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Unravelling the mysteries of the subpolar North Atlantic

Why should we care about what is going on in the cold and stormy subpolar North Atlantic? I can give you at least three very good reasons:
  1. First of all, the dynamics of this region are crucially important for modulating climatic conditions in North-Western Europe. So basically this is what keeps the UK’s weather relatively mild for its latitudes.
  2. Secondly, deep-water is formed in the Labrador Sea and this is a key process within the global thermohaline circulation. 
  3. The transport of heat and freshwater by the Subpolar North Atlantic has an impact on global climate, marine ecosystems, hurricanes, and even on rainfall in the African Sahel, the Amazon and parts of the US.  
Main circulation patterns in the North Atlantic. Orange-yellow lines are
surface, warmer currents and blue lines are deep, colder currents.

How do we know what is happening up there? 

Up until now, the subpolar North Atlantic has been inadequately measured and climate models largely fail to represent its features accurately. Last week, Dr Penny Holliday from the National Oceanography Centre (Southampton) visited Bristol to give a departmental seminar in the School of Geographical Sciences, titled “Circulation and variability in the subpolar North Atlantic”. From her talk we got to know more about the importance of long-term monitoring of the circulation in the subpolar North Atlantic and about two major ongoing monitoring programmes. These are providing precious observational data that will help scientists understand more about the interannual to multidecadal variability in these regions, in order to improve the skills of our predictions.

OSNAP (Overturning in the Subpolar North Atlantic Programme) is an international programmed that started in 2014 and includes partners from USA, UK, Canada, China, France, Germany, and the Netherlands. OSNAP is designed to provide for the first time a continuous record of measurements across the entire subpolar North Atlantic, similarly to the RAPID observational system at 26°N which has been monitoring the subtropical gyre since 2004.  Within UK-OSNAP, Penny is leading the observations being made in the deep western boundary current near Greenland.
Penny Holliday on the first UK-OSNAP (plus Extended Ellett
Line and RAGNARoCC) cruise in summer 2014
The Extended Ellett Line is a project led by the National Oceanography Centre (Southampton) and SAMS (The Scottish Association for Marine Science). It represents one of a small number of long-term, high-quality physical time series in the North Atlantic Ocean. This hydrographic section was started in 1975 by David Ellet, initially only in the Rockall Trough. In 1996 the section was extended up to Iceland. The expedition now runs once a year and the data collected includes physical (e.g. temperature, salinity, velocity), chemical (e.g. iron, nutrients, carbon) and biological (e.g. phytoplankton) measurements.  Penny is one of the two Principal Investigators for the Extended Ellett Line.

Most recent findings 

While some more time will be necessary before seeing the first results of the OSNAP project, the most recent significant discovery from the Extended Ellett Line is the importance of the episodic southward flow of the Wyville Thomson Overflow Water. Recent observations highlighted the necessity to include its contribution in the calculations of the heat transport through the Rockall Trough.  In addition, after four decades of observations, it has been observed that the top layers (0-800m) of the ocean in these regions have warmed and exhibit shorter timescale variability.

Data from the 2014 cruise has also shown that temperature and salinity in 2014 were lower compared to the previous 10 years. This suggests that the North Atlantic subpolar gyre would have increased its circulation and expanded, bringing cooler and fresher water into the eastern regions.

Life at sea in the subpolar North Atlantic

The oceanographic cruises organised within these two programmes also offer the chance to several students and early career scientists to get a taste of what life at sea really means.
Penny was one of my supervisors during my MSc in Southampton, where for my research project I was analysing the results of a new simulation with a high-resolution ocean model in the North Atlantic subpolar regions (we have recently published those results). One year or so later, Penny was recruiting some extra people for one of the Extended Ellett Line cruises and she must have remembered our conversations about how I had always wanted to go on a research cruise. So there I was, ready to board the RRS James Cook as part of the physical oceanography team, sailing from Scotland to Iceland. It was such an amazing experience: I think I will be forever grateful to Penny for making my wish come true!
Myself (left) and Natalia Serpetti (right) taking sea water samples from the CTD
(conductivity-temperature-depth instrument) and looking very happy
during the Extended Ellett Line cruise in 2013.
Life at sea is actually pretty hard work and definitely not a holiday. Initial sea sickness aside, and ignoring the fact that I was waking up a 4 am every morning (yes, I had the unluckiest shift ever!), the memories that I will cherish the most are about all the things that I learnt, the awesome people I met, the breathtaking sunrises and sunsets over Iceland (at least due to the unlucky shift I got to see both of them everyday!), the pilot whales occasionally following the ship, and the power of the ocean which makes you feel so small and insignificant. Probably I will also always remember the entire night that some of us spent scooping up and sieving mud from a deep sea sledge, while listening to pretty bad club music: that was actually great fun!


This blog is written by Cabot Institute member Alice Marzocchi, School of Geographical Sciences, at the University of Bristol.  Follow Alice on Twitter @allygully.
Alice Marzocchi

Twitter contacts: @np_holliday    @uk_osnap    @osnap_updates  

Read Alice's other blog: The conference crashers! What are a geophysicist, a climate modeller, and a geochemist doing at a Social Sciences conference?


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