Posts Tagged 'South Pacific'

Dimethylsulfoniopropionate (DMSP) and dimethyl sulfide (DMS) dynamics in the surface ocean

Dimethyl sulfide (DMS) is a trace gas produced in the ocean that plays an important role in climate and contributes to the Earths energy balance. DMS is a product of the enzymatic cleavage of dimethyl sulfoniopropionate (DMSP), which is produced by certain phytoplankton species and bacteria. Processes within the DMS/P cycles in the surface ocean are complex and vary with time and space. In the sea surface microlayer (SML), which is the interface between the ocean and the atmosphere, DMS concentration may be altered relative to subsurface water (SSW), by elevated biological activity, light intensity, and gas exchange. The aim of this thesis is to determine the importance of the SML in DMS/P dynamics and air-sea exchange by developing a more robust technique for SML sampling to better understand the dynamics of DMSP and DMS, and comparing their dynamics in the SML and SSW in coastal waters and the open ocean. In addition, the impact of warming and ocean acidification on DMS/P dynamics is investigated to determine how they will be impacted by future climate change.

To characterize DMS dynamics in the SML, a more effective method for sampling trace gases in the SML was developed (Chapter 2). The method is reliant on diffusion through a gas-permeable tube due to the concentration gradient. The floating tube was tested and calibrated under semi-controlled conditions using coastal water, where its reproducibility, accuracy and effectiveness were established. The potential benefits of this new technique for sampling trace gases in the SML include reduced loss of DMS to air. The higher reproducibility and accuracy compared to other techniques confirmed the potential of the floating tube technique for trace gas measurement in the SML.

The method developed in Chapter 2 was applied in sampling of DMS in the SML along a coastal-open ocean gradient (Chapter 3), and in various water masses of the open ocean (Chapter 4). In both chapters, DMSP and DMS dynamics were related to biological, biogeochemical, and physical properties of the SML and SSW. Sampling was conducted over 3 months at three different stations with different degrees of coastal and open water influence around Wellington, New Zealand in Chapter 3. DMSP was significantly enriched in the SML in most sampling events and DMSP and DMS enrichments were influenced by biological production and bacterial consumption. Overall, there was no temporal trends or coastal-offshore gradient in DMS or related biogeochemical variables in the SML. However, DMS concentration, and also DMS to DMSP ratio, were significantly correlated with solar radiation indicating a role for light as a determinant of DMSP and DMS in the SML. In open ocean waters around the Chatham Rise, east of New Zealand, the SML and SSW in water masses of different phytoplankton composition and biomass were sampled (Chapter 4). There was no chlorophyll a enrichment in the SML, and bacterial and DMSP enrichment were only apparent at one station, despite sampling within a phytoplankton bloom. Furthermore, there were no relationships between DMSP and phytoplankton biomass or community composition in the SML, although DMSP was negatively correlated with PAR. DMS was only significantly enriched in the SML at one station. DMS and DMSP concentrations were correlated in both SML and SSW, with the differing slopes attributed to DMS loss in the SML. Daily deck incubations were carried out to quantify DMSP and DMS processes in the SML, including the net effect of light on DMS/P, bacterial consumption of DMS/P and DMS production, and DMS air-sea flux. Air-sea flux was the main pathway with a DMS flux of 1.0-11.0 µmol m-2 d-1 that concurs with climatological predictions for the region. Excluding air-sea emission, biological DMS production was the dominant process in the SML relative to biological consumption and the net effect of light. SML DMS yield was not significantly different to that in the SSW, and consequently processes within the SML do not significantly affect regional DMS emissions.

The impact of ocean acidification and warming on DMSP and DMS concentrations was established for New Zealand coastal waters. Four mesocosm experiments, in which temperature and pH were manipulated to values projected for the years 2100 and 2150, were carried out over three years with the initial phytoplankton community differing in composition and bloom status (Chapter 6:). Temporal changes in DMSP and DMS were established and linked to changes in community composition and biogeochemistry. Results indicate that future warming may have greater influence on DMS production than ocean acidification. The observed reduction in DMSP at warmer temperatures was associated with changes in phytoplankton community, and in particular with a decrease in small flagellates. As nutrient availability also influenced the response this should also be considered in models of future DMS. Although DMS concentration decreased under future conditions of ocean acidification and higher temperature, this decrease was not as significant as reported by other studies.

