Seasonal POC fluxes at BATS estimated from 210Po deficits

In this study at the Bermuda Atlantic Time-series Study (BATS) site we demonstrate that the polonium-lead disequilibrium system may perform better as a tracer of organic carbon export under low-flux conditions (in this case, < 2.5 mmol C m(-2) d(-1)) than under bloom conditions in an oligotrophic setting. With very few exceptions, the POC flux predictions calculated from the water-column Po-210 deficit were within a factor of 2 of the POC flux caught in surface-tethered sediment traps. However, we found higher correlation between size-fractionated particulate Po-210 activity and POC concentration in November 2006 (r=0.93) than in January (r=0.79) and during the spring bloom in March 2007 (r=0.80). We suggest that this is due to the ability of polonium to distinguish between bulk mass flux and organic carbon export under oligotrophic and lithogenic-driven flux regimes. Further, we found that the POC/Po ratio on particles was largely independent of size class between 10 and 100 mu m (P=0.13) during each season, supporting the notion that export in this oligotrophic system is driven by sinking aggregates of smaller cells and not by large, individual cells. (C) 2009 Elsevier Ltd. All rights reserved.