Eastern Guaymas Basin: laminated but not anoxic
Abstract
Site MD02-2513, eastern Guaymas Basin, challenges the accepted hypothesis about the circumstances and sequence of events leading to the occurrence of annually laminated (varved) sediment. By convention, under a climate regime of strong seasonal contrast, high productivity in a restricted basin enhances a preformed OMZ and inhibits bioturbation, resulting in the preservation of varves. The comparison of the high-resolution log of the sediment fabric and continuous XRF data from Core MD02-2513 reveal that laminated intervals over the last ~90 ka BP are characterised by an increase of oxygenation above background levels and are accompanied by lows of terrestrial and biogenic flux indicating that the preserving factor is rapid burial rather than high sedimentation rate (ie high seasonality and low rainfall). Intervals of diffuse/discontinuous laminations are times of high terrestrial and biogenic flux indicating comparatively low seasonality and high rainfall. Brief periods of relatively high anoxic conditions occur within homogeneous intervals and are accompanied by exceptionally high biogenic flux, indicating there was no seasonal contrast. Long homogenous intervals occur during the last glacial due to lowered sea level and the consequent removal of the upwelling cell offshore. The changes in Guaymas Basin seasonality are most probably caused by alterations to the migration pattern of the North Pacific Subtropical High due to the growth and decay of the North American ice sheets.
- Publication:
-
AGU Fall Meeting Abstracts
- Pub Date:
- December 2009
- Bibcode:
- 2009AGUFMPP13A1387C
- Keywords:
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- 0404 BIOGEOSCIENCES / Anoxic and hypoxic environments;
- 1050 GEOCHEMISTRY / Marine geochemistry;
- 4912 PALEOCEANOGRAPHY / Biogeochemical cycles;
- processes;
- and modeling;
- 9355 GEOGRAPHIC LOCATION / Pacific Ocean