Stocks and dynamics of dissolved and particulate organic matter in the southern Ross Sea, Antarctica

Dissolved and particulate organic matter was measured during six cruises to the southern Ross Sea. The cruises were conducted during late austral wint er to autumn from 1994 to 1997 and included coverage of various stages of t he seasonal phytoplankton bloom, The data from the various years are compil ed into a representative seasonal cycle in order to assess general patterns of dissolved organic matter (DOM) and particulate organic matter (POM) dyn amics in the southern Ross Sea. Dissolved organic carbon (DOC) and particul ate organic carbon (POC) were at background concentrations of approximately 42 and 3 muM C, respectively, during the late winter conditions in October . As the spring phytoplankton bloom progressed, organic matter increased, a nd by January DOC and POC reached as high as 30 and 107 muM C, respectively , in excess of initial wintertime conditions. Stocks and concentrations of DOC and POC returned to near background values by autumn (April). Approxima tely 90% of the accumulated organic matter was partitioned into POM, with m odest net accumulation of DOM stocks despite large net organic matter produ ction and the dominance of Phaeocystis antarctica, Changes in NO3 concentra tion from wintertime values were used to calculate the equivalent biologica l drawdown of dissolved inorganic carbon (DICequiv). The fraction of DICequ iv drawdown resulting in net DOC production was relatively constant(ca. 11% ), despite large temporal and spatial variability in DICequiv drawdown. The C:N (molar ratio) of the seasonally produced DOM had a geometric mean of 6 .2 and was nitrogen-rich compared to background DOM. The DOM stocks that ac cumulate in excess of deep refractory background stocks are often referred to as "semi-labile" DOM. The "semi-labile" pool in the Ross Sea turns over on timescales of about 6 months. As a result of the modest net DOM producti on and its lability, the role DOM plays in export to the deep sea is small in this region. (C) 2000 Elsevier Science Ltd. All rights reserved.