Download Read the article

bioscience⏐explained
Vol 3 ⏐ No 2
1346
Jarl-Ove Strömberg
Kristineberg Marine Research Station
Fiskebäckskil, Sweden
Climate change and the ocean
Climate variability and climate change
It may seem like an easy task to distinguish between
variability and a more or less permanent trend in a
change. However, it is difficult since variability may include cyclic phenomena with long and irregular pulses
and our recordings of climate events are often too short
to make definite evaluations of their character.
We do have a few good examples of recurring events
with a periodicity of a few years to a few tens of years.
The first may be exemplified by the ENSO events (El
Niño/Southern Oscillation) in the equatorial Pacific
Ocean and the second by the North Atlantic Oscillation
(NAO). Although both have been studied for decades
our possibilities to predict when we can expect a
change are limited.
During an El Niño period a warmer than normal ocean
current hits the northern west coast of South America
shifting the cold current that normally runs outside this
coast away and causing torrential rainfall over land in
Peru and Chile where otherwise the climate is dry and
we find desert conditions. This in term causes floods
and mudslides and has large socio-economic consequences in these countries. One factor behind this is a
slow build-up of warm water in the Indonesian ocean
region (at times possibly caused by stronger than normal trade winds) and since there is an open communication across the Pacific Ocean this warm water has to
flow eastward as an equatorial counter-current. In the
mid 1970-ties the effect was thought to be localised to
the South American coast and the first person to “predict” an El Niño event was a Peruvian lady scientist who
observed the arrival of a planktonic crab, which did not
occur in the usually cold waters offshore. In those days
females were not allowed onboard Peruvian research
vessels. Later the ENSO phenomenon has shown to be
much more complicated, being a coupled oceanatmosphere phenomenon and having far-reaching effects also in California, southern Africa, the Indian
Ocean and Australia. Predictability is still limited to
about half a year and its occurrence varies interannually between 2 to 6-7 years. Also its strength varies considerably (1).
CORRESPONDENCE TO
Prof. Jarl-Ove Strömberg
Kristineberg Marine Research
Station, Fiskebäckskil, Sweden
e-mail: [email protected]
www.bioscience-explained.org
The NAO is a shift in winter climate in the north Atlantic
and has as its main driving force varying strengths of
the atmospheric high over the Azores (the subtropical
high) and low over Iceland. With a stronger than normal Azoric high and a deeper than normal Icelandic low
we get what is termed a positive NAO, with a dry Mediterranean area and a wet and stormy situation in northCOPYRIGHT © by the Author, 2007
bioscience⏐explained
Vol 3 ⏐ No 2
western Europe and Asia with south-westerly winds
dominating. A negative NAO means wet weather over
the Mediterranean area and dry and cool weather with
mainly northerly wind over western and northern
Europe. Then the subtropical high over the Azores is
weak as is the Icelandic low. The different phases may
last from some years to 20 or more years. At present
(2006) we are in a long-lasting positive phase (2). Although these kinds of variability may be affected by
more far-reaching climate change, we normally regard
them as having “natural” forcing factors – not human
induced ones.
Figure 1. NAO index is here shown
from about 1860 to 2000. A positive value is shown in red and a
negative index in blue. Permission
by Prof. Dr. Martin Visbeck. (For
more information see:
http://ldeo.columbia.edu/NAO)
Climate change means a long lasting trend (possibly
over centuries or millennia) which may or may not be
irreversible on a human time-scale. If we look on a
geological time-scale the earth has experienced ice
ages about every 100 000 years for the last million
years which would best fit with a change in solar radiation caused by the earth’s orbit around the sun – going
from an almost circular to an oval shape. Other longlasting behaviour of our globe is a change in the tilt of
spin axis going from 22.1 to 24.5 degrees and back in
about 41 000 years. Finally there is a wobbling in the
rotation over periods of 23 000 years. Undoubtedly
these changes have influences on the global climate,
but these are only partly understood. When looking at
relatively short term variations in solar radiation, like
the effect of sunspot frequency with an 11 years cycle,
these can so far not be accounted for major climate
changes (3).
