We have recently encountered many stations with lower surface fluorescence and fewer diatom chains.

The microplankton community at these stations is diverse and includes dinoflagellates like Ceratium (A) and Dinophysis (D), large mixotrophic ciliates (C, maybe Laboea?), and some diatom chains (B). This contrasts with the earlier communities that were dominated by chain diatoms like Chaetoceros, Pseudonitzschia, and Rhizosolenia.

We now appear to be making coherent maps of biooptical quantities that agree with remote sensing images.

The map below shows red backscatter for all 4 platforms, in a coordinate system centered on float 48 for days 132-134. Note the gliders circling the float. The large red (high backscatter) feature in the middle is sampled by all 4 floats consistently as are some of the surrounding bluer regions.

Live from the N. Atlantic, Mike Sieracki and Nicole Poulton (Bigelow Laboratory) provide these insights into the phytoplankton community using FlowCAM and flow cytometric analyses.

Diatom images from the FlowCAM imaging-in-flow system.

The community at CTD#1, 3.5m is dominated but Chaetoceros (left). Many healthy looking chains, but some look on their way out with lots of attached cells (maybe choanoflagellates along for the ride?). Some diatom aggregates were seen.

Size histogram of phytoplankton < 20µm.

We would like to compare the chlorophyll signals between the nine WET Labs chlorophyll fluorometers we have deployed on the floats and gliders. This could be done in raw counts, after subtracting the dark counts (the reading of the fluorometer with the sensor taped over) to remove any constant sensor offset. However, even then the fluorometers slightly different signal gains, due to variations in the electronic components in the fluorometers.

We are finding that the WET Labs C-Star beam transmissometers on the floats are much more sensitive to the initial bloom dynamics than backscattering at 700 nm. We are seeing about 50 counts descrease in transmissivity vs. 5-10 counts increase in b_bp. So, acknowledging this, let's examine one diagnostic we'll be using during the course of the bloom: beam attenuation vs. chlorophyll fluorescence.

Raw C-Star counts in N. Atlantic seawater are reading *higher* than those observed in pure fresh water (0.2 um filtered Milli-Q) at U.W. lab just before deployment.

For example, in water below 100 m, C-Star 1063 on float 48 is reading counts > 3971, which is the "reference" value found using Milli-Q and used in the current beam-c calculation. High counts greater than the U.W. reference value (3924) are also found for C-Star 1062 on float 47 in 150+ m water.