The Impact of Warm Core Rings on Middle Atlantic Bight Shelf Temperature and Shelf Break Velocity (original) (raw)

2022, Journal of Geophysical Research: Oceans

Warm Core Rings (WCRs) form from large meanders of the Gulf Stream that are pinched off, leaving an anti-cyclonic eddy of warm salty water north of the Gulf Stream. These rings can abut the Middle Atlantic Bight (MAB) shelf as they move westward through the Slope Sea until they are reabsorbed into the Gulf Stream. Disruptions to mean shelf break currents as well as large shelf temperature anomalies have been attributed to adjacent rings (e.g., Beardsley et al., 1985; Forsyth et al., 2020; Gawarkiewicz et al., 2019). Observations have shown that more rings have been formed annually since 2000, leading to the possibility that there are more frequent disruptions to the shelf system (Gangopadhyay et al., 2019). With this increase in the number of ring formations per year, understanding how rings are able to impact the shelf is increasingly important. Early studies of WCRs combined limited in-situ observations with satellite thermal imaging to study the properties of the rings and their interactions with the shelf (e.g., Bisagni, 1983; Churchill et al., 1986; Joyce, 1984; Morgan & Bishop, 1977). These studies quantified dynamical properties of the rings, and estimated cross-shelf fluxes associated with warm streamers which cross onto the shelf even as the ring core remains over the slope. Estimates of the ring-driven cross-shelf heat flux suggest that they play a key role in the yearly heat budget for the shelf (Morgan & Bishop, 1977). Individual shelf streamers were also observed to carry a significant fraction of the annual slope water transport to the shelf as estimated from salinity (Churchill et al., 1986). The cross-shelf water mass exchange is modified by both warm streamers moving onto the shelf, and also cold streamers pulled Abstract Warm Core Rings (WCRs) are known to disrupt the shelf flow as well as drive strong heat transport onto the Middle Atlantic Bight shelf. We examine 27 rings sampled by the container ship Oleander, 16 rings which have in-situ velocity data and 11 rings identified from satellite sea surface height but with in-situ temperature data, to study the variability in rings' impact on shelf break velocities and on the temperature of the adjacent shelf. WCRs that have higher rotational velocities and are closer to the shelf are found to exert greater influence on the along-shelf velocities, with the fastest and closest rings reversing the direction of flow at the shelf break. As rings approach the study site, the Shelfbreak Jet is faster than when the rings are about to exit the study site, likely due to first steepening then flattening of the isopycnals at the Shelfbreak Front. Rings also have lasting impacts on the shelf temperature: rings with faster rotational velocities cool the shelf and rings with slower rotational velocities warm the shelf. The evolution of temperature on the shelf as a ring passes is strongly tied to the season. During warmer seasons, when temperature stratification on the shelf is strong, a ring cools the shelf; during periods of weak thermal stratification, rings tend to warm the shelf. Rings which cool the shelf are additionally associated with increased upwelling as they pass the study site. Plain Language Summary Warm Core Rings are large rotating masses of Gulf Stream water that have been isolated from the Gulf Stream and move through the Slope Sea next to the shelf. We identify and study 16 rings from ship board observations off the coast of New Jersey, and additionally study 11 more rings using a combination of limited ship observations and satellite data. Typical velocities at the shelf break in this region are to the southwest. Rings which rotate more quickly tend to disrupt the normal velocities over the shelf and shelf break and can even reverse these currents. As a ring approaches the study site the southwest velocities over the shelf break are enhanced, and when a ring is exiting the study site the southwest velocities at the shelf break are reduced. Rings exert a lasting influence on the temperature on the shelf. During warmer seasons, rings tend to cool the shelf, while in cooler seasons rings tend to warm the shelf. FORSYTH ET AL.