Upper Ocean Temperature Variability in the North Atlantic and Southern Oceans: Insights from Adjoint and Forward Modeling

Abstract

Temperature variability in the upper ocean plays a primary role in global climate, carbon uptake by the ocean, and the general circulation of the ocean, and is therefore a subject of intense study. Changes in the North Atlantic and Southern Oceans are of particular interest due to their importance to global circulation through attempts to understand observed trends and variability over previous decades. In this thesis, we employ and expand a number of methodologies to better understand temperature variability. Chapter 1 focuses on sea surface temperature (SST) variability in the North Atlantic Ocean, where SST proxy records reveal significant heterogeneity in low-frequency variability within the basin. We employ an ensemble of past millennium climate simulations in order to better understand what drives this heterogeneity, finding that some leading dynamical modes can explain part, but not all, of the observed pattern. Chapters 2 and 3 focus on the Southern Ocean and employ an ocean model adjoint to compute optimal atmospheric patterns that drive variability in the ocean using Dynamics-weighted Principal Component Analysis (DPCA). In Chapter 2, DPCA is used to investigate zonal-mean SST variability, and the results are compared with the role of the Southern Annular Mode, which is the canonical mode of variability in the region. In Chapter 3, we expand the DPCA methodology to account for multiple atmospheric variables, and apply it to understand drivers of zonal asymmetry in the upper 700 meters of the Southern Ocean. Together, these chapters introduce and expand novel methods for better understanding how and why temperature variations arise within the ocean.