Characteristics of an Advective Marine Heatwave in the Middle Atlantic Bight in Early 2017

Glen Gawarkiewicz,Paula Fratantoni,Harvey Seim,Ke Chen,Anna M Mercer,Lu Han,Aubrey Ellertson,Sara Haines,Frank Bahr,Jacob Forsyth

doi:10.3389/fmars.2019.00712

Abstract

There has been wide interest in marine heatwaves and their ecological consequences in recent years. Most analyses have focused on remotely sensed sea surface temperature data due to the temporal and spatial coverage it provides in order to establish the presence and duration of heatwaves. Using hydrographic data from a variety of sources, we show that an advective Marine Heatwave was initiated by an extreme shelfbreak exchange event in late December 2016 south of New England, with temperature anomalies measuring up to 6°C and salinity anomalies exceeding 1 PSU. Similar features were observed off of New Jersey in February 2017, and are associated with the Shelfbreak Front migrating from its normal position to mid-shelf or further onshore. Shelf water of 34 PSU was observed just north of Cape Hatteras at the 30 m isobath and across the continental shelf in late April 2017. These observations reveal that the 2017 Marine Heatwave was associated with a strong positive salinity anomaly, that its total duration was approximately 4 months, and its advective path extended roughly 900 km along the length of the continental shelf in the Middle Atlantic Bight. The origin of this Marine Heatwave is likely related to the presence of Warm Core Rings adjacent to the shelfbreak south of New England.

Highlights

There has been considerable attention focused recently on Marine Heatwaves, which are warm anomalies persisting for days to months and on spatial scales from one to a thousand kilometers or more (Hobday et al, 2016)
We suggest that the continental shelf south of Nantucket Shoals has in recent years become a hotspot for shelfbreak exchange, with Warm Core Ring water masses preferentially carried onshore in this region
While other factors, including mixing dynamics, impact chlorophyll production, the Marine Heatwave likely contributed to the low productivity on the northeastern continental shelf in 2017

Summary

Introduction

There has been considerable attention focused recently on Marine Heatwaves, which are warm anomalies persisting for days to months and on spatial scales from one to a thousand kilometers or more (Hobday et al, 2016). The Pioneer Array is a multi-scale shelfbreak observatory designed to study shelfbreak exchange processes, while the Shelf Research Fleet utilizes the commercial fishing fleet in Rhode Island to regularly sample the continental shelf using CTDs provided by Woods Hole Oceanographic Institution (WHOI). Data from these two programs have revealed a dramatic warming event in January 2017 south of New England in which warm water fish typically found in the Gulf Stream were caught at the 30 m isobath off Block Island, RI (Gawarkiewicz et al, 2018). This event was not examined closely in context with historical data from the region, nor was the fate of the warm water flooding the continental shelf established in Gawarkiewicz et al (2018)

Methods

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Discussion

Conclusion