Water Column Stratification in the Antarctic Zone of the Southern Ocean During the Mid‐Pleistocene Climate Transition

Water Column Stratification in the Antarctic Zone of the Southern Ocean During the Mid‐Pleistocene Climate Transition

We use biogenic silica (opal) mass accumulating rates (MARs) at Ocean Drilling Program Site 745B to infer upwelling, and by extension upper water column stratification, on glacial to interglacial time scales during the mid‐Pleistocene climate transition (MPT; 1.2–0.6 Ma). Distinct variations in the...

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Bibliographic Details
Published in:Paleoceanography and paleoclimatology Vol. 33; no. 5; pp. 432 - 442
Main Authors: Billups, Katharina, York, Kelsee, Bradtmiller, Louisa I.
Format: Journal Article
Language:English
Published: Hoboken Blackwell Publishing Ltd 01-05-2018
Subjects:
Antarctic zone
Benthos
biogenic silica
Climate
Climate change
Deep water
Deep water circulation
Drilling
Evolution
Foraminifera
glacial
Glaciation
Ice sheets
Ice thickness
interglacia
Interglacial periods
Isotopes
Maxima
mid‐Pleistocene
Northern Hemisphere
Ocean circulation
Oceans
Opal
Pleistocene
Preservation
Sediment
Sediments
Silica
Silicon dioxide
Southern Ocean
Stratification
Terrigenous sediments
Thickening
Upwelling
Water circulation
Water column
Water stratification
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Summary:We use biogenic silica (opal) mass accumulating rates (MARs) at Ocean Drilling Program Site 745B to infer upwelling, and by extension upper water column stratification, on glacial to interglacial time scales during the mid‐Pleistocene climate transition (MPT; 1.2–0.6 Ma). Distinct variations in the percent biogenic silica content of the sediments parallel the global benthic foraminiferal δ18O stack affording the derivation of an orbital‐scale age model. Opal MARs confirm that silica production/preservation was indeed at a minimum at each of the glacial maxima during the entire MPT consistent with the late Pleistocene model that links upwelling of dissolved silica with water column stratification. A unique relationship between opal MARs and benthic foraminiferal δ13C values in the South Atlantic suggests that during the midpoint of the MPT stratification may also be causally related to deep water circulation. However, there is no evidence that cooling during the MPT and the evolution of the 100 kyr climate cycle are linked to changes in water column stratification. Terrigenous sediment MARs, on the other hand, which can be inferred from the proportion of biogenic silica in the sediments at this particular site, provide evidence for increased glacial activity on Antarctica beginning with the onset of the MPT and culminating in a maximum during its midpoint (Marine Isotope Stage 22, 0.9 Ma). Thereafter, glacial activity decreases and we speculate that the evolution of the 100 kyr cycle is associated with a thickening ice sheet after reaching maximum extent somewhat analogous to the processes proposed for Northern Hemisphere ice sheets. Key Points A biogenic silica record from the Antarctic Zone of the Indian Ocean shows orbital‐scale variations Water column stratification was enhanced during glacial intervals between 1.2 and 0.6 Ma There is evidence for a link between stratification and deep water circulation during the midpoint of the mid‐Pleistocene Transition
ISSN:2572-4517
2572-4525
DOI:10.1029/2018PA003327