The results in this thesis contribute to a better understanding of DMSP and DMS dynamics in the surface ocean. The floating tube method developed to sample DMS in the SML, will permit the study of DMS in the SML in various oceanic regions with improved accuracy. This technique may also have potential for measuring other trace gases in the SML. Application of this technique in coastal and open ocean waters demonstrated differences in DMS dynamics in the SML between these regions. DMS enrichment in the SML was rarely found, and DMS enrichment does not affect DMS air-sea flux significantly. Biological and biogeochemical variables and DMS/P process rates need to be established to further understanding of DMS/P dynamics in the SML and near surface water. Finally, results suggest that impacts of future climate change on DMS emissions may not be as significant as reported elsewhere, but that phytoplankton community composition plays a role and must be considered in future scenario models to better predict future DMS emissions. 

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Effect of low pH on growth and shell mechanical properties of the Peruvian scallop Argopecten purpuratus (Lamarck, 1819)

Highlights

  • Argopecten purpuratus shell growth was reduced by 9% in low pH exposure.
  • A. purpuratus net calcification was reduced about 10% in low pH exposure.
  • Shell microhardness of A. purpuratus was positively affected by low pH.

Abstract

Dissolution of anthropogenic CO2 modifies seawater pH, leading to ocean acidification, which might affect calcifying organisms such as bivalve mollusks. Along the Peruvian coast, however, natural conditions of low pH (7.6–8.0) are encountered in the habitat of the Peruvian scallop (Argopecten purpuratus), as a consequence of the nearby coastal upwelling influence. To understand the effects of low pH in a species adapted to these environmental conditions, an experiment was performed to test its consequences on growth, calcification, dissolution, and shell mechanical properties in juvenile Peruvian scallops. During 28 days, scallops (initial mean height = 14 mm) were exposed to two contrasted pH conditions: a control with unmanipulated seawater presenting pH conditions similar to those found in situ (pHT = 7.8) and a treatment, in which CO2 was injected to reduce pH to 7.4. At the end of the experiment, shell height and weight, and growth and calcification rates were reduced about 6%, 20%, 9%, and 10% respectively in the low pH treatment. Mechanical properties, such as microhardness were positively affected in the low pH condition and crushing force did not show differences between pH treatments. Final soft tissue weights were not significantly affected by low pH. This study provides evidence of low pH change shell properties increasing the shell microhardness in Peruvian scallops, which implies protective functions. However, the mechanisms behind this response need to be studied in a global change context.

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Ocean futures for the world’s largest yellowfin tuna population under the combined effects of ocean warming and acidification

The impacts of climate change are expected to have profound effects on the fisheries of the Pacific Ocean, including its tuna fisheries, the largest globally. This study examined the combined effects of climate change on the yellowfin tuna population using the ecosystem model SEAPODYM. Yellowfin tuna fisheries in the Pacific contribute significantly to the economies and food security of Pacific Island Countries and Territories and Oceania. We use an ensemble of earth climate models to project yellowfin populations under a high greenhouse gas emissions (IPCC RCP8.5) scenario, which includes, the combined effects of a warming ocean, increasing acidification and changing ocean chemistry. Our results suggest that the acidification impact will be smaller in comparison to the ocean warming impact, even in the most extreme ensemble member scenario explored, but will have additional influences on yellowfin tuna population dynamics. An eastward shift in the distribution of yellowfin tuna was observed in the projections in the model ensemble in the absence of explicitly accounting for changes in acidification. The extent of this shift did not substantially differ when the three-acidification induced larval mortality scenarios were included in the ensemble; however, acidification was projected to weaken the magnitude of the increase in abundance in the eastern Pacific. Together with intensive fishing, these potential changes are likely to challenge the global fishing industry as well as the economies and food systems of many small Pacific Island Countries and Territories. The modelling framework applied in this study provides a tool for evaluating such effects and informing policy development.

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Climate vulnerability assessment of key fishery resources in the Northern Humboldt Current System

The Northern Humboldt Current System sustains one of the most productive fisheries in the world. However, climate change is anticipated to negatively affect fish production in this region over the next few decades, and detailed analyses for many fishery resources are unavailable. We implemented a trait-based Climate Vulnerability Assessment based on expert elicitation to estimate the relative vulnerability of 28 fishery resources (benthic, demersal, and pelagic) to the impacts of climate change by 2055; ten exposure factors (e.g., temperature, salinity, pH, chlorophyll) and 13 sensitivity attributes (biological and population-level traits) were used. Nearly 36% of the species assessed had “high” or “very high” vulnerability. Benthic species were ranked the most vulnerable (gastropod and bivalve species). The pelagic group was the second most vulnerable; the Pacific chub mackerel and the yellowfin tuna were amongst the most vulnerable pelagic species. The demersal group had the relatively lowest vulnerability. This study allowed identification of vulnerable fishery resources, research and monitoring priorities, and identification of the key exposure factors and sensitivity attributes which are driving that vulnerability. Our findings can help fishery managers incorporate climate change into harvest level and allocation decisions, and assist stakeholders plan for and adapt to a changing future.

