Posts Tagged 'field'



Impact de l’acidification et du réchauffement sur les communautés planctoniques de l’estuaire du Saint-Laurent et la production de diméthylsulfure (in French)

Anthropogenic carbon dioxide (CO2) emissions have increased since the industrial revolution, leading to modifications in atmospheric CO2 content and an increase in oceanic CO2 partial pressures (pCO2). The uptake of CO2 by the oceans has resulted in a lowering of surface water pH, corresponding to an increase in the acidity of the oceans by ~30 % compared with pre-industrial times. Furthermore, climate change resulting from the accumulation of anthropogenic CO2 in the atmosphere is responsible for the observed warming of sea surface temperatures since the mid 20th century. The fate of planktonic communities in the face of these changes in the marine environment over the next century remains uncertain. Even less understood are the possible interactions of acidification and warming on the production of dimethylsulfide (DMS), a sulfur-containing gas produced by planktonic communities and involved in climate regulation. The aim of this thesis is to determine the impact of heightened pCO2 on the development of the phytoplanktonic blooms in the Lower St. Lawrence Estuary (LSLE), and their production of DMS, as well as to evaluate how concomitant warming could modulate the effects of acidification. Two intricate experiments were carried out during this study. First, a microcosm experiment (~20 L) was conducted in the summer of 2013 to assess the effects of pCO2 on the development of the LSLE spring diatom bloom, paying special attention to the microbial processes governing the production of DMS. Second, a multifactorial mesocosm experiment (~2600 L) was carried out in the fall of 2014 to investigate the combined effects of pCO2 and temperature on the development of the fall bloom in the LSLE and the production of DMS. Results from our microcosm experiment show that the blooming phytoplankton community of the LSLE during spring is resistant to pCO2 increases superior to the expected values for 2100. This resistance likely reflects its adaptation to the estuarine setting, an environment known for rapid and intense fluctuations of pCO2. This first experiment has also highlighted a reduction of the average concentrations of DMS by 15 and 40 % in planktonic assemblages respectively subjected to pCO2 of ~1850 μatm and ~2700 μatm compared to the control (~775 μatm). Parallel incubations have shown, using 35S-DMSPd, that the negative effect of acidification on DMS mostly stemmed from a decrease in the conversion efficiency of DMSP to DMS by bacteria. The second experiment has also highlighted a strong resistance of the diatom Skeletonema costatum to a wide range of pH (~8.0–7.2), and corresponding pCO2 (~90–3000 μatm). In this study, a warming of 5 °C accelerated the development and decline of the bloom, but did not affect the integrated primary production over the duration of the experiment. As in the first experiment, heightened pCO2 resulted in a decrease of average concentrations of DMS of ~66 % in the most acidified mesocosms compared to the least acidified mesocosms at in situ temperature (10 °C). However, the negative effect of an increase in pCO2 on the net production of DMS could be mitigated by a warming of surface waters. Indeed, my results reveal that the net production of DMS was higher at 15 °C compared to 10 °C over the whole pCO2 gradient in our mesocosm study. These novel results suggest that warming of surface waters could mitigate, at least partly, the negative effect of acidification on DMS net production in the LSLE and perhaps in the world’s oceans.

Continue reading ‘Impact de l’acidification et du réchauffement sur les communautés planctoniques de l’estuaire du Saint-Laurent et la production de diméthylsulfure (in French)’

First ROV exploration of the Perth Canyon: canyon setting, faunal observations, and anthropogenic impacts

This study represents the first ROV-based exploration of the Perth Canyon, a prominent submarine valley system in the southeast Indian Ocean offshore Fremantle (Perth), Western Australia. This multi-disciplinary study characterizes the canyon topography, hydrography, anthropogenic impacts, and provides a general overview of the fauna and habitats encountered during the cruise. ROV surveys and sample collections, with a specific focus on deep-sea corals, were conducted at six sites extending from the head to the mouth of the canyon. Multi-beam maps of the canyon topography show near vertical cliff walls, scarps, and broad terraces. Biostratigraphic analyses of the canyon lithologies indicate Late Paleocene to Late Oligocene depositional ages within upper bathyal depths (200–700 m). The video footage has revealed a quiescent ‘fossil canyon’ system with sporadic, localized concentrations of mega- and macro-benthos (∼680–1,800 m), which include corals, sponges, molluscs, echinoderms, crustaceans, brachiopods, and worms, as well as plankton and nekton (fish species). Solitary (Desmophyllum dianthus, Caryophyllia sp., Vaughanella sp., and Polymyces sp.) and colonial (Solenosmilia variabilis) scleractinians were sporadically distributed along the walls and under overhangs within the canyon valleys and along its rim. Gorgonian, bamboo, and proteinaceous corals were present, with live Corallium often hosting a diverse community of organisms. Extensive coral graveyards, discovered at two disparate sites between ∼690–720 m and 1,560–1,790 m, comprise colonial (S. variabilis) and solitary (D. dianthus) scleractinians that flourished during the last ice age (∼18 ka to 33 ka BP). ROV sampling (674–1,815 m) spanned intermediate (Antarctic Intermediate Water) and deep waters (Upper Circumpolar Deep Water) with temperatures from ∼2.5 to 6°C. Seawater CTD profiles of these waters show consistent physical and chemical conditions at equivalent depths between dive sites. Their carbonate chemistry indicate supersaturation (Ωcalcite ∼ 1.3–2.2) with respect to calcite, but mild saturation to undersaturation (Ωaragonite ∼ 0.8–1.4) of aragonite; notably some scleractinians were found living below the aragonite saturation horizon (∼1,000 m). Seawater δ13C and nuclear bomb produced Δ14C compositions decrease in the upper canyon waters by up to ∼0.8‰ (<800 m) and 95‰ (<500 m), respectively, relative to measurements taken nearby in 1978, reflecting the ingress of anthropogenic carbon into upper intermediate waters.

