Uncertainties and what we don't know about acid oceans
By Dr J Floor Anthoni (2007)
In the science of ocean acidification, our
ignorance exceeds our knowledge by a large margin. In this chapter we leave
the word to scientists who are experts in this field. Future will tell
whether their fears will be substantiated, and whether uncertainties will
ever become certainties. Reader please read this in order to get an idea
of the validity of other assertions and whether fears can be substantiated.
Fears: these fears have originated from scientists.
if current trends continue, the oceans will acidify to an extent and at
rates that have not occurred for tens of millions of years.
increased acidity could make the 'biological pump', the sinking of limestone
shells and dead organisms to the bottom of the ocean, less efficient, and
threfore the sequestration of carbon from the air.
could have severe consequences for organisms that make external CaCO3 shells
changes in ocean chemistry may affect the availability of nutrients and
toxins to marine organisms.
a decrease in pH generally increases the proportion of free dissolved forms
of toxic metals.
changes in organisms could reduce their food value.
pH could have a disastrous influence on egg-laying and reproduction.
reduced calcification rate could lead to declining coral cover and weaker
a reduction of shell causes plankton organisms to float up to the surface,
rather than stay balanced.
effects of CO2 could have cascading effects through food webs, with possible
consequences for ecosystem structure and elemental cycling.
any decrease in calcification is likely to have significant consequences
like the weakening of coral skeletons and reef structures.
any changes in calcification wil have important implications for the global
various groups of marine organisms will experience significant alterations
in their geographical ranges.
almost 30% of warm-water corals have disappeared since the beginning of
coral calcification is directly proportional to the aragonite saturation.
with weaker coral reefs, human populations are at increased risk of tsunamis
coccolithophore blooms may disappear, affecting oceanic ecosystems and
deep water corals.
reduced coccolithophore blooms may result in less DMS and have a warming
effect on the planet.
marine fisheries and shellfish fisheries could be seriously affected.
high-metabolism organisms like squid may be affected.
marine plankton systems could be destabilised.
it is certain that net production of CaCO3 will decrease in the
Missing science: this is what insider
scientists think is missing. It is also a call for funding of course. However,
it shows just how large our ignorance really is.
the global carbon cycle is still uncertain with respect to fluxes, stocks
and residence times
it is not known whether the sea produces or absorbs CO2. There is certainly
a lively exchange with the air.
it is not known how much enters the sea by diffusion and how much by photosynthesis
the amount of carbon released by human activity is not well known, for
it includes habitat change and soil degradation
the carbonate chemistry of the sea has not been measured in the presence
of calcium ions and carbonate deposits.
the influence of the sea bottom with its carbonate deposits on ocean chemistry
the CO2 data from ice cores is still questionable. Too much value is ascribed
to these, and conflicts are not investigated.
the effect of pH on nutrient speciation for essential nutrients P, N, S,
iron and silicic acid is unknown.
there is no data on the growth and composition of marine plankton in enriched
CO2, and whether species can adapt.
some benthic algae (seaweeds) become much more productive with increased
CO2. More study required.
the effect of CO2 on reproductivity of fish and other animals must be studied.
how calcium skeletons and shells are formed is not known. The methods of
calcification are unknown.
too little is known aboutt he production of the gases N2O, CH4 and DMS
an how CO2 could affect these.
research is needed to better understand the vulnerabilities, resilience
and adaptability of marine organisms and ecosystems.
determine the calcification response to elevated CO2 in benthic calcifiers
such as corals (including cold-water corals), coralline algae, foraminifera,
molluscs, and echinoderms; and in planktonic calcifiers such as coccolithophores,
foraminifera, and shelled pteropods;
Discriminate the various mechanisms of calcification within calcifying
groups, through physiological experiments, to better understand the cross-taxa
range of responses to changing seawater chemistry;
Determine the interactive effects of multiple variables that affect calcification
and dissolution in organisms (saturation state, light, temperature, nutrients)
through continued experimental studies on an expanded suite of calcifying
Establish clear links between laboratory experiments and the natural environment,
by combining laboratory experiments with field studies;
Characterize the diurnal and seasonal cycles of the carbonate system on
coral reefs, including commitment to long-term monitoring of the system
response to continued increases in CO2;
In concert with above, monitor in situ calcification and dissolution in
planktonic and benthic organisms, with better characterization of the key
environmental controls on calcification;
Incorporate ecological questions into observations and experiments; e.g.,
How does a change in calcification rate affect the ecology and survivorship
of an organism? How will ecosystem functions differ between communities
with and without calcifying species?