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The Patagonian fisheries over time: facts and lessons to be learned to face global change

Environmental and anthropic stressors have triggered unprecedented effects on the marine ecosystem. The global increase of marine temperature and acidification caused changes in fish availability and thus catches worldwide. Fostered by a legal framework favoring the investment in extractive capacity, industrial fishing in Atlantic Patagonia grew markedly since the 1960s, leading to the overexploitation of certain stocks. Nowadays, the regulatory system of individual transferable quotas is enforced for hake, but most resources in Patagonia continue being managed under an olympic system lacking planning for sustainability. We analyzed the vulnerability of the Patagonian fisheries to environmental (water temperature and acidification) and human stressors (overexploitation and market forces) in terms of their exposure, sensitivity, and adaptive capacity. Most of the Patagonian fisheries have operated in a scenario of low exposure to climate change. The shellfisheries, however, exhibited the highest sensitivity, as well as the lowest adaptive capacity, to acidification. Regarding the anthropic stressors, both the king crab and shrimp fisheries scored highly sensitive to overexploitation and market forces. Finally, the fisheries targeting the king crab and the Bonaerense demersal fish assemblage evidenced the lowest adaptive capacity against market forces. We propose management options for each case within the context of the Ecosystem Approach to Fisheries.

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Global predictions of coral reef dissolution in the Anthropocene

Arising from K. Davis et al. Communications Earth & Environment https://doi.org/10.1038/s43247-021-00168-w (2021)

Coral reef frameworks are constructed by calcifying organisms and are highly sensitive to ocean acidification. Shifting baselines in seawater chemistry have already had measurable impacts on net ecosystem calcification (Gnet) on coral reefs1, and projections of ocean acidification portray a poor future for reefs in the Anthropocene2. While experimental approaches have revealed much about this trajectory, we lack a clear understanding of: i) the drivers and predictors of net calcification at ecosystem scales, and ii) accurate predictions of when ecosystem calcification will reach net dissolution in the 21st century.

Through a meta-analysis approach, the recent study in Communications Earth & Environment by Davis et al.3 provides important insights into ecosystem-scale calcification on coral reefs. Based upon 53 publications spanning 36 coral reef sites around the world, the study provides a more nuanced understanding of the global drivers of Gnet. Cover of reef calcifiers (predominantly corals) and depth are key predictors of global ecosystem calcification, with evidence of seasonality and wave action as additional factors influencing Gnet3. The meta-analysis outlines important knowledge gaps and research needs and highlights the limited data available for assessing changes in ecosystem calcification at the same reefs through time.

Under future projections, ocean acidification is expected to shift coral reefs from a state of net calcification to net dissolution through reductions in pH and aragonite saturation states (Ωa)4,5. The exact timing of this is unclear, in part due to methodological differences, but estimates of when coral reefs will cross a tipping point to net dissolution vary substantially from 2031 to 20826, 20707, and 2060 to 20804. Through the compilation of Gnet from a subset of sites with repeated measurements (6 of the 36 available coral reefs; n = 29 of the available 116 surveys), Davis et al.3 extrapolate linear predictions of Gnet decline (1975–2017) to conclude that average global net-zero calcification will occur around the year 2054, based on a decline in Gnet of 4.3 ± 1.9% yr−1.

Extrapolating estimates of Gnet into the 21st century based upon the available historical data is complex. We identify four issues with this approach:

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A seamless ensemble-based reconstruction of surface ocean pCO2 and air–sea CO2 fluxes over the global coastal and open oceans

We have estimated global air–sea CO2 fluxes (fgCO2) from the open ocean to coastal seas. Fluxes and associated uncertainty are computed from an ensemble-based reconstruction of CO2 sea surface partial pressure (pCO2) maps trained with gridded data from the Surface Ocean CO2 Atlas v2020 database. The ensemble mean (which is the best estimate provided by the approach) fits independent data well, and a broad agreement between the spatial distribution of model–data differences and the ensemble standard deviation (which is our model uncertainty estimate) is seen. Ensemble-based uncertainty estimates are denoted by ±1σ. The space–time-varying uncertainty fields identify oceanic regions where improvements in data reconstruction and extensions of the observational network are needed. Poor reconstructions of pCO2 are primarily found over the coasts and/or in regions with sparse observations, while fgCO2 estimates with the largest uncertainty are observed over the open Southern Ocean (44 S southward), the subpolar regions, the Indian Ocean gyre, and upwelling systems.

