Last Saturday we spent some time trying to find a missing item. It was a surface buoy of a mooring, used to transfer data from the instruments on the mooring to shore using a satellite connection. It’s not a big buoy, but we have an accurate position of where it should be.

So starting at 7 am, we searched for the buoy. There were some waves but the visibility was excellent. We were on the lookout for a yellow buoy, possibly a green buoy (as “biology” often grows on surface objects) or just a bunch of seagull sitting on something. We did see two whales, but no buoy.

The buoy has some ability to move around, as it’s connected to the top of the mooring by a long line. The captain started a search pattern to cover this region. The sailed lines back and forth about two ship lengths (120 m) apart. Since we could easily see whales and seagulls about 500 m away we were slowly getting worried that we may not find this buoy, no matter how hard we tried.

In fact, the reason why we were there is that the buoy’s owners hadn’t heard from it for a while. It stopped sending data sometime in February. Usually this means that the buoy is there, but that the electronic have given up. Water might have gotten in and shorted the batteries. That is why we brought a replacement for it, which we were going to swop out for the broken buoy. But we were starting to suspect it may be gone altogether.

To be sure we weren’t looking in the wrong spot we “pinged” the mooring it was supposed to be attached to. Using an acoustic transducer we can query the releases attached to the anchor of the mooring and see how far away from us they are. If the distance is much more than the water depth we would be in the wrong spot, but we clearly weren’t. Three queries along the perimeter of the search circle told us the mooring was exactly in the middle of it. At least that was good news, the mooring is still there and likely all the instruments are too.

The next day we found a possible explanation for what happened to the buoy. The data from a nearby mooring showed that the top of that mooring had been “blown down” by strong ocean currents during winter. You can imagine it to be similar to a tree bending over in strong winds. During these blow down events the top of the mooring is much deeper and these higher pressures are recorded by the instruments. This year the top instrument showed it had been blown down much deeper then usual, down to 1000 m depth. The current meters in the mooring also recorded strong flow during this time. We had already been told by the Icelanders that it had been a cold and windy winter. They weren’t exaggerating! We’re not too surprised that a small surface buoy dragged down into the deep didn’t survive.

p.s. There is one alternate explanation going around on the ship and that is that one of whales was sitting on it. It was suspiciously close to the middle of the circle…