HR: 0800h
AN: C41A-0184    [Abstracts]
TI: The Biogeochemistry of Dissolved Organic Matter and Nutrients in two Large Arctic Estuaries and Potential Implications for our Understanding of the Arctic Ocean System
AU: * Amon, R M
EM: amonr@tamug.edu
AF: Texas A&M University at Galveston, 5007 Avenue U, Galveston, TX 77551 United States
AU: Meon, B
EM: bmeon@awi-bremerhaven.de
AF: Alfred Wegener Institute for Polar and Marine Research, Am Handelshafen 12, Bremerhaven, 27515 Germany
AB: The discharge, composition and fate of dissolved organic matter (DOM) and nutrients was investigated in two of the largest Arctic rivers, Yenisei and Ob, in order to assess their role for the biogeochemistry of the Kara Sea, and the potential of terrestrial DOM as tracer for the Arctic Ocean. Ultrafiltered DOM (UDOM) from the 2 river-estuary systems was characterized by high C/N ratios (34 - 49), depleted stable carbon isotope values (less than -26.5 per mill), depleted stable nitrogen isotope values (1.8 - 4.2 per mill), and enriched delta 14C values (84 - 307 per mill). The distribution of DOM and its chemical properties indicated no major loss processes during estuarine mixing but showed considerable variability between the rivers and years suggesting a variable input of plankton-derived DOM. The input of plankton-derived DOM was reflected in elevated neutral sugar yields, decreased C/N ratios, but variable stable carbon isotope values. In contrast, stable nitrogen isotope values appear to be more reliable indicators to distinguish terrestrial from plankton-derived DOM in this estuarine system. Based on stable nitrogen isotope values we estimate that between 6 and 16% of the DOM in the river and estuaries is of plankton origin. Clear differences were found in the chemical composition of DOM size fractions. Plankton-derived DOM was more abundant in the higher molecular weight fractions whereas terrestrial-derived DOM dominated the lower molecular weight fraction. This suggests a more heterogeneous origin of DOM than is revealed from looking at the composition of the bulk DOM. Compiling the information from this study with previous studies indicates that river input of DOM and nutrients is not the main driver of autotrophic and heterotrophic processes in the Kara Sea ecosystem. Consistent with previous reports, we found the terrestrial fraction of river DOM to be largely conservative in the estuaries underscoring the potential of terrestrial DOM as a tracer in the Arctic Ocean, especially when combined with standard hydrographic measurements.
DE: 4805 Biogeochemical cycles (1615)
SC: Cryosphere [C]
MN: 2004 AGU Fall Meeting