Archive for May, 2013

Der saure Ozean im Jahr 2100 (audio; in German)

Experiment mit Riesenreagenzgläsern

Wahrsager blicken via Glaskugel in die Zukunft, Wissenschaftler schauen lieber in Reagenzgläser – in dem Fall sogar in Riesenreagenzgläser. Mit diesen sogenannten Mesokosmen wollen die Forscher den Zustand der Meere im Jahre 2100 simulieren, denn eines ist klar: der CO2-Gehalt in der Atmosphäre steigt!

Die Weltmeere nehmen das Gas auf und als Folge werden sie immer saurer. Welche Konsequenzen diese Versauerung für das Leben im Ozean hat, erforscht Ulf Riebesell. Er ist Professor für biologische Ozeanographie am Helmholtz-Zentrum für Ozeanforschung in Kiel und Leiter des Langzeitexperiments im schwedischen Gullmarsfjord.

Continue reading ‘Der saure Ozean im Jahr 2100 (audio; in German)’

Spatiotemporal variability of dimethylsulphoniopropionate on a fringing coral reef: the role of reefal carbonate chemistry and environmental variability

Oceanic pH is projected to decrease by up to 0.5 units by 2100 (a process known as ocean acidification, OA), reducing the calcium carbonate saturation state of the oceans. The coastal ocean is expected to experience periods of even lower carbonate saturation state because of the inherent natural variability of coastal habitats. Thus, in order to accurately project the impact of OA on the coastal ocean, we must first understand its natural variability. The production of dimethylsulphoniopropionate (DMSP) by marine algae and the release of DMSP’s breakdown product dimethylsulphide (DMS) are often related to environmental stress. This study investigated the spatiotemporal response of tropical macroalgae (Padina sp., Amphiroa sp. and Turbinaria sp.) and the overlying water column to natural changes in reefal carbonate chemistry. We compared macroalgal intracellular DMSP and water column DMSP+DMS concentrations between the environmentally stable reef crest and environmentally variable reef flat of the fringing Suleman Reef, Egypt, over 45-hour sampling periods. Similar diel patterns were observed throughout: maximum intracellular DMSP and water column DMS/P concentrations were observed at night, coinciding with the time of lowest carbonate saturation state. Spatially, water column DMS/P concentrations were highest over areas dominated by seagrass and macroalgae (dissolved DMS/P) and phytoplankton (particulate DMS/P) rather than corals. This research suggests that macroalgae may use DMSP to maintain metabolic function during periods of low carbonate saturation state. In the reef system, seagrass and macroalgae may be more important benthic producers of dissolved DMS/P than corals. An increase in DMS/P concentrations during periods of low carbonate saturation state may become ecologically important in the future under an OA regime, impacting larval settlement and increasing atmospheric emissions of DMS.

Continue reading ‘Spatiotemporal variability of dimethylsulphoniopropionate on a fringing coral reef: the role of reefal carbonate chemistry and environmental variability’

A short history of ocean acidification science in the 20th century: a chemist’s view

This review covers the development of ocean acidification science, with an emphasis on the creation of ocean chemical knowledge, through the course of the 20th century. This begins with the creation of the pH scale by Sørensen in 1909 and ends with the widespread knowledge of the impact of the “High CO2 Ocean” by then well underway as the trajectory along the IPCC scenario pathways continues. By mid-century the massive role of the ocean in absorbing fossil fuel CO2 was known to specialists, but not appreciated by the greater scientific community. By the end of the century the trade-offs between the beneficial role of the ocean in absorbing some 90% of all heat created, and the accumulation of some 50% of all fossil fuel CO2 emitted, and the impacts on marine life were becoming clear. This paper documents the evolution of knowledge throughout this period.

Continue reading ‘A short history of ocean acidification science in the 20th century: a chemist’s view’

Symbiodinium community composition in scleractinian corals is not affected by life-long exposure to elevated carbon dioxide

