Report 6: Can we have ice with that?
Steve Nicol, Voyage Leader
On Saturday we had our first encounter with pack ice. The first hint had come from the bird observers, Adrian and Andrew, who claimed to have seen ice-loving snow petrels, but ornithologists are notoriously excitable creatures so no one really paid them any mind. However, shortly afterwards they were vindicated when a thin white line appeared on the horizon to port and as we settled into another CTD cast we could see the barrier of ice to our south. The satellite imagery we had been sent suggested that there would be a tongue of ice covering the base of Transect One but because of cloudy conditions our most recent images were some five days old and conditions can change rapidly at this time of year. Because this transect extends furthest to the south, one of our concerns has always been that we might not be able to make much progress in this region because of consolidated ice in late January.
We are trying to get up onto the continental shelf on all of our transects and this means going to 69° 18' S on Transect One. So far the ice conditions have been fairly benign with loose pack making progress relatively easy and not impeding data collection. In heavy ice it is difficult to find an adequate parking space for the CTD and trawls become tricky as ice floes can snag the wire. Additionally, ice banging against the hull can ruin the acoustic signals, and thick ice can make progress painfully slow. The weather has been in our favour though, with seas so calm that there have been complaints from some extreme oceanographers aboard who claim they only signed up because of the notoriously mountainous seas found in this area.
The light as we moved into the sea ice was magical with sunlight filtering through the low clouds and, coupled with the mirror-calm sea, the conditions for viewing wildlife were nearly perfect – had there been any wildlife to view. An occasional whale blew in the distance but the surface of the water lay mainly undisturbed – if a single krill had breached we would have known about it.
However, as we moved into the ice, krill became apparent on the sounders and a quick trawl brought several hundred aboard and they are now to be found happily growing away in So Kawaguchi's custom built krill Hilton. As we begin to move up the continental slope and towards the shelf we ought to see more krill and hence more krill predators such as seals, whales and penguins – but then such theories have a way of being discredited when tested out on the water.
The sea-ice zone is thought to be one of the powerhouses of Antarctic productivity. Algae are trapped in growing sea ice in autumn and, as they are held near the surface in good light conditions, they grow and form communities which can be so dense that they stain the ice brown. These communities can form pastures that are grazed by herbivores in winter and spring and then, when the ice melts, they are released into the surface water and begin to grow. The melting ice is fresher than the underlying seawater so tends to float on it and the algae are trapped in the well-lit surface layer where they multiply rapidly. This is the bloom that feeds the herbivores of the region, particularly krill, and ultimately is the source of energy for all the animals of the sea-ice zone.
All around us are ice floes with conspicuous layers of algae ranging from yellow to brown. As the ship brushes them aside they turn over to reveal their heavily pigmented underside and occasionally a startled group of krill which had been feeding on the algal layer until their breakfast was rudely interrupted by the passage of the Aurora.
As we head down Transect One the fruits of our labour on the preceding Transect 12 (yes, those inscrutable oceanographers have been at it again) are beginning to emerge. The wall in the mess is now decorated with plots derived from the CTD in gaudy primary colours (to appeal to the biologists) and this has prompted stimulating discussion.
Simon Marsland was heard resorting to polysyllables as he tried to explain how finding no significant difference in either temperature or salinity across vast sections of the Southern Ocean was, in itself a significant difference. Not to be outdone, Toby has appropriated a whole corridor to advertise the results of the acoustic survey in a no-holes-barred, blow-by-blow account of every krill that he has pinged. So far there is one, postage stamp sized echogram positioned at a height that anyone who is shorter than Toby (that's 83 of us) cannot see without binoculars and a stepladder.
Those concentrating on the more microscopic end of the food chain are reporting spectacular successes in their ground-breaking research but are refusing to disclose them on the grounds that this will severely compromise their commercial potential, might preclude them being published in 'Nature' and besides they are too busy collecting data and watching re-runs of 'Alias' to conduct any analyses. Others are more secretive still and although the abundance of whales and seabirds could easily be calculated from the number of delighted squeaks and yelps from the observation teams, no hard data have yet emerged – resulting in some furious eyelash-batting by Bec.
By the middle of this week we will have completed this transect and will have enough data to construct a few more theories which we will be able to demolish on our next sampling line, Transect 3 – or will it be re-named Transect 17?