Global warming
If a change in solar radiation is not the cause for global
warming, then we need to look for other influencing
factors. There is an almost total agreement among scientists that during the last century there was a global
temperature increase of about 0.6oC, most of which, or
0.4oC, occurred during the last 25 years. It is most accentuated on the northern hemisphere (north of 20oN)
because of the continents with an increase of close to
0.7oC, while the ocean dominated southern hemisphere
(south of 20oS) has had an increase of 0.3oC. There is
also an almost total scientific agreement that the main
www.bioscience-explained.org
2
COPYRIGHT © by the Author, 2007
bioscience⏐explained
Vol 3 ⏐ No 2
forcing factor is the concentration of greenhouse gases
in the atmosphere, especially that of CO2, although also
methane (CH4), nitrous oxide (N2O) and freons (CCl2F2)
are major contributors. Measurements of atmospheric
CO2 started in a serious way by the end of the 1950-ies
on the top of Maona Loa on the island of Hawaii. It was
then 315 ppm and has since risen to 380 ppm in less
than 60 years. Pre-industrial level has been found to be
280 ppm. A new insight in earlier long-term variation
was received from analyses of enclosed air bubbles in
continental ice sheets on Antarctica and Greenland,
which showed that during the last 450 millennia concentration never reached above 300 ppm and then for
most of the time was far below 250 ppm. (4). There is
little or no doubt that the dramatic increase in CO2 concentration in the last 100 years is the result of human
perturbation and then mainly due to burning of fossil
fuels. The increase from 350 to 380 ppm did not take
longer than less than 20 years, while during the preindustrial era the quickest build up of 30 ppm took
about 1000 years. Estimates of human production of
CO2 indicate that only about half of it stays in the atmosphere and that the other half is transferred into the
ocean. This is then the major reason for an observed
seawater acidification (See more below).
The Intergovernmental Panel on Climate Change (IPCC)
of the United Nation has investigated various scenarios
for the future and estimate that by end of the 21st century the CO2 concentration in the atmosphere could be
anywhere between 490 and 1260 ppm corresponding to
an increase from pre-industrial level with 75 to 350%.
During the industrial era methane concentration in the
atmosphere has increased from 750 ppm to about 1600
ppm and corresponding levels for nitrous oxide is a
raise from 275 ppm to 315 ppm. Increase in methane
is due to human activity but is also resulting from melting permafrost soil of tundra regions and seeps from
ocean sediment deposits of methane hydrate.
In radiative forcing (in Wm-2) this means an increase by
1.5 for CO2, 0.5 for CH4, and 0.15 for N2O.
For meteorologists and oceanographers the above is
generally accepted as facts but it has taken a long time
to convince politicians and most media that this is bad
news and some counteractions are needed. It was
therefore a surprise to see the front page of the U.S.
Time Magazine in early April 2006:”Be worried. Be very
worried. Climate change isn’t some vague future problem – it’s already damaging the planet at an alarming
pace” (5).
www.bioscience-explained.org
3
COPYRIGHT © by the Author, 2007
bioscience⏐explained
Vol 3 ⏐ No 2
How will global warming affect the ocean?
•
Sea level rise
1. Water expansion: When water heats up it expands. A doubling of the atmospheric CO2 concentration has by some models been estimated to
give a temperature rise of the oceanic surface water of 3-4oC, and a sea level rise of 40-50 cm. For
many low coastal areas and islands this is enough
to create serious problems.
2. Melting continental ice sheets: There are two
schools of thought: (a) because of increased precipitation on the upper parts of the ice sheets with
a build-up of ice, a faster flow of ice towards the
periphery, and increased iceberg formation and
melting at the edges, the ice mass will not change
dramatically and thus the sea level will not be affected in a major way; (b) precipitation will not
increase on the upper parts, but the melting at
the peripheries of the ice sheets will indeed increase resulting in a loss of ice mass and melting
of ice shelves. Sea level will rise depending on
degree of melt off. This could mean at least one
meter by 2100.
