CARBOOCEAN

CARBOOCEAN Integrated Project (IP) aims at an accurate assessment of the marine carbon sources and sinks. Target is to reduce the present uncertainties in the quantification of net annual air-sea CO2 fluxes by a factor of 2 for the world ocean and by a factor of 4 for the Atlantic Ocean. The IP will deliver description, process oriented understanding and prediction of the marine carbon sources and sinks with special emphasis on the Atlantic and Southern Oceans on a time scale –200 to +200 years from now. Expected breakthroughs by CARBOOCEAN IP will be firm answers to the following as yet unresolved questions:

The CO2 Group of IIM is involved in 3 of the 5 core themes

Core Theme 1: North Atlantic and Southern Ocean CO2 air-sea exchange on a seasonal-to-interannual scale.

One of the goals of this Core Theme 1 is the description and quantification of the CO2 air-sea exchange on a seasonal-to interannual scale for the Atlantic Ocean and the Southern Ocean, using an observing system for surface marine CO2 in the Atlantic. CO2 sinks through combination of in situ measurements, satellite data, and models will be developed. The IIM CO2 Group contribute to this Core Theme with a VOS (voluntary observing ships) line on board BIO Las Palmas from Cartagena (Spain) to Ushuaia (Argentina) and with the fixed station MINAS (Multidisciplinary Iberian North Atlantic Station) located in the North Atlantic..

A deployment of a CARIOCA buoy was done in October 2005 at position 43ºN, 11ºW, to measure in real time the salinity, temperature, chlorophyll, oxygen and CO2 in surface water. The buoy also provides air temperature and wind velocity. These variables are very important to study the impact of climate change in the Iberian basin. Samples are taken routinely to calibrate the CARIOCA sensors.

Distribution of the different variables measured in MINAS.

Core Theme 2: Detection of decadal-to-centennial Atlantic and Southern Ocean carbon inventory changes

Understanding the distribution of anthropogenic carbon (CANT) in the ocean and quantifying the CANT inventories are important issues to reduce the uncertainties attached to the present global carbon budget, analysing the coupling of the carbon cycle and climate as well as to identify the changes in ocean biogeochemical cycles including present and future ocean acidification. All these questions are central in CARBOOCEAN. Many data-based approaches have been developed and applied at regional or global scales. However different methods may lead to different results. An intercomparison CANT exercise was made in the WP9 framed in this Core Theme 2, applying 4 different approaches methods to the same data set: one zonal section in the North Atlantic and one long meridional section from the Arctic to the Antarctic continent. Except for the Polar Regions, an important agreement among the approaches exists. A new method (phy-Ctº) was developed by CSIC-IIM using the subsurface layer to define the boundary conditions for the calculation of Cant.

From the specific inventories of Cant (mol·m-2) plotted in the following figure (Vázquez-Rodríguez, et al., GBC 2007) it can be seen how all of the methods give reasonably coincident inventories except for that obtained using the GLODAP data, which is obtained the C* method (Lee et al. 2003 and Gruber, 1998). The greatest similarities occur in the subtropical and equatorial regions. The GLODAP inventory stand out from the rest of results in the Southern Ocean, giving significantly lower numbers (5 mol·m-2). Furthermore, we need test these different methods with model-generated synthetic data in different scenarios and specific regions.

Core Theme 3: Carbon uptake and release at European regional scale

Based on the results obtained in this IIM CO2 Group (Rios et al., 2001, Alvarez et al., 2005), the Mediterranean Water (MW) is composed of 85% Central Water and 15% Mediterranean Overflow Water (MOW). Besides, a small portion of Central Waters penetrates through the Strait of Gibraltar at the Mediterranean Sea where the deep water will be formed in the Levantine zone and Lion Gulf. According to this mechanism 0.07 Pg C·y-1 of Central Waters are drawdown to form MW. Although this rate seems to be small, it represents 26% of the rate of the CANT transported by the thermohaline circulation in the North Atlantic. The importance of the Gibraltar strait as a CANT penetration zone and CANT exchange contributing to the global carbon budgets, was the cause to establish a fixed station in the strait call GIFT (GIbraltar Fixed Time series station). This GIFT station is monitored by the ICMAN group