[1] To investigate the processes influencing the evolution of stratification over continental shelves a moored array was deployed on the New England shelf from August 1996 to June 1997. Temperature, salinity, and current observations spanning the water column were obtained at four midshelf sites, along with meteorological measurements at a central site to estimate the wind stress and the surface heat and freshwater fluxes. Four processes contributed to the seasonal evolution of the stratification. (1) The breakdown of the seasonal thermocline in fall was primarily due to wind forcing, not surface cooling, and occurred in four discrete steps associated with westward, along-coast wind stress events. Eastward wind stress events of similar magnitude did not reduce the stratification. (2) The water at midshelf remained stratified throughout most of the winter due to saltier shelfslope front water displaced onshore by anomalously strong and persistent eastward alongcoast wind stresses. (3) The gradual redevelopment of the thermocline, beginning in April, was primarily a one-dimensional response to increasing surface heat flux. (4) Stratification in early April and throughout May was substantially enhanced by lowsalinity water associated with river runoff from southern New England that was driven eastward and offshore by upwelling-favorable (eastward) wind stresses.

Heat and salt balances over the New England shelf are examined using 10 month time series of currents, temperature, and salinity from a four element moored array and surface heat and freshwater fluxes from a meteorological buoy. A principal result is closure of the heat budget to 10 W m−2. The seasonal variation in depth‐average temperature, from 14°C in September to 5°C in March, was primarily due to the seasonal variation in surface heat flux and a heat loss in winter caused by along‐shelf advection of colder water from the northeast. Conductivity sensor drifts precluded closing the salt balance on time scales of months or longer. For time scales of days to weeks, depth‐average temperature and salinity variability were primarily due to advection. Advective heat and salt flux divergences were strongest and most complex in winter, when there were large cross‐shelf temperature and salinity gradients at the site due to the shelf‐slope front that separates cooler, fresher shelf water from warmer, saltier slope water. Onshore flow of warm, salty slope water near the bottom and offshore flow of cooler, fresher shelf water due to persistent eastward (upwelling‐favorable) winds caused a temperature increase of nearly 3°C and a salinity increase of 0.8 in winter. Along‐shelf barotropic tidal currents caused a temperature decrease of 1.5°C and a salinity decrease of 0.7. Wave‐driven Stokes drift caused a temperature increase of 0.5°C and a salinity increase of 0.4 from mid December to January when there were large waves and large near‐surface cross‐shelf temperature and salinity gradients.

No abstract

The Woods Hole Oceanographic Institution (WHOI) Hawaii Ocean Timeseries (HOT) Site (WHOTS), 100 km north of Oahu, Hawaii, is intended to provide long-term, high-quality air-sea fluxes as a part of the NOAA Climate Observation Program. The WHOTS mooring also serves as a coordinated part of the HOT program, contributing to the goals of observing heat, fresh water and chemical fluxes at a site representative of the oligotrophic North Pacific Ocean. The approach is to maintain a surface mooring outfitted for meteorological and oceanographic measurements at a site near 22.75°N, 158°W by successive mooring turnarounds. These observations will be used to investigate air-sea interaction processes related to climate variability. .0′W in 4756 m of water. This was followed by meteorological intercomparisons and CTDs at the WHOTS-4 and WHOTS-3 sites. The WHOTS-3 mooring was recovered on June 28th followed by CTD operations at the HOT site and shipboard meteorological observations at several sites to the south of the mooring site. This report describes these cruise operations, as well as some of the in-port operations and pre-cruise buoy preparations.iv

<p>High-wind events predominantly cause the rapid breakdown of seasonal stratification on mid-latitude continental shelfs. It is well established that downwelling-favorable wind forcing, i.e., wind vectors with the coastline to their right (on the northern hemisphere), leads to enhanced coastal destratification. A categorization scheme for high-wind events has identified the two atmospheric weather patterns that locally cause such favorable wind conditions on the Southern New England shelf and have the largest contribution to the annual breakdown of stratification in the region. These patterns are i) cyclonic storms that propagate south of the continental shelf and cause strong anticyclonically rotating winds, and ii) persistent large-scale high-pressure systems over eastern Canada causing steady north-easterly winds. Despite both patterns generally producing downwelling-favorable winds on the shelf, the two patterns differ in their wind direction steadiness and tend to produce opposite temperature and salinity contributions to destratification, implying differences in the dominant processes driving ocean mixing. We hypothesize that local mechanical mixing and surface cooling dominate for cyclonic storms due to their strong wind energy input and shear production. In contrast, the weaker but steady downwelling-favorable winds from high-pressure systems can lead to an enhanced cross-shelf Ekman cell that advects salty and less buoyant Slope Water onto the continental shelf. To assess which process dominates for the different impactful high-wind event patterns, we apply a simplified two-dimensional mixed-layer model framework that incorporates horizontal buoyancy gradients across the shelfbreak front. The model allows to determine the stratification change caused by one-dimensional surface forcing (wind stress and surface buoyancy flux) and Ekman-driven advection individually. Observations from moorings and glider transects across the shelfbreak, provided by the Ocean Observatories Initiative Coastal Pioneer Array (2015-2022) at the Southern New England shelfbreak, allow a comparison to investigate the importance of along-shelf processes for predicting shelf stratification changes on synoptic to intra-seasonal timescales.</p>