It is always exciting when science and art intersect. This summer, science illustrator Natalie Renier created this beautiful image to help CSUMB REU student Melia Paguirigan communicate her research about diatom aggregation:
The biological pump is very complex, and this image helped Melia communicate the components of that process that were directly related to her project.
To see more of Natalie Renier’s work, visit her website:
Posted by CSUMB REU student Melia Paguirigan:
This summer I participated in the California State University Monterey Bay Research Experience Undergraduate program, with Dr. Colleen Durkin as my mentor. Our project investigated the role of diatom community composition and morphology in aggregation. We collected whole seawater samples from Monterey Bay.
Then I used a roller table to make aggregates.
In the lab, we used microscopy techniques to quantify the community composition of the aggregates and the corresponding surface water.
The data was then used to identify if diatoms differentially aggregate and if morphology was driving differential aggregation. Throughout this process I was able to become familiar with over 20 diatom genera, using their shape and colony formation as identifiers.
(Note from Colleen: Melia estimates that she counted >21,000 individual diatom cells this summer! She found significantly different phytoplankton compositions in aggregates compared to the total community in seawater, suggesting that some genera tend to be incorporated into aggregates more than others. Melia plans to present this data at a conference later this year.)
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:
The main reason I enjoy working at the microscope is that I never know exactly what I will see. Today while counting a preserved phytoplankton sample collected at the Rhode Island shelf break I spotted these cells:
This is a chain of diatom cells (genus: Detonula, I think) undergoing a life cycle stage that allows them to get bigger. Diatom cells get smaller every time they divide. At some point, the cells are too small to divide anymore and must form either sexual stages or auxospores to get big again. In this photo the top cell in the chain is relatively small and does not appear to be vegetative (i.e. able to divide). The second cell down the chain has a small top half and a much larger bottom half. This cell formed an auxospore. The third and forth cells down the chain are large and contain cytoplasm and chlorophyll (the yellow pigment). These cells are probably the daughter (and grand-daughter) cells of that auxospore. Because the cells are in a chain, it is possible to see the history of this life cycle response.
I found a very similar image of Detonula auxospores here.
Our study of phytoplankton associated with sinking particles was recently published in the journal Limnology and Oceanography. (link to open access publication)
The amount of carbon that sinks out of the surface ocean in the form of organic particles is highly variable and difficult to predict, in part because the ecological processes that lead to the export of these particles are complicated. In this study, we attempted to resolve the mechanism of particle export across a large ocean basin, with a special focus on phytoplankton cells.
T
his data was collected in 2013 during a 45 day research cruise on the R/V Knorr (aka: the DeepDOM cruise). We sailed from Uruguay to Barbados and deployed sediment traps all along the way (see locations on the map). You can see a video about this project here, and on the “Science Videos” page.
I used sediment traps containing a gel layer at the bottom to resolve the identity of individual particles and cells sinking out of the surface ocean (see micrographs in the map figure). The observation that excited me the most was the presence of individual phytoplankton cells in the gel layer. How could such tiny “particles” sink out of the surface ocean? We used a statistical approach to hypothesize how these tiny, slow-sinking cells were transported out of the sunlit surface ocean where they grow.
At most locations, phytoplankton appeared to be associated with sinking fecal pellets and aggregates; they were most likely carried along with these fast sinking detrital particles. However, at several locations sinking phytoplankton cells did not seem to be associated with detrital particles. At two locations, intact and living diatoms appeared to be sinking by themselves, suggesting that they could sink fast enough to be transported out of the surface ocean. Alternatively, they may have been transported by physical mixing. Coccolithophores were particularly dominant at 3 of the observed locations, and we hypothesize that they were either transported by sinking, physical mixing, or in association with detrital aggregates.
We hope that these methods will continue to resolve the mechanisms of “the biological pump” in future studies. With a better understanding of the types of particles responsible for carbon uptake by the ocean, and mechanisms responsible for their transport to the deep sea, the global carbon cycle can be better quantified.
This project was a collaboration with Ben Van Mooy (WHOI), Sonya Dyhrman (Columbia/LDEO), and Ken Buesseler (WHOI), who are also coauthors.
The “EN572” cruise aboard the R/V Endeavor was a success. My goals on this cruise were to link the phytoplankton communities growing in the surface with the particle types sinking out of the surface. We observed a very abundant and diverse phytoplankton community, including many different species of diatom and dinoflagellates.
The sinking particles were dominated by large, fluffy aggregates. The aggregates contained many of the phytoplankton cells that we observed in the surface waters.
Now that we are all back on land, it is time to analyze the samples and all the data that we collected. Stay tuned!
On this cruise we are deploying three different types of sediment traps, a remotely operated vehicle, and are recovering a glider. We are also taking water samples from the ship. One of our goals is to determine how best to coordinate these instruments with one another in order to resolve particle flux and the conditions affecting carbon export.
The Wire Walker profiles through the water column while drifting with the currents.
The surface tethered sediment trap collects sinking particles in the tubes tethered to the line at 5 different depths.
The neutrally buoyant sediment trap (NBST) floats 150 meters deep and measures sinking particles with the collects sinking particles with an optical sensor and also preserves sinking particles in the tubes.
This morning we set sail, heading for the Rhode Island continental shelf break. We are sailing on the R/V Endeavor:
Unfortunately, Melissa, the chief scientist had to stay on the dock, because she is beyond the pregnancy threshold for sailing on a cruise.
Instead, Melissa will be acting as chief scientist from shore and will stay connected with the ship through the University of Rhode Island’s “telepresence” capabilities. Camera and microphones connect Melissa on shore with the ship. Meg Estapa is acting as the on-ship chief scientist.
Video from our cruise is streaming live on Youtube, and at this link:
http://innerspacecenter.org/en572
This week I am sailing on the R/V Endeavor off the coast of Rhode Island. The cruise is lead by chief scientist Melissa Omand. We’ll be deploying three different types of sediment traps and many other instruments that will resolve the physical and chemical environment over short time periods and small spatial scales. These types of measurements will help us study the complex processes that are important in transporting particles and phytoplankton out of the surface ocean and into the deep ocean. Today we were preparing sediment traps, and realized we needed to make a few new parts.
