Regional Differences in Sea Level Rise Between the Mid‐Atlantic Bight and the South Atlantic Bight: Is the Gulf Stream to Blame?

Abstract

Recent studies appear to show that a "hot spot" for accelerated sea level rise (SLR) shifted around 2010 from the Mid-Atlantic Bight (MAB) to the South Atlantic Bight (SAB) and south Florida. The role of the Gulf Stream (GS) in this shift was thus investigated. The findings show that in the~15-20 years before, SLR was accelerating in the MAB due to weakening and southward shifting of the GS. After 2010, however, SLR started slowing down in the MAB due to strengthening and northward shifting of the GS. Thermosteric effects seen in altimeter data indicate a warming trend south of 35°N that started around 2010 and contributed to increased SLR south of Cape Hatteras. However, in the MAB, after the GS separated from the coast, the warming of the Subtropical Gyre and cooling of nearshore waters resulted in an opposite SLR response and strengthening of the GS front. Oscillations with periods of 2-5 years dominated the GS flow and coastal sea level variability, but the GS in the MAB is often out of phase with the GS in the SAB due to eddies and recirculation gyres. These oscillations can create temporal changes in SLR rates that are~10 times larger than the long-term trend, so recent changes in the local "hot spot" may not be interpreted as a sign of a shift in the long-term trend, but more likely a temporal shift associated with interannual and decadal variations in the North Atlantic.Plain Language Summary Regional changes in sea level rise (SLR) rates along the U.S. EastCoast and the role of the Gulf Stream (GS) in those changes are investigated, explaining why the largest SLR rates were found north of Cape Hatteras before 2010 and south of Cape Hatteras after 2010. Before 2010 SLR was accelerating in the MAB due to weakening and southward shifting of the GS, but after 2010 SLR started slowing down in the MAB due to strengthening and northward shifting of the GS. Because of the GS dynamics and its distance to shore, a warming trend south of 35°N that started around 2010 had different sea level response in the north and south. Oscillations with periods of 2-5 years were also investigated.

Global sea level reconstruction for 1900–2015 reveals regional variability in ocean dynamics and an unprecedented long weakening in the Gulf Stream flow since the 1990s

“…The Norfolk station at the southern end of the Chesapeake Bay was chosen because it is one of the US cities currently facing some of the largest impacts of sea level rise and increased flooding. This tide gauge record was subject to numerous studies that link coastal sea level there with changes in ocean dynamics (Ezer, 2001(Ezer, , 2013Ezer and Corlett, 2012;Ezer et al, 2013;Ezer and Atkinson, 2014). While this tide gauge was part of the reconstruction, it is not completely independent from RecSL, so the hybrid reconstruction has been validated thoroughly using random independent unassimilated sites (see the Supplement in Dangendorf et al, 2019).…”

“…The long tide gauge record (starting in 1927) at Sewells Point in Norfolk, VA (in the lower Chesapeake Bay), has been the subject of many studies due to the acceleration in flooding at this city (Boon, 2012;Ezer and Corlett, 2012;Ezer, 2013;Ezer and Atkinson, 2014); this location can be used to represent sea level variability in the MAB (Ezer et al, 2013). Note that due to the coarse resolution, the reconstruction completely omits the Chesapeake Bay.…”

“…Land subsidence associated with the Glacial Isostatic Adjustment (GIA) plus local geological, cryospheric and hydro-T. Ezer and S. Dangendorf: Global sea level reconstruction for 1900-2015 logical processes increase local sea level rise along the US East Coast relative to the global rates (Boon, 2012;Miller et al, 2013;Frederikse et al, 2017;Gehrels et al, 2020). An additional factor, less understood, is acceleration and deceleration due to the dynamic response to changes in ocean circulation; for example, a potential slowdown in the GS and AMOC (which the GS is part of) can increase coastal sea level along the western North Atlantic coasts (Ezer and Corlett, 2012;Sallenger et al, 2012;Ezer et al, 2013;Ezer and Atkinson, 2014;Rahmstorf et al, 2015;Little et al, 2019). Therefore, it is important to study regional climatic changes for flood-prone coastal communities.…”

Global sea level reconstruction for 1900–2015 reveals regional variability in ocean dynamics and an unprecedented long weakening in the Gulf Stream flow since the 1990s

“…where offshore GS dynamics are an important driver of coastal sea level rise and variability (Blaha, 1984;Leverman et al, 2005;Ezer, 2001Ezer, , 2013Ezer, , 2015Ezer, , 2019Ezer et al, 2013;Salenger et al, 2012;Yin et al, 2013;Domingues et al, 2018).…”

“…The lower correlation in the MAB (though statistically significant at 95%) seems due to a phase lag between the upstream SAB and the downstream MAB. This incoherence between the GS and coastal sea level on the two sides of Cape Hatteras (i.e., the SAB versus the MAB) was investigated in several recent studies Valle-Levinson et al, 2017;Domingues et al, 2018;Ezer, 2019). EMD analysis further compares relationship between the GS-SAB proxy (derived from east-west sea level difference) and the observed FC for different modes (Fig.…”