Archive for February, 2008

Small sea creatures may be the ‘canaries in the coal mine’ of climate change

As oceans warm and become more acidic, ocean creatures are undergoing severe stress and entire food webs are at risk, according to scientists at a press briefing this morning at the annual meeting of the American Association for the Advancement of Science in Boston.

Gretchen Hofmann, associate professor of biology at the University of California, Santa Barbara, has just returned from a research mission to Antarctica where she collected pteropods, tiny marine snails the size of a lentil, that she refers to as the ‘potato chip’ of the oceans because they are eaten widely by so many species. The National Science Foundation’s Office of Polar Programs funded the expedition.

Continue reading ‘Small sea creatures may be the ‘canaries in the coal mine’ of climate change’

Tiny snail crucial to Antarctic life may be wiped out

A tiny marine snail that grows no bigger than a lentil supports an entire community of animals in the southern oceans. But the food chain is in danger of collapse, because warmer seas are making it impossible for the snail to survive.

Scientists have found that, as the seas around Antarctica become warmer and more acidic, pteropod snails that are the ultimate food source for everything from fish and seals to penguins and whales are at greater risk of being wiped out.

Continue reading ‘Tiny snail crucial to Antarctic life may be wiped out’

Climate Change Has Major Impact On Oceans

Climate change is rapidly transforming the world’s oceans by increasing the temperature and acidity of seawater, and altering atmospheric and oceanic circulation, reported a panel of scientists at the American Association for the Advancement of Science annual meeting in Boston.

Continue reading ‘Climate Change Has Major Impact On Oceans’

Short-term dissolution response of pelagic carbonate sediments to the invasion of anthropogenic CO2: A model study

This study addresses the potential for and the quantification of dissolution of marine calcium carbonate (CaCO3) sediments occurring on century timescales in response to the invasion of anthropogenic CO2. It presents results obtained with the global biogeochemical model PISCES interactively coupled to a global sediment model. The latter represents the principal reactions involved in early diagenesis of biogenic opal, CaCO3, and organic matter. The model reproduces observed distributions of core top CaCO3 content and bottom water carbonate chemistry (e.g., [CO3 2]). Starting from the climatological state, a model experiment is carried out according to the standard CMIP scenario of atmospheric pCO2 increasing at a rate of 1% per year from 286 to 1144 ppm over a 140 year time period. The invasion of anthropogenic CO2 results in a strong decrease in bottom water [CO3 2] reaching 100 μM in areas of deep water formation in the North Atlantic and mode and intermediate water formation in the Southern Hemisphere. The concomitant decrease in calcite saturation state of bottom waters drives the dissolution of CaCO3. The absolute CaCO3 content averaged over the top first centimeter decreases by up to 6%, while the change in advection calculated at the base of the bioturbated layer (10 cm) is indicative of net erosion. The predicted changes in bottom water chemistry are discussed in terms of their potential impact on benthic communities.

Continue reading ‘Short-term dissolution response of pelagic carbonate sediments to the invasion of anthropogenic CO2: A model study’

Future changes in climate, ocean circulation, ecosystems, and biogeochemical cycling simulated for a business-as-usual CO2 emission scenario until year 4000 AD

A new model of global climate, ocean circulation, ecosystems, and biogeochemical cycling, including a fully coupled carbon cycle, is presented and evaluated. The model is consistent with multiple observational data sets from the past 50 years as well as with the observed warming of global surface air and sea temperatures during the last 150 years. It is applied to a simulation of the coming two millennia following a business-as-usual scenario of anthropogenic CO2 emissions (SRES A2 until year 2100 and subsequent linear decrease to zero until year 2300, corresponding to a total release of 5100 GtC). Atmospheric CO2 increases to a peak of more than 2000 ppmv near year 2300 (that is an airborne fraction of 72% of the emissions) followed by a gradual decline to ∼1700 ppmv at year 4000 (airborne fraction of 56%). Forty-four percent of the additional atmospheric CO2 at year 4000 is due to positive carbon cycle–climate feedbacks. Global surface air warms by ∼10°C, sea ice melts back to 10% of its current area, and the circulation of the abyssal ocean collapses. Subsurface oxygen concentrations decrease, tripling the volume of suboxic water and quadrupling the global water column denitrification. We estimate 60 ppb increase in atmospheric N2O concentrations owing to doubling of its oceanic production, leading to a weak positive feedback and contributing about 0.24°C warming at year 4000. Global ocean primary production almost doubles by year 4000. Planktonic biomass increases at high latitudes and in the subtropics whereas it decreases at midlatitudes and in the tropics. In our model, which does not account for possible direct impacts of acidification on ocean biology, production of calcium carbonate in the surface ocean doubles, further increasing surface ocean and atmospheric pCO2. This represents a new positive feedback mechanism and leads to a strengthening of the positive interaction between climate change and the carbon cycle on a multicentennial to millennial timescale. Changes in ocean biology become important for the ocean carbon uptake after year 2600, and at year 4000 they account for 320 ppmv or 22% of the atmospheric CO2 increase since the preindustrial era.

