Archive for February, 2009

Enhanced ocean carbon storage from anaerobic alkalinity generation in coastal sediments

The coastal ocean is a crucial link between land, the open ocean and the atmosphere. The shallowness of the water column permits close interactions between the sedimentary, aquatic and atmospheric compartments, which otherwise are decoupled at long time scales (≅ 1000 yr) in the open oceans. Despite the prominent role of the coastal oceans in absorbing atmospheric CO2 and transferring it into the deep oceans via the continental shelf pump, the underlying mechanisms remain only partly understood. Evaluating observations from the North Sea, a NW European shelf sea, we provide evidence that anaerobic degradation of organic matter, fuelled from land and ocean, generates total alkalinity (AT) and increases the CO2 buffer capacity of seawater. At both the basin wide and annual scales anaerobic AT generation in the North Sea’s tidal mud flat area irreversibly facilitates 7–10%, or taking into consideration benthic denitrification in the North Sea, 20–25% of the North Sea’s overall CO2 uptake. At the global scale, anaerobic AT generation could be accountable for as much as 60% of the uptake of CO2 in shelf and marginal seas, making this process, the anaerobic pump, a key player in the biological carbon pump. Under future high CO2 conditions oceanic CO2 storage via the anaerobic pump may even gain further relevance because of stimulated ocean productivity.
Continue reading ‘Enhanced ocean carbon storage from anaerobic alkalinity generation in coastal sediments’

Island looks to take a lead in ‘acid oceans’ research

Bermuda could soon be at the centre of research into the acidification of the oceans, under plans being pursued by the Bermuda Institute of Ocean Sciences.

Dr. Andreas Andersson, in a joint effort with BIOS’ Nick Bates and Samantha de Putron, is currently applying for funding to develop an Ocean Acidification Research Centre at the Institute.
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Warm oceans slow coral growth

It’s official: the biggest and most robust corals on the Great Barrier Reef (GBR) have slowed their growth by more than 14 per cent since the “tipping point” year of 1990. Evidence is strong that the decline has been caused by a synergistic combination of rising sea surface temperatures and ocean acidification.

A paper published in the prestigious international journal Science and written by AIMS scientists Dr Glenn De’ath, Dr Janice Lough and Dr Katharina Fabricius is the most comprehensive study to date on calcification rates of GBR corals.
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The influence of hypercapnia and macrofauna on sediment nutrient flux – will ocean acidification affect nutrient exchange?

Rising levels of atmospheric carbon dioxide and the concomitant increased uptake of this by the oceans is resulting in hypercapnia-related reduction of ocean pH. Research focussed on the direct effects of these physicochemical changes on marine invertebrates has begun to improve our understanding of impacts at the level of individual physiologies. However, CO2-related impairment of organisms’ contribution to ecological or ecosystem processes has barely been addressed. The burrowing ophiuroid Amphiura filiformis, which has a physiology that makes it susceptible to reduced pH, plays a key role in sediment nutrient cycling by mixing and irrigating the sediment, a process known as bioturbation. Here we investigate the role of A. filiformis in modifying nutrient flux rates across the sediment-water boundary and the impact of CO2-related acidification on this process. A 40 day exposure study was conducted under predicted pH scenarios from the years 2100 (pH 7.7) and 2300 (pH 7.3), plus an additional treatment of pH 6.8. This study demonstrated strong relationships between A. filiformis density and cycling of some nutrients; A. filiformis activity increases the sediment uptake of phosphate and the release of nitrite and nitrate. No relationship between A. filiformis density and the flux of ammonium or silicate were observed. Results also indicated that, within the timescale of this experiment, effects at the individual bioturbator level appear not to translate into reduced ecosystem influence. Rather the effect of hypercapnia and lowered pH on bacteria and microphytobenthos may have been of greater significance in understanding the changes to nutrient fluxes seen here. However, long term survival of key bioturbating species is far from assured and changes in both bioturbation and microbial processes could alter key biogeochemical processes in future, more acidic oceans.

Continue reading ‘The influence of hypercapnia and macrofauna on sediment nutrient flux – will ocean acidification affect nutrient exchange?’

Effects of the pH/pCO2 control method in the growth medium of phytoplankton

To study the effects of ocean acidification on the physiology of phytoplankton requires that the key chemical parameters of the growth medium, pCO2, pH and Ω (the saturation state of calcium carbonate) be carefully controlled. This is made difficult by the interdependence of these parameters. Moreover, in growing batch cultures of phytoplankton, the fixation of CO2, the uptake of nutrients and, for coccolithophores, the precipitation of calcite all change the inorganic carbon and acid-base chemistry of the medium. For example, absent pH-buffering or CO2 bubbling, a sizeable decrease in pCO2 occurs at a biomass concentration as low as 50 μM C in non-calcifying cultures. Even in cultures where pCO2 or pH is maintained constant, other chemical parameters change substantially at high cell densities. The quantification of these changes is facilitated by the use of buffer capacities. Experimentally we observe that all methods of adjustment of pCO2/pH can be used, the choice of one or the other depending on the specifics of the experiments. The mechanical effect of bubbling of cultures seems to induce more variable results than other methods of pCO2/pH control. While highly convenient, the addition of pH buffers to the medium induces changes in trace metal availability and cannot be used under trace metal-limiting conditions.

Continue reading ‘Effects of the pH/pCO2 control method in the growth medium of phytoplankton’

Off-balance ocean: Acidification from absorbing atmospheric CO2 is changing the ocean’s chemistry

PEOPLE CAN’T walk on water, but scientists say the carbon dioxide emitted by humans into the atmosphere has started to leave noticeable footprints on the ocean.


