Speaker

Carolina Camargo, Postdoctoral Investigator, Woods Hole Oceanographic Institution

From Shelf Break to Shoreline: Coastal Sea Level and Local Ocean Dynamics in the Northwest Atlantic

Abstract

The US East Coast is a heavily populated region, and models project that it will experience faster-than-global rates of sea-level rise in the coming century. Hence it is important to understand the underlying causes of sea-level variability. Along the US East Coast, an important driver of coastal sea-level variability is ocean dynamics, related to both large-scale circulation, such as the Gulf Stream, and also smaller local ocean currents. A relevant circulation feature in this region is the Shelf break jet (SBJ). The SBJ flows equatorward from the Labrador Sea towards the Gulf Stream at Cape Hatteras following the shelf break along the Northeast US coast.

Here, we use seven years of velocity data from the Ocean Observatory Initiative (OOI) Coastal Pioneer Array, together with tide-gauge data from 2014 to 2022 to establish the connection between coastal sea level and local ocean circulation over the shelf and the slope. Located at the New England shelf break, about 75 nautical miles south of Martha’s Vineyard, the Array has seven site moorings, spread from the shelf to offshore of the shelf break. Each mooring contains, among other instruments, an upward-looking ADCP, which measures three-dimensional velocities throughout the water column

At timescales of 1–15 days, southern New England coastal sea level and transport vary in anti-phase, with magnitude-squared coherences of ∼0.5 and admittance amplitudes of ∼0.3 m Sv−1. This relationship has a clear spatial pattern: we find significant coherence between SBJ transport and coastal sea level from the South of New England to as far south as the Delaware coast, depending on frequency. Our results are consistent with a dominant geostrophic balance between along-shelf transport and coastal sea level.

Since the 1–15 day frequency band coincides with the frequency variability of storm surges, we explore the implication of our findings to coastal flooding. Preliminary results indicated that a fraction of the registered floods are related to SBJ variability. Additionally, our results suggest that focusing only on large-scale circulation, such as the Gulf Stream or the overturning, may not be satisfactory for understanding the most basic dynamics essential for making meaningful projections of the future.