments, engaged in a scientific staff recruitment effort from 2009 to 2011 that focused on Climate Research. This search was very successful, resulting in the addition of 5 staff members with climate interests to the PO Department (three Assistant Scientists and two Associate Scientists with Tenure). Here we introduce these five investigators and showcase elements of their present research.
I. Much of Carol Anne Clayson's current research focuses on the global water and energy cycles. Using mostly satellite data, Carol Anne works with hydrologists and atmospheric scientists to estimate the uncertainties remaining in these cycles and investigating if, as climate change models suggest, the water cycle is indeed increasing in strength and if there has been a change in the number of weather and climate extremes across the globe. Early indications are that the distributions of weather events are indeed changing. Carol Anne is also investigating diurnal (day and night) sea surface temperature cycles, to accurately account for earth's heat and water budgets and to quantify the impact of diurnal variations on ocean-atmosphere feedbacks. Her analysis of ten years of data showed that if diurnal sea surface temperatures weren't included in the energy calculations for the tropical ocean, the estimated air-sea fluxes (the rates at which heat is exchanged between ocean and atmosphere) could be in error by up to ten Watts per square meter—an important finding that is helping to motivate continuing investigations of the diurnal sea surface temperature cycle and upper ocean mixing processes.
II. A major reason why the ocean is important for Earth’s climate is that the deep water can be out of contact with and isolated from the sea surface for very long periods of time. This allows carbon compounds taken up from the atmosphere by surface waters to be sequestered(isolated) at depth, reducing (at least temporarily) the amount of carbon dioxide in the atmosphere. The “age” of ocean waters, defined as the time since water was last at the surface, is a valuable way of characterizing the dominant time scales of the ocean circulation. Carbon-14 is a radioactive isotope long used to calculate the age of fossils, artifacts, and other objects, and also for dating ocean water. One of Geoffrey (Jake) Gebbie's research projects that examines how ocean mixing affects the interpretation of carbon-14 levels uses observations of water property, in conjunction with a circulation model, to individually track over 11,000 water parcels from their surfacing locations to the deep ocean interior (in contrast to previous estimates that typically tracked just a handful of surface source waters). Taking mixing properly into account increases the ocean water age estimates by several hundred years; Jake estimates that deep Pacific Ocean waters are well over 1,000 years old. His research suggests that the ocean played a strong role in the large climatic swings of Earth’s past, because ocean waters appear to be renewed on a similar timescale to the waxing and waning of large ice sheets during the Ice Age.
III. Amala Mahadevan studies the impact of upper-ocean physical processes on the distributions and cycling of chemicals between living organisms and the ocean environment. Phytoplankton at the base of oceanic ecosystem food chains are also important componentsof the ‘biological pump’—the process in which single-celled plants take up carbon dioxide and sink to deep waters when they die, removing the carbon from contact with the atmosphere. Phytoplankton grow in sunlit waters supplied with nutrients from the deeper waters. What controls the residence time of phytoplankton in surface waters before being carried to deeper/darker depths by currents? What currents transport nutrient-rich deeper waters to the surface? What controls the surface distribution of dissolved carbon, and carbon dioxide exchange with the atmosphere? How do upper-ocean physical processes facilitate the export of organic carbon to depth? Amala explores these questions with dynamical models that describe mixed-layers, fronts, eddies and internal waves. Her goal is to improve our understanding of the oceanic carbon cycle and its response and feedback to increasing atmospheric carbon dioxide and changing climate.
IV. While mechanisms inducing climate variability tend to have broad spatial scales, strong interactions among the earth system components often yield regionally-distinct patterns of change. Hyodae Seo seeks to understand how earth system components interact with each other to determine regional-scale climate variability, and, in turn, how these influence the local-scale climate processes relevant to human society. In one current project, Hyodae, working with others, has analyzed 30-year records of summertime water temperatures from coastal weather buoys and remote sensing data on the western U.S. continental shelf. His work reveals a significant cooling trend in sea surface temperature (at an average rate of about âÃ‚Â€Ã‚Â‘0.2 °C per decade) that is more prominent off south-central California than the Oregon-northern California coast. This coastal upwelling is an oceanic process poorly accounted for in climate models and data, but it appears to have intensified in the past 30 years due to more upwelling-favorable winds interacting with the regional coastal landforms. These small-scale climate signals that have significant implications for local weather, rainfall and diurnal cycles likely occur in coastal regions beyond the U.S. West Coast.
