Archive for November, 2006

Sour sea change

The oceans are in danger, and we are responsible.

It’s more than a matter of overfishing, global warming, rising sea levels and catastrophic current changes, though we have had a hand it that.

Scores of scientists have been studying and monitoring the effects of carbon dioxide on the ocean’s waters. And the news is not good…

Trenton Times, 26 November 2006. Article.

Large accumulation of anthropogenic CO2 in the East (Japan) Sea and its significant impact on carbonate chemistry

This paper reports on a basin-wide inventory of anthropogenic CO2 in the East (Japan) Sea determined from high-quality alkalinity, chlorofluorocarbon, and nutrient data collected during a summertime survey in 1999 and total dissolved inorganic carbon data calculated from pH and alkalinity measurements. The data set comprises measurements from 203 hydrographic stations and covers most of the East Sea with the exception of the northwestern boundary region. Anthropogenic CO2 concentrations are estimated by separating this value from total dissolved inorganic carbon using a tracer-based (chlorofluorocarbon) separation technique. Wintertime surface CFC-12 data collected in regions of deep water formation off Vladivostok, Russia, improve the accuracy of estimates of anthropogenic CO2 concentrations by providing improved air-sea CO2 disequilibrium values for intermediate and deep waters. Our calculation yields a total anthropogenic CO2 inventory in the East Sea of 0.40 ± 0.06 petagrams of carbon as of 1999. Anthropogenic CO2 has already reached the bottom of the East Sea, largely owing to the effective transport of anthropogenic CO2 from the surface to the ocean interior via deep water formation in the waters off Vladivostok. The highest specific column inventory (vertically integrated inventory per square meter) of anthropogenic CO2 of 80 mol C m−2 is found in the Japan Basin (40°N−44°N). Comparison of this inventory with those for other major basins of the same latitude band reveal that the East Sea values are much higher than the inventory for the Pacific Ocean (20−30 mol C m−2) and are similar to the inventory for the North Atlantic (66−72 mol C m−2). The substantial accumulation of anthropogenic CO2 in the East Sea during the industrial era has caused the aragonite and calcite saturation horizons to move upward by 80−220 m and 500−700 m, respectively. These upward movements are approximately 5 times greater than those found in the North Pacific. Both the large accumulation of anthropogenic CO2 and its significant impact on carbonate chemistry in the East Sea suggest that this sea is an important site for monitoring the future impact of the oceanic invasion of anthropogenic CO2.

Park, G.-H., K. Lee, P. Tishchenko, D.-H. Min, M. J. Warner, L. D. Talley, D.-J. Kang, and K.-R. Kim, 2006. Large accumulation of anthropogenic CO2 in the East (Japan) Sea and its significant impact on carbonate chemistry. Global Biogeochemical Cycles 20, GB4013, doi:10.1029/2005GB002676. Article.

The Darkening Sea

Elizabeth Kolbert reports on the impact of carbon-dioxide emissions on the ocean, which is resulting in “ocean acidification” and threatening the entire marine ecosystem (“The Darkening Sea,” p. 66). Kolbert explains that acidification is caused by the decrease in the ocean’s pH level due to its uptake of carbon dioxide, or CO2, noting that the ocean, which covers seventy per cent of the earth’s surface, absorbs and releases gases from and into the atmosphere at roughly equal rates. “But change the composition of the atmosphere, as we have done, and the exchange becomes lopsided: more CO2 from the air enters the water than comes back out,” she writes. Kolbert reports that humans have already pumped some hundred and twenty billion tons of carbon into the oceans, to produce a .1 decline in surface pH, which represents a rise in acidity of roughly thirty per cent. “This year alone, the seas will absorb another 2 billion tons of carbon, and next year it is expected that they will absorb another 2 billion tons,” Kolbert reports. “Every day, every American, in effect, adds forty pounds of carbon dioxide to the oceans.” Kolbert writes, “Because of the slow pace of deep-ocean circulation and the long life of carbon dioxide in the atmosphere, it is impossible to reverse the acidification that has already taken place. Nor is it possible to prevent still more from occurring. Even if there were some way magically to halt the emission of CO2 tomorrow, the oceans would continue to take up carbon until they reached a new equilibrium with the air. . . . Humans have, in this way, set in motion change on a geological scale. The question that remains is how marine life will respond.”

The New Yorker, 20 November 2006. Web site.

