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Ocean and Climate Studies
 




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.

(OO-179-O)
Air-snow exchange of nitric and nitrous acids at South Pole.
Jack Dibb, University of New Hampshire.

Nitrogen is a ubiquitous species in nature - a routine volume of dry air is over three-quarters nitrogen and converting dinitrogen into a form available to plants and animals is a crucial step in the terrestrial nitrogen cycle (using biological fixation, bacteria and blue-green algae generate about 1.3 x 108 metric tons). Thus, it is to be found all over Antarctica, in the atmosphere, on the surface, and in the ice. Does this current picture extend into the past? Much scientific effort has been expended on sampling snow and ice cores for indications of what the atmosphere contained when a given segment or strata of the core was buried. But the basic model, at least for nitrogen, may be faulty.

During the first field season in 1998-99 field season, scientists working on "Investigations of sulfur chemistry in the antarctic troposphere" (ISCAT, project OO-270-O) found reactive nitrogen in the atmospheric boundary layer above Amundsen-Scott South Pole Station at levels greatly exceeding those predicted from standard gas phase tropospheric chemistry models. Since it is highly unlikely that these nitrogen species could have been transported in from lower latitudes, it was conjectured that there is a local source within the antarctic snow cover. This supposition has enormous consequences for experimental theory, because it means that the snow does not act as a simple accumulator and integrator of atmospheric trace gases and, significantly, that observed concentrations in snow and ice cores cannot be simply taken as reflecting atmospheric conditions at the time the snow was falling.

ISCAT researchers continue their 4-year study with another season in the field. During the 2000-2001 austral summer, they will look more closely at nitrogen-oxide chemistry. This includes measurements of nitric acid and nitrous acid in the atmosphere and in the snow. These data will in turn guide the ISCAT observational field program as it proceeds.(O-179-O)

(OO-201-O)
Longwave radiation processes on the antarctic plateau.
Stephen G. Warren and Von P. Walden, University of Washington.

Thermal infrared ("longwave") radiation is an important component in the energy balance between the atmosphere and Earth's surface. On the antarctic continent, radiation processes dominate the surface energy budget. In summer the budget involves four terms - Incoming solar radiation, reflected solar radiation, long-wave radiation emitted by the atmosphere, and long-wave radiation emitted by the snow surface. In winter after the sun sets, the short-wave terms fall to zero. The emitted long-wave radiation increases with temperature, so the surface temperature is determined by the balance of radiation fluxes.

This project entails an experimental study of long-wave radiation processes near the surface at Amundsen-Scott South Pole Station. We will take high-resolution spectral measurements of the longwave radiation at the snow surface. A Fourier-transform Interferometer installed in late 2000 will operate through a full year. Supporting observations will also be made of how temperature and humidity vary with height in the lower atmosphere and of the ice crystals in the atmospheric boundary layer. The research also includes experiments concerning the emission characteristics of snow, of ice crystals in the atmosphere, of clouds, 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 improve climate models with more detailed radiation processes. (OO-201-O)

(OO-204-O)
Atmospheric oxygen variability in relation to annual-to-decadal variations in terrestrial and marine ecosystems.
Ralph F. Keeling, Scripps Institution of Oceanography.

Oxygen, the most abundant element on the Earth, comprises about a fifth of the atmosphere. But much of the Earth's oxygen resides in other chemical species - in water, rocks and minerals and, of course, in flora and fauna that recycle it (both 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; our project includes a subset of sample collections being made at a series of baseline sites around the world. These data should help to improve estimates of the processes whereby oxygen is cycled throughout the global ecosystem, specifically, through photosynthesis and atmospheric mixing rates; also better predictions of net exchange rates of carbon dioxide with biota on land and in the oceans. An important part of the measurement program entails developing absolute standards for oxygen-in-air, to ensure stable long-term calibration. We are also 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 should help enhance our understanding of the processes that regulate the buildup of carbon dioxide in the atmosphere and of the change processes - especially climate change - that regulate ecological functions on land and in the sea.(OO-204-O)

(OO-225-O)
Shelf and bottom-water formation near east antarctic polynyas and glaciers.
Richard T. Fairbanks, Lamont-Doherty Earth Observatory.

As seawater becomes colder and more saline, its density increases. Thermohaline circulation involves a deep water flow pattern that arises as such saltier, colder water sinks; it finally reaches an equilibrium level and begins to move more or less horizontally. But how does the increased salinity develop?