V. Temperature anomalies in the ocean (differences between observed temperatures and expected or average temperatures) persist much longer than the higher-frequency variability in the atmosphere. Better understanding of the links between sea surface temperatures (SST) and regional climate can help improve seasonal and longer term rainfall forecasts: a vital capability for water and agricultural management, as global populations continue to rise and uncertainty related to long-term climate change abounds. Caroline Ummenhofer studies SST variability and its role in modulating regional rainfall and drought. One of her foci is the Indo-Pacific and Australasian region, for which she combines observations, a wide range of model products, and paleoclimate reconstructions to identify patterns and investigate the physical mechanisms producing them. Such studies improve our understanding of the Indian and Pacific Oceans’ influence on drought in Indian Ocean-rim countries affected by monsoon systems over a range of timescales. The success or failure of the Asian monsoon can mean the difference between prosperity and severe hardship in the affected regions; clearly a better understanding of Indo-Pacific climate drivers on the monsoon is desirable.
Beyond these additions to the PO scientific staff, Postdocs Marieke Femke de Jong, Jean-Baptiste Gilet, Jeremy Kasper, Paolo Luzzatto-Fegiz. Melissa Omand, Gauher Shaheen, Robert Todd and Jinbo Wang, and Research Associate II Carolina Nobre joined the Department in 2011, while Magdalena Andres transitioned from Postdoc to Assistant Scientist. Senior Scientists Jim Price and Terry Joyce, Senior Research Specialist Dick Limeburner and Senior Information Systems Assistant I Jane Dunworth-Baker retired in 2011; the first 3 were subsequently appointed as Emeritus. Also leaving us in 2011 were Postdocs Liz Douglass and Emily Shroyer.
We applaud Emeritus Scientist Joe Pedlosky for being awarded the Maurice Ewing Medal from the American Geophysical Union, Associate Scientist with Tenure Lou St. Laurent for receiving the Nicholas P. Fofonoff Award from the American Meteorological Society, and Senior Scientist Bob Weller for being elected Fellow of the American Association for the Advancement of Science.
—John M. Toole, Department Chair
2010 Research Highlights
Our branch of ocean science focuses on the physics of ocean currents, the role of those flows in the earth’s climate system and their interaction with the ocean geochemical- and eco-systems. Physical oceanographic research involves a blend of approaches including direct observation using instruments operated in the field by scientists and technicians or sampling autonomously, design and carrying out of laboratory experiments, and application of analytical and numerical approaches to solving the governing fluid dynamical equations appropriate for a given problem. At the time of this writing in late December 2010, our department encompassed a scientific staff of 31 individuals with an additional 7 scientist emeriti and a combined postdoctoral scholar and postdoctoral investigator group of 8, who collaborate with and are supported by a technical staff of 64. In addition, there are currently 21 Joint Program students enrolled in a physical oceanography curriculum.
