Ship’s Log: Collaborative East Antarctic Marine Census

On board the Aurora Australis, Voyage Leader, Dr Martin Riddle, captured the excitement of the CEAMARC sea-bed surveys in his ‘situation reports’. The voyage also supported another Australian-led International Polar Year project – Climate of Antarctica and the Southern Ocean (CASO).

Date: 21/12/07. Position: 62°48′S, 142°51′E. Ice conditions: nil

In transit to the main sampling area for both CEAMARC and the southern CASO sites. The third Continuous Plankton Recorder tow is currently in the water. Yesterday afternoon the first bulk seawater sample was collected for metagenomic analysis using techniques based on those developed for sequencing the human genome.

Date: 23/12/07. Position: 65°59′S, 142°39.6′E. Ice conditions: 2/10 loose pack ice

The ship is now doing scientific activities around the clock with most people working 12 hour shifts. Transfer of equipment between the decks in preparation for the CEAMARC sampling went smoothly yesterday. We started set-up of the first Polynya mooring at about 1600 hrs and this was deployed by 2030. During the night the remaining three moorings were prepared and deployed, with the last one in the water by 0400 hrs. We then moved through loose pack-ice to the first of the CEAMARC sites (Ceamarc-27) and at 0715 deployed the first of the CEAMARC sampling equipment – the very robust epibenthic sled, which collects the top layer of seabed and anything living in it. The first organism to be photographed, tagged and bagged was an octopus. The sled contained enough sea-bed animals to keep a large team happily sorting for several hours – zoot alors! qu’est-ce que c’est? We have since collected a CTD water sample and used the box-corer to collect a relatively undisturbed sample of the seabed sediment. We have tested the procedure for deploying the beam trawl and are fine tu

Date: 25/12/07 Position: 66°20′S, 143°17′E Ice conditions: distant icebergs

Sampling for CEAMARC has become more stream-lined. Having tested a range of samplers at the first sites, we are now focusing our efforts on those that proved most effective. The combination of samplers that we are now using is giving us a broad representative sample of the full suite of sea-bed animals, including excellent very high definition still photographs from the trawl-mounted camera system. The team of designers and builders in the AAD’s Science Technical Support section are to be congratulated for their combined skills in producing rugged equipment that works under very difficult conditions. A highlight of today’s hauls has been the first solitary corals for the trip. The skeletons of these animals are made from aragonite – the form of calcium most susceptible to ocean acidification. The specimens collected today were from 700 m and had very delicate, friable shells. It will be interesting to see whether they are found at the deeper sites where, because of the increased water pressure, the aragonitic calcium will have a greater tendency to dissolve. Oh yes … and Happy Christmas to everyone.

Date: 28/12/07 Position: 66°33′S, 143°19′E Ice conditions: continent in sight

We are sampling in some very dramatic country. One trawl last night was taken from the lip of a very steep drop-off, going from 130 m depth to more than 400 m in a very short distance. Although the trawl was on the sea-bed very briefly, it came up with a good haul of giant sponges and fish, indicating an area of very high production. As we move into some of the deeper sites we are beginning to see the first of the giant crustaceans which are characteristic of the Antarctic. Overnight we caught amphipods that were 5 cm long and isopods more than 8 cm long — these groups include the sand-hoppers and sea-slaters which, around the coast of Australia, are usually less than a centimetre long. We have completed 20% of our sampling stations.

Date: 03/01/08. Position: 66°34′S, 144°41′E. Ice conditions: distant icebergs

After riding out 40 to 50 knot winds for the first day and a half of the New Year, conditions had abated sufficiently by 1600 hrs yesterday to allow sampling to re-commence. Overall impressions of the sea-bed invertebrate communities are that the diversity and species composition on the Adélie Bank seems roughly equivalent to that known from at Dumont D'Urville at shallower depths (40–200 m), but tends to decrease in Commonwealth Bay, possibly because of increased iceberg scouring. Two stations (38 and 36) show strikingly different benthic communities compared to surrounding stations, with many anemones, synascidians and serolid isopods. These stations are situated well beneath the action of icebergs at the bottom of the Georges V Basin where water conditions may play a role in shaping very different assemblages. The multi-beam data, previously collected in this area by the US research vessel the Nathaniel Palmer, provides a very detailed picture of the sea-bed, including tracks of past iceberg scouring . The data is proving invaluable for interpreting the relationship between the living communities and the physical environment of the sea-bed.

