Can the Gulf Stream induce coherent short-term fluctuations in sea level along the US East Coast? A modeling study

Abstract

Much attention has been given in recent years to observations and models that show that variations in the transport of the Atlantic Meridional Overturning Circulation (AMOC) and in the Gulf Stream (GS) can contribute to interannual, decadal, and multi-decadal variations in coastal sea level (CSL) along the US East Coast. However, less is known about the impact of short-term (time scales of days to weeks) fluctuations in the GS and their impact on CSL anomalies. Some observations suggest that these anomalies can cause unpredictable minor tidal flooding in low-lying areas when the GS suddenly weakens. Can these short-term CSL variations be attributed to changes in the transport of the GS? An idealized numerical model of the GS has been set up to test this proposition. The regional model uses a 1/12°grid with a simplified coastline to eliminate impacts from estuaries and small-scale coastal features and thus isolate the GS impact. The GS in the model is driven by inflows/outflows, representing the Florida Current (FC), the Slope Current (SC), and the Sargasso Sea (SS) flows. Forcing the model with an oscillatory FC transport with a period of 2, 5, and 10 days produced coherent CSL variations from Florida to the Gulf of Maine with similar periods. However, when imposing variations in the transports of the SC or the SS, they induce CSL variations only north of Cape Hatteras. The suggested mechanism is that variations in GS transport produce variations in sea level gradient across the entire GS length and this large-scale signal is then transmitted into the shelf by the generation of coastal-trapped waves (CTW). In this idealized model, the CSL variations induced by variations of ∼10 Sv in the transport of the GS are found to resemble CSL variations induced by ∼5 m s −1 zonal wind fluctuations, though the mechanisms of wind-driven and GS-driven sea level are quite different. Better understanding of the relation between variations in offshore currents and CSL will help to improve the prediction of both short-term water level anomalies that cause flooding, as well as spatial variations in long-term sea level variability and coastal sea level rise.

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

“…The high anticorrelations found between the GS flow and SLR along the MAB coast demonstrated the impact of the GS on the coast (e.g., Figure 10 in Ezer et al, 2013). It is suggested that in addition to the direct GS-coastal sea level relation that results in anticorrelation between the GS strength and sea level rise (Ezer, 2016;, there is another mechanism associated with warming of the Subtropical Gyre that can result in opposing coastal sea level response between the SAB and the MAB. While Vale-Levinson et al suggested that these changes are related to cumulative impacts from NAO and ENSO variations, Domingues et al suggested that warming of the FC causes the increased SLR there, while changes in air pressure and wind contributed to a slowdown of SLR in the MAB.…”

“…• A recent shift in the location of a hot spot for accelerated sea level rise along the U.S. East Coast was investigated • Changes in the Gulf Stream strength and position around 2010 seemed to explain the regional changes in coastal sea level • Interannual and decadal variations in the Gulf Stream can contribute to temporal and spatial changes in sea level rise rates (Hughes & Meredith, 2006;Huthnance, 1978) and limit transfer of signals between the MAB and the SAB, as demonstrated by numerical simulations (Ezer, 2016(Ezer, , 2017.…”

“…Numerous studies indicate that on a wide range of time scales, from daily changes to interannual and decadal variations, weakening in the GS flow (i.e., decreasing surface geostrophic current associated with sea level slope across the GS) is related to elevated coastal sea level on the onshore side of the current (Ezer, 2015(Ezer, , 2016Ezer et al, 2013;Ezer & Atkinson, 2014, 2017Goddard et al, 2015;Park & Sweet, 2015;Wdowinski et al, 2016). Combining GS's induced sea level anomalies with long-term SLR trends and land subsidence resulted in an increase in unpredictable minor flooding (so called "sunny day" or "nuisance" flooding) in coastal cities such as Norfolk, VA, or Miami, FL (Ezer & Atkinson, 2014;Park & Sweet, 2015;Wdowinski et al, 2016).…”

Future Nuisance Flooding in Norfolk, VA, From Astronomical Tides and Annual to Decadal Internal Climate Variability

“…This flooding can also be exacerbated by changes in ocean circulation, such as variations in the Gulf Stream, and from natural internal climate variability, all of which affect sea level (Carson et al, 2015;Ezer, 2016;Ezer & Atkinson, 2017). Natural internal climate variability (IC) on annual to decadal timescales includes signals such as seasonal cycles, El Niño Southern Oscillation, and Pacific Decadal Oscillation, among others.…”

Editorial—the 7th International Workshop on Modeling the Ocean (IWMO 2015)

“…The subjects of papers in this Topical Collection include one on process study of the gravity current (Berntsen et al 2016), three on data assimilations (Margvelashvili et al 2016;Peng et al 2016;Zheng et al 2016), two on basin-scale modeling and observational data analyses (Ezer 2016;Quan et al 2016), two on coastal processes (Liu and Chua 2016;Zhu et al 2016), and two on sediment resuspension and tranport (Qiao et al 2016;Yang et al 2016). Berntsen et al (2016) conducted a high-resolution model experiment using a non-hydrostatic model to simulate plume down a canyon under rotation.…”