Constraining the vertical movement of OMZ waters in Santa Barbara Basin for the past 15 ky
Abstract
Here we constrain the upper vertical boundary of the California Margin Oxygen Minimum Zone (OMZ) through the past 15ky, with focus on the Bölling-Alleröd (B/A) warm interval. The depth range of the OMZ along the California Margin is responsive to events of rapid warming, however the spatial extent and underlying mechanism for the synchrony is not clear. We construct a depth transect within Santa Barbara Basin (34° 15’N, 119° 45’W) using a core from 418m water depth (MV0811-15JC), and previously investigated cores from 481m (MD02-2504) and 570m (MD02-2503) water depths. Isotope stratigraphy and radiocarbon dating (planktonic calcite) were used to generate a working age model. Foraminiferal and micro-invertebrate assemblages and preserved sediment laminations constrain the movement of low-oxygen water. Oxygen isotopic values at all three sites record similar surface water δ18O shifts over the deglaciation (1.5‰ magnitude; based upon planktonic foraminifera G. bulloides) and a smaller but analogous δ18O shift is seen in benthic records (0.5‰ magnitude; based on benthic foraminifera U. peregrina). All three cores exhibit a ~1‰ decrease in G. bulloides (planktonic) δ13C values across the deglaciation, and then a return to more stable values of ~-0.75‰ during the Holocene. All three cores show an increase in δ13C values of benthic foraminfera U. peregrina at the onset of the Holocene (~1‰ positive shift); in the future, these records may be coupled with total organic carbon analyses to understand the role of productivity and terrestrial carbon export in influencing OMZ strength. During the B/A lamination records indicate strong hypoxia below 480m; however laminations are not preserved at 418m. In contrast, benthic foraminiferal assemblages show similar responses (albeit more muted the in shallowest site) to low-oxygen concentrations during the B/A, with species N. stella, B. tumida, and B. tenuata dominating at all three sites. At the 418m site, the proxies in the B/A indicate marginally low oxygen conditions; strong enough to affect benthic foraminifera assemblages, yet not strong enough to preserve annual laminations like those seen in the deeper sites. These results indicate that OMZ waters ephemerally and intermittently shoaled above 418m during the B/A.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2010
- Bibcode:
- 2010AGUFMPP33B1669M
- Keywords:
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- 4802 OCEANOGRAPHY: BIOLOGICAL AND CHEMICAL / Anoxic environments;
- 4834 OCEANOGRAPHY: BIOLOGICAL AND CHEMICAL / Hypoxic environments;
- 4901 PALEOCEANOGRAPHY / Abrupt/rapid climate change