Saturday, 19 July 2008

Chasing pink dye

The last couple of days have been monotonous for the birders (very few birds & those seen are nearly exclusively gannets – check out Andy’s blog to get an idea of how they’re enjoying sitting looking at a blank sea). But elsewhere on the ship there is more excitement. We got a really nice clear porpoise click train on the last CPOD deployment (at MS3 – the bottom of the bank), meanwhile Inigo’s camera came up with two uneaten fish (these had gone down frozen), one fish skeleton, and a good sample of the amphipods (sea lice) that are devouring them (see picture above). These were only 6mm long, but some of the ones he’s seen on the camera look more like 5cm long (what with those & the massive conger eels, I think I’ll stay above water thank you!). Others took more simple pleasures – like working outside in the sun (see Matthew Palmer from POL (turbulence man) in the picture to the right).

But the most excitement was in the ‘pink dye team’: Mark Inall (SAMS), Claire Neil (University of Strathclyde) and John Beaton (SAMS). Like earlier in the cruise (see previous blog & picture above of Mark & Claire tracking the dye), the pink dye was injected with a long tube with a weight on the end, into the thermocline (the layer that forms between the warmer surface water and the colder bottom water). They then track its dispersion using the fluorometer (measures the amount of colour in the water column) on the scanfish (the CTD that goes up and down the water column towed behind the ship) – so they can track the dye both vertically and horizontally through space. They tracked the dye after 4 hours, 12 hours, 24 hours and 36 hours, grabbing snatches of sleep in-between. It actually moves with the tidal & wind currents quite a lot even before the dispersal occurs, which means it’s quite challenging to find, even with the drogue with a satellite transmitter on it so you can track the currents (it only gives a position once an hour – so it’s a bit of a guessing game between position updates!). Between Mark, Claire & John and the Captain, they seemed to have a lot of fun trying to calculate the exact position of the dye, and then getting the ship to travel through where they thought the dye would be. Captain Peter Sargeant (pictured right) seemed to enjoy this task immensely, probably a bit like solving the cryptic crosswords he has stashed on the bridge ;o) Anyway, between their combined efforts in predicting tidal & wind drift they were successful and managed to find & track its dispersal over the bank. I’m not sure what they discovered since they finished at 1am and are now tucked up in their cabins catching up on sleep (well except the Captain). Incidentally - you can't get a better captain in my book - Peter is calm, spry and nearly always smiling :o) We have a great crew on the ship.

Meanwhile there have been more CTDs, more ‘giants tights’ bongo samples of zooplankton (there looks like a lot less biomass of zooplankton at the new control site MS5 from early conversations with Beth this morning), more sediment cores… and a very interesting talk about the phytoplankton & bacterial communities that Keith Davidson’s team are investigating. I’ll try and talk about their work a bit more in the next blog. As to me – I’ve been working up some of the fish data to see if we can solve part of the mystery behind few benthic fish on Inigo’s lander, and few feeding birds. As far as I can see there are a lot of fish down there – but then I mainly look at mid-water fish on the echosounder – so I can’t say very much about the fish in the top 10m or on the bottom. So maybe the fish aren’t close enough to the surface for the birds (and not enough marine mammals to bring the fish to the surface in bait balls), and they are mainly mid-water fish rather than bottom fish. It will be interesting to see what the fishermen catch when they come along after us – whether they find benthic fish (like plaice, sole… which Inigo isn't seeing on his lander but we were expecting), and what fish species come up in the mid-water (pelagic) trawls. That starts on Monday, with Beth co-ordinating their fishing efforts having pored for many hours over the fish echograms to work out where they should fish so we can find out what we’re seeing on the fish echosounder.

Still a lot of fun activities ahead… but let’s hope for more birds & marine mammals to break up the birder monotony. And on that note, I will end with an apt picture of gannets flying into the sunset…
gannets flying into the sunset... (& I'm sure the birders would be happy if they didn't come back!)

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