After deploying a bunch of drifters on Monday morning, we also deployed two Lagrangian floats. These floats are designed to sink and drift along with water of a particular density. If water was being subducted along the front in the past two days, we hope that these floats went along for the ride! Today we retrieved them to download their data.
After sunrise we did more surveying to find a good location for an array of 48 drifters. We deployed this sequence of drifters along a transect to look at the flow of water at a series of depths. The drifters have different length cables so that the drogues (also known as “holey socks” because of their appearances), which pull them along, will be following the water at different depths. These drifters are special because they are mostly biodegradable, using canvas for the drogues and copper balls for floats instead of plastic. Even though studying the ocean is important, that doesn’t mean scientists get a free pass on ocean plastic pollution! And, of course, we do retrieve some of the things we deploy! It took a big team effort to deploy all of the drifters in a short time! Nearly all of the scientific staff and many crew members participated in this! This drifter experiment was designed by Irina Rypina and Ben Hodges at WHOI.
Today is a very busy day with a lot of deployments of different types of equipment. Before daybreak we deployed a wirewalker, an instrument that moves with the currents while profiling up and down to observe the upper water column. Its up and down motion is powered by the waves! It measures the flow velocity as well as the temperature, salinity, and biological variables. We hope that this will complement our many surveys by showing us how the properties of the flow evolve as we follow the front.
Yesterday and today, we’ve been experiencing relatively high winds, at least for the Mediterranean — around 20 knots most of the time and occasionally up to 40 knots! This has limited our ability to deploy and retrieve floats and drifters, but we’ve kept up with the UCTD and EcoCTD as much as possible, and CTDs and water sampling continue regardless of the weather! Tomorrow we’re heading west, where the waves are a bit smaller and we’ll be able to deploy more of the instruments that need recovery, such as the wirewalker and the Lagrangian floats.
This afternoon, we tested out the V-wing, an instrument that we tow behind the ship. The V-wing is built so that it dives deeper into the water column as the ship moves faster. This means we can control the depth at which the V-wing takes measurements by moving the ship faster or slower, or by changing the length of the cable that attaches the V-wing to the ship. The V-wing has an ADCP to measure current velocities, and we can also add instruments to the tow chain such as a CTD.
This morning we took a tour of the engine room and saw the multitude of important machines that keep the ship running. We learned that the ship uses diesel generators to power electric engines. This sacrifices some efficiency but lets us change direction quickly, which we need for scientific research! We also saw some very large ropes and cables.
Microstructure profiles from the N/O Pourquoi Pas? are done! This instrument, operated by Francesco Falcieri coming from an Italian Institute based in Venice (CNR-ISMAR), will be moved onto the RV SOCIB during our port call in Almeria on April 3rd.
The profiler free-falls vertically through the water column to measure very small vibrations at scales of centimetres. Scientists used those measurements to infer turbulence activity in the ocean that mixes water irreversibly. But the profiler also measures other variables, such as temperature, conductivity, turbidity and fluorescence. We collected 43 profiles over this first week – with more to come from the RV SOCIB!
Today we recovered an OGS ADCP drifter after releasing it yesterday morning. This drifter moves with the currents, measuring current velocities along the way to give us more information about how the water is moving in this area. Since the Pourquoi Pas? is so large, the crew lowered a zodiac over the side using the crane so Pierre and 3 crew members could retrieve the drifter.
Using a crane to lower the zodiac over the side
Pulling the drifter from the water
A nice view of the Pourquoi Pas? from the zodiac