2016.08.10 – Loss of the OBEM at the Mid-Atlantic Ridge…
Our past few days have been a mixture of great excitement, hope and loss. As the British saying goes, “worse things happen at sea”, and there is no doubt that we are definitely at sea. In fact, some of us are well into their 3rd month on Blue Mining ‘cruises’, at 26°N Mid-Atlantic Ridge. Sven (Geomar, and leader of work package 1), Iain and Adeline (both NOC students), Sophia (Uni Lisbon) and Florian (our advisor from IFREMER) were on cruise M127 that left in May and June, and then joined cruise JC138 in early July.
The term ‘cruise’ is a rather unfortunate one as it gives the impression that we are sitting around, sipping cocktails by a swimming pool, being waited on hand and foot, and generally enjoying a life of leisure. How far removed from the truth. Our French colleagues call scientific cruises ‘campaigns’, which is a much better term. Perhaps ‘expedition’ or ‘mission’, or some other word that summons up connotations that are more in line with the heroic efforts that our ‘cruises’ seem to always inevitably entail. Never-the-less, here we are, approaching the last few days of science on our Blue Mining cruise JC138 on the good ship RRS James Cook who’s tenth anniversary is this month.
We have not been idle. The Sputnik team (with a little help from the DASI crew) assembled and launched their 10m square metal detector and surveyed both the MIR zone and the central area of extinct massive sulphide mounds that include the ones we have been diving on with the HyBIS ROV and drilling with the robot drill RD2. The experimental metal detector is called Martemis, apparently after the Greek goddess (Artemis) and Martin Wallatz-Vogt, who spent a lot of time and effort building the instrument at Geomar (Martin, that is, not the goddess). Sebastian (our Sputnik team leader) explains that Atremis was the Geek goddess of chastity, virginity, the hunt, the moon and of the natural environment. So that explains everything…..
The surveys were hampered at first by a loss of both the sub-sea navigation and the instrument’s altimeter data. The former was a result of the ship using its powerful thruster to keep a slow but precise course at the expense of acoustic quiet, while the altimeter got a very clear echo from the 10m loop suspended 12m below the main logging frame.
Near the seafloor, the swell heaved the ship up and down rather rapidly a few times and the logging frame tangled slightly in one of its suspension rope and tilted at 20° to one side. This accident proved fortunate as the altimeter, now looking obliquely sideways, locked on to the seafloor instead of the coil loop, and that solved the first problem. The second bit of luck came as we discovered a way to boost the signal on the ships acoustic navigation transceiver and we were able to get the location of Martemis. The surveys then proceeded as planned and on time.
The trouble with being in the middle of the Atlantic Ocean is that it is a very large place and we are very small. A reminder of just how big it is, and how small we are, came last night when we released an Ocean Bottom Electromagnetic Instrument (OBEM) from the seafloor 3600m below us, and then promptly lost it. How did this happen? The story is simple: we sent an acoustic command to the OBEM, it replied that it had dropped its anchor weight and was ascending. It came to the surface and sent us a radio signal, but its flashing light had failed. Darkness was approaching fast and we spent the next four hours searching in vain. The whole sorry episode served to remind all of us how remote we are, how fickle even the most basic technology can be, and what little chance anyone would have if they fell overboard.
Old fisher folk will tell you that ‘what the sea takes away, she eventually gives back’. While you may think that this only applies to things that float, it also applies to the things that sink. Beneath the sea the things may be ‘out of sight’ for most of us, but its not gone. Hence we have a strict policy of never ever discarding anything over the side apart from food waste (to feed the fish) and only when we are far from shore. Despite this, we sometime have mishaps. As reported in last week’s blog, for us, it was the empty core barrel accidently dropped from RD2. For someone else, it was a right-footed boot. Its really amazing to find such tiny objects on the vastness of the seafloor. Assuming a random distribution and the tiny area we have explored, there must be billions of boots on the deep ocean floor…….
Our early technical trials and tribulations with RD2 are behind us as the robot drill coring deep in to the mineral deposits. We have focused on the newly discovered (Blue Mining) sulphide mound we have called Rona Mound (after the late Peter Rona who spend many years studying the TAG area). The drill has bored three holes in to the mound, each getting deeper. The current hole will be the last, and we aim to log it (with our down-hole logging tools) and then cap it with a ‘packer’ or cork. The cap will allow the fluids and microbes in the hole to re-equilibrate and enable us to revisit to sample the fluids through a titanium pipe and valve with a submarine or ROV during future ‘cruises’.
Once again, Berit is busy at her diamond saw, cutting the rocks ready for describing, sub-sampling and on board analysis. We have two XRF’s on board, and they give us an indication of the composition of the rocks and sediments. With 4 days of science to go, we are pushing very hard to get another site surveyed by our HyBIS ROV, to drop an new LED beacon and drill our first hole into the MIR mound. If all goes to plan, we are able do it. Watch this space.
By Bram Murton, Chief Scientist JC138
Follow: #Bluemining @Bramatsea