Seasonal cycle of CO2 from the sea ice edge to island blooms in the Scotia Sea, Southern Ocean

The Scotia Sea region contains some of the most productive waters of the Southern Ocean. It is also a dynamic region through the interaction of deep water masses with the atmosphere. We present a first seasonally-resolved time series of the fugacity of CO2 (fCO(2)) from spring 2006, summer 2008, autumn 2009 and winter (potential temperature minimum) along a 1000 km transect from the pack ice to the Polar Front to quantify the effects of biology and temperature on oceanic fCO(2). Substantial spring and summer decreases in sea surface fCO(2) occurred in phytoplankton blooms that developed in the naturally iron-fertilised waters downstream (north) of South Georgia island (54-55 degrees S, 36-38 degrees W) and following sea ice melt (in the seasonal ice zone). The largest seasonal fCO(2) amplitude (Delta fCO(2)) of -159 mu atm was found in the South Georgia bloom. In this region, biological carbon uptake dominated the seasonal signal, reducing the winter maxima in oceanic fCO(2) by 257 mu atm by the summer. In the Weddell-Scotia Confluence, the southern fringe of the Scotia Sea, the shift from wintertime CO2-rich conditions in ice covered waters to CO2 undersaturation in the spring blooms during and upon sea ice melt created strong seasonality in oceanic fCO(2). Temperature effects on oceanic fCO(2) ranged from Delta fCO(2) (sst) of similar to 55 mu atm in the seasonal ice zone to almost double that downstream of South Georgia (98 mu atm). The seasonal cycle of surface water fCO(2) in the high-nutrient low-chlorophyll region of the central Scotia Sea had the weakest biological control and lowest seasonality. Basin-wide biological processes dominated the seasonal control on oceanic fCO(2) (Delta fCO(2) (bio) of 159 mu atm), partially compensated (43%) by moderate temperature control (Delta fCO(2) (sst) of 68 mu atm). The patchwork of productivity across the Scotia Sea creates regions of seasonally strong biological uptake of CO2 in the Southern Ocean. (C) 2015 Elsevier B.V. All rights reserved.