Archive Page 2

Ocean acidification and photic‐zone anoxia at the Toarcian Oceanic Anoxic Event: insights from the Adriatic Carbonate Platform

Severe global climate change led to the deterioration of environmental conditions in the oceans during the Toarcian Stage of the Jurassic. Carbonate platforms of the Western Tethys Ocean exposed in Alpine Tethyan mountain ranges today offer insight into this period of environmental upheaval. In addition to informing understanding of climate change in deep time, the effect of ancient carbon cycle perturbations on carbonate platforms have important implications for anthropogenic climate change; the patterns of early Toarcian environmental deterioration are similar to those occurring in modern oceans. This study focuses on the record of the early Toarcian Oceanic Anoxic Event (ca 183.1 Ma) in outcrops of the north‐west Adriatic Carbonate Platform in Slovenia. Amidst environmental deterioration, the north‐west Adriatic Platform abruptly transitioned from a healthy, shallow‐water environment with diverse metazoan ecosystems to a partially drowned setting with low diversity biota and diminished sedimentation. An organic carbon‐isotope excursion of ‐2.2‰ reflects the massive injection of CO2 into the ocean‐atmosphere system and marks the stratigraphic position of the Toarcian Oceanic Anoxic Event. A prominent dissolution horizon and suppressed carbonate deposition on the platform are interpreted to reflect transient shoaling of the carbonate compensation depth to unprecedentedly shallow levels as the dramatic influx of CO2 overwhelmed the ocean’s buffering capacity, causing ocean acidification. Trace metal geochemistry and palaeoecology highlight water column deoxygenation, including the development of photic‐zone anoxia, preceding and during the Toarcian Oceanic Anoxic Event. Ocean acidification and reduced oxygen levels likely had a profoundly negative effect on carbonate‐producing biota and growth of the Adriatic Platform. These effects are consistent with the approximate doubling of the concentration of CO2 in the ocean‐atmosphere system from pre‐Toarcian Oceanic Anoxic Event levels, which has previously been linked to a volcanic triggering mechanism. Mercury enrichments discovered in this study support a temporal and genetic link between volcanism, the Toarcian Oceanic Anoxic Event and the carbonate crisis.

Continue reading ‘Ocean acidification and photic‐zone anoxia at the Toarcian Oceanic Anoxic Event: insights from the Adriatic Carbonate Platform’

Vulnerability of global coral reef habitat suitability to ocean warming, acidification and eutrophication

Coral reefs are threatened by global and local stressors. Yet, reefs appear to respond differently to different environmental stressors. Using a global dataset of coral reef occurrence as a proxy for the long‐term adaptation of corals to environmental conditions in combination with global environmental data, we show here how global (warming: sea surface temperature; acidification: aragonite saturation state, Ωarag) and local (eutrophication: nitrate concentration, and phosphate concentration) stressors influence coral reef habitat suitability. We analyse the relative distance of coral communities to their regional environmental optima. In addition, we calculate the expected change of coral reef habitat suitability across the tropics in relation to an increase of 0.1°C in temperature, an increase of 0.02 μmol/L in nitrate, an increase of 0.01 μmol/L in phosphate and a decrease of 0.04 in Ωarag. Our findings reveal that only 6% of the reefs worldwide will be unaffected by local and global stressors and can thus act as temporary refugia. Local stressors, driven by nutrient increase, will affect 22% of the reefs worldwide, whereas global stressors will affect 11% of these reefs. The remaining 61% of the reefs will be simultaneously affected by local and global stressors. Appropriate wastewater treatments can mitigate local eutrophication and could increase areas of temporary refugia to 28%, allowing us to ‘buy time’, while international agreements are found to abate global stressors.

