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