Northwest of the Perth Abyssal Plain is a long NE-SW trending trough,
with two large seamounts on top of it. The trough is suspected to be
an extinct mid-oceanic ridge and the seamounts origins are largely
unknown. The northern seamount is called the Batavia Knoll, probably
after some German or Dutch discoverer, and is easily recognized as a
high anomaly on the gravity maps of the region ? this was our first
dredge site.
First order of a dredge is major SWATHing of the area to get a very
good understanding of the seabed bathymetry. We SWATHed back and
forth for 12 hours along a zig-zag path above the underwater
mountain, revealing a steep 4km drop from the unusually flat top to
the trough. Another interesting attribute was the high amount of
gullies leading to the trough relative to almost none going down to
the Abyssal Plain on the other side.
Choosing the best dredge line is not very difficult bit still demands
careful consideration, depending on your objectives. Since we aim to
understand the origin of Batavia Knoll, a line with the least
possible sediment was needed, preferably a fault scarp, in order to
get to the crystalline basement of the feature. It was decided that
one of the gullies leading down to the trough would be dredged. The
captain took us over the gully 4 times until he was confident that
the depth soundings were accurate and no potential snags awaited
below. Needless to say, many dredge nets have been lost to the abyss
so all precautions must be taken.
As day broke the crew lined up in their orange overalls on the back
deck to let out the gear. The dredge net is made up of a rectangular
metal box, resembling a mouth, on the one end of which a large
heavy-duty chain mesh cage is attached. Also attached to the mouth
are two metal canisters meant for picking up loose sediment.
Back in the Ops room we anxiously watched the winch cable tension for
spikes. One spike too many and the 5ton cable could snap leaving our
net at the bottom. Luckily the first mate of the ship has never lost
a net yet.
Our on-board geochemists: Jacqueline Halpin, Nathan Daczko, Maddy
Kobler and Robyn Gardner, are ecstatic about the loot. Big chunks of
felsic continental rocks with huge crystals, mafic amphibolites and a
huge bright gold sandstone nugget have been dredged up. Put together
these might have big implications for the evolution of Batavia Knoll.
Could this be a piece of India left behind as it slowly waved goodbye
?
I have thought about the seasickness you must endure,recalling a sufferers observation that he feared he would not die soon.I suppose the residents of Freemantle are used to seeing young crews mistaken for a group afflicted by Tourettes , lurching, crouching and swaying , arms flailing, grabbing for unseen handrails. Sprinting to expel the contents of one's stomach overboard only to sense, too late , your intestines emptying out into your pants .I suppose you have developed a heightened awareness of your sphincters.
ReplyDeleteI notice the excessive use of the question marks in your blogs.Is this the young scientist questioning everything or the result of a keyboard permanently in motion?
While you track the Abyssal Plain in search of India's lost luggage,I left Conaky for Paris .For one thing, I left behind 'poulet grille diabole avec riz', one of the few passable dishes on the menu.The chef was referring to some Mexican chilli source no doubt, though I had to return the dish to him more than once, with a message that it was indeed diabolical.But here in the 8th Arrondsement's Friday morning neighbourhood food market, I wondered at pigeon,caille,phaison, poulet,lappin as well as the irresistible offerings of boulangers , chocolatuers and patisseries, more akin to your floating food emporium.
Solvitur ambulato- it is solved by walking.You happen to be in a labyrinth.Walk it to freedom.
I spent the morning walking Montmarte ,gazing out over Paris' rooftops.
I thought of you staring out at the sea.
And what did we both see ? Perchance, ourselves.