Posts Tagged 'sediment'

Assessing the influence of ocean acidification to marine amphipods: A comparative study

CO2 increases in the ocean may occur both by the capacity of CO2 exchanges with its dissolved form between atmosphere and surface seawater as well by CO2 leaks during the carbon capture and storage (CCS) process. The decrease in seawater pH may result in a reduction in the concentration of both hydroxide and carbonate (OH– and CO32 −). The main aim of this work is to conduct an ecotoxicology comparative survey using two amphipod species from Europe and Brazil exposed to different acidification (CO2) scenarios. For it, an integrative approach based on the weight of evidence was used for comparative proposes to identify the effects on the amphipods association with the acidification and with the related mobility of metals. The results demonstrate that the Ampelisca brevicornis species is more sensitive to pH reductions than the Hyale youngi species. Furthermore, this study has demonstrated that the CO2 enrichment in aquatic ecosystems would cause changes on the mobility of certain metals (Zn, Cu and As). The results of Principal Component Analysis (PCA) showed that the dissolved Zn in overlying water was strongly correlated with the decrease in the pH and was associated with increased toxicity of the sediment to the exposed organisms, mainly for the A. brevicornis species from Spain. Nevertheless, similar results were found in relation to the mortality of amphipods in low pH values for all sediment tested. Concluding, it is highlighted the importance of comparative studies in different types of environment and improve the understood of the risks associated with the ocean acidification.

Continue reading ‘Assessing the influence of ocean acidification to marine amphipods: A comparative study’

Core-top calibration of B/Ca in Pacific Ocean Neogloboquadrina incompta and Globigerina bulloides as a surface water carbonate system proxy

Practical methods for reconstructing past ocean carbonate chemistry are needed to study past periods of ocean acidification and improve understanding of the marine carbonate system’s role in the global climate cycles. Planktic foraminiferal B/Ca may fill this role, but requires better understanding and improved proxy calibrations. We used Pacific Ocean core-top sediments to generate new calibrations of the B/Ca proxy for past carbonate system parameters in two upwelling/subpolar species of asymbiotic planktic foraminifera (Globigerina bulloides and Neogloboquadrina incompta ). Both species show significant positive correlation of B/Ca with calcite saturation (Ωcalcite) and carbonate ion concentration ([View the MathML source]) across a broad range of environmental conditions. This suggests a calcification rate control on B/Ca incorporation (as Ωcalcite regulates calcification rate), in agreement with recent inorganic calcite studies. This is also consistent with a surface entrapment model of trace element incorporation into CaCO3. In neither species is B/Ca significantly correlated with pH, suggesting that pH does not directly regulate boron incorporation, and that calculation of pH directly from foraminiferal B/Ca is not suitable. Correlations between B/Ca and [B(OH)4−], [B(OH)4−/HCO3−], and [B(OH)4−]/DIC) are weaker than with Ωcalcite. Boron partition coefficients View the MathML source show little or no correlation with [CO32−] or temperature and vary widely, providing no support for application of KD to calculate carbonate system parameters from B/Ca. We also discuss potential effects of depth-related dissolution, temperature, and salinity on B/Ca. These empirical calibrations linking foraminiferal calcite B/Ca with Ωcalcite provide a strong tool for reconstructing the past ocean carbonate system and improve our understanding of the proxy’s geochemical basis.

Continue reading ‘Core-top calibration of B/Ca in Pacific Ocean Neogloboquadrina incompta and Globigerina bulloides as a surface water carbonate system proxy’

Timing of global regression and microbial bloom linked with the Permian-Triassic boundary mass extinction: implications for driving mechanisms

New high-resolution U-Pb dates indicate a duration of 89 ± 38 kyr for the Permian hiatus and of 14 ± 57 kyr for the overlying Triassic microbial limestone in shallow water settings of the Nanpanjiang Basin, South China. The age and duration of the hiatus coincides with the Permian-Triassic boundary (PTB) and the extinction interval in the Meishan Global Stratotype Section and Point, and strongly supports a glacio-eustatic regression, which best explains the genesis of the worldwide hiatus straddling the PTB in shallow water records. In adjacent deep marine troughs, rates of sediment accumulation display a six-fold decrease across the PTB compatible with a dryer and cooler climate as indicated by terrestrial plants. Our model of the Permian-Triassic boundary mass extinction (PTBME) hinges on the synchronicity of the hiatus with the onset of the Siberian Traps volcanism. This early eruptive phase released sulfur-rich volatiles into the stratosphere, thus simultaneously eliciting a short-lived ice age responsible for the global regression and a brief but intense acidification. Abrupt cooling, shrunk habitats on shelves and acidification may all have synergistically triggered the PTBME. Subsequently, the build-up of volcanic CO2 induced a transient cool climate whose early phase saw the deposition of the microbial limestone.

