SEA Currents: Robert C. Seamans
April 14, 2017
We Sail For Science
39° 28.2’S x 157°53.2’W
Sailing on a starboard tack under the four lowers. Wind ExN force 5, seas SExS 7 ft. 7/8 stratocumulus cloud cover. 15.0°C
The wind has filled in the past couple days and we have been able to sail full and bye (as close to the wind as possible) to make our way north and east to Tahiti. It has been wonderful to sail again, the endless thrum of the motor replaced with the hum of the wind as it blows through the rigging.
Yesterday, the students wrapped up their creature features with a presentation on Hyperiid Amphipods during class. Také and Romina presented on amphipod’s parasitic relationship to salps to the tune of “Your Welcome” from Moana.
The past week and a half we have gotten back into the regular swing of things in the world of science. Students have been busy working on diagrams of science deployments and turned in these assignments this afternoon. Hold on, let me back up. Science? Deployments? Yup. If you haven’t caught on yet we sail (or more accurately, stop sailing) for science, twice a day, for what we call “morning” and “evening station.” Every day, weather permitting, we will heave to on a port tack (position the ship perpendicular to the wind with the sails backed so we drift slowly down wind in a falling leaf-like motion) for morning station and again in the evening or just slow to a speed of 2 kts depending what’s on the docket for evening station.
Maneuvering the ship to get into the proper position for science at the right time requires collaboration and communication between lab and deck. Morning station usually begins with a 9:30 “splash time”(the time we hope to get the gear in the water) and consists of a phytoplankton net, a Secchi disc (used to calculate the depth of 1% light level) followed by a carousel deployment. The carousel holds a CTD (measures conductivity, temperature, and depth), a fluorometer, an oxygen sensor, and 12 Niskin bottles programed to close at different depths. We usually deploy the CTD to a depth of about 1000 meters. During this time we get a couple buckets of water from the surface of the ocean and collect samples to analyze them for chlorophyll-a, pH, alkalinity, pH, nutrients (NO3, PO4), and microplastics.
Once the carousel is back on deck and stowed we get the ship up to a speed of 2 kts for my personal favorite, the Neuston tow. The Neuston is the air/sea interface, and the net is designed to sample the uppermost layer of the water. A plastic bottle captures the things that are too big to float through the mesh of the net, the stuff we want to look at: zooplankton! Evening station (approximately 2330) usually just consists of a Neuston tow and surface station. On a few select nights we will also do a meter net deployment – a large net (1 meter in diameter) that is towed at depth on the wire. This makes for an exciting time because wire deployment + moving ship can be sketchy…so far we have only done one. Rumor is we will do one tonight!
We gather all this information, which means that it all needs to be processed! pH, alkalinity, and net tows are processed on watch. Chlorophyll-a samples are filtered and frozen to be processed in a large batch later. NO3 and PO4 samples are frozen and also processed in a large batch. Right now, the scientists are working on the somewhat stressful and intense process of using precise chemistry to process PO4 samples on a
My favorite thing to process is the Neuston tow. You get to see everything that was collected in the net and conduct a 100-count under the dissecting scope. We count 100 organisms, recording what they are as we go along to get a better understanding of what’s hanging out in the Neuston layer. There are usually lots of copepods and other fun zooplankton to look at. My favorites are small blue siphonophores called Porpita porpita. They look like small blue sunbursts!
Why do all this work? These deployments and samples help us better understand how the physical, chemical, and biological oceanography of the ocean changes as we sail through a transition zone from temperate to
tropical waters through oceans that haven’t been studied a whole lot. Last night around 22:30, C-Watch deployed an Argo Float: a device that floats on the surface of the ocean and goes up and down the water column, gathering the same data we collect with our CTD. It then transmits this data to a satellite. Scientists all over the world have access to this data currently being collected by 3,000+ Argo floats that have been deployed.
So why sail? Because the experience of learning something new, how to work together as a group, on a boat in the middle of the ocean where all that matters is the task at hand, the people you are with, and the 7 mile radius of ocean you can see is irreplaceable. What can I say? I can’t help but keep coming back,