Breakdown of Ocean Stratification during Deglaciation - Evidence from the Ocean's Si Cycle
Abstract
Increased stratification of the ocean (relative to today) is one of several general mechanisms that have been proposed to explain lower atmospheric carbon dioxide concentrations during glacial times. Breakdown of this stratification during deglaciation is suggested to have released carbon dioxide trapped in the deep sea to the atmosphere. Carbon isotope records from ice cores and from marine sediment cores have been cited as evidence for this mechanism. Were this true, then one would expect to find corroborating evidence from the ocean silicon cycle. Biogenic opal (Si) is regenerated, on average, at greater depths than are carbon, nitrogen and phosphorus. Therefore, increased stratification would have trapped Si preferentially, relative to other nutrients, in the deep ocean. Breakdown of stratification would have likewise increased preferentially (relative to other nutrients) the supply of dissolved Si to surface waters in certain regions, stimulating diatom growth. In support of this idea, we find that opal burial rates at several sites around the Southern Ocean, south of the Antarctic Polar Front, increased sharply at about 16 ka BP. Within the uncertainty of the age models, we find a simultaneous increase in opal burial in the eastern equatorial Pacific Ocean (EEP). We interpret these features to be signals of the deglacial breakdown of ocean stratification. Within a single EEP core, we find that the rise in opal burial rate followed the initial drop in carbon isotopic composition of planktonic foraminifera by about 2 - 3 ka. This may reflect a phased breakdown of ocean stratification in which intermediate waters were ventilated much earlier than deep waters. Whether or not a phased breakdown is born out by further work, the initial rise in opal accumulation, both in the Southern Ocean and in the EEP, seems to have occurred when North Atlantic Deep Water formation was at a minimum (i.e., during Heinrich Event 1), indicating a Southern Ocean source for the reinvigorated ventilation of the deep sea.
- Publication:
-
AGU Spring Meeting Abstracts
- Pub Date:
- May 2005
- Bibcode:
- 2005AGUSMOS13A..01A
- Keywords:
-
- 3022 Marine sediments: processes and transport;
- 3344 Paleoclimatology;
- 4207 Arctic and Antarctic oceanography;
- 4267 Paleoceanography;
- 4825 Geochemistry