Freshwater and iceberg flux impacts with BISICLES-NEMO (Deliverable D6.1)

Icebergs calve off the Antarctic Ice Sheet and melt in the Southern Ocean. The freshwater they deposit in the ocean can have an important influence on the density structure of the ocean and, hence, the circulation of globally important water masses. This deliverable explores how changes in the rate of melting of icebergs under increased atmospheric CO2 concentration are projected onto different Southern Ocean density layers that outcrop around Antarctica. In addition, we consider the extreme case of a hypothetical Ross Ice Shelf collapse triggering the calving of a large number of icebergs around Antarctica over a short period. It is important to explore the impact of iceberg meltwater on density space because transport in the interior ocean occurs mostly along density layers. Outcropping density layers connect the surface Southern Ocean to the abyss and to the overturning circulation. The outcropping and the volume of water in the densest layers change in response to greenhouse gas-induced warming. This analysis is conducted using a coupled configuration of the UK Earth System Model (UKESM), whose ocean domain is represented by the NEMO model (Nucleus for European Modelling of the Ocean; Madec and the NEMO System Team, 2024; Marsh et al., 2015; Merino et al., 2016). The ocean domain is coupled to a Unified Model (UM) atmosphere and a BISICLES ice sheet model.