Posts Tagged 'chemistry'

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’

Development of an economical, autonomous pHstat system for culturing phytoplankton under steady state or dynamic conditions

Laboratory investigations of physiological processes in phytoplankton require precise control of experimental conditions. Chemostats customized to control and maintain stable pH levels (pHstats) are ideally suited for investigations of the effects of pH on phytoplankton physiology, for example in context of ocean acidification. Here we designed and constructed a simple, flexible pHstat system and demonstrated its operational capabilities under laboratory culture conditions. In particular, the system is useful for simulating natural cyclic pH variability within aquatic ecosystems, such as diel fluctuations that result from metabolic activity or tidal mixing in estuaries. The pHstat system operates in two modes: (1) static/set point pH, which maintains pH at a constant level, or (2) dynamic pH, which generates regular, sinusoidal pH fluctuations by systematically varying pH according to user-defined parameters. The pHstat is self-regulating through the use of interchangeable electronically controlled reagent or gas-mediated pH-modification manifolds, both of which feature flow regulation by solenoid valves. Although effective pH control was achieved using both liquid reagent additions and gas-mediated methods, the liquid manifold exhibited tighter control (± 0.03 pH units) of the desired pH than the gas manifold (± 0.10 pH units). The precise control provided by this pHstat system, as well as its operational flexibility will facilitate studies that examine responses by marine microbiota to fluctuations in pH in aquatic ecosystems.

Continue reading ‘Development of an economical, autonomous pHstat system for culturing phytoplankton under steady state or dynamic conditions’

Factors affecting coral recruitment and calcium carbonate accretion rates on a Central Pacific coral reef

Coral recruitment and calcium carbonate (CaCO3) accretion are fundamental processes that help maintain coral reefs. Many reefs worldwide have experienced degradation, including a decrease in coral cover and biodiversity. Successful coral recruitment helps degraded reefs to recover, while CaCO3 accretion by early successional benthic organisms maintains the topographic complexity of a coral reef system. It is therefore important to understand the processes that affect coral recruitment and CaCO3 accretion rates in order to understand how coral reefs recover from disturbances.

The aim of this thesis was to determine how biophysical forcing factors affect coral recruitment, calcification and bioerosion on a pristine coral reef. I used artificial settlement tiles to measure coral recruitment and CaCO3 accretion at ten sites (four on the fore reef, four on the Western Reef Terrace and two at the Entrance Channel) at Palmyra Atoll. Fungia skeletons and pieces of dead coral rock were used to measure bioerosion rates, which were combined with the CaCO3 accretion rates to obtain a net CaCO3 budget of the reef substratum. Interactions between coral recruits and other benthic organisms on the settlement tiles were recorded to determine the settlement preferences and competitive strength of coral recruits. The settlement preference of Pocillopora damicornis for divots shaped like steephead and bumphead parrotfish bites marks was determined by adding P. damicornis larvae to a container with a settlement tile with the aforementioned divots.

I found that coral recruitment and CaCO3 accretion are influenced by biophysical forcing factors. Most pocilloporids likely recruit close to their parents while the origin of poritid larvae is much more distant. Pocilloporid recruitment rates were also significantly correlated with the successional stage of the benthic community on the settlement tiles, especially the cover of biofilm and bryozoa. Biofilm and crustose coralline algae (CCA) were preferred as settlement substrata by coral larvae, however both pocilloporids and poritids settled on a large number of different benthic substrata. P. damicornis larvae showed a significant settlement preference for divots shaped like parrotfish bite marks over a flat settlement surface. Coral recruits were good competitors against encrusting algae but were often outcompeted by filamentous and upright algae. Settlement tiles were almost entirely colonised by benthic organisms within three to twelve months of deployment. The mass of CaCO3 deposited onto the settlement tiles negatively correlated with herbivore grazing pressure on the benthic community. Bioerosion rates within pieces of coral (internal bioerosion) increased over time but overall bioerosion rates (internal and external) rarely exceeded CaCO3 deposition by CCA.

My results show how variability in biophysical forcing factors leads to natural variation in coral recruitment and CaCO3 accretion. This thesis highlights the importance of measuring herbivore grazing, CCA and turf algae cover to gain a better understanding of reef resilience. I conclude that models constructed for Caribbean reefs may not be suited to predict resilience in Pacific reefs and that within the Pacific, two different kinds of resilience models need to be constructed, one for human-inhabited coral reefs and one for uninhabited coral reefs.

Continue reading ‘Factors affecting coral recruitment and calcium carbonate accretion rates on a Central Pacific coral reef’

Environmental controls on the growth, photosynthetic and calcification rates of a Southern Hemisphere strain of the coccolithophore Emiliania huxleyi

We conducted a series of diagnostic fitness response experiments on the coccolithophore, Emiliania huxleyi, isolated from the Subtropical Convergence east of New Zealand. Dose response curves (i.e., physiological rate vs. environmental driver) were constructed for growth, photosynthetic, and calcification rates of E. huxleyi relative to each of five environmental drivers (nitrate concentration, phosphate concentration, irradiance, temperature, and pCO2). The relative importance of each environmental driver on E. huxleyi rate processes was then ranked using a semi-quantitative approach by comparing the percentage change caused by each environmental driver on the measured physiological metrics under the projected conditions for the year 2100, relative to those for the present day, in the Subtropical Convergence. The results reveal that the projected future decrease in nitrate concentration (33%) played the most important role in controlling the growth, photosynthetic and calcification rates of E. huxleyi, whereas raising pCO2 to 75 Pa (750 ppm) decreased the calcification : photosynthesis ratios to the greatest degree. These findings reveal that other environmental drivers may be equally or more influential than CO2 in regulating the physiological responses of E. huxleyi, and provide new diagnostic information to better understand how this ecologically important species will respond to the projected future changes to multiple environmental drivers.

