Finding long lost buoys (not pronouced like boys) !

So we are still bobbing around the North Atlantic nearer to Greenland now...almost heading back home via Iceland! The Google Earth image above shows all of the mooring and CTD stations that we are completing along the OSNAP E transect! You can see our position tracking on the Marine Traffic website: https://www.marinetraffic.com/ais/details/ships/9688946

Here is the position of the mooring buoys south of Iceland. Firstly we sampled within Rockall Trough, which is near Scotland, then we scooted over to the Icelandic Basin followed by the western Irminger Basin, and we are now working our way back to Reykjavik. 

Why are we here? WHOI (Woods Hole Oceanographic Institute) explains: ''The vast interface of ocean and atmosphere constitutes one of the Earth’s great interactive engines. The OSNAP program is investing the upper-ocean and atmospheric processes and their influences on one another.'' The mooring buoys that we are deploying are aiding in researching this.

No wildlife for most of the trip, so at least the sun and clouds are giving us something to look at!


This diagram from the OSNAP website (http://www.o-snap.org/) explains the parts of the oceanographic circulation system that we are trying to capture and analyze, trying to figure out how they are changing and in turn changing our climate. Below is just how we plan to do that and have been doing for the past few years.

As part of this program we have chucked a few ARGO floats over the side that over the next few years will bob around the ocean mapping all of the surface currents by measuring their salinity and temperature. These subsurface floats will trace the pathways of overflow waters in the basin to assess the connectivity of currents crossing the OSNAP line.

The main discussion on this blog post is about sub-surface moorings. There are various types of moorings that can be categorized as surface-based, sub-surface, or bottom-mounted. This cruise is centered around retrieving and then redeploying an array of sub-surface moorings. This cruise is part of the OSNAP (Overturning in the Subpolar North Atlantic Program) program, which is ''is an international program designed to provide a continuous record of the full-water column, trans-basin fluxes of heat, mass and freshwater in the subpolar North Atlantic. The OSNAP observing system consists of two legs: one extending from southern Labrador to the southwestern tip of Greenland across the mouth of the Labrador Sea (OSNAP West), and the second from the southeastern tip of Greenland to Scotland (OSNAP East). 

 

So on to the mooring deployment. Here is the mooring diagram of one of the moorings in the Irminger Current, which is used to deploy and retrieve each mooring. You can see the aforementioned ADCP in the orange buoy at around 500m depth. To record temperature and salinity, multiple Microcats are attached to the cable. This is a Seabird instrument that records temperature, depth and salinity - basically, a small CTD; it has a specific serial number to keep track of which instrument recorded which data - very important for calibration of the instrument! Prior to deployment, each Microcat is attached to the CTD so that it can be calibrated against the CTD rosette data, to pressure test it, to check the accuracy of the measurements and to ensure that the data is being recorded correctly. The instrument will then be set up to record at a certain time so that it starts to collect data as soon as it is attached to the wire and deployed at a certain depth (in two years time it will then be collected and the data recorded..a lithium battery ensures power for that length of time)!
 
All instruments on the mooring are deployed in a particular order with specific depth allocations.

 
These subsurface buoys (near the surface) hold the wire up straight within the water column; hence keeping the tension of the wire taut.
 
The wire is measured out and along it mooring buoys are attached and then at regular intervals different instruments are placed along the wire: mostly Microcats and current meters.
 
 So much money sat on this table ^^






 One of the main instruments attached to the center of the big orange buoys are ADCPs (Acoustic Doppler Current Profilers). These diagrams explain how this data is collected. By using a Doppler shift of backscattered sound pulses, the ADCP maps the particulates floating through the water column and works out the current direction and speed.
 




 
Another way this is used in the marine industry is to work out where the bottom of the sea bed is.







At the bottom a big weight, the anchor, is attached to the end of the wire: this is deployed last and pulls the long system down through the water column.


My favorite fact about these weights are that they are actually recycled..can you guess what these are? They are actually old train wheels welded together...the only bad thing that they are never retrieved so there are thousands of weights left on the seafloor from these deployments. The only good thing I can see from it is that they make a good substrate for biology to grow on...!