Figure 2. The influence on the
atmosphere by the various greenhouse gases or particles is very
obvious by the steep inclines in all
four cases above. Source: Intergovernmental Panel on Climate
Change.
www.bioscience-explained.org
Present investigations do not give a consistent
picture. More snowfall has been reported on top
of the Greenland ice sheet, but there are also pictures of large “lakes” of melt-water on the top
with ice cracks below through which water could
drain. In the Antarctic Peninsula area large ice
shelves have broken loose and started to drift
away and melt. With a large part of the western
Antarctic ice sheet being partly under sea water
level this part could melt rapidly with higher seawater temperature. If this happens a major sea
4
COPYRIGHT © by the Author, 2007
bioscience⏐explained
Vol 3 ⏐ No 2
level rise may occur which will flood large low lying coastal areas with catastrophic effects. Most
models do not support such a development, but
rather high air temperatures in the Antarctic Peninsular region have been recorded recently.
3. Storm surges: Increased sea surface temperature
will offer more energy for the development of hurricanes, typhoons, and strengthen monsoons, that
will inundate coastal areas hit by these storms.
Although they have temporary effects they may
be disastrous for the stricken areas both on land
and in the shallow waters. In the last few years
there are indications of more frequent storms and
more violent winds
•
Changes in ocean circulation and heat transport
1. Change in terrestrial runoff: Warmer air can carry
more humidity and increase precipitation and
runoff to the adjacent sea areas. North-western
Europe and Asia may experience this with increased draining of fresh water into the Arctic
Ocean. This may also occur on the North American side of the Arctic. With more fresh water at
the surface this will mean that the cold Greenland
current along east Greenland will carry less salt
than at present.
Figure 3. The figure shows the result of various models of global
sea level rise by the end of the present century. The uncertainty
considering the melt off from the continental ice sheets is also
indicated. Source: Intergovernmental Panel on Climate Change.
www.bioscience-explained.org
5
COPYRIGHT © by the Author, 2007
bioscience⏐explained
Vol 3 ⏐ No 2
2. Melting of sea ice: Depending on the rise in the
air temperature over the Arctic and possibly
warmer surface water entering both from the Pacific and the Atlantic Oceans the extent of the sea
ice as well as its thickness will be affected. There
are already reports of less and thinner sea ice in
the Arctic Ocean. If this development continues
and more open water subsists the reflection of solar radiation will decrease and more heat will be
absorbed in the surface water. This may accelerate the melting of sea ice and further add to the
extent of open water during summer months.
During the winter fresh surface water will easily
freeze, but not cause deepwater convection to the
present extent. Obviously this will have major effects on the upper parts of the Arctic marine ecosystem but also on the transport of oxygen- and
nutrient-rich water.
Melting and disappearance of sea ice in large areas of the Antarctic waters might occur with dramatic effects on the whole Antarctic marine and
terrestrial ecosystems.
3. Surface and deep ocean circulation: There are
two major areas for deep ocean water formation;
both are in the Atlantic sectors of the polar areas.
The one in the north is in the Greenland/Iceland
Sea or in the Labrador Sea. In these areas cold
water from the Arctic Ocean via the Greenland
Current flows south and during winter sea ice is
formed, which leaves cold and salty and thus
heavy water under the ice. This dense water sinks
to form a south flowing deep-water current. It has
been said to be the site for the motor or engine
for the great ocean conveyor belt. Should this
stop or at least be reduced in strength there is the
risk that the Gulf Stream and its continuation in
the Transatlantic Current will take a more southerly route and thus give colder weather to northern Europe and warmer to the areas to the south.
