Ocean absorption of anthropogenic carbon dioxide (CO2) emissions mitigates the impacts of climate change but also causes ocean acidification, putting marine organisms and ecosystems at risk. Carbon dynamics in coastal environments, driven by interactions with terrestrial processes, benthic ecosystems and unique physical oceanographic processes make these ecosystems more vulnerable to ocean acidification and compounding stressors such as eutrophication, hypoxia, and warming due to climate change. Coastal margins, including shelf seas, represent areas of high biological productivity that provide important economic and cultural marine ecosystem services and play a significant role in the global carbon cycle. However, coastal processes are typically not well represented or constrained in Earth System Models despite their significance to the global carbon budget and sensitivity to human impacts. Understanding the drivers of regional carbon cycles is necessary for predicting how a system will respond to anthropogenic perturbation. The research presented herein focuses on investigating the drivers of seasonal carbon cycle, air-sea CO2 exchange and implications for ocean acidification in the coastal margins around New Zealand. Observational data collected regularly since 1998 at stations spanning subantarctic and subtropical waters, along with 4 years (2015 – 2019) of observations from a coastal ocean observing network were used to evaluate regional carbon cycles. Methods to integrate modelled and reanalysis data with observational data were developed to leverage sparsely sampled datasets to better understand the processes that control the seasonal carbon cycles and drivers of long-term variability. Nearshore coastal environments exhibited the largest seasonal to interannual variability in pH compared to shelf seas, consistent with the influence of terrestrial processes, freshwater fluxes, and dominance of benthic ecosystems on carbonate chemistry in these systems. Overall, subtropical shelf waters in the northern North Island are a stronger sink for atmospheric CO2 (4.66 mol C m-2 y-1) than subantarctic waters off the South Island (0.84 mol C m-2 y-1). CO2 fluxes are driven by air-sea gradients that are controlled by seasonal thermodynamics, biological production, and physical transport. Subtropical sites exhibit a dominance of seasonal temperature variability compared to subantarctic sites. Circulation was found to play a large role the seasonal carbon cycles around New Zealand. Advective fluxes export dissolved inorganic carbon (DIC) from the northeastern shelf of the North Island while they add DIC along the southeastern shelf break of the South Island. Decadal variability in advection along the southeastern shelf is correlated with the El Nino Southern Oscillation and Southern Annual Mode, which has reduced advection of DIC into this region, so maintaining the regional sink strength for atmospheric CO2. These changes in ocean circulation and warming due to climate change have also reduced solubility of CO2 during 2009-2018 by 2%. Simulations using the Regional Ocean Modelling System (ROMS) were used to improve understanding of how terrestrial interactions affect seasonal mixed layer dynamics and carbonate chemistry in coastal and shelf waters off the southeast the South Island. Terrestrial freshwater fluxes were shown to have a large impact on the seasonal salinity and heat budgets which are dominated by advection and turbulent mixing along the Subtropical Front. A coupled biogeochemical ROMS was developed for a domain along the northeastern shelf of the North Island which included the Firth of Thames and Hauraki Gulf. A hydrological model was used to estimate terrestrial fluxes of freshwater, nutrients, organic matter, dissolved oxygen, and heat, which enabled sensitivity analysis of coastal carbonate chemistry and air-sea gas exchange to terrestrial inputs and deconvolution of the seasonal carbon budget. Inner Firth primary production was driven nearly entirely by terrestrial nitrate loading but sensitivity to loading diminished along the land-shelf spatial gradient. Terrestrial organic matter had limited impact on seasonal air-sea exchange and carbon export. The total carbon exported from the Hauraki Gulf was estimated to be ~8 Tg C y-1 with the model, but this may represent an overestimate due to the simplicity of the biological model used. Although this model showed high skill in reproducing seasonal phytoplankton biomass, it did not reproduce hypoxic conditions observed seasonally due to inadequately represented benthic processes. This modelling framework was successful in informing drivers of the seasonal air-sea CO2 exchange across this land-ocean gradient. These studies indicate vulnerability of New Zealand’s coastal ecosystems to climate change and anthropogenic stressors. The results show the relative importance of ocean circulation, biological processes, changes in ocean heat and salinity, and land-ocean interactions in modulating carbon cycling over seasonal to decadal time scales. Methods developed within this research show how model and observational data can be combined to investigate climate change questions important for sustainable resource management.
