Posts Tagged 'North Atlantic'

Impact of carbonate saturation on large Caribbean benthic foraminifera assemblages

Increasing atmospheric carbon dioxide and its dissolution in seawater have reduced ocean pH and carbonate ion concentrations, with potential implications on calcifying organisms. To assess the response of large Caribbean benthic foraminifera to low carbonate saturation conditions, we analyzed benthic foraminifers’ abundance and relative distribution in surface sediments in proximity to low-carbonate-saturation submarine springs and at adjacent control sites. Our results show that the total abundance of large benthic foraminifera was significantly lower at the low-pH submarine springs than at control sites, although responses were species specific. The relative abundance of high-magnesium, porcelaneous foraminifera was higher than that of hyaline foraminifera at the low-pH springs due to the abundant Archaias angulatus, a chlorophyte-bearing foraminifer, which secretes a large and robust test that is more resilient to dissolution at low-calcite saturation. The different assemblages found at the submarine springs indicate that calcareous symbiont-barren foraminifera are more sensitive to the effects of ocean acidification than agglutinated and symbiont-bearing foraminifera, suggesting that future ocean acidification will likely impact natural benthic foraminifera populations.

Continue reading ‘Impact of carbonate saturation on large Caribbean benthic foraminifera assemblages’

Development of a low-cost marine pCO2 sensor to characterise the natural variability of coastal carbonate chemistry in the context of global change

To aid the investigation into natural variability of coastal carbonate chemistry, pCO2 sensors are an invaluable tool for ease of in-situ data collection. However, these sensors can require not only specific expertise of utilisation but are also inaccessible to many due to high cost. In lieu of an expensive sensor, the most common way to measure pCO2 in seawater is with discrete sampling of water and subsequent analysis for two of the three parameters of the carbonate system (dissolved inorganic carbon (DIC), Total alkalinity (AT) or pH) which is then used to calculate a final pCO2 value. This method requires a substantial amount of cost, time and labour to not only retrieve seawater from depth, but also employ precise expertise in analyses with each step being potentially fraught with human error.

This research addressed these issues by developing a low-cost, easy-to-use sensor which efficiently and accurately measured coastal marine pCO2. This required a research and development stage where the sensor and housing design was tested at The University of Glasgow (Chapter 2 and 3) and also deployed in a temperate (Chapter 4) and tropical (Chapter 5) field environment. Seawater samples were also taken and their carbonate chemistry analysed in conjunction with sensor readings to calibrate and confirm the accuracy of the sensor. Along with the developed sensor and the collection of in-situ pCO2 data, other marine variables were also measured (pH, dissolved oxygen, chlorophyll, salinity, temperature, depth, photosynthetically active radiation, dissolved inorganic carbon and total alkalinity) to obtain a characterisation of the areas and an analysis of the drivers behind these variables.

The observed variability in the temperate area of Caol Scotnish, Loch Sween, Scotland was shown to be highly dependent on biological activity and the tidal action which exchanged different water masses into and out of the site. The observed variability in the tropical area of El Quseir, Egypt was shown to be highly dependent on biological activity, temperature and weather events. The sensor coped well in characterising the concentrations of pCO2 in both sites. There is a larger fluctuation of pCO2 in the tropical site than compared with the temperate site which is dictated by the relative hydrography in each area and the particular weather conditions experienced.

Continue reading ‘Development of a low-cost marine pCO2 sensor to characterise the natural variability of coastal carbonate chemistry in the context of global change’

Planar optode observation method for the effect of raindrop on dissolved oxygen and pH diffusion of air–water interface

