Diagnosing the variability in temperature and velocity in the Middle Atlantic Bight

Observations of hydrographic and dynamical properties on the Middle Atlantic Bight shelf document strong variability at time scales spanning events that last a few days to century long trends. This thesis studies individual processes which impact shelf temperature and velocity structure, and quantifies the mean velocity conditions at the shelf break. Chapter 2 uses model output to study the dynamics that lead to the breakdown of summertime thermal stratification, and how the processes which reduce stratification vary from year to year. In summer, the atmosphere heats the surface of the ocean, leading to strong thermal stratification with warm water overlying cool water. During fall, strong storm events with downwelling-favorable winds are found to be the primary process by which stratification is reduced. The timing of these events and the associated destratification varies from year to year. In Chapter 3, the velocity structure of the New Jersey shelf break is examine, with a focus on the Shelfbreak Jet. Using 25 years of velocity measurements, mean velocity sections of the Shelfbreak Jet are created in both Eulerian and stream coordinate frameworks. The jet exhibits strong seasonal variability, with maximum velocities observed in spring and minimum velocities in summer. Evidence is found that Warm Core Rings, originating from the Gulf Stream and passing through the Slope Sea adjacent to the New Jersey shelf, tend to shift the Shelfbreak Jet onshore of its mean position or entirely shutdown the Shelfbreak Jet’s flow. At interannual timescales, variability in the Shelfbreak Jet velocity is correlated with the temperature on the New Jersey Shelf, with temperature lagging by about 2 months. Chapter 4 focuses on the impact of Warm Core Rings on the velocity and temperature structure on the New Jersey shelf. Warm Core Rings that have higher azimuthal velocities and whose cores approach closer to the shelf are found to exert greater influence on the shelf’s along-shelf velocities, with the fastest and closest rings reversing the direction of flow at the shelf break. Warm Core Rings are also observed to exert long-lasting impacts on the shelf temperature, with faster rings cooling the shelf and slower rings warming the shelf. Seasonal changes in thermal stratification strongly affect how rings alter the shelf temperature. Rings in summer tend to cool the shelf, and rings throughout the rest of the year generally warm the shelf.

The recurring impact of storm disturbance on black sea bass (Centropristis striata) movement behaviors in the Mid-Atlantic Bight

Storm events are a significant source of disturbance in the Middle Atlantic Bight, in the Northwest Atlantic, that cause rapid destratification of the water column during the late summer and early fall. Storm-driven mixing can be considered as a seasonal disturbance regime to demersal communities, characterized by the recurrence of large changes in bottom water temperatures. Black sea bass are a model ubiquitous demersal species in the Middle Atlantic Bight, as their predominantly sedentary behavior makes them ideal for tagging studies while also regularly exposing them to summer storm disturbances and the physiological stresses associated with thermal destratification. To better understand the responsiveness of black sea bass to storm impacts, we coupled biotelemetry with a high-resolution Finite Volume Community Ocean Model (FVCOM). During the summers of 2016–2018, 8–15 black sea bass were released each year with acoustic transponders at three reef sites, which were surrounded by data-logging receivers. Data were analyzed for activity levels and reef departures of black sea bass, and fluctuations in temperature, current velocity, and turbulent kinetic energy. Movement rates were depressed with each consecutive passing storm, and late-season storms were associated with permanent evacuations by a subset of tagged fish. Serial increases in bottom temperature associated with repeated storm events were identified as the primary depressor of local movement. Storm-driven increases in turbulent kinetic energy and current velocity had comparatively smaller, albeit significant, effects. Black sea bass represents both an important fishery resource and an indicator species for the impact of offshore wind development in the United States. Their availability to fisheries surveys and sensitivity to wind turbine impacts will be biased during periods of high storm activity, which is likely to increase with regional climate change.

Larval Behavior and Protective Implications for Sea Scallops and Surf Clams within the Middle Atlantic Bight: Part One, a Sensitivity Study

In this study, sensitivity studies of larval behaviors were performed, using numerical modeling and analytical methods, for sea scallops (Placopecten magellanicus) and surf clams (Spisula solidissima) in the Middle Atlantic Bight during 2006 and 2010. Based on multiple experiments, a regional ocean modeling system (ROMS) was implemented as the primary physical model, and larval individual behavior models (IBMs) for sea scallops and surf clam larvae were implemented and coupled to the ROMS. To simulate the physical environment and larval behavior using a series of numerical experiments, he coupled ROMS and IBMs were then employed and were driven by realistic dynamic forcing (e.g., winds, tides, and climatological mean boundaries), thermo-dynamic fluxes (e.g., solar radiation, sensible and latent heating), and hydrological forcing for larval behaviors such as vertical swimming and sinking, horizontal drifting with currents, growth, and settlement. Various growth patterns, release types, and larval behavioral parameters were analyzed and are summarized here, based on implications for the protection of sea scallops and surf clam larvae in the Middle Atlantic Bight.