Presently there are indications of a weaker deepwater formation in the Greenland/Iceland Sea and
a weaker Transatlantic Current. However Norwegian scientists have shown that although this current transports less water it is warmer than before and thus there is not yet a reduction in the
heat transport to the Norwegian and Barents
Seas.
Computer simulations predict and support a weakening in the heat transport via ocean circulation
from the tropics to higher latitudes in the North
Atlantic (6).
www.bioscience-explained.org
6
COPYRIGHT © by the Author, 2007
bioscience⏐explained
Vol 3 ⏐ No 2
Figure 4. A very generalized
picture of the major ocean
cur-rents is given here. Blue
currents are in the deep sea
and orange are at the ocean
surface. Deep-sea water is
formed in the North Atlantic
and in the Weddell Sea in
Antarctica. The deep waters
enter the surface in the North
Indian and Pacific Oceans.
Several things are not shown
in the pic-ture, e.g. the way
Antarctic deep water penetrates way north in the Atlantic underneath the Arctic deep
t
In the Antarctic Weddell Sea the second major
deep sea water formation occurs. This is denser
than the Arctic deep water but joins the eastern
deep flow of the conveyor belt. In the Atlantic it
reaches a little north of the equator and forms the
deepest water of the South Atlantic. In the north
regions of the Indian and Pacific Oceans the deep
currents come up to the surface and from then on
stay at the ocean surface on the way back to the
Atlantic.
If we speculate that the deep water formation as
of the present should stop because of global
warming there is the risk of a separation between
a shallow and a deep ocean. In the shallow ocean
a saturation of CO2 would occur and speed up the
increase of this gas in the atmosphere with a further warming effect.
A detrimental effect to the deep faunas of the
oceans would be the loss of oxygen circulation
from the surface. However, it is also a possibility
of deep circulation with a strong surface evaporation and thus dense water formation.
This is already occurring in the eastern Mediterranean Sea.
•
www.bioscience-explained.org
Ocean biogeochemistry
1. Salinity shifts / haloclines: As mentioned above
an excess of freshwater on the surface in the Arctic may have strong effect on the deep water convection in the Greenland/Iceland and Labrador
Seas. It is also likely to change the heat radiation
budgets in the Arctic.
7
COPYRIGHT © by the Author, 2007
bioscience⏐explained
Vol 3 ⏐ No 2
Changes in sea ice distribution will certainly have an
influence on the marine plankton flora. This might
then cause a change in the production of dimethylsulfide, which acts as condensation nucleus
and is thus responsible for the Arctic mist, which
also affects the radiation budgets.
2. Turbidity: More river water or melt water from
continental ice and glaciers reaching into the sea
will increase turbidity in coastal and near coastal
areas.
Effects of this could be e.g. change in algal vertical distribution because of light dependence, excess of sediments which may harm coral reefs or
build up unstable sediment packs which will cause
turbidity currents affecting benthic faunas over
large depth ranges.
•
Marine biology
1. Some recorded changes in abundance and/or distribution
There are relatively few clear examples that can
be attributed to global warming. Every species
has one or a few centres of its distribution where
fluctuations in abundance may occur but where
they can always be found. However, the closer
one gets to the periphery of its distribution the
greater the risk is that it is missing during a season or a time period, which could vary considerably in length before reappearing in the same area.
Such fluctuations are common and may often be
caused by extreme weather situations – e.g. extra
cold or warm temporary seasons, which could affect general survival of any part of the life cycle,
availability of food, failure in reproduction for a
number of reasons, predation pressure etc. Two
examples may be brought up at this point, one
dealing with the plankton community of the North
Sea and one with a rocky intertidal community on
the California coast.
a. A certain amount of warming of the North Sea
has been recorded during the last decades, which
has affected the distribution of two planktonic copepod species, the cold-temperate Calanus finmarchicus and the warm-temperate C. helgolandicus. These species are very closely related
but occupy specific thermal niches The former
species has a thermal boundary at 10-11oC and
the second one at 14oC. Since the late 1980s C.
helgolandicus has dominated in the North Sea especially later in the years. However, the total Calanus biomass has declined considerably since the
late 1980s (7).
www.bioscience-explained.org
8
COPYRIGHT © by the Author, 2007
bioscience⏐explained
Vol 3 ⏐ No 2
A shift in geographic distribution is what can be
expected with a gradual and consistent warming.