Continue reading ‘First ROV exploration of the Perth Canyon: canyon setting, faunal observations, and anthropogenic impacts’

Marine CO2 system variability in a high arctic tidewater-glacier fjord system, Tempelfjorden, Svalbard

Highlights

• The marine CO2 system was investigated in an Arctic fjord between 2015 and 2017.

• Primary production caused the largest changes observed in pCO2 and the saturation state of aragonite.

• Air-sea CO2 uptake and freshwater release governed the surface pCO2 over the melt season.

• At least a freshwater fraction larger than 50% was needed to provide aragonite undersaturated waters.

• An excess in the salinity normalized DIC, corrected for primary production/respiration, was found in the deepest water.

Abstract

The marine CO2 system in Tempelfjorden (Svalbard) was investigated between August 2015 and December 2017 using total alkalinity, pH, temperature, salinity, oxygen isotopic ratio, and nutrient data. Primary production resulted in the largest changes that were observed in the partial pressure of CO2 (pCO2, 140 μatm) and the saturation state of aragonite (ΩAr, 0.9). Over the period of peak freshwater discharge (June to August), the freshwater addition and air-sea CO2 uptake (on average 15.5 mmol m−2 day−1 in 2017) governed the surface pCO2. About one fourth of the uptake was driven by the freshening. The sensitivity of ΩAr to the freshwater addition was investigated using robust regressions. If the effect of air-sea CO2 exchange was removed from ΩAr, a freshwater fraction larger than 50% (lower range of uncertainty) was needed to provide aragonite undersaturated waters. This study shows that ΩAr and freshwater fraction relationships that are derived from regression techniques and the interpretation thereof are sensitive to the effect of air-sea CO2 exchange. Since the freshening in itself only drives a fraction of the air-sea CO2 uptake, studies that do not account for this exchange will overestimate the impact of freshwater on ΩAr. Finally, in the summer an excess in the salinity normalized dissolved inorganic carbon, corrected for aerobic primary production/respiration, of on average 86 μmol kg−1 was found in the deepest water of the fjord. This excess is suggested to be a result of enhanced CO2 uptake and brine release during the period of sea ice growth.

Continue reading ‘Marine CO2 system variability in a high arctic tidewater-glacier fjord system, Tempelfjorden, Svalbard’

Anthropogenic ocean warming and acidification recorded by Sr/Ca, Li/Mg, δ11B and B/Ca in Porites coral from the Kimberley region of northwestern Australia

Highlights

• Ocean warming has accelerated since the 1970s in the nearshore Kimberley.

• Coral calcification remains less affected and ‘normal’ seasonal coral internal carbonate chemistry is observed.

• Under intensified warming, coral’s ability to concentrate metabolic DIC has been reduced.

• Ocean acidification has led to the secular reduction of pHcf.

Abstract

The impact of climate changes on corals living in naturally extreme environments is poorly understood but crucial to longer-term sustainability of coral reefs. Here we report century-long temperature (Sr/Ca and Li/Mg) and calcifying fluid (CF) carbonate chemistry (δ11B and B/Ca) records for a long-lived (1919 to 2016) Porites coral from the high thermally variable Kimberley region of northwestern Australia. We investigate how increasing temperatures and ocean acidification are manifested in the carbonate chemistry of coral’s CF and impacts of climate change on calcification. Using Sr/Ca and Li/Mg multiproxy we show that annual temperature in the nearshore Kimberley exhibited a gradual increase (0.009 ± 0.003 °C/yr) from the 1920s onward. However for the most recent years (2000–2015) more rapid summer warming (0.05 ± 0.01 °C/yr) are registered, indicative of intensified warming. Despite that, we find no significant trend for calcification rate of this coral over the past century, as well as ‘normal’ seasonal variability in coral’s CF carbonate chemistry. Importantly, the coral’s ability to concentrate inorganic carbon seems to be affected by recent warming, with reduced DICcf observed during 2008 to 2015, while the minimally-affected pHcf acts to compensate the decreases of DICcf with the calcification rate showing only slight decrease. Additionally, we also find that ocean acidification has clearly led to the long-term reduction in the pH of the CF.

