Posts Tagged 'chemistry'



Seasonal changes of trace elements, nutrients, dissolved organic matter, and coastal acidification over the largest oyster reef in the Western Mississippi Sound, USA

Seasonal changes of trace elements, nutrients, dissolved organic matter (DOM), and carbonate system parameters were evaluated over the largest deteriorating oyster reef in the Western Mississippi Sound using data collected during spring, summer, and winter of 2018, and summer of 2019. Higher concentrations of Pb (224%), Cu (211%), Zn (2400%), and Ca (240%) were observed during winter of 2018 compared to summer 2019. Phosphate and ammonia concentrations were higher (> 800%) during both summers of 2018 and 2019 than winter of 2018. Among the three distinct DOM components identified, two terrestrial humic-like components were more abundant during both spring (12% and 36%) and summer (11% and 33%) of 2018 than winter of 2018, implying a relatively lesser supply of humic-like components from terrestrial sources during winter. On the other hand, the protein-like component was more abundant during summer of 2019 compared to rest of the study period, suggesting a higher rate of autochthonous production during summer 2019. In addition, to their significant depth-wise variation, ocean acidification parameters including pH, pCO2, CO32−, and carbonate saturation states were all higher during both summers of 2018 and 2019. The measured variables such as trace elements, organic carbon, suspended particulates, and acidification parameters exhibited conservative mixing behavior against salinity. These observations have strong implications for the health of the oyster reefs, which provides ecologically important habitats and supports the economy of the Gulf Coast.

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Feedbacks of CaCO3 dissolution effect on ocean carbon sink and seawater acidification: a model study

The oceanic absorption of atmospheric CO2 acidifies seawater, which accelerates CaCO3 dissolution of calcifying organisms, a process termed dissolution effect. Promoted CaCO3 dissolution increases seawater ALK (alkalinity), enhancing ocean carbon sink and mitigating ocean acidification. We incorporate different parameterizations of the link between CaCO3 dissolution and ocean acidification into an Earth System Model, to quantify the feedback of the dissolution effect on the global carbon cycle. Under SRES A2 CO2 emission scenario and its extension with emissions of 5,000 PgC in ~400 years, in the absence of the dissolution effect, accumulated ocean CO2 uptake between year 1800 and 3500 is 2,041 PgC. The consideration of the dissolution effect increases ocean carbon sink by 195–858 PgC (10–42%), and mitigates the decrease in surface pH by 0.04–0.17 (a decrease of 10–48% in [H+] (hydrogen ion concentration)), depending on the prescribed parameterization scheme. In the epipelagic zone, relative to the Arc-Atlantic Ocean, the Pacific-Indian Ocean experiences greater acidification, leading to greater dissolution effects and the resultant stronger feedbacks on ocean carbon sink and acidification in the Pacific-Indian Ocean. Noteworthy, the feedback of dissolution effect on ocean carbon sink can be comparable with or stronger than the feedback from CO2-induced radiative warming. Our study highlights the potentially critical role played by CaCO3 dissolution effect in the ocean carbon sink, global carbon cycle and climate system.

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Carbonate system data tracing freshwater inflow into the Ross Sea through the eastern gate and along the Ross Ice Shelf (Antarctica)

The eastern Ross Sea is a key area to understand the role of the Amundsen Sea inflow of freshwater that can influence the Ross Sea water properties and salt budget. A survey was carried out in the eastern Ross Sea during the austral summer 2019–20 to evaluate the contribution of the Amundsen Sea Water (ASW) to the salinity variability. A total of 248 seawater samples were collected f\or the analysis of total alkalinity (AT) and pH. The data collected were used together with temperature and salinity to obtain a full description of the carbonate system properties including total inorganic carbon (CT), CO2 partial pressure (pCO2), calcium carbonate saturation state of aragonite and calcite (Ω), and Revelle factor. Moreover, we estimated the anthropogenic carbon (Cant) throughout the TrOCA method to better understand the carbon cycle, also considering the effect of atmospheric CO2 uptake on ocean acidification. We used principal component analysis (PCA) to investigate the major controls on the carbonate system parameters with the aim of defining their sensitivity as chemical tracers. The changes in carbonate chemistry in surface waters were mainly due to the physical properties. AT and pH traced the entry of the ASW showing limited mixing between water masses on the shelf area. Shelf waters were enriched in Cant, which resulted lower than the estimated value for shelf waters produced in western Ross Sea.

