Salinity Intrusions, Rings, AUVs, Turbulence and Squid (SIRATES)

Today we sample a 40x40km area east of our home base along the 71°W longitude line. With CTD casts we want to get a first overview about the extent of a 2^nd intrusion area. While steaming to our next station, let’s take the time to feature our underwater robots of the REMUS family. We have 3 Remus-100’s with us on board the Armstrong, Darter, Edgar, and Sellers. These vehicles have a depth rating of 100 meters.

How do the REMUS missions work?

The vehicles communicate differently when at the surface and while underwater. At the surface, they’re use Wifi, make satellite phone calls, and get GPS coordinates from satellite. However, none of these systems work underwater and signals between the ship and the REMUS get transferred acoustically.

The vehicles are equipped with a variety of instruments to measure temperature, salinity, nitrate, dissolved organic matter, water velocity, and many variables more. In addition, we can make videos with a GoPro. Depending on the mission, the instrumentation can be adapted.

How does the AUV-Team’s day look like:

After a daily discussion with the science team, our AUV-Team (Amy, Noa, and Maaya) choose the best suited Remus for the day’s mission data goals and prepare the vehicle for deployment. A so-called Towfish, the 25kHz transducer used to acoustically communicate with the vehicles, is secured to the boat railing and lowered into the water prior to deployment. Once the vehicle is in the water and communications between us and the vehicle are established, we send the vehicle on its mission and stay within acoustic range until it’s time for recovery.

For more information on the AUV’s and the SciBotics team head to their website linked here.

Today had its ups and downs… 98 ups and downs to be precise: The VMP samples the water column like a yo-yo: Up and down… When releasing it, it falls down with a constant velocity and measures salinity, turbulent mixing, and many other variables. Then, we recover it with a motorized deep-sea fishing reel. One cast takes about 3min which allows great spatial resolution. Check out our salinity transact below.

Alone on the ocean? No! We regularly get visited by lots of lovely animal friends. Check out our naturalist corner for some pictures (accessible at the top of the page just beneath the banner/title).

 

Thanks to our AUVs we can sample at two locations at the same time. Yesterday  we released AUV Polaris that will sample a pre-defined box throughout the next couple of days. Every time it surfaces, its position and data will be transferred via satellite. You can follow Polaris’s progress on the site linked here.

Hurricane Claudette seems to pass us further south than originally expected. Thus, we did not need to seek shelter close to Martha’s Vineyard and were able to stay close to the intrusions. …

And we had our first squid-sighting! While taking evening CTDs close to the nose of the intrusion the squid were drawn in by the ship’s lights.

Everything must come to an end… even an intrusion that comes onto the shelf and travels northward into fresher shelf waters. In order to estimate how the intrusions spreads, it is very important to sample the whole nose with high resolution.

This morning AUV Edgar found a nose. That means it’s time for our high-resolution instrument: The Vertical Microstructure Profiler (VMP). The delicate probes at the end of the 5ft-long instrument are smaller than a millimeter and measure over 500-times per second. This allows to estimate turbulence and mixing which could bring up nutrients further to the surface. When passing the nose, we saw a ton of jellyfish. Squids haven’t made it onto our AUV cameras, yet.

tl;dr: The VMP – today’s MVP!

After an exciting start into the cruise today’s focus is on our Autonomous Underwater Vehicles (AUVs). These underwater-robots transact the water column in a zick-zack pattern, and provide us with a large variety of data, including videos from an upward-looking camera (stay tuned). Since our CTD-casts from yesterday revealed strong spatial variability on scales larger than 5nm, we hope that the AUVs fills in the gaps on smaller scales.

Wow! Nobody of us had imagined that we will find a salinity intrusion that fast. But already in the afternoon (and with around 80m of water below out feet) the excitement on the science deck was unbounded: We found not just ONE intrusion, but TWO.

… heading further south now to check from where it might have come onshore.

After a year of delays the SIRATES finally set sail! We’re all excited and am looking forward to sharing our impressions from out of sea.

The trip started with with a three hour journey from Woods Hole to our first CTD station. A CTD is an oceanographic sensor system that measures the conductivity, temperature and depth throughout the water column.  This allows oceanographers to study the composition of the different interacting layers. The plan is to do nine profiles from  41°N, 71°W going southward.

But first, who are we on board? Here is a picture of us:

Since it is the Salinity Intrusion Experiment, it is a good time to show what the intrusion looks like.

Here is an example of a salinity intrusion from our Chief Scientist Glen Gawarkiewicz, WHOI. This is what an intrusion looks like in a vertical profile.