Continue reading ‘Anthropogenic ocean warming and acidification recorded by Sr/Ca, Li/Mg, δ11B and B/Ca in Porites coral from the Kimberley region of northwestern Australia’

Characterization of Pacific oyster Crassostrea gigas proteomic response to natural environmental differences

Global climate change is rapidly altering coastal marine ecosystems that are important for food production. A comprehensive understanding of how organisms will respond to these complex environmental changes can come only from observing and studying species within their natural environment. To this end, the effects of environmental drivers—pH, dissolved oxygen content, salinity, and temperature—on Pacific oyster Crassostrea gigas physiology were evaluated in an outplant experiment. Sibling juvenile oysters were outplanted to eelgrass and unvegetated habitat at 5 different estuarine sites within the Acidification Nearshore Monitoring Network in Washington State, USA, to evaluate how regional environmental drivers influence molecular physiology. Within each site, we also determined if eelgrass presence, which buffered pH conditions, changed the oysters’ expressed proteome. A novel, 2-step, gel-free proteomic approach was used to identify differences in protein abundance in C. gigas ctenidia tissue after a 29 d outplant by (1) identifying proteins in a data-independent acquisition survey step and (2) comparing relative quantities of targeted environmental response proteins using selected reaction monitoring. While there was no difference in protein abundance detected between habitats or among sites within Puget Sound, C. gigas outplanted at Willapa Bay had significantly higher abundances of antioxidant enzymes and molecular chaperones. Environmental factors at Willapa Bay, such as higher average temperature, may have driven this protein abundance pattern. These findings generate a suite of new hypotheses for lab and field experiments to compare the effects of regional conditions on physiological responses of marine invertebrates.

Continue reading ‘Characterization of Pacific oyster Crassostrea gigas proteomic response to natural environmental differences’

Seasonal DNA methylation variation in the flat tree oyster Isognomon Alatus from a mangrove ecosystem in North Biscayne Bay, Florida

Epigenetic analyses constitute an emerging approach for better understanding of the mechanisms underlying environmental responses and their role during acclimatization and adaptation across diverse ecosystems. The expansion of environmental epigenetic studies to a broader range of ecologically and environmentally relevant organisms will enhance the capability to forecast ecological and evolutionary processes, as well as to facilitate a retrospective assessment of stress exposures in biomonitor organisms through “epigenetic footprinting” analyses. With such purpose, the present study monitored spatial and temporal variation in abiotic parameters (temperature, salinity, pH, and horizontal visibility) over a 2-y period in a mangrove ecosystem located in North Biscayne Bay (North Miami, FL). The obtained data were subsequently compared with epigenetic modifications (global genome-wide DNA methylation levels) in the flat tree oyster Isognomon alatus, used as a sentinel model organism across experimental sites. The obtained results revealed a certain level of seasonality in temporal DNA methylation patterns, which seem to be primarily associated with changes in temperature and horizontal visibility. These results constitute the first long-term study combining spatial and temporal epigenetic analyses in a marine organism in its natural environment, laying the initial groundwork to assess the biomonitoring potential of environmental epigenetic analyses.

Continue reading ‘Seasonal DNA methylation variation in the flat tree oyster Isognomon Alatus from a mangrove ecosystem in North Biscayne Bay, Florida’

Reduced Symbiodiniaceae diversity in Palythoa tuberculosa at a heavily acidified coral reef

Symbiodiniaceae diversity in hosts is known to change with the environment and particularly with temperature and light intensity. However, higher levels of pCO2, as could be expected under future ocean acidification scenarios, have been documented to show little to no effect in influencing the diversity of Symbiodiniaceae in hosts in previous studies. In this study, we examined hypervariable psbAncr sequences to identify the Cladocopium (former Symbiodinium ‘Clade C’) diversity within the zooxanthellate zoantharian Palythoa tuberculosa at an acidified reef in southern Japan. Palythoa tuberculosa were collected from a reef at the volcanic island of Iwotorishima in southern Japan; specimens from a high pCO2 site and from a nearby control (normal pCO2) site (Inoue et al. in Nat Clim Change 3:683–687, 2013). We observed a statistically significant reduction in Cladocopium diversity at the high pCO2 site with only one Cladocopium lineage present, compared to at the control site with two lineages present. Our results demonstrate that higher pCO2 can potentially negatively influence the diversity of host Symbiodiniaceae within anthozoan hosts, an important implication in the face of ongoing ocean acidification and climate change.

Continue reading ‘Reduced Symbiodiniaceae diversity in Palythoa tuberculosa at a heavily acidified coral reef’


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Ocean acidification in the IPCC AR5 WG II

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