Our estimate of the global net sink for the period 1985–2019 is 1.643±0.125 PgC yr−1 including 0.150±0.010 PgC yr−1 for the coastal net sink. Among the ocean basins, the Subtropical Pacific (18–49 N) and the Subpolar Atlantic (49–76 N) appear to be the strongest CO2 sinks for the open ocean and the coastal ocean, respectively. Based on mean flux density per unit area, the most intense CO2 drawdown is, however, observed over the Arctic (76 N poleward) followed by the Subpolar Atlantic and Subtropical Pacific for both open-ocean and coastal sectors. Reconstruction results also show significant changes in the global annual integral of all open- and coastal-ocean CO2 fluxes with a growth rate of  PgC yr−2 and a temporal standard deviation of 0.526±0.022 PgC yr−1 over the 35-year period. The link between the large interannual to multi-year variations of the global net sink and the El Niño–Southern Oscillation climate variability is reconfirmed.

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Responses of a natural phytoplankton community from the Drake Passage to two predicted climate change scenarios

Contrasting models predict two different climate change scenarios for the Southern Ocean (SO), forecasting either less or stronger vertical mixing of the water column. To investigate the responses of SO phytoplankton to these future conditions, we sampled a natural diatom dominated (63%) community from today’s relatively moderately mixed Drake Passage waters with both low availabilities of iron (Fe) and light. The phytoplankton community was then incubated at these ambient open ocean conditions (low Fe and low light, moderate mixing treatment), representing a control treatment. In addition, the phytoplankton was grown under two future mixing scenarios based on current climate model predictions. Mixing was simulated by changes in light and Fe availabilities. The two future scenarios consisted of a low mixing scenario (low Fe and higher light) and a strong mixing scenario (high Fe and low light). In addition, communities of each mixing scenario were exposed to ambient and low pH, the latter simulating ocean acidification (OA). The effects of the scenarios on particulate organic carbon (POC) production, trace metal to carbon ratios, photophysiology and the relative numerical contribution of diatoms and nanoflagellates were assessed. During the first growth phase, at ambient pH both future mixing scenarios promoted the numerical abundance of diatoms (∼75%) relative to nanoflagellates. This positive effect, however, vanished in response to OA in the communities of both future mixing scenarios (∼65%), with different effects for their productivity. At the end of the experiment, diatoms remained numerically the most abundant phytoplankton group across all treatments (∼80%). In addition, POC production was increased in the two future mixing scenarios under OA. Overall, this study suggests a continued numerical dominance of diatoms as well as higher carbon fixation in response to both future mixing scenarios under OA, irrespective of different changes in light and Fe availability.

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Heterogeneous environmental seascape across a biogeographic break influences the thermal physiology and tolerances to ocean acidification in an ecosystem engineer

Aim

Understanding how spatio-temporal environmental variability influences stress tolerance, local adaptation and phenotypic variation among populations is a key challenge for evolutionary ecology and climate change biology. Coastal biogeographic breaks are natural laboratories to explore this fundamental research question due to the contrasting environmental conditions experienced by natural populations across these regions.

Location

In the South East Pacific (SEP) coast, a major break (30º-32ºS) is characterized by extreme natural variability in sea surface temperature (SST) and carbonate chemistry parameters related to temporal and spatial dynamics in upwelling events. Calcifying organisms inhibiting this zone are exposed to marked fluctuations and clines in SST that together with naturally acidified waters can impact their metabolism, calcification and fitness, making them particularly prone to the effects of climate change (e.g. ocean acidification, OA). We investigated to what extent the spatial and temporal environmental variability (in SST and seawater carbonate conditions) that characterizes the biogeographic break in the SEP influences intra-specific differences in the thermal ecology and the tolerances to OA of the limpet Scurria araucana.

Methods

During two years, we conducted field surveys of limpet populations at sites across the SEP break (27ºS, 30ºS and 32ºS). We collected individuals from each population to test for geographic differences in morphometric (e.g. total buoyancy weight, shell length) and physiological (e.g. oxygen consumption rate, cardiac activity and thermal performance curves; TPC) responses to local environmental conditions (Tº and pH/pCO2) and to simulated OA scenarios.

Results

Populations of SAraucana exhibit high tolerance to OA with no signal of geographic influence on this attribute. However, inter-population differences in thermal physiology (metabolic rates and performances) were found across the biogeographic break in the SEP coast. Limpets from the central part of the break (30ºS) exhibit higher thermal performance compared to limpets from populations at both sides of the break.

