OSNAP 2026 expedition: servicing parts of the AMOC monitoring array

By Elodie Duyck

We’ve now been on the RV Neil Armstrong for about a week, and we just reached the Irminger Sea. The Irminger Sea is located east of Greenland, and we will be working in this region for most of the remainder of the expedition. In this blog, I will tell you a little bit more about what we will be doing here in the coming weeks 

We are currently servicing the Ocean Observatory Initiative (OOI) moorings and will soon after be heading to the OSNAP array. OSNAP (for Overturning in the Subpolar North Atlantic Program) is an international research project that aims to better understand and measure changes of the Atlantic Meridional Overturning Circulation (AMOC) in the subpolar region. The OSNAP mooring array extends from the Canadian to the Scottish coast via Greenland, and is composed of about 50 moorings, that have been taking measurements since 2014. 

Anchored instruments in the ocean current

So… what are moorings? Moorings are cables that are anchored to the bottom of the ocean, and are maintained vertical thanks to flotation buoys. They can be up to a few kilometers deep! Along this cable, we attach instruments that measure water properties at given depths. We are most interested in the temperature, salinity, and pressure of the waters, as well as its velocity. For instance, one of the instruments we use in our moorings is an Acoustic Doppler Current Profiler (ADCP), which can measure the velocity of the water in a range of 500m. Another instrument is the Microcat, which we use to measure the temperature and the salinity of sea water. The instruments that are mounted on the cable store data locally. This means that to obtain the data recorded by each instrument, we need to bring them out of the water with a ship. 

Data collection, calibrating, servicing and redeploying

Every two years, OSNAP-scientists therefore go to sea to collect data from the instruments at each mooring location. We release the mooring from its anchor, bring it on deck, download data from all of the instruments, calibrate them, change batteries, exchange old instruments, and finally redeploy the mooring. This is a complex process that can take up to two days for each mooring. In addition to working on the mooring and the instruments, we also make full depth measurements of the water column (called “profiles”). These are used to calibrate the mooring data, and to obtain high-resolution observations of the properties of seawater along the mooring array. We’ll write more about all of this in the coming weeks.

On this expedition, we will be servicing the 11 OSNAP moorings that are located on the mid-atlantic ridge: 5 from NIOZ on the western side of the ridge (the Irminger Sea), and 6 from our US colleagues on the eastern side of the ridge (the Iceland basin). During the summer, other ships will be doing the same in other parts of the OSNAP array. The data we will be collecting this year will allow to build a 12-years timeseries of ocean currents and variability in the subpolar region. This will help to get a better understanding of how changes in this region affect the AMOC. We’ll send updates throughout the expedition to tell you more about the mooring deployment process, the instruments we use, but also our life onboard a research ship. 

What does a mooring look like?

Below, a schematic depiction of one of the NIOZ moorings we will be recovering and redeploying, alongside with photos of all the different parts of the mooring. The photos show flotation buoys, different instruments that are attached to the mooring cable, including an ADCP and Microcats, as well as the mooring anchor. Photos by Nora Fried and Elodie Duyck