Date: 04/01/08. Position: 66°19′S, 143°59′E Ice conditions: isolated bergs

We are approaching the end of this stage of the CEAMARC sampling and when conditions allow we will return to the Polynya moorings to move the Pole Compass. The big isopods, amphipods and sea-spiders of the past few days were put firmly in their place last night by the arrival of the Big Polychaete. This magnificent scale-worm was about nine inches (230 mm) long, 3.5 inches (90 mm) across, with scales more than one inch (24 mm) in diameter and weighed about 330 gm – at just three to the kilo this is by far the largest polychaete seen by any of the benthic ecologists on board. We have since captured video imagery of these monsters scurrying along the sea-bed as the trawl approaches. To top it off, the scale-worms arrived complete with their own over-size parasitic nematodes (up to 4 inches long) infesting the space under the scales.

Date: 06/01/08. Position: 65°39.6′S, 143°02.4′E. Ice conditions: isolated bergs, bergy bits

We all expected the Big Polychaete to be the undisputed highlight of the voyage, however, the Southern Ocean continues to turn-up surprises. Yesterday, while sampling the transect from 400 m to 2,100 m down the shelf, we blew out the trawl net as we tried to bring it on deck after sampling the 800 m site. The video footage from the trawl-mounted camera explained why. Almost the entire day shift crammed into the electronics cupboard to see the footage and, after the first gasps of ‘incroyable!', watched in hushed awe as a scene rivalling the best parts of the Great Barrier Reef was revealed. The sea-bed was 100% covered with living material – colourful branching coralline species and gorgonians forming the major lower storey structure and large branching sponges the upper storey. Amongst this were numerous sea-stars, sea-cucumbers, crustacea and fish of types at yet unseen. After repairing the trawl nets we returned to re-sample the site, this time being very cautious with the time allowed for the trawl to be on the bottom, and were rewarded with a relatively small catch, but with many species not previously collected. In marked contrast the communities at 1,600 m and 2,100 m were rather sparse, with much un-colonised rock and coarse sediment visible, but again the samples, although small, contained many species new to us. The deck crew must be congratulated for their skill and persistence in successfully sampling these very difficult environments, without which the scientists would have nothing. We have now commenced the main CASO (Climate of Antarctica and the Southern Ocean) sampling for the voyage.

Date: 08/01/08. Position: 62°58′S, 145°44′E. Ice conditions: open water

CTD sampling of waters from the sea surface to the sea-bed continues around the clock for CASO – a major multinational project for the International Polar Year involving scientists from 18 nations, led by Australia. CASO will provide the first circumpolar snapshot of the physical and biogeochemical state of the Southern Ocean as a benchmark for the assessment of past and future change. It will also demonstrate the feasibility of a sustained Southern Ocean observing system. CASO will continue on another voyage in March, during which a transect from Hobart to Antarctica will be sampled. On this voyage, CASO is focused on the region close to the Antarctic continental shelf and the fate of cold, dense Antarctic Bottom Water from the Mertz Polynya. This region is one of the few places in the ocean where surface waters are made sufficiently dense to allow them to sink to the deep ocean. This transfer of water from the surface to the abyss is part of a global system of ocean currents known as the overturning or thermohaline circulation, which strongly influences Earth's climate. Our measurements are aimed at understanding how the Antarctic contribution to this global current system works and whether it is changing. We are presently re-occupying sites first measured on Aurora Australis in the 1994–05 season.

