The strong southerly winds responsible for the surfacing of the thermocline on July 17, continued through July 20, causing the newly formed upwelling front to move further offshore. After the winds relaxed late on July 20 to light and variable for several days, explosive growth of the upwelling center with an embedded cyclonic eddy was observed in the real-time AVHRR-derived sea surface temperatures and CODAR-derived surface currents. The physical survey vessel (Caleta) equipped with the towed ADCP and CTD/Fluorometer systems was dispatched to sample the northern cross-shelf transect (Black line). The Survey REMUS AUV was sent to sample along a southern cross-shelf transect between Node B and Mooring C (red line). By mid-day, Turbulence REMUS was sent along an intermediate cross-shelf line extenting from the center of the cyclonic eddy across the upwelling front (white line).
Two concurrent parallel velocity sections obtained from the SWATH towbody on Caleta and the REMUS AUV are displayed above, with the alongshore velocity displayed as color-coded contours and the cross-shore velocity indicated with arrows. On the offshore side of both sections, the previously observed northward flowing surface jet is located on the warm side of the upwelling front. On the inshore side, a new subsurface feature was discovered. In the final 4 kilometer range cells for both sections, a strong southward flowing subsurface jet is observed in the alongshore flow within the eddy.
Concurrent CTD/Fluorometer sections also were acquired with the undulating towbody (Caleta) along the northernmost transect. The upwelling front is observed on the offshore side of the temperature section at a range of 8 kilometers. On the inshore side between 24 and 28 kilometers, the isotherms spread vertically possibly due to mixing by the strong subsurface jet. The corresponding fluorometer section along this transect reveals extremely high phytoplankton concentrations nearshore below the thermocline, and virtually no signal offshore above the thermocline. Finally, the speed of sound in sea water for the same transect is shown. The subsurface data acquired from the adaptive sampling surveys gave us our first indication that the source of the phytoplankton within this upwelling center is this previously unknown subsurface jet flowing southward nearshore below the thermocline.