Dynamics of a stepped carbon-isotope excursion: Ultra high-resolution study of Early Toarcian environmental change

In the Toarcian (Early Jurassic; ~ 183 Myr ago), the ocean–atmosphere system was subject to one of the largest perturbations of the carbon cycle in the last 250 Myr known as the Toarcian Oceanic Anoxic Event (T-OAE). This event was accompanied by a − 6‰ negative carbon-isotope excursion (CIE) caused by massive injection of isotopically light carbon into the ocean–atmosphere system, possibly from destabilisation of gas hydrates. This study reveals the pacing and sequence of events leading up to the CIE and to widespread deposition of organic-rich sediments. The very high-resolution isotopic record from exceptionally well-preserved carbonate and organic matter from the Paris Basin enables recognition of increased CO₂ levels ~ 130 kyr in advance of the major negative CIE. An accelerated increase in the pCO₂ is registered ~ 25 kyr before the onset of this negative excursion and was so rapid and so intense that it led to a water column undersaturated with respect to calcium carbonate in the Paris Basin. Undersaturation is expressed as a dramatic drop in the accumulation of the biogenic calcite produced by the surface-dwelling calcifiers. These environmental perturbations, representing precursor phases of CO₂ injection, predate the first step towards relatively light carbon-isotope in carbonate and organic matter and are tentatively attributed to Karoo–Ferrar magmatism. This negative shift was registered slightly earlier in terrestrial carbon than marine carbonate. Subsequent global warming is credited with liberating isotopically light carbon, and ultimately fostered anoxia in the Paris Basin: the response of these cumulative inputs of carbon to the Earth system. Isotopic and sedimentological evidence indicates continuously elevated phytoplanktonic productivity throughout the first step of the negative CIE, suggesting that the biological pump accelerated the drawdown of excess carbon leading to temporary recovery of carbonate sedimentation, ~ 45 kyr after the first step of the CIE. This re-establishment of the saturation state of the water column was only fleeting before the later stepwise release of isotopically light carbon.

Resource allocation and extracellular acid-base status in the sea urchin Strongylocentrotus droebachiensis in response to CO2 induced seawater acidification

Anthropogenic CO₂ emission will lead to an increase in seawater pCO₂ of up to 80-100 Pa (800-1000 μatm) within this century and to an acidification of the oceans. Green sea urchins (Strongylocentrotus droebachiensis) occurring in Kattegat experience seasonal hypercapnic and hypoxic conditions already today. Thus, anthropogenic CO₂ emissions will add up to existing values and will lead to even higher pCO₂ values >200 Pa (>2000 μatm). To estimate the green sea urchins’ potential to acclimate to acidified seawater, we calculated an energy budget and determined the extracellular acid base status of adult S. droebachiensis exposed to moderately (102 to 145 Pa, 1007 to 1431 μatm) and highly (284 to 385 Pa, 2800 to 3800 μatm) elevated seawater pCO₂ for 10 and 45 days.

A 45 – day exposure to elevated pCO₂ resulted in a shift in energy budgets, leading to reduced somatic and reproductive growth. Metabolic rates were not significantly affected, but ammonium excretion increased in response to elevated pCO₂. This led to decreased O:N ratios. These findings suggest that protein metabolism is possibly enhanced under elevated pCO₂ in order to support ion homeostasis by increasing net acid extrusion. The perivisceral coelomic fluid acid-base status revealed that S. droebachiensis is able to fully (intermediate pCO₂) or partially (high pCO₂) compensate extracellular pH (pH_e) changes by accumulation of bicarbonate (maximum increases 2.5 mM), albeit at a slower rate than typically observed in other taxa (10 day duration for full pH_e compensation). At intermediate pCO₂, sea urchins were able to maintain fully compensated pH_e for 45 days. Sea urchins from the higher pCO₂ treatment could be divided into two groups following medium-term acclimation: one group of experimental animals (29%) contained remnants of food in their digestive system and maintained partially compensated pH_e (+2.3 mM HCO₃⁻), while the other group (71%) exhibited an empty digestive system and a severe metabolic acidosis (-0.5 pH units, -2.4 mM HCO₃⁻). There was no difference in mortality between the three pCO₂ treatments.

The results of this study suggest that S. droebachiensis occurring in the Kattegat might be pre-adapted to hypercapnia due to natural variability in pCO₂ in its habitat. We show for the first time that some echinoderm species can actively compensate extracellular pH. Seawater pCO₂ values of >200 Pa, which will occur in the Kattegat within this century during seasonal hypoxic events, can possibly only be endured for a short time period of a few weeks. Increases in anthropogenic CO₂ emissions and leakages from potential sub-seabed CO₂ storage (CCS) sites thus impose a threat to the ecologically and economically important species S. droebachiensis.

Study: Ocean acidity exceeds natural norms (audio)

Rapidly rising CO2 emissions change ocean chemistry

New research suggests an overload of carbon dioxide in the oceans is posing a serious threat to marine life, food security and tourism.

While most CO2 emissions from automobiles, buildings and factories go into the atmosphere, one-third ends up in the oceans, changing ocean chemistry and making seawater more acid.

A study in Nature Climate Change tracks ocean acidity over 21,000 years of climate history. Tobias Friedrich, co-author and post-doctoral fellow at the University of Hawaii International Pacific Research Center says the record shows natural increases in CO2 concentrations in the atmosphere over time and differences from region to region.

Letter from Antarctica: Hunting ocean acidification at the South Pole

Onboard the Aurora Australis

11.30 am, 6 January 2012

It’s day one of the Mawson Centenary Cruise to Commonwealth Bay in Antarctica, and while all other expeditioners are lying low adjusting to the swell of the Southern Ocean, Team Acid has begun searching for shelled zooplankton – the tiny creatures at the bottom of the food chain and those most at risk of changing ocean chemistry or ‘ocean acidification’.

If there is evidence to be found of the effects of chemical change on marine biological systems, Team Acid is looking in the right spot.

Not only do the world’s oceans play a crucial role in capturing CO2 (they currently capture a quarter of our emissions each year), the polar oceans capture a disproportionate share of this because of the so-called ‘champagne effect’.