Radionuclides measured in surface water samples from the South Atlantic

In the nutrient-rich Southern Ocean, Fe is a vital constituent controlling the growth of phytoplankton. Despite much effort, the origin and transport of Fe to the oceans are not well understood. In this study we address the issue with geochemical data and Nd isotopic compositions of suspended particle samples collected from 1997 to 1999 in the South Atlantic Sector of the Southern Ocean. Al, Th, and rare earth element (REE) concentrations as well as 143Nd/144Nd isotopic ratios in acetic acid-leached particle samples representing the lithogenic fraction delineate three major sources: (1) Patagonia and the Antarctic Peninsula provide material with eNd > -4 that is transported toward the east with the polar and subpolar front jets, (2) the south African shelf, although its influence is limited by the circumpolar circulation and wind direction, can account for material with eNd of -12 to -14 adjacent to South Africa, and (3) East Antarctica provides material with eNd of -10 to -15 to the eastern Weddell Sea and adjacent Antarctic Circumpolar Current. For this region we interpret the Nd isotopic evidence in combination with oceanographic/atmospheric constraints as evidence for supply of significant amounts of terrigenous detritus by icebergs.

在营养盐充足的南大洋中，铁（Fe）是调控浮游植物生长的关键限制因子。尽管已有大量研究投入，入海铁的来源与输运机制仍未被充分阐明。本研究依托1997至1999年间于南大洋南大西洋扇区采集的悬浮颗粒物样品的地球化学数据与钕（Nd）同位素组成，对该问题展开探讨。对代表陆源组分的乙酸浸提颗粒物样品的分析结果显示，铝（Al）、钍（Th）、稀土元素（REE）浓度及143Nd/144Nd同位素比值可明确三大主要来源：（1）巴塔哥尼亚与南极半岛可提供εNd值大于-4的物质，此类物质随极地与亚极地锋面射流向东输运；（2）南非陆架虽受环极环流与风向限制，影响范围有限，但其可为南非邻近海域提供εNd值介于-12至-14之间的物质；（3）东极可为威德尔海东部及邻近的南极绕极流区域提供εNd值介于-10至-15之间的物质。针对本研究区域，我们结合海洋学与大气学约束条件对钕同位素证据进行解读，证实冰山为该区域输送了大量陆源碎屑物质。