Main conclusions

Variation in SST has a greater effect shaping inter-population differences in thermal physiology of the limpet Saraucana. These physiological differences are aligned the thermal heterogenous seascape along the biogeographic break in the SEP. Contrarily, temporal and spatial variation in seawater carbonate conditions does not influence inter-population differences in phenotypic response populations, but an overall high tolerance to OA.

Continue reading ‘Heterogeneous environmental seascape across a biogeographic break influences the thermal physiology and tolerances to ocean acidification in an ecosystem engineer’

The Ostrea chilensis pallial cavity: nursery, prison, and time machine

Brooding in bivalves is a reproductive strategy that benefits larvae by protecting them from predators and adverse ambient conditions. Recent studies on brooding oysters (Ostrea spp.) have shown, however, that chemical conditions in the pallial cavity, in which the brood is held, rapidly decline soon after valve closure, representing an inescapable prison for larvae. Conditions in the pallial cavity among open, ventilating females are less well understood. This study examined how conditions in the pallial cavities of non-brooding O. chilensis females respond to prevailing environmental conditions and female valve gaping and respiration. Two separate microsensors (O2 and pH) were placed in the pallial cavities of 12 non-brooding females while valve gapes were recorded. The experiments were carried out in December 2019 using oysters collected from the Quempillén estuary in southern Chile (41° 52ʹ S, 73° 46ʹ W). As in previous studies, pallial cavity conditions were influenced by ambient O2, pH, and temperature. There were clear, quantifiable relationships between valve movement, respiration, and pallial cavity pH. Even among ventilating oysters, the pallial cavities can acidify the fluid bathing larvae. Thus, there is the potential for larvae in brooding females to be exposed to carbonate conditions predicted for the future—hence a time machine. These data suggest that brooding can apply evolutionary pressure on larvae to develop traits that help them cope with conditions in the pallial cavity, which may also be exapted to confer fitness under ocean acidification.

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Temporal dynamics of surface ocean carbonate chemistry in response to natural and simulated upwelling events during the 2017 coastal El Niño near Callao, Peru

Oxygen minimum zones (OMZs) are characterized by enhanced carbon dioxide (CO2) levels and low pH and are being further acidified by uptake of anthropogenic atmospheric CO2. With ongoing intensification and expansion of OMZs due to global warming, carbonate chemistry conditions may become more variable and extreme, particularly in the eastern boundary upwelling systems. In austral summer (February–April) 2017, a large-scale mesocosm experiment was conducted in the coastal upwelling area off Callao (Peru) to investigate the impacts of ongoing ocean deoxygenation on biogeochemical processes, coinciding with a rare coastal El Niño event. Here we report on the temporal dynamics of carbonate chemistry in the mesocosms and surrounding Pacific waters over a continuous period of 50 d with high-temporal-resolution observations (every second day). The mesocosm experiment simulated an upwelling event in the mesocosms by addition of nitrogen (N)-deficient and CO2-enriched OMZ water. Surface water in the mesocosms was acidified by the OMZ water addition, with pHT lowered by 0.1–0.2 and pCO2 elevated to above 900 µatm. Thereafter, surface pCO2 quickly dropped to near or below the atmospheric level (405.22 µatm in 2017; Dlugokencky and Tans, 2021; NOAA/Global Monitoring Laboratory (GML)) mainly due to enhanced phytoplankton production with rapid CO2 consumption. Further observations revealed that the dominance of the dinoflagellate Akashiwo sanguinea and contamination of bird excrements played important roles in the dynamics of carbonate chemistry in the mesocosms. Compared to the simulated upwelling, natural upwelling events in the surrounding Pacific waters occurred more frequently with sea-to-air CO2 fluxes of 4.2–14.0 mmol C m−2 d−1. The positive CO2 fluxes indicated our site was a local CO2 source during our study, which may have been impacted by the coastal El Niño. However, our observations of dissolved inorganic carbon (DIC) drawdown in the mesocosms suggest that CO2 fluxes to the atmosphere can be largely dampened by biological processes. Overall, our study characterized carbonate chemistry in nearshore Pacific waters that are rarely sampled in such a temporal resolution and hence provided unique insights into the CO2 dynamics during a rare coastal El Niño event.

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Upper environmental pCO2 drives sensitivity to ocean acidification in marine invertebrates

Minimizing the impact of ocean acidification requires an understanding of species responses and environmental variability of population habitats. Whereas the literature is growing rapidly, emerging results suggest unresolved species- or population-specific responses. Here we present a meta-analysis synthesizing experimental studies examining the effects of pCO2 on biological traits in marine invertebrates. At the sampling locations of experimental animals, we determined environmental pCO2 conditions by integrating data from global databases and pCO2 measurements from buoys. Experimental pCO2 scenarios were compared with upper pCO2 using an index considering the upper environmental pCO2. For most taxa, a statistically significant negative linear relationship was observed between this index and mean biological responses, indicating that the impact of a given experimental pCO2 scenario depends on the deviation from the upper pCO2 level experienced by local populations. Our results highlight the importance of local biological adaptation and the need to consider present pCO2 natural variability while interpreting experimental results.

