Enhanced ventilation of the North Atlantic subtropical gyre thermocline during the last glaciation

Article Abstract:

The western North Atlantic Ocean's subtropical gyre thermocline, a circulation pattern marked by a steep vertical gradient in water temperature, differed significantly during the last glacial maximum (LGM). Measurements of delta-13C and delta-18O in foraminifera from the Bahamas were used to deduce that the LGM gyre was less oxygenated than in modern times. Moreover, the LGM gyre was less plentifully supplied with nutrients, suggesting that a stronger, more uniform thermocline ventilation prevailed at the LGM. The entire North Atlantic upper water column was probably nutrient-starved during the LGM.

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Millennial-scale changes in North Atlantic circulation since the last glaciation

Article Abstract:

There has been little palaeoceanographic study of subtropical gyres which are dominant oceanic features of wind-driven circulation, reflecting climate changes. Cd/Ca ratios in the shells of benthic foraminifera from the Bahamas are presented, confirming that nutrient concentrations in the North Atlantic subtropical gyre were lower during the last Glacial Maximum, than they are now. It is thought that the Younger Dryas cooling could have been achieved via the formation of intermediate waters that were not as effective at heating the North Atlantic than North Atlantic Deep Water.

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Cool surface waters of the subtropical North Pacific Ocean during the last glacial

Article Abstract:

A controversial result of the CLIMAP project reconstruction of past sea surface temperature (SST), is that large regions of the subtropical Pacific Ocean were warmer during the last glacial period, than currently. There has been a lack of well-preserved, high-resolution marine sediment from the area. Oxygen-isotope compositions and species assemblages of planktonic foraminifera have been used to estimate glacial SST of the subtropical North Pacific Ocean. Results suggest that the SST was cooler during the last glaciation than currently, contrary to CLIMAP results.

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