The Decadal View of the Mid-Atlantic Bight from the COOLroom: Is Our Coastal System Changing?

Spatial ocean-observing technologies are permitting researchers to collect data for sustained periods on broad continental shelves. Key technologies used are satellites, high-frequency (HF) radar, and autonomous underwater gliders, which together have allowed study of Mid-Atlantic Bight (MAB) dynamics for the past decade. MAB stratification is the dominant feature regulating annual phytoplankton productivity Stratification begins in the spring, and by early Summer forms one of the worlds sharpest thermoclines (temperatures range from similar to 30 degrees to 8 degrees C in just a few meters). Strong stratification deprives the euphotic zone of nutrients until it erodes later in the year. Therefore, it is not surprising that during late autumn and winter, when stratification has eroded, the largest and most recurrent MAB phytoplankton blooms are observed. These fall/winter blooms Occur on the inner shelf; the offshore extent of the phytoplankton appears to be limited by light. Comparison of data from the 1970s and 1980s to the last decade Suggests phytoplankton bloom size on the MAB has changed, with the magnitude of the fall and winter blooms declining,. Declines in the fall are consistent with the hypothesis that erosion of MAB stratification is occurring later in the season. Declines in winter appear to be associated with an increase in winter winds that enhance winter mixing, which in turn increases the light limitation of the phytoplankton. The increase in winter winds occurred during transition to a positive phase of the Atlantic Multidecadal Oscillation. Our experience emphasizes the importance of spatial time series for studying broad continental shelves.