Cruise News

Crozet Cruising 1/1/2006

HAPPY NEW YEAR from all on the RRS Discovery!

Time is flying by and it is the New Year already! There have not been any blogs recently, because we have been hard at work characterising our Southern, low productivity site! Our first results clearly show that M6 is very different to M5, both in terms of the biology and particularly sediment type.

Benthic Crozet study area – a reminder of the location of the main sites, M5 and M6

The sediment is so soft here that we have been having real problems collecting the material in our cores. After one successful megacore, there followed a series of blanks, which considering that each one takes about 4 hours becomes very frustrating! However, last night we made a bit of a breakthrough and have now struck on a more successful strategy. This involves using less weight and hoping that the corer doesn’t sink in so far the mud washes over the top of the tubes!

The notable thing about the sediments is that often, there is a layer of colourless fluff, or “goop” on the surface. This may come from a phytoplankton bloom earlier in the summer; its colourless appearance suggests that it is not fresh, or that perhaps it is not terribly organic rich. Until we recover the sediment traps and carry out some detailed chemistry, we cannot be too certain.

Sediment core collected at M6. Note the layer of “goop” (scientific term!) on the surface. The surface is pretty heterogeneous, as you can see in the photograph of the surface from above the core (right).

Two good trawls have been achieved at Station M6. As expected the trawls at Station M6 had fewer animals in the catch and a total weight about one third, on average, of that collected at Station M5. A few species were similar between the two sites, but their abundance was very much lower at Station M6. Holothurians (sea cucumbers) accounted for 90% of the biomass of the trawl samples at Station M5, whereas they contributed only 70% of the biomass at Station M6. Overall, the species that were dominant at Station M6 were very different than those at Station M5. Of particular note was the presence of a very small holothurian called Kolga at Station M6. Several hundred specimens, about 1cm long, were picked off the fine mesh liner of the trawl cod end. However, as the mesh of the trawl overall is about 4cm it is likely that thousands of specimens were lost through the trawl mesh while it was on the seabed. Kolga is notable for the way it suddenly occurs in mass abundances in the deep sea, perhaps only for a year or two, often forming dense herds of sea cucumbers of several thousands wandering over the abyssal plain mud surface. It is possible that the mass occurrences of Kolga are related to episodic fluxes of organic matter to the seabed.

Sadly, early this morning disaster struck our third trawl. The wire parted with 8000 m trailing behind the ship and the trawl and wire were lost. This now means that we cannot complete our trawling or our video sledge! Hopefully we have enough data to be able to do a comparison between sites, but we will certainly now have to rely on other photographic systems. WASP, or Wide Angle Surface Photography is one such technique – more of that in another blog!