Seawater carbonate chemistry and net dissolution rate for experiment of Shiraho reef

Acidification of the oceans by increasing anthropogenic CO2 emissions will cause a decrease in biogenic calcification and an increase in carbonate dissolution. Previous studies have suggested that carbonate dissolution will occur in polar regions and in the deep sea where saturation state with respect to carbonate minerals (Omega) will be <1 by 2100. Recent reports demonstrate nocturnal carbonate dissolution of reefs, despite a Omega a (aragonite saturation state) value of >1. This is probably related to the dissolution of reef carbonate (Mg-calcite), which is more soluble than aragonite. However, the threshold of Omega for the dissolution of natural sediments has not been clearly determined. We designed an experimental dissolution system with conditions mimicking those of a natural coral reef, and measured the dissolution rates of aragonite in corals, and of Mg-calcite excreted by other marine organisms, under conditions of Omega a > 1, with controlled seawater pCO2. The experimental data show that dissolution of bulk carbonate sediments sampled from a coral reef occurs at Omega a values of 3.7 to 3.8. Mg-calcite derived from foraminifera and coralline algae dissolves at Omega a values between 3.0 and 3.2, and coralline aragonite starts to dissolve when Omega a = 1.0. We show that nocturnal carbonate dissolution of coral reefs occurs mainly by the dissolution of foraminiferans and coralline algae in reef sediments.

Bulk density, and peat and net carbon accumulation of samples from Selwyn lake, Canada

Peat and net carbon accumulation rates in two sub-arctic peat plateaus of west-central Canada have been studied through geochemical analyses and accelerator mass spectrometry (AMS) radiocarbon dating. The peatland sites started to develop around 6600-5900 cal. yr BP and the peat plateau stages are characterized by Sphagnum fuscum peat alternating with rootlet layers. The long-term peat and net carbon accumulation rates for both profiles are 0.30-0.31 mm/yr and 12.5-12.7 gC/m**2/yr, respectively. These values reflect very slow peat accumulation (0.04-0.09 mm/yr) and net carbon accumulation (3.7-5.2 gC/m**2/yr) in the top rootlet layers. Extensive AMS radiocarbon dating of one profile shows that accumulation rates are variable depending on peat plateau stage. Peat accumulation rates are up to six times higher and net carbon accumulation rates up to four times higher in S. fuscum than in rootlet stages. Local fires represented by charcoal remains in some of the rootlet layers result in very low accumulation rates. High C/N ratios throughout most of the peat profiles suggest low degrees of decomposition due to stable permafrost conditions. Hence, original peat accretion has remained largely unaltered, except in the initial stages of peatland development when permafrost was not yet present.

Seawater carbonate chemistry and net photosynthesis, C/N ratio, growth rate, size of Ostreococcus tauri in a laboratory experiment

Phytoplankton are the basis of marine food webs, and affect biogeochemical cycles. As CO2 levels increase, shifts in the frequencies and physiology of ecotypes within phytoplankton groups will affect their nutritional value and biogeochemical function. However, studies so far are based on a few representative genotypes from key species. Here, we measure changes in cellular function and growth rate at atmospheric CO2 concentrations predicted for the year 2100 in 16 ecotypes of the marine picoplankton Ostreococcus. We find that variation in plastic responses among ecotypes is on par with published between-genera variation, so the responses of one or a few ecotypes cannot estimate changes to the physiology or composition of a species under CO2 enrichment. We show that ecotypes best at taking advantage of CO2 enrichment by changing their photosynthesis rates most should increase in relative fitness, and so in frequency in a high-CO2 environment. Finally, information on sampling location, and not phylogenetic relatedness, is a good predictor of ecotypes likely to increase in frequency in this system.