Upper ocean export of particulate organic carbon and biogenic silica in the Southern Ocean along 1701W

Upper-ocean fluxes of particulate organic carbon (POC) and biogenic silica (bSi) are calculated from four US JGOFS cruises along 1701W using a thorium-234 based approach. Both POC and bSi fluxes exhibit large variability vs. latitude during the seasonal progression of diatom dominated blooms. POC fluxes at 100m of up to 50mmolCm 2 d 1 are found late in the bloom, and farthest south near the Ross Sea Gyre. Biogenic Si fluxes also peak late in the bloom as high as 15mmol Sim 2 d , but this flux peak occurs at a different latitude, just south of the Antarctic Polar Front (APF), which is centered around 601S along this cruise track. The ratios of both POC and bSi export relative to their production rates are large, suggesting an efficient biological pump at these latitudes. The highest relative bSi/POC flux ratios at 100m are found just south of the APF, coincident with a bSi/POC flux peak seen in 1000m traps during this same program by Deep-Sea Research II (submitted). These data suggest that efficient export at these latitudes can support the high accumulation rates of bSi found in the sediments under and south of the APF, despite the generally low biomass and productivity levels in this region. r 2001 Published by Elsevier Science Ltd.