Continue reading ‘Vulnerability of global coral reef habitat suitability to ocean warming, acidification and eutrophication’

A 17-year dataset of surface water fugacity of CO2 along with calculated pH, aragonite saturation state and air–sea CO2 fluxes in the northern Caribbean Sea

A high-quality dataset of surface water fugacity of CO2 (fCO2w)1, consisting of over a million observations, and derived products are presented for the northern Caribbean Sea, covering the time span from 2002 through 2018. Prior to installation of automated pCO2 systems on cruise ships of Royal Caribbean International and subsidiaries, very limited surface water carbon data were available in this region. With this observational program, the northern Caribbean Sea has now become one of the best-sampled regions for pCO2 of the world ocean. The dataset and derived quantities are binned and averaged on a 1∘ monthly grid and are available at http://accession.nodc.noaa.gov/0207749 (last access: 30 June 2020) (https://doi.org/10.25921/2swk-9w56; Wanninkhof et al., 2019a). The derived quantities include total alkalinity (TA), acidity (pH), aragonite saturation state (ΩAr) and air–sea CO2 flux and cover the region from 15 to 28∘ N and 88 to 62∘ W. The gridded data and products are used for determination of status and trends of ocean acidification, for quantifying air–sea CO2 fluxes and for ground-truthing models. Methodologies to derive the TA, pH and ΩAr and to calculate the fluxes from fCO2w temperature and salinity are described.

Continue reading ‘A 17-year dataset of surface water fugacity of CO2 along with calculated pH, aragonite saturation state and air–sea CO2 fluxes in the northern Caribbean Sea’

Understanding alkalinity to quantify ocean buffering

Ocean alkalinity plays a major role in ocean’s carbon uptake, in buffering, and in calcium carbonate production and dissolution, and it impacts and is affected by various biogeochemical processes.

The ocean plays a major role in reducing the impact of climate change by absorbing both heat and carbon dioxide. To date it has taken up over 90 per cent of the excess heat in the climate system and about 25 per cent of the human released carbon dioxide. However, the uptake of carbon dioxide changes the chemistry of seawater, a process known as ocean acidification. This has major consequences for the organisms living in the ocean and reduces the role of the ocean as a carbon dioxide sink. A recent article published in Reviews of Geophysics explores ocean alkalinity and its impact on biogeochemical processes. Here, the authors give an overview of its role in carbon dioxide uptake and in limiting changes in ocean chemistry.

Continue reading ‘Understanding alkalinity to quantify ocean buffering’

What is ocean acidification? (audio)

In 2007, baby oysters began dying by the millions at the Whiskey Creek Shellfish Hatchery on the Oregon coast.

At first, the owners suspected bacterial contamination was to blame.

“Once they partnered with academics and other regional managers, they found out it was actually ocean acidification,” says Charlotte Regula-Whitefield.

Continue reading ‘What is ocean acidification? (audio)’

More carbon in the ocean can lead to smaller fish

As humans continue to send large quantities of carbon into the atmosphere, much of that carbon is absorbed by the ocean, and UConn researchers have found high CO2 concentrations in water can make fish grow smaller.

Researchers Christopher Murray Ph.D. ’19, now at the University of Washington, and UConn Associate Professor of Marine Sciences Hannes Baumann have published their findings in the Public Library of Science (PLoS One).

Continue reading ‘More carbon in the ocean can lead to smaller fish’

The recent state and variability of the carbonate system of the Canadian Arctic in the context of ocean acidification (update)