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Spatial variability in aerosol composition and its seawater acidification potential in coastal waters of the western coastal Bay of Bengal

Deposition of atmospheric dust is reported to acidify surface waters in the northern Bay of Bengal (BoB). To examine the spatial variability in content and composition of total suspended matter (TSP), aerosol samples were collected at four locations (Damra, Chilika, Vizag and Chennai) along the east coast of India in the marine atmospheric boundary layer (MABL) to evaluate its impact on pH of surface waters due to deposition on surface waters using microcosm experiments. The concentration of total suspended matter (TSP) and [SO42– + NO3] increased from southern (146 and 6.16 µg m–3, respectively) to northern coastal BoB (197 and 34.57 µg m–3, respectively) due to the influence of pollutants from Indo-Gangetic Plain (IGP) in the north and dominant marine sources in the southern coastal BoB. The ionic balance in aerosols suggested that acidification potential (neutralization potential) increased (decreased) from southern to northern BoB. The dissolution of aerosols in surface seawater lowered pH by 0.018 ± 0.002 to 0.135 ± 0.005 in the coastal BoB with a higher decrease in the north than south. Our study suggests that aerosol dissolution in seawater results in ocean acidification in proportion to acidic anions (e.g., SO42–, NO3). In addition, organic acids, such as carboxylic acids, aromatic (Benzoic acid) and hydroxy acids (Lactic and glycolic acids) also contribute significantly to ocean acidification and their contribution needs further evaluation.

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A baseline assessment of coastal pH variability in a temperate South African embayment: implications for biological ocean acidification research

Compared with the open ocean, knowledge of pH variability in coastal waters is rudimentary, especially in Africa. This is concerning as quantifying local pH conditions is critical when assessing the response of coastal species to future ocean acidification scenarios. The objective of this study was to capture some of the variability in pH at scales and sites relevant to coastal marine organisms in a South African temperate embayment (Algoa Bay, Indian Ocean). We used a sampling approach that captured spatial (at a resolution of ∼10 km), monthly and diel (24-hour) variability in pH and associated physical and biological parameters at offshore and shallow inshore sites in Algoa Bay. We found that pH and associated parameters (temperature, calculated pCO2, chlorophyll a) varied over space and time in Algoa Bay. The range in pH was 0.30 units at offshore sites and 0.46 at inshore sites, and the average pH was 8.10 (SD 0.06) and 8.10 (SD 0.13) at these sites, respectively, which is typical for coastal environments. Our results showed that both biological factors (at the offshore sites) and salinity (at the inshore sites) may influence temporal and spatial variability in pH. We also identified a shallow inshore site with high levels of macroalgal growth that had consistently higher average daytime pH levels (8.33 [SD 0.07]), which may serve as an ocean acidification refuge for coastal marine species. This is the first comprehensive pH-monitoring study to be implemented in a nearshore coastal area in Africa and provides recommendations for monitoring in other understudied regions.

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Assessing the influence of ocean alkalinity enhancement on a coastal phytoplankton community (update)

