Abstract
Regional sea-level rise is characterized by decadal acceleration and deceleration periods that typically stem from oceanic climate variability. Here, we investigate decadal sea-level trends during the altimetry era and pin down the associated ocean circulation changes. We find that decadal subpolar gyre cooling (warming), strengthening (weakening), widening (shrinking) since the mid-2000s (early 1990s) resulted in negative (positive) sea level trends of −7.1 mm/yr ± 1.3 mm/yr (3.9 mm/yr ± 1.5 mm/yr). These large-scale changes further coincide with steric sea-level trends, and are driven by decadal-scale ocean circulation variability. Sea level on the European shelf, however, is found to correlate well with along-slope winds (R = 0.78), suggesting it plays a central role in driving the associated low-frequency dynamic sea level variability. Furthermore, when the North Atlantic is in a cooling (warming) period, the winds along the eastern boundary are predominantly from the North (South), which jointly drive a slowdown (rapid increase) in shelf and coastal sea level rise. Understanding the mechanisms that produce these connections may be critical for interpreting future regional sea-level trends.
Highlights
We observe that a strong subpolar gyre during the CP (WP) is associated with a strengthened wind-stress curl, a horizontally expanded gyre, a southeastwards shifted NAC pathway. These results support the notion of reduced advection of warm and saline subtropical waters into the northeast Atlantic and a role for Sverdrup dynamics. These cold and fresh periods lead to a lower steric anomaly that communicates with the east Atlantic shelf through along-slope winds, which play a major role in producing the interannual-to-decadal dynamic shelf sea-level variability in the east Atlantic and in modulating the pace of decadal coastal sea level rise in the North and Norwegian Seas
We suggest that our results may have implications for decadal European sea-level predictions based on the climate state of the North Atlantic Ocean, which have been shown to exhibit substantial skill in the SPNA62
European shelf and coastal sea levels increased rapidly (e.g. Fig. 3b) as a response to the strong westerly winds associated with the North Atlantic Oscillation, despite an anomalously cold North Atlantic Ocean
Summary
These cold (warm) and fresh (saline) periods lead to a lower (higher) steric anomaly that communicates with the east Atlantic shelf through along-slope winds (via Ekman transport and upwelling/downwelling processes), which play a major role in producing the interannual-to-decadal dynamic shelf sea-level variability in the east Atlantic and in modulating the pace of decadal coastal sea level rise in the North and Norwegian Seas. We have in this study decomposed the correlation pattern between steric height and coastal sea level shown by Dangendorf et al.[37] and Frederikse et al.[38], explained its associated spatio-temporal variability and revealed that it emerges as a result of a complex combination of oceanic processes involving overturning and gyre-scale circulation changes as well as along-slope winds.
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