Continue reading ‘Timing of global regression and microbial bloom linked with the Permian-Triassic boundary mass extinction: implications for driving mechanisms’

Ocean acidification changes abiotic processes but not biotic processes in coral reef sediments

In coral reefs, sediments play a crucial role in element cycling by contributing to primary production and the remineralization of organic matter. We studied how future ocean acidification (OA) will affect biotic and abiotic processes in sediments from two coral reefs of the Great Barrier Reef, Australia. This was investigated in the laboratory under conditions where water-sediment exchange was dominated by molecular diffusion (Magnetic Island) or by porewater advection (Davies Reef). OA conditions (+ΔpCO2: 170–900 µatm, -ΔpH: 0.1–0.4) did not affect photosynthesis, aerobic and anaerobic organic matter remineralization and growth of microphytobenthos. However, microsensor measurements showed that OA conditions reduced the porewater pH. Under diffusive conditions these changes were limited to the upper sediment layers. In contrast, advective conditions caused a deeper penetration of low pH water into the sediment resulting in an earlier pH buffering by dissolution of calcium carbonate (CaCO3). This increased the dissolution of Davis Reef sediments turning them from net precipitating (-0.8 g CaCO3 m-2 d-1) under ambient to net dissolving (1 g CaCO3 m-2 d-1) under OA conditions. Comparisons with in-situ studies on other reef sediments show that our dissolution rates are reasonable estimates for field settings. We estimate that enhanced dissolution due to OA will only have a minor effect on net ecosystem calcification of the Davies Reef flat (< 4%). However, it could decrease recent sediment accumulation rates in the lagoon by up to 31% (by 0.2–0.4 mm year-1), reducing valuable reef space. Furthermore, our results indicate that high-magnesium calcite is predominantly dissolving in the studied sediments and a drastic reduction in this mineral can be expected on Davis Reef lagoon in the near future, leaving sediments of an altered mineral composition. This study demonstrates that biotic sediment processes will likely not directly be affected by OA. Ensuing indirect effects of OA-induced sediment dissolution on biotic processes are discussed.

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Daily variation in net primary production and net calcification in coral reef communities exposed to elevated pCO2

The threat represented by ocean acidification (OA) for coral reef has received considerable attention because of the sensitivity of calcifiers to changing water carbonate chemistry. However most studies have focused on the organismic response of calcification to OA, and only a few have addressed community-level effects, or investigated parameters other than calcification, such as photosynthesis. Light (Photosynthetically Active Radiation, PAR) is a driver of biological processes on coral reefs, and the possibility that these processes might be perturbed by OA has important implications for community function. Here we investigate how CO2 enrichment affects the relationships between PAR and community net O2 production (Pnet), and between PAR and community net calcification (Gnet), using experiments on three coral communities constructed to match (i) the back reef of Moorea, French Polynesia, (ii) the fore reef of Moorea, and (iii) the reef flat of Oahu, Hawaii. The results were used to test the hypothesis that OA affects the relationship between Pnet and Gnet. For the three communities tested, pCO2 did not affect the Pnet-PAR relationship, but it affected the intercept of the hyperbolic tangent curve fitting the Gnet-PAR relationship for both reef communities in Moorea (but not in Oahu). For the three communities, the slopes of the linear relationships between Pnet and Gnet were not affected by OA, although the intercepts were depressed by the inhibitory effect of high pCO2 on Gnet. Our result indicates that OA can modify the balance between net calcification and net photosynthesis of reef communities by depressing community calcification, but without affecting community photosynthesis.