Ocean alkalinity enhancement (OAE) is a proposed method to counteract climate change by increasing the alkalinity of the surface ocean and thus the chemical storage capacity of seawater for atmospheric CO2. The impact of OAE on marine ecosystems, including phytoplankton communities which make up the base of the marine food web, is largely unknown. To investigate the influence of OAE on phytoplankton communities, we enclosed a natural plankton community from coastal Tasmania for 22 d in nine microcosms during a spring bloom. Microcosms were split into three groups, (1) the unperturbed control, (2) the unequilibrated treatment where alkalinity was increased (+495 ± 5.2 µmol kg−1) but seawater CO2 was not in equilibrium with atmospheric CO2, and (3) the equilibrated treatment where alkalinity was increased (+500 ± 3.2 µmol kg−1) and seawater CO2 was in equilibrium with atmospheric CO2. Both treatments have the capacity to increase the inorganic carbon sink of seawater by 21 %. We found that simulated OAE had significant but generally moderate effects on various groups in the phytoplankton community and on heterotrophic bacteria. More pronounced effects were observed for the diatom community where silicic acid drawdown and biogenic silica build-up were reduced at increased alkalinity. Observed changes in phytoplankton communities affected the temporal trends of key biogeochemical parameters such as the organic matter carbon-to-nitrogen ratio. Interestingly, the unequilibrated treatment did not have a noticeably larger impact on the phytoplankton (and heterotrophic bacteria) community than the equilibrated treatment, even though the changes in carbonate chemistry conditions were much more severe. This was particularly evident from the occurrence and peak of the phytoplankton spring bloom during the experiment, which was not noticeably different from the control. Altogether, the inadvertent effects of increased alkalinity on the coastal phytoplankton communities appear to be rather limited relative to the enormous climatic benefit of increasing the inorganic carbon sink of seawater by 21 %. We note, however, that more detailed and widespread investigations of plankton community responses to OAE are required to confirm or dismiss this first impression.

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Decoupling of estuarine hypoxia and acidification as revealed by historical water quality data

Graphical abstract.

Hypoxia and acidification are commonly coupled in eutrophic aquatic environments because aerobic respiration is usually dominant in bottom waters and can lower dissolved oxygen (DO) and pH simultaneously. However, the degree of coupling, which can be weakened by non-aerobic respiration and CaCO3 cycling, has not been adequately assessed. In this study, we applied a box model to 20 years of water quality monitoring data to explore the relationship between hypoxia and acidification along the mainstem of Chesapeake Bay. In the early summer, dissolved inorganic carbon (DIC) production in mid-bay bottom waters was dominated by aerobic respiration, contributing to DO and pH declines. In contrast, late-summer DIC production was higher than that expected from aerobic respiration, suggesting potential buffering processes, such as calcium carbonate dissolution, which would elevate pH in hypoxic waters. These findings are consistent with contrasting seasonal relationships between riverine nitrogen (N) loads and hypoxic and acidified volumes. The N loads were associated with increased hypoxic and acidified volumes in June, but only increased hypoxic volumes in August, when acidified volume declines instead. Our study reveals that the magnitude of this decoupling varies interannually with watershed nutrient inputs, which has implications for the management of co-stressors in estuarine systems.

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Observed and projected impacts of coastal warming, acidification, and deoxygenation on Pacific oyster (Crassostrea gigas) farming: a case study in the Hinase Area, Okayama Prefecture and Shizugawa Bay, Miyagi Prefecture, Japan

Coastal warming, acidification, and deoxygenation are progressing, primarily due to the increase in anthropogenic CO2. Coastal acidification has been reported to have effects that are expected to become more severe as acidification progresses, including inhibiting formation of the shells of calcifying organisms such as shellfish. However, compared to water temperature, an indicator of coastal warming, spatiotemporal variations in acidification and deoxygenation indicators such as pH, aragonite saturation state (Ωarag), and dissolved oxygen in coastal areas of Japan have not been observed and projected. Moreover, many species of shellfish are important fisheries resources, including Pacific oyster (Crassostrea gigas). Therefore, there is concern regarding the future combined impacts of coastal warming, acidification, and deoxygenation on Pacific oyster farming, necessitating evaluation of current and future impacts to facilitate mitigation measures. We deployed continuous monitoring systems for coastal warming, acidification, and deoxygenation in the Hinase area of Okayama Prefecture and Shizugawa Bay in Miyagi Prefecture, Japan. In Hinase, the Ωarag value was often lower than the critical level of acidification for Pacific oyster larvae, although no impact of acidification on larvae was identified by microscopy examination. Oyster larvae are anticipated to be affected more seriously by the combined impacts of coastal warming and acidification, with lower pH and Ωarag values and a prolonged spawning period, which may shorten the oyster shipping period and lower the quality of oysters. No significant future impact of surface-water deoxygenation on Pacific oysters was identified. To minimize the impacts of coastal warming and acidification on Pacific oyster and related local industries, cutting CO2 emissions is mandatory, but adaptation measures such as regulation of freshwater and organic matter inflow from rivers and changes in the form of oyster farming practiced locally might also be required.

