Inner-shelf ocean dynamics and seafloor morphologic changes during Hurricane Sandy

Abstract

A B S T R A C THurricane Sandy was one of the most destructive hurricanes in US history, making landfall on the New Jersey coast on October 30, 2012. Storm impacts included several barrier island breaches, massive coastal erosion, and flooding. While changes to the subaerial landscape are relatively easily observed, storm-induced changes to the adjacent shoreface and inner continental shelf are more difficult to evaluate. These regions provide a framework for the coastal zone, are important for navigation, aggregate resources, marine ecosystems, and coastal evolution. Here we provide unprecedented perspective regarding regional inner continental shelf sediment dynamics based on both observations and numerical modeling over time scales associated with these types of large storm events. Oceanographic conditions and seafloor morphologic changes are evaluated using both a coupled atmospheric-ocean-wave-sediment numerical modeling system that covered spatial scales ranging from the entire US east coast (1000 s of km) to local domains (10 s of km). Additionally, the modeled response for the region offshore of Fire Island, NY was compared to observational analysis from a series of geologic surveys from that location. The geologic investigations conducted in 2011 and 2014 revealed lateral movement of sedimentary structures of distances up to 450 m and in water depths up to 30 m, and vertical changes in sediment thickness greater than 1 m in some locations. The modeling investigations utilize a system with grid refinement designed to simulate oceanographic conditions with progressively increasing resolutions for the entire US East Coast (5-km grid), the New York Bight (700-m grid), and offshore of Fire Island, NY (100-m grid), allowing larger scale dynamics to drive smaller scale coastal changes. Model results in the New York Bight identify maximum storm surge of up to 3 m, surface currents on the order of 2 ms −1 along the New Jersey coast, waves up to 8 m in height, and bottom stresses exceeding 10 Pa. Flow down the Hudson Shelf Valley is shown to result in convergent sediment transport and deposition along its axis. Modeled sediment redistribution along Fire Island showed erosion across the crests of inner shelf sand ridges and sedimentation in adjacent troughs, consistent with the geologic observations.

Physical response of a back‐barrier estuary to a post‐tropical cyclone

“…Simulated subtidal fluctuations lagged behind the observations due in part to the large‐scale model forcing in this area during Hurricane Sandy [ Warner et al ., ]. The main source of uncertainty in simulating storm conditions such as Hurricane Sandy is the available wind forcing.…”

Rapid shelf‐wide cooling response of a stratified coastal ocean to hurricanes

“…Because this process is robust across these two extreme cases drawn from the 30 year envelope of MAB summer cyclones, it will be critical to resolve and forecast the same process for future storms, with the goal of lowering the uncertainty in predictions of TC impacts. Realistic 3‐D coupled models that assimilate coastal observatory data and that are capable of predicting the ahead‐of‐eye‐center stratified coastal ocean cooling processes will be critical [e.g., Zambon et al ., ; Warner et al ., ]. The increasingly populated [ Peduzzi et al ., ] at‐risk coastlines—the Northeast U.S. and northeastern China and Korea—adjacent to the two most stratified seas in the world—the MAB and Yellow Sea—will be increasingly vulnerable to TCs as sea levels rise [ Hansen et al ., ], as TCs more frequently and severely undergo rapid intensification just before landfall [ Emanuel , ], and if maximum TC intensities continue to migrate poleward [ Kossin et al ., ].…”

“…Further, the differences between the deep, open ocean processes and the coastal processes are stark due to the influence of the bottom boundary layer and coastal wall in shallow water [ Glenn et al ., ; Seroka et al ., ]. It is critical to close this gap, with the goal of improving the simulation of coastal ocean physics in coupled TC intensity models [e.g., Zambon et al ., ; Warner et al ., ].…”

Coastal Ocean Response and Its Feedback to Typhoon Hato (2017) Over the South China Sea: A Numerical Study

“…In addition to the extensive studies on the ocean response and feedback in the open oceans, some studies have also paid attention to the response of the shallow ocean water in coastal regions, where the thermodynamic and dynamic features often change significantly due to the development of the bottom boundary layer and the wind-driven coastal circulation during the forced period (e.g., Liu et al, 2011;Warner et al, 2017). Among these studies, Mahapatra et al (2007) suggested that the left-shifted cold wake after TC Orissa (1999) was due to the impedance of the coastline to the circulation in the Bay of Bengal.…”