GC51A-1049 0800h
Surface Flux Measurements at King Sejong Station in West Antarctica
The Antarctic Peninsula is important in terms of global warming research due to pronounced increase of air temperature over the last century. The first eddy covariance system was established and turbulent fluxes of heat, water vapor, CO2 and momentum have been measured at King Sejong Station (62 \deg 13>S, 58 \deg 47>W) located in the northern edge of the Antarctic Peninsula since December in 2002. Our objectives are to better understand the interactions between the Antarctic land surface and the atmosphere and to test the feasibility of the long-term operation of eddy covariance system under extreme weather conditions. Various lichens cover the study area and the dominant species is Usnea fasciata-Himantormia. Based on the analyses on turbulent statistics such as integral turbulence characteristics of vertical velocity (w) and heat (T), stationarity test and investigation of correlation coefficient, they follow the Monin-Obukhov similarity and eddy covariance flux data were reliable. About 50 % of total retrieved sensible heat flux data could be used for further analysis. We will report on seasonal variations of energy and mass fluxes and environmental variables. In addition, factors controlling these fluxes will be presented. Acknowledgement: This study was supported by "Environmental Monitoring on Human Impacts at the King Sejong Station, Antarctica" (Project PP04102 of Korea Polar Research Institute) and Eco-technopia 21 project (Ministry of Environment of Korea).
GC51A-1050 0800h
Impacts of Recent Warming on a Floating Ice Tongue in Northern Greenland
The recent collapse of ice shelves in West Antarctica and to the Ward Hunt Ice Shelf, Ellesmere Island, Canada, has been interpreted as evidence of accelerated climate change in the high latitudes. To improve our understanding of the stability of glaciers in northern Greenland a combination of field data, remote sensing observations and modeling is used to investigate both bottom and surface melt processes on the Petermann Gletscher (81 N, 60 W). The Petermann Gletscher is similar to other more well-known ice shelves because it has a large floating section, or ice tongue, that is 20-km wide by 70-km long. This purpose of this work is to describe in detail the surface climate of the Petermann Gletscher from automatic weather station (AWS) data. Emphasis in placed on describing surface energy exchanges that have controlled ablation over the 3 most recent summer seasons (2002-4). Projection of ablation over the entire surface of the ice tongue using a degree-day model shows that surface lowering of the ice tongue in 2002-3 is 50 percent higher than a 53-year proxy melt record established from AWS measurements at nearby Alert, Ellesmere Island. If this warming trend continues the increased thinning rate is likely to yield enhanced calving rates at the ice front of the Petermann Gletscher, which could ultimately weaken and fracture the floating ice tongue.
GC51A-1051 0800h
Ice Core Evidence of Recent Changes in Summer Melt Intensity of the Southern Greenland Ice Sheet
Knowledge of past Greenland Ice Sheet surface melting extent and intensity, and associated climatic controls, is critical to understanding the current and future mass balance of the ice sheet. Surface melting is greatest along the margins of the Greenland Ice Sheet, but leaves no simple record of past patterns or intensity at low elevations. This makes it difficult to place ongoing changes in melt extent in a longer temporal context, and to determine the role of melting in the recent lowering of the surface at the margins of the ice sheet. At higher elevations melt leaves a clear record in the firn and ice, and the ice sheet stratigraphy can provide a unique record of past changes in surface melt extent. We present results of stratigraphic analyses of ten ice-cores from the southern Greenland Ice Sheet, spanning the past 25-100+ years. We use these results to investigate spatial and temporal changes in melt across the southern Greenland Ice Sheet for the past century. In general, the ice-core melt records show high interannual variability, as well as significant decadal variability. All the cores show a significant reduction in surface melt in 1992 and 1993 following the Mt. Pinatubo eruption. Many, but not all, cores also show an overall increase in melt extent towards the present. These stratigraphic records are compared to nearby automatic weather station records located on the ice sheet, longer-term records from coastal meteorological stations, as well as local surface temperature and meteorological model results based on ERA-40 reanalysis data from the European Center for Medium Range Weather Forecasts (ECMWF.) These records are combined to provide a more comprehensive view of the climatic controls of changes in surface melt over the southern Greenland Ice Sheet throughout the 20th century.