Continue reading ‘Evaluating the drivers of air-sea CO2 exchange and ocean acidification in coastal waters around New Zealand’Posts Tagged 'biogeochemistry'
Evaluating the drivers of air-sea CO2 exchange and ocean acidification in coastal waters around New Zealand
Published 24 July 2023 Science ClosedTags: biogeochemistry, chemistry, field, South Pacific
Carbonate pump feedbacks on alkalinity and the carbon cycle in the 21st century and beyond
Published 19 July 2023 Science ClosedTags: biogeochemistry, chemistry, globalmodeling, modeling
Ocean acidification is likely to impact all stages of the ocean carbonate pump, i.e. the production, export, dissolution and burial of biogenic CaCO3. However, the associated feedbacks on anthropogenic carbon uptake and ocean acidification have received little attention. It has previously been shown that Earth system model (ESM) carbonate pump parameterizations can affect and drive biases in the representation of ocean alkalinity, which is critical to the uptake of atmospheric carbon and provides buffering capacity towards associated acidification. In the sixth phase of the Coupled Model Intercomparison Project (CMIP6), we show divergent responses of CaCO3 export at 100 m this century, with anomalies by 2100 ranging from -74 % to +23 % under a high-emissions scenario. The greatest export declines are projected by ESMs that consider pelagic CaCO3 production to depend on the local calcite/aragonite saturation state. Despite the potential effects of other processes on alkalinity, there is a robust negative correlation between anomalies in CaCO3 export and salinity-normalized surface alkalinity across the CMIP6 ensemble. Motivated by this relationship and the uncertainty in CaCO3 export projections across ESMs, we perform idealized simulations with an ocean biogeochemical model and confirm a limited impact of carbonate pump anomalies on twenty-first century ocean carbon uptake and acidification. However between 2100 and 2300, we highlight a potentially abrupt shift in the dissolution of CaCO3 from deep to subsurface waters when the global scale mean calcite saturation state reaches about 1.23 at 500 m (likely when atmospheric CO2 reaches 900 to 1100 ppm). During this shift, upper ocean acidification due to anthropogenic carbon uptake induces deep ocean acidification driven by a substantial reduction in CaCO3 deep dissolution following its decreased export at depth. Although the effect of a diminished carbonate pump on global ocean carbon uptake and surface ocean acidification remains limited until 2300, it can have a large impact on regional air-sea carbon fluxes, particularly in the Southern Ocean.
Continue reading ‘Carbonate pump feedbacks on alkalinity and the carbon cycle in the 21st century and beyond’Spatial and temporal variations in sea surface pCO2 and air-sea flux of CO2 in the Bering Sea revealed by satellite-based data during 2003–2019
Published 18 July 2023 Science ClosedTags: biogeochemistry, chemistry, field, North Pacific
The understanding of long-time-series variations in air-sea CO2 flux in the Bering Sea is critical, as it is the passage area from the North Pacific Ocean water to the Arctic. Here, a data-driven remote sensing retrieval method is constructed based on a large amount of underway partial pressure of CO2 (pCO2) data in the Bering Sea. After several experiments, a Gaussian process regression model with input parameters of sea surface temperature, sea surface height, mixed-layer depth, chlorophyll a concentration, dry air mole fractions of CO2, and bathymetry was selected. After validation with independent data, the root mean square error of pCO2 was< 24 μatm (R2 = 0.94) with satisfactory performance. Then, we reconstructed the sea surface pCO2 in the Bering Sea from 2003 to 2019 and estimated the corresponding air-sea CO2 fluxes. Significant seasonal variations were identified, with higher sea surface pCO2 in winter/spring than in summer/autumn in both the basin and shelf area. Semiquantitative analysis reveals that the Bering Sea is a non-temperature-dominated area with a mean temperature effect on pCO2 of 12.7 μatm and a mean non-temperature effect of −51.8 μatm. From 2003 to 2019, atmospheric pCO2 increased at a rate of 2.1 μatm yr−1, while sea surface pCO2 in the basin increased rapidly (2.8 μatm yr−1); thus, the CO2 emissions from the basin increased. However, the carbon sink in the continental shelf still continuously increased. The whole Bering Sea exhibited an increasing carbon sink with the area integral of air-sea CO2 fluxes increasing from 6 to 19 TgC over 17 years. Meanwhile, the seasonal amplitudes in pCO2 in the shelf area also increased, approaching 14 μatm per decade. The reaction of the continuously added CO2 in continental seawater reduced the ocean CO2 system capacity. This is the first study to present long-time-series satellite data with high resolution in the Bering Sea, which is beneficial for studying the changes in ocean ecosystems and carbon sink capacity.
