Inter-annual variability in the stratification regime off the Mid-Atlantic Bight shelf.

The Mid-shelf area of the Mid Atlantic Bight (MAB) has some of the most stratified continental shelf water on the planet and encompasses the location of the 1976 Anoxic Episode, where intense stratification was one important element of the synergism resulting in anoxia and extensive fish/shellfish mortalities (Campbell & O’Reilly,1988). Bi-weekly transects in 2005-2007 obtained from Coastal Ocean Buoy (COBY) cruises showed a clear seasonal progression of the water column, with strong stratification during summer followed by mixing during late fall, winter, and spring. In the shelf waters of the region, the summer patterns in the vertical stratification of the phytoplankton community parallel spatial patterns in physical density stratification. The subsurface phytoplankton maxima track the thermocline/pycnocline. Dense phytoplankton biomass found in the thermocline/pycnocline represents a potentially highly significant source of carbon/energy for herbivores. The water-leaving radiance detected by passive ocean color satellites such as VIIRS and MODIS is from just the upper 1/5th of the productive euphotic layer (O’Reilly & Zetlin, 1998). Consequently, these strong subsurface chlorophyll maxima are not detected. Yearly sampling of the same COBY transects from 2008 to 2019 reveal similar spatial patterns in stratification with a clear inter-annual variability of the strength of the thermocline/pycnocline. In this study we show the effect of the stratification on the chlorophyll and oxygen field and what consequences it may have for chlorophyll detection from satellites from this region.