GC51A-1052 0800h
Evidence and Implications of Recent Climate Change in Northern Alaska and Other Arctic Regions
The Arctic climate is changing. Permafrost is warming, hydrological processes are changing and biological and social systems are also evolving in response to these changing conditions. Knowing how the structure and function of arctic terrestrial ecosystems are responding to recent and persistent climate change is paramount to understanding the future state of the Earth system and how humans will need to adapt. Our holistic review presents a broad array of evidence that illustrates convincingly; the Arctic is undergoing a system-wide response to an altered climatic state. New extreme and seasonal surface climatic conditions are being experienced, a range of biophysical states and processes influenced by the threshold and phase change of freezing point are being altered, hydrological and biogeochemical cycles are shifting, and more regularly human sub-systems are being affected. Importantly, the patterns, magnitude and mechanisms of change have sometimes been unpredictable or difficult to isolate due to compounding factors. In almost every discipline represented, we show how the biocomplexity of the Arctic system has highlighted and challenged a paucity of integrated scientific knowledge, the lack of sustained observational and experimental time series, and the technical and logistic constraints of researching the Arctic environment. This study supports ongoing efforts to strengthen the interdisciplinarity of arctic system science and improve the coupling of large scale experimental manipulation with sustained time series observations by incorporating and integrating novel technologies, remote sensing and modeling.
GC51A-1053 0800h
Climatological Significances of Ice Core Records from the Mt. Nianquentanglha, Southern Tibetan Plateau
Delta D and net accumulation records covering the period AD 1952-1998 were reconstructed using a 29.5 m ice core from the col of the Lanong Glacier (5850 m a.s.l.) on the eastern saddle of Mt. Nianquentanglha, southern Tibetan Plateau (TP). Using NCEP/NCAR Reanalysis data, we investigate the relationships between ice core records and primary components of the climate system. Linear correlation analysis between Delta D and climate components for the 47 year overlap period indicates that Delta D variations are strongly correlated with summer (JJA) precipitation, winter (DJF) pressure, and geopotential height in both winter and summer over the South Asian and TP region (r above 0.34, p below 0.01). In detail, a negative correlation between Delta D and summer precipitation appears in the regions of Indian continent, Bay of Bengal, while a positive correlation exists over the north of TP. It agrees with amount effect on Delta D values during summer monsoon season considering that the majority of moisture in the south of TP comes from the India Ocean, while local moisture in TP always has higher Delta D values in summer. A negative relationship between Delta D and winter air pressure over central Asia suggests high pressure works as a barrier for winter moisture transportation by the Westerly which holds higher Delta D values compared with summer precipitation Delta D. Negative correlations between Delta D and geopotential height in both summer and winter over Asia indicate stronger atmospheric circulations over Asia correspond with lower Delta D values. Accumulation from the ice core is positively correlated with sea surface temperature (SST) over the Indian Ocean and 500 mb summer air temperature in South Asia and Indian Ocean, indicating high SST causes more moisture transported to the southern TP. Accumulation variations are positively correlated with geopotential height over the South Asia and Indian Ocean, while negatively correlated with these in the region of Siberia during both summer and winter, suggesting that the steeper gradient of air pressure from the Indian Ocean to the north increases precipitation over Mt. Nianquentanglha region. Meanwhile, a positive relationship between accumulation and winter Tibetan air pressure shows that stronger Tibetan High may cause more precipitation in the region.
GC51A-1054 0800h
The Role of Local Cyclone Activity in Spitsbergen Winter Temperatures and Fram Strait Sea Ice Export
Winter temperatures at Spitsbergen were at the core of the Arctic warming of the 1920s and Fram Strait ice export was part of the Great Salinity Anomaly of the 1960s. Along with Iceland and the Barents Sea, the region around Fram Strait and Spitsbergen is one of three northernmost Atlantic centers of high winter cyclone frequencies. The role of local winter cyclone activity and cyclogenesis in the climate of this area is examined. Cyclones moving toward, over and west of Spitsbergen occur in relatively mild, low ice export winters, and then continue into the Arctic basin north of Greenland and the Canadian archipelago. Cyclogenesis is also frequent off the northeast Greenland coast over the East Greenland Current during these winters associated with south-southwesterly flow around unusually high pressure over Scandinavia. Anomalously cold/high ice export winters have little cyclone activity around Fram Strait and cyclone activity is then concentrated in the Barents Sea and Eurasia side of the Arctic basin. Only 30% of the variance in time series of Spitsbergen temperatures and Fram Strait ice export is shared, possibly because cyclonic heat advection over Spitsbergen also brings northerly flow over the East Greenland Current, just as do Barents Sea cyclones.
