laboratory

Yesterday as I was looking under the microscope at particles collected from the bottom of the ocean, and I came across this beautiful cell(s):

This centric diatom is surrounded by a halo of smaller coccolithophore cells.  The circle in the center is the diatom.  You can see the nano-patterns on the silica valve and some yellow/brown-ish chlorophyll inside the cell.  Surrounding the cell are atleast 6 coccolithophores cells (smaller circles) and a ring of their coccoliths (the brown-ish looking mass).  The silica frustules of diatoms and calcium carbonate coccoliths of coccolithophores are relatively heavy biominerals, and may increase carbon export out of the surface ocean by “ballasting” sinking particles.  There is some debate in the literature about which biomineral is more important in exporting carbon.  This diatom-coccolithophore association illustrates my opinion: they are probably both very important.

This sample was collected in a sediment trap 4000 m deep, at the Station M time-series.  I am currently counting phytoplankton within the particles collected over the past 30 years in these sediment traps in collaboration with Ken Smith and Crissy Huffard at MBARI, and thanks to support from  a 2017 New Faculty Award from the California Sea Grant.

Read more from Sea Grant here:
https://caseagrant.ucsd.edu/news/special-focus-awards-support-new-faculty-resilient-coastal-communities
https://caseagrant.ucsd.edu/project/how-does-climate-change-affect-the-export-of-phytoplankton-to-the-seafloor

Last week I visited Melissa Omand’s lab at the University of Rhode Island to analyze sediment trap samples collected on the R/V Endeavor.  Unfortunately I was not able to go on the cruise, but I was still lucky enough to look at the exciting samples they brought back.

The types of samples collected on this cruise were very similar to those we collected in November.  Sediment traps collected sinking particles in the water column.  Above you can see how the number of sinking particles decreased with depth. These are images of the polyacrylamide gel jars placed in the bottom of traps at 4 depths spanning the upper mesopelagic zone.  The 60 meter trap was full of zooplankton fecal pellets (the long stringy particles).  At 150 meters, fluffy diatom aggregates appeared (mostly containing Pseudo-nitzschia), but sinking fecal pellets were also still abundant.  At high magnification, it became apparent that the traps were also chock-full of tiny little particle which turned out to be individual sinking coccolithophore cells. They are only about 10 micrometers big, and difficult to image clearly, but you can just make out the circular coccolith plates covering the outside of this cell .

Although there is still much analysis to be done, these first observations are already exciting and represent a very different particle export environment than what we observed last November, which was dominated by large organic aggregates and large diatom cells.

On a related note, the URI Inner Space Center created several short videos about the research cruise last November.  Here are the films explaining the sediment traps.

Meg Estapa explaining the neutrally buoyant sediment traps:

Me, explaining the particle work:

Pat Kelly explaining the surface-tethered sediment trap array and in-situ pumps: