Correlation between nitrogen isotopic ratios and productivity of calcareous nannoplankton: Evidence for the biological consumption of nitrate controlling nitrogen isotopic fluctuation

Itsuro Kita, Hidenao Hasegawa, Tokiyuki Sato, Tatsuya Hayashi, Makoto Kojima

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Abstract

We investigated the relation between δ15Norg values of organic matter and the number of nannofossil in marine sediments during a period from 300 ka to 1300 ka, using the core samples from ODP Hole 1006A, off Great Bahama Bank of the Caribbean Sea. Theδ15N org values and the number of nannofossil (absolute abundance of coccoliths) fluctuate in the ranges of +0.1 %o to +5.8 %o and 1 x 108 to 30 x 108 specimens/g, respectively, with a clear positive correlation. As the number of nannofossil increases, δ15N org values become greater. These changes are closely linked to 100-ky and 41-ky variations in δ18Opianktonic values of planktonic foraminifera (Globigerinoides ruber), reflecting mixing of surface water in the photic zone and bottom water brought about by the trade wind which became stronger during glacial period. δ15Norg values (+0.1 to +5.8 %o) of marine sediments from the Caribbean Sea fluctuate within a range lower than those (+4 to +10 %o) from the Arabian Sea under the strong influence of upwelling during interglacial period. The difference in the fluctuation ranges of δ15Norg values between these areas seems to reflect that in the amount of nitrate carried from bottom water to surface water under the influence of the trade wind and monsoon and its consumption rate by phytoplankton. These results corroborate the consideration that δ15Norg values of marine sediments can be related directly to changes in productivity of phytoplankton.

Original languageEnglish
Pages (from-to)59-66
Number of pages8
JournalFossils
Issue number86
Publication statusPublished - Oct 1 2009

All Science Journal Classification (ASJC) codes

  • Palaeontology

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