Posts Tagged 'globalmodelling'

Global coral reef ecosystems exhibit declining calcification and increasing primary productivity

Long-term coral reef resilience to multiple stressors depends on their ability to maintain positive calcification rates. Estimates of coral ecosystem calcification and organic productivity provide insight into the environmental drivers and temporal changes in reef condition. Here, we analyse global spatiotemporal trends and drivers of coral reef calcification using a meta-analysis of ecosystem-scale case studies. A linear mixed effects regression model was used to test whether ecosystem-scale calcification is related to seasonality, methodology, calcifier cover, year, depth, wave action, latitude, duration of data collection, coral reef state, Ωar, temperature and organic productivity. Global ecosystem calcification estimated from changes in seawater carbonate chemistry was driven primarily by depth and benthic calcifier cover. Current and future declines in coral cover will significantly affect the global reef carbonate budget, even before considering the effects of sub-lethal stressors on calcification rates. Repeatedly studied reefs exhibited declining calcification of 4.3 ± 1.9% per year (x̄  = 1.8 ± 0.7 mmol m−2 d−1 yr−1), and increasing organic productivity at 3.0 ± 0.8 mmol m−2 d−1 per year since 1970. Therefore, coral reef ecosystems are experiencing a shift in their essential metabolic processes of calcification and photosynthesis, and could become net dissolving worldwide around 2054.

Continue reading ‘Global coral reef ecosystems exhibit declining calcification and increasing primary productivity’

A pronounced spike in ocean productivity triggered by the Chicxulub impact

Abstract

There is increasing evidence linking the mass-extinction event at the Cretaceous-Paleogene boundary to an asteroid impact near Chicxulub, Mexico. Here we use model simulations to explore the combined effect of sulfate aerosols, carbon dioxide and dust from the impact on the oceans and the marine biosphere in the immediate aftermath of the impact. We find a strong temperature decrease, a brief algal bloom caused by nutrients from both the deep ocean and the projectile, and moderate surface ocean acidification. Comparing the modeled longer-term post-impact warming and changes in carbon isotopes with empirical evidence points to a substantial release of carbon from the terrestrial biosphere. Overall, our results shed light on the decades to centuries after the Chicxulub impact which are difficult to resolve with proxy data.

Plain Language Summary

The sudden disappearance of the dinosaurs and many other species during the end-Cretaceous mass extinction 66 million years ago marks one of the most profound events in the history of life on Earth. The impact of a large asteroid near Chicxulub, Mexico, is increasingly recognised as the trigger of this extinction, causing global darkness and a pronounced cooling. However, the links between the impact and the changes in the biosphere are not fully understood. Here, we investigate how life in the ocean reacts to the perturbations in the decades and centuries after the impact. We find a short-lived algal bloom caused by the upwelling of nutrients from the deep ocean and nutrient input from the impactor.

Continue reading ‘A pronounced spike in ocean productivity triggered by the Chicxulub impact’

				
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Ocean acidification in the IPCC AR5 WG II

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