Saturday, 14 November 2015

Mid-Atlantic Ridge Moorings Completed

We are now effectively two-thirds of the way through the cruise with the last of our moorings on the Mid-Atlantic Ridge recovered and redeployed yesterday. The bathymetry around the ridge poses some challenges to find relatively flat sites of the right depth for the mooring designs. Luckily for us though we have covered these sites many times over the last decade so have very good knowledge of the varying depths for these areas. But essentially we can just deploy the replacement mooring back where we recovered the previous one from (unless we were unable to recover the mooring, which does sometimes happen).

Looking at the swath survey data of these regions now it’s amazing that we managed to find suitable sites back on the original deployment cruise in 2004. On the Discovery of then (see yesterday’s blog post) we only had a single beam echosounder to give us a measurement of the depth in a thin line along the ship’s track. Swath echosounder data gives us a much wider sweep (or swath!) of data so we can see more of the seabed to the sides of the ship track, and on previous cruises we have conducted more comprehensive surveys to build a larger map.

The bathymetry around our MAR3 mooring site. For reference this plot covers an area approximately 10 by 15 miles.
The depth is critical for some of our moorings. Our mooring at the MAR1 site is our longest and covers from 5150m deep to 50m below the surface. As a comparison a 1% error in the wire lengths would put the top of the mooring on the surface where it would be at increased risk from wave motion and passing shipping. A difference of 50m is also considerably less than some of the variations in height that we see on the seabed around our Mid-Atlantic Ridge moorings. So it’s good that we know what to expect at these sites now!

One of my favourite representations of the scale of depth that we are dealing with is shown in the picture below comparing the height of our MAR1 mooring with some well-known buildings.

Our tallest mooring shown against some famous buildings for scale

So now we have a few days until we get to our next mooring site at 70°W. A lot of eyes have been looking over the weather forecasts over the last few days as it at one point seemed that we were going to be facing a bit of a storm as we got to the WB6 site, but the current forecast predicts that this won’t be anywhere near as bad as first thought.

No comments:

Post a Comment