TY - JOUR
T1 - Revisiting nutrient utilization in the glacial Antarctic
T2 - Evidence from a new method for diatom-bound N isotopic analysis
AU - Robinson, Rebecca S.
AU - Brunelle, Brigitte G.
AU - Sigman, Daniel Mikhail
N1 - Copyright:
Copyright 2008 Elsevier B.V., All rights reserved.
PY - 2004/9
Y1 - 2004/9
N2 - Isotopic measurements of diatom-bound nitrogen, using a wet chemical oxidation combined with the "denitrifier" method for nitrate analysis, show significant offsets from previously published combustion-based measurements. This offset is attributed to a gaseous nitrogen blank associated with the diatom's opal frustule. Moreover, experimentation with multiple chemical cleaning protocols demonstrates that diatom microfossils from the clay-rich sediments of the glacial Antarctic are more difficult to clean than Holocene materials. New downcore profiles from the Antarctic show no change in the diatom-bound N 15N/14N between the last glacial and the Holocene in the Atlantic sector, and the elevation of glacial diatom-bound 15N/14N relative to the Holocene in the Indian sector is smaller than in previous measurements. These data suggest no change in the degree of nitrate utilization in the Atlantic sector and at most a 20% increase (from ∼25 to 45%) in the Indian sector. The new measurements suggest that, during the last ice age in the Atlantic sector of the Antarctic, the atmospheric source of biologically available iron was not so great as to become significant relative to the iron supply from below. Given the apparent spatial variability in the degree of nitrate drawdown, more work is required to develop an adequate picture of the glacial Antarctic nutrient field.
AB - Isotopic measurements of diatom-bound nitrogen, using a wet chemical oxidation combined with the "denitrifier" method for nitrate analysis, show significant offsets from previously published combustion-based measurements. This offset is attributed to a gaseous nitrogen blank associated with the diatom's opal frustule. Moreover, experimentation with multiple chemical cleaning protocols demonstrates that diatom microfossils from the clay-rich sediments of the glacial Antarctic are more difficult to clean than Holocene materials. New downcore profiles from the Antarctic show no change in the diatom-bound N 15N/14N between the last glacial and the Holocene in the Atlantic sector, and the elevation of glacial diatom-bound 15N/14N relative to the Holocene in the Indian sector is smaller than in previous measurements. These data suggest no change in the degree of nitrate utilization in the Atlantic sector and at most a 20% increase (from ∼25 to 45%) in the Indian sector. The new measurements suggest that, during the last ice age in the Atlantic sector of the Antarctic, the atmospheric source of biologically available iron was not so great as to become significant relative to the iron supply from below. Given the apparent spatial variability in the degree of nitrate drawdown, more work is required to develop an adequate picture of the glacial Antarctic nutrient field.
KW - Antarctic
KW - Glacial/interglacial
KW - Nutrient status
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U2 - 10.1029/2003PA000996
DO - 10.1029/2003PA000996
M3 - Article
AN - SCOPUS:11144274655
SN - 0883-8305
VL - 19
SP - PA3001 1-13
JO - Paleoceanography
JF - Paleoceanography
IS - 3
ER -