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Short-term variation of ooid mineralogy in the Triassic-Jurassic boundary interval and its environmental implications: evidence from the equatorial Ghalilah Formation, United Arab Emirates

Highlights

• Provide data from potentially continuous Tr-J carbonate sections

• Provide detailed studies of Tr-J ooids that have been scarcely studied before

• Give more information about Tr-J extinction-recovery scenarios

• Variation of ooid mineralogies serves as a new marker for ocean acidification in the equatorial realm.

Abstract

In the Triassic-Jurassic (T-J) interval, only a few continuous carbonate sections have been reported, and detailed studies about ooids and their significance are scarce. This study focuses on abundant ooids in potentially continuous T-J carbonate sections representing equatorial, shallow marine environments. Mineralogical changes of ooids are proposed as a marker for transitional marine chemistry including carbonate saturation after ocean acidification and provide information about crisis and recovery scenarios for the initial CIE (carbon isotope excursion) and subsequent positive CIE. In the Ghalilah Formation, United Arab Emirates (UAE), the Sakhra Member is deposited immediately above the T-J boundary. Based on field work and thin section observation, the Sakhra Member can be divided into three coarsening-upward cycles (in ascending order, named C1–C3), each of which consists of peloidal mudstone/wackestone in the lower part and oolitic packstone/grainstone in the upper part. Petrological observation (thin section, SEM), stable isotope (inorganic carbon and oxygen) and elemental analysis suggest temporal change of original mineralogy from C1 to C3 ooids: from high-Mg calcite in C1 ooids to aragonite in C2 and C3 ooids. The mineralogical change of ooids is possibly related to variations in seawater carbonate saturation. The lower carbonate saturation indicated by C1 ooids reflects a transitional period before recovery from ocean acidification due to massive and rapid release of acidic gases (CO2 and SO2) by CAMP eruptions. Subsequently, from C1 to C3 ooids, seawater gradually experienced increasing carbonate saturation and increasing microbial carbonate precipitation. Increased microbial activities combined with elevated terrestrial influx may have significantly reduced the atmospheric CO2 concentration and restored carbonate saturation, which laid the foundation for full biotic recovery.

Continue reading ‘Short-term variation of ooid mineralogy in the Triassic-Jurassic boundary interval and its environmental implications: evidence from the equatorial Ghalilah Formation, United Arab Emirates’

Anthropogenic impacts on mangrove and saltmarsh communities in eastern Australia

The global phenomenon of mangrove encroachment into saltmarshes has been observed across five continents. It has been proposed that this encroachment is driven in part by rising atmospheric CO2 concentration and reduced salinity in saltmarshes resulting from rising sea levels enhancing the establishment success of mangrove seedlings. However, this is yet to be empirically tested at the community-level. In this study, we examined the effect of CO2 and salinity on seedling growth of two mangrove species, Aegiceras corniculatum and Avicennia
marina, grown individually and in a model saltmarsh community in a glasshouse experiment. We found that the shoot (210%) and root (91%) biomass of the saltmarsh species was significantly greater under elevated CO2. As a result, both mangrove species experienced a stronger competitive effect from the saltmarsh species under elevated CO2. Nevertheless, A. marina seedlings produced on average 48% more biomass under elevated CO2 when grown in competition with the saltmarsh species which they used to grow taller suggesting they were light
limited. In contrast, A. corniculatum growth did not significantly differ between CO2 treatments. However, it had on average 36% greater growth under seawater salinity compared to hypersaline conditions. Avicenna marina seedlings were not affected by salinity. From these results, we suggest that although CO2 and salinity are not universal drivers determining saltmarsh-mangrove boundaries, it is likely that rising atmospheric CO2 concentration and reduced salinity associated with sea level rise will enhance the establishment success of mangrove seedlings in saltmarshes, which may facilitate mangrove encroachment in the future.