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Biomechanical characterization of scallop shells exposed to ocean acidification and warming

Increased carbon dioxide levels (CO2) in the atmosphere triggered a cascade of physical and chemical changes in the ocean surface. Marine organisms producing carbonate shells are regarded as vulnerable to these physical (warming), and chemical (acidification) changes occurring in the oceans. In the last decade, the aquaculture production of the bivalve scallop Argopecten purpuratus (AP) showed declined trends along the Chilean coast. These negative trends have been ascribed to ecophysiological and biomineralization constraints in shell carbonate production. This work experimentally characterizes the biomechanical response of AP scallop shells subjected to climate change scenarios (acidification and warming) via quasi-static tensile and bending tests. The experimental results indicate the adaptation of mechanical properties to hostile growth scenarios in terms of temperature and water acidification. In addition, the mechanical response of the AP subjected to control climate conditions was analyzed with finite element simulations including an anisotropic elastic constitutive model for a two-fold purpose: Firstly, to calibrate the material model parameters using the tensile test curves in two mutually perpendicular directions (representative of the mechanical behavior of the material). Secondly, to validate this characterization procedure in predicting the material’s behavior in two mechanical tests.

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Microbial alkalinity production and silicate alteration in methane charged marine sediments: implications for porewater chemistry and diagenetic carbonate formation

A numerical reaction-transport model was developed to simulate the effects of microbial activity and mineral reactions on the composition of porewater in a 230-m-thick Pleistocene interval drilled in the Peru-Chile Trench (Ocean Drilling Program, Site 1230). This site has porewater profiles similar to those along many continental margins, where intense methanogenesis occurs and alkalinity surpasses 100 mmol/L. Simulations show that microbial sulphate reduction, anaerobic oxidation of methane, and ammonium release from organic matter degradation only account for parts of total alkalinity, and excess CO2 produced during methanogenesis leads to acidification of porewater. Additional alkalinity is produced by slow alteration of primary aluminosilicate minerals to kaolinite and SiO2. Overall, alkalinity production in the methanogenic zone is sufficient to prevent dissolution of carbonate minerals; indeed, it contributes to the formation of cemented carbonate layers at a supersaturation front near the sulphate-methane transition zone. Within the methanogenic zone, carbonate formation is largely inhibited by cation diffusion but occurs rapidly if cations are transported into the zone via fluid conduits, such as faults. The simulation presented here provides fundamental insight into the diagenetic effects of the deep biosphere and may also be applicable for the long-term prediction of the stability and safety of deep CO2 storage reservoirs.

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In situ skeletal growth rates of the solitary cold-water coral Tethocyathus endesa from the Chilean Fjord region

Cold-water corals (CWC) can be found throughout a wide range of latitudes (79°N–78°S). Since they lack the photosymbiosis known for most of their tropical counterparts, they may thrive below the euphotic zone. Consequently, their growth predominantly depends on the prevalent environmental conditions, such as general food availability, seawater chemistry, currents, and temperature. Most CWC communities live in regions that will face CaCO3 undersaturation by the end of the century and are thus predicted to be threatened by ocean acidification (OA). This scenario is especially true for species inhabiting the Chilean fjord system, where present-day carbonate water chemistry already reaches values predicted for the end of the century. To understand the effect of the prevailing environmental conditions on the biomineralization of the CWC Tethocyathus endesa, a solitary scleractinian widely distributed in the Chilean Comau Fjord, a 12-month in situ experiment was conducted. The in situ skeletal growth of the test corals was assessed at two sites using the buoyant weight method. Sites were chosen to cover the naturally present carbonate chemistry gradient, with pH levels ranging between 7.90 ± 0.01 (mean ± SD) and 7.70 ± 0.02, and an aragonite saturation (Ωarag) between 1.47 ± 0.03 and 0.98 ± 0.05. The findings of this study provide one of the first in situ growth assessments of a solitary CWC species, with a skeletal mass increase of 46 ± 28 mg per year and individual, at a rate of 0.03 ± 0.02% day. They also indicate that, although the local seawater chemistry can be assumed to be unfavorable for calcification, growth rates of T. endesa are comparable to other cold-water scleractinians in less corrosive waters (e.g., Lophelia pertusa in the Mediterranean Sea).

