Patrick Brett: Investigating model sensitivity to different freshwater forcing distributions using ACCESS-ESM1.5
Authors:
Patrick Brett1,2, Ariaan Purich1,2
Affiliations:
1Monash University, Victoria, Australia, 2Research Initiative for Securing Antarctica’s Environmental Future (SAEF)
Abstract:
The surface waters along the Antarctic margin are freshening as mass loss from the Antarctic ice sheets and shelves increases. This mass loss, and resulting freshening, is projected to accelerate over the coming century. However, models generally lack interactive ice sheet components and so underestimate the volume of freshwater entering the Southern Ocean. This is a key uncertainty in future projections and so it is critically important to understand the climate response to freshwater forcing. In particular, model sensitivity to different freshwater forcing parameters remains poorly constrained. Here we present results from two different idealised freshwater forcing experiments using ACCESS-ESM1.5 to explore the model’s response to different horizontal freshwater distributions. We demonstrate significant differences in the temporal and spatial response of both the Southern Ocean, and global climate. Our findings demonstrate that ACCESS-ESM1.5, and possibly other models, may be sensitive to the distribution of freshwater forcing, with important implications for interpreting previous studies and designing methods of freshwater addition
Context:
Most CMIP6 models, including ACCESS-ESM1.5, lack interactive ice sheets and shelves, and so underestimate the volume of freshwater entering the Southern Ocean because of changes in Antarctic mass balance. Hence, there is significant uncertainty regarding the sensitivity of models to different parameters around additional freshwater forcing.
Method
Here we performed two experiments as part of the SOFIA (Southern Ocean Freshwater Input from Antarctica) initiative’s experimental framework designed to investigate the model response to the horizontal distribution of additional freshwater forcing. Freshwater forcing flux of 0.1 Sv was added in two different distributions for 100 years with five ensemble members for each experiment.
Results
Differences in both long and short term climatological response to the two distributions were identified. Notable examples include the response of Antarctic sea ice, deep water formation, AMOC circulation and the position of the ITCZ. Our results suggest that ACCESS-ESM1.5 is sensitive to the distribution of freshwater fluxes.
Audience
Researchers investigating freshwater forcing, ACCESS-ESM development
Keywords:
Southern Ocean, Ice Shelves, Meltwater, Sea ice, Ocean dynamics, Meltwater distribution