One way that water on the antarctic continental shelf increases in salinity is through coastal polynyas; formed by strong offshore winds, polynyas create fields of ice and water often referred to as major sea ice and salt "factories." The newly formed ice is blown seaward, allowing more ice to form along the coast, and this continental shelf water increases its salinity as it freezes. Since polynyas have areas of thin ice and even open water subject to evaporation, heat is lost to the atmosphere more readily; this too increases the density of the shelf water. This heavier shelf water then sinks, fills any depressions in the bottom, and is gravitationally driven down the continental slope into deeper waters.

Researchers in this project are interested in how the formation of dense water masses on the antarctic continental shelves may be affected by the periodic flushing of relatively warm circumpolar deep water; specifically, does the intrusion of warm water enhance the rate at which dense water forms? We also expect to find evidence of an additional process - the intrusion of relatively warm water onto the continental shelf, overriding the shelf water and essentially shutting down the densification processes - at work in this area.

We will observe water-mass modification processes on the continental shelf off the Adélie Coast in East Antarctica, focusing on a quasi-permanent area of open water near the Mertz and Ninnis Glacier tongues, the so-called Mertz polynya. Using the icebreaking research ship Nathaniel B. Palmer, we will obtain data at a closely spaced array of hydrographic stations over the continental shelf and slope along the George V Coast in the austral summer. These data will complement a similar winter study, conducted by the Australian National Antarctic Program. (OO-225-O)

(OO-226-O)
Measurements of the size, shape, scattering-phase function, and extinction coefficient of ice crystals at Amundsen-Scott South Pole Station.
R. Paul Lawson, SPEC, Inc., Boulder, Colorado.

Clouds are both the cause and result of atmospheric phenomena; one of their primary roles is as a reflector of solar energy - coming both from space and radiated/reflected from the Earth. And what are clouds? Broadly, clouds form when rising damp air expands to the point that it approaches saturation. With nowhere else to go, water molecules condense onto any local, available aerosol particles - the aggregation becomes a cloud.

A number of theoretical and experimental studies have demonstrated that a cloud particle's size as well as its shape - and specifically ice crystals - strongly determine how it will reflect and radiate light (and energy). Looking especially at cirrus clouds, this project will classify cloud particles by size and shape and will also investigate the light-scattering properties of ice crystals in the atmosphere above Amundsen-Scott South Pole Station.

In cooperation with an ongoing radiation transfer program, we will deploy two high-resolution, digital cloud-particle imagers. The particle images, concentrations, and size distributions will be processed on site. Our software permits us to reject artifacts, and to compute various size and shape parameters, scattering characteristics, and ice/water proportions.

These data will complement several concurrent experiments concerning the emission characteristics of snow, ice crystals in the atmosphere, and greenhouse gases near the surface. With measurements of such environmental conditions as cloud-base altitude, temperature, and humidity structure, our data should allow us to develop new algorithms to substantially improve representations of radiation processes in general circulation models. We also expect to enhance the climatology of cloud-particle and cloud properties. (OO-226-O)

(OO-254-O)
Chlorine- and bromine-containing trace gases in the antarctic.
Reinhold A. Rasmussen and M.A.K. Khalil, Oregon Graduate Institution of Science and Technology.

Although the Earth's climate is a massively complex system, at certain levels of the atmosphere interactions are predictable. Disregarding the ubiquitous and dynamic water vapor, more than 99.9 percent of atmospheric molecules are either nitrogen, oxygen, or the chemically inert "noble gases" (chiefly argon). Scientists have confirmed this baseline medium as largely unchanged for several hundred million years.

However, much of the atmospheric "action" - acid rain, ozone depletion, smog - comes from the reactive trace species, which occur in small amounts but precipitate many crucial chemical events. There are thousands of these, but fewer than 200 are commonly present in a typical volume of air. It is not known for how long and in what proportions these have been prominent actors in atmospheric chemistry. Chlorofluorocarbons, for example, are one problematic species, but a suite of other airborne trace constituents to be found in atmospheric gases derive 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 in other alterations of the Earth's climate.

This project continues to investigate seasonal trends in trace gas concentrations, by collecting a year-long suite of air samples at Palmer Station. They will 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)

(OO-257-O) and (OO-264-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)

The National Oceanic and Atmospheric Administration (NOAA) has been conducting 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. Time-series analyses of the data that is being collected over a period of years should provide insight into several phenomena of particular interest:

• seasonal and temporal variations in greenhouse gases,

• stratospheric ozone depletion,

• trans-antarctic transport and deposition,

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

• the development of polar stratospheric clouds over Antarctica.