Ocean acidification (OA) is expected to negatively affect coral reefs, however little is known about how OA will change the coral-algal symbiosis on which reefs ultimately depend. This study investigated whether there would be differences in coral Symbiodinium types in response to OA, potentially improving coral performance. We used denaturing gradient gel electrophoresis (DGGE) of the internal transcribed spacer 2 (ITS2) region of ribosomal DNA to investigate the dominant types of Symbiodinium associating with six species of scleractinian coral that were exposed to elevated partial pressures of carbon dioxide (pCO2) in situ from settlement and throughout their lives. The study was conducted at three naturally occurring volcanic CO2 seeps (pCO2 ~500 to 900 ppm, pHTotal 7.8 – 7.9) and adjacent control areas (pCO2 ~390 ppm, pHTotal ~8.0 – 8.05) in Papua New Guinea. The Symbiodinium associated with corals living in an extreme seep site (pCO2 >1000 ppm) were also examined. Ten clade C types and three clade D types dominated the 443 coral samples. Symbiodinium types strongly contrasted between coral species, however, no differences were observed due to CO2 exposure. Within five species, 85 – 95% of samples exhibited the same Symbiodinium type across all sites, with remaining rare types having no patterns attributable to CO2 exposure. The sixth species of coral displayed site specific differences in Symbiodinium types, unrelated to CO2 exposure. Symbiodinium types from the coral inhabiting the extreme CO2 seep site were found commonly throughout the moderate seeps and control areas. Our finding that symbiotic associations did not change in response to CO2 exposure suggest that, within the six coral hosts, none of the investigated 13 clade C and D Symbiodinium types had a selective advantage at high pCO2. Acclimatisation through changing symbiotic association therefore does not seem to be an option for Indo-Pacific corals to deal with future OA.

Continue reading ‘Symbiodinium community composition in scleractinian corals is not affected by life-long exposure to elevated carbon dioxide’

Effects of elevated pCO2 on the metabolism of a temperate rhodolith Lithothamnion corallioides grown under different temperatures

Coralline algae are considered among the most sensitive species to near future ocean acidification. We tested the effects of elevated pCO2 on the metabolism of the free living coralline alga Lithothamnion corallioides (“maerl”) and the interactions with changes in temperature. Specimens were collected in North Brittany (France) and grown for 3 months at pCO2 of 380 (ambient pCO2), 550, 750 and 1000 μatm (elevated pCO2) and at successive temperatures of 10°C (ambient temperature in winter), 16°C (ambient temperature in summer) and 19°C (ambient temperature in summer + 3°C). At each temperature, gross primary production, respiration (oxygen flux) and calcification (alkalinity flux) rates were assessed in the light and dark. Pigments were determined by HPLC. Chl a, carotene and zeaxanthin were the three major pigments found in L. corallioides thalli. Elevated pCO2 did not affect pigment content while temperature slightly decreased zeaxanthin and carotene content at 10°C. Gross production was not affected by temperature but was significantly affected by pCO2 with an increase between 380 and 550 μatm. Light, dark and diel (24 h) calcification rates strongly decreased with increasing pCO2 regardless of the temperature. Although elevated pCO2 only slightly affected gross production in L. corallioides, diel net calcification was reduced by up to 80 % under the 1000 μatm treatment. Our findings suggested that near future levels of CO2 will have profound consequences for carbon and carbonate budgets in rhodolith beds and for the sustainability of these habitats.

Continue reading ‘Effects of elevated pCO2 on the metabolism of a temperate rhodolith Lithothamnion corallioides grown under different temperatures’

A middle Eocene carbon cycle conundrum

The Middle Eocene Climatic Optimum (MECO) was an approximately 500,000-year-long episode of widespread ocean–atmosphere warming about 40 million years ago, superimposed on a long-term middle Eocene cooling trend. It was marked by a rise in atmospheric CO2 concentrations, biotic changes and prolonged carbonate dissolution in the deep ocean. However, based on carbon cycle theory, a rise in atmospheric CO2 and warming should have enhanced continental weathering on timescales of the MECO. This should have in turn increased ocean carbonate mineral saturation state and carbonate burial in deep-sea sediments, rather than the recorded dissolution. We explore several scenarios using a carbon cycle model in an attempt to reconcile the data with theory, but these simulations confirm the problem. The model only produces critical MECO features when we invoke a sea-level rise, which redistributes carbonate burial from deep oceans to continental shelves and decreases shelf sediment weathering. Sufficient field data to assess this scenario is currently lacking. We call for an integrated approach to unravel Earth system dynamics during carbon cycle variations that are of intermediate timescales (several hundreds of thousands of years), such as the MECO.

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Multistressor impacts of warming and acidification of the ocean on marine invertebrates’ life histories

Benthic marine invertebrates live in a multistressor world where stressor levels are, and will continue to be, exacerbated by global warming and increased atmospheric carbon dioxide. These changes are causing the oceans to warm, decrease in pH, become hypercapnic, and to become less saturated in carbonate minerals. These stressors have strong impacts on biological processes, but little is known about their combined effects on the development of marine invertebrates. Increasing temperature has a stimulatory effect on development, whereas hypercapnia can depress developmental processes. The pH, pCO2, and CaCO3 of seawater change simultaneously with temperature, challenging our ability to predict future outcomes for marine biota. The need to consider both warming and acidification is reflected in the recent increase in cross-factorial studies of the effects of these stressors on development of marine invertebrates. The outcomes and trends in these studies are synthesized here. Based on this compilation, significant additive or antagonistic effects of warming and acidification of the ocean are common (16 of 20 species studied), and synergistic negative effects also are reported. Fertilization can be robust to near-future warming and acidification, depending on the male–female mating pair. Although larvae and juveniles of some species tolerate near-future levels of warming and acidification (+2°C/pH 7.8), projected far-future conditions (ca. ≥4°C/ ≤pH 7.6) are widely deleterious, with a reduction in the size and survival of larvae. It appears that larvae that calcify are sensitive both to warming and acidification, whereas those that do not calcify are more sensitive to warming. Different sensitivities of life-history stages and species have implications for persistence and community function in a changing ocean. Some species are more resilient than others and may be potential “winners” in the climate-change stakes. As the ocean will change more gradually over coming decades than in “future shock” perturbation investigations, it is likely that some species, particularly those with short generation times, may be able to tolerate near-future oceanic change through acclimatization and/or adaption.