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Climate change, marine resources and a small Chilean community: making the connections

Climate change is affecting large-scale oceanic processes. How and when these changes will impact those reliant on marine resources is not yet clear. Here we use end-to-end modeling to track the impacts of expected changes through the marine ecosystem on a specific, small community: Cochamó, in the Gulf of Ancud wider area, Chile. This area is important for Chilean fisheries and aquaculture, with Cochamó reliant on both lower and upper trophic level marine resources. We applied the GOTM-ERSEM-BFM coupled hydro-biogeochemical water-column model to gauge lower-trophic level marine ecological community response to bottom-up stressors (climate change, ocean acidification), coupled to an existing Ecopath with Ecosim model for the area, which included top-down stressors (fishing). Social scientists also used participatory modeling (Systems Thinking and Bayesian Belief Networking) to identify key resources for Cochamó residents and to assess the community’s vulnerability to possible changes in key resources. Modeling results suggest that flagellate phytoplankton abundance will increase at the cost of other species (particularly diatoms), resulting in a greater risk of harmful algae blooms. Both climate change and acidification slightly increased primary production in the model. Higher trophic level results indicate that some targeted pelagic resources will decline (while benthic ones may benefit), but that these effects might be mitigated by strong fisheries management efforts. Participatory modeling suggests that Cochamó inhabitants anticipate marine ecosystem changes but are divided about possible adaptation strategies. For climate change impact quantification, detailed experimental studies are recommended based on the dominant threats identified here, with specific local species.

Continue reading ‘Climate change, marine resources and a small Chilean community: making the connections’

The carbon and nitrogen budget of Desmophyllum dianthus—a voracious cold-water coral thriving in an acidified Patagonian fjord


In the North Patagonian fjord region, the cold-water coral (CWC) Desmophyllum dianthus occurs in high densities, in spite of low pH and aragonite saturation. If and how these conditions affect the energy demand of the corals is so far unknown. In a laboratory experiment, we investigated the carbon and nitrogen (C, N) budget of D. dianthus from Comau Fjord under three feeding scenarios: (1) live fjord zooplankton (100–2,300 µm), (2) live fjord zooplankton plus krill (>7 mm), and (3) four-day food deprivation. In closed incubations, C and N budgets were derived from the difference between C and N uptake during feeding and subsequent C and N loss through respiration, ammonium excretion, release of particulate organic carbon and nitrogen (POC, PON). Additional feeding with krill significantly increased coral respiration (35%), excretion (131%), and POC release (67%) compared to feeding on zooplankton only. Nevertheless, the higher C and N losses were overcompensated by the threefold higher C and N uptake, indicating a high assimilation and growth efficiency for the krill plus zooplankton diet. In contrast, short food deprivation caused a substantial reduction in respiration (59%), excretion (54%), release of POC (73%) and PON (87%) compared to feeding on zooplankton, suggesting a high potential to acclimatize to food scarcity (e.g., in winter). Notwithstanding, unfed corals ‘lost’ 2% of their tissue-C and 1.2% of their tissue-N per day in terms of metabolism and released particulate organic matter (likely mucus). To balance the C (N) losses, each D. dianthus polyp has to consume around 700 (400) zooplankters per day. The capture of a single, large krill individual, however, provides enough C and N to compensate daily C and N losses and grow tissue reserves, suggesting that krill plays an important nutritional role for the fjord corals. Efficient krill and zooplankton capture, as well as dietary and metabolic flexibility, may enable D. dianthus to thrive under adverse environmental conditions in its fjord habitat; however, it is not known how combined anthropogenic warming, acidification and eutrophication jeopardize the energy balance of this important habitat-building species.

Continue reading ‘The carbon and nitrogen budget of Desmophyllum dianthus—a voracious cold-water coral thriving in an acidified Patagonian fjord’

Biogeochemical feedbacks to ocean acidification in a cohesive photosynthetic sediment

