Tidal dynamics and ice cavities in AWI-ESM2: modelling and implications

Abstract

Earth system models (ESMs) serve as effective numerical tools for studying our planet. Advances in computational capability have provided scientists with the opportunity to explore the Earth’s complex system. While many processes have been considered within individual components of the Earth’s system or in multi-sphere interactions, there remains a significant demand for establishing more integrated ESMs. In this thesis, the author primarily implements a global tide module and an ice-shelf cavity module into AWI-ESM2. Ocean tides play a crucial role in the global ocean system due to tidal mixing. Tidal mixing is an important process in the deep ocean because it can lift dense water from the depths, thereby maintaining global stratification and the Thermohaline Circulation. Previous studies have examined tidal effects using either an explicit tide model or a parameterisation of tidal mixing. However, comparing these two approaches could yield further insights into the tidal impact on the global ocean and climate. By evaluating both methods within the same model, the author discusses their advantages and disadvantages, contributing to a more comprehensive understanding of the tidal effect on global ocean circulation and climate. Previous climate modelling simulations often ignore Antarctic ice-shelf cavities due to their relatively small area. However, ice-sheet modelling studies have highlighted the potential for accelerated melting of the Antarctic Ice Sheet in a warming climate. Inspired by this, the author incorporates Antarctic ice-shelf cavities into AWI-ESM2. By comparing simulations with and without these cavities, the results reveal a significant impact on both pre-industrial and future-warming climates. This underscores the crucial role of hydrosphere−cryosphere interactions in the Earth’s system. Marine geological studies have proposed that during past glacial periods, a kilometer-thick ice shelf covered the Arctic Ocean and Nordic Seas. Additionally, freshwater is hypothesised to have been stored in this vast basin. To explore this further, the author conducts simulations using an assumed pan-Arctic ice shelf in AWI-ESM2. Through two-dimensional idealised experiments, the author identifies two distinct time scales for freshening beneath such an ice shelf. The upper ocean experiences a rapid freshening process, while the lower ocean undergoes a slower freshening process. Theoretical estimates provide insight into the time scale required for freshening the Arctic−Nordic Seas basin in the presence of such an ice shelf. These implementations in AWI-ESM2 not only validate the studies presented in this thesis but also pave the way for potential research on Earth’s past, present and future climate.