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Pathfinder v1.0.1: a Bayesian-inferred simple carbon–climate model to explore climate change scenarios

The Pathfinder model was developed to fill a perceived gap within the range of existing simple climate models. Pathfinder is a compilation of existing formulations describing the climate and carbon cycle systems, chosen for their balance between mathematical simplicity and physical accuracy. The resulting model is simple enough to be used with Bayesian inference algorithms for calibration, which enables assimilation of the latest data from complex Earth system models and the IPCC sixth assessment report, as well as a yearly update based on observations of global temperature and atmospheric CO2. The model’s simplicity also enables coupling with integrated assessment models and their optimization algorithms or running the model in a backward temperature-driven fashion. In spite of this simplicity, the model accurately reproduces behaviours and results from complex models – including several uncertainty ranges – when run following standardized diagnostic experiments. Pathfinder is an open-source model, and this is its first comprehensive description.

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Shelled pteropod abundance and distribution across the Mediterranean Sea during spring

Highlights

  • First estimate of pteropod distribution across the Mediterranean Sea in spring.
  • Highest abundance recorded in the oligotrophic Eastern Mediterranean basin.
  • Temperature, aragonite saturation, oxygen and salinity main drivers of distribution.
  • Pteropods and planktic foraminifera are inversely distributed in the Med Sea.

Abstract

Thecosome pteropods are a dominant group of calcifying pelagic molluscs and an important component of the food web. In this study, we characterise spring pteropod distribution throughout the Mediterranean Sea, an understudied region for this common group of marine calcifying organisms. This semi-enclosed sea is rapidly changing under climatic and anthropogenic forcings. The presence of surface water biogeochemical gradients from the Atlantic Ocean/Gibraltar Strait to the Eastern Mediterranean Sea allowed us to investigate pteropod distribution and their ecological preferences. In the ultra-oligotrophic Eastern Mediterranean Sea, we found the mean upper 200 m pteropod standing stock of 2.13 ind. m-3 was approximately 5x greater than the Western basin (mean 0.42 ind. m-3). Where standing stocks were high, pteropods appeared largely in the same family grouping belonging to Limacinidae. Temperature, O2 concentration, salinity, and aragonite saturation (Ωar) explain 96% of the observed variations in the community structure at the time of sampling, suggesting that pteropods might show a preference for environmental conditions with a lower energetic physiological demand. We also document that pteropods and planktonic foraminifera have an opposite geographical distribution in the Mediterranean Sea. Our findings indicate that in specific pelagic ultra-oligotrophic conditions, such as the Eastern Mediterranean Sea, different feeding strategies could play an important role in regulating calcifying zooplankton distribution.

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CalcPlotAnomaly: a set of functions in MATLAB for the computation and plotting of anomalies of oceanographic and meteorological parameters

Highlights

  • An Octave-compatible MATLAB code for computing anomalies over whole time periods, months and seasons.
  • CalcPlotAnomaly functions include time series and grids in the anomaly computation.
  • The computation results can be plotted with CalcPlotAnomaly.
  • CalcPlotAnomaly is a system that can be used in decision-making to minimize the impact of natural disasters.

Abstract

CalcPlotAnomaly is a set of source code functions implemented in MATLAB and compatible with Octave, these functions are used for the computation of oceanographic (physical and biogeochemical), and meteorological parameter anomalies that are used by geoscientists and decision-makers. They use as input time-ordered data from observed data (in situ, satellite, or radar) and interannual model outputs (raw data, analysis, or reanalysis). These anomalies can be computed over the whole period, by months or seasons. Also included are functions for plotting anomalies in the form of time series.

