Has been observing the
acidification of the Black Sea
waters in XX century?
Alexander Polonsky
Marine Hydrophysical Institute
2011
Sea water acidification: what is it?
Keeling curve for monthly atmospheric CO2 concentration at Mauna
Loa Observatory, Hawaii demonstrates its rise. Associated pH
decreasing is acidification. At the same time pH changes can be due
to natural processes.
Total yearly CO2
anthropogenic
emission is about
10 Gt now (in C
equivalent)
Science (2009).
CO2 + H2O <=> [H]+ + [HCO3]pH is a measure of the acidity. Pure water is
neutral, if a pH close to 7.0 (at 25°C). Solutions
with a pH less than 7 are said to be acidic and
solutions with a pH greater than 7 are alkaline.
pH approximately equals to p[H], the negative
logarithm (p[H], base 10) of the molar
concentration of dissolved hydro ions
(Wikipedia).
“Ocean acidification refers to a reduction in the pH of the
ocean over an extended period, typically decades or longer,
which is caused primarily by uptake of carbon dioxide from
the atmosphere, but can also be caused by other chemical
additions or subtractions from the ocean. Anthropogenic
ocean acidification refers to the component of pH reduction
that is caused by human activity”
Definition, approved by
Surface ocean pH decline vs total carbon
emissions and release time. Dangerous level is
0.2 to 0.3 per century (Science, 2008)
Variability of air/water pCO2 and pH in the
North tropical Pacific: 1988-2008
Time series of (top) atmospheric
CO2 and surface ocean pCO2
and (bottom) surface ocean pH
at the atmospheric Mauna Loa
Observatory (MLO) on the island
of Hawai‘i and Station ALOHA in
the subtropical North Pacific
north of Hawai‘i, 1988–2008.
After (Science, 2010)
In situ pH trend is about
-0.2 per century
Recent changes in ocean temperature, acidity, and carbonate ion concentration. (A) Surface
temperature anomaly for January 2010 relative to the mean for 1951–1980. (B) The same
data presented in (A) as a function of latitude. (C) Estimated change in annual mean sea
surface pH between the pre-industrial period (1700s) and the 1990s. (D) Estimated change in
annual mean sea surface carbonate ion concentration between the pre-industrial period
(1700s) and the 1990s [Science, 2010]
Number of pH observations in the
Black Sea in XX century
Time series of Black Sea pH
8.8
9.2
Surface
10 m
8.6
8.8
8.4
8.4
8.2
8
8
7.6
7.8
1920
1940
1960
1980
2000
8.6
1920
1940
1960
1980
2000
1960
1980
2000
8.2
100 m
8.4
1000 m
8.1
8
8.2
7.9
8
7.8
7.8
7.7
7.6
7.6
1920
1940
1960
1980
2000
1920
1940
Average seasonal pH distribution at
100 m (left) and mean pH profile (right)
8.9
8.8
8.7
8.6
8.5
8.4
8.3
8.2
8.1
8
7.9
7.8
7.7
7.6
7.5
7.4
44
43
42
February -March
30
32
34
36
38
40
0
400
800
1200
1600
44
2000
7.6
42
32
34
36
8
8.2
8.4
8.6
Vertical profile of the average
(1924-2000) pH in the Black sea
August-September
30
7.8
38
40
Space distribution of Ekman vertical
decadal velocity in winter (10-6 m per sec)
1951-1960
1981-1990
Weakening of
upward velocity
1961-1970
1991-2000
1971-1980
2000-2007
Intensification of
upward velocity
The principal reason of interdecadal regional (Black
sea) atmospheric variability is Atlantic
Multidecadal Oscillation
ΔP,Δφ
4.0
1
2.0
0.0
2
-2.0
-4.0
1880
1920
1960
2000
Variations of SLP difference in Azores High
and Iceland Low (curve 1) and difference of
latitudes of these atmospheric centers of
action (curve 2) in winter (Polonsky et al,
2004).
Frequency of winter Black sea cyclones
In fact, this is manifestation of Atlantic
Multidecadal Oscillation (Polonsky,
Voskresenskaya, Bardin, 2007)
Principal results
• The pH decreasing (acidification ?) occurred in
the Black Sea between ~1980 and 2000.
• The rate of pH decreasing for the last decade of
XX century exceed 0.2 pH units per decade in
the upper sea layers.
• Such high level of pH decreasing is mostly due
to intensification of the upward motion in the
subsurface layers in 1960-80’s. This leads to
pH decreasing in the upper layers because pH
is decreasing to the depth.