A possible secondary effect of this is that the
European cod, Gadus morhua, which during
young stages prefer C. finmarchicus as a food
item, may have had its reproductive success influenced by this shift. The decline of cod in the
North Sea may thus be the result of overfishing in
conjunction with a change of the food resources
as a result of global warming.
Warming of the sea water does not only mean a
possible shift in distribution but also a change in
abundance. This has been particularly noticeable
in the North Sea and in the North Atlantic when
looking at changes from 1960 to 1995. Both in
samples taken by the Continuous Plankton Recorder of Sir Alister Hardy Foundation for Ocean
Science (SAHFOS) and from satellite observations
a rather dramatic increase in phytoplankton biomass has been recorded (8).
b. The rocky intertidal invertebrate fauna of the central California coast was studied in detail in a
comparison between 1931-33 and 1993-94 (9,
10). Another investigation had shown that during
these 60 years the annual mean shoreline ocean
temperature increased by 0.75oC and the maximum summer temperature was 2.2oC warmer in
1983-93 than in 1921-31. The net result was that
out of 45 species studied eight of nine southern
species increased significantly in abundance and
of eight northern species five decreased in abundance. Possible causes for such change other than
global warming were considered (e.g. ENSO associated effects, change in predator populations, anthropogenic impacts, or random variation) but
ruled out.
2. Predicted and possible coming changes in floral
and faunal distributions
a. in the plankton:
There is no doubt that a gradual warming of the
sea will have an effect on the distribution of many
planktonic organisms with a general northward
shift on the northern hemisphere and a similar
southward shift on the southern hemisphere.
There is a fear that bacteria and virus that can
normally not survive in cold or moderately warm
water will be able to change their distribution
similarly. During warm summers, like we have
had in north-eastern Europe in late years, presence of E. coli bacteria in coastal waters has frequently been reported and many popular swimming places have been temporarily closed. Such
instances have increased during the last few
years. These outbreaks obviously have an anthro-
www.bioscience-explained.org
9
COPYRIGHT © by the Author, 2007
bioscience⏐explained
Vol 3 ⏐ No 2
pogenic background and do not reflect a geographic spread but rather a better survival of the
bacteria (e.g. Escherichia coli), because of higher
water temperature during summer.
However, there are relatively recent reports on
mass mortalities in many major marine taxa due
to disease outbreaks. In reef corals exposed to
high temperatures not only bleaching occurs but
their resistance to new diseases is weakened
causing a very high mortality.
Also marine mammals are victims of new pathogens at an increased rate. It seems that new diseases typically emerge through change of host or
distributional range of already known pathogens.
Whether the major cause for spread is climatic or
due to human activities is hard to decide with our
present knowledge, but a combination of the two
is very likely (11). The pathogenic agent has
rarely been identified but bacteria are commonly
found in corals and virus in seals, dolphins and
some fish species. Protozoan parasites have been
reported to infect oysters in the Gulf of Mexico
with prevalence during El Niño events. Harwell et
al. conclude ”that a better understanding of the
origins of emergent disease and invertebrate immunity is needed before we can evaluate the role
of changing environments in host-pathogen interactions. Studies of invertebrate resistance to disease will not only provide important insights for
management of commercial and natural populations, but also will yield molecules and compounds
with biomedical applications”.
The bacterium causing cholera is Vibrio cholerae.
It spreads easily around the globe and has resulted in many pandemics. In the present context
it is of interest that the bacteria have an association with zooplankton, especially chitinaceous
taxa, e.g. copepods, and spreading of the disease
can have a cause in ocean currents along coastal
areas.