Improve the accounting of coral reef and open ocean carbonate budgets through
combined measurements of seawater chemistry, CaCO3 production, dissolution
and accumulation, and, in near-shore environments, bioerosion and off-shelf
export of CaCO3;
Quantify and parameterize the mechanisms that contribute to the carbonate
system, through biogeochemical and ecological modeling, and apply such
modeling to guide future sampling and experimental efforts;
Develop protocols for the various methodologies used in seawater chemistry
and calcification measurements.
Study the effect of pH change on nutrients
Dissolution of open-ocean carbonate sediments needs further study.
Pre-industrial carbon cycling in the coastal zone is not well understood
because human activity has already significantly altered the natural carbon
Measurements of coastal zone carbon fluxes are currently insufficient to
determine the response of coastal carbonate systems.
Identification of a “CO2 signal” is difficult because calcification rates
in the field are a response to multiple variables (light, temperature,
nutrients, etc.), and particularly to rising temperature.
The relationship between photosynthesis and calcification in benthic calcifiers
remains poorly understood.
Identifying the various calcification mechanisms across taxa can streamline
efforts to understand future responses to saturation state.
The component of the carbonate system - CO3 , saturation state, pH - that
controls calcification rate has not been adequately determined.
How decreased calcification rates will affect the long-term survival of
benthic calcifiers is unknown.
The role of calcification in multiple life stages may play a critical role
in organism survival.
Several years may be necessary to determine whether benthic calcifiers
can adapt or acclimate to different carbonate chemistry conditions.
The effects of changing calcification and dissolution on reef ecosystem
functioning are unknown.
The effects of reduced saturation state on bioerosion rates are unknown.
The role of reef-building in coral reef ecosystem functioning is complex
and not fully understood.
Conditions controlling sediment dissolution (including suspended sediment)
and the potential impact on coral reef carbonate chemistry are poorly understood.
Calcification and photosynthesis in coccolithophores and foraminifera are
The molecular and physiological mechanisms that control the calcification
response in planktonic organisms to changes in the CO2 system are
The synergistic impacts of increased pCO2 with light, nutrients, and temperature
are largely unknown.
The suite of planktonic calcifiers includes larval stages of many benthic
invertebrates but almost no information exists on how these early calcifying
stages may be affected by decreased carbonate saturation state.
It is not known whether planktonic calcifiers require calcification to
Long-term impacts of elevated pCO2 on reproduction, growth, and survivorship
of planktonic calcifying organisms have not been investigated.
If reduced calcification decreases a calcifying organism’s fitness or survivorship,
then such calcareous species may undergo shifts in their latitudinal distributions
and vertical depth ranges as the CO2/carbonate chemistry of seawater changes.
The potential impacts of increased CO2 on planktonic ecosystem structure
and functions are unknown.
Decreased saturation states can affect both the production and dissolution
of biogenic CaCO3, yet most studies have neglected dissolution rates.
CaCO3 dissolution is substantial in the upper water column, but little
is known about the mechanisms that control this dissolution or how they
may change with future increased CO2.
Misconceptions: scientists agree that
some of past reasoning was incorrect, however solid proof remains absent.
Increasing atmospheric CO2 will increase rather than decrease pH of marine
CO2 fertilization of zooxanthellae will lead to an increase in coral calcification
Warmer water temperatures will significantly offset decreases in saturation
The effect of global warming on calcification will outweigh the effects
of decreased saturation state
Carbonate dissolution in coral reef sediments will buffer the overlying
Reader, as you can see,
our ignorance exceeds our knowledge by a vast margin.
go to part 1, introduction and
conclusion <==> go to part2, how
CO2 affects the oceans