Expansion of pelagic denitrification during early Pleistocene cooling

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doi: 10.1016/j.epsl.2013.12.022
Author(s): Robinson, Rebecca S.; Etourneau, Johan; Martinez, Philippe M.; Schneider, Ralph
Author Affiliation(s): Primary:
University of Rhode Island, Graduate School of Oceanography, Providence, RI, United States
Other:
Université Pierre et Marie Curie, France
Université Bordeaux 1, France
Christian-Albrechts-Universität zu Kiel, Germany
Volume Title: Earth and Planetary Science Letters
Source: Earth and Planetary Science Letters, Vol.389, p.52-61. Publisher: Elsevier, Amsterdam, Netherlands. ISSN: 0012-821X CODEN: EPSLA2
Note: In English. Includes appendices. 94 refs.; illus., incl. 1 table, sketch map
Summary: Bioavailable nitrogen is removed from the oceans in oxygen-deficient benthic and pelagic environments by denitrification. Future warming is predicted to reduce ocean oxygenation and to cause hypoxic regions to expand, potentially accelerating denitrification. A compilation of high-resolution sedimentary nitrogen isotope (δ15N) records from the eastern tropical Pacific, North Pacific, and the Arabian Sea, and a global multi-site survey are presented as evidence for weak pelagic denitrification at the end of the Pliocene warm period. Mean δ15N values increased in the major oxygen minimum zones (OMZs) between 2.1 and 1.5 Ma. Pelagic denitrification strengthened during a period of long term global cooling, despite solubility driven increases in initial oxygen contents of Antarctic intermediate and Subantarctic mode waters ventilating the OMZs. This trend is opposite to the predicted mean trend for a cooling ocean as well as to the observed glacial-interglacial variation. Several alternatives to explain the shift are proposed, including a rise in net respiration, a progressive increase in the ventilation age of the deep ocean associated with million year scale, secular cooling, and a shoaling of the remotely ventilated thermocline to shallow depths corresponding to the zone of peak subsurface respiration. Given no evidence for a net increase in production, we assert that large-scale, climate-driven changes in ocean circulation regulate long timescale variations in the extent of pelagic denitrification. Additional data and modeling are required to fully explain the observations. Abstract Copyright (2014) Elsevier, B.V.
Year of Publication: 2014
Research Program: ODP Ocean Drilling Program
Key Words: 24 Surficial Geology, Quaternary Geology; Arabian Sea; Atlantic Ocean; Benthic environment; Bioavailability; Ceara Rise; Cenozoic; Denitrification; East Pacific; Equatorial Atlantic; Equatorial Pacific; Indian Ocean; Isotope ratios; Isotopes; Leg 117; Leg 154; Leg 167; Leg 202; Lower Pleistocene; N-15/N-14; Nitrogen; North Atlantic; North Pacific; Northeast Pacific; ODP Site 1012; ODP Site 1242; ODP Site 724; ODP Site 929; Ocean Drilling Program; Ocean circulation; Oxygen; Pacific Ocean; Paleo-oceanography; Paleoclimatology; Paleoenvironment; Pelagic environment; Pleistocene; Quaternary; Stable isotopes; Thermocline; Ventilation
Coordinates: N055834 N055834 W0434423 W0434423
N075100 N075100 W0833600 W0833600
N325002 N325002 W1195853 W1195853
N182742 N182743 E0574709 E0574708
Record ID: 2014025779
Copyright Information: GeoRef, Copyright 2017 American Geosciences Institute. Reference includes data from CAPCAS, Elsevier Scientific Publishers, Amsterdam, Netherlands