A breathing ocean

Latitude: 62°48′  N
Longitude: 002°36′ W
Waveheight: 2.5 meters
Water temperature: 6.7 Celcius
by Gisle Nondal & Emil Jeansson

A group from the Uni Bjerknes Centre and the Bjerknes Centre for Climate Research in Bergen, Norway, are on-board to perform measurements related to the oceanic cycling of carbon, in addition to measurements estimating the flux of oxygen directly involved in biological activity.

The parameters describing the oceanic carbon cycle include total inorganic carbon dissolved in the seawater (DIC), total alkalinity, pH, and the partial pressure of CO2 (pCO2).

Projected ocean acidification in the North Atlntic, and related impacts on corals by 2020, 2060 and 2100: from better (blue) to worse (orange) conditions for coral skeletal growth. Source: Climate Change 2007: The Physical Science Basis. Intergovernmental Panel on Climate Change (IPCC).

DIC includes both the natural amount of CO2 in the water, but also the amount that has been added due to man-made activities (the so-called anthropogenic, or excess, CO2). CO2 mixes down into the water and dissolves, and since CO2 behaves as an acid in seawater this can decrease the pH (acidity) of the water.

The resulting ocean acidification is of great concern for fisheries and different types of aquaculture, and is expected to be an increasing problem in the future as CO2 emissions rise.

The alkalinity reflects the buffer capacity of the water, and is of concern due to the lower pH levels that is a result of the elevated levels of CO2 in the atmosphere. We also perform continuous measurements of pCO2 and pH, using the ship’s seawater intake (typically located at about 5m depth below our feet).

The quantities of data collected, every 20 sec to a minute, are significant, but it means the temporal resolution is suffiecint to gain an insight into what goes on in the upper part of the ocean during this time of year.

At each of the stations we also sample water from different depths, and determine the amount of DIC and pH. Using the data we calculate the concentration of alkalinity and pCO2, and so we can describe the complete carbon system.

In addition to the carbon parameters we also perform continuous measurements of the ratio between the dissolved gases oxygen (O2) and argon (Ar) in the surface waters. O2 and Ar are physically very similar, and by measuring the ratio between the two compounds one can discount the amount of oxygen injected in the water by physical processes (e.g. mixing and solubility in the water), and determine the amount of oxygen directly resulting from photosynthesis.

This offers another method to estimate the productivity in the water, and to the best of our knowledge, the first time it is applied in the Nordic Seas.

Additional Resources:
Lesson Plans:
Ocean Acidification, (K9-12) by COSEE NOW, link
Ocean Acidification Practicals (K6-12) by C-MORE Hawaii SOEST, link
Coral bleeching: Making the oceans whiter (K6-8) link

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