17:15 〜 18:45
[MIS10-P10] Spatio-temporal variability of warm water inflows into the Totten Ice Shelf cavity
キーワード：東南極、トッテン氷河、暖水流入、棚氷融解
The Totten Glacier in East Antarctica, with an ice volume equivalent to >3.5 m of global sea-level rise, is grounded below sea level and, therefore, vulnerable to ocean forcing. A recent study integrating in-situ observation and numerical modeling (Hirano et al., 2023) showed that warm modified Circumpolar Deep Water (mCDW) is circulating toward the Totten Ice Shelf (TIS) along the deep submarine channels and especially the deep Totten Trough (bottom depth >1000 m) plays a critical role in regulating ocean heat transport by mCDW inflows into the TIS cavity. Still, however, the variability of the mCDW inflows that relate to the TIS basal melt rate and, consequently, ice sheet stability is largely unknown due to a lack of time series records in the region.
As a next step toward a better knowledge of the ocean-driven continental-ice mass loss process, we initiated long-term mooring observations in the deep Totten Trough, which connects the Sabrina Depression on the continental shelf with the TIS cavity, since March 2022. Then, in March 2023, we successfully recovered the first year-round mooring record from the trough. The mooring time series shows inflows of the warm, saline, and low dissolved oxygen mCDW throughout the year. The seasonal cycle of the mCDW temperature is characterized by a peak in the fall (from April to June, T = 0.2 ~ 0.4oC), a rapid decrease during the winter months to less than 0oC (from July to September, T = -0.4oC at minimum), and then a gradual increase toward summer (from October to March, T = -0.2 ~ 0.2oC). The year-round range of the mCDW temperature reaches up to ~0.8oC, comparable to the observed interannual variability in the same trough (Hirano et al., 2023).
In March 2023, we also successfully conducted the shipboard observations in the region underneath the TIS until a year ago. Along the branched deep trough, the mCDW temperature decreases to less than 0oC as it flows downstream, and the thermocline depth deepens more than 100 m. Such sharp spatial discrepancies in the mCDW properties suggest that the interaction between the thermocline depth and the local shallower sill in the trough modulates the temperature of the water reaching the TIS cavity. Thus, the new data tell us that we need to consider not only the mCDW modification by wind and buoyancy forcing over the Totten continental shelf before reaching the deep trough but also the topographically modulated thermocline depth/mCDW temperature to evaluate with more precision the variability of ocean heat transport that would ultimately regulate the TIS basal melt rate.
As a next step toward a better knowledge of the ocean-driven continental-ice mass loss process, we initiated long-term mooring observations in the deep Totten Trough, which connects the Sabrina Depression on the continental shelf with the TIS cavity, since March 2022. Then, in March 2023, we successfully recovered the first year-round mooring record from the trough. The mooring time series shows inflows of the warm, saline, and low dissolved oxygen mCDW throughout the year. The seasonal cycle of the mCDW temperature is characterized by a peak in the fall (from April to June, T = 0.2 ~ 0.4oC), a rapid decrease during the winter months to less than 0oC (from July to September, T = -0.4oC at minimum), and then a gradual increase toward summer (from October to March, T = -0.2 ~ 0.2oC). The year-round range of the mCDW temperature reaches up to ~0.8oC, comparable to the observed interannual variability in the same trough (Hirano et al., 2023).
In March 2023, we also successfully conducted the shipboard observations in the region underneath the TIS until a year ago. Along the branched deep trough, the mCDW temperature decreases to less than 0oC as it flows downstream, and the thermocline depth deepens more than 100 m. Such sharp spatial discrepancies in the mCDW properties suggest that the interaction between the thermocline depth and the local shallower sill in the trough modulates the temperature of the water reaching the TIS cavity. Thus, the new data tell us that we need to consider not only the mCDW modification by wind and buoyancy forcing over the Totten continental shelf before reaching the deep trough but also the topographically modulated thermocline depth/mCDW temperature to evaluate with more precision the variability of ocean heat transport that would ultimately regulate the TIS basal melt rate.