Many of the research activities highlighted in the 2009 annual report were sustained through 2010. Geographically, these investigations span all major oceans on the earth and nearly from pole to pole, from the very near shore regions to the deep. Below, a subset of these projects are summarized, working north to south:
• Several PO Department members carried out research projects focused on the Arctic Ocean and adjoining subpolar seas, many of which contribute to the long-term Arctic Observing Network (AON) effort. In 2010, Rick Krishfield supported the WHOI Ice-Tethered Profiler (ITP) program of drifting buoys deployed on Arctic sea ice as well as Andrey Proshutinsky’s sustained measurement program (Beaufort Gyre Observing System, BGOS) centered in the Canada Basin northeast of Alaska. ITPs were deployed near the North Pole in April using aircraft and in the Canada Basin in October from icebreaker, the latter in conjunction with the annual BGOS cruise during which an array of bottom-mounted moorings were serviced and ship sampling was conducted. One focus of these research efforts is the changing inventory of low-salinity surface waters that have been observed in the past to occasionally overflood the subpolar deep convection sites and shut down intermediate and deep water production for a time. Closer to the coast, Al Plueddemann led a team that deployed an autonomous underwater vehicle under the sea ice near Barrow, Alaska in March, while later in the year, Bob Pickart deployed moorings on the continental shelf that contribute to the AON and carried out shipboard sampling on two cruises, accompanied by postdoc Emily Shroyer. These studies are interested in documenting the Pacific Ocean waters that enter the Arctic through Bering Strait then spread east along the continental shelf and slope. On the theoretical front, Proshutinsky continued to direct the international Arctic Ocean Model Intercomparison Project whose annual meeting this year attracted more than 100 participants. In addition, Mike Spall investigated the relative role of air-sea buoyancy and wind stress forcing in driving overturning circulations in high-latitude marginal seas, while Jiang Yang studied the dynamics of the dense water overflows from such basins.
• Fiamma Straneo continued her innovative and challenging research program investigating the ocean influences on Greenland glaciers. In March she led a team to Sermilik Fjord to make the first wintertime observations of the ocean waters touching the base of the glacier. Owing to the absence of significant outflow of cold melt water from the glacier, the ocean temperatures in winter were warmer than what she observed the previous summer. Straneo returned to East Greenland in August-September to recover moorings that she had deployed in Sermilik and Kangerdlugssuaq Fjords the previous summer. Complementing this field work, Claudia Cenedesi has designed a series of laboratory experiments to investigate the dynamics of fjord ocean water interactions with a glacier tongue. This work has revealed the possibility of mid-depth intrusions of glacier-influenced waters extending from the glacier front, not unlike what Straneo has at times observed.
• At subpolar latitudes in the Atlantic Ocean, Amy Bower initiated a joint field program with German investigators looking at deep waters flowing through the Charlie Gibbs Fracture Zone, a series of deep passages through the MidAtlantic Ridge near 52°N. This moored array is planned to be in place for two years. Mike McCartney’s OCCI/ARI-funded glider program to sample the southward-flowing dense waters near Grand Banks returned one section across the current before the glider was lost; he is planning a second deployment in spring 2011. Dave Fratantoni contributed to several research efforts using ocean gliders, including using these autonomous instruments to acoustically track whales.
• Following the Atlantic deep waters further south, Ruth Curry together with Kurt Polzin initiated a measurement program in the area between Bermuda, Puerto Rico and the MidAtlantic Ridge to better understand the abyssal water circulation in this region and investigate the role of vertical mixing in driving that flow. The initial cruise of the program successfully deployed a moored array on the eastern flank of the Bermuda Rise in September despite significant interruption by Hurricane Igor. Curry is also involved in the Line W sustained measurement program with Terry Joyce, John Toole, McCartney and Lamont-Doherty Earth Observatory scientist Bill Smethie that is sampling the equatorward flow of the Deep Western Boundary Current over the continental slope southeast of Woods Hole. The 6-element Line W moored array was successfully recovered and redeployed in October. Joyce, together with Young-Oh Kwon, Fratantoni, Straneo, J.J. Park and postdoc Xujing Davis and others are continuing to analyze the CLIMODE observations obtained in the Gulf Stream during winter, and making comparisons together with Steve Jayne, Tom Farrar and postdoc Liz Douglass to the comparable region in the North Pacific sampled during the KESS program, while postdoc Magdalena Andres joined a research cruise looking at flow through the Ryuku Island arc.
