Seasonal patterns of water column particulate organic carbon and fluxes in the Ross Sea, Antarctica

Abstract

The standing stock of particulate organic carbon (POC) was determined during five cruises in the Ross Sea in 1996 and 1997 and compared with primary production of carbon measured in short-term 14C-incubations and the flux of organic carbon collected in moored sediment traps. POC concentrations were estimated from transmissometer profiles that were calibrated with discrete POC bottle samples from each cruise. The mean standing stock of POC integrated to a depth of 100 m and averaged along a 330 km transect at 76.5°S in mid-October (early spring) was only 240 mmol C m −2 , but more than doubled to 560 mmol C m −2 10 days later. By mid-January (summer) the standing stock had increased by an order of magnitude to ∼5300 mmol C m −2 , but dropped to 3500 mmol C m −2 one week later. By late April (autumn), the standing stock was only 200 mmol C m −2 . The following spring the standing stock increased from 700 mmol C m −2 in late November to 2200 mmol C m −2 in early December. Despite the high standing stock in the photic zone in summer, 1997, little POC was collected in the moored sediment traps until late summer (February–March) when the traps showed an increase in POC and silica flux. A three-fold increase in POC flux occurred in autumn (March–April) dominated by pteropods, but the standing stock of POC in the photic zone at that time was very low. Light-scattering sensor data suggest that, although present in all seasons, aggregates were most abundant in autumn and were distributed throughout the water column. These aggregates may have temporarily stored POC and provided food support for a pteropod population that died and settled into the traps in March–April. Still, the trap POC flux was only 5% of the peak standing stock. Resuspension and lateral advection of recently settled organic matter from a nearby topographic high may explain the larger flux measured in the deep sediment traps, a flux that continued into winter.