Model Simulations of Carbon Sequestration in the Northwest Pacific by Patch Fertilization

Iron fertilization of nutrient-rich surface waters of the ocean is one possible way to help slow the rising levels of atmospheric CO2 by sequestering it in the oceans via biological carbon export. Here, I use an ocean general circulation model to simulate a patch of nutrient depletion in the subpolar northwest Pacific under various scenarios. Model results confirm that surface fertilization is an inefficient way to sequester carbon from the atmosphere (Gnanadesikan et al., 2003), since only about 20% of the exported carbon comes initially from the atmosphere. Fertilization reduces future production and thus CO2 uptake by utilizing nutrients that would otherwise be available later. Effectively, this can be considered as leakage when compared to a control run. This “effective” leakage and the actual leakage of sequestered CO2 cause a significant, rapid decrease in carbon retention (only 30-45% retained after 10 years and less than 20% after 50 years). This contrasts markedly with the almost 100% retention efficiency for the same duration using the same model, when carbon is disposed directly into the northwest Pacific (Matsumoto and Mignone, 2005). As a consequence, the economic effectiveness of patch fertilization is poor in two limiting cases of the future price path of carbon. Sequestered carbon in patch fertilization is lost to the atmosphere at increasingly remote places as time passes, which would make monitoring exceedingly difficult. If all organic carbon from one-time fertilization reached the ocean bottom and remineralized there, acidification would be about -0.05 pH unit with O2 depletion about -20 mmol kg-1. These anomalies are probably too small to seriously threaten deep sea biota, but they are underestimated in the model because of its large grid size. The results from this study offer little to advocate purposeful surface fertilization as a serious means to address the anthropogenic carbon problem.

Matsumoto M., 2006. Model Simulations of Carbon Sequestration in the Northwest Pacific by Patch Fertilization. Journal of Oceanography, 62(6):887-902. Article.

Cyanobacterial calcification, carbon dioxide concentrating mechanisms, and Proterozoic-Cambrian changes in atmospheric composition

Photosynthetic uptake of inorganic carbon can raise the pH adjacent to cyanobacterial cells, promoting CaCO3 precipitation. This effect is enhanced by CO2 concentrating mechanisms that actively transport HCO3- into cells for carbon fixation. CO2 concentrating mechanisms presumably developed in response to atmospheric decrease in CO2 and increase in O2 over geological timescales. In present-day cyanobacteria, CO2 concentrating mechanisms are induced when the atmospheric partial pressure of CO2 (pCO2) falls below ~0.4%. Reduction in pCO2 during the Proterozoic may have had two successive effects on cyanobacterial calcification. First, fall in pCO2 below ~1% (33 times present atmospheric level, PAL) resulted in lower dissolved inorganic carbon (DIC) concentrations that reduced pH buffering sufficiently for isolated CaCO3 crystals to begin to nucleate adjacent to cyanobacterial cells. As a result, blooms of planktic cyanobacteria induced precipitated ‘whitings’ of carbonate mud in the water column whose sedimentary accumulation began to dominate carbonate platforms ~1400–1300 Ma. Second, fall in pCO2 below ~0.4% (10 PAL) induced CO2-concentrating mechanisms that further increased pH rise adjacent to cells and promoted in vivo cyanobacterial sheath calcification. Crossing of this second threshold is indicated in the fossil record by the appearance of Girvanella 750–700 Ma. Coeval acquisition of CO2 concentrating mechanisms by planktic cyanobacteria further stimulated whiting production. These inferences, that pCO2 fell below ~1% ~1400–1300 Ma and below ~0.4% 750–700 Ma, are consistent with empirical and modelled palaeo-atmosphere estimates. Development of CO2 concentrating mechanisms was probably temporarily slowed by global cooling ~700–570 Ma that favoured diffusive entry of CO2 into cells. Lower levels of temperature and DIC at this time would have reduced seawater carbonate saturation state, also hindering cyanobacterial calcification. It is suggested that as Earth emerged from ‘Snowball’ glaciations in the late Neoproterozoic, global warming and O2 rise reactivated the development of CO2 concentrating mechanisms. At the same time, rising levels of temperature, calcium ions and DIC increased seawater carbonate saturation state, stimulating widespread cyanobacterial in vivo sheath calcification in the Early Cambrian. This biocalcification event promoted rapid widespread development of calcified cyanobacterial reefs and transformed benthic microbial carbonate fabrics.

Riding R., 2006. Cyanobacterial calcification, carbon dioxide concentrating mechanisms, and Proterozoic–Cambrian changes in atmospheric composition. Geobiology 4(4), 299-316. Article.

Coral bleaching will hit the world’s poor

… Climate change is responsible for increased sea surface temperatures and ocean acidification – due to higher levels of dissolved CO2 – which lead to increased mass coral bleaching and mortality, reduced growth of corals and weakened animal skeletons. More acid ocean waters have already reduced coral reef calcification, and therefore growth rates and structural strength of coral skeletons, by 30 percent.

IUCN press release, 17 November 2006.

