Paul Goddard Abstracts
Paul Goddard
Ph.D. Candidate
Global Change GIDP Minor
American Geophysical Union Fall Meeting
San Francisco, California
December 14-18, 2015
Professional Abstract
Lay Abstract
CO2–Induced Ocean Climate Change around Antarctica in GFDL CM2.5 and CM2.6
Authors
Paul Goddard1, Jianjun Yin1 and Stephen Griffies2
1. Department of Geosciences, University of Arizona, Tucson, Arizona, USA
2. Geophysical Fluid Dynamics Laboratory/NOAA, Princeton, New Jersey, USA
We use two high resolution climate models recently developed at GFDL (CM2.5 and CM2.6) to investigate CO2–induced ocean climate change around Antarctica and its implication for the Antarctic ice sheet melt. We consider both long-term control runs and the idealized 1% per year CO2 doubling experiments. In particular, we focus on the role of three different mechanisms impacting the transport of heat from the ocean interior onto the continental shelf of Antarctica, which are responsible for the basal melt of ice shelves. Firstly, the southward shift of the westerlies in the doubling CO2 experiments leads to a weakening of the easterlies near the continental edge, thereby decreasing Ekman downwelling. The decreased downwelling allows the transport of heat from the ocean interior onto the continental shelf. Secondly, the increase in surface wind velocity in the CO2 experiments lead to more energetic mesoscale eddies and greater heat transport across the shelf break. Thirdly, the lower salinity of shelf water in the CO2 experiments due to the freshwater addition and a decline in sea ice formation enhances baroclinicity near the shelf break and strengthens the Antarctic Slope Front current which behaves as a barrier to heat transport onto the continental shelf.
Across the globe, the present and future of Antarctic’s ice sheets is under much scrutiny.With the melt potential of raising global sea levels by one meter per year, the current acceleration of ice sheet melt raises concern. Observations reveal that warm waters from the ocean interior are creeping underneath the ice shelves and melting them from below. Presently, more snow is falling on the periphery of the ice sheets and ice shelves; the added mass increases the flow and discharge of ice into the ocean. Both mechanisms accelerate upstream ice flow and result in land ice mass loss to the ocean. My work is to investigate how well these mechanisms are simulated in the Geophysical Fluid Dynamics Laboratory’s (GFDL) new high resolution models, CM2.5 and CM2.6. The ocean resolution (i.e., grid size) is 1/4° longitude-latitude for CM2.5 and 1/10° longitude-latitude for CM2.6; whereas previous generation models have 1° resolution. The advantage of high resolution models is the ability to model ocean dynamics underneath ice shelves and in between narrow inlets, while the previous coarse models could not. Additionally, the GFDL CM2.6 is considered an ocean mesoscale eddy-resolving model. Mesoscale ocean eddies are small, 1-10 kilometer diameter whirlpools of water. They are very important for the transport of nutrients and heat in the ocean. Our results show that heat transport by ocean eddies and changes in coastal winds both contribute to the warming under the ice shelves. Additionally, and unique from observations and previous model studies, is an interesting mechanism that results from the freshening of coastal waters from the decrease of sea ice and increase in precipitation under atmosphere CO2 increase. The ocean freshening above the continental shelf results in an increase in an ocean current that surrounds the continent. The strengthening of this current prevents heat from journeying from the ocean interior toward the ice shelves. I am working with my advisor, Jianjun Yin at the University of Arizona and Stephen Griffies at GFDL, Princeton, New Jersey, on publishing a paper regarding these findings.