Nutrient regime at the siliceous belt of the Atlantic sector of the Southern Ocean during the past 660 ka

Abstract

[1] Sediment cores from Ocean Drilling Program sites 1094 and 1093 hold the most extensive and most detailed records of carbon and nitrogen isotopes of diatom-bound organic matter in the Atlantic sector of the Southern Ocean over the past 660 ka. These records were combined with summer sea surface temperatures and winter sea ice that were deduced from diatom transfer functions to reconstruct the nutrient regime at the northern and southern boundaries of the siliceous belt at latitudes 53°S and 50°S, respectively. The strong coupling between carbon and nitrogen isotope records at site 1093 suggests that the diatom productivity was influenced mainly by changes in nutrient availability. The anticorrelation between the carbon and nitrogen isotopes at site 1094 suggests that the diatom productivity was closely linked to global temperature changes, sea ice coverage, and dissolved CO 2 concentration. A detailed comparison of the nitrogen isotope records between the two sites shows three time intervals that represent different nutrient regimes. The nutrients at site 1093, which is close to the Polar Front, were dominated by eddies and meanders that sustained relatively high productivity at times of stratification or reduced ventilation, whereas at site 1094 the nutrients were influenced by ventilation processes.Citation: Schneider-Mor, A., R. Yam, C. Bianchi, M. Kunz-Pirrung, R. Gersonde, and A. Shemesh (2008), Nutrient regime at the siliceous belt of the Atlantic sector of the Southern Ocean during the past 660 ka, Paleoceanography, 23, PA3217,

Developing a methodology for carbon isotope analysis of lacustrine diatoms

“…As the input of terrestrial organic matter to the open oceans is low, productivity plays a large role in determining the isotopic signature of oceanic DIC which then contributes to δ 13 C diatom . This supports the interpretation of δ 13 C diatom values from Southern Ocean cores as representing changes in productivity, where low δ 13 C diatom during the Last Glacial Maximum is thought to suggest an increase in the availability of 12 C due to low phytoplankton productivity [21,35] .…”

“…Comparison of δ 13 C diatom values measured in sediments from Lake Challa, Simba Tarn and Small Hall Tarn [23] with studies from ocean sediments [20][21][22] and contemporary diatoms from the English Lake District (Barker, unpublished data).…”

“…Diatom frustules contain proteins (pleuralins, silaffins and long chain polyamines) that are central to silica sequestration to form the frustule and are then entombed within the silica cell wall structure [17][18][19] . Analyses of δ 13 C diatom in Southern Ocean cores [20][21][22] highlight the feasibility and applicability of this technique in palaeoceanography. However, this 4 method has not yet been applied to lake sediments where more numerous carbon sources pose significant challenges for the interpretation of the palaeoenvironmental record.…”

Stable isotopes from diatom silica

“…For example, assuming the atmosphere and surface water are in equilibrium, calculated that 3‰ and 1‰ of the measured 4‰ difference in δ 13 C diatom between the last glacial and modern day are attributable to changes in productivity and pCO 2 respectively. Similarly, results in Crosta et al (2005) and Schneider-Mor et al (2005; detail change in δ 13 C diatom in the Southern Ocean over the last 640 ka also related to changes in productivity, nutrient availability and pCO 2 concentrations.…”

“…Crosta et al, 2005;Schneider-Mor et al, 2005 where changes in δ 15 N diatom have been shown to be anti-correlated with those in δ 30 Si diatom . The increased usage of nitrate documented in these studies during glacial periods has been used to provide further support for the silicic acid leakage hypothesis (see Section 2.2).…”