The fate of pelagic CaCO3 production in a high CO2 ocean: a model study

This model study addresses the change in pelagic calcium carbonate production (CaCO<sub>3</sub>, as calcite in the model) and dissolution in response to rising atmospheric CO2. The parameterization of CaCO3 production includes a dependency on the saturation state of seawater with respect to calcite. It was derived from laboratory and mesocosm studies on particulate organic and inorganic carbon production in Emiliania huxleyi as a function of pCO2. The model predicts values of CaCO3 production and dissolution in line with recent estimates. The effect of rising pCO2 on CaCO3 production and dissolution was quantified by means of model simulations forced with atmospheric CO2 increasing at a rate of 1% per year from 286 ppm to 1144 ppm over a 140 year time-period. The simulation predicts a decrease of CaCO3 production by 27%. The combined change in production and dissolution of CaCO3 yields an excess uptake of CO2 from the atmosphere by the ocean of 5.9 GtC over the period of 140 years.

Gehlen M., Gangstø R., Schneider B., Bopp L., Aumont O., & Ethe C., 2007. The fate of pelagic CaCO3 production in a high CO2 ocean: a model study. Biogeosciences 4: 505-519. Article.

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Mode and tempo of the Paleocene-Eocene thermal maximum in an expanded section from the Venetian pre-Alps

The central part of the Piave River valley in the Venetian pre-Alps of NE Italy exposes an expanded and continuous marine sediment succession that encompasses the Paleocene series and the Paleocene to Eocene transition. The Paleocene through lowermost Eocene succession is >100 m thick and was deposited at middle to lower bathyal depths in a hemipelagic, near-continental setting in the central western Tethys. In the Forada section, the Paleocene succession of limestone-marl couplets is sharply interrupted by an ∼3.30-m-thick unit of clays and marls (clay marl unit). The very base of this unit represents the biostratigraphic Paleocene-Eocene boundary, and the entire unit coincides with the main carbon isotope excursion of the Paleocene-Eocene thermal maximum event. Concentrations of hematite and biogenic carbonate, δ13C measurements, and abundance of radiolarians, all oscillate in a cyclical fashion and are interpreted to represent precession cycles. The main excursion interval spans five complete cycles, that is, 105 ± 10 k.y. The overlying carbon isotope recovery interval, which is composed of six distinct limestone-marl couplets, is interpreted to represent six precessional cycles with a duration of 126 ± 12 k.y. The entire carbon isotope excursion interval in Forada has a total duration of ∼231 ± 22 k.y., which is 5%–10% longer than previous estimates derived from open ocean sites (210–220 k.y.). Geochemical proxies for redox conditions indicate oxygenated conditions before, during, and after the carbon isotope excursion event. The Forada section exhibits a nonstepped sharp decrease in δ13C (−2.35‰) at the base of the clay marl unit. The hemipelagic, near-continental depositional setting of Forada and the sharply elevated sedimentation rates throughout the clay marl unit argue for continuous rather than interrupted deposition and show that the initial nonstepped carbon isotope shift was not caused by a hiatus. A single sample at the base of the unit lacks biogenic carbonate. Preservation of carbonate thereafter improves progressively up-section in the clay marl unit, which is consistent with a prodigiously abrupt and rapid acidification of the oceans followed by a slower, successive deepening of the carbonate compensation depth. Increased sedimentation rates through the clay marl unit (approximately the main interval of the carbon isotope excursion) are consistent with an intensified hydrological cycle driven by super-greenhouse conditions and enhanced weathering and transport of terrigenous material to this near-continental, hemipelagic environment in the central western Tethys.

The sharp transition in lithology from the clay marl unit to the overlying limestone-marl couplets in the recovery interval and the coincident shift toward heavier δ13C values suggest that the silicate pump and continental weathering, the cause of the enhanced terrigenous flux to Forada, stopped abruptly. This implies that the source of the light CO2 eased to be added to the ocean-atmosphere system at the top of the clay marl unit.

Giusberti L, Rio D, Agnini C, Backman J, Fornaciari E, et al., 2007. Mode and tempo of the Paleocene-Eocene thermal maximum in an expanded section from the Venetian pre-Alps. Geological Society of America Bulletin 119(3): 391–412. Article.

California Adopts First Phase of Ocean Preserves

California wildlife regulators adopted a sweeping ocean protection plan on Friday, the first such statewide effort in the country, intended to establish a network of underwater refuges.

