Calcareous Ooze: C02 Problems 229
In constrast, in the equatorial areas of !he central Pacific, increased fertility leads
to an increased supply of calcareous shells which goes well beyond the increased
supply of organic matter in this region. Carbonate readily transits to the sea floor,
while organic carbon tends to be filtered out on the long way down (see Fig. 6.1).
Consequently, the ratio of calcitic shell to organic carbon is relatively high in the
pelagic realm, which is favorable for the preservation of calcite. Nevertheless, some
of the carbonate also dissolves above the lysocline, due to organic matter supply.
Preservation is never perfect.
8.5.5 Why Is There a CCD? The ultimate reason why abyssal waters dissolve
calcite is that organisms supply calcium carbonate to the sea floor in excess of the
amount that can be sedimented over the long run. This amount is fixed by !he influx
from the continents and from hydrothermal sources. The shell supply to the ocean
floor that exceeds the overall influx ultimately depletes the ocean of calcium carbonate, which results in bottom waters that are sufficiently undersaturated to redissolve
!he excess supply of calcium carbonate to the sea floor. Thus, a dynamic steady state
is maintained. From this simple "book-keeping" concept, it can be readily inferred
that, through geologic time, an overall increase in productivity leads to an overall
increase in dissolution, and vice versa.
Of course, we must be careful not to extrapolate too far back, when using the
present ocean as a model for the past. Mass production of coccoliths (or better,
nannofossils) began sometime in the early Cretaceous, of planktonic foraminifers in
the late Cretaceous. Also, if !he ocean was less well mixed in the Mesozoic than
today (say, because of less vigorous deep water production), this would have greatly
affected the general nature of !he CCD at !he time.
8.5.6 A Global Experiment. At the present time, mankind is engaged in a global
experiment involving carbonate dissolution, as well as climatic change. We - the
industrial nations mainly - are burning off enormous amounts of coal and oil at an
increasing rate. Large-scale deforestation is proceeding in !he tropics and elsewhere,
for the sake of agricultural development and for wood products and fuel. The resulting carbon dioxide enters !he atmosphere. So far, an amount equivalent to almost 50
% of the C02 originally present in !he atmospheres has been added within the past
century. About one half of this amount has entered the ocean, the rest has stayed in
the atmosphere (Fig. 8.13a). Eventually, over the next few centuries, some ten times
the original C02 in the atmosphere could be added, if the readily available coal and
oil is burned.
How will !he ocean react to the continuing (and perhaps increasing) input of C02?
In the long run, the ocean floor will neutralize most of the industrial C02 through
the dissolution of carbonate (Fig. 8.13b):
C02 + H20 + CaC03 ---t Ca 2 + + 2HCO-3 .
(8.1)
Thus, the industrial C02-pulse will produce a hiatus on the sea floor. A thickness of
about I m of carbonate sediment will have to be dissolved from the carbonate-bearing
sea floor, assuming that available coal and oil deposits are burned up. Initially, how-
In constrast, in the equatorial areas of !he central Pacific, increased fertility leads
to an increased supply of calcareous shells which goes well beyond the increased
supply of organic matter in this region. Carbonate readily transits to the sea floor,
while organic carbon tends to be filtered out on the long way down (see Fig. 6.1).
Consequently, the ratio of calcitic shell to organic carbon is relatively high in the
pelagic realm, which is favorable for the preservation of calcite. Nevertheless, some
of the carbonate also dissolves above the lysocline, due to organic matter supply.
Preservation is never perfect.
8.5.5 Why Is There a CCD? The ultimate reason why abyssal waters dissolve
calcite is that organisms supply calcium carbonate to the sea floor in excess of the
amount that can be sedimented over the long run. This amount is fixed by !he influx
from the continents and from hydrothermal sources. The shell supply to the ocean
floor that exceeds the overall influx ultimately depletes the ocean of calcium carbonate, which results in bottom waters that are sufficiently undersaturated to redissolve
!he excess supply of calcium carbonate to the sea floor. Thus, a dynamic steady state
is maintained. From this simple "book-keeping" concept, it can be readily inferred
that, through geologic time, an overall increase in productivity leads to an overall
increase in dissolution, and vice versa.
Of course, we must be careful not to extrapolate too far back, when using the
present ocean as a model for the past. Mass production of coccoliths (or better,
nannofossils) began sometime in the early Cretaceous, of planktonic foraminifers in
the late Cretaceous. Also, if !he ocean was less well mixed in the Mesozoic than
today (say, because of less vigorous deep water production), this would have greatly
affected the general nature of !he CCD at !he time.
8.5.6 A Global Experiment. At the present time, mankind is engaged in a global
experiment involving carbonate dissolution, as well as climatic change. We - the
industrial nations mainly - are burning off enormous amounts of coal and oil at an
increasing rate. Large-scale deforestation is proceeding in !he tropics and elsewhere,
for the sake of agricultural development and for wood products and fuel. The resulting carbon dioxide enters !he atmosphere. So far, an amount equivalent to almost 50
% of the C02 originally present in !he atmospheres has been added within the past
century. About one half of this amount has entered the ocean, the rest has stayed in
the atmosphere (Fig. 8.13a). Eventually, over the next few centuries, some ten times
the original C02 in the atmosphere could be added, if the readily available coal and
oil is burned.
How will !he ocean react to the continuing (and perhaps increasing) input of C02?
In the long run, the ocean floor will neutralize most of the industrial C02 through
the dissolution of carbonate (Fig. 8.13b):
C02 + H20 + CaC03 ---t Ca 2 + + 2HCO-3 .
(8.1)
Thus, the industrial C02-pulse will produce a hiatus on the sea floor. A thickness of
about I m of carbonate sediment will have to be dissolved from the carbonate-bearing
sea floor, assuming that available coal and oil deposits are burned up. Initially, how-