Archive for October, 2006

Benthic foraminiferal Li/Ca: Insights into Cenozoic seawater carbonate saturation state

Benthic foraminiferal Li/Ca decreases down a Norwegian Sea holothermal depth transect, suggesting that the saturation state of seawater with respect to calcium carbonate influences foraminiferal Li/Ca. Benthic foraminiferal Li/Ca increases by 17% across the glaciation event in the early Oligocene, which likely reflects the increase in seawater saturation state evidenced by the concomitant deepening of the calcite compensation depth. Following the establishment of the Antarctic ice sheet, benthic foraminiferal Li/Ca bears a remarkable resemblance to the estimated oxygen isotopic composition of seawater, suggesting that during this time seawater saturation was largely controlled by glacioeustatically driven changes in shallow-water carbonate accumulation rates.

Lear CH, Rosenthal Y (2006) Benthic foraminiferal Li/Ca: Insights into Cenozoic seawater carbonate saturation state. Geology 34(11): 985–988. Article.

Evidence for an acidic ocean on Mars from phosphorus geochemistry of Martian soils and rocks

Recent analyses of elemental concentrations and mineralogy of iron-bearing compounds of Martian soils and rocks by the Mars Exploration Rovers at Meridiani Planum and Gusev Crater demonstrate that phosphorus concentration is correlated with sulfur and chlorine. The positive correlation of these three elements with each other in soils at both sites argues for a globally homogeneous soil component. Sulfur, and possibly chlorine, in Martian soils and Meridiani Planum outcrop rocks is likely derived from volcanic exhalations, but phosphorus must be derived from the weathering of igneous rocks. Here we show that the similar concentration of phosphorus in soils at the two Mars Exploration Rover sites, coupled with positive correlations to chlorine and sulfur, is best explained as resulting from mixing and homogenization of phosphate, sulfate, and chloride in a large acidic aqueous reservoir, such as an acidic ocean. Acidic thin-film or acid-fog weathering cannot readily produce the similar P/S and P/Cl ratios of soils measured on Mars, and more important, cannot explain the high phosphorus content of ancient (ca. 3–4 Ga) sulfate-rich rocks in outcrop at Meridiani. The existence of a global acidic hydrosphere or ocean at some time in early Martian history can also explain the lack of extensive carbonate deposits on the Martian surface.

Greenwood JP, Blake RE (2006) Evidence for an acidic ocean on Mars from phosphorus geochemistry of Martian soils and rocks. Geology. 34(11): 953–956. Article.

A global catastrophe of our own making

Ocean acidification: Extra carbon dioxide in the atmosphere dissolves in seawater causing an increase in ocean acidification. The predicted increase in acidification over the next century have not been experienced for hundreds of thousands of years. One outcome could be the death of many marine ecosystems, such as coral reefs. More than 1 billion people worldwide currently rely on fish as their primary source of animal protein.

By Steve Connor, The Independent, 31 October 2006. Article.

Climate change threatens human welfare

Former chief World Bank economist Nicholas Stern says climate change, if nothing is done about it, will increase worldwide deaths from malnutrition and heat stress, and diseases such as malaria could become more widespread. Report predicts droughts, floods, water shortages and extreme weather if economies continue path.

By Michael Mccarthy, The Hamilton Spectator, 31 October 2006. Article.

Calcification in Aquatic Ecosystems: Physiology, Biogeochemistry, and Response to Environmental Change

4-9 February 2007

"SS13 – Calcification in Aquatic Ecosystems: Physiology, Biogeochemistry, and Response to Environmental Change" to be held at the ASLO 2007 Aquatic Sciences Meeting, Santa Fe, USA, 4-9 February 2007. The goal of this session is to report recent advances in the field of calcification in both marine and freshwater ecosystems. All spatial and temporal scales will be included, from molecular to global, and across geologic time through the present and future. Topics of interest include, but are not limited to: (1) molecular control, (2) transport pathways, (3) estimates of calcification at the organism, community and global scales, and (4) response to elevated pCO2 and temperature. Both experimental and modeling approaches are welcome.

Conveners: Jean-Pierre Gattuso and Joanie Kleypas.

More info

Modelling the response of marine ecosystems to increasing levels of CO2

Workshop, February 13-15, 2007, Plymouth UK

Scope of the workshop

The high CO2 workshop will focus on biogeochemical changes and ecosystem functionality (such as production, nutrient cycling and community structure) in time scales of around 100-150 years. Acidification and changes to carbonate chemistry will be the main drivers under consideration but the workshop will also address the impacts caused by changes to mixing, stratification and nutrient supply due to climate change. Consideration of ocean carbon cycling in the long term and temperature driven species extinctions or invasions will probably be more peripheral to this workshop. The workshop will encompass both shelf and oceanic waters and consider both pelagic and benthic systems, calcifiers and non-calcifiers and the range of trophic levels.