Continue reading ‘Spatial and temporal variations in sea surface pCO2 and air-sea flux of CO2 in the Bering Sea revealed by satellite-based data during 2003–2019’Feeding in mixoplankton enhances phototrophy increasing bloom-induced pH changes with ocean acidification
Published 14 July 2023 Science ClosedTags: biogeochemistry, BRcommunity, communitymodeling, modeling, phytoplankton, protists, zooplankton
Plankton phototrophy consumes CO2, increasing seawater pH, while heterotrophy does the converse. Elevation of pH (>8.5) during coastal blooms becomes increasingly deleterious for plankton. Mixoplankton, which can be important bloom-formers, engage in both photoautotrophy and phagoheterotrophy; in theory, this activity could create a relatively stable pH environment for plankton growth. Using a systems biology modelling approach, we explored whether different mixoplankton functional groups could modulate the environmental pH compared to the extreme activities of phototrophic phytoplankton and heterotrophic zooplankton. Activities by most mixoplankton groups do not stabilize seawater pH. Through access to additional nutrient streams from internal recycling with phagotrophy, mixoplankton phototrophy is enhanced, elevating pH; this is especially so for constitutive and plastidic specialist non-constitutive mixoplankton. Mixoplankton blooms can exceed the size of phytoplankton blooms; the synergisms of mixoplankton physiology, accessing nutrition via phagotrophy as well as from inorganic sources, enhance or augment primary production rather than depressing it. Ocean acidification will thus enable larger coastal mixoplankton blooms to form before basification becomes detrimental. The dynamics of such bloom developments will depend on whether the mixoplankton are consuming heterotrophs and/or phototrophs and how the plankton community succession evolves.
Continue reading ‘Feeding in mixoplankton enhances phototrophy increasing bloom-induced pH changes with ocean acidification’Biological modification of coastal pH depends on community composition and time
Published 14 July 2023 Science ClosedTags: biogeochemistry, chemistry, field, North Pacific
Biological processes play important roles in determining how global changes manifest at local scales. Primary producers can absorb increased CO2 via daytime photosynthesis, modifying pH in aquatic ecosystems. Yet producers and consumers also increase CO2 via respiration. It is unclear whether biological modification of pH differs across the year, and, if so, what biotic and abiotic drivers underlie temporal differences. We addressed these questions using the intensive study of tide pool ecosystems in Alaska, USA, including quarterly surveys of 34 pools over 1 year and monthly surveys of five pools from spring to fall in a second year. We measured physical conditions, community composition, and changes in pH and dissolved oxygen during the day and night. We detected strong temporal patterns in pH dynamics. Our measurements indicate that pH modification varies spatially (between tide pools) and temporally (across months). This variation in pH dynamics mirrored changes in dissolved oxygen and was associated with community composition, including both relative abundance and diversity of benthic producers and consumers, whose role differed across the year, particularly at night. These results highlight the importance of the time of year when considering the ways that community composition influences pH conditions in aquatic ecosystems.
