Presenter: Catherine Garcia (UH Manoa)

Description:
Profiling of bio-optical properties using autonomous sensors provides rapid information on particle accumulation.  While the North Pacific Subtropical Gyre is seasonally stratified and nutrient depleted, pulses of phytoplankton blooms and particle export have been annually observed at the peak of summer stratification at Station ALOHA. In August 2021, we targeted a mesoscale anticylonic eddy with elevated satellite chlorophyll. Combining sensors from multiple platforms (Wirewalkers and Seagliders) improved the temporal and spatial reconstruction of the characteristics of the chlorophyll patch. The Wirewalker observations showed that, within the mixed layer, both beam attenuation and chlorophyll fluorescence declined over the course of several days and then remained stable in the anticyclone. Over these two weeks, we also observed a sustained maximum in beam attenuation baseline and spike frequency at the base of the mixed layer (near 50m) consistently above the maximum chlorophyll fluorescence (near 125m). Wirewalker observations have finer temporal and vertical resolution than Seaglider observations, but they only covered a 10-day period in the eddy, while two Seagliders continued to monitor the developing anticyclone for upwards of a month more. To leverage the strengths of both sampling platforms, we compared their simultaneous measurements of particle backscatter and chlorophyll fluorescence. Though intercomparison among different platforms remains difficult, this dataset will provide a bio-optical baseline for the identification of anomalous conditions associated with blooms near Station ALOHA.