Millennial changes in North Atlantic oxygen concentrations

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doi: 10.5194/bg-13-211-2016
Author(s): Hoogakker, B. A. A.; Thornalley, D. J. R.; Barker, S.
Author Affiliation(s): Primary:
University of Oxford, Department of Earth Sciences, Oxford, United Kingdom
Other:
University College London, United Kingdom
Cardiff University, United Kingdom
Volume Title: Biogeosciences
Source: Biogeosciences, 13(1), p.211-221. Publisher: Copernicus GmbH on behalf of the European Union, Katlenburg-Lindau, International. ISSN: 1726-4170
Note: In English. 83 refs.; illus., incl. 1 table
Summary: Glacial-interglacial changes in bottom water oxygen concentrations [O2] in the deep northeast Atlantic have been linked to decreased ventilation relating to changes in ocean circulation and the biological pump (Hoogakker et al., 2015). In this paper we discuss seawater [O2] changes in relation to millennial climate oscillations in the North Atlantic over the last glacial cycle, using bottom water [O2] reconstructions from 2 cores: (1) MD95-2042 from the deep northeast Atlantic (Hoogakker et al., 2015) and (2) ODP (Ocean Drilling Program) Site 1055 from the intermediate northwest Atlantic. The deep northeast Atlantic core MD95-2042 shows decreased bottom water [O2] during millennial-scale cool events, with lowest bottom water [O2] of 170, 144, and 166 ± 17 µmol kg-1 during Heinrich ice rafting events H6, H4, and H1. Importantly, at intermediate depth core ODP Site 1055, bottom water [O2] was lower during parts of Marine Isotope Stage 4 and millennial cool events, with the lowest values of 179 and 194 µmol kg-1 recorded during millennial cool event C21 and a cool event following Dansgaard-Oeschger event 19. Our reconstructions agree with previous model simulations suggesting that glacial cold events may be associated with lower seawater [O2] across the North Atlantic below ∼ 1 km (Schmittner et al., 2007), although in our reconstructions the changes are less dramatic. The decreases in bottom water [O2] during North Atlantic Heinrich events and earlier cold events at the two sites can be linked to water mass changes in relation to ocean circulation changes and possibly productivity changes. At the intermediate depth site a possible strong North Atlantic Intermediate Water cell would preclude water mass changes as a cause for decreased bottom water [O2]. Instead, we propose that the lower bottom [O2] there can be linked to productivity changes through increased export of organic material from the surface ocean and its subsequent remineralization in the water column and the sediment.
Year of Publication: 2016
Research Program: ODP Ocean Drilling Program
Key Words: 24 Surficial Geology, Quaternary Geology; Atlantic Ocean; Biochemistry; Bottom water; C-13/C-12; Carbon; Cenozoic; Chemical composition; Climate change; Concentration; Cores; Dansgaard-Oeschger cycles; Dissolved oxygen; Foraminifera; Geochemical cycle; Glacial environment; Heinrich events; Holocene; Ice rafting; Isotope ratios; Isotopes; Leg 172; MIS 4; Marine environment; Meltwater; Microfossils; North Atlantic; Nutrients; ODP Site 1055; Ocean Drilling Program; Ocean circulation; Oxygen; Paleo-oceanography; Productivity; Quaternary; Reconstruction; Sea water; Solutes; Stable isotopes; Ventilation
Coordinates: N374800 N374800 W0101000 W0101000
N324704 N324704 W0761711 W0761711
Record ID: 2019022269
Copyright Information: GeoRef, Copyright 2019 American Geosciences Institute. Reference includes data from Copernicus Gesellschaft, Katlenburg-Lindau, Germany