Date: 13/01/08. Position: 66°03.7′S, 141°17.7′E. Ice conditions: large icebergs, open water

The second phase of CEAMARC benthic sampling started very well with six stations completed in the last 24 hrs. We have re-aligned some sites based on very accurate bathymetry obtained using a multi-beam swath mapping depth sounder, to get a better series of samples from shallow to deep. Yesterday’s samples from 400 m, 800 m and 1100 m were an interesting contrast to those from a similar depth series which, at 800 m, was dominated by a colourful garden of filter-feeding coralline species. Yesterday’s 800 m site had a very sparse covering of surface-living filter-feeders, such as sponges and bryozoans, but had very large numbers of Macrourus whitsoni or rat-tails, a common fish from these depths throughout the world. The sea-bed photographs indicated a lot of ‘marine snow’ (organic particulates) in the water and a piscean wall of mouths – fish waiting on the seabed for food to be washed past them by the currents. So although only 20 miles apart and sharing the common characteristics of very high productivity and biomass, the benthic fauna at these sites were intriguingly different.

Date: 15/01/08. Position: 66°24.4′S, 139°47.6′E. Ice conditions: icebergs, bergy bits, growlers

Trying to sample the deep (1200 m) basin yesterday was very frustrating. Twice we had the cod-end of the trawl blow out and recovered only a very small haul retained by the coarser outer mesh. The trawl-mounted video camera provided only brief but tantalising glimpses of a sea-bed covered with large numbers of surface feeding sea-cucumbers between long periods of total darkness, caused when the trawl sank to its armpits in the fine diatomaceous ooze. After about 10 hours of trying we moved on to the next site at 800 m on the basin slope and, while sampling, considered options for completing the deep basin. The 800 m site was sampled in reasonable time, so we returned to the deep site and deployed the French beam, with the intention of floating it briefly across the bottom. The trawl was on the bottom for about eight minutes and came up with a fine haul. The community was dominated by the large elasipodid sea-cucumbers seen on the video, looking very like fat little hippopotamuses grazing on the sea-bed, but included many other species including sea-stars (similar to Acodontaster and Cuenotaster), brittle stars (cf Astrotoma), stalked tunicates (cf Molgula), large gastropods, many small bivalves and several pelagic octopus.

Date: 19/01/08. Position: 65°37′S, 141°04.3′E. Ice conditions: large iceberg, bergy bits, growlers

As predicted, sampling the very rugged seabed in this canyon system at the edge of the continental shelf has been difficult. At the cost of some torn trawl nets, we have managed to get imagery and samples down to 1500m, with the very diverse seabed offering up a similarly diverse fauna. Last night we recorded the most fish species from any one trawl – 16 including at least one which was new to this survey. The benthic invertebrates were similarly diverse with a great range of sedentary groups, such as sponges, bryozoans (lace coral), tunicates (sea squirts), gorgonians and some very large solitary corals, forming the main supporting structure for an equally diverse variety of mobile groups such as polychaete worms, amphipod crustaceans, ophiuroids (brittle stars), crinoids (feather stars), echinoids (sea urchins), asteroids (sea stars), pycnogonids (sea spiders) and a range of molluscs. Early this morning we stopped the benthic work temporarily and switched our efforts to sampling the waters around the very large iceberg nearby, with the intention of identifying whether it is a source of trace nutrients that might stimulate plankton growth. Satellite imagery indicates the iceberg is about 35 km long by 18 km wide. The berg is designated B-17A and came into this region in October 2006 from a large chunk of the Ross Ice Shelf that calved in April 2000.

Date: 20/01/08. Position: 65°24.7′S, 139°50.7′E. Ice conditions: open water

Yesterday water samples were collected from seven sites at a range of distances from the large iceberg using the Fast Rescue Craft. While sampling was happening, the Aurora Australis maintained its position down-wind and down-current to ensure there was no risk of the ship contaminating the surface waters. These samples are to be analysed for ultra-low levels of trace elements and even the presence of the ship’s hull in the immediate sampling area could compromise the results . The CEAMARC sampling officially finished at 12:08am. Overall, 82 different sites were occupied during CEAMARC, with samples collected from at least 78 sites; well in excess of the 67 sites we had hoped for. Everyone involved is to be congratulated for putting in an enormous and sustained effort to achieve such an excellent result.