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Ocean and Climate Systems  

Ocean and Climate Systems
Though it borders the world's major oceans, the Southern Ocean system is like no other in the world, with four times more water than the Gulf Stream, 400 times more than the Mississippi River. It is a sea where average temperatures don't reach ºC in summer, where even the water itself is so distinctive that it can be identified thousands of miles away in currents that originated here. These Antarctic Bottom Waters provide the major source of cooling for the world's oceans. In fact, if the earth is a heat engine, Antarctica should be viewed as its circulatory cooling component.

The climate in Antarctica is also unique, linked as it is to the extreme conditions of the land and sea below the troposphere (the inner region of the atmosphere, up to between 11 and 16 kilometers). This ocean/atmosphere environment defines and constrains the marine biosphere, and in turn has a dynamic relationship with the global ocean and with weather all over the planet. Few major energy exchanges on Earth can be calculated without factoring in these essential antarctic phenomena. As such, they are both an indicator and a component of climate change.

The Ocean and Climate Systems program sponsors research that will improve understanding of the high-latitude oceanic environment, including the global exchange of heat, salt, water, and trace elements; there is also an emphasis on sea-ice dynamics, as well as the dynamic behavior and atmospheric chemistry of the troposphere. Major program elements include:

Physical oceanography: The dynamics and kinematics of the polar oceans; the interaction of such forces as wind, solar radiation, and heat exchange; water-mass production and modification processes; ocean dynamics at the pack-ice edge; and the effect of polynyas on ventilation.

Chemical oceanography: The chemical composition of sea water and its global differentiation, reactions among chemical elements and compounds in the ocean, fluxes of material within ocean basins and at their boundaries, and the use of chemical tracers to oceanic processes across a range of temporal and spatial scales.

Sea-ice dynamics: The material characteristics of sea-ice, from the individual crystal level to the large-scale patterns of freezing, deformation, and melting.

Meteorology: Atmospheric circulation systems and dynamics, including the energy budget; atmospheric chemistry; transport of atmospheric contaminants to the antarctic; and the role of large and mesoscale systems in the global exchange of heat, momentum, and trace constituents.

Monitoring Antarctic Bottom Water.
Martin Visbeck, Lamont-Doherty Earth Observatory

The Antarctic Bottom Water is the coldest (and therefor the densest) natural water to be found on Earth, created as ice shelves melt into seawater and sink to the bottom. It occurs in the nether regions of the Southern Ocean, separated from the world's great oceans to the north by the Polar Front water that provides a virtual barrier to the heat transfer from those more temperate and less stormy waters.

The global importance of Antarctic Bottom Water is linked to its subsequent long journey across the ocean floor to the Northern Hemishphere. The patterns and strengths of this current are crucial to the heat balance of the global ecosystem, for this process provides crucial oxygen to those seas, as well as reducing their temperature to nearly ºC.

This project monitors the outflow of Antarctic Bottom Water from the Weddell Sea into the Scotia Sea, as it begins its journey northward. (OO-124-O)

Longwave radiation processes on the antarctic plateau.
Stephen G. Warren and Thomas C. Grenfell, University of Washington.

Long-wave radiation [also called infrared (IR) or thermal radiation] is an important component in the energy balance of the atmosphere. On the antarctic continent radiation processes dominate the surface energy budget. In summer the balance is made up of four terms primary solar energy in two forms (incoming and reflected short-wave radiation), and both emitted and reflected long-wave radiation. In austral winter after the sun sets, the short-wave terms fall to zero. The emitted long-wave radiation varies with temperature; thus the radiation balance at the surface determines the surface temperature.

This project entails an experimental study of long-wave radiation processes near the surface at South Pole station. We are developing instrumentation capable of high resolution measurements of the IR fluxes at the snow surface a so-called Fourier Transform Interferometer that will be deployed in late 1999 and operated through the following austral winter. Supporting observations will also be made of the temperature and moisture profiles in the lower atmosphere, and of ice crystals in the atmospheric boundary layer.

The research also includes several experiments concerning the emission characteristics of snow, of ice crystals in the atmosphere, and of greenhouse gases near the surface. Determining the concurrent environmental conditions (such as cloud-base altitude, temperature and humidity-structure), and the sizes and concentrations of ice crystals, will contribute to the newly developing climatology of cloud properties, and should substantially improve how radiation processes are represented in general circulation models. (OO-201-O)

Antarctic Meteorological Research Center: 1996-2000.
Charles R. Stearns and John T. Young, University of Wisconsin at Madison.

