Modeling the nitrogen and carbon cycling in Marguerity Bay, Antarctica: annual variations in ammonium and Net Community Production

Y. Serebrennikova, K.A. Fanning, and J. Walsh

A quasi-two dimensional biogeochemical model was applied to Marguerite Bay in order to investigate the differences in the cycles of nitrogen and carbon in Marguerite Bay dissolved inorganic pools and plankton communities between the 2000-2001 and 2001-2002 seasons. The impetus for the modeling effort was the observation made during the SO GLOBEC program field surveys in the austral autumns of 2001 and 2002 that showed an approximately two-fold decrease in Net Community Production (NCP) and ammonium stocks from autumn 2001 to autumn 2002 (Serebrennikova and Fanning, 2004).

The model's nutrient fields compare favorably to the observations made during the LTER and SO GLOBEC surveys in both the 2000-2001 and 2001-2002 field years. NCP was mainly controlled by the availability of light to phytoplankton: greater sea ice presence led to a shorter period of phytoplankton bloom in 2001-2002 than in 2000-2001. A combination of factors caused the decrease in ammonium stocks between the two years. First, lower primary production led to lower bacterial ammonification during the second study year. Second, lesser ammonium was excreted by zooplankton due to the reduction in zooplankton stocks in 2002. Overall, model results show that up to 45% of the ammonium produced per year was remineralized by bacteria in Marguerite Bay.

STATUS UPDATE:

10/18/07: Received final version with U.S. GLOBEC contribution number.