Archive for the 'Science' Category

Decadal-scale acidification trends in adjacent North Carolina estuaries: competing role of anthropogenic CO2 and riverine alkalinity loads

Decadal-scale pH trends for the open ocean are largely monotonic and controlled by anthropogenic CO2 invasion. In estuaries, though, such long-term pH trends are often obscured by a variety of other factors, including changes in net metabolism, temperature, estuarine mixing, and riverine hydrogeochemistry. In this study, we mine an extensive biogeochemical database in two North Carolina estuaries, the Neuse River estuary (NeuseRE) and New River estuary (NewRE), in an effort to deconvolute decadal-scale trends in pH and associated processes. By applying a Generalized Additive Mixed Model (GAMM), we show that temporal changes in NewRE pH were insignificant, while pH decreased significantly throughout much of the NeuseRE. In both estuaries, variations in pH were accompanied by increasing river discharge, and were independent of rising temperature. Decreases in bottom-water pH in the NeuseRE coincided with elevated primary production in surface waters, highlighting the importance of eutrophication on long-term acidification trends. Next, we used a simple mixing model to illustrate the impact of changing river discharge on estuarine carbonate chemistry. We found that increased riverine alkalinity loads to the NewRE likely buffered the impact of CO2-intrusion-induced acidification. In the NeuseRE, however, elevated dissolved inorganic carbon loads further decreased the buffering capacity, exacerbating the effects of CO2-intrusion-driven acidification. Taken together, the findings of this study show that future trajectories in estuarine pH will be shaped by complex interactions among global-scale changes in climate, regional-scale changes in precipitation patterns, and local-scale changes in estuarine biogeochemistry.

Continue reading ‘Decadal-scale acidification trends in adjacent North Carolina estuaries: competing role of anthropogenic CO2 and riverine alkalinity loads’

Time‐of‐detection as a metric for prioritizing between climate observation quality, frequency, and duration

We advance a simple framework based on “time‐of‐detection” for estimating the observational needs of studies assessing climate changes amidst natural variability, and apply it to several examples related to ocean acidification. This approach aims to connect the Global Ocean Acidification Observing Network “weather” and “climate” data quality thresholds with a single dynamic threshold appropriate for a range of potential ocean signals and environments. A key implication of the framework is that measurement frequency can be as important as measurement accuracy, particularly in highly variable environments. Pragmatic cost‐benefit analyses based on this framework can be performed to quantitatively determine which observing strategy will accomplish a given detection goal soonest and resolve a signal with the greatest confidence, and to assess how the tradeoffs between measurement frequency and accuracy vary regionally.

Continue reading ‘Time‐of‐detection as a metric for prioritizing between climate observation quality, frequency, and duration’

Contrasting effects of acidification and warming on dimethylsulfide concentrations during a temperate estuarine fall bloom mesocosm experiment

The effects of ocean acidification and warming on the concentrations of dimethylsulfoniopropionate (DMSP) and dimethylsulfide (DMS) were investigated during a mesocosm experiment in the Lower St. Lawrence Estuary (LSLE) in the fall of 2014. Twelve mesocosms covering a range of pHT (pH on the total hydrogen ion concentration scale) from 8.0 to 7.2, corresponding to a range of CO2 partial pressures (pCO2) from 440 to 2900 µatm, at two temperatures (in situ and +5 ∘C; 10 and 15 ∘C) were monitored during 13 days. All mesocosms were characterized by the rapid development of a diatom bloom dominated by Skeletonema costatum, followed by its decline upon the exhaustion of nitrate and silicic acid. Neither the acidification nor the warming resulted in a significant impact on the abundance of bacteria over the experiment. However, warming the water by 5 ∘C resulted in a significant increase in the average bacterial production (BP) in all 15 ∘C mesocosms as compared to 10 ∘C, with no detectable effect of pCO2 on BP. Variations in total DMSP (DMSPt = particulate + dissolved DMSP) concentrations tracked the development of the bloom, although the rise in DMSPt persisted for a few days after the peaks in chlorophyll a. Average concentrations of DMSPt were not affected by acidification or warming. Initially low concentrations of DMS (<1 nmol L−1) increased to reach peak values ranging from 30 to 130 nmol L−1 towards the end of the experiment. Increasing the pCO2 reduced the averaged DMS concentrations by 66 % and 69 % at 10 and 15 ∘C, respectively, over the duration of the experiment. On the other hand, a 5 ∘C warming increased DMS concentrations by an average of 240 % as compared to in situ temperature, resulting in a positive offset of the adverse pCO2 impact. Significant positive correlations found between bacterial production and concentrations of DMS throughout our experiment point towards temperature-associated enhancement of bacterial DMSP metabolism as a likely driver of the mitigating effect of warming on the negative impact of acidification on the net production of DMS in the LSLE and potentially the global ocean.

