HR: 08:05h
AN: GC21B-01 INVITED    [Abstracts]
TI: 20th century trends in the Russian hydrologic cycle
AU: * Smith, L C
EM: lsmith@geog.ucla.edu
AF: University of California, Los Angeles (UCLA), Department of Geography, Los Angeles, CA 90095-1524, United States
AB: Russia has the greatest northern land area, coastal shelves, terrestrial carbon stocks, and river outflows of any nation. Its rivers deliver enormous loads of freshwater, dissolved material, and nutrients to the Arctic Ocean. Carbon storage in Siberian peatlands is large, tightly coupled with hydrology, and depends crucially on whether wetter or drier soil conditions prevail. Therefore, it is plausible that shifts in precipitation, surface wetness, or river runoff could alter the carbon balance, oceanography, and ecoystems of the world's largest high-latitude land mass. Natural hydroclimatic variability, however, is notoriously high in Arctic environments. Therefore, correct identification of long-term anthropogenic trends requires statistical analysis of historical records and sampling over broad geographical areas. This talk provides an overview of the various late 20th century hydrologic trends observed in northern Russia. An overall +7 percent increase in river discharge to the Arctic Ocean now appears to have been driven substantially by increased precipitation. A primary mechanism underlying the discharge increase was enhanced groundwater flow, which rose in the late 20th century. To what extent this phenomenon simply reflects the precipitation increase or another process like improved infiltration through seasonally frozen ground is unknown; what is clear is that minimum river "low-flows" are rising across Russia. In contrast, there has been no broadly coherent increase in the magnitude of the annual spring flood, although some shifts towards earlier peak timing are evident. A dendrochronological reconstruction of annual river outflows suggests that the late 20th century discharge increase, while large, is not unprecedented over the past 200 years. Since no shutdowns in oceanic Meridional Overturning Circulation (MOC) occurred during that time, this finding tempers concerns about any such shutdown in the immediate future. Permafrost thaw is causing Siberian lakes to grow and expand in continuous permafrost but to shrink and drain further south in marginal permafrost. Geochemical samples from West Siberia suggest that thawing permafrost will enhance river loads of total dissolved solids (TDS), dissolved organic carbon (DOC), and nutrients (N, P). However, permafrost thaw cannot fully explain the rising river water levels. The interactions of permafrost and seasonally frozen ground with surface and groundwater systems, and their concomitant response to expected climate warming in the region, remain largely unknown.
UR: http://lena.sscnet.ucla.edu
DE: 0702 Permafrost (0475)
DE: 0704 Seasonally frozen ground
DE: 0744 Rivers (0483, 1856)
DE: 1621 Cryospheric change (0776)
DE: 1833 Hydroclimatology
SC: Global Environmental Change [GC]
MN: 2007 Fall Meeting