Variations in the Mass Field Over 1.5 Years at a Persistent Convergent Shelf Front

Harvey Seim, University of North Carolina at Chapel Hill, Earth, Marine, and Environmental Sciences, Chapel Hill, NC, United States, Catherine Richardson Edwards, Skidaway Institute of Oceanogr, Savannah, GA, United States, Dana K Savidge, Skidaway Inst Oceanography, Savannah, GA, United States, Sara Haines, University of North Carolina at Chapel Hill, Earth, Marine, and Environmental Sciences, Chapel Hill, United States, Lu Han, University of North Carolina at Chapel Hill, Marine Sciences, Chapel Hill, United States, John Bane, University of North Carolina at Chapel Hill, Chapel Hill, NC, United States and Glen Gawarkiewicz, Woods Hole Oceanographic Institution, Woods Hole, MA, United States
Abstract:
Observations from shelf moorings and glider surveys deployed offshore of North Carolina from April 2017 to November 2018 are used to characterize the temperature, salinity and density variations of water masses converging on the shelf. The stark contrast in temperature and salinity of southward-flowing Mid-Atlantic Bight (MAB) and northward-flowing South Atlantic Bight (SAB) waters allows us to use an along-shelf line of moorings to estimate the time-varying position of the front that separates them. The glider surveys provide a more detailed view of the frontal structure. The position of the front moves by as much as 100 km, with the most rapid translations associated with strong southward winds. Near-bottom MAB water is the most dense water type for nearly the entire sampling period, while near-surface MAB water is the least dense water type during summer and fall due to low salinity. For roughly a month in fall 2017 SAB waters were most dense, clearly reversing the alongshelf gradient, but for the majority of the time SAB water density is within the range of the MAB densities, or of equal density (seen during late 2017). Mid-depth salinity intrusions are common in the southern MAB during periods of strong vertical stratification.