by Hakim Abdi, Laura Matkala, Lauriane Quéléver and Nandita Rajan
Fishermen have been following the wind and the waves for ages, but in atmospheric research this is a relatively new field of interest. Oceans are, however, a significant sink for sink for atmospheric carbon dioxide (CO2). They can also release CO2 through different pathways.
Many people relate climate change and CO2 emissions to the burning of fossil fuels (https://www3.epa.gov/climatechange/ghgemissions/gases/co2.html). Some are aware that forests, and plants in general exchange CO2 with the atmosphere (http://globecarboncycle.unh.edu/CarbonCycleBackground.pdf). What is not perhaps often considered by the public is that waterbodies, such as seas can be sinks or sources of atmospheric CO2 too. This means that they can take up or release CO2 from and to the atmosphere. (http://www.pmel.noaa.gov/co2/story/Ocean+Carbon+Uptake). Our group worked on a dataset from Young Sound fjord, north-eastern Greenland (http://www.asp-net.org/content/2014-young-sund-campaign) with an attempt to figure out what could be the driving atmospheric factors behind the flux of CO2 from water in these types of fjord ecosystems and how climate change affects water sea exchanges.
Our flux data covered the time period from early June to late September 2014. A flux of gas tells you how much of the aforementioned gas moves through a unit area during a fixed period of time, in this case how much CO2 moves through an area of one square meter in one second. Since the ice melts quite late and the freezing starts rather early in Young Sound (http://www.int-res.com/articles/meps/175/m175p261.pdf), we were able to examine the CO2 flux in different ice conditions. As expected, we observed significantly more flux events when there was very small ice cover or in total absence of ice compared to the situation with full ice cover. Three very clear flux events stood out from the data. These events took place in early and late July and late August.
When a strong wind blows the seawater towards the shore, the water eventually hits the ground and causes the formation of tiny spray droplets of water. These droplets will rise just above the water surface and start releasing CO2 to the atmosphere. Basically they give away all the liquid to the surrounding air until there’s only salt left. This salt then returns to the water. However, this depends on the droplet’s residence time in the air. Some sea spray particles will fall back to the sea and not evaporate all water (https://www.nrdc.org/onearth/science-sea-spray). The weather was windy and the wind blowing from the direction of north-west or north during the flux events. The sea and the shoreline of the fjord are in these wind directions. The wind coming directly along the shoreline of the Young Sound fjord could accelerate sea spray droplet formation even more than the wind coming from the sea. The other variables we looked at also seemed to support the theory that sea spray is the main contribution on these CO2 fluxes events, but unfortunately things are not that simple.
Sea spray-mediated CO2 flux is a topic, which has been poorly studied so far and we were analyzing a limited amount of data. Additionally, to make things even more complicated, there are also two other pathways contributing to CO2 and other gas exchange between the sea surface and the atmosphere. In fact, the partial pressure difference of a gas between the sea and the atmosphere is considered as most important pathway. The third pathway one is called bubble-mediated exchange.
In scientific research there are always matters that could be improved. Sometimes there’s not enough data, sometimes there’s too much data and people don’t know what to do with it. As this course was not only concentrating on natural sciences, we also faced the fact of having a limited amount of time for the data handling. It would also have been very useful to have marine data from the Young Sound Fjord. In general this still gave us, a group of four people who knew almost nothing about sea-air gas transfer before the course, a nice introduction to the topic.