Hurricane Dorian Impacts on Northeast US Shelf Marine Hydrography and Ecosystem

Mara Freilich1, Astrid Pacini2, Justin Joseph Suca3, Lukas Lobert4, E. Taylor Crockford2, Benjamin Nash Granzow5, Jinshi Chen6, Seth Cones3, Faith Duffy4, Alan Gaul4, Jianhua Gong2, Cora Hersh2, Max Jahns4, Alexandra Jones7, Arianna Krinos4, Lei Ma4, Phadtaya Poemnamthip4, Miraflor Santos4, Iulia Streanga4, Ruijiao Sun4, Lina Taenzer8 and Glen Gawarkiewicz2, (1)Massachusetts Institute of Technology, Earth, Atmospheric, and Planetary Sciences, Cambridge, MA, United States, (2)Woods Hole Oceanographic Institution, Woods Hole, MA, United States, (3)Woods Hole Oceanographic Institution, Biology Department, Woods Hole, MA, United States, (4)Woods Hole Oceanographic Institution, Woods Hole, United States, (5)Woods Hole Oceanographic Institution, Marine Chemistry and Geochemistry, Woods Hole, MA, United States, (6)Woods Hole Oceanographic Institution, Physical Oceanography, Woods Hole, United States, (7)Woods Hole Oceanographic Institution, Woods Hole, PA, United States, (8)Massachusetts Institute of Technology, EAPS, Cambridge, MA, United States
As Hurricane Dorian moved through the North Atlantic, the wind-induced changes in water mass structure produced an anomalous circulation on the US Northeast Shelf that persisted for weeks. This anomalous circulation resulted in unusual biological community structure in the region. Prior to the arrival of Hurricane Dorian, a large warm core ring was 100 nm to the southeast of Cape Cod, MA, USA. Upon arrival of tropical storm-force winds in the area, water from the warm core ring moved onto the shelf due to Ekman transport, with filaments reaching onto the shelf up to the 55-meter isobath. The evolution of the water mass structure and circulation is studied using satellite data, the Ocean Observatories Initiative Pioneer Array, and biophysical sampling that took place two weeks after Hurricane Dorian, from September 20-September 22. Data from this hydrographic and biological survey of the shelf and slope south of Woods Hole, MA along the Northeast US Shelf Long-Term Ecological Research (NES-LTER) cross-shelf transect are presented.

Abrupt salinification and warming of the hydrography extended significantly further inshore than anticipated, with TSG and ADCP data indicating that the front was located near the 40 m isobath. Most surprisingly, this frontal zone was associated with significant weakening of the westward flow generally found in this region. On the inshore end of the shelf, this warm and salty filament water overlaid the remnants of the Cold Pool, was in the bottom 10 m of the water column. Towards the shelf break, the warm core ring water was present over the whole water column. There was a second frontal zone near the shelfbreak where a deeper ring filament was present, harboring warmer (up to and exceeding 24C) and saltier (36) water than on the shelf.

Coincident with these sharp, filament associated hydrographic gradients, biological productivity on the inner shelf exhibited unique and anomalous structure driven by the warm water of Gulf Stream origin. Plankton community structure--from picoplankton to zooplankton--was patchy in the frontal regions.

Hurricane Dorian induced long-lasting changes in the physical and biological conditions on the shelf. This case study elaborates a mechanism by which hurricanes have sustained impacts on an economically important ecosystem.