Mean sea‐level variability along the northeast American Atlantic coast and the roles of the wind and the overturning circulation

Abstract

The variability in mean sea level (MSL) during 1950-2009 along the northeast American Atlantic coast north of Cape Hatteras has been studied, using data from tide gauges and satellite altimetry and information from the Liverpool/Hadley Centre (LHC) ocean model, thereby providing new insights into the spatial and temporal scales of the variability. Although a relationship between sea level and the overturning circulation can be identified (an increase of approximately 1.5 cm in MSL for a decrease of 1 Sv in overturning transport), it is the effect of the nearshore wind forcing on the shelf that is found to dominate the interannual sea-level variability. In particular, winds are found to be capable of producing low-frequency changes in MSL (''accelerations'') in a narrow coastal band, comparable to those observed by the tide gauges. Evidence is presented supporting the idea of a '''common mode'' of spatially coherent lowfrequency MSL variability, both to the north and south of Cape Hatteras and throughout the northwest Atlantic, which is associated with large spatial-scale density changes from year to year.

Temperature-driven global sea-level variability in the Common Era

“…Conversely, over 1000-1400 CE, while GSL was falling, detrended RSL fell in New Jersey (P > 0.90) while it rose in North Carolina (P ≥ 0.99). This pattern is consistent with changes in the Gulf Stream (16) or in mean nearshore wind stress (19). If driven by the Gulf Stream, it suggests a weakening or polar migration of the Gulf Stream over 0-700 CE, with a strengthening or equatorial migration occurring over 1000-1400 CE.…”

Spatial Patterns of Sea Level Variability Associated with Natural Internal Climate Modes

“…This SSH dipole resembles the distinctive fingerprint of AMOC variability (Figure 1 of Zhang 2008), except that the extension to the US Northeast coast from the Subpolar Gyre disappears in the AMOC fingerprint. This difference may indicate the importance of local winds in driving coastal sea level particularly north of Cape Hatteras, as suggested by recent studies (Andres et al 2013;Woodworth et al 2014). Surv Geophys (2017) 38:217-250 231 Recently, accelerated SLR along the US northeast coast, particularly in the ''hotspot'' from Cape Hatteras to Cape Cod since the 1950s, has been detected using tide gauge observations (Sallenger et al 2012).…”

“…In the western North Atlantic and along the US east coast, existing studies suggest the dominance of wind stress curl over the basin interior in driving westward-propagating Rossby waves, affecting interannual and decadal (periods [3 years) sea level variability from 18°N to 38°N (e.g., Sturges and Hong 1995;Hong et al 2000;Thompson and Mitchum 2014). The regional along-shelf wind stress is shown to be important for interannual sea level variability from Nova Scotia to North Carolina (e.g., Andres et al 2013;Woodworth et al 2014). Near the eastern boundary of the North Atlantic, coherent decadal sea level variability has been observed during the past century (e.g., Kolker and Hameed 2007;Miller and Douglas 2007;Woodworth et al 2010;Sturges and Douglas 2011;Calafat et al 2012), and it has been attributed to forcing by local longshore winds and coastal wave propagation (e.g., Sturges and Douglas 2011;Calafat et al 2012), with mass redistribution having a small contribution ).…”

“…Andres et al (2013), however, argued that the changes observed along the coast and over the shelf appear to influence the Gulf Stream path downstream of Cape Hatteras, rather than the changes in Gulf Stream transport affecting coastal sea level. Woodworth et al (2014) analyzed the results from data-assimilative OGCM experiments (also see Williams et al 2014) with and without wind stress forcing for the 1950-2009 period and suggested that although a relationship between US northeast coast sea level change and the AMOC variation can be identified (an increase of *1.5 cm in sea level for a decrease of 1 Sv in MOC transport), it is the surface wind stress particularly the regional wind over the shelf that dominates the sea level variability along the US northeast coast.…”

Accelerated sea level rise and Florida Current transport

“…For example, Woodworth et al (2014) related AMOC and wind stress to MSL finding that wind stress dominates at interannual and shorter timescales. Ezer et al (2013) analyzed the MSL elevation gradient across the western boundary of the Gulf Stream, Florida Current transport, and coastal sea level at 10 tide gauges in the Chesapeake Bay and middle Atlantic coast concluding that the Gulf Stream has shifted from a 6-8 year oscillation cycle to a continuous weakening trend since about 2004, and that this trend may be responsible for a recent acceleration of middle Atlantic coast sea level rise (Sallenger et al, 2012).…”