Significant long-term increase of fossil fuel CO2 uptake from reduced marine calcification

Analysis of available plankton manipulation experiments demonstrates a previously unrecognized wide range of sensitivities of biogenic calcification to simulated anthropogenic acidification of the ocean, with the "lab rat” of planktic calcifiers, Emiliania huxleyi not representative of calcification generally. We assess the implications of the experimental uncertainty in plankton calcification response by creating an ensemble of realizations of an Earth system model that encapsulates a comparable range of uncertainty in calcification response. We predict a substantial future reduction in marine carbonate production, with ocean CO2 sequestration across the model ensemble enhanced by between 62 and 199 PgC by the year 3000, equivalent to a reduction in the atmospheric fossil fuel CO2 burden at that time of up to 13%. Concurrent changes in ocean circulation and surface temperatures contribute about one third to the overall importance of reduced plankton calcification.

Ridgwell A., Zondervan I, Hargreaves J. C. , Bijma J., Lenton T. M., 2006.  Significant long-term increase of fossil fuel CO2 uptake from reduced marine calcification. Biogeosciences Discussions, 3, 1763-1780, 2006. Article.

Oceanic implications for climate change policy

Under the United Nations convention on the law of the sea (1982), each participating country maintains exclusive economic and environmental rights within the oceanic region extending 200 nm from its territorial sea, known as the exclusive economic zone (EEZ). Although the ocean within each EEZ is undoubtedly an anthropogenic CO2 sink, it has been over-looked within international climate policy. In this paper I use an area-weighted scaling argument to show that the inclusion of the EEZ CO2 sink within national carbon accounts would have significant implications in tracking national greenhouse commitments to any future climate change policy initiative. The advantages and disadvantages for inclusion of the EEZ CO2 sink into global climate change policy are also explored. The most compelling argument for including the EEZ CO2 sink is that it would enhance the equity and resources among coastal nations to combat and adapt against future climate change that will inherently impact coastal nations more so than land locked nations. If included, the funds raised could be used for either monitoring or adaptive coastal infrastructure among the most vulnerable nations. On the other hand, the EEZ anthropogenic CO2 sink cannot be directly controlled by human activities and could be used as a disincentive for some developed nations to reduce fossil-fuel related greenhouse gas emissions. This may therefore dampen efforts to ultimately reduce atmospheric greenhouse gas concentrations. In consideration of these arguments it is therefore suggested that an “EEZ clause” be added to Kyoto and any future international climate policy that explicitly excludes its use within national carbon accounts under these international climate frameworks.
McNeil BI, 2006. Oceanic implications for climate change policy. Environmental Science & Policy 7(9):595-606. Article.

CO2 Sensing at Ocean Surface Mediated by cAMP in a Marine Diatom

Marine diatoms are known to be responsible for about a quarter of global primary production and their photosynthesis is sustained by inorganic carbon-concentrating mechanisms and/or C4 metabolism. Activities of the inorganic carbon-concentrating mechanism are attenuated under enriched [CO2]; however, impacts of this factor on primary productivity and the molecular mechanisms of CO2 responses in marine diatoms are unknown. In this study, transgenic cells were generated of the marine diatom Phaeodactylum tricornutum by the introduction of a beta-glucuronidase reporter gene under the control of an intrinsic CO2-responsive promoter, which is the sequence between –80 to +61 relative to the transcription start site of a chloroplastic-carbonic anhydrase gene, ptca1, obtained from P. tricornutum. The activity of the ptca1 promoter was effectively repressed in air-level CO2 by treating cells with a 1.0 mM cAMP analog, dibutyryl cAMP, or a cAMP phosphodiesterase inhibitor, 3-isobutyl-1-methylxanthine. Deletion of the intrinsic cAMP-response element from the ptca1 promoter caused a lack of repression of the reporter gene uidA, even under elevated [CO2] and a null phenotype to the strong repressive effects of dibutyryl cAMP and 3-isobutyl-1-methylxanthine on the ptca1 promoter. Deletion of the cAMP-response element was also shown to cause derepression of the uidA reporter gene in the dark. These results indicate that the cytosolic cAMP level increases under elevated [CO2] and represses the ptca1 promoter. This strongly suggests the participation of cAMP metabolism, presumably at the cytosolic level, in controlling CO2-acquisition systems under elevated [CO2] at the ocean surface in a marine diatom.

Harada H., Nakajima K., Sakaue K., Matsuda Y. CO2 sensing at ocean surface mediated by cAMP in a marine diatom. Plant Physiol. 142: 1318-1328. Article.

Expert Says Oceans Are Turning Acidic

NAIROBI, Kenya — The world’s oceans are becoming more acidic, which poses a threat to sea life and Earth’s fragile food chain, a climate expert said Thursday.

Oceans have already absorbed a third of the world’s emissions of carbon dioxide, one of the heat-trapping gases blamed for global warming, leading to acidification that prevents vital sea life from forming properly.

“The oceans are rapidly changing,”said professor Stefan Rahmstorf on the sidelines of a U.N. conference on climate change that has drawn delegates from more than 100 countries to Kenya.”Ocean acidification is a major threat to marine organisms.”, 9 Novembre 2006. Article.

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Ocean acidification in the IPCC AR5 WG II

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