Continue reading ‘Anthropogenic impacts on mangrove and saltmarsh communities in eastern Australia’

Water motion and vegetation control the pH dynamics in seagrass-dominated bays

Global oceanic pH is lowering, which is causing great concern for the natural functioning of marine ecosystems. Current pH predictions are based on open ocean models; however, coastal zones are dynamic systems with seawater pH fluctuating temporally and spatially. To understand how coastal ecosystems will respond in the future, we first need to quantify the extent that local processes influence the pH of coastal zones. With this study, we show that over a single diurnal cycle, the total pH can fluctuate up to 0.2 units in a shallow seagrass-dominated bay, driven by the photosynthesis and respiration of the vegetation. However, these biologically controlled pH fluctuations vary significantly over small distances. Monitoring conducted at neighboring sites with contrasting hydrodynamic regimes highlights how water motion controls the extent that the local pH is altered by the metabolism of vegetation. The interactive effects of hydrodynamics and vegetation were further investigated with an in situ experiment, where the hydrodynamics were constrained and thus the local water residence time was increased, displaying the counteractive effect of hydrodynamics on the pH change caused by vegetation. With this research, we provide detailed in situ evidence of the spatial variation of pH within marine ecosystems, highlighting the need to include hydrodynamic conditions when assessing the pH-effects of vegetation, and identifying potential high-pH refuges in a future low pH ocean.

Continue reading ‘Water motion and vegetation control the pH dynamics in seagrass-dominated bays’

Does seawater acidification affect zooxanthellae density and health in the invasive upside‐down jellyfish, Cassiopea spp.?

Ocean acidification is the decline in seawater pH that results from the absorption of atmospheric carbon dioxide (CO2). Decreased pH has negative effects on survivability, growth, and development in many marine calcifiers, potentially resulting in reduced coral species richness. This reduction in richness could open new niche space, allowing the spread of invasive species, such as the upside‐down jellyfish (Cassiopea spp.). Like corals, this jellyfish forms symbiotic relationships with zooxanthellae, photosynthetic dinoflagellates. This study focused on the effect of seawater acidification in Cassiopea spp. We monitored zooxanthellae density and two measures of health (bell diameter and volume) in individuals of Cassiopea sp. at three pH levels chosen to mimic different open‐ocean average conditions: 8.2, representing pre‐industrial revolution conditions; and 7.9 and 7.6, representing predicted declines in pH in the next century. Zooxanthellae density and health of the jellyfish were measured twice—prior to experimental manipulations and after four weeks of exposure to experimental pHs—in three consecutive trials. The effects of pH and Trial on proportional change in jellyfish attributes were analyzed using generalized linear mixed models. We found no significant effects of either factor. These results indicate that decreasing seawater pH has no apparent negative effect on zooxanthellae density or health in Cassiopea, which suggests that these jellyfish may be relatively insensitive to the impacts of ocean acidification, heightening its potential as an invasive species.

Continue reading ‘Does seawater acidification affect zooxanthellae density and health in the invasive upside‐down jellyfish, Cassiopea spp.?’

Recent pace of change in human impact on the world’s ocean

Humans interact with the oceans in diverse and profound ways. The scope, magnitude, footprint and ultimate cumulative impacts of human activities can threaten ocean ecosystems and have changed over time, resulting in new challenges and threats to marine ecosystems. A fundamental gap in understanding how humanity is affecting the oceans is our limited knowledge about the pace of change in cumulative impact on ocean ecosystems from expanding human activities – and the patterns, locations and drivers of most significant change. To help address this, we combined high resolution, annual data on the intensity of 14 human stressors and their impact on 21 marine ecosystems over 11 years (2003–2013) to assess pace of change in cumulative impacts on global oceans, where and how much that pace differs across the ocean, and which stressors and their impacts contribute most to those changes. We found that most of the ocean (59%) is experiencing significantly increasing cumulative impact, in particular due to climate change but also from fishing, land-based pollution and shipping. Nearly all countries saw increases in cumulative impacts in their coastal waters, as did all ecosystems, with coral reefs, seagrasses and mangroves at most risk. Mitigation of stressors most contributing to increases in overall cumulative impacts is urgently needed to sustain healthy oceans.

