C53A-01 INVITED 13:45h
Changes in Cloud Cover over the Arctic Seas from 1980-2002.
Winter and spring changes in cloudiness are compared over the arctic seas from the TOVS (TIROS Operational Vertical Sounder) Polar Pathinder retrievals and two separate datasets derived from the Advanced Very High Resolution Radiometer (AVHRR). All satellite products exhibit significant decreases in cloud fraction over the arctic seas during winter (December, January, February) on the order of 5%/decade. An equally striking increase in spring (March, April, May) cloudiness is evident from the TOVS Pathfinder (TPP) and the extended AVHRR Polar Pathfinder (APP-X) projects . Regionally these positive trends can be as large as 15%/decade. Surface observations from the Russian drifting meteorological stations are consistent with satellite- observed changes during the 1980s. Negative trends in spring cloud cloudiness reported by Comiso [2003] are in conflict with these findings. Spring changes in cloudiness are associated with changes in the atmospheric circulation. Changes in cloudiness have a direct impact on the radiation budget at the Arctic surface. Potenital links to the freshwater budget will be discussed.
C53A-02 14:05h
Development of Bias-Corrected Precipitation Database and Climatology for the Arctic Regions
Precipitation is one of the key components in hydrological modeling and process studies. It is also the most important variable in global change analyses, as change of precipitation will have a major impact on hydrology, climate and ecosystems. It has been recognized that significant (up to 100%) systematic errors (biases) exist in the gauge-measured precipitation records and these biases must be documented and corrected in order to obtain a compatible, accurate data set for large-scale hydrological and climatic investigations. The climate of the high latitudes is characterized by low temperature, generally low precipitation and high winds. Because of the special condition in the high latitudes, the biases in precipitation gauge observations are enhanced and need special attention. This presentation will review an ongoing NSF project that directly addresses the problem of biases of precipitation measurements in the high latitude regions. This work has been based on the extensive research experiments, particularly on the WMO Solid Precipitation Measurement Intercomparison Project. It defines the accuracy of precipitation measurements, and implements the consistent bias-correction methodologies for the high latitude regions (Alaska, northern Canada, Siberia, northern Europe, Greenland, and the Arctic Ocean). The goal of this research is to develop the unbiased and compatible precipitation database (including grid products) and climatology for the pan-Arctic. This research is particularly relevant to studies of climate change and fresh water cycle in arctic regions, such as the SEARCH and Arctic-CHAMP. The results of this study will improve our understanding of the spatial and temporal variability of precipitation and its contribution to the freshwater balance of the high-latitude land and ocean systems. They will also be useful to analyses of global climate change and validation of the GCM/RCM.
http://www.uaf.edu/water
C53A-03 INVITED 14:20h
Are Increasing Freshwater Inputs To The Arctic Ocean Linked To Climate Change?
The global hydrological cycle has shown evidence of acceleration over the past 40 years. Evidence includes increasing evaporation from low latitude oceans and increasing precipitation, especially at high latitudes. Net melting of arctic glaciers plus runoff from Eurasian arctic rivers alone have added about 4000 km$^{3}$ of extra (anomaly from baseline conditions) freshwater to the Arctic Ocean since about 1960. Glacier melt is primarily driven by arctic warming. The Eurasian discharge monitoring includes 2/3 of total Eurasian runoff which comprises 60% of pan-arctic runoff. An investigation of mechanisms driving changes in Eurasian runoff showed that dams, fires and permafrost melt were probably not the major factors causing increased discharge. The discharge changes appear to be driven by the acceleration of the hemispheric hydrologic cycle driven by warming and possibly by shifts in wind directions. Over the same 40 years the high latitude oceans have freshened. A coordinated effort to reconcile the changes in freshwater inputs with changes in freshwater inventory of the Arctic Ocean, Nordic Seas and North Atlantic over the past 40-50 years would be a valuable contribution.
