It was a Dark and Stormy Night
It’s dark, humid, and the seas are threatening to wash over the deck at any moment. It doesn’t matter, we are already a bit wet, and there is still work to be done.
Nancy Prouty and I were sitting on upside down buckets on the port side of the NOAA Ship Nancy Foster, near the CTD (a device that samples water at different depths) waiting for the last collecting bottles (called Niskins) to finish filtering. We were using a set-up that allowed us to filter six bottles at a time through an in-line filter system to collect trace minerals to minimize contamination. A pump sucked the water through the filters, and the goal was to get all 5 liters per bottle filtered, a process that was taking longer than expected. This led to lots of questions, ranging from “I wonder why bottle 4 took so much longer than bottle 5?” and “Is there an airlock in this tube” and of course ”Wonder what kind of ice cream is in the freezer?”
Nancy works for the United State Geological Survey (USGS) in Santa Cruz, CA as a research oceanographer. She is on this mission to describe the chemical characteristics in the water column and particles to ultimately advance her and colleague Brendan Roark (Texas A&M) studies in using corals as recorders of past climate and environmental variability.
We performed 4 CTDs over the course of the day. The seas were too rough to launch and recover the ROV. (For more information about the basics of CTDs check out “CTD 101:Remote Sensing Basics” by Eric Hanneman). After launching off the port side, the CTD descends to the bottom fairly smoothly, and then ascends, stopping at specific locations to collect and trap water. Nancy is collecting samples for four different measurements; these include neodymium, carbon and oxygen isotopes of the seawater, and trace metal composition of the particles in the water. These measurements will lead to a better understanding of what physical and chemical processes are influencing the environment where the corals live.
It was searching for these trace minerals that had us on the deck in the dark, looking for bubbles in the tubes that indicate a Niskin bottle is empty and the filtration is finished. The first time we did filtration the initial six bottles took nearly an hour and a half to filter, and the final six took about forty minutes. We deployed the final CTD of the night about sunset, but waited to process the samples until the Lander (see “Collecting Sediments and Marine Snow” by Eric Hanneman for background on the Lander) was nearly launched. We had to contend with rough seas and the impatience that begins to set in after working fairly consistently for more than 14 hours, and knowing that there are a few more ahead before you can call it a night.
However sitting there, waiting and watching the pump pressure, we noticed some patterns and came up with some questions. In general it appears that the water collected from closer to the bottom took longer to filter, while the water collected towards the top of the water column filtered faster. If we get a chance to filter tonight, we plan to keep a record of the length of time each bottle takes to see if our hypothesis is correct. That, and eat our ice cream before we head out.