Christopher A. Linder

A climatology of the shelfbreak front in the Middle Atlantic Bight

Description of the shelfbreak front in the Middle Atlantic Bight is hampered by the extreme variability of the front. In order to gain insight into both the seasonal variability and regional variations in the mean frontal structure and associated baroclinic jet, historical data are used to produce two-dimensional climatological fields of temperature and salinity for the region south of Nantucket shoals, along the south flank of Georges Bank, and off the coast of New Jersey. Associated cross-shelf fields of density and geostrophic velocity are also computed. The climatological temperature and salinity are consistent with previous descriptions of the frontal hydrography. The temperature contrast across the front varies seasonally between 2° and 6°C. The salinity contrast is 1.5–2, with little seasonal variation. The near-surface density gradients are strongest during the winter and weakest during the summer, when the seasonal thermocline is established. The cross-frontal density gradients are strongest near the foot of the front. Despite the inherent smearing of frontal gradients incurred by averaging over large temporal and spatial scales, the geostrophic velocity field south of Nantucket shows a strong (0.2–0.3 m s−1) baroclinic jet associated with the frontal density gradients. The core of the jet, having a width of 15–20 km, is located near the 150-m isobath. Transport calculations for the flow over the outer shelf and slope are in the range of 0.2–0.3 Sverdrups (Sv) to the west. This is comparable to the estimated transport (0.4 Sv) shoreward of the 100-m isobath.

Seasonal characteristics of bottom boundary layer detachment at the shelfbreak front in the Middle Atlantic Bight

(approximately 26.0 kg m 3 ) is fairly constant throughout the year. However, the vertical scale of the detached layer varies significantly with season, extending 6080 m above the bottom in winter and spring, but only 2040 m above the bottom in summer. The vertical scale is controlled by the strength and depth of the seasonal pycnocline. The observations suggest that the detached layer is capable of extending into the euphotic zone during winter and spring. INDEX TERMS: 4528 Oceanography: Physical: Fronts and jets; 4211 Oceanography: General: Benthic boundary layers; 4219 Oceanography: General: Continental shelf processes; 4279 Oceanography: General: Upwelling and convergences; KEYWORDS: bottom boundary layer, shelfbreak front, Middle Atlantic Bight

A surface‐trapped intrusion of slope water onto the continental shelf in the Mid‐Atlantic Bight

A high-resolution hydrographic transect across the shelfbreak south of Nantucket Shoals in August, 1995, revealed an unusual surface-trapped intrusion of saline Slope water onto the continental shelf. The intrusion was confined to the upper 25 m of the water column and penetrated 15 km shoreward of the 100-m isobath, the typical position of the shelfbreak front. The maximum salinity within the intrusion was 35.0. Several strong jets were present within the surface layer with maximum velocities between 0.30 and 0.44 m s -1 in the alongshelf direction. Satellite thermal imagery confirms the presence of a warm-core ring at the offshore edge of the section and shows a warm feature penetrating shoreward of the 100-m isobath.

Shelfbreak frontal structure and processes north of Cape Hatteras in winter

Author Posting.

Oceanographic and sound speed fields for the ESME workbench

The authors describe the effort to provide three-dimensional global thermohaline and sound speed fields for use in the effects of sound in the marine environment (ESME) workbench suite of programs. The primary fields used are from the modular ocean data assimilation system (MODAS), developed by Fox et al. The system provides global thermohaline and sound speed fields on a daily basis using environmental inputs from the U.S. Navy as well as remote sensing of sea surface temperature and sea surface height. To examine the MODAS fields, the authors also used data from the Southern California Bight collected by the California Cooperative Fisheries Investigations as well as high-resolution hydrographic data collected over the continental shelf south of New England as part of the shelfbreak PRIMER experiment. MODAS performs well for features such as large-scale boundary currents and eddies but is more limited in resolving features such as shelfbreak and coastal fronts, which have small spatial and temporal correlation scales. Because of the considerable computational needs of other ESME modules and its use as a planning tool, the authors present a pragmatic approach for future applications