Monday, November 2, 2009
Lat: 18° 21’N Long: 081° 51’W
Water depth: ~2500m
At times like this, when time is closing in on us, working out how to make use of the last few days of the cruise can prove quite tricky. Last night we finally got a good dive to the seafloor. Trouble is, the seafloor wasn’t quite so good to us. We landed on piles of lava with varying amounts of sediment and for the entire dive that is pretty much what we saw, everywhere, all the way up one side of the hill we had targeted (although we didn’t stop to look too closely, anticipating there were vents up the top) and all the way back down the other side. At around 6am it was time call things quits and bring Nereus back home. So what to do next?
Looking ahead we came up with a range of plans: (a) go back down and survey the other half of the same hill more thoroughly in the hope that it would be more rewarding than last night’s dive; (b) pursue a different set of plume signals from Leg 1 that were not so strong but might be easier to locate on the seafloor; (c) drive up a long-lived fault half-way down the ridge where hydrothermally altered rocks had previously been located or (d) dive to the top of that same shallow hill based on a hunch that the high concentrations of dissolved methane that we found at shallow depths in the southern half of the ridge on Leg 1 might be coming from their summit.
To follow up on the latter idea we conducted two more CTD stations this afternoon just off the top of that large feature (termed a detachment fault or, more poetically, a Mega-Mullion) which showed up both in the dissolved methane concentrations Jill & Jeff measured as in Ko-ichi’s Eh electrode sensor data. Gambling that we may have tracked those signals down to one of two shallow hills atop the very summit, that is what we’re going after in Nereus dive 26 tonight.
Not least in our minds when reaching this decision is the news that our good weather window may already be up – so diving to a target at 2100m rather than ~5000m means we may at least manage to get one more good complete dive in before weather issues mean we have to call Nereus back. Sad to think this might be our last Nereus dive, just a day after we got our first good one in ROV mode, but as I suspect I mentioned more than once in Leg 1, sometimes at sea you just have to accept what Nature provides and do the best you can with it.
Given that we came out of Florida 4 weeks ago not knowing if there would even be evidence of active venting anywhere on the Mid-Cayman Rise, I guess it would be churlish to do anything else but be happy with what we have already achieved, scientifically. And the fact that we successfully drove a deep diving submersible around for something like 10 hours yesterday at the bottom of a very deep ocean, from the back of a rather small research ship, is something that should make both our Nereus engineers and the Cape Hatteras crew very proud – if that doesn’t set some kind of new world record, I would be very surprised.
Our last bot of news for today is that we had more cruise members set off for home. Our friends from National Geographic TV had sailed down to meet up with us over the weekend but this morning, right after Nereus was on deck, it was time for them – plus our science colleagues Cindy and Julie S – to depart back to shore: don’t worry, they left Katy from the NatGeo team with us in case we do yet make that final “Eureka” breakthrough before the week is out.
What I have to start facing up to, however, is the worst case possibility that, having overcome the concerns that maybe we would have NO hydrothermal signals to pursue in Leg 2 we would, instead, have a multitude of interesting potential targets and yet still not get the opportunity to follow any one of them all the way back to their source at the seabed.