Continue reading ‘Biological modification of coastal pH depends on community composition and time’The potential role of Posidonia oceanica for mitigating acidification on coastal waters of Europe
Published 12 July 2023 Science ClosedTags: biogeochemistry, biological response, chemistry, field, Mediterranean, mitigation, phanerogams, review
Ocean acidification is a major environmental concern that has significant ecological., economic, and social implications. The plantation and restoration of seagrass meadows in coastal waters, specifically Posidonia oceanica, is one possible method to combat ocean acidification and has the potential to have a significant positive impact on the marine environment and the overall state of the biosphere. As there has been a decline of Posidonia oceanica of about 30% in the Mediterranean Sea over the past three decades to about 1.2 mio ha in the Mediterranean Sea, the positive effects of the sea grass have diminished due to anthropogenic influence. Still, its importance as a carbon sink should not be underestimated. By using recent literature and different studies that have been analysed of the capacity of sea grass to mitigate the impacts of ocean acidification and the effects on the marine ecosystems, supported by several experiments that have been conducted, this thesis demonstrated the importance of Posidonia oceanica. The experiments showed that seagrass ecosystems have higher pH than ecosystems without seagrass, with a mean difference of 0.43. As the pH is interlocked with the CO2-levels and the oxygen levels, also experiments on these factors have been conducted. In general, the concentration of oxygen with P. oceanica present is 2mg/L higher than without. Equally, the CO2 concentration was lower with P. oceanica present. The Posidonia oceanica meadows present in the Mediterranean Sea are able to fixate about 13,3 mio tons of CO2, which is equal to 0,3% of Europeans CO2 emissions. About 2,8 mio tons of CO2 are sequestered by the sea grass, which is about 0,07% of European CO2 emissions. Furthermore, recent plantation efforts show the successful restoration of seagrass meadows and their overall benefits for the regional environment. Overall, this paper provides valuable insights into the potential role of seagrass meadows in mitigating ocean acidification and improving marine biosystems while providing specific numbers to support its findings.
Continue reading ‘The potential role of Posidonia oceanica for mitigating acidification on coastal waters of Europe’Physiological response of an Antarctic cryptophyte to increasing temperature, CO2, and irradiance
Published 12 July 2023 Science ClosedTags: abundance, Antarctic, biogeochemistry, biological response, growth, laboratory, light, multiple factors, otherprocess, photosynthesis, phytoplankton, primary production, temperature
The Southern Ocean, a globally important CO2 sink, is one of the most susceptible regions in the world to climate change. Phytoplankton of the coastal shelf waters around the Western Antarctic Peninsula have been experiencing rapid warming over the past decades and current ongoing climatic changes will expose them to ocean acidification and high light intensities due to increasing stratification. We conducted a multiple-stressor experiment to evaluate the response of the still poorly studied key Antarctic cryptophyte species Geminigera cryophila to warming in combination with ocean acidification and high irradiance. Based on the thermal growth response of G. cryophila, we grew the cryptophyte at suboptimal (2°C) and optimal (4°C) temperatures in combination with two light intensities (medium light: 100 μmol photons m−2 s−1 and high light [HL]: 500 μmol photons m−2 s−1) under ambient (400 μatm pCO2) and high pCO2 (1000 μatm pCO2) conditions. Our results reveal that G. cryophila was not susceptible to high pCO2, but was strongly affected by HL at 2°C, as both growth and carbon fixation were significantly reduced. In comparison, warming up to 4°C stimulated the growth of the cryptophyte and even alleviated the previously observed negative effects of HL at 2°C. When grown, however, at temperatures above 4°C, the cryptophyte already reached its maximal thermal limit at 8°C, pointing out its vulnerability toward even higher temperatures. Hence, our results clearly indicate that warming and high light and not pCO2 control the growth of G. cryophila.