Continue reading ‘Recent pace of change in human impact on the world’s ocean’

La terminologie de la géoingénierie marine. Une contribution au projet IATE-CvT (in French)

Pour la première fois mentionnée dans la politique en 1965 par le comité consultatif scientifique du président des États-Unis, la géoingénierie (ou : ingénierie climatique) est une préoccupation relativement nouvelle. Plus de cinquante ans plus tard, le sujet reste néanmoins une topique controversée. La question reste : jusqu’où peut-on intervenir dans le climat afin de contrebalancer le changement climatique d’origine anthropocène ? La géoingénierie fait référence aux techniques développées pour lutter contre le changement climatique en supprimant les gaz à effet de serre de l’atmosphère de l’un côté et de l’autre en augmentant la quantité de lumière solaire réfléchie vers l’espace à partir de la terre et des océans (Shepherd, J. G. 2009). C’est un domaine actuel qui peut éventuellement impliquer chacun sur terre. Le domaine se trouve au cœur de nombreux sommets internationaux (p. ex. le COP21 de 2015 à Paris) et suscite non seulement des questions au niveau de la technologie, mais également au niveau éthique (jusqu’où peut-on altérer la nature ?), politique (protocole de Kyoto, 1997), philosophique (« on est Dieu »), sociologique (les conséquences pour les habitants), biologique (les conséquences pour les espèces) et économique (qui paye ?). Comme la géoingénierie est une préoccupation relativement nouvelle, la terminologie internationale laisse encore à désirer. Le domaine étant en pleine voie de développement, les scientifiques du domaine ne se préoccupent guère avec les mots qu’ils appliquent. Reste la tâche aux terminologues de décrire, nommer et normer les termes. Dans ce travail sont traités dix termes venant de la géoingénierie marine. Les termes ont été rencontrés dans des publications scientifiques anglaises, puis décrits en anglais, français et néerlandais de manière à les intégrer dans les bases de données terminologiques IATE et la base terminologique du Centrum voor Terminologie (CvT ; Centre pour Terminologie).

Continue reading ‘La terminologie de la géoingénierie marine. Une contribution au projet IATE-CvT (in French)’

Carbon dynamics in a marsh-influenced marine-dominated ecosystem

A combination of global climate change, local anthropogenic pressures, and naturally occurring processes have impacted biogeochemical cycling in coastal systems. Here, a coastal estuarine ecosystem in North Carolina is studied in order to determine spatial relations, seasonal changes, and overall fluxes of carbon, as well as the influences of these factors on the biogeochemistry of the system as a whole. Partial pressure of carbon dioxide (pCO2), percent dissolved oxygen (DO), particulate organic carbon (POC), total dissolved inorganic carbon (DIC), total alkalinity (TA), and carbon isotopes of organic and inorganic carbon—amongst additional data—were collected from numerous study locations in the Cape Lookout region of North Carolina in April 2017, October 2017, April 2018, June 2018, and October 2018. Carbon isotopes of POC ranging between -30 and -17.79‰ coupled with a decreasing trend in C/N values moving down-estuary indicate that the organic carbon in the system is mainly sourced from upland vascular plant and agricultural inputs, with a small influence from in-estuary Spartina marsh grasses. The majority of the estuary was oversaturated with CO2 compared to the atmosphere during all seasons, with the marsh-creek Smyrna Creek consistently exhibiting the most extreme pCO2 values, peaking at 14606 µatm in the head of the creek in June 2018. Some estuarine sites were occasionally undersaturated in CO2, likely from local phytoplankton blooms occurring during spring and summer. Carbon flux from these three creeks into Jarrett Bay is evident, as is further flux of CO2 through the sound and out into the ocean where the CO2-saturated estuarine waters combine with the less CO2-rich marine waters to produce ocean values of ~625 µatm. TA values throughout the system range from 1872–2342 µmol kg-1, excluding Smyrna and Williston marsh-creeks which exhibited anomalous TA in several different seasons. Omitting these two creeks, the remainder of the system shows an increasing spatial TA trend moving down estuary over the salinity gradient with the lowest values in Jarrett Bay and the highest values in the ocean. Due to seasonal mixing trends, DIC concentration increased down-estuary in the Summer and Spring and decreased over the salinity gradient in the Fall; however, the head of Smyrna Creek typically exhibited notably high DIC compared to the rest of the system, as CO2 is the main contributor to DIC within the salt marsh. Plotting DIC against TA indicates that inorganic carbon likely originates from a combination of sulfate reduction, denitrification, CO2 invasion, and aerobic respiration. Calculations of air–sea CO2 flux indicate that the estuarine waters as a whole are a significant source of CO2 to the atmosphere with an average air–sea CO2 flux of 13.4 mmol m-2 day-1.

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OA-ICC HIGHLIGHTS

Ocean acidification in the IPCC AR5 WG II

OUP book