Modelling the ocean circulation and mixing processes of the Last Glacial Maximum using the Community Earth System Model (iCESM1.2) and the Internal Wave Mixing parameterization IDEMIX

The Last Glacial Maximum (~21 ka) is the most recent glacial period when the ice sheet
coverage was at its greatest extent (8% of Earth's surface), and the atmospheric CO2
concentration was ~190 ppm. During this period, the continental shelves were exposed and
the global-mean sea level was lower by ~130 m compared to today. This project hypothesizes
that decrease in sea level caused tidal-energy dissipation to shift from the shelves to the open-
ocean resulting in enhanced vertical mixing in the deep ocean. The aim of this project is to
study the global ocean circulation and the marine biogeochemical processes of the LGM
climate state using an energetically consistent ocean mixing scheme: Internal Wave
Dissipation, Energy, and Mixing (IDEMIX) in the fully coupled isotope-enabled Earth
System Model (iCESM1.2). For this study, only the tidal-induced mixing is investigated.
Hence the tidal forcing is considered as the only source for generating internal waves in
IDEMIX parameterisation. The model uses the "KPP+IDEMIX" approach as the combined
vertical mixing parameterization. While the KPP is activated only in the mixed layer (up to ~
1 km), IDEMIX is applied only to the interior ocean, where the dissipation is generated by the
tidal forcing at the ocean floor. In our simulations, we use 2° resolution for the atmosphere
and 1° for the ocean, and we simulate LGM and pre-industrial climate states with and without
IDEMIX. The modal bandwidth tuning parameter (j★) in IDEMIX determines the number of
excited vertical modes, which affects how fast the energy propagates from the bottom to the
upper ocean. We perform the sensitivity experiments by using different j★ values in our LGM
simulations and investigate its impact on the vertical mixing and the ocean state.