Continue reading ‘Contrasting effects of acidification and warming on dimethylsulfide concentrations during a temperate estuarine fall bloom mesocosm experiment’

Spatio-temporal distribution of physicochemical and bacteriological parameters in the north area of Monastir bay, eastern coast of Tunisia

Temporal characterization of physicochemical and bacteriological parameters of the Monastir bay was conducted out on 12 stations, during six sampling periods in 2014. Results showed a seasonal variation on the physicochemical parameters of the water masses (temperature, salinity, oxygen, pH, and turbidity) and well-oxygenated waters. Results indicated the absence of mineral phosphorus and the presence of low concentration of organic phosphorus in the stations close the coastline. Mineral nitrogen represented completely by nitrate, and organic nitrogen was detected everywhere during all sampling periods without any particular distribution. Chlorophyll-a concentrations present at low ratio characterizing an oligotrophic ecosystem showed two peaks, one during spring (April, May) and second in fall (September), and were significantly correlated with temperature (R2 = 0.82). Statistical analysis of different physicochemical parameters showed a correlation between temperature pH and oxygen. ANOVA tests showed a significant difference inter-sampling periods and between stations. Bacterial flora is dominated by halotolerant germs, which showed higher concentrations in the southern part of the studied area and are inversely correlated with salinity, turbidity, oxygen, and organic nitrogen (respectively R2 = − 0.62; − 0.79; − 0.84; − 0.72). The same evolution pattern was observed in mesophilic non-halo-obligate microflora. The Vibrionaceae concentration was correlated with water temperature and was within the standards for marine waters. Fecal coliform bacteria are absent in the studied area during all sampling periods. No particularity in water quality was noticed in this ecosystem, which characterized a good state. However, one can say that the collected data on physicochemical and bacteriological evolution can provide baseline information for assisting management of the Monastir bay, which represented a typical and important model of south Mediterranean Sea.

Continue reading ‘Spatio-temporal distribution of physicochemical and bacteriological parameters in the north area of Monastir bay, eastern coast of Tunisia’

Impacts of global warming and elevated CO2 on sensory behavior in predator-prey interactions: a review and synthesis

Ecosystems are shaped by complex interactions between species and their environment. However, humans are rapidly changing the environment through increased carbon dioxide (CO2) emissions, creating global warming and elevated CO2 levels that affect ecological communities through multiple processes. Understanding community responses to climate change requires examining the consequences of changing behavioral interactions between species, such as those affecting predator and prey. Understanding the underlying sensory process that govern these interactions and how they may be affected by climate change provides a predictive framework, but many studies examine behavioral outcomes only. This review summarizes the current knowledge of global warming and elevated CO2 impacts on predator-prey interactions with respect to the relevant aspects of sensory ecology, and we discuss the potential consequences of these effects. Our specific questions concern how climate change affects the ability of predators and prey to collect information and how this affects predator-prey interactions. We develop a framework for understanding how warming and elevated CO2 can alter behavioral interactions by examining how the processes (steps) of sensory cue (or signal) production, transmission and reception may change. This includes both direct effects on cue production and reception resulting from changes in organismal physiology, but also effects on cue transmission resulting from modulation of the physical environment via physical and biotic changes. We suggest that some modalities may be particularly prone to disruption, and that aquatic environments may suffer more serious disruptions as a result of elevated CO2 and warming that collectively affect all steps of the signaling process. Temperature by itself may primarily operate on aspects of cue generation and transmission, implying that sensory-mediated disruptions in terrestrial environments may be less severe. However, significant biases in the literature in terms of modalities (chemosensation), taxa (fish), and stressors (elevated CO2) examined currently prevents accurate generalizations. Significant issues such as multimodal compensation and altered transmission or other environmental effects remain largely unaddressed. Future studies should strive to fill these knowledge gaps in order to better understand and predict shifts in predator-prey interactions in a changing climate.

