Thursday, November 5, 2009
Down to the wire
Position at 11h30 EDT – CTD 56
Lat: 18° 32’N Long: 081° 44’W
Water depth: ~4850m
Funny how fast things can change at sea. We finally got the CTD working again last night after about 8 hours becalmed in vent-infested waters and have made out like bandits ever since. Actually that’s not quite exactly true. Due to a slight miscommunication error we ran a 6 hour tow-yo between suppertime and midnight last night that didn’t go right through our strongest plumes from earlier in the cruise as planned but, instead, flew past about 400m to the south and measured nothing, all the way. So we have the southern limits to where the vents can be REALLY well constrained now. Overnight we sailed back to our shallow site about 15 miles SW of here and lowered the CTD just before breakfast. The in situ sensor data didn’t look specially promising there , either, but we collected samples from each 50m up above the seafloor anyway and were duly rewarded for our persistence. Jeff and Jill measured the highest dissolved methane concentrations of the trip – by about a factor of two – in their samples from that cast and so we also collected samples for everything else we came equipped to sample for: metals, helium isotopes and microbial studies. Not bad for an early morning shift.
This afternoon the work got even better. We lined our CTD tow-yo run back up (in the correct position, this time) and ran a line that went right over the vent-site. The 30 minutes when we were right in the core of the plume not only coincide with our two previous strongest sets of anomalies (1 each from Leg 1 and Leg 2) but also coincide with when we were passing directly over a small semicircular feature that is about 200m across and 20m high, sticking out from the base of a volcanic cliff. How do we know it is sticking out from a volcanic cliff? Because it is the SAME cliff that we dived on with Nereus last weekend! Honestly – we were within 200m of the vents, twice, earlier in the cruise: on our last dive with Nereus in AUV mode on Leg 1 and our first proper dive in ROV mode earlier in Leg 2. Unfortunately, being 200m off still counts as a long way away when your mapping device can only see 40m to a side and your cameras can only see 10m or less in any direction. Call that a swing and a miss.
But there’s no point feeling sorry for ourselves and wondering “what if?”. This evening we are lowering the CTD back down, right over the site, in the hope of collecting another complete set of great samples, just like we collected at the shallow site this morning. And we’re also keeping a close eye on the weather. Our forecasts continue to be grim but this afternoon the winds have been below 15 knots when they were predicted to be closer to 20 and the waves were definitely lower than yesterday. If things continued in that trend we could still be in with a shout. Trouble is, that is NOT what is predicted and its no good launching Nereus just because the weather is good now. It is what the weather will be like 12 hours later, when we need to be able to bring the vehicle safely back aboard that matters. So we’ll remain poised and ready – like coiled springs – and optimistic right up until our time runs out:– about 36 hours from now. In the meantime, I have just remembered that we do also have one other last trick up our sleeve. Although we don’t have much variety of scientific gear aboard ship – after we had loaded Nereus and the CTD there wasn’t room for much more – we do have a small grab system that we could mount on the bottom of the CTD cable, instead of the CTD itself. So if tomorrow comes around, and we do already have all the water samples from here that we need, then even if Nereus still cannot be launched, we may yet be able to get David, Julie and Max some pretty cool samples from the seafloor.
We’re definitely not done yet - but I’ll still keep hoping for that one last Nereus dive…