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Ocean acidification around the UK and Ireland

KEY FACTS

What is already happening

  • Atmospheric CO2 exceeded 414 ppm in 2021 and has continued to increase by approximately 2.4 ppm per year over the last decade. The global ocean absorbs approximately a quarter of anthropogenic carbon dioxide (CO2) emissions annually.
  • The North Atlantic Ocean contains more anthropogenic CO2 than any other ocean basin, and surface waters are experiencing an ongoing decline in pH (increasing acidity). Rates of acidification in bottom waters are occurring faster at some locations than in surface waters.
  • Some species are already showing effects from ocean acidification when exposed to short-term fluctuations and could be used as indicator species for long-term impacts on marine ecosystems.

What could happen in the future

  • Models project that the average continental shelf seawater pH will continue to decline to year 2050 at similar rates to the present day, with rates then increasing in the second half of the century, depending on the emissions scenario.
  • The rate of pH decline in coastal areas is projected to be faster in some areas (e.g. Bristol Channel) than others, such as the Celtic Sea.
  • Under high-emission scenarios, it is projected that bottom waters on the North-West European Shelf seas will become corrosive to more soluble forms of calcium carbonate (aragonite). Episodic undersaturation events are projected to begin by 2030.
  • By 2100, up to 90% of the north-west European shelf seas may experience undersaturation for at least one month of each year.
  • High levels of nearshore variability in carbonate chemistry may mean that some coastal species have a higher adaptative capacity than others. However, all species are at increased risk from extreme exposure episodes.
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Ocean biogeochemical modelling

Ocean biogeochemical models describe the ocean’s circulation, physical properties, biogeochemical properties and their transformations using coupled differential equations. Numerically approximating these equations enables simulation of the dynamic evolution of the ocean state in realistic global or regional spatial domains, across time spans from years to centuries. This Primer explains the process of model construction and the main characteristics, advantages and drawbacks of different model types, from the simplest nutrient–phytoplankton–zooplankton–detritus model to the complex biogeochemical models used in Earth system modelling and climate prediction. Commonly used metrics for model-data comparison are described, alongside a discussion of how models can be informed by observations via parameter optimization or state estimation, the two main methods of data assimilation. Examples illustrate how these models are used for various practical applications, ranging from carbon accounting, ocean acidification, ocean deoxygenation and fisheries to observing system design. Access points are provided, enabling readers to engage in biogeochemical modelling through practical code examples and a comprehensive list of publicly available models and observational data sets. Recommendations are given for best practices in model archiving. Lastly, current limitations and anticipated future developments and challenges of the models are discussed.

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Ocean acidification and warming significantly affect coastal eutrophication and organic pollution: a case study in the Bohai Sea

Highlights

  • Ocean acidification alone favors eutrophication and organic pollution.
  • Warming alone inhibits eutrophication and organic pollution.
  • Interactions between acidification and warming may exacerbate organic pollution.
  • Their interactions may mitigate the progress of eutrophication.

Abstract

Most coastal ecosystems are faced with novel challenges associated with human activities and climate change such as ocean acidification, warming, eutrophication, and organic pollution. However, data on the independent or combined effects of ocean acidification and warming on coastal eutrophication and organic pollution at present are relatively limited. Here, we applied the generalized additive models (GAMs) to explore the dynamics of coastal eutrophication and organic pollution in response to future climate change in the Bohai Sea. The GAMs reflected the fact that acidification alone favors eutrophication and organic pollution, while warming alone inhibits these two variables. Differently, the interactions between acidification and warming in the future may further exacerbate the organic pollution but may mitigate the progress of eutrophication. These different responses of eutrophication and organic pollution to acidification and warming may be attributed to algae growth and microbial respiration, as well as some physical processes such as stratification.

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Long-term variability of satellite derived total alkalinity in the southwest Bay of Bengal

Highlights

  • Computed TA data validated in BoB region.
  • Spatial and temporal variability in TA are mostly due to variability in SSS and SST.
  • TA in BoB region, seasonal and inter-annual pattern over past 17 years.