So if everything has gone well - such as the wire has been measured out correctly, the boat is positioned at the correct place and has been slowly steaming towards the drop-off point in order to keep the wire taut - then the system should end up like this:

It's been sunny for a few days here and there...weirdly when we were closest to Scotland! I did ask them to drop me off as we were very close to the Island of Pabbay (which I'm visiting in a few weeks) but they just laughed! 

Then, when the mooring has been deployed, we need to know exactly where it is as in order to pick it up again in two years time. To do this we complete a trilateration, which as it's name suggests is a position determination using three different points. From the ship, we send out a ping to the acoustic releases attached to the bottom of the mooring, just above the anchor. When the release hears this ping, it will send a ping back; using the velocity of sound in water and the time it takes to receive the returning ping, the on-board instrumentation works out the distance from the ship to the release. We repeat this procedure at three locations within a triangle around where the anchor was dropped, enabling us to work out the exact final location and depth of the mooring. We then hope that everything was calculated correctly, and the mooring is not too shallow or too deep or too far away from the target position.... quite an operation!

When it's time to retrieve a mooring that has been busy collecting oceanographic data for the last two years, we also use the acoustic releases. Each release has a unique individual 'release code'. The ship pings the release by using this individual special high-frequency acoustic signal, which causes a small pin to pull back and release the mooring. So then it is all eyes on deck to see where it will (hopefully) surface, hopefully near the position where it was trilaterated the 2 years prior. There are two acoustic releases should one fail.

 

Everyone eagerly looks out...

It's then a game of hooking the line and attaching this to the back of the ship so that the winch can slowly bring it in.

 

After two years and being a good substrate within the water column life grows. 

Jeanne and I have been sampling molluscs and anemones off the buoys for Winnie back at SAMs to see the effects that microplastics are having on these animals.

Here Bill's students watch him hose down the mooring buoy ready for deployment! This is the OSNAP blog..you can read from our PSO Bill Johns who's from Miami about what's been happening the last few weeks in his summary: http://www.o-snap.org/news-events/blog/ Another good explanation of this through photos can be found here: http://staff.washington.edu/dushaw/mooring/


Moving on from the ASSASIN game which was genuinely enjoyed by all we have moved onto a cribbage tournament..before I play I need to learn the rules...!

To put what we are doing into context here is a NERC podcast by SAM's very own Estelle and Stuart: https://nerc.ukri.org/planetearth/stories/1549/



To finish here are some scientific research papers that highlight the key findings of what these particular mooring buoys can tell us (Click on the links to have a read):

Holliday, N.P., S. Bacon, S.A. Cunningham, S.F. Gary, J. Karstensen, B.A. King, F. Li, and E.L. McDonagh, 2018. Subpolar North Atlantic Overturning and Gyre-scale Circulation in the Summers of 2014 and 2016. J. Geophys. Res. Oceans, 123, doi: 10.1029/2018JC013841.

Li, F. and M.S. Lozier, 2018. On the linkage between Labrador Sea Water volume and overturning circulation in the Labrador Sea: a case study on proxies.  Journal of Climate, 31, 5225–5241, doi: 10.1175/JCLI-D-17-0692.1.

Lozier, M.S., S. Bacon, A.S. Bower, S.A. Cunningham, M.F. de Jong, L. de Steur, B. deYoung, J. Fischer, S.F. Gary, B.J.W. Greenan, P. Heimbach, N.P. Holliday, L. Houpert, M.E. Inall, W.E. Johns, H.L. Johnson, J. Karstensen, F. Li, X. Lin, N. Mackay, D. P. Marshall, H. Mercier, P.G. Myers, R. S. Pickart, H.R. Pillar, F. Straneo, V. Thierry, R.A. Weller, R.G. Williams, C. Wilson, J. Yang, J. Zhao, and J.D. Zika, 2017. Overturning in the Subpolar North Atlantic Program: a new international ocean observing system. Bulletin of the American Meteorological Society, 98, 737-752, doi: http://dx.doi.org/10.1175/BAMS-D-16-0057.1

Zou, S., M.S. Lozier, W. Zenk, A. Bower, W. Johns, 2017. Observed and modeled pathways of the Iceland Scotland Overflow Water in the eastern North Atlantic, Progress in Oceanography, 159 (221-222), doi: 10.1016/j.pocean.2017.10.003