Atlantic Water in the Nordic Seas : A satellite altimetry perspective on ocean circulation

• Main Author: Broomé, Sara
• Format: Doctoral or Postdoctoral Thesis
• Language: English
• Published: Stockholms universitet, Meteorologiska institutionen (MISU) 2020
• Subjects: Arctic Ocean climate; ocean heat transport; sea surface height; topographic control; Lagrangian trajectories; Climate Research; Klimatforskning; Oceanography; Hydrology and Water Resources; Oceanografi; hydrologi och vattenresurser; Meteorology and Atmospheric Sciences; Meteorologi och atmosfärforskning; Arctic; Arctic Ocean; Nordic Seas
• Online Access: http://urn.kb.se/resolve?urn=urn:nbn:se:su:diva-176273

The Atlantic Water in the Nordic Seas contributes to the mild climate of Northern Europe and is the main oceanic source of heat for the Arctic. The northward bound transport of the warm and saline Atlantic Water is mediated by a topographically constrained cyclonic boundary current along the Norwegian continental slope. The analysis within this thesis is based on satellite observations of dynamic Sea Surface Heights (SSH) from 1993 to the recent present, combined with both hydrographic observations and modelling. It provides some new perspectives and results, as well as corroborates the essential role of bottom topography for the circulation in the Nordic Seas. In the first part of the thesis, the topographic constraint is used in the analysis by examining the satellite-derived SSH along topographic contours. We find stationary along-contour anomalies that indicate deviations from strict topographic steering. However, we show that these deviations are dynamically consistent with, and can be explained by, potential vorticity conservation in an adiabatic steady-state model for flow over a topographic slope. The analysis along topographic contours is further developed to study northward-propagating, low-frequency ocean temperature signals. These signals have an expression in the SSH and their propagation speed is remarkably slow compared to the current speed. We propose a conceptual model of shear dispersion effects, in which the effective advection speed of a tracer is determined not only by the rapid current core, but by a mean velocity taken over the cross-flow extent of Atlantic Water. The model predicts a reduced effective tracer advection velocity, comparable to the one observed. The close connection between anomalies in SSH and heat content is further used to study decadal variability in the Nordic Seas. There is a shift in decadal trends in the mid-2000s, from a period of strong increase in SSH and heat content to a more stagnant period. We find this variability to be forced remotely, rather than by local ...