Continue reading ‘Daily variation in net primary production and net calcification in coral reef communities exposed to elevated pCO2’

Investigating controls on boron isotope ratios in shallow marine carbonates

The boron isotope-pH proxy has been widely used to reconstruct past ocean pH values. In both planktic foraminifera and corals, species-specific calibrations are required in order to reconstruct absolute values of pH, due to the prevalence of so-called vital effects — physiological modification of the primary environmental signals by the calcifying organisms. Shallow marine abiotic carbonate (e.g. ooids and cements) could conceivably avoid any such calibration requirement, and therefore provide a potentially useful archive for reconstructions in deep (pre-Cenozoic) time. However, shallow marine abiotic carbonates could also be affected by local shifts in pH caused by microbial photosynthesis and respiration, something that has up to now not been fully tested. In this study, we present boron isotope measurements from shallow modern marine carbonates, from the Bahama Bank and Belize to investigate the potential of using shallow water carbonates as pH archives, and to explore the role of microbial processes in driving nominally ‘abiogenic’ carbonate deposition. For Bahama bank samples, our boron-based pH estimates derived from a range of carbonate types (i.e. ooids, peloids, hardground cements, carbonate mud, stromatolitic micrite and calcified filament micrite) are higher than the estimated modern mean-annual seawater pH values for this region. Furthermore, the majority (73%) of our marine carbonate-based pH estimates fall out of the range of the estimated pre-industrial seawater pH values for this region. In shallow sediment cores, we did not observe a correlation between measured pore water pH and boron-derived pH estimates, suggesting boron isotope variability is a depositional rather than early diagenetic signal. For Belize reef cements, conversely, the pH estimates are lower than likely in situ seawater pH at the time of cement formation. This study indicates the potential for complications when using shallow marine non-skeletal carbonates as marine pH archives. In addition, variability in δ11B based pH estimates provides additional support for the idea that photosynthetic CO2 uptake plays a significant role in driving carbonate precipitation in a wide range of shallow water carbonates.

Continue reading ‘Investigating controls on boron isotope ratios in shallow marine carbonates’

Development and application of foraminiferal carbonate system proxies to quantify ocean acidification in the California Current

The oceanic uptake of anthropogenic carbon has mitigated climate change, but has also resulted in a global average 0.1 decline in surface ocean pH over 20th century known as ocean acidification. The parallel reduction in carbonate ion concentration ([CO32-]) and the saturation state of seawater (Ω) has caused many major calcium carbonate-secreting organisms such as planktonic foraminifera to exhibit impaired calcification. We develop proxy calibrations and down core records that use calcification and geochemical characteristics of planktonic foraminifera as proxies for the marine carbonate system. This study focuses specifically on the surface ocean chemistry of the California Current Ecosystem (CCE), which has been identified as a region of rapidly progressing ocean acidification due to natural upwelling processes and the low buffering capacity of these waters. The calibration portion of this study uses marine sediments collected by the Santa Barbara Basin (SBB), California sediment-trapping program located in the central region of the CCE. We calibrate the relationships of Globigerina bulloides calcification intensity to [CO3 2-] and the B/Ca ratios of G. bulloides, Neogloboquadrina dutertrei and Neogloboquadrina incompta shells to Ω calcite using in situ measurements and model simulations of these independent variables. By applying these proxy methods to down core, our records from the SBB indicate a 20% reduction in foraminiferal calcification since ~1900, translating to a 35% decline in [CO 32-] in the CCE over this period. Our high-resolution calcification record also reveals a substantial interannual to decadal modulation of ocean acidification in the CCE related to the sign of Pacific Decadal Oscillation and El Niño Southern Oscillation. In the future we can expect these climatic modes to both enhance and moderate anthropogenic ocean acidification. Based on our historic record, we predict that if atmospheric CO2 reaches 540 ppm by the year 2100 as predicted by a conservative CO3 pathway, [CO32-] will experience a net reduction of 55%, resulting in at least a 30% reduction in calcification of planktonic foraminifera that will likely be mirrored by other adversely affected marine calcifiers.

Continue reading ‘Development and application of foraminiferal carbonate system proxies to quantify ocean acidification in the California Current’

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Ocean acidification in the IPCC AR5 WG II

OUP book