GC51A-1055 0800h
Changes in Terrestrial Snow and Ice Following the Little Ice Age in the Queen Elizabeth Islands, Arctic Canada
Climate change during the 20th and 21st centuries has resulted in extensive modification of polar regions; this trend is expected to continue as predicted temperature increases there exceed those elsewhere on the globe (IPCC, 2001). The instrumental temperature record in the Canadian High Arctic extends back only $\sim$55 years, therefore, it is essential to investigate other proxy records to determine variability over longer time scales. This will provide a more meaningful measure of natural variability and the longer record will serve as a reference against which modern and future conditions may be compared and modelled. A substantial reduction in terrestrial ice cover in the Queen Elizabeth Islands (QEI) following the Little Ice Age (LIA) ($\sim$1600 to 1900 AD), is indicated by widespread, light-toned patches of poorly vegetated terrain, extending back to the modern ice mass. These patches display abrupt outer margins (trimlines), which record the former position and maximum extent of perennial snow and ice, and in many cases, mark their former equilibrium-line altitude (ELA). Therefore, trimlines on a regional scale serve as an important proxy for measuring late Holocene environmental change and a means of estimating climatic change. Classification methods were employed with high-resolution multispectral imagery (ASTER and Landsat 5 and 7) to map trimlines and modern ice margins throughout the QEI, and 1959/60 ice outlines for the same area were obtained from the National Topographic Database (NTDB) (provided by Geomatics Canada). Results indicate reductions in terrestrial ice cover throughout the QEI ranging from $\sim$27 to 84% since the termination of the LIA. Regional patterns related to ice reduction and changes in the ELAs will be discussed, and initial estimates of temperature and precipitation changes will also be presented.
GC51A-1056 0800h
Phytoplankton distributions and their nutrient environment in the Eastern Bering Sea.
After 1997, coccolithophorids blooms have been frequently observed by research vessels and satellites in the Eastern Bering Sea shelf, where diatoms have previously been dominate. Here, we present CTD, Chl-a, nutrient and phytoplankton data collected during cruises of the T/S Oshoro-Maru and R/V Mirai vessels from 2000 to 2003. Our goal is to refine the relation between phytoplankton distribution and water characteristics, and the controlling features of coccolithophorids blooms in the Eearstern Bering Sea. Samplings were carried out alone 166_E#8249;W from 55_E#8249;N to 59_E#8249;N. For cell counting, seawater samples were filtered through a 25-mm Millipore HA filter, and identification and counting of phytoplankton was performed with a scanning electron microscope. The scale of bloom and abundance of coccolithophorids were different in each year. The most dominant phytoplankton group was coccolithophorids in 2000, which agrees with the large bloom observed by satellite. In 2001, diatoms dominated at 70% and coccolithophorids accounted for 30% at 58, 58.5_E#8249;N. In 2002 and 2003, diatoms dominated at nearly 100% at all stations. Coccolithophorids abundance was nearly halted by pycnocline, since coccolithophorids existed in the middle shelf domain, which is known to be an area of cold-water pool distribution. The difference in density between the surface mixed layer and the cold-water pool gradually increased from 1980 to 2002, that is, seawater stratification in the middle shelf domain was strengthened as the result of the increased surface temperature and decreased salinity that have occurred recently. When stratification strengthens, the supply of nutrients to the surface from the cold-water pool is reduced. Consequently, coccolithophorids take precedence over diatoms in this condition. However, if the decreased salinity in the surface water depended on the increased river discharge, then the nutrients in the surface water would increase. River discharge has two peaks (spring and late summer) in one year (Chikita, 2001). Since river water contains high volumes of silicate and iron, an increase in river discharge would lead to the predominance of diatoms. The frequency and timing of storms, which influence the thickness of the surface mixed layer, may be another controlling factor of coccolithophorids blooms. In fact, there was a second peak in October 2000 and in August 2001. In 2000, the thickness of the surface mixed layer increased from July to September. Because the timing of storms and river discharges in summer controlled the stratification in the middle shelf domain, it greatly influenced the species_f composition of phytoplankton. In 2002 and 2003, the phytoplankton concetrations distribute peaks respectively at the south and north. The dominant classes are centric diatoms in the south, and is penate diatoms in the north, caused by defferent nutrients and temperature distribution. The sources of nutrients to the Estern bering Sea can be classified into three groups: up welling at the shelf edge, from the cold water pool, and from riverwater. The nutrients of surface water are high in the south and are low in the north, and dispense the diffenrent phytoplankton distribution.