Cooperative Institute for Research in Environmental Sciences

Impact of changes in the Arctic Ocean freshwater budgets on AMOC strength

Impact of changes in the Arctic Ocean freshwater budgets on AMOC strength

Dr. Alexandra Jahn

INSTAAR and ATOC
University of Colorado Boulder

Abstract:

The Arctic is changing rapidly, but what do these changes mean for the global climate? One way that Arctic changes can potentially impact global climate is through changes in the amount and phase of freshwater exported from the Arctic to the North Atlantic. There it can impact the deep water formation in the North Atlantic, and ultimately the strength of the Atlantic meridional overturning circulation (AMOC). In this talk, I will show how simulated changes in the Arctic freshwater budget impact AMOC strength, in climate simulations for the 21st to 23rd century and for a previous warm period, the Pliocene, which occurred 3 million years ago. In particular, I will show that in simulations with the Community Earth System Model (CESM) for the 21st to 23rd century, the maximum strength of the AMOC decreases proportionally to the applied CO2 forcing (Jahn and Holland, 2013). This weakening of the overturning is caused by a reduction or shut down of North Atlantic deep convection due to a surface freshening originating in the Arctic Ocean. For the Pliocene, I will show how changes in the representation of three small Arctic gateways to the Pacific and Atlantic Ocean (Bering Strait, Northwest Passage, Nares Strait) change the magnitude and phase of the simulated Arctic freshwater export in the CESM, which leads to changes in the AMOC strength (Otto-Bliesner et al., 2016). By closing all of the small gateways, in agreement with a recent new PRISM4 reconstruction, the Arctic freshwater export decreases and the AMOC strength increases. This improves the agreement of the simulated Pliocene climate in the North Atlantic with proxy reconstructions.

Dr. Alexandra Jahn

INSTAAR and ATOC
University of Colorado Boulder

References:          

•Jahn, A., and M. M. Holland (2013), Implications of Arctic sea ice changes for North Atlantic deep convection and the meridional overturning circulation in CCSM4-CMIP5 simulations, Geophys. Res. Lett., 40, 1206–1211, doi:10.1002/grl.50183.

•Otto-Bliesner, B. L., A. Jahn, R. Feng,E. C. Brady, A. Hu, and M. Löfverström (2016), Amplified North Atlantic warming in the late Pliocene by changes in Arctic gateways, Geophys. Res. Lett., 44, doi:10.1002/2016GL071805.

date

Wednesday, March 15, 2017
11:00am

location

East Campus, RL-2, room 155

Event Type

Seminar