The Antarctic Meteorological Research Center (AMRC) is one of three research centers in the Science and Engineering Technology Center at McMurdo Station. It is a major center for meteorological research, and an ongoing experiment to improve operational synoptic (simultaneous atmospheric conditions/weather over a broad area) forecasting.

AMRC relies primarily on the Man-Computer Interactive Data Access System (McIDAS), a versatile computer-based system for organizing, manipulating, and integrating antarctic environmental data. It captures the flow of meteorological information from polar-orbiting satellites, automatic weather stations (AWS), operational station synoptic observations, and research project reports. McIDAS also receives weather forecasts and other environmental data products from outside Antarctica, and acts as a repository for existing archived databases.

Developed at the University of Wisconsin in the mid-1970s, McIDAS receives meteorological data from various sources: Standard synoptic observations, radiosonde profiles, satellite-based visible and infrared imagery, atmospheric profiles inverted from multispectral scanning sensors, and nonstandard data such as thematic ozone mapping spectrometer (TOMS) data, synthetic aperture radar (SAR) sea-ice information, and the AWS network observations. The system automatically registers, calibrates, and locates (by geographical coordinates) the input information, providing work station access to the combined database. Features available to the work station operator include: Sectorization, false color, enhancements, brightness stretching, overlays, looping, and differencing all specifically keyed to synoptic meteorological research and weather forecasting. Because the look angles from geostationary satellites are so low, McIDAS relies primarily on data streams from the polar orbiters (AVHRR/HRPT and DMSP).

To fully use the power of McIDAS to produce meteorological data in the service of forecasting and research, data links to facilitate communications have been established with a number of scientific weather facilities world-wide; for example:

Australian Bureau of Meteorology (ABOM)

University of Wisconsin Space Science and Engineering Center (SSEC)

Fleet Numerical Oceanography Center (FNOC) in Monterey, California

European Center for Medium Range Weather Forecasts (ECMRWF) in Reading, U.K. (OO-202-O)

Atmospheric oxygen variability in relation to annual-to-decadal variations in terrestrial and marine ecosystems.
Ralph F. Keeling, Scripps Institution of Oceanography.

Oxygen is the most abundant element on the Earth. Airborne, it comprises about a fifth of the atmosphere. But much of the Earth's oxygen exists in water, rocks and minerals, and of course in flora and fauna who recycle it directly and as carbon dioxide through the processes of photosynthesis and respiration.

Thus scientists are interested in measuring the concentration of molecular oxygen and carbon dioxide in air samples. This project is part of sample collections being made at a series of baseline sites around the world. The data should help to improve estimates of the processes whereby oxygen is cycled throughout the global ecosystem, specifically:

net exchange rates of carbon dioxide with biota on land and in the oceans,

photosynthesis rates, and

atmospheric mixing rates.

An important part of the measurement program entails developing absolute standards for oxygen-in-air, to ensure stable long-term calibration. We also are conducting surveys of the oxidative oxygen/carbon ratios of both terrestrial- and marine-based organic carbon, hoping to improve the quantitative basis for linking the oxygen and carbon dioxide geochemical cycles.

These results are needed to enhance our understanding of the processes that regulate the buildup of carbon dioxide in the atmosphere. They should also contribute to our understanding of the change processes especially climate change that regulate ecological functions on land and in the sea. (OO-204-O)

Chlorine- and bromine-containing trace gases in the antarctic.
Reinhold A. Rasmussen and M.A.K. Khalil, Oregon Graduate Institute of Science and Technology.

Airborne trace constituents in atmospheric gases come from both biogenic and anthropogenic sources. Scientists monitor them closely, as they have been implicated in depletion of the ozone layer over Antarctica as well as other alterations of the Earth's climate.

This study will investigate the seasonal trend of trace gas concentrations by collecting a year-long suite of air samples at Palmer Station. Samples will subsequently be analyzed at the Oregon Graduate Center for a number of trace components, especially chlorine- and bromine-containing species.

