‘Team CO2’ on DY116
On DY116 Anita and Sue are ‘Team CO2’ measuring carbon dioxide and other gases in the surface ocean around the PAP site. The PAP site has one of the longest biogeochemical time series records in Europe and we started making year-round surface CO2 measurements here 18 years ago to look at changes in greenhouse gases and ocean acidification. The site is a key component of two ocean networks that are interested in our time series measurements: ICOS (Integrated Carbon Observation System https://www.icos-ri.eu/) and EMSO (European Multidisciplinary Seafloor and water column Observatory http://emso.eu/).
The technology has improved with time (we tested some very new samplers and sensors last year in an inter-comparison exercise https://papobservatory.wordpress.com/2019/07/03/icos-inter-comparison-at-dy103/). This year we have equipped the Met Office PAP surface buoy with relatively large membrane-based sensors to measure CO2 in both the seawater and the atmosphere.
This year we will use a new Met Office surface buoy, which is taller than any we have used previously. The challenge of running gas lines from sensors at the base to the top of the buoy was taken on by Nick and Paul onboard.
The ship is equipped with a surface sea water supply that we connected to a flow through system that compares measurements to gas standards. We spent quite a bit of time running yet more gas lines outside to the standard bottle. The system is so compact that it can even be used on sailing ships (https://www.oceanblogs.org/oceanobsvor/about/). It is made by SubCtech (https://subctech.com/) in Germany and this particular system has also been used with a ‘FerryBox’ making trips between Plymouth and Roscoff until very recently. By using this underway system, we will generate a CO2 map of our study area at the start of the buoy deployment, all referenced back to gas standards. This will be a great bench mark for our ongoing buoy-based CO2 measurements.
The sensors on the buoy are from Canada (Pro-Oceanus https://pro-oceanus.com/). They will continue to collect CO2 data throughout the year and we will use these measurements to improve our estimates of carbon dioxide exchange between the atmosphere and the seawater in this productive part of the North Atlantic. It will help in our studies of ocean acidification to investigate how this varies with the changing seasons and from year to year. On DY116 we will be matching up our underway and surface measurements with samples taken from the surface seawater supply.
We will also take samples from the Niskin bottles on the CTD frame, where we have another CO2 sensor (https://www.4h-jena.de/en/maritime-technologies/sensors/hydrocrco2/). The bottles are fired at various depths, down to nearly 5000m – providing a depth profile and absolute reference samples for all of our measurements.
The work is supported by CLASS (Climate Linked Atlantic Sector Science https://projects.noc.ac.uk/class-project/) and iFADO (Framework for the Atlantic Deep Ocean https://www.ifado.eu/). We will have to wait to see the results when we analyse our samples back in the laboratory ashore.