Master thesis defense by Maliha Khan

Title: The role of oceanic signals due to D/O oscillations in the time scale of interhemispheric coupling

Abstract: This study aimed to a) distinguish between the relevant processes leading to abrupt warming events in the Northern hemisphere (NH), and b) to determine how heat enters the Southern Ocean and continues toward the Antarctica. Unlike many other models, the Community Earth System Model version 1 (CESM1) reconstructs self-sustained DO and AIM events. The outputs from its Last Glacial Maximum (LGM) experiment are applied to solve the climate mystery. For part a, the stochastic processes and the internal variability in the ocean were analyzed. The atmospheric stochastic processes e.g. the North Atlantic oscillations (NAO) and the wind-stress changes at several sites in the Atlantic Ocean showed to not have any influence on the break-up of sea ice in the NH. However, an oceanic dominance was detected with the temperature and salinity as the main drivers for leading the climate transitions in the NH. In part b, a description of how the heat which is originated in the DO cycles travels southward and causes the AIM is presented. We discovered that the ocean signal, which travels to the South Atlantic (SA) and Southern Ocean (SO), undergoes intermediate time scales and the in-depth southern-most signal has triangular shapes. Our research of the underlying mechanisms was inspired by Pedro et. al. (2018) [15], we found that about 2/3 of the global meridional ocean heat transport (MOHT) crosses the ACC via eddy fluxes. The eddy compartments of the MOHT have differed but the surface air temperature and ocean temperature rises to match the order of magnitude. The mystery gave rise to look for heat-pathways elsewhere for the southward travelling warm signal. The southeast tilt of the barotropic stream function (BSF) along with the large gyres in the SO are proposed to play an important role in both capturing the heat from the northern edge of the ACC and to circulate and redistribute the heat to the entire SO and to Antarctica.

Supervisor: Markus Jochum

Censor: Søren Larsen (DTU)