• Anthony Kirincich has been busy this year installing and validating a new measurement system at the Martha’s Vineyard Coastal Observatory. Data from this multiple-antenna radar system is used to infer the surface velocity of the ocean over an approximately 6 by 12 mile swath south of the island. Anthony is planning to use this system to investigate the dynamics of the inner shelf circulation. Relatedly, new Assistant Scientist Irina Rypina is planning a massive surface drifter experiment within Kirincich’s sampling area to both validate the radar system and investigate natural flow boundaries within the ocean that may be explored using dynamical systems theory, a branch of theoretical fluid dynamics that Larry Pratt also studies. Complementing this coastal field work, Ken Brink and Steve Lentz engaged in theoretical studies of bottom boundary layers and topographic flow rectification.
• In the far western North Pacific, Jayne, Douglass, and Ken Decoteau (in support of Lou St. Laurent) participated in a cruise to study the evolution cold sea surface temperature wakes that develop behind typhoons (and hurricanes). This work called for a careful mix between the need to sample close to a storm but not too close! Also in the region, Glen Gawarkiewicz, Karl Helfrich and St. Laurent worked this year to analyze data obtained in previous years from the East and South China Seas with one focus being non-linear internal waves.
• Several PO Department members contributed to measurement programs in the Gulf of Mexico after the Deepwater Horizon oil platform disaster. Marshall Swartz prepared and mounted instrumentation aboard ships that sampled the water properties in the region of the spill; Dan Torres sailed on two of those cruises in June and July. In addition, Breck Owens and colleagues operated an ocean glider that surveyed the oil spill region autonomously, sending back data in real time via satellite. Jayne was secunded by the U.S. Coast Guard to assist with their evaluation of proposed oil spill mitigation strategies.
• Bower, Lentz, Farrar, Dick Limeburner and Jim Churchill were involved in field programs to the Red Sea in association with KAUST again this year. Highlights include an extensive hydrographic survey of the eastern Red Sea in March, and moored instrument deployments/recoveries in May-June and December. Jayne developed and taught a course to 60 students at the University in January/February.
• Ray Schmitt continued laying groundwork for the SPURS study of sea surface salinity variability in conjunction with the NASA Aquarius satellite. Lisan Yu and Bob Weller’s OAFlux air-sea exchange data set will contribute to this study using its estimates of ocean evaporation.
• The Upper Ocean Processes group had another busy year servicing their long-term surface moorings in the central low-latitude North Atlantic (Plueddemann lead), off Hawaii and west of Chile (Weller leads). In addition, UOP designed, built, provided to the Australian Government, and helped deploy a surface mooring south of Tasmania as part of the Australian IMOS (Integrated Marine Observing System). Weller and Farrar continued their sampling of eddy variability and vertical mixing in the upper ocean in the region around that latter mooring using underway CTDs and a Vertical Microstructure Profiler. Their work, in conjunction with analysis of data collected the year before with Straneo, seeks to quantify the different cooling and freshening processes at work in the upper ocean under the persistent stratus clouds that characterize this region. Kudos go out in particular to Jeff Lord and Ben Pietro for their efforts aboard the vessel B.I.C Humbolt to rescue the buoy off Chile that had gone adrift in July, and to Hazel Salazar for assisting with the logistics of that charter.
• As noted in last year’s report, Curry and Douglass completed the reoccupation of the 32°S hydrographic section initiated by Macdonald (Australia to Tahiti) with a January/February cruise (Tahiti to Valparaiso), and happened to return home just before the major earthquake that struck Chile later that month.
• St. Laurent, Toole, Krishfield, Decoteau and Dave Wellwood were at sea on the ill-fated DIMES (Diapycnal and Isopycnal Mixing Experiment in the Southern Ocean) cruise southwest of Chile at that time (fortunately far enough away from the epicenter to experience no effects of the quake). However, earlier in the cruise R/V Thompson Captain Phil Smith suffered a major heart attack and died. Despite this tragedy, an extensive survey of the anthropogenic tracer that AOPE scientist Jim Ledwell deployed one year earlier was completed along with ocean turbulence observations done by the PO contingent. Both the tracer dispersion rate and turbulence data suggest that the vertical mixing in the Antarctic Circumpolar Current away from rough bathymetry is remarkably weak.
