The objectives of the proposed work are focused on evaluating the impact of freshwater released by ice melt around the margins of Antarctica and Greenland within the Department of Energy’s Energy Exascale Earth System Model (E3SM), with goals both to advance understanding of the critical processes and also to identify the most useful metrics for cross-comparing melt-water input within multiple models. Our findings will be interpreted in the context of recent high-latitude observations. Investigating freshwater inputs has been identified as a research priority, because freshwater is not only an indicator of ice melt and correspondingly of sea level rise (when land ice melts), but it is also tied to sea-ice distributions and has the potential to influence ocean circulation and water masses, both near Greenland and Antarctica as well as in deep ocean basin interiors. Because freshwater concentrations determine density, it also influences mesoscale features and mixing, and ultimately the meridional overturning circulation. Our proposed research will take advantage of global simulations to evaluate all of these interconnected processes.
We will use two generations of global E3SM models forced with reanalysis atmospheric fluxes for 1970-2009 to study Greenland and Antarctic coastal circulations and the exchanges of heat and salt across their respective continental shelves with adjacent interior basins. Ice-sheet melt is represented in two first-generation model simulations that either partially or fully resolve mesoscale eddies in the study regions. These will be compared with the second-generation model that partly resolves eddies at high latitudes but has no representation of freshwater surpluses from ice-sheets. We will compare the simulated mean and variability of the coastal stratification, water masses, and sea-ice characteristics from these simulations with available observations and each other. Modeled freshwater and heat budgets will be used to explain regional salinity and temperature changes over the continental shelf/slope regions. Comparisons among the simulations will shed light on the importance of including freshwater surpluses and resolving mesoscale eddies when modeling change and variability over the past decades in high latitudes.
We will also evaluate 1950 control and subsequent historical simulations using fully coupled models that are part of the Coupled Model Intercomparison Project6 (CMIP6) “HighResMIP” protocol. Of these models, we will only analyze those with the highest horizontal resolution ocean components (~0.1º) which will provide the best resolution of mesoscale processes and features in the study regions. Fully coupled E3SM simulations following this protocol will be compared with the official “HighResMIP” simulations together with the three forced simulations and observations. None of the coupled models include freshwater releases, however an appreciation of the role of the feed-backs among the simulated ocean, sea ice, and atmosphere in the coupled runs will provide a broader context to interpret the importance of freshwater releases around Greenland and Antarctica.