2018 Cruise - JC165

Studying Ocean Acidification at PAP

Written by Sue Hartman.

The amount of biologically active dissolved gases in the surface ocean, such as oxygen and carbon dioxide, changes throughout the year. This seasonal change is influenced by temperature and the growth of plankton. The sensors that we have deployed track changes in all of these variables along with changes in the nutrients that influence the plankton growth.

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Figure 1.  ‘Team CO2’ – setting up the new equipment to measure seawater and atmospheric carbon dioxide.

We now have a long time series of measurements and can see both the seasonal and year to year variations. Examples of the data are on the PAP website www.noc.ac.uk/pap/data. The cold, productive waters of the North Atlantic are especially interesting to study changes in carbon dioxide; this area is a sink for this important greenhouse gas. Whilst this oceanic sink may reduce the atmospheric carbon dioxide the water acidity is increasing and this can have harmful effects on some species. A process very similar to adding dissolved carbon dioxide to water to make soda water. We can track the increase in ocean acidification (a decrease in pH) through direct measurements of pH as well as measuring carbon dioxide.

 

 

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Figure 2.  The box for atmospheric carbon dioxide measurements high up on the buoy mast.

 

The data will be calibrated using the bottle samples – once they have been measured back at NOC. Each year we collect bottle samples to full ocean depth to give us profiles of oxygen, nutrients, carbon dioxide and pH. All of these measurements are used to monitor the influence of ocean acidification at depth and to consider changes in relation to the longer time series.  Currently we are also setting up an underway system to measure carbon dioxide, temperature, salinity and oxygen with the sensors that we have on board to compare with the ships underway systems.

 

 

 

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Figure 3. The pelagic team sampling from the CTD rosette for oxygen, nutrients, dissolved inorganic carbon, chlorophyll and temperature.
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2018 Cruise - JC165

Deployment of the PAP1 mooring

 

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The PAP 1 mooring is a collaboration between four organisations, NMF, OBE, The Met Office and OTEG. Overall design, development and deployment of the physical system is the responsibility of the Sensors and Moorings (S&M) team within the National Marine Facilities (NMF). The surface buoy (a Balmoral ODAS buoy) complete with meteorological sensors is supplied by the Met Office. Ocean Technology and Engineering Group (OTEG) with extensive support from Campbell Ocean Data, look after the electronics communications and power hub and real-time data stream as well as occasional trial sensor deployments. The specifications and scientific data are provided by and for thecustomer; the Ocean  Biogeochemistry and Ecosystems Group.

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The mooring is over 6.5 kilometres in length and sits in 4850 metres (m) of water giving it a 4 kilometre plus watch circle. The majority of the scientific instruments are house in the Autonomous Sensor Platform (ASP) suspended 30 m below the surface buoy.

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Most years the top end of the mooring including the ODAS buoy and the ASP and chain are all that is replaced. This year for the first time in four years, the entire mooring has been serviced, which unusually included stripping down and rebuilding the ODAS buoy at sea to replace the keel and many of the meteorological sensors.

 

Written by Nick Rundle

Senior Technical Officer