Posts Tagged 'North Atlantic'

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’

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’

Varying conditions in intertidal pools: high resolution pH dynamics and primary production

Most studies designed to assess the effects of ocean acidification take place in coastal and intertidal environments, which are characterized by a great variability of its physical and chemical parameters. However, a great number of these studies use fixed pH levels predicted for the future, disregarding natural pH oscillations. In this work we studied the pH oscillations and primary productivity of intertidal rockpools in two rocky shore areas. To provide high resolution continuous pH data we used an autonomous pH measuring system which consisted of a pH sensor, a data logger and a battery encased in a waterproof container. Oxygen concentration and primary production from phytoplankton and macro- phytobentos were also measured. We found a range of pH variation in the pools of 0.07 pH units/day when water dynamics was high and of 0.26 pH units/day when conditions were more stable. Carbonate systems parameters, temperature and oxygen concentration were related and they responded to the day / night cycle and hydrodynamic conditions. We suggest that these natural oscillations in pH and temperature must be taken into account in ocean acidifications studies in order to obtain more accurate results.

Continue reading ‘Varying conditions in intertidal pools: high resolution pH dynamics and primary production’

Changes in temperature, pH, and salinity affect the sheltering responses of Caribbean spiny lobsters to chemosensory cues

Florida Bay is home to a network of shallow mud-banks which act as barriers to circulation creating small basins that are often subject to extremes in temperature and salinity. Florida bay is also important juvenile habitat for the Caribbean spiny lobster Panulirus argus. While our understanding of the effect of environmental changes on the survival, growth, and movement of spiny lobsters is growing, the effect on their chemosensory abilities has not yet been investigated. Lobsters rely heavily on chemical cues for many biological and ecological activities, and here we report on the effect of extreme environmental events in temperature (32 °C), salinity (45ppt), and pH (7.65 pH) on social behavior and sheltering preference in P. argus. Under normal conditions, chemical cues from conspecifics are used by spiny lobsters to identify suitable shelter and cues from stone crabs and diseased individuals are used to determine shelters to be avoided. In all altered conditions, lobsters lost the ability to aggregate with conspecifics and avoid stone crabs and diseased conspecifics. Thus, seasonal extreme events, and potentially future climate change conditions, alter the chemosensory-driven behavior of P. argus and may result in decreased survivorship due to impaired shelter selection or other behaviors.

Continue reading ‘Changes in temperature, pH, and salinity affect the sheltering responses of Caribbean spiny lobsters to chemosensory cues’

Time of emergence of surface ocean carbon dioxide trends in the North American coastal margins in support of ocean acidification observing system design

Time of Emergence (ToE) is the time when a signal emerges from the noise of natural variability. Commonly used in climate science for the detection of anthropogenic forcing, this concept has recently been applied to geochemical variables, to assess the emerging times of anthropogenic ocean acidification (OA), mostly in the open ocean using global climate and Earth System Models. Yet studies of OA variables are scarce within costal margins, due to limited multidecadal time-series observations of carbon parameters. ToE provides important information for decision making regarding the strategic configuration of observing assets, to ensure they are optimally positioned either for signal detection and/or process elicitation and to identify the most suitable variables in discerning OA-related changes. Herein, we present a short overview of ToE estimates on an OA variable, CO2 fugacity f(CO2,sw), in the North American ocean margins, using coastal data from the Surface Ocean CO2 Atlas (SOCAT) V5. ToE suggests an average theoretical timeframe for an OA signal to emerge, of 23(±13) years, but with considerable spatial variability. Most coastal areas are experiencing additional secular and/or multi-decadal forcing(s) that modifies the OA signal, and such forcing may not be sufficiently resolved by current observations. We provide recommendations, which will help scientists and decision makers design and implement OA monitoring systems in the next decade, to address the objectives of OceanObs19 (http://www.oceanobs19.net) in support of the United Nations Decade of Ocean Science for Sustainable Development (2021–2030) (https://en.unesco.org/ocean-decade) and the Sustainable Development Goal (SDG) 14.3 (https://sustainabledevelopment.un.org/sdg14) target to “Minimize and address the impacts of OA.”

Continue reading ‘Time of emergence of surface ocean carbon dioxide trends in the North American coastal margins in support of ocean acidification observing system design’

Effects of elevated CO2 on a natural diatom community in the subtropical NE Atlantic

Diatoms are silicifying phytoplankton contributing about one quarter to primary production on Earth. Ocean acidification (OA) could alter the competitiveness of diatoms relative to other taxa and/or lead to shifts among diatom species. In spring 2016, we set up a plankton community experiment at the coast of Gran Canaria (Canary Islands, Spain) to investigate the response of subtropical diatom assemblages to elevated seawater pCO2. Therefore, natural plankton communities were enclosed for 32 days in in situ mesocosms (∼8 m3 volume) with a pCO2 gradient ranging from 380 to 1140 μatm. Halfway through the study we added nutrients to all mesocosms (N, P, Si) to simulate injections through eddy-induced upwelling which frequently occurs in the region. We found that the total diatom biomass remained unaffected during oligotrophic conditions but was significantly positively affected by high CO2 after nutrient enrichment. The average cell volume and carbon content of the diatom community increased with CO2. CO2 effects on diatom biomass and species composition were weak during oligotrophic conditions but became quite strong above ∼620 μatm after the nutrient enrichment. We hypothesize that the proliferation of diatoms under high CO2 may have been caused by a fertilization effect on photosynthesis in combination with reduced grazing pressure. Our results suggest that OA in the subtropics may strengthen the competitiveness of (large) diatoms and cause changes in diatom community composition, mostly under conditions when nutrients are injected into oligotrophic systems.

Continue reading ‘Effects of elevated CO2 on a natural diatom community in the subtropical NE Atlantic’

Early development and metabolic physiology of the temperate lesser spotted shark (Scyliorhinus canicula) under high CO2 levels

Although sharks thrive in many different kinds of habitats and evolved to fill many ecological niches across a wide range of habitats, these animals are characterized by the limited capability to adapt rapidly to future climate change. Thus, the objective of the present dissertation was to analyze the potential impact of seawater acidification (OA, high CO2 levels ~1000 μatm) on the early development and physiology of the temperate shark Scyliorhinus canicula. More specifically, we evaluated OA effects on: i) development time and first feed, ii) Fulton condition of the newborns, iii) survival, iv) routine metabolic rate (RMR), v) maximum metabolic rate (MMR), and vi) aerobic scope (AS). The duration of embrygenesis ranged from 118 to 125 days, and after hatching, the mean number of days to start feeding (i.e. first feeding) varied between 4 and 6 days. In both endpoints there were no significant differences among treatments (i.e. normocapnia and hypercapnia; p >0.05). Juvenile survival (after 150 days post-hatching) also did no change significantly under high CO2 levels (p >0.05). Regarding energy expenditure rates and aerobic window, there were no significant differences in RMR, MMR, and AS among treatments (p-value > 0.005). In the overall, we argue that these findings are associated to the fact that S. canicula is a benthic, cosmopolitan and temperate shark usually exposed to great variations of abiotic factors, like those experienced in the highly-dynamic western Portuguese coast (with seasonal upwelling events). Although the present dissertation only investigated acclimation processes, it is plausible to assume that this shark species will not be greatly affected by future acidification conditions.

Continue reading ‘Early development and metabolic physiology of the temperate lesser spotted shark (Scyliorhinus canicula) under high CO2 levels’


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Ocean acidification in the IPCC AR5 WG II

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