Climate change could irreversibly modify Southern Ocean ecosystems. Marine ecosystem model (MEM) ensembles can assist policy making by projecting future changes and allowing the evaluation and assessment of alternative management approaches. However, projected future changes in total consumer biomass from the Fisheries and Marine Ecosystem Model Intercomparison Project (FishMIP) global MEM ensemble highlight an uncertain future for the Southern Ocean, indicating the need for a region-specific ensemble. A large source of model uncertainty originates from the Earth system models (ESMs) used to force FishMIP models, particularly future changes to lower trophic level biomass and sea ice coverage. To build confidence in regional MEMs as ecosystem-based management tools in a changing climate that can better account for uncertainty, we propose the development of a Southern Ocean Marine Ecosystem Model Ensemble (SOMEME) contributing to the FishMIP 2.0 regional model intercomparison initiative. One of the challenges hampering progress of regional MEM ensembles is achieving the balance of global standardised inputs with regional relevance. As a first step, we design a SOMEME simulation protocol, that builds on and extends the existing FishMIP framework, in stages that include: detailed skill assessment of climate forcing variables for Southern Ocean regions, extension of fishing forcing data to include whaling, and new simulations that assess ecological links to sea-ice processes in an ensemble of candidate regional MEMs. These extensions will help advance assessments of urgently needed climate change impacts on Southern Ocean ecosystems.

Antarctic Bottom Water (AABW) production supplies the deep limb of the global overturning circulation and ventilates the deep ocean. While the Weddell and Ross Seas are recognised as key sites for AABW production, additional sources have been discovered in coastal polynya regions around East Antarctica, Vincennes Bay being the latest. Vincennes Bay, despite encompassing two distinct polynya regions, is considered the weakest source, producing Dense Shelf Water (DSW) only just dense enough to contribute to the lighter density classes of AABW found offshore. Importantly, the network of local glaciers and upstream Totten Ice Shelf system are all reportedly thinning and the freshwater input from such melting is likely to influence water mass structure. Accordingly, Vincennes Bay presents an interesting test case for DSW/AABW sensitivity to climate-driven changes in Antarctic coastal oceanography. Here we provide the first detailed observations of the Vincennes Bay shelf region and surrounds, using CTD data from instrumented elephant seals in late summer/early fall. We find that Vincennes Bay has East Antarctica’s warmest recorded intrusions of modified Circumpolar Deep Water (mCDW), intrusions that both hinder sea-ice production and contribute salt to new DSW formation. Warm mCDW is also observed to be driving basal melt in Vincennes Bay, as seal CTD data provide the first direct observational evidence for inflow of basal melt to this region. As the most marginal of AABW sources, Vincennes Bay is a particularly useful region for assessment of the sensitivity of AABW production to changes in climate.