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Plio-Pleistocene ocean circulation changes in the GOA and its impacts on the carbon and nitrogen cycles and the CIS development

Sánchez Montes, M.L.; Romero, O.E.; Cowan, A.E.; Müller, J.; Moy, C.M.; LLoyd, J.M.; McClymont, E.L.

Plio-Pleistocene ocean circulation changes in the GOA and its impacts on the carbon and nitrogen cycles and the CIS development Thumbnail


Authors

M.L. Sánchez Montes

O.E. Romero

A.E. Cowan

J. Müller

C.M. Moy



Abstract

The modern Gulf of Alaska (GOA) is a high nutrient low chlorophyll (HNLC) region, estimated to be important for nutrient cycling and CO2 exchange. Little is known of the GOA evolution over the Pliocene and Pleistocene as well as its impact on the Cordilleran Ice Sheet (CIS) development, when other evidence for changing North Pacific circulation has emerged. We analysed IODP Expedition 341 Site U1417 sediments, which extend through the Plio-Pleistocene transition (4-1.7 Ma), focussing on productivity-related biomarkers (alkenones, brassicasterol), siliceous microfossils and bulk carbon and nitrogen stable isotopes. Our results show two dominant water column regimes: one characterised by high silica and low organic matter preservation, containing microorganism remains from a mix of habitats (4-3.7 Ma) and a second characterised by low biogenic silica and increased organic matter preservation of microorganisms from dominantly open ocean habitats (3.33-3.32 Ma and 2.8-1.66 Ma). An increase of phytoplankton diversity (3.7-3.35 Ma, 3.19-2.82 Ma) characterises the two transitions of water column conditions, from oxygenated to reductive, that we attribute to a change from ocean mixing to strong stratified conditions with some occasional mixing. The biogeochemical changes in the GOA follow 400 and 100 kyr eccentricity cycles which are also reflected in changes in the CIS. We conclude that the CIS expansion created HNLC conditions in the GOA during the Mid Piacenzian Warm Period (MPWP) and the early Pleistocene. In turn, positive feedbacks increased marine productivity export, atmospheric CO2 drawdown and further CIS expansion.

Citation

Sánchez Montes, M., Romero, O., Cowan, A., Müller, J., Moy, C., LLoyd, J., & McClymont, E. (2022). Plio-Pleistocene ocean circulation changes in the GOA and its impacts on the carbon and nitrogen cycles and the CIS development. Paleoceanography and Paleoclimatology, 37(7), Article e2021PA004341. https://doi.org/10.1029/2021pa004341

Journal Article Type Article
Acceptance Date Jun 21, 2022
Online Publication Date Jun 29, 2022
Publication Date 2022-07
Deposit Date Jun 30, 2022
Publicly Available Date Jul 1, 2022
Journal Paleoceanography and Paleoclimatology
Publisher American Geophysical Union
Peer Reviewed Peer Reviewed
Volume 37
Issue 7
Article Number e2021PA004341
DOI https://doi.org/10.1029/2021pa004341

Files

Accepted Journal Article (2.3 Mb)
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Copyright Statement
An edited version of this paper was published by AGU. Copyright (2022) American Geophysical Union.








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