This work should contribute to a better understanding of the buildup of trace constituents, particularly those of high-latitude marine origin. (OO-254-O)

South Pole monitoring for climate change: Amundsen-South Pole Station.
David Hofman, Climate Monitoring and Diagnostics Laboratory, National Oceanographic and Atmospheric Administration, Palmer Station. (OO-257-O)

James T. Peters, Environmental Research Laboratories, National Oceanic and Atmospheric Administration. (OO-264-O)

The National Oceanic and Atmospheric Administration (NOAA) has been engaged in studies to determine and assess the long-term buildup of global pollutants in the atmosphere. The NOAA Climate Monitoring and Diagnostic Laboratory team will continue long-term measurements of trace atmospheric constituents that influence climate and the ozone layer.

These measurements will be enable time-series analyses of multiyear data records. Phenomena of particular interest are:

seasonal and temporal variations in greenhouse gases,

stratospheric ozone depletion,

transantarctic transport and deposition,

the interplay of the trace gases and aerosols with solar and terrestrial radiation fluxes on the polar plateau, and

the development of polar stratospheric clouds over Antarctica.

Four scientists will work from the Amundsen-Scott South Pole Station observatory during the austral summer, and two NOAA personnel will stay over the winter (working from the Atmospheric Research Observatory) to measure carbon dioxide, methane, carbon monoxide, aerosols, chlorofluorocarbons, and other trace constituents. Concurrent measurements will be made of water vapor, surface and stratospheric ozone, wind, pressure, air and snow temperatures and atmospheric moisture. Other personnel at Palmer Station also will collect carbon dioxide samples in support of this project.

These measurements will allow us to determine the rates at which concentrations of these atmospheric constituents change, and will suggest likely sources, sinks, and budgets. Our work also includes collaborating with climate modelers and diagnosticians to determine how the rates of change of these parameters affect climate.

Drake Passage expendable bathythermograph program.
Ray Peterson, University of California.

The Antarctic Circumpolar Current (ACC) is a powerful force that drives waters in the Southern Ocean; four times as fast as the Gulf Stream, for example. Wherever the distance between Antarctica and other continents is narrowed so-called chokepoints such as The Drake Passage off the tip of South America and the sea regions between Antarctica and the Cape of Good Hope and Tasmania, respectively the current is even stronger. Scientists deploy bottom pressure gauges and similar instruments 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.

Specifically since 1996, scientists in this research project have collected data to characterize the water mass variability in the Drake Passage, to describe temperature and circulation variability in the Southern Ocean, and to define the role of the Southern Ocean in the global climate system. This season, using a high-density expendable bathythermograph (XBT), we will make expendable current/temperature/depth (XCTD) observations to measure the seasonal and year-to-year temperature fluctuations in the upper ocean within the Drake Passage.

To clearly describe inter-annual and seasonal changes in upper-ocean temperature, we need closely-spaced, underway XBT and XCTD measurements to be made on every Laurence M. Gould cruise throughout the year. As the ship crosses the Drake Passage, approximately 60 XBT profiles and 12 XCTD profiles (measuring salinity) are made, beginning and ending at the 200 meter bathymetric contour on either side of the passage. XBT casts are spaced approximately 1 hour apart, although sampling is more frequent across the Subantarctic, Polar, and ACC fronts, as the water temperature changes more rapidly in these regions. (OO-260-O)

Katabatic winds in eastern Antarctica and their interaction with sea ice.
Gerd Wendler, University of Alaska, Fairbanks.

Katabatic winds are driven by the flow of cold dense air down a mountain or glacier slope, especially in regions subject to radiational cooling of the Earth's surface. These winds can drive the sea ice offshore and are responsible for extremely high heat fluxes from the ocean to the atmosphere. They are also implicated in the formation of polynyas areas of open ocean within sea ice. This project continues an international collaboration (France, Australia and the United States) to study katabatic winds along the coast of Antarctica.

A number of weather stations collect data: One newly installed station 15 kilometers inland is sited at a point where atmospheric wind models predict extremely high average wind speeds; two other strings of existing automatic weather stations will continue to collect data; one that runs from France's Dumont d'Urville station inland to Dome C, at an altitude of some 3,200 meters; the other string runs along the coast, including stations at Cape Denison and Port Martin, an area where the highest average surface wind speeds on Earth have been recorded a monthly average of 27.8 meters per second.

Project scientists hope to produce a numerical model of the structure of the region's atmosphere, which will incorporate a more detailed terrain map as well as a new mesoscale model developed by French scientists. Another goal is to analyze the formation, persistence and size of offshore polynyas as a function of wind speed; data from satellite-based active microwave imagery (synthetic aperture radar) will be combined with the observed meteorological data in that analysis. A final application of this work is to enlarge the body of information being collected by Australian and Japanese station networks (to the west of these stations) in hopes of assessing the influence of cyclonic storm systems on the drainage flow along the coast. (OO-263-O)

Circumpolar deep water and the West Antarctic Ice Sheet.
Stanley S. Jacobs and Martin Visbeck, Lamont-Doherty Earth Observatory, Columbia University.

