SEA Currents: Robert C. Seamans
May 12, 2020
No need to fear, autonomous data collection is here!
14 degrees 22.1’ N 147 degrees 06.0’ W
Ship’s Heading & Speed
300T, 6.8 knots
Days Underway and Trip Log
Day 34, 5226 nm
Sunny and 25.5 degrees C with winds out of the NExE force 5. Sailing on a starboard reach under the four lowers, tops’l and JT with a shallow reefed mains’l.
Description of Location
532 nm SExE of Cape Kuma Kahi Light, Hawai’i Island, Hawai’i
These days, our global demand for science is apparent. We sit on the edge of our seat awaiting the results of the newest coronavirus treatments, relying heavily on scientists working worldwide to provide hope for our future. This is the short-game - we're in the weeds and need a solution yesterday.
In oceanography, we're playing the long game. We've heard Earth scientists' and policy makers' reports of projections for Earth's climate dependent on our past and future choices, and I could talk about how overwhelming those reports are, or how we're not doing enough to reduce our global impact. But I think we are all already stressed enough about the state of our world right now, eh?
So instead I'd like to talk about what we, the crew on the Robert C. Seamans, are doing. We're out in the middle of the Pacific, while the whole University National Oceanographic Laboratory System (UNOLS) research fleet is docked, and we're collecting data! Because we're on a schedule, we can't stop for deployments like we would on a normal SEA cruise, but we have other options. For one, our flow-through seawater system collects data points on the salinity, temperature, colored dissolved organic matter (CDOM) content, chloraphyll-a content, and turbidity of the surface water for every minute that we transit through international or US waters.
We are also helping contribute to the largest subsurface ocean sampling mission - the ARGO Float Project - an array of thousands of autonomous underwater vehicles dispersed across the global oceans. Ideally, this array is evenly distributed with about one float per three degrees latitude/longitude, but in reality, floats consolidate in some areas and are absent in others. Over the past four days we have been able to deploy three ARGO floats (provided by the Scripps Institution of Oceanography) into two of these gaps along our transit.
These floats will spend most of their lifespan drifting with the ocean currents at their neutrally buoyant depth of 1km below the ocean surface. Every nine days of drifting, they will change their buoyancy by pumping hydraulic oil from an external bladder to an internal reservoir to increase their density and descend to a maximum depth of 2 km before turning around and beginning their ascent to the surface. Along their ascent, they will collect conductivity (salinity), pressure (depth), and temperature data from the top 2 km of the water column. The floats will then transmit their location and vertical profile via communication satellites back to land where the data is made available to the scientific community and the public within 24 hours of transmittance. Floats complete about 100-150 profiles over the course of their battery life.
This temperature and salinity, and inferred current data (interpolated from each position of data transmittance) is essential to our numerical models (important for future climate predictions, seasonal weather forecasts, and informing our understanding of air-sea interactions during tropical storms), aids our understanding heat storage in the ocean (vital for our future climate and sea-level predictions), and is the basis for mapping large-scale average oceanic flow. The platform of autonomous data collection in the ARGO Float Program has made available an enormous volume of data which would have otherwise been impossible to collect through other classic oceanographic sampling methods such as satellites (which can only sample the surface ocean) and research ships (with high operational costs, slow speeds, and limited data supply vs. demand).
So, even while our research vessels are docked, causing the rescheduling of research cruises planned years in advance, our autonomous sampling instruments - ARGO floats, satellites, and more - are still chugging along, measuring our world.
- Ella Cedarholm, Assistant Scientist, C Watch
Editor's Note: In response to the coronavirus pandemic, all SEA Semester students departed our ships on or before March 18, with modifications made to the cruise tracks to ensure swift travel home. A small, dedicated professional crew aboard the SSV Robert C. Seamans is working in a closed community to return the ship to US waters. The crew complied with New Zealand's 14 day self-isolation period to establish & maintain crew health prior to departing on their open ocean passage.