Continue reading ‘Impacts of global warming and elevated CO2 on sensory behavior in predator-prey interactions: a review and synthesis’

Warming and CO2 enhance Arctic heterotrophic microbial activity

Ocean acidification and warming are two main consequences of climate change that can directly affect biological and ecosystem processes in marine habitats. The Arctic Ocean is the region of the world experiencing climate change at the steepest rate compared with other latitudes. Since marine planktonic microorganisms play a key role in the biogeochemical cycles in the ocean it is crucial to simultaneously evaluate the effect of warming and increasing CO2 on marine microbial communities. In 20 L experimental microcosms filled with water from a high-Arctic fjord (Svalbard), we examined changes in phototrophic and heterotrophic microbial abundances and processes [bacterial production (BP) and mortality], and viral activity (lytic and lysogenic) in relation to warming and elevated CO2. The summer microbial plankton community living at 1.4°C in situ temperature, was exposed to increased CO2 concentrations (135–2,318 μatm) in three controlled temperature treatments (1, 6, and 10°C) at the UNIS installations in Longyearbyen (Svalbard), in summer 2010. Results showed that chlorophyll a concentration decreased at increasing temperatures, while BP significantly increased with pCO2 at 6 and 10°C. Lytic viral production was not affected by changes in pCO2 and temperature, while lysogeny increased significantly at increasing levels of pCO2, especially at 10°C (R2 = 0.858, p = 0.02). Moreover, protistan grazing rates showed a positive interaction between pCO2 and temperature. The averaged percentage of bacteria grazed per day was higher (19.56 ± 2.77% d-1) than the averaged percentage of lysed bacteria by virus (7.18 ± 1.50% d-1) for all treatments. Furthermore, the relationship among microbial abundances and processes showed that BP was significantly related to phototrophic pico/nanoflagellate abundance in the 1°C and the 6°C treatments, and BP triggered viral activity, mainly lysogeny at 6 and 10°C, while bacterial mortality rates was significantly related to bacterial abundances at 6°C. Consequently, our experimental results suggested that future increases in water temperature and pCO2 in Arctic waters will produce a decrease of phytoplankton biomass, enhancement of BP and changes in the carbon fluxes within the microbial food web. All these heterotrophic processes will contribute to weakening the CO2 sink capacity of the Arctic plankton community.

Continue reading ‘Warming and CO2 enhance Arctic heterotrophic microbial activity’

Insights from GO-SHIP hydrography data into the thermodynamic consistency of CO2 system measurements in seawater

Highlights
• The thermodynamic consistency of CO2 system measurements was investigated.

• Errors in CO2 measurements are unlikely to be the main cause of inconsistencies.

• There are likely systematic errors in K1, K2, and the total boron-salinity ratio.

• An unaccounted source of alkalinity may be present in the open ocean.

Abstract
Due to advances in technology, routine seawater pH measurements of excellent repeatability are becoming increasingly common for studying the ocean CO2 system. However, the accuracy of pH measurements has come into question due to a widespread observation, from a large number of carefully calibrated state-of-the-art CO2 measurements on various cruises, of there being a significant pH-dependent discrepancy between pH that was measured spectrophotometrically and pH calculated from concurrent measurements of total dissolved inorganic carbon (CT) and total alkalinity (AT), using a thermodynamic model of seawater

acid-base systems. From an analysis of four recent GO-SHIP repeat hydrography datasets, we show that a combination of small systematic errors in the dissociation constants of carbonic acid (K1 and K2), the total boron-salinity ratio, and in CT and AT measurements are likely responsible for some, but not all of the observed pH-dependent discrepancy. The residual discrepancy can only be fully accounted for if there exists a small, but meaningful amount (~4 μmol kg–1) of an unidentified and typically neglected contribution to measured AT, likely from organic bases, that is widespread in the open ocean. A combination of these errors could achieve consistency between measured and calculated pH, without requiring that any of the shipboard measurements be significantly in error. Future research should focus on establishing the existence of organic alkalinity in the open ocean and constraining the uncertainty in both CO2 measurements and in the constants used in CO2 calculations.

Continue reading ‘Insights from GO-SHIP hydrography data into the thermodynamic consistency of CO2 system measurements in seawater’


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Ocean acidification in the IPCC AR5 WG II

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