Scientists have been concerned for years that lower ocean pH caused by absorption of CO2 emissions could decrease calcification processes underlying the growth of shells and corals’ hard exteriors. Besides studying that phenomenon, they are investigating how acidification alters the concentration and behavior of the ocean’s trace metals, some of which are nutrients for marine life. They are also looking into some unexpected consequences of ocean acidification, such as disruptions to sound propagation and transmission of chemical cues. Some scientists believe the net effect of these and other yet undiscovered changes may threaten the survival of a wide variety of marine organisms.

Continue reading ‘Off-balance ocean: Acidification from absorbing atmospheric CO2 is changing the ocean’s chemistry’

Calcification, a physiological process to be considered in the context of the whole organism

Marine organisms that produce calcium carbonate structures are predicted to be most vulnerable to a decline in oceanic pH (ocean acidification) based on the understanding that calcification rates will decrease as a result of changes in the seawater carbonate chemistry thereby reducing carbonate ion concentration (and associated saturation states). Coastal seas are critical components of the global carbon cycle yet little research has been conducted on acidification impacts on coastal benthic organisms. Here, a critical appraisal of calcification in six benthic species showed, contrary to popular predictions, calcification can increase, and not decrease, in acidified seawater. Measuring the changes in calcium in isolated calcium carbonate structure as well as structures from live animals exposed to acidified seawater allowed a comparison between a species’ ability to calcify and the dissolution affects across decreasing levels of pH. Calcium carbonate production is dependant on the ability to increase calcification thus counteracting an increase in dissolution. Comparison with paleoecological studies of past high carbon dioxide (CO2) events presents a similar picture. This conclusion implies that calcification may not be the critical process impacted by ocean acidification; particularly as all species investigated displayed physiological trade offs including reduced metabolism, health, and behavioural responses, in association with this calcification upregulation, which possess as great a threat to survival as an inability to calcify.

Continue reading ‘Calcification, a physiological process to be considered in the context of the whole organism’

Evidence for Ocean Acidification in the Great Barrier Reef of Australia

Geochemical records preserved in the long-lived carbonate skeleton of corals provide one of the few means to reconstruct changes in seawater pH since the commencement of the industrial era. This information is important in not only determining the response of the surface oceans to ocean acidification from enhanced uptake of CO2, but also to better understand the effects of ocean acidification on carbonate secreting organisms such as corals, whose ability to calcify is highly pH dependent. Here we report an ~200 year 11B isotopic record, extracted from a long-lived Porites coral from the central Great Barrier Reef of Australia. This record covering the period from 1800 to 2004 was sampled at yearly increments from 1940 to the present and 5-year increments prior to 1940. The 11B isotopic compositions reflect variations in seawater pH, and the 13C changes in the carbon composition of surface water due to fossil fuel burning over this period. In addition complementary Ba/Ca, 18O and Mg/Ca data was obtained providing proxies for terrestrial runoff, salinity and temperature changes over the past 200 years in this region. Positive thermal ionization mass spectrometry (PTIMS) method was utilized in order to enable the highest precision and most accurate measurements of 11B values. The internal precision and reproducibility for 11B of our measurements are better than ±0.2‰ (2), which translates to a precision of better than ±0.02 pH units. Our results indicate that the long-term pre-industrial variation of seawater pH in this region is partially related to the decadal-interdecadal variability of atmospheric and oceanic anomalies in the Pacific. In the periods around 1940 and 1998 there are also rapid oscillations in 11B compositions equivalent changes in pH of almost 0.5 units. The 1998 oscillation is co-incident with a major coral bleaching event indicating the sensitivity of skeletal 11 B compositions to loss of zooxanthellate symbionts. Importantly, from the 1940’s to the present-day, there is a general overall trend of ocean acidification with pH decreasing by about 0.2 to 0.3 units, the range being dependent on the value assumed for the fractionation factor α(B3-B4) of the boric acid and borate species in seawater. Correlations of 11B with 13C during this interval indicate that the increasing trend towards ocean acidification over the past 60 years in this region is the result of enhanced dissolution of CO2 in surface waters from the rapidly increasing levels of atmospheric CO2, mainly from fossil fuel burning. This suggests that the increased levels of anthropogenic CO2 in atmosphere has already caused a significant trend towards acidification in the oceans during the past decades. Observations of surprisingly large decreases in pH across important carbonate producing regions, such as the Great Barrier Reef of Australia, raise serious concerns about the impact of Greenhouse gas emissions on coral calcification.

Continue reading ‘Evidence for Ocean Acidification in the Great Barrier Reef of Australia’

Ocean acidification disorients fish, riles up scientists

I may need to start a file for ‘ocean impacts we hadn’t thought of’. First there was the projection that the seas will get noisier as a result of ocean acidification, which whale conservation groups were running with at a UN conference in December. Now researchers report in PNAS that ocean acidification may make fish larvae lose the sense of smell they use to find a home.

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Our ocean backyard: what’s happening to the ocean’s chemistry?

Our vast, blue ocean nurtures and feeds the Earth’s natural systems. It provides a home to the world’s largest habitat and creates its weather by interacting with the atmosphere.

The ocean also controls our planet’s temperature by absorbing the greenhouse gas carbon dioxide, providing a buffer from the effects of atmospheric climate change.

But that dissolved carbon dioxide has lowered seawater’s pH, which measures its acid or base level. Ocean pH has dropped from 8.21 to 8.10 since the mid-1700s when industrial activity and an increase in carbon dioxide output began. Seawater remains on the basic side of the pH scale; it’s unlikely it will ever become acidic. But the small changes have bigger consequences, which many believe can be fixed — if the will exists.

Continue reading ‘Our ocean backyard: what’s happening to the ocean’s chemistry?’

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Ocean acidification in the IPCC AR5 WG II

OUP book