The bacterium may also survive in association
with aquatic vegetation, e.g. water hyacinths and
blue-green bacteria (Anabaena). We have in this
bacterium a clear possible connection between
global climate, global change and human health
(12).
Another example is V. parahaemolyticus which
causes gastroenteritis.
It is found in oysters and since they often are
eaten raw the risk for human infection is high. An
outbreak of this disease in Alaska in 2004 has
been attributed to rising seawater temperature.
www.bioscience-explained.org
10
COPYRIGHT © by the Author, 2007
bioscience⏐explained
Vol 3 ⏐ No 2
Since 1997 it has increased by 0.21oC per year.
Before that year the disease was never recorded
so far north. (13).
b. in grazers and higher predators:
In Antarctic waters we find two dominating grazers, Antarctic krill (Euphausia superba) and salps
(e.g. Salpa thompsoni). They are normally not
found in the same waters. Krill prefer areas with
high phytoplankton production like the southwest
Atlantic sector, from the Antarctic Peninsula towards South Georgia, while salps tolerate warmer
water than krill and are found in areas with lower
productivity. Krill abundance also correlates positively with extensive sea ice areas of the previous
year, meaning that the larval and sub-adult krill
take advantage of the rich flora on the underside
of the ice during the winter period. The krill is also
largely protected from predation when under the
ice. As adults they then feed on the rich planktonic algae in the ice-free water during the summer.
Very large parts of the upper Antarctic ecosystem, both in the sea and on land, have krill as the
main food source. In the sea it is true for many
species of squids and fish and obviously also for
the baleen whales that come to these waters in
the summer. Most of the Antarctic seal species, all
penguins and many other birds also feed rather
exclusively on krill while there seem to be very
few predators on the gelatinous salps.
Thus krill is a key organism in the Antarctic ecosystem and fluctuations in their abundance may
have a big influence on the Antarctic food web in
general. A recent study (14) indicates that >50%
of the krill stocks are found in the Atlantic sector
mentioned above, but also that their densities
have declined since the 1970s while the salps
have increased.
Surprisingly enough the western Antarctic Peninsula has been found to be one of the fastest
warming areas of the world and the duration of
the winter sea ice is becoming shorter and the
deep ocean temperatures have increased. Thus
we can expect to see effects on the populations of
the various predators of these krill stocks.
www.bioscience-explained.org
11
COPYRIGHT © by the Author, 2007
bioscience⏐explained
Vol 3 ⏐ No 2
Figure 5. The krill Euphausia superba is a key species in the Antarctic
marine ecosystem. It occurs in large swarms of several metric tons
(sometimes in megaswarms of hundreds of tons) although the maximum size of an individual is less than 6 cm. They feed mainly on phytoplankton and are heavily predated on by whales, seals, penguins and
other marine birds as well as by fish and squids. They are almost never
found in any numbers in the same water masses as salps (Photo by J-O
Strömberg).
Figure 6. Salps are wholly planktonic and efficient filter-feeding tunicates that live on phytoplankton. They may occur as gelatinous individuals, as in this picture of the Antarctic Salpa thompsoni, or they reproduce rapidly under favourable feeding conditions to form colonies of
long chains of connected individuals (Photo by Laurence Madin, Woods
Hole Oceanographic Institution).
www.bioscience-explained.org
12
COPYRIGHT © by the Author, 2007
bioscience⏐explained
Vol 3 ⏐ No 2
c. in calcareous organisms:
Recently a new threat to the marine biota has
been revealed (15). With increased atmospheric
carbon dioxide also more and more of this gas is
dissolved in the surface waters of the oceans resulting in a gradual acidification. The reason for
this is that the predominant ion formed is bicarbonate. The increase in concentration of CO2 in
the atmosphere from 280 to 380 ppm since the
start of the industrial revolution in early 1800 has
had the effect that the average ocean pH has
changed from about 8.16 to 8.05 and may by the
end of the present century be 7.9.
