The Distribution of C-14 and Ar-39 in the Weddell Sea

Carbon 14 and Ar-39 data from the Weddell Sea are presented and discussed. Values of DELTA C-14 and Ar-39 are low in the winter mixed layer (DELTA C-14 almost-equal-to -90 to -125 parts per thousand; Ar-39 almost-equal-to 85% modern). These low values are consistent with the surface layer dynamics which is dominated by entrainment of relatively old water of circumpolar origin and reduced gas exchange during sea ice cover. The DELTA C-14 and Ar-39 values of the deep and bottom waters range from -160 to -150 parts per thousand and 38 to 57% modern, respectively. The DELTA C-14 values of Weddell Sea Bottom Water (WSBW) found in the central Weddell Sea along a 0-degrees longitude section are only slightly higher than those of the overlying Weddell Sea Deep Water (WSDW) showing that the influence of bomb C-14 on these waters is small. Part of the WSBW with higher DELTA C-14 values observed in the northwestern Weddell Sea seems to escape through the South Sandwich Trench, and part seems to mix from a boundary current into the central Weddell Sea. The observed C-14 distribution is consistent with the hypothesis that Ice Shelf Water (ISW) is a source of WSBW. A simple conceptual model of the surface layer dynamics is used to estimate the prebomb DELTA C-14 values of Surface Water and Winter Water to be about -140 and -130 parts per thousand, respectively. Using mixing ratios between WSDW and shelf water derived from temperature/salinity and He-3 data, the prebomb DELTA C-14 values of WSBW are estimated to be -157 parts per thousand (potential temperature of WSBW: -0.7-degrees-C). The Ar-39 concentration of WSBW with a potential temperature of -0.7-degrees-C is determined to be 57% modern. Bomb radiocarbon water column inventories are estimated and discussed.