Phytoplankton dynamics and bottom water oxygen during a large bloom in the summer of 2011

During the summer of 2011 a large phytoplankton bloom occurred off the New Jersey coast, which was monitored using an existing ocean observatory. There was public concern about the root causes of the phytoplankton bloom and whether it reflected anthropogenic loading of nutrients from the Hudson River or whether it reflected coastal upwelling. We used the MARACOOS network to determine what were the likely drivers of the phytoplankton bloom. The bloom was studied using satellites, HF radar, a Hydroid REMUS and Webb Slocum gliders. Chlorophyll concentrations were over an order of magnitude larger than the decadal mean of ocean color data and the bloom was initiated by upwelling winds throughout the month of July that continued to dominate the wind patterns until the passage of Hurricane Irene. The high concentrations of phytoplankton resulted in the supersaturated oxygen values in the surface waters; however the flux of organic matter resulted in oxygen saturation values of <60% in the coastal bottom waters, which is sufficient to stress benthic communities in the MAB. Discrete samples identified the bloom was dominated by mixed assemblages of motile dinoflagellates. The passage of Hurricane Irene increased the oxygen saturation at depth by close to 20%, but was not sufficient to terminate the bloom. A re-analysis of the CODAR clearly indicated that the shelf wide bloom most likely originated from nearshore the New Jersey coast. Upwelling provided the source water that fueled the bloom. Alternating winds transported the bloom offshore and across the Mid-Atlantic Bight. This is consistent with past studies that observed regions of recurrent hypoxia on the New Jersey inner shelf are more related to coastal upwelling than riverine inputs.