Abstract

The seasonal and inter-annual variability of Total Alkalinity (TA) concentration was studied in the Bay of Bengal from 2003 to 2019 by using MODIS-Aqua derived sea surface temperature (SST) and sea surface salinity (SSS) products. The satellite derived TA showed a positive relationship with in-situ TA with (R2 = 0.67, RMSE = ±27.53 μMol/kg, SEE = ±32.16 and uncertainty error = 2287μMol/kg). The seasonal SST, SSS and TA portray the clear seasonal pattern between the seasons without any rapid change increase or decrease in trend observed over the years. In contrast to other seasons, the spring inter-monsoon was observed to have a warm surface water temperature with high salinity and TA. Strong wind and excessive cloud cover during the summer monsoon result in the reduction of ocean surface heat, which favours sea surface cooling and shallow mixed layer depth, resulting in low SST, SSS, and TA compared to the spring inter-monsoon. During fall inter-monsoon, the reversal of East India coastal current directs warm water from north to south and the weak wind that prevails in this region enhances stratification. During winter, low-saline water compensates the static stability loss by thermal inversion from the sea surface resulting in surface cooling with coldest SST, low SSS and TA during this period.

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Impact of ocean acidification and ocean warming on the oxidation of dissolved Fe(II) in coastal and open Southern Ocean water

The Southern Ocean is the largest region where major nutrients such as nitrate, silicate and phosphate are present in excess, yet the crucial micronutrient element iron (Fe) is scarce. It is well established that the Southern Ocean is key in exporting carbon to greater depths through biomass production by phytoplankton, but Fe is metabolically required for photosynthesis. Changes in uptake of carbon and heat to the ocean will impact ocean acidification and ocean warming. These anthropogenically linked processes are projected to lead to a drop in ocean pH by 0.2 units and an increase in the ocean’s temperature by 2°C by the end of the century and are already known to have tremendous ecological impacts on the ocean’s flora and fauna. However, little is known about how changes in ocean temperature and pH could alter the nutrient composition in future oceans.

Regarding nutrients, this work focuses on the dissolved (d) element Fe. It is essential for photosynthesis, but also a limiting element in the Southern Ocean due to limiting sources leading to low availability. Iron exists in two redox states in seawater. While the species dFe(III) is stable in seawater and occurs in relatively higher concentrations, its redox partner dFe(II) is tied to several physico-chemical processes impacting its oxidation time and overall presence. The importance of dFe(II) also lies with its accessibility for phytoplankton in its reduced oxidative state. The overall aim of this study was to investigate changes in concentration, speciation, and availability of the ‘more’ bioavailable, rapidly oxidizing Fe species dFe(II) under a changing Southern Ocean scenario.

Chapter 2 addressed the redox behaviour of dFe(II) and dFe(III), where several questions were explored for further experimental planning. The main question was how the coastal and open ocean systems differ in their dFe(II) concentrations and how ocean acidification and ocean warming impact Fe redox chemistry in both systems. I therefore performed controlled acidification and temperature alteration experiments in coastal and open ocean water taken from the Tasmanian coast and the Southern Ocean. This large dataset enabled us to project for future ocean dFe(II) concentrations and oxidation rates. I observed that a reduction in ocean pH by 0.2 units doubles the dFe(II) oxidation time in the open ocean and tripled in coastal water through model-based experiments. In contrast to these high impacts from pH, an increase in temperature by 1°C accelerated the oxidation by ~ 1.1 times (13% in coastal water and 8% in open ocean water). Therefore, realistic changes in temperature are likely to have small impacts on the oxidation of dFe(II) in both water systems compared to the proposed changes in pH.

For phytoplankton, these results pose contradicting outcomes, and studies display mixed results once parameters such as ocean warming, and acidification are combined. An increase in temperature might lead to less or no growth once a certain temperature threshold is crossed. Similarly, a decrease in pH is also thought to impact phytoplankton physiology. It also depends on the severity of acidification and the phytoplankton species itself. Ocean warming could reduce phytoplankton growth, despite increased Fe availability due to higher solubility in warmer water. Regarding ocean acidification, on the other hand, dFe(II) could become available for an extended time, therefore enabling further uptake of dFe(II) by phytoplankton for that time. When comparing mixed effects of ocean acidification and warming, a reduction in pH might have a greater impact on the dFe(II) oxidation than just temperature. Temperature changes, however, might be a greater concern in the near future before ocean acidification becomes relevant.