The plan, unanimously approved by members of the California Fish and Game Commission, will create a statewide system of connected ocean preserves where fishing and other human activities would be limited or banned.

The first phase sets aside the waters along a 200-mile stretch of the coast, including tidal areas that fan out three miles from shore, to protect marine habitat between Point Conception, near Santa Barbara, and Half Moon Bay, about 25 miles south of here.

Environmental advocates hailed the vote, with the Natural Resources Defense Council calling the approved plan a “balanced compromise using high quality science.” But commercial fishermen say the plan does little more than further restrict their industry.

“Just protecting part of the ocean won’t work,” said Zeke Grader, executive director of the Pacific Coast Federation of Fishermen’s Associations. “We can’t just restrict fishermen. We need to address pollution and acidification of the oceans.”

The New York Times, 14 APril 2007. Article.

B/Ca in planktonic foraminifera as a proxy for surface seawater pH

Boron isotope systematics indicate that boron incorporation into foraminiferal CaCO3 is determined by the partition coefficient, KD (= inline equation), and [B(OH)4 −/HCO3 −]seawater, providing, in principle, a method to estimate seawater pH and PCO2. We have measured B/Ca ratios in Globigerina bulloides and Globorotalia inflata for a series of core tops from the North Atlantic and the Southern Ocean and in Globigerinoides ruber (white) from Ocean Drilling Program (ODP) site 668B on the Sierra Leone Rise in the eastern equatorial Atlantic. B/Ca ratios in these species of planktonic foraminifera seem unaffected by dissolution on the seafloor. KD shows a strong species-specific dependence on calcification temperature, which can be corrected for using the Mg/Ca temperature proxy. A preliminary study of G. inflata from Southern Ocean sediment core CHAT 16K suggests that temperature-corrected B/Ca was 30% higher during the last glacial. Correspondingly, pH was 0.15 units higher and aqueous PCO2 was 95 μatm lower at this site at the Last Glacial Maximum. The covariation between reconstructed PCO2 and the atmospheric pCO2 from the Vostok ice core demonstrates the feasibility of using B/Ca in planktonic foraminifera for reconstructing past variations in pH and PCO2.

Yu, J., H. Elderfield, and B. Hönisch (2007), B/Ca in planktonic foraminifera as a proxy for surface seawater pH. Paleoceanography 22, PA2202, doi:10.1029/2006PA001347. Abstract.

Overloaded oceans

Ocean acidification is a real and potentially devastating consequence of climate change that demands immediate attention.

An excess of fossil fuel-derived carbon dioxide is causing profound changes in ocean chemistry. These changes are some of the most pressing problems presented by the burning of fossil fuels, but they get little attention.

A small but growing number of scientists are turning their thoughts to the oceans and their findings demand that we take action.

Tony Haymet, ninemsn, 30 March 2007. Article.

Global warming ‘threatening’ shellfish

MUSSELS, among other shellfish species, are reportedly in danger of being wiped out by increasing greenhouse gas levels in seawater.

Certain types of shellfish are being threatened by the rise of global warming, European scientists have discovered.
Most shellfish are at some risk, but the worst affected species are oysters and mussels, which are in serious danger of being wiped out because of the increase in greenhouse gas levels in seawater, according to the scientists.

The report, which was carried out by French and Dutch scientists at France’s CNRS research centre and the Netherlands Institute of Ecology has found that rising levels of acid in the sea caused by carbon dioxide emissions are threatening some of the world’s most popular edible shellfish. Scientists said the carbon dioxide (Co2) was preventing oysters and mussels from producing shells, making them slow to develop and vulnerable to predators.
The report also found that the creatures’ shells were reduced by up to 25% in seawater, with Co2 levels predicted for the end of this century. Increasing Co2 levels in the water led to the shells dissolving completely. It is estimated that 25-million tonnes of Co2 are absorbed by the sea.

Fishfarmer Magazine, 21 March 2007. Article.

Ocean Acidification Predicted To Harm Shellfish, Aquaculture

In 2100, mussels are expected to calcify their shells 25 percent slower than currently; oysters, 10 percent slower. This will be caused by the continued release and accumulation of carbon dioxide in the air: one third of it will be absorbed by the ocean water, thereby making it more acid. Scientists of the Netherlands Institute of Ecology (NIOO-KNAW) report in Geophysical Research Letters, together with a French colleague, on the potentially major consequences for aquaculture and coastal nature.

Science Daily, 18 March 2007. Article


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