C53A-04 14:40h
Linking River-to-Ocean Through Temporal and Spatial Variation in Runoff Tracers in the Arctic Ocean
The mixing of runoff into surface water of the Arctic Ocean has been incompletely resolved because of limited seasonal sampling. Pan-Arctic River Transport of Nutrients, Organic Matter and Suspended Sediments (PARTNERS) and Shelf Basin Interactions (SBI) are two on-going research programs that are now helping to document more extensive seasonal variation in runoff tracers such as oxygen-18/oxygen-16 ratios, lignin, dissolved organic carbon (DOC), and excitation fluorometry at major river mouths, and over the shelf, slope and basin of the Arctic Ocean. Using data that indicate multi-annual persistence of the runoff signal in offshore surface waters entrained in the Beaufort Gyre, we show that the oxygen isotope end-member for runoff is modulated seasonally and is dependent upon both river source and seasonal path of input. A Haardt fluorometer used in 2002 on the SBI cruises on the Chukchi and Beaufort Seas was not well correlated with DOC as has been observed in the Eurasian Arctic. However, data from a denitrification indicator, N**, also serves as a functional tracer for Bering Sea-origin waters that have been in contact with continental shelf sediments. This nutrient-based indicator is well correlated with the Haardt fluorometer signal in the Chukchi Sea in the absence of freshwater contributions from melted sea ice. This suggests that release of organic materials from productive continental shelf sediments may also influence the Haardt fluorometer signal independent of runoff DOC. Experimental shipboard incubations of shelf and slope sediments corroborate significant releases of DOC from benthic sediments. Seasonal variation in the oxygen isotope composition of runoff, among various Arctic river sources and the river component within Bering Strait as well as the introduction of freshwater contributed from melted sea ice will also be discussed.
http://arctic.bio.utk.edu
C53A-05 14:55h
Land-sea Coupling in a Changing Arctic: Implications of Increasing River Discharge for Biogeochemical Cycling Over the Eurasian Shelf
While feedbacks between increasing arctic river discharge and global ocean circulation have been highlighted over the past few years, the potential influence of increasing river discharge on biogeochemical cycling in the Arctic Ocean has been given less attention. In this presentation we will evaluate changes in water and nutrient fluxes from major rivers to the Barents, Kara, and Laptev seas from the 1930s to present. Long-term changes in water and nutrient fluxes to these seas are relatively small in comparison to average annual fluxes. However, the changes have not been evenly distributed throughout the year, and account for much larger proportions of average fluxes during some months. In particular, flow regulation from dams on the Ob, Yenisey, and Lena rivers has greatly increased winter discharge. The combined influence of increased winter discharge on stratification, nutrient supply, and spring production in shelf waters will be discussed. Increased stratification is expected to decrease total production. At the same time, the proportion of production supported by river-born nutrients is expected to increase. Nitrate and silicate dynamics will be given particular emphasis. Silicate concentrations are much higher than nitrate concentrations in the Eurasian arctic rivers (and both are relatively low in ocean waters feeding the Eurasian shelf). Thus, changes in silicate supply accompanying increased river discharge have a greater potential than do changes in nitrate supply to influence production in shelf waters. Higher silicate to nitrate ratios would support a shift in the producer assemblage in favor of diatoms.
C53A-06 15:10h
Simulated variability and change in 20th and 21st century Arctic freshwater budgets
Variability and change in Arctic ocean freshwater budgets has large potential climate implications, including influences on Arctic sea ice growth and deep water formation in the northern North Atlantic. In this study, variability and change in ensemble 20th century simulations of the Community Climate System Model, version 3 are presented. This includes an analysis of the timeseries of river runoff, precipitation and evaporation, and ice and ocean transports. Comparisons to observations are made where possible. Atmospheric circulation patterns and other factors associated with the freshwater budget variability are assessed to determine the mechanisms driving variability and change over the 20th century simulations. Additionally, information on the simulated natural versus forced changes in the system are discussed. Finally, IPCC scenario runs are examined to identify projected changes in the Arctic freshwater budgets over the next century.
C53A-07 15:25h
The Arctic Freshwater Budget: model results, comparisons to data, implications
A detailed characterization of the fresh water reservoir of the Arctic Ocean, as simulated by the University of Victoria Earth System Climate Model (Uvic-ESCM) is presented. These runs combine a full, 3 dimensional, global ocean circulation model, a simple land surface model, and an elastic-viscous-plastic ice model coupled to an energy moisture balance model, with specified wind forcing from NCEP renalsysis data. The model has increased resolution in the Arctic Ocean, which is the focus of this set of experiments. The sea ice export produced by this model compare well with in-situ and satellite-derived measurements of the volume and area fluxes, as well as some other model simulations. The mean seasonal cycle and the year-to-year variability in the temperature and salinity structure of the peripheral seas of the Arctic Ocean, the precipitation minus evaporation and river runoff are compared with the NCEP reanalysis and in-situ data. The model shows a link between the atmospheric circulation regimes over the Arctic region, and the fresh water reservoir and fluxes out of the Arctic. We find a positive correlation between the cyclonicity and the export of liquid and frozen fresh water from the Arctic. For the liquid part, the amplitude of the response to changes in atmospheric forcing is smaller than that of the ice and lags the forcing by several months. The magnitude of the fresh water reservoir changes (both solid and liquid) are compared; and their (net and individual) effect on the meridional overturning circulation of the Atlantic, as measured by its stream function, is assessed. A fresh water budget for the full (Arctic) ice-ocean system is presented as well as the exchange between fresh water in the solid and liquid phase within the system.