Testing Methods for Reconstructing Glacial Antarctic Circumpolar Current Transport in an Isotope-Enabled Climate Model

The Antarctic Circumpolar Current (ACC) plays a vital role in the interbasin exchange of ocean properties. A robust method to reconstruct the ACC baroclinic transport is helpful to assess the ACC's sensitivity to a changed climate. Here we test the reconstruction methods at the Last Glacial Maximum (LGM; similar to 20 ka) using end-member water masses in a fully coupled, isotope-enabled Community Earth System Model. Model results suggest that the density profile at the northern side of ocean margins across the ACC can be reconstructed well from end-member water masses of Subtropical Surface Water (STSW), Antarctic Intermediate Water (AAIW), and Lower Circumpolar Deep Water. One additional pore fluid observation at 1,000 m can substantially improve transport reconstruction and is essential to constrain the sign of change in ACC transport during the LGM. Moreover, the uncertainty in transport calculation is large when salinities for STSW and AAIW are reconstructed independently based on the delta O-18(sw)-Salinity relationship of surface and intermediate waters in the South Indian Ocean. More direct measurements of LGM temperature and salinity may allow better transport reconstruction.

Automated summary

The Antarctic Circumpolar Current (ACC) is crucial for the exchange of ocean properties between basins, and reconstructing ACC baroclinic transport is important for assessing its sensitivity to climate change. Using end-member water masses, the density profile across the ACC at the Last Glacial Maximum (LGM) can be effectively reconstructed. Additional pore fluid observations at 1,000 m depth can significantly improve transport reconstruction and help constrain changes in ACC transport during the LGM.