The air–water interface is an important boundary where material exchanges, it has important influence on ecosystem and biogeochemical cycle. The rain can change the balance of interface, improve the exchange rate of gas flux, and make the distribution of dissolved oxygen and pH around the interface change in horizontal and vertical direction. Based on planar sensing film with highly spatial and temporal resolution which can provide the characteristics of two-dimensional distribution information, we carry out the simulation experiment of raindrops about oxygen and pH distribution in air–water interface using double parameters planar optode. The experimental data are analyzed from the gas transfer velocity, the kinetic energy flux and the sea-air flux of oxygen. The results show that rainfall process plays an important role in adjusting dissolved oxygen and pH of the surface water, the raindrop can break the balance of micro surface of water–gas interface mechanism, increase the gas transfer velocity and promote the dissolution of oxygen in the atmosphere in water to make a average increase of about 2.3 mg/L in vertical direction 23 mm. The impact of rainfall on pH of the water surface within 12 mm is relatively obvious, the pH value decreased by an average of 0.2–0.4 units, indicating that the raindrop promoted the migration of the atmosphere in the air–water interface, and the dissolved CO2 caused the surface water acidification. This study provides a novel technical method for understanding the influence of raindrops on the dissolved oxygen concentration and pH of the surface water in low wind-impacting area and static-water area.

Continue reading ‘Planar optode observation method for the effect of raindrop on dissolved oxygen and pH diffusion of air–water interface’

Response of pelagic calcifiers (Foraminifera, Thecosomata) to ocean acidification during oligotrophic and simulated up-welling conditions in the subtropical North Atlantic off Gran Canaria

Planktonic Foraminifera and thecosome pteropods are major producers of calcite and aragonite in the ocean and play an important role for pelagic carbonate flux. The responses of planktonic foraminifers to ocean acidification (OA) are variable among the species tested and so far do not allow for reliable conclusion. Thecosome pteropods respond with reduced calcification and shell dissolution to OA and are considered at high risk especially at high latitudes. The present investigation was part of a large-scale in situ mesocosm experiment in the oligotrophic waters of the eastern subtropical North Atlantic. Over 62 days, we measured the abundance and vertical flux of pelagic foraminifers and thecosome pteropods as part of a natural plankton community over a range of OA scenarios. A bloom phase was initiated by the introduction of deep-water collected from approx. 650 m depth simulating a natural up-welling event. Foraminifers occurred throughout the entire experiment in both the water column and the sediment traps. Pteropods were present only in small numbers and disappeared after the first two weeks of the experiment. No significant CO2 related effects were observed for foraminifers, but cumulative sedimentary flux was reduced at the highest CO2 concentrations. This flux reduction was most likely accompanying an observed flux reduction of particulate organic matter (POM) so that less foraminifers were intercepted and transported downward.

Continue reading ‘Response of pelagic calcifiers (Foraminifera, Thecosomata) to ocean acidification during oligotrophic and simulated up-welling conditions in the subtropical North Atlantic off Gran Canaria’

The ability of macroalgae to mitigate the negative effects of ocean acidification on four species of North Atlantic bivalve (updated)

Coastal ecosystems can experience acidification via upwelling, eutrophication, riverine discharge, and climate change. While the resulting increases in pCO2 can have deleterious effects on calcifying animals, this change in carbonate chemistry may benefit some marine autotrophs. Here, we report on experiments performed with North Atlantic populations of hard clams (Mercenaria mercenaria), eastern oysters (Crassostrea virginica), bay scallops (Argopecten irradians), and blue mussels (Mytilus edulis) grown with and without North Atlantic populations of the green macroalgae, Ulva. In six of seven experiments, exposure to elevated pCO2 levels ( ∼ 1700µatm) resulted in depressed shell- and/or tissue-based growth rates of bivalves compared to control conditions, whereas rates were significantly higher in the presence of Ulva in all experiments. In many cases, the co-exposure to elevated pCO2 levels and Ulva had an antagonistic effect on bivalve growth rates whereby the presence of Ulva under elevated pCO2 levels significantly improved their performance compared to the acidification-only treatment. Saturation states for calcium carbonate (Ω) were significantly higher in the presence of Ulva under both ambient and elevated CO2 delivery rates, and growth rates of bivalves were significantly correlated with Ω in six of seven experiments. Collectively, the results suggest that photosynthesis and/or nitrate assimilation by Ulva increased alkalinity, fostering a carbonate chemistry regime more suitable for optimal growth of calcifying bivalves. This suggests that large natural and/or aquacultured collections of macroalgae in acidified environments could serve as a refuge for calcifying animals that may otherwise be negatively impacted by elevated pCO2 levels and depressed Ω.

