Tangaroa — Week 6, 6-12 March 20086-9 March 2008Scott Island & beyond — written by John MitchellAfter completion of the first abyssal station in the northern part of our survey — at a depth of 3500m — we moved on to our last seamount station next to Scott Island. Scott Island is very small (400m by 200m) and isolated, lying about 310 nautical miles northeast from Cape Adare. Its companion — Haggit's Pillar — is an impressive 62m high volcanic stack sitting 200m northwest of the island. We are sampling in this area to compare the biodiversity with that of the Balleny Islands some 500 nautical miles to the west that have been sampled in earlier expeditions by Tangaroa. Scott Island was first discovered in December 1902 by Lieutenant Colbeck on the vessel Morning while heading south to supply Scott's 1901-04 expedition on HMS Discovery.
The benthic community around Scott Island is very abundant compared to the seamounts that we sampled further south on this chain last week. The seabed in waters shallower than 400m is covered with numerous sea pens, brittle stars, anemones, and sea stars (below, left). A seabed of solid volcanic rock and rubble in some areas often made the sampling difficult (below, right).
We've now finished sampling in this area and are moving west to the Admiralty Seamount chain about 250 nautical miles to the west, in between the Balleny Islands and Scott Island.
Science ReportNeuston sampling — written by Julie Hall (NIWA)
Neuston is the name for zooplankton that live in the top few centimetres of the ocean. To sample these organisms we have a specialised net which is towed, right on the surface at about 1.5 knots, from the side of the ship. We've had limited opportunities to deploy the neuston net during the voyage because of the sea and ice conditions we've encountered. In rough seas, the net bounces from wave top to wave top and does not sample the neuston effectively. When the sea is cold (as it has been), newly forming grease ice fills the net, sometimes creating a giant seawater slushy! (below, left). When we have succeeded in sampling, the dominant organisms have been salps (planktonic relatives of sea squirts; below, centre and right) and amphipods, (small crustaceans that are related to sandhoppers).
Into deeper waters — written by David Bowden (NIWA)
Moving progressively away from the central and southern Ross Sea, the contrast between benthic communities on the shelf and the deeper slope and abyssal environments is pronounced. Shelf habitats were characterised by densely-populated assemblages of organisms that filter plankton and detritus out of the water (suspension-feeders) and organisms that ingest sediments rich in microbial food (deposit-feeders). These have now given way to a visually monotonous seabed of uniform fine mud scattered with glacial drop stones in the abyss. These depths are sparsely populated compared with the shelf and the conspicuous inhabitants are now deposit-feeding organisms and their predators. Similar changes are found with depth at all latitudes, but the dominance of suspension-feeding taxa in shallow habitats of the Ross Sea makes the contrast particularly striking.
The DTIS camera deployment at our first abyssal sampling site in the northern part of our survey area revealed a seabed of fine mud scattered with black stones. The most conspicuous organisms were large holothurian echinoderms (a group which includes sea cucumbers, below, left) distinctly different to those from the shelf and slope.
These are deep sea animals found over a wide latitudinal range, rather than the exclusively Antarctic fauna we have seen up to now. Even those that look like the familiar Scotoplanes sp. ‘sea pigs’ of the Ross Sea, are actually from a different family (Elipiidae), which is widespread in the deep sea below 2000m. These deep-water holothurians often have bizarre protuberances, such as the dorsal spike on the Phsychropotes sp. specimen (above, right). We can only guess at the purpose of these appendages at this stage. New species and records continue to flow — written by Malcolm Clark (NIWA) and Stefano Schiaparelli (Italian National Antarctic Museum)
Our last few days in the Ross Sea have seen continued discoveries of new species or new records of invertebrates. Invertebrate taxa are so diverse that experts onboard can only identify some of the groups with certainty. It is therefore likely that many new species or records for the Ross Sea will remain unconfirmed until samples are sent to experts around the world after the voyage. However, there are a number of animals that have been caught or photographed that we are confident are new species, new records, or are adding a lot of information about poorly known groups. These include a crinoid (or sea lily) of the genus Bathycrinus in shallow waters, a sea urchin Pourtalesia species and the gastropod (snail) Miomelon turnerae at 2200m. More on those in the next installment.
