Saturday, 19 January 2008

Settled in

We are now about three weeks into the cruise and everyone is settling into the routine of transect, survey, 2-day station.

The transects is a series of CTDs - density profiles to the bottom (well, about 10m off the bottom is the aim, and neither Mags or I have hit the bottom yet, wouldn't be good). This will be used with a series of other transects (taken at different times, oceanography is a compromise) to look at the water properties flowing into and out of the Scotia Sea to look at how the water must mix vertically and horizontally (actually along and across layers of constant density, which isn't quite the same thing) to get from what flows in to what flows out. This will be compared to direct measurements of this mixing from other cruises.

The surveys are normally 24 hours, sometimes 6 hours to characterise the area we are working in for 2 days - looking at how the point measurements relate to the larger scale and also looking for strong gradients in water properties we don't want to cross - we had a very strong gradient last station but only crossed it once and that was after we closed the net, so it was OK. We have two guys recording seabirds in a 300m box off the bridge wings during these surveys and during the transect. I'm free from the survey discipline and keep telling them what they missed behind the ship! On the last survey they recorded 50 Fin Whales and 2 Humpbacks on their side of the ship, and there were plenty more the other side and when we were turning round as well.

Fin Whales, some of many

The stations are a mix of activities to see what is in the water, from the nutrients (nitrate, silicate and iron), physiological condition of phytoplankton and associated nutrient (iron in this place) and light constraints, through small zooplankton (especially life stages Oithona similis, a copepod abundant enough to be filtered from 20l of water, collected from 12 depths during a dedicated shallow CTD cast), krill (life stages, abundance and dimensions to compare with acoustic backscatter, genetic effect on diurnal cycles), pteropods (snail-like things that are very hard to get on board without damaging them) up to fish (myctophids, one potential new species caught at the last station). Always hard to see how things are working out during the cruise (and more so before half way) but things have generally gone well, most of the kit is working and we are catching krill and fish (apparently not a given!).

Incubators - water is collected and put in bottles, incubated in pumped seawater to keep it cool and shaded (a known amount, different between the boxes) from the sun, to simulate being under a certain depth of water. Some bottles have iron added to see what difference that makes.

LHPR (someone-someone Plankton Recorder) catches small zooplankton against a gauze that rotates every 2 minutes, to give a profile through the water column. A specialist in flat zooplankton then picks the animals off the gauze.

MOCNESS (Multiple Opening/ Closing Net and Environmental Sampling System), opens and closes at different depths (via someone sat at a computer) so sample relatively small things at known depths between 1000m and the surface.

RMT25 (25 metre squared net opening) coming back on deck. The winches are run by crew, but scientists pull the net on (the four guys with harnesses on). Used to sample large things (up to myctophid fish) down to 1000m. A smaller version (RMT8) is used to catch Krill near the surface and bring them back alive.

Geraint and Jose recording the non-fish part of a catch

Some of the fish, from between 1000m and 700m deep.

We have also pushed southwards into the ice to repeat a line of CTDs to look for changes in water mass properties associated with changes in sea ice or land-ice inflow. We are taking samples of water to analyse (well, for someone else to analyse) for oxygen 18 isotope ratio (to the common oxygen 16). Being heavy, O18 fractionates during evaporation (it preferentially doesn't) so land-ice is low in O18 compared to sea-ice so it can be used to distinguish between fresh water from land-ice melt (via icebergs) and sea-ice melt. We had a couple of hours at Signy research station as well, long enough to roll some empty oil drums past some Elephant Seals and walk out to a stream to collect fresh water running down from an icecap, as an end-member for the O18 ratios (no sea ice at all). Was fun to get out for a short walk (through fresh snow, up to 2 feet deep) and talk to the base assistant (professional cameraman, mostly video). No Emperor Penguins despite lots of searching, one very southerly King Penguin got me excited though (and was a good record in it's own right). One Minke Whale amongst the ice, missed a Killer Whale by about a minute and saw what must have been a Leopard Seal - only saw a grey thing roll very quickly, but the 50 penguins radiating out from that spot at full speed was something of a clue.

Pushing through the broken ice floes.

Crabeater Seals - seen fairly frequently through the ice.

Snow Petrel - typical species of the ice, only rarely seen over open water

The ice edge, as we left.

Yes, we did do some work down there, exact locations of CTDs varied from planned locations as we needed to find a large enough hole in the ice.

The ship, from Signy (apparently the area was free of snow the previous evening)

The cargo tender that brought us, some empty oil drums and some fresh veg in. We didn't have to stop, but it was clearly much appreciated by the guys on base, and everyone enjoyed having a bit of a walk.

One of the locals

There is running water here, honest (we had to dig down to it)

One of the many small islands around the South Orkneys.

Some stunning sights, helped by the sun being out on the northern side of the islands.

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