Project scientists will 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. To further determine how the rates of change of these parameters affect climate, we are collaborating with climate modelers and diagnosticians. (OO-257-O) and (OO-264-O)

(OO-260-O)
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. The current is even stronger wherever the distance between Antarctica and neighboring land is narrowed. These are the so-called chokepoints, such as The Drake Passage off the tip of South America and the sea regions between Antarctica and both the Cape of Good Hope and Tasmania. To determine the fluctuations in the transport of the ACC, scientists deploy bottom pressure gauges and similar instruments; this data can then be ranged against currents in the subtropical and subpolar gyres and to the wind field over the southern oceans.

Specifically since 1996, scientists in this research project have been collecting 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 high-density expendable bathyermographs (XBT) launched from the USAP's research ship Laurence M. Gould, we will measure current, temperature, and depth for seasonal and year-to-year temperature fluctuations in the upper ocean within the Drake Passage. Since the water changes more rapidly there, we will execute frequent casts across the Subantarctic, Polar, and ACC fronts. (OO-260-O)

(OO-263-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 where radiation significantly cools the Earth's surface. These winds are strong enough to drive the sea ice offshore at any time of the year, which often leads to coastal polynyas - areas of open ocean within the sea ice. As these coastal polynyas (in winter) experience extremely high heat fluxes from the ocean to the atmosphere - two orders of magnitude greaer than would solid ice - the resultant cold tends to breed large amounts of sea ice and Antarctic bottom water.

To obtain more detailed information on these fluxes, the United States Coast Guard ice breakers (for this project, the Polar Sea) maintain instruments to measure the heat fluxes as a function of ice concentration, ice thickness and type of ice. Further, this project continues the international collaboration (France, Australia and the United States) to study katabatic winds and the interaction with sea ice along the coast of Adélie and King George Lands.

A number of weather stations collect meteorological data: One array strings from the interior (Dome D at 3280 meters) to the coast (D 10) near the French station Dumont d'Urville; 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 (mps).

We plan to analyze the effect of these winds on the formation, persistence and size of coastal polynyas. The meteorological data we derive will be ranged against data from satellite-based active microwave imagery (synthetic aperture radar).

We are also interested in assessing the influence of cyclonic storm systems on the drainage flow along the coast; our data on this will be combined with that collected by Australian, French and Japanese station networks (to the west of these stations).

We are also producing 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. This model will not only predict average mean winter conditions (previously done), but also extreme events, where wind speeds commonly exceed 50 mps. (OO-263-O)

(OO-270-O)
Investigation of Sulfur Chemistry in the Antarctica Troposphere (ISCAT).
Douglas D. Davis and Fred L. Eisele,Georgia Institute of Technology.

Sulfur is one of the basic elements to be found in nature, and constructing a sulfur budget for a region - or for the planet - is a complex undertaking, especially since so much sulfur is also emitted by industrial activities. Biogenic emissions (coming from a live source) derive primarily from the oceans, where microorganisms emit the gas dimethyl sulfide (DMS).

Atmospheric sulfur chemistry is an important component in the study of climate change issues because of the so-called aerosols. These are minute airborne particles from sources both natural (volcanic emissions and oceanic phytoplankton production) and anthropogenic (emitted sulfur compounds from industry and biomass fires form minute particles in the atmosphere). Their atmospheric fate is complex; they reflect solar radiation, produce atmospheric haze and acid rain, and affect ozone depletion. Sulfate particles in the atmosphere may also act as condensation nuclei for water vapor and thereby enhance global cloudiness. Paleoclimatologists have been able to reconstruct the variability and natural background level of atmospheric aerosols from sulfur oxidation products preserved in ice cores.

This project brings together over a dozen investigators from five institutions to focus on two major gaps in knowledge -

• to improve substantially our current understanding of the oxidation chemistry of biogenic sulfur in the polar environment, and

• to improve the climatic interpretation of sulfur-based signals in antarctic ice-core records.

The South Pole provides a natural laboratory for this investigation because the atmospheric boundary layer there presents a homogeneous and relatively simple environment from which to unravel the photochemically driven oxidation chemistry of dimethyl sulfide. The results of the ice core work, however, depend on understanding how the physical and chemical environment of the oxidation process affects the relative concentrations of the oxidation products that become buried in the ice. Observations will be made of a wide-ranging suite of sulfur species such as DMS and its oxidation products, as well as photochemically important compounds such as carbon monoxide, nitrous oxide, water vapor, and non-methane hydrocarbons.

We hope to provide, for the first time, a quantitative picture of exactly which atmospheric sulfur compounds are released and conveyed into the antarctic interior, as well as an account of the sulfur chemistry active in the atmosphere over Antarctica. (OO-270-O)

(OO-275-O)
Operation of an aerosol sampling system at Palmer Station.
Gail dePlannque and Colin G. Sanderson, Environmental Measurements Laboratory, U.S. Department of Energy.

