By Jan Strugnell, British Antarctic Survey

Four different scientists with very different research interests have been collecting samples of seawater from the water column using the CTD. The CTD is an instrument used for measuring a number of parameters from the water column (including Conductivity/salinity, Temperature and Depth) and can also be used for collecting water samples from a number of depths throughout the water column. For this weeks diary entry I had a chat to each of them about their science.

National Oceanograpy Centre/University Southampton and BAS PhD student, Rachel Malinowska has been collecting water samples for her PhD using the CTD. Rachel is taking a depth transect from 10 depths (from as deep as 4500 m) from 6 sites around the Bellinghausen and Amundsen Seas and is looking at the differences in bacterial community structure from the sea surface to the sea floor. She has previously investigated bacterial community composition and abundance from sediments in the Southern Ocean and she is now interested in determining whether the breakdown of organic matter occurs during its fall through the water column or in the sediment of the deep sea. Rachel is also interested in comparing bacterial communities in surface water from different regions around Antarctica. She already has samples from the Scotia Arc and Kerguelen and is now adding samples from the Bellingshausen and Amundsen Sea for this biogeographical comparison.

Paul Carter is a PhD student from the Bristol Isotope Group (Bristol University, Earth Sciences Department) and is also collecting water using CTD’s but is hoping to gain very different information from the samples. Paul collects water samples to extract a trace metal called Neodymium. Neodymium originates in rocks on the land but over very long periods of time some of it washes into the oceans. It is present in tiny concentrations in the Southern Ocean (around 20-30 picomoles per kilogram!), but even at this small concentration it is a useful water mass trace and can be used to help determine the movement of water masses around Antarctica and the world’s oceans. Paul collects water at 500 m depth intervals throughout the water column to just above the sea floor. Due to the very tiny concentrations of Neodymium present in the Southern Ocean, Paul needs to filter 4 litres of water for a single sample. He will analyse the water samples for their Neodymium concentration using Mass Spectrometry back in Bristol. Paul’s work is the first study to look at Neodymium concentrations in Antarctic waters.

Dr David Pearce is a microbiologist at BAS and works for the Long Term Monitoring Programme (LTMS B task 7). David is also collecting water from the CTD for a microbial metagenomics project. Microbes include those organisms which are not visible to the naked eye. David is interested in extracting and sequencing the entire microbial DNA present in the water samples he collects to obtain a picture of the ‘whole environmental genome’ from his samples. He is hoping to use this to build up a picture of the physiological potential of these microbes. David samples water from a 30 m depth, as this in the middle of the highest concentration of phytoplankton in the water column. In turn, there are likely to be high concentrations of other tiny microbes in the water which are feeding upon this phytoplankton, and he therefore hopes to collect a high diversity of microbes at this depth. David collects around 300 litres of water per sample, which he then concentrates down to a 300 micro litre volume on board the JCR, which he will use as a starting point for his genetic work back at BAS.

Briony Hull is a 1st year PhD student at BAS (QWAD project) and Manchester University. She has been collecting water samples from a range of depths in order to calibrate the salinity sensors on the CTD. She is using an onboard salinometer to measure salinity in the water column as this gives a more accurate measure than the CTD. Briony is using the information from the CTD in conjunction with data from the Acoustic Doppler Current Profiler (ADCP) to investigate currents on the continental slope. Specifically she is trying to determine if these currents are strong enough to resuspend sediment. The reason she is looking at this is because there are a number of channels present on the continental slope in Western Antarctica and she is trying to determine what has led to their formation, and whether it is possible that they are caused by turbidity currents, or by other factors, such as melt water or tidal forces. Her work is the first of this kind to be done in Antarctica.