Millennial changes in North Atlantic oxygen concentrations
[摘要] Glacial–interglacial changes in bottom water oxygen concentrations [O2]in the deep northeast Atlantic have been linked to decreased ventilationrelating to changes in ocean circulation and the biological pump (Hoogakkeret al., 2015). In this paper we discuss seawater [O2] changes inrelation to millennial climate oscillations in the North Atlanticoverthe last glacial cycle, using bottom water [O2] reconstructions from 2cores: (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 deepnortheast Atlantic core MD95-2042 shows decreased bottom water [O2]during millennial-scale cool events, with lowest bottom water [O2] of170, 144, and 166 ± 17 µmol kg−1 during Heinrich ice raftingevents H6, H4, and H1. Importantly, at intermediate depth core ODP Site 1055,bottom water [O2] was lower during parts of Marine Isotope Stage 4 andmillennial cool events, with the lowest values of 179 and 194 µmol kg−1recorded during millennial cool event C21 and a cool event followingDansgaard–Oeschger event 19. Our reconstructions agree with previous modelsimulations suggesting that glacial cold events may be associated with lowerseawater [O2] across the North Atlantic below ∼ 1 km(Schmittner et al., 2007), although in our reconstructions the changes areless dramatic. The decreases in bottom water [O2] during North AtlanticHeinrich events and earlier cold events at the two sites can be linked towater mass changes in relation to ocean circulation changesand possiblyproductivity changes. At the intermediate depth site a possible strong NorthAtlantic Intermediate Water cell would preclude water mass changes as acause for decreased bottom water [O2]. Instead, we propose that thelower bottom [O2] there can be linked to productivity changes throughincreased export of organic material from the surface ocean and itssubsequent remineralization in the water column and the sediment.
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[效力级别] [学科分类] 地球化学与岩石
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