Trace elements as regulators (iron) and recorders (uranium, protactinium, thorium, beryllium) of biological productivity in the ocean.

摘要

The input to and removal from the ocean of reactive trace elements is important for regulating and recording marine biological productivity. During the upwelling season off Oregon, I found iron concentrations are generally high and non-limiting, due to a large input from sediments and from the Columbia River. However, the input of iron can be temporally and spatially uncoupled from the input of macronutrients. An enhanced supply of iron to the Southern Ocean has also been implicated in increased biological productivity of this region during glacial times. Here I show that the distribution of authigenic uranium in sediments of the Atlantic sector is consistent with a greater flux of organic carbon during the Last Glacial Maximum (LGM) relative to today.; Long-lived radionuclides with accurately known inputs to the ocean are valuable tools for studying the behavior of reactive elements in the modern ocean, and for recording past changes in particle flux. The concentrations of 230Th, 231Pa and 10Be in sediment trap material was used to calculate partition coefficients as a function of particle composition. The results suggest opal (carbonate) has a higher (lower) affinity for Pa and Be, and a lower (higher) affinity for Th, relative to other particle types. High 231Pa/230Th and 10Be/230Th ratios in Southern Ocean sediments are the result of scavenging by opal, which does not fractionate between Pa and Th or between Be and Th, and are not due to quantitative scavenging of nuclides advected into the Southern Ocean in association with the overturning circulation.; I have reconstructed the accumulation rate of biogenic and lithogenic components in the SW Pacific sector of the Southern Ocean, using 230 Th to corrected for sediment focusing and winnowing. During the LGM, the accumulation rate of opal, biogenic barium and organic carbon was greatly reduced, relative to today, within the Antarctic Circumpolar Current (ACC) south of the Antarctic Polar Front (APF). An inter-basin comparison points to a South American source for the enhanced input of lithogenic material to Southern Ocean sediments during the LGM, and suggests productivity north of the APF during the LGM was greatest in the Atlantic and lowest in the Pacific.