A Pomona – Pitzer team is participating in an oceanographic research cruise in the Eastern North Pacific. This is the first blog post from our students on the cruise.
The cruise is a part of the project funded by the NSF Chemical Oceanography Program to study the role of a special nutrient, Dissolved Organic Nitrogen, or DON, in supporting phytoplankton growth in the one of the largest ecosystems on earth, the Pacific Subtropical Gyre. The ocean gyres are extremely nutrient-poor regions, yet life persists there. Recently, DON has been suggested as the main source of nitrogen in these regions. The teams of four PIs - from University of New Hampshire, Texas A&M, University of Minnesota and Pomona College set out to figure out how much of the plankton growth relies on DON in these “ocean deserts".
Near the equator and the California coast it’s expected that upwelling of subsurface nutrients, including nitrate, supports phytoplankton growth. When phytoplankton grow, they also release DON that could be transported by currents into the Pacific Subtropical Gyre, where nutrients are scarce. There, deprived of other sources of nutrients, phytoplankton is likely to depend on the transported DON. On the cruise, multiple teams, using geochemical and molecular methods will look for evidence of organic nutrient production near the equator and California coast, and then consumption of the organic nutrients in the interior of the gyres along the cruise transect. This gives rise to the cruise acronym, “DONUT” - Dissolved Organic Nitrogen Utilization Transect. After more than a year of preparation, the teams are now at sea, led by Rob Letsher (UNH), Angie Knapp (TAMU), Rene Boiteau (UNM) and Masha Prokopenko (Pomona College).
Elle and Charlotte are keeping the blog, where they are reporting weekly on our North Pacific Adventures. See what they have to say!
Week 1: June 21st - June 28th
And we’re off! The RV Kilo Moana departed San Diego on Sunday, June 21 — the last time we would see land for another month. We spent two days loading in the Port of San Diego, setting up in the labs, assembling the instruments, getting acquainted with each other. Two Pomona technicians, Austin Cordova and Kyle McCarthy helped us to set up and waved us goodbye.
Within the first few hours, we arrived at station one and were ready for a full day of sampling. The science crew consisted of 17 people — a mixture of professors, students, and technicians. On board, there are participants from eight different academic institutions: in addition to four original teams, groups from Scripps Institution of Oceanography, University of South Florida, Stanford and University of Southern California are participating, all with their own unique missions for the next four weeks. The research includes biogeochemical, organic geochemistry, molecular biology and isotopic studies.
In the first few days, one of our main responsibilities was assisting Professor Prokopenko with the setup of the Membrane Inlet Mass Spectrometer (MIMs), an instrument that constantly measures the concentration of different gases in water. For this cruise we are focused on the O2/Ar ratio as an indicator of biological productivity. As the boat moves, water from the underway is pumped through the systems to give us O2/Ar measurements along the ship’s path, which will be used to calculated Net Community Production along the cruise track (finger’s crossed). We collected samples from every station using the Conductivity Temperature Depth (CTD) Rosette, which allowed everyone to obtain the water they needed from different depths — the deepest of this week being around 4,000 meters.
We also learned how to filter this seawater, measuring particulate organic carbon and nitrogen to get insight into primary productivity. In the first week, we filtered around 500 liters of seawater! We even found a copepod who had survived the trip from 1,000 meters below the surface (don’t worry, we released him back into the ocean!). Finally, we learned how to collect samples for N2O gas which will be analyzed after the cruise by Professor Manning at UCONN. Jen Karolewski, lab technician from Stanford, taught us how to ensure the samples do not have bubbles and preserve them with NaOH. These samples are taken from both the underway (typically every 4 hours) and from the CTD.
This week, we learned a lot of fundamental sampling techniques and got the opportunity to learn from many different scientists. We will talk about the work other teams are doing in the next installment of this blog. We also saw a lot of wildlife, including fish, seabirds, sharks, and a lot of copepods!