More information

V.I. prominent task in force discussions

ST. THOMAS – As the U.S. Coral Reef Task Force meeting officially opened Wednesday after several days of preliminary meetings and workshops, Virgin Islands coral reefs remained in the forefront of discussion.
Hot topics for the gathering were touched upon as scientists from as far away as Australia spoke during the opening meeting: Coral bleaching and disease. Ocean acidification. Federally threatened coral species. Plans for 2008, designated as International Year of the Reef.

By L. Freehill. The Virgin Islands Daily News, Thursday, October 26th 2006

Response to Comment on “Preindustrial to Modern Interdecadal Variability in Coral Reef pH”

Coral reefs are exceptional environments where changes in calcification, photosynthesis, and respiration induce large temporal variations of pH. We argue that boron isotopic variations in corals provide a robust proxy for paleo-pH which, together with the likely concomitant changes in the reconstructed partial pressure of CO2 (PCO2) calculated by Matear and McNeil, fall within ranges that are typical of modern coral reef ecosystems.

Pelejero C., Calvo E., McCulloch M. T., Marshall J. F, Gagan M. K., Lough J. M., and Opdyke, B. N. Response to Comment on “Preindustrial to Modern Interdecadal Variability in Coral Reef pH”. Science 314 (5799), 595c. [DOI: 10.1126/science.1128502]. Article.

Comment on “Preindustrial to Modern Interdecadal Variability in Coral Reef pH”

Based on the boron isotopic composition of coral from the southwestern Pacific, Pelejero et al. (Reports, 30 September 2005, p. 2204) suggested that natural variations in pH can modulate the impact of ocean acidification on coral reef ecosystems. We show that this claim cannot be reconciled with other marine carbon chemistry constraints and highlight problems with the authors’ interpretation of the paleontologic data.

Matear and McNeil, 2006. Comment on “Preindustrial to Modern Interdecadal Variability in Coral Reef pH”. Science 314(5799), 595b. [DOI: 10.1126/science.1128198]. Article.

Species-specific responses of calcifying algae to changing seawater carbonate chemistry

Uptake of half of the fossil fuel CO2 into the ocean causes gradual seawater acidification. This has been shown to slow down calcification of major calcifying groups, such as corals, foraminifera, and coccolithophores. Here we show that two of the most productive marine calcifying species, the coccolithophores Coccolithus pelagicus and Calcidiscus leptoporus, do not follow the CO2-related calcification response previously found. In batch culture experiments, particulate inorganic carbon (PIC) of C. leptoporus changes with increasing CO2 concentration in a nonlinear relationship. A PIC optimum curve is obtained, with a maximum value at present-day surface ocean pCO2 levels (∼360 ppm CO2). With particulate organic carbon (POC) remaining constant over the range of CO2 concentrations, the PIC/POC ratio also shows an optimum curve. In the C. pelagicus cultures, neither PIC nor POC changes significantly over the CO2 range tested, yielding a stable PIC/POC ratio. Since growth rate in both species did not change with pCO2, POC and PIC production show the same pattern as POC and PIC. The two investigated species respond differently to changes in the seawater carbonate chemistry, highlighting the need to consider species-specific effects when evaluating whole ecosystem responses. Changes of calcification rate (PIC production) were highly correlated to changes in coccolith morphology. Since our experimental results suggest altered coccolith morphology (at least in the case of C. leptoporus) in the geological past, coccoliths originating from sedimentary records of periods with different CO2 levels were analyzed. Analysis of sediment samples was performed on six cores obtained from locations well above the lysocline and covering a range of latitudes throughout the Atlantic Ocean. Scanning electron micrograph analysis of coccolith morphologies did not reveal any evidence for significant numbers of incomplete or malformed coccoliths of C. pelagicus and C. leptoporus in last glacial maximum and Holocene sediments. The discrepancy between experimental and geological results might be explained by adaptation to changing carbonate chemistry.

Langer, G., M. Geisen, K.-H. Baumann, J. Kläs, U. Riebesell, S. Thoms, and J. R. Young (2006), Species-specific responses of calcifying algae to changing seawater carbonate chemistry, Geochem. Geophys. Geosyst., 7, Q09006, doi:10.1029/2005GC001227. Article

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Ocean acidification in the IPCC AR5 WG II

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