Due to this projection of temperature being a more imminent concern, I targeted the limiting element Fe in its less investigated form dFe(II). I observed how temperature alone impacts growth of two Southern Ocean phytoplankton species. I therefore ran an dFe(II)-enrichment incubation experiment in Chapter 3 with differing temperatures (3°C, 5°C, and 7°C) in coastal and open ocean water from the Southern Ocean using the well-studied haptophyte Phaeocystis antarctica and the diatom Fragilariopsis cylindrus. These enrichment experiments with altered temperatures overall confirmed that phytoplankton growth was elevated once 5 nM dFe(II) were added. In other words, freely available dFe(II) was present, almost regardless of the temperature increase from 3°C to 7°C. This could implicate that an increase in temperature has beneficial effects on growth in the case of higher concentrations of freely available dFe(II). However, these values of future dFe(II) concentrations and oxidation rates under acidified and warmer scenarios are only laboratory-based projections, to better understand the dFe(II) presence and demand by phytoplankton species in a future Southern Ocean.

In Chapter 4, a one-month field study onboard the RV Investigator was conducted east of the Australian continent along the East Australian Current (EAC) into nutrient-rich but Fe poor water in the Southern Ocean. I observed the overall distribution of dFe(II) and hydrogen peroxide in this understudied region. The findings suggest that dFe(II) concentrations are very low in the observed area of the open Southern Ocean (< 0.1 nM) compared to coastal waters (> 0.5 nM), likely driven by differences in terrestrial Fe inputs. Hydrogen peroxide was generally higher in the southern stations within the upper 200 m (~60 nM) while the dFe(II) : dFe ratios are 10 % higher than reported for previous Southern Ocean studies. High biological activity in the upper water extending to the frontal mixing zone where the two major currents meet (EAC and STF), may further have led to the observed low dFe concentrations and high H22O22 concentrations. Occasional higher dFe(II) peaks found in this area in surface water may be the result of several external sources such as rain or vertical transport from seamounts but also due to biological or physico-chemical impacts such as photochemical reduction or uptake by phytoplankton.

Overall, the work in this study advances our understanding of the coupled effects of the climate change parameters ocean acidification and ocean warming on the dFe(II) oxidation, with implications for its availability to phytoplankton and overall sources in the region east and south-east of Tasmania in coastal and open ocean water. The experimental approaches taken suggest a higher impact of ocean acidification compared to ocean warming and a potential benefit for phytoplankton species preferring dFe(II).

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Corals adapted to extreme and fluctuating seawater pH increase calcification rates and have unique symbiont communities

Ocean acidification (OA) is a severe threat to coral reefs mainly by reducing their calcification rate. Identifying the resilience factors of corals to decreasing seawater pH is of paramount importance to predict the survivability of coral reefs in the future. This study compared corals adapted to variable pH (i.e., 7.23-8.06 pH units) from the semi-enclosed lagoon of Bouraké, New Caledonia, to corals adapted to more stable seawater pH (i.e., 7.90-8.18 pH units). In a 100-day aquarium experiment, we examined the physiological response and genetic diversity of Symbiodiniaceae from three coral species ( Acropora tenuis , Montipora digitata and Porites sp.) from both sites under three stable pH conditions (i.e., 8.11, 7.76, 7.54 pH units) and fluctuating pH conditions (i.e., between 7.56 and 8.07 pH units). Bouraké corals consistently exhibited higher growth rates than corals from the stable pH environment, with specific ITS2 intragenomic variant profiles. While OA generally decreased coral calcification by ca. 16%, Bouraké coralsshowed higher growth rates (21 to 93% increase, depending on species with all pH conditions pooled) than those from the stable pH environment. This superior performance coincided with divergent ITS2-like profiles with better consistency for both variable and low pH conditions. This response was not gained by corals from the more stable environment exposed to variable pH during the four-month experiment, suggesting that such a kind of plasticity is time dependent. Future long-term experiments should address the exposure duration required to confer fitness benefits for sustained calcification, hopefully fast enough to cope with the ongoing rapid OA.

