Estimating Net Community Production Using Dissolved InorganicCarbon Content in the Amundsen Sea Polynya, Antarctica

Abstract

The net community production (NCP) can be estimated using various technique. Here we used the difference of dissolved inorganic carbon (DIC) concentrations in the water column between the surface and deep waters to determine NCP assuming that the deep water preserves the winter characteristics of dissolved inorganic content. This is true in the Amundsen Sea polynya (ASP) as the winter water is detected below the mixed layer. Various literature shows ambiguous definition of the reference depth between the surface and deep waters. We estimated NCP in the Amundsen Sea polynya applying various reference depths relevant to the biological production and vertical mixing. We employed the results from the expedition conducted in ASP during austral summer in 2011. Five reference depths were selected to represent the winter water for which biological activity paused; (1) potential temperature minimum depth (pTmin), (2) euphotic depth (Ed), (3) mixed layer depth (MLD), and (4) 100 m and (5) 200 m nominal depths. Our investigation shows that the mean water depths in ASP increase in the following order; Ed, MLD, pTmin, 100 m, and 200 m. Corresponding NCP also increases as DIC concentration continually increase with depth. To determine the optimal reference depth for NCP, we examined the relationship between nutrients at the 5 depths defined above. We discuss the results from our investigation in the presentation.