Speaker: Dr Fabio Boeira Dias
Date: Wednesday 11 October 2023
Time: 1:00 pm
Location: Presented live from the CCRC Seminar room and live streamed Via Zoom
Abstract
The Antarctic margin has a key role in the tipping points associated with the collapse of the lower limb of the global meridional overturning circulation and with the irreversible sea-level rise due to the collapse of floating ice shelves. The Water mass transformation (WMT) around the Antarctic margin controls Antarctica Bottom Water formation and the strength of the abyssal limb of the GMOC, but the mechanisms of WMT on the Antarctic shelf - specially underneath the floating ice shelves - are poorly known due to limited, summer-biased, observations and limitation in modelling coastal polynyas in global climate model. In the first part of this seminar, I will present results on the mechanisms controlling the rate of WMT in the Antarctic shelf, and their sensitivity to model horizontal resolution, topographic resolution, and tides. We used the Whole-Antarctica Ocean Model (WAOM), a circum-Antarctic ocean-ice shelf model, to assess the contribution of surface fluxes, mixing, and ocean-ice shelf interaction to the WMT on the continental shelf. WMT rates are dominated by the salt budget, where mixing of meltwater within the ice shelf cavities induces buoyancy gain at lighter density classes (27.2 < σθ < 27.6 kg m-3), while salt input associated with sea-ice growth in coastal polynyas drives buoyancy loss at heavier densities (σθ > 27.6). Regional analyses highlight processes controlling heat exchange across the continental shelf in different sectors of the Antarctic margin, with the model resolution the most important factor for WMT sensitivity in the two of the three most sensitive sectors: East and West Antarctica. In the Filchner-Ronne sector, the tidal forcing has primary importance, followed by the model resolution. These results underline the importance of fine grid resolution and tides to adequately represent water mass transformations on the shelf that directly influence the abyssal global overturning circulation.
In the second part of this seminar, I will show ongoing work on the processes of cross-shelf and cross-calving front heat transport using the same WAOM model. The basal melt of the ice shelves is a primary driver of the Antarctic ice Sheet mass loss, where oceanic processes transport heat towards the ice shelf cavities. Thus, understanding the mechanisms of heat transport towards rapidly thinning ice shelves such as in the Totten Glacier in the East Antarctica is key to understand future changes that might lead to the ice shelf collapse - Totten itself drains the equivalent of 3.5m of global sea-level rise. Previous WAOM experiments showed that the WMT in the East Antarctica is highly sensitive to model horizontal resolution, mostly due to distinct representation of the ASC (Dias et al. 2023). However, the relative importance of the ASC, mesoscale eddies, and tides for the heat transport across the continental slope and in the calving (ice shelf) front have not been investigated in the vicinity of the Totten Glacier.