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Tropical cyclone-induced coastal acidification in Galveston Bay, Texas

Intense rainfall from tropical cyclones has the potential to induce coastal acidification, which will become more common and severe as climate change continues. We collected carbonate chemistry samples from Galveston Bay, Texas before and after Hurricane Harvey in 2017 and 2018. Here, we show ecosystem level acidification and calcium carbonate undersaturation in Galveston Bay following the storm. This acidification event, driven by extreme rainfall from Harvey, persisted for over 3 weeks because of prolonged flood mitigation reservoir releases that continued for over a month after the storm. In addition, the large volume of stormwater led to high oyster mortality rates in Galveston Bay and acidification may have impeded recovery of these vital reefs. It is also likely that undersaturation has occurred outside of our study, unrecorded, following other high-rainfall storms. The projected increase in tropical cyclone rainfall under climate change may thus represent a significant threat to coastal calcifying ecosystems.

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Global decrease in heavy metal concentrations in brown algae in the last 90 years

Graphical abstract

Highlights

  • A decline in metal pollution in algae is widespread in coastal ecosystems worldwide.
  • Decrease in algae concentrations may not also occur in seawater but in bioavailability.
  • Decreases began from 70’s coinciding with the implementation of environmental policies.
  • Legislation and ocean acidification can impact on the heavy metal content in algae.

Abstract

In the current scenario of global change, heavy metal pollution is of major concern because of its associated toxic effects and the persistence of these pollutants in the environment. This study is the first to evaluate the changes in heavy metal concentrations worldwide in brown algae over the last 90 years (>15,700 data across the globe reported from 1933 to 2020). The study findings revealed significant decreases in the concentrations of Cd, Co, Cr, Cu, Fe, Hg, Mn, Pb and Zn of around 60–84% (ca. 2% annual) in brown algae tissues. The decreases were consistent across the different families considered (Dictyotaceae, Fucaceae, Laminariaceae, Sargassaceae and Others), and began between 1970 and 1990. In addition, strong relationships between these trends and pH, SST and heat content were detected. Although the observed metal declines could be partially explained by these strong correlations, or by adaptions in the algae, other evidences suggest an actual reduction in metal concentrations in oceans because of the implementation of environmental policies. In any case, this study shows a reduction in metal concentrations in brown algae over the last 50 years, which is important in itself, as brown algae form the basis of many marine food webs and are therefore potential distributors of pollutants.

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Carbon and nutrient cycling in Antarctic landfast sea ice from winter to summer

Seasonal cycling in carbon, alkalinity, and nutrients in landfast sea ice in Hangar Cove, Adelaide Island, West Antarctic Peninsula, were investigated during winter, spring, and summer 2014–2015. Temporal dynamics were driven by changes in the sea-ice physicochemical conditions, ice-algal community composition, and organic matter production. Winter sea ice was enriched with dissolved inorganic carbon (DIC) and inorganic nutrients from organic matter remineralization. Variations in alkalinity (Alk) and DIC indicated that abiotic calcium carbonate (ikaite) precipitation had taken place. Relative to other nutrients, low phosphate (PO4) concentrations potentially resulted from co-precipitation with ikaite. Seawater flooding and meltwater induced variability in the physical and biogeochemical properties in the upper ice in spring where nutrient resupply supported haptophyte productivity and increased particulate organic carbon (POC) in the interstitial layer. Rapid nitrate (NO3) and DIC (< 165 μmol kg−1) uptake occurred alongside substantial build-up of algal biomass (746 μg chlorophyll a L−1) and POC (6191 μmol L−1) during summer. Silicic acid drawdown followed NO3 depletion by approximately 1 month with a shift to diatom-dominated communities. Accumulation of PO4 in the lower ice layers in summer likely resulted from PO4 released during ikaite dissolution in the presence of biofilms. Increased Alk : DIC ratios in the lower ice and under-ice water suggested that ikaite dissolution buffered against meltwater dilution and enhanced the potential for atmospheric CO2 uptake. This study revealed strong seasonality in carbon and nutrient cycling in landfast sea ice and showed the importance of sea ice in biogeochemical cycling in seasonally ice-covered waters around Antarctica.

Continue reading ‘Carbon and nutrient cycling in Antarctic landfast sea ice from winter to summer’

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