Water column

About: Water column is a research topic. Over the lifetime, 13706 publications have been published within this topic receiving 496626 citations.

Seasonality in the flux of natural radionuclides and plutonium in the deep Sargasso Sea. Technical report

Abstract: A record of radionuclide fluxes at a deep-ocean station near Bermuda (32/sup 0/ 05 min N, 64/sup 0/ 15 min W) was obtained from analysis of a 3-year collection of sediment-trap samples. The trap was placed at a depth of 3200 m, 1000 m above the sea floor, and the samples were recovered at 2-month intervals. Concentrations of U-238, -234, Th-232, -230, -228, Pa-231, Pb-210, Po-210, and Pu-239 and -240 were measured in the trapped material. Most of the radionuclide activity was found in the <37-micron sieved fraction. All radionuclide fluxes showed seasonal variations in phase with the variations in total sediment flux, which had been previously shown to be closely tied to the annual cycle of primary production in the overlying surface water. Seasonal variations are especially noteworthy for Th-230 and Pa-231, considering that most of their production occurs in the water column below the euphotic zone. Evidently the seasonal influence is transmitted downward by the varying particle flux so that radionuclide scavenging rates at depth, as well as at the surface, are affected. It is suggested that this could be brought about by seasonal variations in the flux of marine snow or in the rate of fecal-matter productionmore » in the deep-water column. Keywords: Pelagic sedimentation.« less

Seasonality in the flux of natural radionuclides and plutonium in the deep Sargasso Sea

Abstract: A record of radionuclide fluxes at a deep-ocean station near Bermuda (32°05′N, 64°15′W) was obtained from analysis of a 3-year collection of sediment-trap samples. The trap was placed at a depth of 3200 m, 1000 m above the sea floor, and the samples were recovered at 2-month intervals. Concentrations of 238U, 234U, 232Th, 230Th, 228Th, 231Pa, 210Po, and 239, 240Pu were measured in the trapped material. Most of the radionuclide activity was found in the <37-gmgm sieved fraction. All of the radionuclide fluxes showed seasonal variations that were in phase with the variations in total sediment flux, which were shown in earlier work to be closely tied to the annual cycle of primary production in the overlying surface water. The seasonal variations are especially noteworthy for 230Th and 231Pa, considering that most of their production occurs in the water column below the euphotic zone. Evidently the seasonal influence is transmitted downward by the varying particle flux so that radionuclide scavenging rates at depth, as well as at the surface, are affected. It is suggested that this could be brought about by seasonal variations in the flux of marine snow or in the rate of fecal-matter production in the deep-water column. Fluxes of 230Th and 231Pa integrated over the annual cycle yielded a trapping efficiency of 105 ± 17% for the PARFLUX sediment trap used in this investigation.

The carbon cycle and biogeochemical dynamics in lake sediments

Abstract: The concentrations of organic carbon (OC) and CaCO 3 in lake sediments are often inversely related. This relation occurs in surface sediments from different locations in the same lake, surface sediments from different lakes, and with depth in Holocene sediments. Where data on accumulation rates are available, the relation holds for organic carbon and CaCO 3 accumulation rates as well. An increase of several percent OC is accompanied by a decrease of several tens of percent CaCO 3 indicating that the inverse relation is not due to simple dilution of one component by another. It appears from core data that once the OC concentration in the sediments becomes greater than about 12%, the CO 2 produced by decomposition of that OC and production of organic acids lowers the pH of anoxic pore waters enough to dissolve any CaCO 3 that reaches the sediment-water interface. In a lake with a seasonally anoxic hypolimnion, processes in the water column also can produce an inverse relation between OC and CaCO 3 over time. If productivity of the lake increases, the rain rate of OC from the epilimnion increases. Biogenic removal of CO 2 and accompanying increase in pH also may increase the production of CaCO 3 . However, the decomposition of organic matter in the hypolimnion will decrease the pH of the hypolimnion causing greater dissolution of CaCO 3 and therefore a decrease in the rain rate of CaCO 3 to the sediment-water interface.