• The Neutrally-Buoyant Sediment Trap(NBST), a novel technology developed by Jim Valdes in conjunction with MC&G scientist Ken Buesseler, samples sinking biological material in the upper ocean over time periods of 1-30 days. In 2010, Jim and associates deployed NBST instruments off Bermuda (continuing a long-term program) and near the Antarctic Peninsula in the Southern Ocean – one of the latter marked the 100th deployment of NBSTs since the first in 2004 (with loss of only 2 systems over that time). Also this year, Jim began testing the next generation instrument he helped to develop: the Twilight Zone Explorer (TSEX).
• In mid December, Dick Limeburner and Will Ostrom (AOPE) traveled to McMurdo Station, Antarctica to install a set of velocity, temperature and salinity sensors in the waters below the floating tongue of the Ross Ice Shelf. Notably, the sensors are configured to transmit data to an electronics package sitting atop the ice, and then via satellite to WHOI. Limeburner reports that the Ross Sea Ice Shelf is the largest ice shelf in the world - about the size of France - and is 200-600m thick, overlying a seawater cavity that is about 600m thick; their observations represent the first real-time data from under an Antarctic Ice Shelf. In addition, this year Rick Krishfield supported New Zealand investigators who, at the same time Limeburner and Ostrom were working, deployed a WHOI Ice-Tethered Profiler in land-fast sea ice adjacent to the ice shelf. That system has been returning high-vertical resolution temperature and salinity information between 8 and 400 m depth 8 times per day since November 23.
• Three new Assistant Scientists joined the PO Department this year: Rypina, Jake Gebbie and Hyodae Seo. Rypina works to understand dispersion and transport barriers in geophysical flows using dynamical system theory and float observations. Gebbie and Seo were recruited under a multi-department Climate Initiative, begun in late 2009. Seo is a regional atmospheric modeler who is studying air-sea interaction in various environments. Gebbie applies models to diagnose ocean interior water property distributions in both the modern ocean and distant past, as well as to develop understanding of the tropical coupled ocean-atmosphere system.
• December 2010 marked the 50th anniversary of the first mooring deployment by the WHOI Buoy Group. The modern descendents of that facility: the WHOI Rigging Shop, Upper Ocean Processes Group, and Subsurface Mooring Operations Group, led by Rick Trask, Jeff Lord and Scott Worrilow respectively, continue the tradition, now having deployed in total nearly 1500 deep-ocean moorings. Amy Bower was presented with an Unsung Heroine Award by the Massachusetts Commission on the Status of Women, and elected Fellow of the American Meteorology Society. Glen Gawarkiewicz was recognized by the Taiwan National Science Council and U.S. Office of Naval Research for his 10 years of effort in support of the ASIAEX, VANS/WISE, and QPE programs. Other department members continue to work in service to the community: Mike Spall serves as Chief Editor of the Journal of Physical Oceanography and Ken Brink assumed a lead-editor position this year with the Journal of Marine Research, while Dave Fratantoni and Andrey Proshutinsky were named editors for the Journal of Atmospheric and Oceanic Technology and Journal of Geophysical Research, respectively. Ray Schmitt served on two National Academy Panels this past year: the first - "Advancing the Science of Climate Change" for the "America's Climate Choices" study, the second - "Marine and Hydrokinetic Energy Technology Resource Assessments." Bob Weller was appointed by the Secretary of the Navy to -, and approved for service on the “Ocean Resources and Research Advisory Panel.” Spall continued to serve on the Scientific Steering Committee for CLIVAR. In 2010, Joint Program students Jessica Benthuysen, Beatriz Peña-Molino, Tatiana Rykova and Katherine Silverthorne were awarded Ph. D. degrees while Rebecca Walsh Dell earned a Ms. degree and is continuing in the program.