Circumpolar Deep Water (CDW) is a relatively warm water mass (+1.0ºC or warmer) found on the outer edge of the continental shelf; normally it is confined by an oceanic front that provides a barrier to the colder and saltier waters of the shelf. In the Amundsen Sea, for example, the deeper parts of the continental shelf are filled with nearly undiluted CDW. The temperature gradient causes this CDW to mix upward and deliver significant amounts of heat both to the base of floating glacier tongues and to the ice shelf. As a consequence, the melt rate beneath the Pine Island Glacier averages ten meters (m) of ice per year, and some specific local areas lose twenty m. By comparison, typical melt rates beneath the Ross Ice Shelf cost it only twenty to forty centimeters of ice per year.

This project focuses on the dynamics of CDW on the Amundsen Sea shelf, specifically in the regions of the Pine Island and Thwaites Glaciers, and the Getz Ice Shelf. Both the Pine Island and Thwaites Glaciers move very fast, and have a major influence on the regional ice mass balance of West Antarctica.

Specifically, we hope to:

delineate the frontal structure of the continental shelf sufficiently to measure the major routes of CDW inflow, meltwater outflow, and the westward evolution of CDW influence;

use that data set to validate a three-dimensional model (currently under construction) of sub-ice ocean circulation; and

refine the estimates of in situ melting on the mass balance of the West Antarctic Ice Sheet.

This research should help to elucidate antarctic glaciology by assessing the combined effect of global change on the antarctic environment. The observational program will be carried out from the research ship Nathaniel B. Palmer in February and March, 2000. (OO-274-O)

Operation of an aerosol sampling system at Palmer Station.
Gail dePlannque and Colin G. Sanderson, Environmental Measurements Laboratory, U.S. Department of Energy.

The Environmental Measurements Laboratory [(EML); a unit of the U.S. Department of Energy based in New York City] installed an array of instruments at Palmer Station in 1990: A high-volume aerosol sampler, a gamma-ray spectrometer, and a link to the National Oceanic and Atmospheric Administration's ARGOS satellite system. Sampling data from Antarctica contributes to EML's Remote Atmospheric Measurements Program, part of its worldwide surface-air sampling program. (OO-275-O)

Particulate organic carbon production and export in the Indian sector of the Southern Ocean: A United States-China collaborative research project.
Cynthia Pilskaln, University of Maine at Orono.

The Polar Front Zone, where the cold, dense waters of the antarctic meet the warmer waters of the northern oceans, is subject to major currents and water displacements beneath the sea. Each austral spring, phytoplankton bloom in this region. Scientists believe the blooms are driven by nutrient transport brought to the surface, as intermediate and deep water masses are ventilated. Each year, the theory goes, such blooms are the primary source of particulate organic carbon (POC) and biogenic silica flux to the ocean bottom. But the theory remains to be tested, as no data exist on the amount of particulate organic matter that is sinking through the water column. Without such quantitative measurements in this region, the hypothesized relationships between biomass production and the currents must remain undefined.

As part of a collaboration between the University of Maine and the Chinese Antarctic Research Expedition (CINARE), we will study the biological production and export flux of biogenic matter in response to ventilation of intermediate and deep water masses within the Polar Front Zone. The shipboard work will be done aboard the Chinese antarctic resupply vessel, working off Prydz Bay in the Indian Ocean sector.

The initial phase of our work consists of setting out a time-series sediment-trap mooring at approximately 64S 73E. The biweekly-to-monthly trap samples will be analyzed for their organic constituents and, in conjunction with primary productivity observations, will provide the basic data from which export values can be derived. Data gathered in this effort will be enhanced by the historical dataset that CINARE has obtained in this area over the past decade.

Our work will be carried out in collaboration with the State Oceanic Administration (SOA) of the People's Republic of China and the Chinese Antarctic Research Expedition. In addition to providing time on the antarctic resupply vessel, the SOA will sponsor the primary productivity experiments on board ship and will provide the supporting hydrographic measurements. The collaborating American scientists will provide the hardware for the moored sediment trap and will bring their expertise in making these observations to standards developed for the Joint Global Ocean Flux Study. All samples and data will be shared between the U.S. and Chinese investigators, and the data analysis will be carried out jointly. (OO-278-O)

Antarctic automatic weather station program: 1998-2001.
Charles Stearns, University of Wisconsin at Madison.

