Week 2: June 28th - July 5th
The RV Kilo Moana completed the southern leg of its journey on July 2, when it reached the 3Nº, just 300 km short of being on the equator. As we crossed the intertropical convergence zone (ITCZ), the weather became hot and humid, but after rain showers, we saw a lot of rainbows! We also encountered many whitetip oceanic sharks and watched from the deck as they hunted a school of mahi mahi.
We continued sampling and filtering and also kept a close watch on MIMS. The device started showing undersaturation of oxygen once we left productive equatorial waters, which means oxygen is being respired faster than it’s produced by photosynthesis, or there is a source of low O2-waters advected into the mixed layer. We also got the opportunity to learn more about what the other science parties are working on.
Scientists on board are collecting samples that they will bring back to the lab to measure the concentration and molecular and isotopic composition of dissolved organic nitrogen to help identify which regions of the cruise transect produce new organic nutrients, and which regions consume organic nutrients.
Vincent Johnson, lab technician from Scripps Institute of Oceanography, taught us how to filter particulates to be used for HPLC (high-performance liquid chromatography). He is also measuring on board dissolved oxygen and salinity, and collects samples for dissolved inorganic carbon (DIC). At station 4, he deployed the first of a series of Biogeochemical-Argo floats and will be deploying them on several more stations. These are part of an international program that manages robotic floats in the ocean, which collect data and send it through satellites to Scripps. The instruments on the floats collect data on temperature, salinity, biological productivity, and more!
Dr. Jen Karolewski, lab technician from Stanford, studies different isotopes and uses them to understand biogeochemical processes. On this cruise, Dr. Karolewski is collecting and preserving samples that will be used to measure the nitrogen and oxygen isotopic ratios of nitrite, N2O and nitrate - the main forms of biologically cycled nitrogen. By analyzing the abundance of different isotopes, she can trace the reactions of nitrogen transformations by living organisms at different depths in the ocean. We also asked Dr. Karolewski about her background and why oceanography is so important to her. “The Earth really should have been named oceania… the oceans are the circulatory system of the globe,” she said. “We are changing the earth and the oceans so much. It's really important to understand how it works so we can understand what is going to happen.”
Chief scientist Professor Rob Letscher from the University of New Hampshire brought a group of scientists on the Kilo Moana to study dissolved organic matter production and utilization, especially the different forms of nitrogen and phosphorus, used in photosynthesis. Stella Rowley, a PhD student at UNH, is measuring ammonia and enzymes activity, while Maya Tabor is collecting dissolved organic phosphorus for her Master’s project. The UNH group is also leading a power series of 3 sets of incubations, set up on 3 different stations, with 11 distinct treatments in each set to determine controls and rates of DON breakdown by the microbial community – this is one of the core components of the DONUT project.
The team from Texas A&M, led by co-chief scientist Professor Angie Knapp, is researching both microbial communities and geochemical tracers. Abby Day and Emma Scott Wellman are recent graduates from A&M and Emma is starting as a graduate student. Abby is collecting samples for DNA and looking at the distribution of eukaryotic organisms in surface and deep water, and also specifically monitoring microbial communities in the Clarion-Clipperton Zone, a region of deep-sea mining in the central North Pacific. Emma is filtering and freezing seawater to measure nitrate isotopes, and also measuring silicate as a metric for productivity and tracer of which water mass we’re sampling from.
Principle Investigator (PI) Professor Rene Boiteau is leading a group from the University of Minnesota that is focused on identifying specific dissolved organic molecules and metabolites. These molecules are produced as waste products by some marine algae and bacteria, but they contain important nutrients like nitrogen and phosphorus (one microbe’s trash is another microbe’s treasure). However, some molecules are harder to recycle than others, and the goal of these analyses is to determine if certain metabolites can be transported great distances before they are re-used, representing an important flux of ‘semi-labile’ organic nutrients that could be important for feeding algae in the North Pacific Gyre. The group includes two PhD students: Caini Huang and CJ Denault. To accomplish this, the team filters seawater from the CTD and incubations to separate out the particulates and isolate the dissolved molecules. Then, these molecules are captured using ‘solid phase extraction’, where organic molecules stick to a resin to concentrate them from dilute seawater. Back at the university, Caini will use ultra-high performance liquid chromatography-Orbitrap mass spectrometry (UHPLC-Orbitrap-MS) to determine the composition of molecules and their distributions across the cruise track. Because this method misses some of the more polar metabolites, CJ is also collecting and freezing some smaller samples which will undergo a chemical reaction that makes it easier to capture the missing part using solid phase extraction.
We ended the week with some fun and had a wonderful Fourth of July celebration! The science party celebrated with the ship’s crew over a delicious barbeque, karaoke, and a cornhole tournament (which, unfortunately, no representatives of the 5Cs won). It was so fun to relax with the crew and fellow scientists and get to know each other better!
Next week, we will talk about our experiences as we move into the Pacific Subtropical Gyre. We are expecting to see different patterns of nitrogen consumption and biological productivity as we enter the nutrient deficient waters.