What is happening underwater in the Mid-Atlantic?

Nice time series posts the last two days have identified that this year so far has been exceptionally warm according to satellite remote sensing data.  This lead us to initiate shelf sampling by conducting a survey of the Mid-Atlantic Bight using a Webb glider.  The Webb glider was launched as part of the Rutgers undergraduate ocean observatory class and graduate student glider training on March 22, 2012.  It has been a successful shelf-wide crossing capturing a dynamic period of dramatic shifts in weather forcing of the shelf. Tonight on April 6th, the current plan is for recovering the glider on Monday (9th), which is good as it has crossed the shelf, and is sitting offshore NJ over the weekend in power saving mode until it is recovered.

The glider has crossed the shelf and made it back to close to shore spanning a 261 kilometers of data collection (below).  The glider flight path has indicated largely a mean southerly depth averaged current flow (below).

What does the data collected by the glider show?  The temperature story shows a complex set of processes operating.  When the glider was deployed and started it’s transect offshore, the shelf was starting to stratify.  For the first 3-days of the transect the bottom temperatures were below 9 degrees.  In contrast the surface waters were above 10 degrees.  On 27th through 29th the Mid-Atlantic was affected by strong winds, the net result was erosion of the shelf stratification as the glider continued its movement offshore.  By the 30th the glider was encountering warm highly saline waters offshore before it turned around and began to transect back to shore. During the transect back to shore the glider encountered variable weather forcing leading to a range of conditions from well mixed to mildly temperature stratified water columns.  The salinity data showed nearshore waters having lower salinity waters presumably associated the outflow of coastal rivers.  The isothermal conditions were associated with high salinity waters.

What are the biological and chemical properties associated with the hydrographic conditions?  The colored dissolved organic fluorescence (often correlated with the humic and fulvic acids associated with river waters) was highest near shore and decreased as the water depth increased.  Optical backscatter (proxy for particle concentrations) showed high concentrations inshore and over the middle of the shelf in the surface waters.  This agreed nicely with the phytoplankton concentrations as measured by chlorophyll fluorescence. In the deeper waters the increased concentrations of particles and chlorophyll fluorescence correspond with the spring bloom, which occurs offshore (deeper than 50 meters).  The oscillations in the chlorophyll fluorescence in the surface waters (0 to 10 meters) was associated with the daily increases in sunlight which lead to physiological adjustments (via fluorescence quenching).