James Clark Ross — Week 5, 21-27 March 2008

22 March 2008 — Census of Antarctic Marine Life diary

By Jan Strugnell

The last few days we have been searching for suitable coring sites and coring for the geologists for the BAS CACHE-PEP-G program. This focus of this program is to investigate the last 10, 000 years of Earth history and specifically how the Antarctic climate has interacted with the global climate. The program uses ice cores, lake sediments and marine sediments to build up this picture.


On this cruise, the geologists are trying to find marine sediments that have built up over the last 10,000 years. Marine sediments are built up over time from tiny photosynthetic algae, specifically siliceous diatoms. When these diatoms are alive they live in the surface layers of the world’s oceans. Different diatom assemblages thrive under different conditions of nutrients, temperature, light and ice conditions. When the diatoms die they sink to the sea floor and therefore this builds up a picture of past climatic conditions in the sediments. By taking a core of these sediments, the geologists are able to essentially look back through time and use the diatom assemblages as indicators of past conditions climatic changes.


To date, there are no published records of these diatom assemblages from the entire Pacific area of the Southern Ocean! Therefore the aim of this part of the cruise is to obtain some cores from this region of Antarctica to get a better idea the climatic patterns in this area over the last 10,000 years. The geologists are using a piston corer to do this, and hope to obtain a number of 10-12 metre long cores of sediment from this region.


The picture below is of a siliceous marine diatom. The presence of is indicative of sea ice whilst the presence of Chaetoceros dichaete is indicative of high productivity.


25 March 2008 — Census of Antarctic Marine Life diary

By Jan Strugnell

Epibenthic sledge (EBS) sorting

Although the majority of the trawling is now completed for the biologists on board, the work has not stopped! There is still plenty of activity in the laboratories and computer rooms to process all of the samples.


Steffi, Dave and Adrian have been spending a lot of time looking down their microscopes sorting the animals that were caught in the Epibenthic sledge (EBS). The animals caught in the EBS typically range in size from 7 mm to 70 cm, although it must be said that some of the largest animals we caught were also captured in the EBS, including a sea cucumber at least 50 cm long!


We are lucky that we have a number of taxonomic experts on board to sort the animals. We have experts on polychaetes (Adrian), bryozoans (Dave) and isopods (Steffi) and so much of the identification and fine level sorting can be done whilst we are on board. Katrin, the group leader (back at BAS) is also an expert mollusc taxonomist. The rest of the animals that cannot be identified are sorted into taxonomic groups and sent to experts at a later date to be identified.


The sampling design of the EBS was set up to try and determine the scales upon which biodiversity is organised in the Amundsen Sea region, as very little is understood of the patterns of abundance, dominance and richness of animals in the Southern Ocean. The EBS sampling design was organised to sample at 3 sites (including inside and outside of Pine Island Bay) with 6 replicates at 500 m at each site and 2 replicates at 1000 m and 1500 m. Both a lower and an upper net on the EBS collected at each of these sites. This comprises a total of 60 samples to be sorted through!! Box cores were also taken from each site and these will provide a measure of grain size and organic content of the sediment at each location.


Commonly there are in order of 1200 animals in a single sample and so this is quite a labour intensive task! So far the initial work on these samples reveals them to be incredibly diverse — with 13 Phyla identified in a single sample. This is an impressive and remarkable level of diversity and represents 1/3 of the major animal body plans that exist on the planet! When completed, this work will provide some strong insight into the geographic and bathymetric scale at which biodiversity is organised in this region, and is likely to turn the Amundsen sea area from perhaps the world's least known sea, into a region in which we have the best idea of the structure of biodiversity in the Southern Ocean.



Previous week — Week 4

Next week — Week 6


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Cousteau ATS International Polar Year 2007-2008 SCAR MarBin CCAMLR SCAR COMNAP Census of Marine Life
20 May, 2008