BLACK SEA 2000
Hello from 42 deg north, 34 deg east!
We're experiencing a welcome lull in activity on the R/V NORTHERN HORIZON as we switch out equipment on the cable, so I have some time to write.
We had the tandem vehicle ROV system in the water for the last 59 hours with no problems. This is a remarkable achievement for the engineers, considering that Lil Herc is a spankin' new vehicle on its first operational deployment. It shows that (MIT Course 13 alum) Jim Newman did a great job building the vehicles. It also suggests that ROV components have become black boxes to be pulled off the shelf and assembled like any other mature technology.
Recovery of IFE's ROV Little Hercules
Jim Newman and Argus vehicle, Li'l Herc's tandem partner
The Argus/Li'l Herc system has been working so well that we ran out of targets to investigate in this survey area. The engineers and technicians are now taking the ROVs off the cable and putting the DSL-120 side scan sonar back on. We'll go surveying again when the 120 is ready to go, probably about eight hours from now. This is good news, as it means most of the science team can sleep, relax a little, process data, and catch up on email.
Launching the DSL-120 deep submergence side scan sonar
This cruise has been interesting, as they all are. The Black Sea is a strange environment, with it anoxic water below about 150 meters. We have been running the side scan sonar and the ROVs around the anoxic interface for two reasons. First, it coincides with the depth of the ancient lake shore. We are looking for cultural remains that date back 7500 years, prior to the sudden inundation hypothesized by geologists Ryan and Pitman. The second reason is that the anoxic water won't support aerobic life, so wood boring organisms won't be present to devour shipwrecks.
The sonar traces above the anoxic layer look normal. The seafloor appears light gray in the data, with targets appearing white and their acoustic shadows black. However, once the sonar dips under the anoxic layer, the seafloor appears black. The sediments there suck up almost all of the acoustic energy. Dr. Ballard says this is a good thing, as any targets in the anoxic waters with relief above the seabed will be "real ringers". We have all been speculating why the anoxic sediments absorb the energy, but no one knows. Dr. Ballard joked that the US Navy ought to paint its submarines in the stuff, and they would be undetectable by sonar.
Some of the life above 150 m is fantastic, too. Two nights ago there was a bloom of critters: billions of ctenophores and little jellyfish-like animals. We call it "sea snot" since there is no biologist on board to enlighten us. The lights of the ROV reflected off their bodies, creating a sensation of driving through a blizzard. Below the anoxic layer, the water is crystal clear and we can see quite well.
Apparently there is a lot of sulfuric acid in the anoxic water. We located some modern debris last night: a 55-gallon drum and a length of iron pipe. Both looked like Swiss cheese, as the corrosive water eats up metal quickly. Wood seems to be preserved, as we had hoped. There are tree branches and logs every so often. We can't tell how old there are without bringing them up to examine, but last year we recovered a piece that Carbon-14 dated to 3800 years old. Jim Newman has expressed some concern for the safety of the vehicles, which have metal components.
"Tetanus," our rusty steel depressor weight used in tandem with the DSL-120, has some aluminum angle iron pieces on it. After the first deep deployment here last week, the angle irons were badly corroded. When I first saw them, I thought they were sacrificial zincs. The surface was pitted and dull gray. Of course, the aluminum acts as an anode for the hundreds of pounds of steel in Tetanus, so electrolytic reduction will take a toll. So far the stainless steel, titanium, and aluminum on Li'l Herc are OK, partly because it hasn't spent as much time in the anoxic layer and partly because it has more sacrificial anodes than Tetanus.
"Tetanus", the depressor weight for the DSL-120 (sonar streaming behind the ship)
I can't wait to see the degree of preservation of shipwrecks in the very deep water. I expect any metal fasteners to be gone, but I hope that wood will be intact. If all the wood we see around 150 m is any indication, ancient wooden ship hulls should survive.
Well, lunch is being served in the mess, so I better get to it.
More to follow,
R/V NORTHERN HORIZON
Black Sea Deep Water Archaeology Project 2000