April 30 2008
April 30 2008
Laura Robinson and her fossil corals from the great trawl haul on 27th April.
Laura Schejter finds a small sponge attached to one of the rocks brought up by the trawl.
Greg Buikema brings up another successful haul of rocks from the seafloor for the geologists.
Biologist Rhian Waller and geologist Julian Pearce take a closer look at the some of the material they found in the dredge.
A dramatic view from the ship this evening.
Today has seen the continuation of dredging in the Scotia Sea, which has yielded lots of great samples for the geologists, and a few small bits of biology (including sponges, which has kept Kate Hendry and Laura Schejter happy!).
Comments from Laura Robinson:
While I was doing my graduate degree I learned about how the skeletons of shallow water corals, like those you find on the Great Barrier Reef, can be used to make records of past conditions in shallow seas. Then I found out about deep-sea corals, and have been working on them for about the last five years. Deep-sea corals record the chemistry of seawater as they form, and our ability to determine how old they are allows us to use ancient samples to reconstruct past conditions in the deep sea. Up until now I have focused on fossilized samples from the North West Atlantic that were collected using submarines and remotely operated vehicles (ROV). These types of deep submergence vehicles are tremendously useful for targeting specific samples.
On this cruise, however, we are using less sophisticated tools for sampling: trawls and dredges that are dragged over the seafloor. One of the reasons for this is that the strong currents and extreme conditions in this part of the ocean would make it unsafe to send a manned submersible to the seafloor. Fortunately by combining careful map-making with trawling we can still collect the samples that we need.
I first met Rhian on a cruise in the North West Atlantic. Although we both live and work in the US we quickly discovered that both of our parents live in the same part of England! Rhian's interest in coral biology and their distributions is the perfect compliment to my paleoclimate research. We need to know how and where coral live today to make sense of our past records. Pairing up to work on this cruise together was the obvious step. Rhian is building on her existing work on the biology and distributions of Antarctic corals, whilst I will be able to use the fossil skeletons to find out how long corals have lived here, and to reconstruct ocean chemistry in this climatically interesting region.
As you may have seen from our previous logs we have already started sub-sampling our new coral collections so that we can start dating them as soon as we get back. We will use two techniques to date the corals, both based on radioactive decay of elements incorporated into the fossil skeletons.
The first is radiocarbon which decays away with a half life of about 6,000 years, allowing us to look back about 40,000 years. The second is based on uranium which has a much longer half life allowing us to date corals back to nearly half a million years.
In the North Atlantic we have found corals lying on the seafloor that are older than two hundred thousand years, and our preliminary work suggests that corals have been living on the Burdwood Bank for over 10,000 years. We hope to find a series of corals covering the time period from the maximum of the last glacial period (~20,000 years ago) through the transition to the warmer climate that we have today. Comparing this data to existing climate records will help us to understand how this transition came about.
We are lucky enough to have a wonderful group of colleagues out here at sea with us and I really cannot envisage a better team. Most of them have already written something for our web.and hopefully you will hear from everyone by the end of the cruise. By that time we hope to have corals from a series of locations that span the Drake Passage, from the tip of South America to the tip of the Antarctic Peninsula. Keep checking back to see how we get on!
Laura Robinson
All photos by Dann Blackwood unless otherwise stated