A new Eulerian iceberg module for climate studies: Formulation and application to the investigation of the sensitivity of the AMOC to iceberg calving

• Main Author: Erokhina, Olga
• Format: Thesis
• Language: English
• Published: Max-Planck-Institut für Meterologie 2020
• Subjects: Hudson; Hudson Strait; Labrador Sea
• Online Access: https://oceanrep.geomar.de/id/eprint/54806/; https://oceanrep.geomar.de/id/eprint/54806/1/Web_BzE_238_Erokhina.pdf

Although it is well known that icebergs play an important role especially for the simulation of glacial climate, e.g. Heinrich events, standard climate models, as used in the Climate Model Intercomparison Project (CMIP), do not contain iceberg modules. Existing iceberg modules are formulated in the Lagrangian framework, optimal for tracking individual icebergs. How- ever, in climate modelling, the key aspect of icebergs is the effect of their melting on the ocean. Therefore, a new formulation of an iceberg module in the Eulerian framework is presented. The module is introduced into the Max Planck Institute Earth System Model (MPI-ESM), allowing to sim- ulate the effect of icebergs on the climate and feedbacks between them. The new iceberg module is tested in a set of simulations with the ice- berg module coupled to the ocean component of MPI-ESM with prescribed observed iceberg calving fluxes. These simulations allow to validate the model against observed iceberg distributions. The sensitivity of the ice- berg module against several model parameters is tested, and an optimal set of parameters, focusing on the iceberg meltwater flux as key variable, is determined. The effect of icebergs on the simulation of iceberg discharge events is investigated in a set of simulations with the full MPI-ESM-Iceberg set-up. The experiments aim at determining the thresholds of the Atlantic Merid- ional Overturning Circulation (AMOC) against a prescribed hosing. In a setting with slowly varying forcing, different types of hosing are compared. In addition to a direct simulation of iceberg calving through the Hudson Strait, two freshwater hosing experiments are performed: a direct point source hosing in the Labrador Sea off the Hudson Strait and a latitude belt hosing between 50◦ and 70◦N. For pre-industrial climate conditions, the results show that the sensitivity of the AMOC to the type of hosing is considerable. The threshold for an abrupt AMOC weakening in the latitude belt hosing is approximately four times lower than in the point ...