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Enhanced carbon pump inferred from relaxation of nutrient limitation in the glacial ocean

Figure 1. pCO2 difference between the atmosphere and the ocean for 1995.

Enhanced carbon pump inferred from relaxation of nutrient limitation in the glacial ocean

Vol 459, No. 7250, pp. 1114-1117, 25 June 2009.

L.E. Pichevin1, B.C. Reynolds2, R.S. Ganeshram1,
I. Cacho3, L. Pena3, K. Keefe4 and R.M. Ellam4
1 School of Geosciences, Grant Institute, University of Edinburgh, West Main Road, EH10 3JW, Edinburgh, UK.
2 IGMR, ETH Zürich, Clausiusstrasse 25, CH-8092 Zürich, Switzerland
3 GRC Geociències Marines, Facultat de Geologia, Universitat de Barcelona C/ Martí Franques s/n 08028 Barcelona, Spain
4 Scottish Universities Environment Research Centre, Rankine Avenue, Scottish Enterprise Technology Park, East Kilbride, G75 0QF, UK.
The modern Eastern Equatorial Pacific (EEP) Ocean is a large oceanic source of carbon to the atmosphere. Primary productivity over large areas of the EEP is limited by silicic acid and iron availability, and because of this constraint the organic carbon export to the deep ocean is unable to compensate for the outgassing of carbon dioxide that occurs through upwelling of deep waters. It has been suggested that the delivery of dust-borne iron to the glacial ocean could have increased primary productivity and enhanced deep-sea carbon export in this region, lowering atmospheric carbon dioxide concentrations during glacial periods. Such a role for the EEP is supported by higher organic carbon burial rates documented in underlying glacial sediments, but lower opal accumulation rates cast doubts on the importance of the EEP as an oceanic region for significant glacial carbon dioxide drawdown. Here we present a new silicon isotope record that suggests the paradoxical decline in opal accumulation rate in the glacial EEP results from a decrease in the silicon to carbon uptake ratio of diatoms under conditions of increased iron availability from enhanced dust input. Consequently, our study supports the idea of an invigorated biological pump in this region during the last glacial period that could have contributed to glacial carbon dioxide drawdown. Additionally, using evidence from silicon and nitrogen isotope changes, we infer that, in contrast to the modern situation, the biological productivity in this region is not constrained by the availability of iron, silicon and nitrogen during the glacial period. We hypothesize that an invigorated biological carbon dioxide pump constrained perhaps only by phosphorus limitation was a more common occurrence in low-latitude areas of the glacial ocean.
Download data from the WDC Paleo archive:
Eastern Equatorial Pacific 35KYr Paleonutrient Data, Text or Excel format.

To read or view the full study, please visit the Nature website.
It was published in Nature, Vol 459, No. 7250, pp. 1114-1117, 25 June 2009.
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