The coastal ocean has been to a large extent ignored in global carbon budgets, even if
the related flows of carbon and nutrients are disproportionately high in comparison with its
surface area (Wollast 1998). It receives massive inputs of organic matter and nutrients from
land, exchanges large amounts of matter and energy with the open ocean across continental
slopes and constitutes one of the most biogeochemically active areas of the biosphere
(Gattuso et al. 1998). Hence, intense air-water CO2 exchanges can be expected in the coastal
ocean (Thomas et al. 2004; Borges 2005; Borges et al. 2005; 2006).
Coastal seas usually exhibit a distinct seasonal cycle of air-sea CO2 fluxes shifting
from a source to the atmosphere to a sink from the atmosphere, to a large extent in relation to
biological activity. The direction and intensity of the air-sea CO2 fluxes are to a large extent
controlled by net ecosystem production (NEP), as exemplified in Figure X for the Southern
Bight of the North Sea (SBNS). The SBNS acts as a sink of atmospheric CO2 and is oversaturated in O2 in April and May during the phytoplankton blooms, and as a source of CO2 to
the atmosphere during the rest of the year due to the degradation of organic matter leading to
an under-saturation in O2. Overall, the SBNS is a sink of atmospheric CO2 due to the seasonal
decoupling of organic matter production and degradation, with a probable export of organic
matter to the adjacent areas in relation to the short flushing time of the water mass in the area
(on average 70 days).
References
Borges A.V. (2005) Do we have enough pieces of the jigsaw to integrate CO2 fluxes in the
Coastal Ocean ? Estuaries, 28(1):3-27
Borges A.V., L.-S. Schiettecatte, G. Abril, B. Delille & F. Gazeau (2006) Carbon dioxide in
European coastal waters, Estuarine, Coastal and Shelf Science, 70(3), 375-387
Borges A.V., B. Delille & M. Frankignoulle (2005) Budgeting sinks and sources of CO 2 in
the coastal ocean: Diversity of ecosystems counts, Geophysical Research Letters, 32, L14601,
doi:10.1029/2005GL023053
Gattuso, J-P., M. Frankignoulle, and R. Wollast (1998) Carbon and carbonate metabolism in
coastal aquatic ecosystems. Annual Review Ecology Systematics 29:405-433.
Schiettecatte L.-S., H. Thomas, Y. Bozec & A.V. Borges (2007) High temporal coverage of
carbon dioxide measurements in the Southern Bight of the North Sea, Marine Chemistry,
106(1-2), 161-173
Thomas, H., Y. Bozec, K. Elkalay, and H. J. W. De Baar (2004) Enhanced open ocean storage
of CO2 from shelf sea pumping. Science 304(5673):1005-1008.
Wollast, R. (1998) Evaluation and comparison of the global carbon cycle in the coastal zone
and in the open ocean, p. 213-252. In K. H. Brink and A. R. Robinson (eds.), The Global
Coastal Ocean. John Wiley & Sons.
Figure X Annual cycle (from June 2003 to May 2004) of the partial pressure of CO2 (pCO2), oxygen saturation
level (%O2 in %), of net ecosystem production (NEP in mgC m-2 d-1) estimated from a dissolved inorganic
carbon mass balance, and air-sea CO2 fluxes (FCO2 in mgC m-2 d-1) in the Southern Bight of the North Sea
(adapted from Schiettecatte et al. 2007).
%O2
100
FCO2
200
150
100
50
0
-50
-100
NEP
400
100
1000
500
300
0
0
-500
200
-100
130
2000
1500
pCO2 (µatm)
200
pCO2
500
-1000
-150
-1500
-200
100
-200
-2000
J J A S O N D J F M A M
Months
120
110
100
90
%O2 (%)
300
FCO2 (mgC m -2 d-1)
400
200
NEP (mgC m -2 d-1)
pCO2 (ppm)
500