1. Seawater-atmosphere CO2 Flux during
RADMED_0216 campaign
Alberto Aparicio-González1, Safo Piñeiro1, Mari Carmen García-Martínez2, Rosa Balbín1, Juan Antonio Jimenez1, Jose Luís López-Jurado1, Francina Moya2
Instituto Español de Oceanografía. 1 Centro Oceanográfico de Baleares. 2 Centro Oceanográfico de Málaga.
In general, it is considered that coastal areas are a sink for CO2 (Borges, 2011) but the mechanisms why sometimes coastal systems act as sources of atmospheric CO2 and others as a sink have still not been described. Lee et al (2011) consider that the Western Mediterranean is an important sink for atmospheric CO2.
The carbon cycle is controlled by physical and biological processes. Physical processes are related to the exchange of CO2 in the atmosphere-ocean interface and also to the transport of CO2 to the deep ocean.
Atmospheric CO2 in seawater depends on the difference of the partial pressures between the atmosphere and the ocean as well as wind speed. The amount of CO2 that is transferred to sea water depends on its solubility which is a function of the temperature.
FCO2
SPATIAL VARIATION
Throughout the campaign, we found negative values of FCO2, which means a net inflow of CO2 from the atmosphere into the sea (mean mmol m-2 d-1). The minimum values (-50 mmol m-2 d-1) (green in Figure 1):
February 9: 40 km east of Barcelona
February 12: 33 km east of Valencia
February 27: in the transect between Ibiza and Mallorca.
PCA
Principal Component Analysis (PCA) was performed to identify the relationship between the variables measured continuously and the FCO2.
The variables used for the ACP are in Table 1. and the results are in Figure 2.
METHODS
RADMED_0216 was developed between 4 and 27 February 2016 along the Spanish Mediterranean coast in the R/V F.P. Navarro. The study area covers the continental shelf and slope from the Alborán Sea (4.4 °W 36.2 °N) to Barcelona (2.1 ° E °N) and to the north of Menorca (4.4 °E, 40.1 °N).
During this survey both open ocean and coastal areas, including the Ebro River Delta were sampled. We measured the mole fraction of carbon dioxide (xCO2) in surface waters and in the atmosphere with a SUNDANS (Surface UNderway carbon Dioxide partial pressure ANalySer) device.
Following SOPs (Standard Operating Procedure) (DOE, 1994) , CO2 Flux (FCO2) was calculated, using salinity and temperature measurements continuously (SeaBird SBE21) and wind speed (PB200 AIRMAR WeatherStation).
Figure 2. PCA results
PC1 collects information related to the sample position and atmospheric conditions. Barometric pressure and air temperature are highly correlated and opposed to the coast distance and the water depth.
PC2 (21% of the variance) opposes FCO2 and atmospheric temperature to fluorescence.
Fluorescence increment causes the lower the FCO2 (more negative) and therefore the CO2 is sinking in the sea from the atmosphere supplying the demand when phytoplankton is growing.
Atmospheric temperature is not correlated to water temperature (r = 0.19), this is because we were sampling in winter and water temperature remains cold during this period (13,5 to 16 °C). Atmospheric temperature shows a greater variation range (between 7 and 21 °C) due to the fact that atmospheric heating and cooling is much easier than that of seawater.
Figure 1. FCO2 in RADMED_0216
Variable PC1 PC2 PC3
AIR_TEM [ºC] , , ,599
BAROMETRIC_PRESSURE [hPa] 0, , ,346
LATITUDE [degree_north] -0, , ,288
FLUOR_mdm [mg m-3] , , ,529
FLUX_CO2 [mmol m-2 d-1] 0, , ,278
DEPTH_mdm [m] , , ,229
DIST_a_COSTA [km] , , ,170
Table 1. PCA results
ACKNOWLEDGMENTS
This work has been partially financed by the probram Action-MED and the ATHAPOC project.
REFERENCES
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