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International Journal of Marine Science 2014, Vol.4, No.72, 1-7
http://ijms.biopublisher.ca
2
owing to the fact that CO
2
is the major driver of
anthropogenic climate change. Additionally, in order
to understand how the changing global environment
may alter the carbon cycle, it is necessary to further
analyse the fluxes and examine the physicochemical
and biological processes that determine them.
1 Data and methods
1.1
Sources of observed data
The observed data used for this research where
obtained from the Porcupine Abyssal Plain and K1
Central Labrador Sea oceanographic mooring sites
in the North Atlantic Ocean (Figure 1).
Figure 1 Map of the North Atlantic Ocean showing the Porcupine Abyssal Plain (49
o
N, 16.5
o
W) and Labrador Sea (56.5
o
N, 52.5
o
W)
1.2
Air-sea CO
2
fluxes estimation
The calculation of CO
2
flux (
f
CO
2
) in ocean and
climate models is based on the indirect bulk method.
The net exchange of CO
2
(
f
) between the ocean surface
and the atmosphere is estimated from the air-sea
difference in partial pressure of CO
2
(
p
CO
2
) and the
gas transfer velocity (
k
) using the equation (Wanninkhof,
1992, 2007; Donelan and Wanninkhof, 2002):
f
CO
2
=
k
×(
)
K
0
×
p
CO
2
(1)
Where
k
is the gas transfer velocity of CO
2
exchange,
is the wind speed,
K
0
is the solubility of CO
2
in seawater
and is a function of salinity and temperature (Weiss,
1974), and
p
CO
2
is mean air-sea
p
CO
2
difference,
p
CO
2
= [(
p
CO
2
-air) – (
p
CO
2
-sw)]
(2)
Where
p
CO
2
-air and
p
CO
2
-sw represent the respective
partial pressure of carbon dioxide in the atmosphere
and seawater (Rutgersson et al., 2008).
The transfer velocity,
k,
is regarded as a function of
wind speed,
, and the Schmidt number (Sc), although
this is still controversial (Weiss et al., 2007;
Rutgersson et al., 2008). The Schmidt number (Sc) is
the ratio of the kinematic viscosity of seawater to the
diffusion coefficient of the considered gas. For wind
speeds larger than 5 ms
− 1
,
k
is proportional to Sc
− 1/2
(Liss and Merlivat, 1986). Different functions which
refer to Sc = 660 (CO
2
at 20 C) have been proposed to
describe
k
660
as a function of wind speed at a reference
height of 10 m (
10
). Wanninkhof (1992) suggested a
quadratic equation:
k
660
= 0.31
2
10
(3)
which gives
k
for any other Sc as
k
= 0.31
2
10
660 /
Sc
(4)
A cubic dependence is given from Wanninkhof and
McGillis (1999):