Distribution of dissolved organic radiocarbon in the Amundsen Sea, Antarctica

Abstract

Marine dissolved organic carbon (DOC), one of the largest reduced carbon pools, plays a crucial role in the global carbon cycle. Carbon isotopic abundances were used as a tracer to examine the source and fate of DOC in the Amundsen Sea, Antarctica. Δ14C values ranged between -260 ‰ and -481 ‰. Δ14C values were higher in the upper layer than in the deep layer and the highest Δ14C value was found in the Amundsen Sea polynya at a depth of 20m. The largest spatial variation of 14C age across the three stations was observed in the mixed layer. Δ14C values were significantly higher in the Amundsen polynya surface layer than in the sea ice zone while DOC concentration was only slightly higher, implying that a fraction of old DOC was removed in the upper layer. All samples collected from the Amundsen Sea were depleted in 13C throughout water column compared to the open oceans. δ13C values ranged from -26.2 to -28.9 ‰ with the mean value of -27.8±0.8 ‰ (n=11). The δ13C and Δ14C distributions suggest that the Amundsen Sea polynya may be a sink of old DOC.