
Meridional circulation during the Last Glacial Maximum explored through a combination of South Atlantic δ 18 O observations and a geostrophic inverse model
Author(s) -
Gebbie Geoffrey,
Huybers Peter
Publication year - 2006
Publication title -
geochemistry, geophysics, geosystems
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.928
H-Index - 136
ISSN - 1525-2027
DOI - 10.1029/2006gc001383
Subject(s) - geology , calcite , zonal and meridional , geostrophic wind , last glacial maximum , climatology , holocene , quaternary , temperature salinity diagrams , glacial period , salinity , oceanography , geomorphology , paleontology
The vertical profile of meridional transport in the South Atlantic is examined by combining paleoceanographic observations with a geostrophic circulation model using an inverse method. δ 18 O calcite observations along the margins of the South Atlantic show that upper‐ocean cross‐basin differences were weaker during the Last Glacial Maximum (LGM) than the Holocene. The δ 18 O calcite observations can be explained by a shift of water‐mass properties without any change in the overturning circulation. Alternatively, they may indicate a reduced LGM cross‐basin density difference and, via the thermal wind relation, a reduced vertical shear. Model inversions of δ 18 O calcite are found to require meridional transports different from the modern only after three assumptions are made: temperature and salinity distributions are spatially smooth, the relationship between salinity and δ 18 O water is linear and spatially invariant, and LGM temperatures are known to within 1°C along the margins. The last assumption is necessary because an independent constraint on temperature or salinity is required to determine density from δ 18 O calcite observations. δ 18 O calcite observations are clearly useful, but before any firm constraints can be placed on LGM meridional transport, it appears necessary to better determine the relationship between δ 18 O calcite and density.