10-12 March 2008Admiralty Seamount — written by John Mitchell
We've spent the last two days sampling the Admiralty Seamount which has a large (12 x 5 nautical miles) flat top at about 460 m deep, and very steep flanks dropping to over 3000 m. The sampling has shown the top to be rather sparse biologically, apart from a couple of small areas which have an abundant and diverse fauna. Further sampling of those areas will be done later in the week. Although we are north of the pack-ice and access to this seamount is generally good, numerous tabular bergs in various stages of disintegration surround us.
We've also started sampling at our last abyssal station in a water depth of 3500 m just northeast of the Admiralty seamount. The immediately obvious difference between this abyssal station and those sampled to the east, is the smaller number of glacial erratics and drop stones found here. As we explained in earlier reports, these are stones plucked by glaciers, carried out to sea on icebergs, and dropped to the seafloor when the icebergs melt.
Science ReportNew species and records from the Ross Sea — Malcolm Clark (NIWA) and Stefano Schiaparelli (Italian National Antarctic Museum)
As promised in our last report, here are some finds from the Ross Sea that we are confident are ‘new’:
Sampling seamounts in the Southern Ocean — written by Malcolm Clark (NIWA)
About a week ago, we left the Ross Sea shelf and slope areas to the south, and headed north through the ice barrier to sample some seamounts and abyssal plains to conclude the survey before returning to New Zealand. The aim is to compare biodiversity in the Scott Island seamount complex with that of the Balleny Islands Seamounts and the Admiralty Seamount to the west.
Seamounts are essentially undersea mountains, arising from the deep waters of the abyssal seafloor, occasionally reaching the surface to form islands, such as Scott Island or the Ballenys. They are usually of volcanic origin, as in the case of the Scott Seamounts, which are believed to have formed about 45 million years ago, and to be a side fracture zone from the main tectonic plate boundary between the Antarctic and Pacific plates. Consequently, they can be large, rugged, and steep.
We headed first to South Scott Seamount and then north to the Scott Plateau just south of Scott Island where several seamounts are charted. We had data on summit position and depth, and had expected (more or less) a regular mountain-like structure, but as we began to survey the area with the multibeam echosounder system, South Scott proved to be a very complex system of small peaks emerging from a ridge-like plateau.
The hull-mounted multibeam echosounder system onboard Tangaroa is a fantastic tool to rapidly determine the bathymetry in this sort of situation, and dramatically improve survey planning in this very rough terrain where gear can be easily damaged. South Scott Seamount rises from depths of 3500 m on the eastern side, to about 600 m on the summits of several of the peaks. The main axis of the seamount lies northeast to southwest, and has seven prominent volcanic cones aligned on the western side.
This site was considered a ‘core’ seamount site, and so we deployed a wide range of different sampling equipment over a 36 hour period (below). We spread our sampling effort around the seamount to encompass a variety of habitats based on its topography, substrate and depth.
Below, right shows some of the seafloor we photographed and sampled.
Deep sea krill — written by Richard O'Driscoll and David Bowden (NIWA)
As the DTIS camera system skimmed the seafloor at a depth of 550 m close to Scott Island, we watched the live low-resolution video feed back up to the ship and saw what looked like shoals of tiny fish swimming away from the approaching camera. Once DTIS was back onboard and the still photographs and high-resolution video were downloaded, we were amazed to discover that what we thought had been fish were, in fact, Antarctic krill (Euphausia superba) (below). The presence of krill at these depths was confirmed in MOCNESS samples from 300-400 m as well as krill-like acoustic signals. Conventional wisdom is that krill form schools within 150 m of the surface, so these observations of krill so deep and so close to the bottom were a surprising and very exciting find. It's uncertain whether this is related to the extremely steep seamount topography of the area, or the behaviour of the krill themselves. Not for the first time in this survey, our observations have thrown up more questions than answers!
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