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Abyssal Atlantic circulation during the Last Glacial Maximum: Constraining the ratio between transport and vertical mixing
 

Summary: Abyssal Atlantic circulation during the Last Glacial Maximum:
Constraining the ratio between transport and vertical mixing
D. C. Lund,1
J. F. Adkins,2
and R. Ferrari3
Received 19 March 2010; revised 23 November 2010; accepted 21 December 2010; published 19 March 2011.
[1] The ocean's role in regulating atmospheric carbon dioxide on glacialinterglacial timescales remains an
unresolved issue in paleoclimatology. Reduced mixing between deep water masses may have aided oceanic
storage of atmospheric CO2 during the Last Glacial Maximum (LGM), but data supporting this idea have
remained elusive. The d13
C of benthic foraminifera indicate the Atlantic Ocean was more chemically
stratified during the LGM, but the nonconservative nature of d13
C complicates interpretation of the LGM
signal. Here we use benthic foraminiferal d18
O as a conservative tracer to constrain the ratio of meridional
transport to vertical diffusivity in the deep Atlantic. Our calculations suggest that the ratio was at least twice
as large at the LGM. We speculate that the primary cause was reduced mixing between northern and
southern component waters, associated with movement of this water mass boundary away from the zone of
intense mixing near the seafloor. The shallower water mass boundary yields an order of magnitude increase
in the volume of southern component water, suggesting its residence time may have increased substantially.

  

Source: Adkins, Jess F. - Division of Geological and Planetary Sciences, California Institute of Technology
Ferrari, Raffaele - Department of Earth, Atmospheric, and Planetary Sciences, Massachusetts Institute of Technology (MIT)

 

Collections: Environmental Sciences and Ecology; Geosciences