DOI: 10.25921/0bwg-7b55
title: NOAA/WDS Paleoclimatology - South Atlantic Late Pleistocene Sea Surface Temperature, Dust and Paleoproductivity Data

description: Fluxes of lithogenic material and fluxes of three palaeo-productivity proxies (organic carbon, biogenic opal and alkenones) over the past 100 000 years were determined using the 230Th-normalization method in three sediment cores from the Subantarctic South Atlantic Ocean. Features in the lithogenic flux record of each core correspond to similar features in the record of dust deposition in the EPICA Dome C ice core. Biogenic fluxes correlate with lithogenic fluxes in each sediment core. Our preferred interpretation is that South American dust, most probably from Patagonia, constitutes a major source of lithogenic material in Subantarctic South Atlantic sediments, and that past biological productivity in this region responded to variability in the supply of dust, probably due to biologically available iron carried by the dust. Greater nutrient supply as well as greater nutrient utilization (stimulated by dust) contributed to Subantarctic productivity during cold periods, in contrast to the region south of the Antarctic Polar Front (APF), where reduced nutrient supply during cold periods was the principal factor limiting productivity. The anti-phased patterns of productivity on opposite sides of the APF point to shifts in the physical supply of nutrients and to dust as cofactors regulating productivity in the Southern Ocean.
description: Lithogenic material fluxes of organic carbon, biogenic opal and alkenones over the past 100,000 years, determined using the 230Th-normalization method. Portions of the data reported here were described previously in the four papers by Sachs and co-workers, cited below, as well as in the paper by Martinez-Garcia et al., cited below. 
EXPLANATION OF DERIVED PARAMETERS: xs230Tho (initial unsupported 230Th concentration):  xs230Tho  refers to the measured value as corrected for ingrowth of 230Th from authigenic and detrital (lithogenic) uranium. These values are calculated using measured concentrations of 230Th, 232Th and 238U, and assuming that all 232Th is detrital in nature. It also assumes a detrital U/Th ratio, which varies by region. Concentrations are finally corrected for decay since deposition. 230Th-normalized mass flux (Flux:  g/cm^2/kyr):  230Th-normalized mass accumulation rate (or flux) For a discussion of this proxy and the relevant corrections and parameters, please see Francois et al. (2004), cited above.
    
Lithogenic content:  The lithogenic content of the dry bulk sediment was calculated from the measured 232Th concentration assuming that the lithogenic material has a uniform 232Th concentration of 10 ppm.  
The 230Th-normalized flux of any constituent can be derived by multiplying the 230Th-normalized mass flux by the reported concentration of the constituent. Alkenone SSTs were calculated using the definition of Uk'37 = C37:2 / (C37:2 + C37:3) and temperature calibration Uk'37 = 0.034*SST + 0.039 from Prahl, F.G., Muehlhausen, L.A., Zahnle, D.L., 1988. Further evaluation of long-chain alkenones as indicators of paleoceanographic conditions. Geochimica et Cosmochimica Acta 52, 2303-2310.