Stable isotope ratios measured on molluscan from the CRP sediment cores in the Ross Sea, Antarctica

Measured d18O values average +2.5 ‰ in the early Miocene and range between +1.26 to +3.24 ‰ in the early Oligocene. The results show that palaeoceanographic conditions in McMurdo Sound during the mid-Cenozoic were significantly different from those of today.

The minimum estimated spring through late summer seasonal temperature range was 3°C during the early Miocene and between 1 and 5°C during the early Oligocene. This compares to the equivalent modern day range of <0.5°C within the sound. Absolute seawater temperatures at <100 m depth were of the order of 5 to 7°C during both time slices, compared to modern day values of -1.4 to - 1.9°C in the same area.