The Sedimentary N Isotope Record From Cariaco Basin - Local and Global Implications
Abstract
In an earlier study, Haug et al. (1998) showed that the 15N/14N of bulk sedimentary N from Cariaco Basin is lower during interglacials, when organic carbon concentrations are higher. These results were interpreted to reflect increased nitrogen fixation responding to increased denitrification during interglacials. However, it could not be discerned whether this feedback was operating strictly on a local basis (within the Cariaco) or whether either the denitrification-driven N loss or the N2-fixation-driven response was occurring on a regional or global scale. Higher resolution measurements of Terminations I and V show a clear time lag of about 4 kyr between the increase in sedimentary N concentration (coincident with the onset of sediment lamination at Termination I) and the decrease in 15N/14N. These data argue against a diagenetic change as the cause for the 15N/14N change. Since the Cariaco is a relatively small basin, this points towards a regional to global cause for at least part of the 15N/14N drop. Moreover, the new data from the last deglaciation show 15N/14N maxima for the period of the Bolling/Allerod and early Holocene, interrupted by the Younger Dryas, and a subsequent decrease until the mid Holocene. Based on studies of the modern Cariaco water column, a local mechanism for these changes can be imagined and will be presented. However, similar deglacial 15N/14N changes in records from Indian and Pacific sediment records suggest that, since early deglaciation, whole ocean changes in nitrate 15N/14N have been recorded in the Cariaco Basin and are responsible for many of the above deglacial changes. Thus, despite the clear structure of the sediment 15N/14N changes, distinguishing local from regional and global signals in the Cariaco Basin sediment record remains a challenge.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2004
- Bibcode:
- 2004AGUFMOS32A..05M
- Keywords:
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- 4805 Biogeochemical cycles (1615);
- 4845 Nutrients and nutrient cycling;
- 4870 Stable isotopes;
- 4267 Paleoceanography;
- 4802 Anoxic environments