Geoscience Reference
In-Depth Information
Summer
Winter
8.3
8.3
8.2
8.2
8.1
8.1
8.0
8.0
7.9
7.9
7.8
7.8
7.7
2000
7.7
2020
2040
2060
2080
2100
2000
2020
2040
2060
2080
2100
300
300
200
200
100
100
Baltic Sea
Aragonite saturation
Aragonite saturation
Calcite saturation
Calcite saturation
Baltic Sea
0
0
2000
2020
2040
2060
2080
2100
2000
2020
2040
2060
2080
2100
Year
Year
Figure 3.6 Twenty-i rst century changes in pH T (top) and [CO 3 2- ] (bottom) for the European seas and the global-ocean average under typical conditions in
summer (left) and winter (right). Results are computed using the IPCC A2 scenario (red) and the IPCC B1 scenario (blue) based on observed A T and assuming
thermodynamic equilibrium between atmosphere and ocean. Results differ from the global ocean mean (solid line, Key et al. 2004 ) because of different
chemical and physical conditions for each of the European seas: Baltic Sea (dot-dash line, A T = 1600 μmol kg -1 , S = 7, T = 0°C in winter and 20°C in summer);
Black Sea (dotted line, A T = 3256 μmol kg -1 , S = 18.075, T = 6.5°C in winter and 24°C in summer); and Mediterranean Sea (dashed line, A T = 2560 μmol
kg -1 , S = 38, T = 13°C in winter and 26°C in summer). Calculations were made using the R software package 'seacarb' (Lavigne and Gattuso 2010 ).
exceptionally low [CO 3 2- ]. Only in the Baltic is the
surface [CO 2 ]/[CO 3 2- ] ratio projected to reach and
even exceed 1.0 during this century. This ratio
reaches unity at pH = (p K 1 + p K 2 )/2 when C T = A C .
As the decline continues to even lower levels of
[CO 3 2- ] and higher levels of [CO 2 ], particularly in
winter, Baltic surface waters reach the point where
C T = A T . At that threshold, the traditional buffer
capacity -(∂pH/∂ A T ) -1 , which characterizes resist-
ance to changes in pH, reaches its minimum
( Egleston et al. 2010). Indeed, at that same thresh-
old, all of the six new buffer factors derived by
Egleston et al. ( 2010 ), dei ned as inversed relative
changes in p CO 2 , [H + ], and [CO 3 2- ] with respect to C T
and A T , also reach their minima.
Although projected changes in pH are largely
insensitive to the A T of seawater, higher A T does
imply a greater uptake of anthropogenic CO 2 ,
which is inextricably linked to greater consump-
tion of carbonate ions. These equilibrium calcula-
tions project that with the A2 scenario, the mean
global ocean reduction in [CO 3 2- ] during the 21st
century will be 97 μmol kg -1 under summer condi-
tions. Summertime reductions in the more alkaline
Mediterranean and Black seas ( A T = 2560 and 3256
μmol kg −1 ) are 24% and 47% greater, whereas the
[CO 3 2- ] reduction in the less alkaline Baltic Sea ( A T =
1600 μmol kg −1 ) is 62% less. Despite these dramatic
differences in absolute changes, the relative change
(absolute change divided by the [CO 3 2- ] in 2000)
 
Search WWH ::




Custom Search