A network of nearly 50 automatic weather stations (AWS) has been established on the antarctic continent and several surrounding islands. These facilities were built to measure surface wind, pressure, temperature and humidity; further, some of them also track other atmospheric variables, such as snow accumulation and incident solar radiation.

Their data are transmitted via satellite to a number of ground stations, and put to several uses: Operational weather forecasting, accumulation of climatological records, general research purposes, and specific support of the U.S. Antarctic Program. The AWS network has grown from a small-scale program in 1980 into a significant data retrieval system that is now extremely reliable, and has proven indispensable for both forecasting and research purposes. This project maintains and augments the AWS, as necessary. (OO-283-M and OO-283-P)

Shipboard acoustic doppler current profiling on Nathaniel B. Palmer and Lawrence M. Gould.
Teresa K. Chereskin, Scripps Institution of Oceanography.

Currents in the Southern Ocean have a profound influence on the world's oceans and therefor upon global temperature and the planet's ecosystem yet some remote regions receive little scientific attention. Using doppler (sound wave transmission and reflection) technology, this project is exploring upper ocean current velocities and will try to generate a quality-controlled data set in one such sparsely sampled and remote region a region which nonetheless appears to play a significant role in global ocean circulation. We will develop and maintain a shipboard acoustic Doppler current profiler (ADCP) program on board the Nathaniel B. Palmer and the Laurence M. Gould, two research ships operated by the United States Antarctic Program.

This work is part of a long-term science goal to characterize the temporal and spatial velocity structure in the Southern Ocean. This will entail measuring the seasonal and annual changes in upper ocean currents within the Drake Passage, combining this information with similar temperature observations, and exploring how the heat exchange varies and how it drives upper ocean currents. (OO-315-O)

The influence of hydrothermal discharge on coastal ocean dissolved iron concentrations at Deception Island, Antarctica.
Anne Sturz, University of San Diego.

Iron plays a crucial role, along with some other trace elements, in fueling biological production. Over large parts of the Southern Ocean inorganic nutrients are under-utilized because (scientists believe) some trace element is insufficient, most probably iron. Yet some shallow regions, within the Bransfield Strait for example, show productivity 50 to 60 times as great as that in the open ocean, where iron is presumed to be abundantly available.

One direct way of probing this problem is to examine specific sources of iron. There is a drowned and breached volcanic crater at Deception Island, Antarctica; might the hydrothermal discharge from this underwater feature provide sufficient dissolved iron to support the regional primary productivity in the ocean?

This study will trace the discharge volume, its iron concentration, and the flushing rate of the crater during a cruise of Laurence M. Gould in November 1999. Since the scientific mission on that cruise is devoted to the study of how pelagic and benthic communities respond to the seasonal variations in the sea ice cover, it will provide a valuable context for the iron study. (OO-319-O)

Record of atmospheric photochemistry in firn at South Pole.
Roger Bales and Joseph R. McConnell, University of Arizona.

Scientists are eager to develop models that will expand their knowledge of current, active dynamic processes into the past. One such process vital to the Earth is photochemistry, how the sun's radiant energy affects conversion of oxygen in the atmosphere. By measuring and interpreting the hydrogen peroxide, formaldehyde, and nitric acid concentrations in the snow and firn at South Pole station, we hope to develop a credible history of the oxidation capacity of the atmosphere over the last two centuries. We also hope to evaluate methods that will confirm statistically significant changes in the concentration of these species over that time.

South Pole station is ideal for this work: The extreme cold makes the chemistry relatively simple; the NOAA Climate Modeling and Diagnostics Laboratory provides a context of high quality meteorological and chemical data; and the station is staffed continuously so that samples can be taken year-round.

We will sample air and near-surface snow throughout the year; during the summer, we will sample and analyze snow pits and firn cores, and will model the air/snow chemistry to try to explain the observed concentrations in the firn. Also in summer, we will sample two snow pits around the perimeter of the snow stake field intensively (for accumulation observations), a process that will establish markers to maintain time control for stratigraphic and chemical horizons.

During earlier work at South Pole and in central Greenland, we have developed and tested physically-based models of air snow exchange of hydrogen peroxide. This project extends that work. (OO-324-O)

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