The biota suffering from this acidification are
plants and animals having calcified exoskeletons
or internal skeletal support in the form of calcite
which is most common in shallow waters or aragonite which predominates in deep waters. Coccolithophores are tiny phytoplankton with elaborately shaped calcite covering which when the
plants bloom give a turquoise colour to the ocean
surface because of reflected light from these organisms. Experiments in mesocosms have shown
that increased acidification reduces the calcite
covering to about half, if the present carbon dioxide level is tripled. This obviously influences the
buoyancy that has secondary effects on the
planktonic organisms feeding on these very abundant types of phytoplankton.
The risk is that they may never reach the sea bottom and the benthic fauna looses an important
food source.
Other organisms at risk include echinoderms, especially sea urchins, crustaceans and corals. Deep
living corals have their skeletons built up of aragonite, which is more soluble than calcite and
thus they ran the risk of having greater difficulties
to build them up.
Tropical coral reefs may also be heavily influenced, besides the risk that exposure to increased
water temperature causes bleaching and the expulsion or death of the symbiotic algae, the
zooxanthellae, which are essential for the survival
of the hermatypic (reef building) corals.
The effect of higher acidity in the water is well
documented in the soft-skinned sea urchins and
sea cucumbers living at depths of more than
about 3500m, where the hydrostatic pressure
causes carbonate to change into bicarbonate.
Shallow living sea urchins exposed to water with
lower than normal pH will have clear difficulties to
keep up their hard and pointed spines and thick
body covering.
www.bioscience-explained.org
13
COPYRIGHT © by the Author, 2007
bioscience⏐explained
Vol 3 ⏐ No 2
Besides effects on skeletons, respiratory problems
have been observed with decreasing pH in many
animals, so metabolic and other physiological effects can be expected.
We are presently in the beginning of understanding the detrimental effects of a lower pH in the
ocean, but it is clear that also small changes may
have profound influences on the functioning of
marine ecosystems. Obviously there are also experts disagreeing with the notion that acidification
will have a major negative influence and they
point toward the great buffering capacity in the
very large ocean realm and the large ocean bottom areas covered with calcareous sediments.
One final point of interest is that ocean acidification may amplify global warming. The reasoning is
that coccolithophores when blooming help to reflect light from the ocean surface. If a lower pH
reduces the bright calcareous covering or the very
number of these plankton and they are replaced
by other non-reflecting plankton species, less light
will be reflected upwards and thus more heat absorbed in the water. Another effect could be the
possible decrease in the production of dimethylsulphide, which functions as condensation seeds
for water vapour and thus for cloud formation
over extensive ocean areas. A reduction in such
cloud formation would certainly affect the global
heat budget.
Hindcasting and forecasting
Hindcasting is a relatively new term for looking back on
historical data and try to understand what happened in
the past. A very modern case of hindcasting is to investigate air bubbles enclosed in continental ice where
analyses can give direct measures of composition of the
air at the time of enclosure. This has been very much
used in climate research and records going back some
800 000 years are now available. Other means are to
be found in deep sea sediments were remains of phytoplankton, foraminiferans, mollusc shells and fish scales
can be used to appreciate what has been going on in
the upper water layers. Especially in areas with laminated sediments a rather precise dating can be made. A
third way is to estimate growth rate in coral heads or
tree rings in old or fossil tree trunks. Isotope techniques are then available for dating the age. This in
combination with data records from present times give
a good background, which can be used in evaluating
models to see how well these fit into the past events.
Forecasting is obviously more difficult and depending
on the development of numerical models. In the beginning they have been very course, but with the addition
of more and more factors that have influences on what
www.bioscience-explained.org
14
COPYRIGHT © by the Author, 2007
bioscience⏐explained
Vol 3 ⏐ No 2
we want to model the more robust they become. This is
well illustrated in the development of climate models
Figure 7. As more and
more factors can be
included in the models
the more reliable they
become, but their robustness need to be
tested and hindcasting
and testing on avail-able
data series must be
done. The figure gives an
indication of the complexity that is gradually
achieved when building
the models. Source:
Intergovernmental Panel
on Climate Change.
