Week 4: July 12th - July 19th
The Kilo Moana reached Oahu, Hawaii on the morning of July 22, which meant that after a month at sea, the DONUT cruise was officially over! We boxed up our samples to be shipped across the country, and (very) carefully packed up the MIMS to be shipped back to its home in Claremont. The last few days were a busy time for MIMS, as it documented our passage through some interesting regions of our westbound leg.
At our last station, there was a puzzling feature of the profile — multiple deep chlorophyll maximums (DCM), which indicate the depth at which phytoplankton can utilize both sunlight from the surface and nutrients from the deep water to photosynthesize. No one was quite sure how there could possibly be multiple DCMs, which we’ll be investigating well into the semester!
Not only did we have some excitement at station 13, but Professor Prokopenko, by looking at a live map of ocean currents and wind patterns, also noticed that we were travelling through multiple eddies on the western side of the Hawaii archipelago. Eddies are localized currents that form closed loops, and on each side of the eddy the current was moving in opposite directions. MIMS showed supersaturation on the edges and undersaturation of oxygen relative to argon in the center of a large cyclonic eddy sitting directly west of the Big island of Hawaii. The work has begun to interpret these observations. We took samples of N2O throughout the eddy which we will soon analyze to better understand the impact of these currents on the nitrogen cycle.
Overall, our time on the Kilo Moana was an unforgettable experience. We learned so much and cannot wait to analyze our data back on campus. We want to thank all the people who have helped us on this journey and everyone who has been following along with this blog. - Charlotte & Ellie