Continue reading ‘The ability of macroalgae to mitigate the negative effects of ocean acidification on four species of North Atlantic bivalve (updated)’

Assessing the impacts of ocean acidification on adhesion and shell formation in the barnacle Amphibalanus amphitrite

Barnacles are dominant members of marine intertidal communities. Their success depends on firm attachment provided by their proteinaceous adhesive and protection imparted by their calcified shell plates. Little is known about how variations in the environment affect adhesion and shell formation processes in barnacles. Increased levels of atmospheric CO2 have led to a reduction in the pH of ocean waters (i.e., ocean acidification), a trend that is expected to continue into the future. Here, we assessed if a reduction in seawater pH, at levels predicted within the next 200 years, would alter physiology, adhesion, and shell formation in the cosmopolitan barnacle Amphibalanus (=Balanus) amphitrite. Juvenile barnacles, settled on silicone substrates, were exposed to one of three static levels of pHT, 8.01, 7.78, or 7.50, for 13 weeks. We found that barnacles were robust to reduced pH, with no effect of pH on physiological metrics (mortality, tissue mass, and presence of eggs). Likewise, adhesive properties (adhesion strength and adhesive plaque gross morphology) were not affected by reduced pH. Shell formation, however, was affected by seawater pH. Shell mass and base plate area were higher in barnacles exposed to reduced pH; barnacles grown at pHT 8.01 exhibited approximately 30% lower shell mass and 20% smaller base plate area as compared to those at pHT 7.50 or 7.78. Enhanced growth at reduced pH appears to be driven by the increased size of the calcite crystals that comprise the shell. Despite enhanced growth, mechanical properties of the base plate (but not the parietal plates) were compromised at the lowest pH level. Barnacle base plates at pHT 7.50 broke more easily and crack propagation, measured through microhardness testing, was significantly affected by seawater pH. Other shell metrics (plate thickness, relative crystallinity, and atomic disorder) were not affected by seawater pH. Hence, a reduction in pH resulted in larger barnacles but with base plates that would crack more readily. It is yet to be determined if such changes would alter the survival of A. amphitrite in the field, but changes in the abundance of this ecologically dominant species would undoubtedly affect the composition of biofouling communities.

Continue reading ‘Assessing the impacts of ocean acidification on adhesion and shell formation in the barnacle Amphibalanus amphitrite’

High resolution pH measurements using a lab-on-chip sensor in surface waters of northwest european shelf seas

Increasing atmospheric CO2 concentrations are resulting in a reduction in seawater pH, with potential detrimental consequences for marine organisms. Improved efforts are required to monitor the anthropogenically driven pH decrease in the context of natural pH variations. We present here a high resolution surface water pH data set obtained in summer 2011 in North West European Shelf Seas. The aim of our paper is to demonstrate the successful deployment of the pH sensor, and discuss the carbonate chemistry dynamics of surface waters of Northwest European Shelf Seas using pH and ancillary data. The pH measurements were undertaken using spectrophotometry with a Lab-on-Chip pH sensor connected to the underway seawater supply of the ship. The main processes controlling the pH distribution along the ship’s transect, and their relative importance, were determined using a statistical approach. The pH sensor allowed 10 measurements h−1 with a precision of 0.001 pH units and a good agreement with pH calculated from a pair of discretely sampled carbonate variables dissolved inorganic carbon (DIC), total alkalinity (TA) and partial pressure of CO2 (pCO2) (e.g., pHDICpCO2). For this summer cruise, the biological activity formed the main control on the pH distribution along the cruise transect. This study highlights the importance of high quality and high resolution pH measurements for the assessment of carbonate chemistry dynamics in marine waters.

Continue reading ‘High resolution pH measurements using a lab-on-chip sensor in surface waters of northwest european shelf seas’

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Ocean acidification in the IPCC AR5 WG II

OUP book