Radionuclides are atoms emitting radioactive energy, some of which occur naturally in the surface air. It is these - as well as nuclear fallout and any accidental releases of radioactivity - that the Environmental Measurements Laboratory's (EML) Remote Atmospheric Measurements Program (RAMP) is designed to detect and monitor. Since 1963 EML, as part of the U.S. Department of Energy, has run the Global Sampling Network to monitor surface air. The RAMP system provides on-site analysis in thirteen different locations around the world, including Palmer Station, Antarctica.

Using a high-volume aerosol sampler, a gamma-ray spectrometer, and a link to the National Oceanic and Atmospheric Administration's ARGOS satellite system, these researchers will continue sampling air at Palmer Station for anthropogenic radionuclides. (OO-275-O)

(OO-278-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 Nathaniel B. Palmer, working off Prydz Bay in the Indian Ocean sector; we will receive help from project GO-073-O researchers in collecting sediment cores and hydrographic data. 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)

(OO-283-M, P, S)
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. 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, including operational weather forecasting, accumulation of climatological records, general research purposes, and specific support of the U.S. Antarctic Program - especially the LTER program at McMurdo and Palmer Stations. 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.

This season three project teams will

• move the AWS at the South Pole away from the dome and toward the Clean Air Sector, anticipating the construction of new facilities;

• maintain and service the AWS stations on Racer Rock, Bonaparte Point and Hugo Island; and

• service other AWS stations, on the Ross Ice Shelf, around the Ross Island region, at Byrd Station, the Siple dome field camp, and along the Adélie Coast, at Terra Nova Bay and on Franklin Island

(OO-283-M)

(OO-283-P)

(OO-283-S)

(OO-314-O)
Measurement of combustion effluent carbonaceous aerosols in the McMurdo Dry Valleys.
Anthony D. Hansen, Magee Scientific Company.

Though Antarctica remains comparatively pristine, there is heightened awareness of the impact the human presence and scientific work being undertaken there could have. To continue a series of assessments of the long-term environmental impact of the U.S. Antarctic Program's operations, we plan to generate a database detailing the abundance of carbonaceous aerosols in the McMurdo Dry Valleys.

The Long-Term Ecological Research (LTER) study site in the Dry Valleys supports a fragile, nutrient-limited ecosystem that could be significantly affected by human activities. Of special concern are deposits of particles from carbonaceous aerosols ("black carbon"). These could be arise from the exhaust of diesel power generators and helicopter operations within the McMurdo Dry Valleys; it is even possible that combustion products from McMurdo Station about 100 kilometers away could migrate to the study area. For three austral summers, we will deploy a real-time optical analyzer at the LTER site to measure the concentration of black carbon, polycyclic aromatic hydrocarbons, and other filterable organic compounds useful in fingerprinting combustion products. (OO-314-O)

(OO-315-O)
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 technology (sound wave transmission and reflection), 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, 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 USAP research ships Nathaniel B. Palmer and Laurence M. Gould.

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

(OO-316-O)
Field experiments and modeling of the breakup of antarctic sea ice.
John P. Dempsey, Clarkson University.

The sea-ice in Antarctica comes and goes with the seasons - from as little as 4 million square kilometers in February to as much as 20 million in September. For scientists this marks something of a moving target, yet the internal dynamics of the ice pack could be much better understood than they are at present. This project focuses on how the antarctic sea-ice cover responds to stresses applied by wind and ocean waves and how the temperature distribution within the sea ice affects these responses. Researchers will conduct experiments on the deformation and fracture of sea ice in McMurdo Sound by applying a series of controlled stresses and observing their effects.

A key effect is the initiation and growth of microcracks within the ice, and large ice floes do not fracture in the same way as small ones do. Thus, for experiments to yield information that is valid for the larger scales that concern scientists, the test scales must be fairly large, some tens of meters. With these m aneuvers we hope to gain detailed information on the microstructure of the ice (such as crystal structure, brine channels, and other flaws in the ice fabric). This will provide a sound theoretical framework to guide the experimental work and the generation of models.

In one component of this project, we are collaborating with the New Zealand Antarctic program; that effort concerns the fracture mechanics of fatigue crack propagation, the use of microstructural observations to verify magnetic resonance measurements of the structure of inclusions in the ice, and the acoustic emissions of fracture zones. (OO-316-O)

(OO-324-O)
Record of atmospheric photochemistry in firn at South Pole.
Roger Bales and Joseph R. McConnell, University of Arizona Desert Research Institute, University of Nevada.

Scientists are eager to develop models about Earth's history, based on their knowledge of current, active dynamic processes. 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.

Amundsen-Scott 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. The summer conditions will also permit us to 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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