Continue reading ‘Future changes in climate, ocean circulation, ecosystems, and biogeochemical cycling simulated for a business-as-usual CO2 emission scenario until year 4000 AD’

Past greenhouse warming provides clues to what the future may hold

If carbon dioxide emissions from the burning of fossil fuels continue on a “business-as-usual” trajectory, humans will have added about 5 trillion metric tons of carbon to the atmosphere by the year 2400. A similarly massive release of carbon accompanied an extreme period of global warming 55 million years ago known as the Paleocene-Eocene Thermal Maximum (PETM).

Continue reading ‘Past greenhouse warming provides clues to what the future may hold’

AAAS: That other carbon problem, ocean acidification

Friday morning’s first sessions included a series of talks on what was termed “the other carbon problem”—ocean acidification. When dissolved in water, carbon dioxide can combine with a single water molecule to form carbonic acid, a process that ultimately lowers the pH of the water. On a global scale, adding more CO2 to the atmosphere will trigger this process to occur on a massive scale. So far, the oceanic pH has dropped by .1 units, but it’s expected to drop another .3 points in the next century unless emissions are curbed.

Continue reading ‘AAAS: That other carbon problem, ocean acidification’

Increased CO2 level threatens coral reefs

A coral reef is made up of thin layers of calcium carbonate (limestone) secreted over thousands of years by billions of tiny soft bodied animals called coral polyps. Coral reefs are the world’s most miscellaneous marine ecosystems and are home to twenty-five percent of identified marine species, including 4,000 species of fish, 700 species of coral and thousands of other plants and animals. Coral reefs occupy less than one quarter of one percent of the Earth’s marine environment, yet they are home to more than a quarter of all known fish species.

And these largest living structures on Earth and the millions of livelihoods which depend upon them are at risk, the most definitive review yet of the impact of rising carbon emissions on coral reefs has concluded. If world leaders do not immediately engage in a race against time to save the Earth’s coral reefs, these vital ecosystems will not survive the global warming and acidification projected for later this century.

It is very important that the public realises that the lack of sustainability in the world’s carbon emissions is causing the quick loss of coral reefs, the world’s most biodiverse marine ecosystem. The rise of carbon dioxide emissions and the resultant climate warming from the burning of fossil fuels are making oceans warmer and more acidic, which is triggering extensive coral disease and choking coral growth toward “a tipping point for functional collapse.”

The coral scientists point out that rising global CO2 emissions embody an ‘irreducible risk’ that will quickly outdo the capacity of local coastal managers and policy-makers to sustain the health of these critical ecosystems, if CO2 emissions are allowed to prolong unrestrained.

Continue reading ‘Increased CO2 level threatens coral reefs’

Ocean acidification workshop, University of Tasmania, Australia

Ocean Acidification – Australian Impacts in the Global Context

University of Tasmania, Australia, 2-4 June 2008

The Department of Climate Change and the Antarctic Climate & Ecosystems CRC are hosting a 3–day ocean acidification workshop from Monday 2 to Wednesday 4 June 2008, at the University of Tasmania.

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Microzooplankton grazing and phytoplankton growth in marine mesocosms with increased CO2 levels

Microzooplankton grazing and algae growth responses to increasing pCO2 levels (350, 700 and 1050 μatm) were investigated in nitrate and phosphate fertilized mesocosms during the PeECE III experiment 2005. Grazing and growth rates were estimated by the dilution technique combined with taxon specific HPLC pigment analysis. Phytoplankton and microzooplankton composition were determined by light microscopy. Despite a range up to 3 times the present CO2 levels, there were no clear differences in any measured parameter between the different CO2 treatments. Thus, during the first 9 days of the experiment the algae community standing stock (SS), measured as chlorophyll a (Chl a), showed the highest instantaneous grow rates (0.02–0.99 d-1) and increased from ca 2–3 to 6–12 μg l1, in all mesocosms. Afterwards the phytoplankton SS decreased in all mesocosms until the end of the experiment. The microzooplankton SS, that was mainly dinoflagellates and ciliates varied between 23 and 130 μg C l1, peaking on day 13–15, apparently responding to the phytoplankton development. Instantaneous Chl a growth rates were generally higher than the grazing rates, indicating only a limited overall effect of microzooplankton grazing on the most dominant phytoplankton. Diatoms and prymnesiophytes were significantly grazed (14–43% of the SS d-1) only in the pre-bloom phase when they were in low numbers and in the post-bloom phase when they were already limited by low nutrients and/or virus lysis. The cyanobacteria populations appeared more effected by microzooplankton grazing, generally removing 20–65% of the SS d1.

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Ocean acidification in the IPCC AR5 WG II

OUP book