Our present picture is based on around three million
measurements that were collected and calculated for the
CO
2
net flux. The data were recorded between 1970 and
2007, and most of the values from the past decade were
obtained through the VOS programme. Regions that are
important for world climate such as the subpolar North
Atlantic and the subpolar Pacific have been reasonably
well covered. For other ocean regions, on the other hand,
there are still only limited numbers of measurements.
For these undersampled regions, the database is present-
ly insufficient for a precise calculation. Still, scientists
have been able to use the available data to fairly well
quantify the oceanic CO
2
sink. For the reference year
2000 the sink accounts for 1.4 Gt C.
This value represents the net balance of the natural car-
bon flux out of the ocean into the atmosphere and, con-
versely, the transport of anthropogenic carbon from the
atmosphere into the ocean. Now, as before, the annual
natural pre-industrial amount of 0.6 Gt C is flowing out of
the ocean. Conversely, around 2.0 Gt C of anthropo genic
carbon is entering the ocean every year, leading to
the observed balance uptake of 1.4 Gt C per year. Be-
cause of the still rather limited amount of data, this meth-
od has had to be restricted so far to the climato logical CO
2
flux, i.e., a long-term average over the entire observation
period. Only now are studies beginning to approach the
possibility of looking at interannual varia bility for this
CO
2
sink in especially well-covered regions. The North
Atlantic is a first prominent example. Surprisingly, the
data shows significant variations between individual
years. Presumably, this is attributable to natural climate
cycles such as the North Atlantic Oscillation, which have
a considerable impact on the natural carbon cycle. Under-
standing such natural variability of the ocean is a pre-
requisite for reliable projections of future development
and change of the oceanic sink for CO
2
.
The second method attempts, with the application of
rather elaborate geochemical or statistical procedures, to
calculate how much of the CO
2
in the ocean is derived
from natural sources and how much is from anthropo-
genic sources, although from a chemical aspect the two
are basically identical, and cannot be clearly distin-
guished. Actually, several procedures are available today
that allow this difficult differentiation, and they general-
ly provide very consistent results. These methods differ,
however, in detail, depending on the assumptions and
approximations associated with a particular method. The
most profound basis for estimating anthropogenic CO
2
in the ocean is the global hydrographic GLODAP data-
set (Global Ocean Data Analysis Project), which was
obtained from 1990 to 1998 through large international
research projects. This dataset:
• includes quality-controlled data on a suite of carbon
and other relevant parameters;
• is based on analyses of more than 300,000 water
samples;
• containsdatathatwerecollectedonnearly100expe-
ditions and almost 10,000 hydrographic stations in the
ocean.
All of these data were corrected and subjected to multi-
level quality control measures in an elaborate process.
This provided for the greatest possible consistency and
comparability of data from a number of different laborato-
ries. Even today, the GLODAP dataset still provides the
most exact and comprehensive view of the marine carbon
cycle. For the first time, based on this dataset, reliable
estimateshave been made of how much anthropogenic
carbon dioxide has been taken up from the atmosphere
by the ocean sink. From the beginning of industrialization
to the year 1994, the oceanic uptake of anthropogenic car-
bon dioxide amounts to 118 ± 19 Gt C. The results indi-
cate that anthropogenic CO
2
, which is taken up every-
where across the ocean’s surface flows into the ocean’s
interior from the atmosphere primarily in two regions.
One of these is the subpolar North Atlantic, where the
CO
2
submerges with deep-water formation to the ocean
depths. The other area of CO
2
flux into the ocean is a belt
between around 30 and 50 degrees of southern latitude.
Here the surface water sinks because of the formation of
water that spreads to intermediate depths in the ocean.
The CO
2
input derived from the GLODAP dataset to
some extent represents a snapshot of a long-term transi-
tion to a new equilibrium. Although the anthropogenic
carbon dioxide continuously enters the ocean from the