Ecosystem feedbacks in response to ocean acidification can amplify or diminish diel pH oscillations in productive coastal waters. Benthic microalgae generate such oscillations in sediment porewater and here we ask how CO2 enrichment (acidification) of the overlying seawater alters these in the absence and presence of biogenic calcite. We placed a 1-mm layer of ground oyster shells, mimicking the arrival of dead calcifying biota (+Calcite), or sand (Control) onto intact silt sediment cores, and then gradually increased the pCO2 in the seawater above half of +Calcite and Control cores from 472 to 1216 μatm (pH 8.0 to 7.6, CO2:HCO3 from 4.8 to 9.6 × 10−4). Porewater [O2] and [H+] microprofiles measured 16 d later showed that this enrichment had decreased the O2 penetration depth (O2-pd) in +Calcite and Control, indicating a metabolic response. In CO2-enriched seawater: (1) sediment biogeochemical processes respectively added and removed more H+ to and from the sediment porewater in darkness and light, than in ambient seawater increasing the amplitude of the diel porewater [H+] oscillations, and (2) in darkness, calcite dissolution in +Calcite sediment decreased the porewater [H+] below that in overlying seawater, reversing the sediment–seawater H+ flux and decreasing the amplitude of diel [H+] oscillations. This dissolution did not, however, counter the negative effect of CO2 enrichment on O2-pd. We now hypothesise that feedback to CO2 enrichment—an increase in the microbial reoxidation of reduced solutes with O2—decreased the sediment O2-pd and contributed to the enhanced porewater acidification.

Continue reading ‘Biogeochemical feedbacks to ocean acidification in a cohesive photosynthetic sediment’

Characterisation of pH variations along the Ba River in Fiji utilising the GEF R2R framework during the 2019 sugarcane season

Within Pacific Small Island Developing States (Pacific SIDS), the ridge-to-reef (R2R) approach has emerged as a framework for monitoring river connectivity between terrestrial and marine ecosystems. The study measured water quality, including pH, over 88.40 km of the Ba River in Fiji. The sampling design focused on measuring spatio-temporal variability in pH throughout the sugarcane season with three rapid sampling periods (RSP1, 2 & 3) along the Ba River, together with continuous measurement of temperature and pH using stationary data loggers at two locations upstream and downstream of the sugar mill. Spatial variability in pH and water quality was characterised before (RSP1 and RSP2) and during (RSP3) the sugarcane season. Mean pH measured before the sugarcane crushing season for RSP1 and RSP2 were 8.16 (± 0.49) and 8.20 (± 0.61) respectively. During the sugarcane crushing season (RSP3), mean pH declined by 3.06 units to 6.94 within 42 m downstream of the sugar mill (P ≤ 0.001). The 3.06 unit decline in pH for RSP3 exceeded both the mean diurnal variation in pH of 0.39 and mean seasonal variation in pH of 2.01. This decline in pH could be a potential source of acidification to downstream coastal ecosystems with implications for coral reefs, biodiversity and fishery livelihoods.

Continue reading ‘Characterisation of pH variations along the Ba River in Fiji utilising the GEF R2R framework during the 2019 sugarcane season’

Morphological, physiological and behavioral responses of an intertidal snail, Acanthina monodon (Pallas), to projected ocean acidification and cooling water conditions in upwelling ecosystems

Highlights

  • Ocean acidification (OA) and ocean cooling (OC) will influence upwelling systems.
  • The snail Acanthina monodon growth, feeding and calcification rates increased with OC.
  • Metabolic rates also increased with OA but only under OC conditions.
  • Self-righting was unaltered, suggesting a complex repertoire of responses to OA and OC.

Abstract

Ocean acidification (OA) is expected to rise towards the end of the 21st century altering the life history traits in marine organisms. Upwelling systems will not escape OA, but unlike other areas of the ocean, cooling effects are expected to intensify in these systems. Regardless, studies evaluating the combined effects of OA and cooling remain scarce. We addressed this gap using a mesocosm system, where we exposed juveniles of the intertidal muricid snail Acanthina monodon to current and projected pCO2 (500 vs. 1500 ppm) and temperature (15 vs. 10 °C) from the southeast Pacific upwelling system. After 9 weeks of experimental exposure to those conditions, we conducted three estimations of growth (wet weight, shell length and shell peristomal length), in addition to measuring calcification, metabolic and feeding rates and the ability of these organisms to return to the normal upright position after being overturned (self-righting). Growth, feeding and calcification rates increased in projected cooling conditions (10 °C) but were unaffected by pCO2 or the interaction between pCO2 and temperature. Instead, metabolic rates were driven by pCO2, but a significant interaction with temperature suggests that in cooler conditions, metabolic rates will increase when associated with high pCO2 levels. Snail self-righting times were not affected across treatments. These results suggest that colder temperatures projected for this area would drive this species growth, feeding and calcification, and consequently, some of its population biology and productivity. However, the snails may need to compensate for the increase in metabolic rates under the effects of ocean acidification. Although A. monodon ability to adjust to individual or combined stressors will likely account for some of the changes described here, our results point to a complex dynamic to take place in intertidal habitats associated with upwelling systems.

Continue reading ‘Morphological, physiological and behavioral responses of an intertidal snail, Acanthina monodon (Pallas), to projected ocean acidification and cooling water conditions in upwelling ecosystems’

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