Coastal sea-level changes driven by oceanic and atmospheric circulation

This thesis investigates the coastal sea-level changes driven by oceanic and atmospheric circulation, with a focus on three ocean basin boundaries in the northern hemisphere: the northeast Atlantic, the northwest Pacific and the northwest Atlantic.

In a first part, the focal point is on the northeast Atlantic and the European shelf and coastal sea level. Observations of the oceanic circulation in the northeast Atlantic are presented, using altimetry observations and in-situ measurements from moored instruments deployed in the last thirty years. Together, these recent observations showcase a poleward flow to the west of Ireland and Scotland: the Rockall Slope Current. In contrast, I find no evidence of an upstream continuation to the Rockall Slope Current which would form a continuous slope circulation circumnavigating Europe. The spatial distribution of sea level induced by an idealised eastern boundary slope circulation, representative of the Rockall Slope Current, is then derived. Both bottom friction as well as the joint effect of baroclinicity and relief are considered in this theoretical study. I demonstrate how the large-scale poleward dynamic height decline in the North Atlantic is mediated to the shelf and eventually affects the coastal sea level thanks to the transport divergence generated by bottom Ekman currents. Through this process, the poleward slope circulation is slowed down. Finally, the sub-annual variability in sea level and currents is investigated. The shelf sea-level changes are found to reflect the alignment of the winds with the along-isobath direction. Analysis of the in-situ current data reveals the build-up of sea level on the shelf leads to changes in along-isobath currents on the outer-shelf and upper-slope.

In a second part, the focal point shifts to the links between subtropical western boundary currents and sea-level variability in the northern hemisphere. The role of the Gulf Stream and of the Kuroshio in driving interannual changes in nearby coastal sea level are conjointly investigated. It is found that the sea level on the Japanese and American coasts is strongly affected by the variability of these major western boundary currents. In particular, path changes of the western boundary currents are responsible for important coastal sea-level variations. Coastal sea-level changes reflect meridional shifts of western boundary currents downstream of their separation from the continental slope. In the northwest Pacific, meandering of the Kuroshio in the region upstream its separation point is also a strong driver of coastal sea-level changes.