Continue reading ‘Multistressor impacts of warming and acidification of the ocean on marine invertebrates’ life histories’

Marine life on acid

Predicting future biodiversity in our changing oceans.

The underwater vents near southern Italy’s Mount Vesuvius are the closest we have to a time machine on fast-forward to the future.

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Increased CO2 stimulates reproduction in a coral reef fish

Ocean acidification is predicted to negatively impact the reproduction of many marine species, either by reducing fertilization success or diverting energy from reproductive effort. While recent studies have demonstrated how ocean acidification will affect larval and juvenile fishes, little is known about how increasing partial pressure of carbon dioxide (pCO2) and decreasing pH might affect reproduction in adult fishes. We investigated the effects of near-future levels of pCO2 on the reproductive performance of the cinnamon anemonefish, Amphiprion melanopus, from the Great Barrier Reef, Australia. Breeding pairs were held under three CO2 treatments (Current-day Control (430μatm), Moderate (584μatm) and High (1032μatm)) for a 9-month period that included the summer breeding season. Unexpectedly, increased CO2 dramatically stimulated breeding activity in this species of fish. Over twice as many pairs bred in the Moderate (67% of pairs) and High (55%) compared to the Control (27%) CO2 treatment. Pairs in the High CO2 group produced double the number of clutches per pair and 67% more eggs per clutch compared to the Moderate and Control groups. As a result, reproductive output in the High group was 82% higher than the Control group and 50% higher than the Moderate group. Despite the increase in reproductive activity, there was no difference in adult body condition between the three treatment groups. There was no significant difference in hatchling length between the treatment groups, but larvae from the High CO2 group had smaller yolks than Controls. This study provides the first evidence of the potential effects of ocean acidification on key reproductive attributes of marine fishes and, contrary to expectations, demonstrates an initially stimulatory (hormetic) effect in response to increased pCO2. However, any long-term consequences of increased reproductive effort on individuals or populations remains to be determined.

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Conservative and non-conservative variations of total alkalinity on the Southeastern Bering Sea Shelf

Recent observations of calcium carbonate (CaCO3) mineral undersaturations on the Bering Sea Shelf have prompted new interest in the physical and biological factors that control the inorganic carbon system in the region. Understanding of the dynamics that influence the spatio-temporal variability of total alkalinity (TA) – one major component of the seawater carbonate system – has been constrained by limited historical data collected across the shelf, and the consensus has been that TA is largely conservative. However, the recently documented undersaturated conditions have the potential to cause substantial non-conservative variability in TA in this region through the dissolution of carbonate minerals. In order to quantify the contribution of carbonate mineral precipitation and dissolution to variability in TA on the southeastern Bering Sea shelf, we examined seasonal observations of TA that were made between 2008 and 2010 as part of the BEST-BSIERP Bering Sea Project. Conservative influences accounted for most of the variability in TA concentrations, with well-constrained mixing dominating in spring and summer of 2008. Bering Shelf Water (BSW) contained a constant ratio of TA to salinity, while river discharge (RW) added TA relative to salinity at a predictable rate. Although substantial organic carbon production and denitrification can cause some non-conservative variation in TA concentrations (a maximum of ~ 15 μmoles kg SW– 1 combined), carbonate mineral dissolution and precipitation were shown to be the most important processes responsible for non-conservative TA – salinity relationships. CaCO3 uptake by the dominant pelagic phytoplankton calcifier (i.e., coccolithophores) was shown to alter TA concentrations by as much as 59 μmoles kg SW– 1. Evidence for shallow-water CaCO3 mineral dissolution was also observed, which caused TA concentrations to increase by as much as 36 μmoles kg SW– 1. Therefore, contrary to our previous understanding, the non-conservative physico-biogeochemical factors observed in this study play an important role in controlling the ocean carbon cycle of the Bering Sea shelf.

Continue reading ‘Conservative and non-conservative variations of total alkalinity on the Southeastern Bering Sea Shelf’

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Ocean acidification in the IPCC AR5 WG II

OUP book