Dolphins

We spotted several dolphins. Some of them want back and forth across the UCTD line that trailed from the back for the ship, as did the seabirds that followed the ship’s lights at night.

Where we went

This map of sea surface height (from satellite) and the geostrophic currents shows the large-scale pattern of the flow. There is much more variability at smaller scales that does not show up on this image. The yellow pins are waypoints and outline our ship track, which went back and forth across the front (between less and more dense waters) and where there was a strong jet (of almost 80 cm/s). The streaks are the trajectories of the some of the drifters that were deployed in the early stages of the experiment.

A second drifter array

At night we deployed a second drifter array in a tight configuration (separated by approximately 1km). At each release location, we deployed 4 drifters — one near surface and the others with drogue depths of 10,30,50m. The separation of these drifters in time, would give an estimate of the vertical shear in the flow. The tight array would help capture the effect of small-scale processes.
For the drifters with a 50 m deep drogue, we used a peg-board to unravel the line between the drogue and the surface buoy.

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The night watch: ready to release four drifters at once.
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Releasing the buoy at the end of the cable. The transmitter is tied to the top of this buoy

 

Deploying drifters

On May 31, we were joined by the Spanish research vessel, SOCIB, and both ships jointly deployed a large array of 56 drifters in a formation. Many of them were SVP drifters, which have a large sock-like drogue at 15 m depth and buoy at the surface. There were also shallow CODE/CARTHE drifters – which have their drag elements just about 1 meter below the surface. All drifters have GPS trackers and transmit their location via satellite. By tracking their positions, we can gain information about the currents. In particular, we were looking for times that the drifter cluster would converge. We can watch them in near-realtime on our computers, as their positions evolve.

 

UCTD watch

By repeatedly dropping the CTD and retrieving it while the ship is underway, we are able to gather vertical profiles of temperature and salinity. The drop and retrieve is done with a winch and motor, but needs to be operated by two people. We can gain several profiles per hour, while the ship is steaming. When the ship is going slower, we gain more horizontal resolution. To cover more ground quickly, we would go faster.

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The winch and motor on the back of the ship

Rendezvous with the SOCIB and CTD test

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The SOCIB, as viewed from the Alliance

At the rendezvous point with the SOCIB, the CTD rosette was lowered to a depth of 300m and the bottles fired to collect seawater. This water is then used for various analysis, including oxygen, chlorophyl and DNA

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The CTD rosette is lowered from this arm into the ocean. The SOCIB is also seen taking measurements.
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Mara Freilich prepares the seawater samples for flow cytometry. These samples are then frozen in liquid nitrogen until the analysis can be completed on land.

uCTD and ecoCTD tested

In preparation for the next 24 hours of sampling, watch leaders and all helpers were trained in how to lower and raise the uCTD and ecoCTD. Both instruments are towed behind the boat as they are deployed and retrieved in order to measure salinity and temperature on depth profiles.

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The uCTD as it is being drawn back onto the boat.