Ocean acidification driven by the uptake of anthropogenic CO2 by the surface oceans constitutes a potential threat to the health of marine ecosystems around the globe. The Arctic Ocean is particularly vulnerable to acidification and thus is an ideal region to study the progression and effects of acidification before they become globally widespread. The appearance of undersaturated surface waters with respect to the carbonate mineral aragonite (ΩA<1), an important threshold beyond which the calcification and growth of some marine organisms might be hindered, has recently been documented in the Canada Basin and adjacent Canadian Arctic Archipelago (CAA), a dynamic region with an inherently strong variability in biogeochemical processes. Nonetheless, few of these observations were made in the last 5 years and the spatial coverage in the latter region is poor. We use a dataset of carbonate system parameters measured in the CAA and its adjacent basins (Canada Basin and Baffin Bay) from 2003 to 2016 to describe the recent state of these parameters across the Canadian Arctic and investigate the amplitude and sources of the system's variability over more than a decade. Our findings reveal that, in the summers of 2014 to 2016, the ocean surface across our study area served as a net CO2 sink and was partly undersaturated with respect to aragonite in the Canada Basin and the Queen Maud Gulf, the latter region exhibiting undersaturation over its entire water column at some locations. We estimate, using measurements made across several years, that approximately a third of the interannual variability in surface dissolved inorganic carbon (DIC) concentrations in the CAA results from fluctuations in biological activity. In consideration of the system's variability resulting from these fluctuations, we derive times of emergence of the anthropogenic ocean acidification signal for carbonate system parameters in the study area.

Continue reading ‘The recent state and variability of the carbonate system of the Canadian Arctic in the context of ocean acidification (update)’

Long-term effects of elevated CO2 on the population dynamics of the seagrass Cymodocea Nodosa: evidence from volcanic seeps

We used population reconstruction techniques to assess for the first time the population dynamics of a seagrass, Cymodocea nodosa, exposed to long-term elevated CO2 near three volcanic seeps and compare them with reference sites away from the seeps. Under high CO2, the density of shoots and of individuals (apical shoots), and the vertical and horizontal elongation and production rates, were higher. Nitrogen effects on rhizome elongation and production rates and on biomass, were stronger than CO2 as these were highest at the location where the availability of nitrogen was highest. At the seep where the availability of CO2 was highest and nitrogen lowest, density of shoots and individuals were highest, probably due to CO2 effects on shoot differentiation and induced reproductive output, respectively. In all three seeps there was higher short- and long-term recruitment and growth rates around zero, indicating that elevated CO2 increases the turnover of C. nodosa shoots.

Continue reading ‘Long-term effects of elevated CO2 on the population dynamics of the seagrass Cymodocea Nodosa: evidence from volcanic seeps’

Physiological and ecotoxicological interactions of copper and ocean acidification in the polychaete worms Hediste diversicolor and Alitta virens

