A survey of the variability in atmospheric oxygen in relation to the global carbon cycle. Ralph F. Keeling, University of California at San Diego, Scripps Institution of Oceanography. The abundance of oxygen in the atmosphere is sensitive at the part-per-million level to biological and anthropogenic activities over a wide range of spatial and time scales. Measurements of variations in atmospheric oxygen, detected through changes in the oxygen-to-nitrogen ratio, can address several important issues pertaining to the global carbon cycle:
An improved understanding of these issues will be valuable for making more accurate forecasts of global climatic and biogeochemical changes in the decades ahead. We have recently measured the oxygen in air samples collected at several locations around the world, and the current project continues our effort to carry out a systematic global survey of the variability in the oxygen-to-nitrogen ratio. Measurements will be carried out using a newly developed interferometric technique for oxygen-to-nitrogen analysis and using gas-handling methods that obtain a precision of 1 part in 200,000 in the oxygen measurement. (S-204)
Research on oceanñatmosphere variability and ecosystem response in the Ross Sea. Robert B. Dunbar, Rice University. This interdisciplinary study, Research on OceanñAtmosphere Variability and Ecosystem Response in the Ross Sea (ROAVERRS), focuses on atmospheric forcing, ocean hydrography, sea-ice dynamics, primary productivity, and pelagicñbenthic coupling in the southwestern Ross Sea. The primary goal is to examine how changes in aspects of the polar climate system, in this case wind and temperature, combine to influence marine productivity on a large antarctic continental shelf. In the Ross Sea, katabatic winds and mesocyclones influence the spatial and temporal distribution of sea ice, as well as the upper ocean mixed-layer depth, and thus control primary production within the sea ice and in the open water system. The structure, standing stock, and productivity of bottom-dwelling biological communities are also linked to meteorological processes through interseasonal and interannual variations in horizontal and vertical fluxes of organic carbon produced in the upper ocean. During this 3-year study, we will investigate links among the atmospheric, oceanic, and biological systems of the southwestern Ross Sea ecosystem. Direct measurements will include
Based on archived meteorological data, we expect that the atmospheric variability during the study period will be such that we will be able to monitor changes in air-flow patterns and their influence on oceanographic and biological patterns and to deduce the direct and indirect links, which are the focus of the research. Results from this study will contribute to our knowledge of atmospheric and oceanic forcing of marine ecosystems and lead to a better understanding of marine ecosystem response to climatic variations. (S-216A)
Research on oceanñatmosphere variability and ecosystem response in the Ross Sea. James Barry, Monterey Bay Aquarium. Our project is part of an interdisciplinary study (Research on OceanñAtmosphere Variability and Ecosystem Response in the Ross Sea, or ROAVERRS) of meteorologic forcing phenomena, sea-ice dynamics, ocean hydrography, primary productivity, and benthic-pelagic coupling in the southwestern Ross Sea, Antarctica. The primary goal is to examine how changes in aspects of the polar climate systemin this case wind and temperatureinfluence marine productivity on a large antarctic continental shelf. In the Ross Sea, winds off the continent and mesocyclones influence the spatial and temporal distribution of ice cover, as well as upper ocean mixed-layer depth. Consequently, they control primary production in sea-ice and open-water systems. The structure, standing stock, and productivity of bottom-dwelling biological communities are also linked to meteorologic processes through interseasonal and interannual variation in horizontal and vertical fluxes of organic carbon produced in the upper ocean. During a 2-year field investigation, we will study links among atmospheric, oceanographic, and biological systems in the southwestern Ross Sea ecosystem. Direct measurements will include
Based on archived meteorologic data, we anticipate that atmospheric variability during the study will allow us to monitor changes in air-flow patterns in the southwestern Ross Sea and determine their influence on oceanographic and biological patterns. The study will contribute to our knowledge of atmospheric and oceanographic forcing of polar marine ecosystems and lead to a better understanding of the polar marine ecosystem response to climate variability. (S-216B)
Modeling primary production of the southern ocean for ROAVERRS. Michael P. Lizotte, University of Wisconsin. As part of the Research on OceanAtmosphere Variability and Ecosystem Response in the Ross Sea (ROAVERRS) program that will be conducted in the southwest Ross Sea between October 1996 and March 1997 and between October 1997 and March 1998, we will model primary production in the water column and sea ice. The focus of the initial modeling studies will be to derive estimates of primary productivity for the southern oceans. These initial estimates will be based on current understanding of the physiology, biochemistry, and ecology of southern ocean phytoplankton and sea-ice algae; climatologies for sea-ice cover, cloud cover, sea-surface temperature, and algal pigments; and existing modeling approaches for depth-dependent primary production in sea ice and water column. One of our primary goals is to make the first determination of the relative amounts of primary production in the water column and in the sea ice using a consistent, modern estimation method (bio-optical modeling) for both systems. Sensitivity analyses will then be performed to guide planning of the ROAVERRS program. These analyses will be directly applicable to planning for Joint Global Ocean Flux Study and for Global Ocean Ecosystem Dynamics activities related to estimating primary production in the southern oceans. Specifically, we will study model sensitivity to sampling scales (temporal and spatial) in the ROAVERRS study region and to variation in the parameters proposed for measurement during ROAVERRS (e.g., algal bio-optics, photosynthetic parameters, spectral quality of light, nutrient concentration, sea-ice thickness, snow cover, water-column mixing rates, and temperature). Following completion of this modeling study, the ROAVERRS program will make improvements to the models based on an expanded databasefor example, tuning the model for different types of sea-ice habitat or phytoplankton bloomsand carry out testing of these models against field observations. (S-216C)
