CONICET | Buscador de Institutos y Recursos Humanos

Underway observations of sea surface temperature, salinity, carbonate systems, pCO2, dissolved O2, nutrients, phytoplankton taxonomy and total chlorophyll-a for three size filters (< 0.5mm, >10mm and 5mm< Chl-a <10mm), and atmosphere CO2 partial pressures were taken in the western Weddell Sea along 10 transects during the austral summer of 2001 to 2006. XBT sections allow identifying the Weddell Front and the Slope Front. Mean values of ΔpCO2 and Chl-a are - 60μatm and 1.45mg∙ m-3. The summer areal mean CO2 uptake in the western Weddell Sea is 7.8 mmol?m-2?day-1. About 88% of this region acts as a CO2 sink. Peaks in the sea-air ΔpCO2 of -200μatm, among the highest in the global ocean, were observed. Upwelling of CO2 rich waters driven by Ekman divergence within the Weddell Sea cyclonic gyre leads to a moderate emission in this region In the Southern Weddell Sea, including the shelf region, the maximum CO2 sink and high chlorophyll concentration are observed. The CO2 capture and the Chl-a concentration are much larger than reported in the eastern Weddell. The horizontal distribution of Chl-al shows that the Weddell is not oligotrophic. Similarly, high chlorophyll values are observed in other regions too. The highest chlorophyll concentration exceeding 5mg∙m-3 is observed near the Slope Front and on the shelf. This Chl-a concentration is remarkably higher than previously reported, suggesting significantly higher biological activity than previously thought. The capture of CO2 in this region is presumably associated with the high abundance of large diatoms (mainly Pseudo-nitzschia). The diatoms abundance and the high biomass may explain the high accumulation rate of opalines and carbon observed in bottom sediments. Our results suggest that the annual uptake of CO2 (0.02GTC?year-1) is about twice of previous estimates, which may have grossly underestimated the role of the biological CO2 pump in this region.