New paper finds deep Arctic Ocean from 50,000 to 11,000 years ago was 1–2°C warmer than modern temperatures

A new paper published in Nature Geoscience finds "From about 50,000 to 11,000 years ago, the central Arctic Basin from 1,000 to 2,500 meters deep was ... 1–2°C warmer than modern Arctic Intermediate Water." This finding is particularly surprising because it occurred during the last major ice age.

Horizontal axis is thousands of years ago with modern temperatures at the left and 50,000 years ago at the right. Temperature proxy of the Intermediate Water Layer of the Arctic Ocean is shown in top graph with degrees C anomaly noted at the upper right vertical axis. Note this graph is on an inverse scale with warmer temps at the bottom and colder temps at the top.

Deep Arctic Ocean warming during the last glacial cycle


T. M. Cronin, G. S. Dwyer, J. Farmer, H. A. Bauch, R. F.
Spielhagen, M. Jakobsson, J. Nilsson, W. M. Briggs Jr &
A. Stepanova

Nature Geoscience (2012) doi:10.1038/ngeo1557


In the Arctic Ocean, the cold and relatively fresh water
beneath the sea ice is separated from the underlying warmer
and saltier Atlantic Layer by a halocline. Ongoing sea ice
loss and warming in the Arctic Ocean have
demonstrated the instability of the halocline, with
implications for further sea ice loss. The stability of the
halocline through past climate variations is unclear.
Here we estimate intermediate water temperatures over the
past 50,000 years from the Mg/Ca and Sr/Ca values of
ostracods from 31 Arctic sediment cores. From about 50 to
11 [thousand years] ago, the central Arctic Basin from 
1,000 to 2,500m was occupied by a water mass we call 
Glacial Arctic Intermediate Water. This water mass was 
1–2°C warmer than modern Arctic Intermediate Water,
with temperatures
peaking during or just before millennial-scale Heinrich cold
events and the Younger Dryas cold interval. We use
numerical modelling to show that the intermediate depth
warming could result from the expected decrease in the flux
of fresh water to the Arctic Ocean during glacial conditions,
which would cause the halocline to deepen and push the
warm Atlantic Layer into intermediate depths. Although not
modelled, the reduced formation of cold, deep waters due to
the exposure of the Arctic continental shelf could also
contribute to the intermediate depth warming.