Continue reading ‘Environmental controls on the growth, photosynthetic and calcification rates of a Southern Hemisphere strain of the coccolithophore Emiliania huxleyi’

Global variability and changes in ocean total alkalinity from Aquarius satellite data

This work demonstrates how large-scale Aquarius satellite salinity data have provided an unprecedented opportunity when combined with total alkalinity (TA) equations as a function of salinity and temperature to examine global changes in the CO2 system. Alkalinity is a gauge on the ability of seawater to neutralize acids. TA correlates strongly with salinity. Spatial variability in alkalinity and salinity exceed temporal variability. Northern Hemisphere has more spatial variability in TA and salinity, while less variability in Southern Ocean TA is due to less salinity variability and upwelling of waters enriched in alkalinity. For the first time it is shown that TA in subtropical regions has increased as compared with climatological data; this is reflective of large-scale changes in the global water cycle. Thus, as temperature and salinity increase in subtropical regions, the resultant increase in TA and ocean acidification is reinforcing that from oceanic uptake of atmospheric CO2.

Continue reading ‘Global variability and changes in ocean total alkalinity from Aquarius satellite data’

Mechanisms leading to the frequent occurrences of hypoxia and a preliminary analysis of the associated acidification off the Changjiang estuary in summer

Based on literature data and shipboard observations, this study investigated the main environmental characteristics of the seafloor topography, current field, front, and upwelling that are closely related to hypoxia occurrence off the Changjiang estuary. The physical processes of the plume front and upwelling off the Changjiang estuary in summer were coupled. The vertical distribution pattern of the plume front was closely related to the upwelling. By reviewing and analyzing the historical summer hypoxia events off the Changjiang estuary, we statistically demonstrated the spatial structure of the horizontal distribution of the hypoxic zone and investigated the location of occurrence zone of the hypoxia. We found that the dissolved oxygen (DO) concentration on the inner continental shelf off the estuary showed a “V” shape in relation to station depth. Therefore, we noted that the hypoxic water on the inner continental shelf mostly occurred on the slopes with steep seafloor topography. Base on the current understanding of the hypoxic mechanisms off the Changjiang estuary, we analyzed the biogeochemical mechanisms that could cause the steep terrain off the Changjiang estuary to become the main areas prone to summer hypoxia and explained the internal relations between the location of the hypoxic zone on the slopes and the plume front and upwelling. The plume front and upwelling off the Changjiang estuary and their coupling were important driving forces of summer hypoxia. The continuous supply of nutrients affected by the interaction of the plume front extension of the Changjiang Diluted Water (CDW) and upwelling and the favorable light conditions were important mechanisms causing the phytoplankton blooms and benthic hypoxia off the Changjiang estuary in summer. By analyzing oxygen utilization, organic carbon mineralization, and nutrient regeneration in the hypoxic zone, we observed that the significant oxygen utilization process off the Changjiang estuary in summer also mainly occurred near the steep slopes with front and upwelling features and confirmed the apparent nutrient loss in the benthic hypoxic zone. Meanwhile, our analysis revealed that the sediment resuspension in the benthic boundary layer in the mud areas off the Changjiang estuary could also affect the oxygen utilization and mineralization of organic carbon and nutrient recycling and regeneration. This study also demonstrated that the steep terrain off the Changjiang estuary was the main location for summer acidification, and the coupling between the plume front and upwelling on the steep slopes was an important physical driving force inducing summer benthic acidification. Finally, we discussed issues to address in future studies of the hypoxic zone and water acidification off the Changjiang estuary.

Continue reading ‘Mechanisms leading to the frequent occurrences of hypoxia and a preliminary analysis of the associated acidification off the Changjiang estuary in summer’

Species-specific responses to ocean acidification should account for local adaptation and adaptive plasticity

Global stressors, such as ocean acidification, constitute a rapidly emerging and significant problem for marine organisms, ecosystem functioning and services. The coastal ecosystems of the Humboldt Current System (HCS) off Chile harbour a broad physical–chemical latitudinal and temporal gradient with considerable patchiness in local oceanographic conditions. This heterogeneity may, in turn, modulate the specific tolerances of organisms to climate stress in species with populations distributed along this environmental gradient. Negative response ratios are observed in species models (mussels, gastropods and planktonic copepods) exposed to changes in the partial pressure of CO2 (pCO2) far from the average and extreme pCO2 levels experienced in their native habitats. This variability in response between populations reveals the potential role of local adaptation and/or adaptive phenotypic plasticity in increasing resilience of species to environmental change. The growing use of standard ocean acidification scenarios and treatment levels in experimental protocols brings with it a danger that inter-population differences are confounded by the varying environmental conditions naturally experienced by different populations. Here, we propose the use of a simple index taking into account the natural pCO2 variability, for a better interpretation of the potential consequences of ocean acidification on species inhabiting variable coastal ecosystems. Using scenarios that take into account the natural variability will allow  understanding of the limits to plasticity across organismal traits, populations and species.

Continue reading ‘Species-specific responses to ocean acidification should account for local adaptation and adaptive plasticity’

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Ocean acidification in the IPCC AR5 WG II

OUP book