For coastal aquatic habitats the change in seawater pH occurring as a result of ocean acidification has the potential to alter the speciation and toxicity of the many contaminants that remain in high concentrations in coastal systems. Of particular concern are metals, such as copper, whose speciation is pH sensitive within the OA range. A meta-analysis of studies to date investigating OA-contaminant interactions using marine invertebrates reveals that 72% of the 44 studies conducted have indeed focused on metals such as copper, with only a few studies looking at polycyclic aromatic hydrocarbons (PAH) and pharmaceuticals. No clear trends in the pH-effect size on contaminant toxicity for either species or contaminant group were present however, suggesting species specific physiological responses may influence this interaction as well as contaminant chemistry. A relatively understudied group were the polychaetes, a key functional group for many coastal sediments. Sediments act as a sink for contaminants where they can accumulate to high concentrations. Hence there is high potential for polychaetes to experience elevated metal exposures under reduced seawater pH as OA progresses. To address this knowledge gap, the responses of two common coastal polychaete, Alitta virens and Hediste diversicolor, were studied under three different experimental scenarios (both water-borne and sediment based) focusing on the physiological and toxicological responses under combined exposures to ocean acidification and copper. Water-borne exposures of Alitta virens to 0.25 μM copper under ambient seawater (pH 8.10) showed a significant increase in DNA damage, along with a rise in both SOD activity and lipid peroxidation. However, when exposed to copper under OA conditions (pH 7.70) there was no further increase in DNA damage and a significant decrease in SOD activity was observed alongside a fall in lipid peroxidation suggesting that OA looks to buffer the toxicity responses to this species. This is in contrast to previous studies using mussels and sea urchins, where copper toxicity responses were significantly higher when exposed under OA conditions. To assess whether local adaptations to high levels of copper contamination influences this OA-copper interaction, a population comparison using a metal resistance population of the harbour ragworm, Hediste diversicolor and a nearby non-resistant population was then conducted. Exposures were run using copper concentrations that elicit comparable toxicity responses, using 0.50 uM copper for the resistant population, compared to 0.25 uM for the non-resistant population, reflecting the two-fold differences in LC50 values for these population. These experiments reveal a significant increase by 19.70% in metabolic rate effect size (the combined stressor when compared to the control) in the resistant population compared to a decrease by 24.02% the non-resistant population, along with differences in ammonia excretion rate and the O:N ratio, thus revealing an energetic cost of this genetic resistance when faced with the combined stressors of OA and copper. These data are in line with the emerging energy limited tolerance to stressors’ hypothesis which states that tolerance to stress can be energy limited, with bioenergetics playing a central role in the tolerance to environmental stress. Finally, a more environmentally realistic exposure scenario was conducted using Alitta virens to test the influence of sediment and tidal cycles on worm acid-base and oxidative stress responses. Field measurements of sediment pH revealed that the pHNBS range over a tidal cycle varies from 6.97 to 7.87, indicating that polychaetes are already experiencing pH’s lower than the predictions for near future open oceans. In aquarium exposures, with overlying water of pHNBS 8.10, sediment pHNBS remained within the range of 7.45 to 7.31, when the overlying water was manipulated to OA conditions (pHNBS 7.70) sediment pHNBS was within the same range as the ambient treatment. The lack of change in sediment pH, despite a 0.40 unit drop in seawater pH, removed any comparative differences in physiological and toxicity end points in the worms between treatments. Tidal emersion induced a slight reduction in sediment pH, with a significant copper effect on sediment pH causing a further decrease in pH levels. Interestingly emersion resulted in a significant OA-copper interaction for coelomic fluid bicarbonate, which increased over the emersion period, however, there was no emersion driven acidosis within coelomic fluid. Overall this work further points to contaminant-OA interactions being species specific driven, in part driven by animal physiology. It also highlights the importance of environmentally relevant exposures with sediment dwelling organisms experiencing lower pH levels than the overlying seawater which could potentially affect metal speciation and could lead to OA-contaminant interactions occurring very differently in this environment. These are important considerations for ecotoxicology studies in the face of global ocean changes.

Continue reading ‘Physiological and ecotoxicological interactions of copper and ocean acidification in the polychaete worms Hediste diversicolor and Alitta virens’

Ocean acidification from below in the tropical Pacific

Identifying ocean acidification and its controlling mechanisms is an important priority within the broader question of understanding how sustained anthropogenic CO2 emissions are harming the health of the ocean. Through extensive analysis of observational data products for ocean inorganic carbon, here we quantify the rate at which acidification is proceeding in the western tropical Pacific Warm Pool, revealing ‐0.0013 ±0.0001 yr‐1 for pH and ‐0.0083±0.0007 yr‐1 for the saturation index of aragonite for the years 1985‐2016. However, the mean rate of total dissolved inorganic carbon increase (+0.81 ±0.06 μmol kg‐1 yr‐1) sustaining acidification was ~20% slower than what would be expected if it were simply controlled by the rate of atmospheric CO2 increase and transmitted through local air‐sea CO2 equilibration. Joint Lagrangian and Eulerian model diagnostics indicate that the acidification of the Warm Pool occurs primarily through the anthropogenic CO2 that invades the ocean in the extra‐tropics, is transported to the tropics through the thermocline shallow overturning circulation, and then re‐emerges into surface waters within the tropics through the Equatorial Undercurrent from below. An interior residence time of several years to decades, acting in conjunction with the accelerating CO2 growth in the atmosphere, can be expected to contribute to modulating the rate of Warm Pool acidification.

Continue reading ‘Ocean acidification from below in the tropical Pacific’


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OA-ICC HIGHLIGHTS

Ocean acidification in the IPCC AR5 WG II

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