Ocean motion on the Yermak Plateau : - tidal and air-ocean interactions

• Main Author: Ersdal, Eli Anne
• Other Authors: orcid:0000-0001-6667-0000
• Format: Doctoral or Postdoctoral Thesis
• Language: English
• Published: The University of Bergen 2020
• Subjects: Arctic; Arctic Ocean; Svalbard; Yermak Plateau; Global warming; Yermak plateau; Spitsbergen
• Online Access: https://hdl.handle.net/11250/2718965

This study focuses on the tidal and atmospheric dynamics controlling the overflow of warm Atlantic Water, crossing over the Yermak Plateau, which can be seen as a doorstep to the Arctic Ocean. The Arctic conditions are changing due to the general global warming, and in order to make good predictions of the future climate north of Svalbard and further into the Arctic Ocean, a good understating of the dynamics controlling the overflow is essential. The Yermak Plateau is known for enhanced diurnal tides caused by topographically trapped waves (TTW). A numerical shelf model has been set up for the southwestern side of the plateau to investigate when the TTW near the diurnal frequency become resonant with zero group velocity, meaning that the diurnal energy does not radiate out of the region, but will accumulate along the slope. The model inputs are slope steepness, background current and stratification, and the result indicates that the group velocity of the TTW near the diurnal frequency becomes zero when the background current is strong, i.e. during winter. Four moorings have measured ocean currents and ocean bottom pressure (OBP) on top of the plateau and the data revealed significant monthly and fortnight tidal periods during winter. The low-frequency Lunar Monthly, Mm, and the fortnightly, MSf, are astronomically forced, but their potentials are weak, especially the potential of MSf. Therefore, we suggest that the observed enhancement of Mm and MSf on top of the plateau during winter, is caused by an energy contribution from the diurnal tides. The superposition of Mm and MSf have been termed the Nonlinear Yermak Tidal Overflow (NYTO), and reached a maximum speed of 15 cm s$^{-1}$ in February 2016. From December to May, the mean volume transport was 1.1 Sv by the NYTO alone. The four moorings located on top of the plateau have been set up to target the Svalbard Branch (SB) and the Spitsbergen Polar Current (SPC). After evaluating the tidal effect on the Atlantic Water flow across the plateau, these ocean data ...