There are almost always factors that have not been
considered in enough detail, and even major factors
might have been missed. This is shown in cases, where
many different models have been applied, that there
are relatively large differences between them.
The major change in future development, as shown in
these climate models, all point in the same direction.
Global warming is a fact. Its cause in the effect of
greenhouse gases is also clear. How this will influence
climate on regional and local levels will clearly vary in
different parts of the globe. Its impact on marine biota
is understood in a gross view but the details are mostly
missing. The influence on the human population will be
dramatic with necessary changes in almost all our interactions with nature.
Some questions and problems:
1. There are several different greenhouse gases that have
an effect on the global climate. Their influence is
named radiative forcing and it is very different for the
various gases. Find on the web the values for CO2,
methane, N2O and some of the CFCs that are active in
this case. (Look e.g. on http://www.ipcc.ch)
2. Carbon dioxide is an active part in the atmosphereocean exchange. It is partly dissolved in the surface
water but it is also actively taken up by the very large
amounts of unicellular algae that dominate in the oce-
www.bioscience-explained.org
15
COPYRIGHT © by the Author, 2007
bioscience⏐explained
Vol 3 ⏐ No 2
anic waters. They use CO2 during their photosynthesis.
By surfing the web, can you find out which parts of the
ocean are of most importance for the CO2 dissolving?
Where do we have the major concentrations of phytoplankton? Where is the so called biological pump most
important?
3.
Discuss with your classmates what might happen if we
get a separation between a shallow and a deep ocean,
and what will the melting of permafrost in the Arctic regions mean for the speed of building up greenhouse
gases in the atmosphere?
References and useful literature:
1.
2.
3.
4.
5.
6.
7.
8.
9.
10.
11.
12.
13.
14.
15.
http://www.cdc.noaa.gov/ENSO/enso.description.html, 2006;
http://iri.columbia.edu/climate/ENSO/currentinfo/QuickLook.ht
ml , 2006
http://www.ldeo.columbia.edu/NAO/, 2006
http://en.wikipedia.org/wiki/Milankovitch_cycles, 2006
J.R. Petit et al. (1999) Climate and atmospheric history of the
past 420 000 years from the Vostok ice core, Antrctica. Nature
399, 429-436.
TIME, April 3, 2006
Quadfasel, D. (2005) Oceanography: The Atlantic heat conveyor
slows. Nature 438: 565-566.
SAHFOS, http://192.171.163.165/research.(2006)
P.C. Reid et al. (1998) Phytoplankton change in the North Atlantic. Nature 391: 546.
J.P. Barry et al. (1995) Climate-related, long-term faunal
changes in a California rocky intertidal community.Science 267:
672-675.
R.D. Sagarin et al. (1999) Climate-related change in an intertidal community over short and long time scales. Ecological
Monographs 69 (4): 465-490.
C.D. Harwell et al. (1999) Emerging marine diseases – Climate
links and anthropogenic factors. Science 285: 1505-1510.
R.R. Colwell (1996) Global climate and infectious disease: The
cholera paradigm. Science 274: 2025-2031.
J.B. McLaughlin et al. (2005) Outbreak of Vibrio parahaemolyticus gastroenteritis associated with Alaskan oysters. New England Journal of Medicine 353(14): 1463-1470.
A. Atkinson et al. (2004) Long-term decline in krill stock and increase in salps within the Southern Ocean. Nature 432: 100103.
J. Ruttimann (2006) News Feature: Sick seas. Nature 442: 978980.
Acknowledgment
The Volvox project is funded by the Sixth Framework Program of the
European Commission.
www.bioscience-explained.org
16
COPYRIGHT © by the Author, 2007