Drake Passage expendable bathythermograph program. Ray Peterson, University of California. This project will analyze data from bottom pressure gauges deployed across choke points for the southern ocean flow. Bottom pressure gauges were deployed between South Africa and the antarctic coast close to the Greenwich Meridian and at two locations spanning the Antarctic Circumpolar Current (ACC) south of Tasmania. Simultaneously, the British deployed similar instruments in the Drake Passage. The main scientific goal of these deployments was to determine the fluctuations in the transport of the ACC and to relate it to those in the subtropical and subpolar gyres and to the wind field over the southern oceans. (S-260)
Optical measurements and modeling to estimate concentration and fluxes of organic matter in the southern oceans. B. Greg Mitchell, University of California at San Diego, and Dariusz Stramski, University of Southern California. As predicted in the 1970s, the stratospheric ozone layer has been diminished as a consequence of anthropogenic release of chlorofluorocarbons. The thinning ozone layer results in increased surface flux of harmful ultraviolet-B (UV-B, 280320 nanometers) radiation relative to ultraviolet-A (UV-A, 320400 nanometers) and visible (400700 nanometers) radiation. Although considerable effort has focused on evaluating the impacts of ozone depletion for antarctic marine communities, effects of increased UV-B radiation in the Antarctic remain virtually unexplored. In particular, few studies have addressed questions related to UV acclimation and photoprotection, questions whose answers are essential for predicting the long-term ecological effects of increased UV-B radiation.
This study will focus on the capacity of diverse marine polar phytoplankton species to acclimate to increasing UV-B levels by synthesizing potentially photoprotective UV-absorbing compounds, known as mycosporinelike amino acids (MAAs). Because convolution of known photo-inhibition action spectra with environmentally realistic spectral irradiance flux indicates that UV-A radiation represents the major portion of photo-inhibiting solar radiation, UV-absorbing compounds are likely to have evolved in response to UV-A wavelengths. If MAAs are to be effective at increased UV-B radiation levels, the cells must be able to synthesize compounds with UV-B absorption at shorter wavelengths of relevance to ozone depletion (e.g., less than 320 nanometers). To date, there is limited evidence as to the efficacy of MAAs in photoprotection or whether UV-B radiation alone can induce MAAs in phytoplankton. We will address the following questions:
We will conduct several experiments with phylogenetically diverse arctic and antarctic isolates in monospecific cultures. Several approaches will be used in the course of this study where cultures will be exposed to ambient irradiance levels of UV-B, UV-A, and visible radiation in varying proportions to simulate present and enhanced UV-B radiation. The use of a single species in culture will allow controlled experiments to test our hypotheses. The results will allow development of predictions concerning the competitive advantage of various polar taxa with respect to alterations to their radiation environment. This effort will improve our understanding of mechanisms of photoprotection in marine polar phytoplankton in response to increasing levels of UV-B radiation. (S-261 and S-262)
Turbulent mixing near the Filchner-Ronne Ice Shelves. Laurence Padman, Oregon State University. This study concerns the formation processes of Weddell Sea Bottom Water, a very cold and saline water mass found at the continental shelf edge of the southernmost Weddell Sea. The formation process is believed to involve saline but warm Circumpolar Deep Water and extremely cold but relatively fresh Ice Shelf Water, but little is known about the process itself. Weddell Sea Bottom Water is important because it is a precursor to Antarctic Bottom Water, a dense, globally distributed water mass. The outflow of Ice Shelf Water from beneath the Filchner-Ronne Ice Shelf has been the subject of a continuing international field program.
In February and March of 1998, a British Antarctic Survey (BAS) cruise on board H.M.S. Endurance will focus on the oceanic and atmospheric exchange processes within the open water at the face of the ice shelf. This study is an integral part of the scientific program of the cruise and will concern the mechanisms responsible for the mixing of Ice Shelf Water with other regional water masses as it emerges from under the ice shelf. The measurements that will form the basis for the analysis include
Dynamic/thermodynamic processes and their contribution to the sea-ice thickness distribution and radar backscatter in the Ross Sea. Martin Jeffries, University of Alaska at Fairbanks. This project is a study of the effects of antarctic sea ice in the global climate system through an examination of how the spatial distribution of ice and snow thickness and of open water is reflected in satellite-based synthetic aperture radar (SAR) imagery. The field investigations will be carried out from the R/V Nathaniel B. Palmer in winter 1998 and summer 1999 and will produce observations of
The SAR images from ERS-2 and RADARSAT will be acquired at the McMurdo ground station and processed at the Alaska SAR Facility. These images will provide information about the large-scale ice motion field and the small-scale ice deformation field, both of which contribute to the observed ice-thickness distribution.
In addition, a study of the spatial and temporal variation of the backscattered microwave energy will contribute to the development of numerical models that simulate the dynamic and thermodynamic interactions among the sea ice, ocean, and atmosphere. The surface data are vital for the extraction of environmental information from the radar data, and for the ultimate validation of interactive models. (S-286)