Seasonal changes in POC export flux in the Chukchi Sea and implications for water column-benthic coupling in Arctic shelves

As part of the 2002 Shelf-Basin Interactions (SBI) process study, measurements of the seasonal variation in the export flux of particulate organic carbon (POC) are reported for the upper waters of the Chukchi Sea. POC fluxes were quantified by determination of Th-234/U-238 disequilibrium and POC/Th-234 ratios in large (> 53 mu m) aggregates collected using in situ pumps. Samples were collected at 35 stations on two cruises, one in predominantly ice-coved conditions during the spring (May 6 June 15) and the other in predominantly open water during the Summer (July 17-August 26). Enhanced particle export was observed in the shelf and slope waters, particularly within Barrow Canyon, and there was a marked increase in Th-234-derived POC particle export at all stations during the summer (July-August) relative to the spring (May-June). Th-234-derived fluxes exhibit significant seasonal and spatial variability, averaging 2.9 +/- 5.3 mmol C m(-2) d(-1) (range 0.031-22mmol C m(-2) d-1) in the spring and increasing-4-fold in the summer to an average value of 10.5 +/- 9.3 mmol C m(-2) d(-1) (range = 0.79-39 mmol C m(-2) d(-1)). The fraction of primary production exported from the upper waters increases from similar to 15% in the spring to similar to 32% in the Summer. By comparison, DOC accumulation associated with net community production represented similar to 6% of primary production (-2mmol C m(-2) d(-1)). The majority of shelf and slope stations indicate a close agreement between POC export and benthic C respiration in the spring, whereas there is an imbalance between POC export and benthic respiration in the Summer. The implication is that LIP to similar to 20% of summer production (similar to 6 +/- 7 mmol C m(-2) d(-1)) may be seasonally exported off-shelf in this productive shelf/slope region of the Arctic Ocean. (c) 2005 Elsevier Ltd. All rights reserved.