Low particulate carbon to nitrogen ratios in marine surface waters of the Arctic

During the Canada's Three Oceans and Joint Ocean Ice Study projects in the summers of 2007 and 2008, we measured particulate organic carbon to nitrogen ratios (POC:PON) throughout the euphotic zone in Subarctic and Arctic waters. Average depth-integrated values (2.65 +/- 0.19) in the Beaufort Sea and Canada Basin (BS-CB domain) were much lower than both the Redfield ratio (6.6) and the average ratios (3.9 to 5.6) measured across other Arctic-Subarctic domains. Average uptake ratios of C and N (rho C:rho N) were also lower (0.87 +/- 0.14) in BS-CB than in the other four domains (2.10 to 3.51). Decreasing POC: PON ratios were associated with low concentrations of phytoplankton C, reduced abundance of biogenic silica (bSiO(2)), a smaller relative contribution of the > 5 mu m fraction to total chlorophyll a and a larger relative contribution of small flagellates (< 8 mu m) to total phytoplankton C. In the subsurface chlorophyll a maximum (SCM) within the BS-CB domain, phytoplankton C represented only similar to 13% of POC; and therefore, the presence of heterotrophic microbes may have decreased POC: PON. These ratios are supported by data obtained during other Arctic programs in 2006, 2008, and 2009. Previous work has suggested a link between freshening of surface waters and increasing dominance of picophytoplankton and bacterioplankton in the Canada Basin, and the low POC: PON ratios measured during this study may be a consequence of this shift. Our results have ramifications for the conversion between C-and N-based estimates of primary productivity, and for biogeochemical modeling of marine Arctic waters.