Continue reading ‘Physiological response of an Antarctic cryptophyte to increasing temperature, CO2, and irradiance’Effects of pH, eelgrass, and settlement substrate on the growth of juvenile magallana (crassostrea) gigas, a commercially important oyster species
Published 6 July 2023 Science ClosedTags: biogeochemistry, biological response, chemistry, communityMF, field, laboratory, mollusks, morphology, multiple factors, North Pacific, performance
Worsening ocean acidification (OA), resulting from ongoing absorption of atmospheric carbon dioxide (CO2) by the oceans, threatens marine life globally. Calcifying organisms, especially their early life stages, are particularly vulnerable; this includes the economically important Pacific oyster, Magallana (Crassostrea) gigas. Uptake of dissolved CO2 through photosynthesis by seagrasses, like eelgrass (Zostera marina), may benefit calcifying organisms by increasing pH and carbonate availability. I conducted laboratory and field experiments to quantify carbonate chemistry modification by eelgrass and potential mitigation of OA impacts on growth in juvenile Pacific oysters. In the laboratory experiment, daytime net photosynthesis by eelgrass increased seawater pH, while nighttime net respiration reduced pH though to a lesser extent; both effects grew stronger as the pH of incoming seawater decreased. This is consistent with the expectation that eelgrass will benefit from increased aqueous CO2 levels and suggests that the importance of carbonate chemistry modification by eelgrass and its role as a refugium may increase as OA proceeds. Under the conditions tested, however, eelgrass effects on pH were modest and did not affect oyster growth in the lab or field. In the lab, oysters settled on shell flour grew faster than those on shell chunks, but unlike those on chunks, the growth rate of oysters on flour decreased significantly in low pH treatments. One hypothesis consistent with these results is that the boundary layer around shell chunks may have slowed oyster growth by limiting food availability but that it also reduced sensitivity to low pH via enhanced carbonate saturation.
Continue reading ‘Effects of pH, eelgrass, and settlement substrate on the growth of juvenile magallana (crassostrea) gigas, a commercially important oyster species’Methane-derived authigenic carbonates – a case for a globally relevant marine carbonate factory
Published 6 July 2023 Science ClosedTags: biogeochemistry, chemistry, globalmodeling, methods, modeling, paleo, review
Precipitation of methane-derived authigenic carbonates (MDAC) is an integral part of marine methane production and consumption, but MDAC’s relative significance to the global marine carbon cycle is not well understood. Here we provide a synthesis and perspective to highlight MDAC from a global marine carbon biogeochemistry viewpoint. MDAC formation is a result and archive of carbon‑sulfur (C – S) coupling in the shallow sulfatic zone and carbon‑silicon (C – Si) coupling in deeper methanic sediments. MDAC constitute a carbon sequestration of 3.93 Tmol C yr−1 (range 2.34–5.8 Tmol C yr−1) in the modern ocean and are the third-largest carbon burial mechanism in marine sediments. This burial compares to 29% (11–57%) organic carbon and 10% (6–23%) skeletal carbonate carbon burial along continental margins. MDAC formation is also an important sink for benthic alkalinity and, thereby, a potential contributor to bottom water acidification. Our understanding of the impact of MDAC on global biogeochemical cycles has evolved over the past five decades from what was traditionally considered a passive carbon sequestration mechanism in a seep-oasis setting to what is now considered a dynamic carbonate factory expanding from deep sediments to bottom waters—a factory that has been operational since the Precambrian. We present a strong case for the need to improve regional scale quantification of MDAC accumulation rates and associated carbonate biogeochemical parameters, leading to their incorporation in present and paleo‑carbon budgets in the next phase of MDAC exploration.
Continue reading ‘Methane-derived authigenic carbonates – a case for a globally relevant marine carbonate factory’CO2 in the surface ocean
Published 3 July 2023 Science ClosedTags: biogeochemistry, chemistry, methods
The global ocean comprises a significant sink for human-emitted carbon dioxide, yet many different processes are at play, causing strong spatial and temporal variations in the distribution of the sea surface pCO2 and the resulting air-sea CO2 fluxes. While dominated by the temperature-driven solubility, physical transport and biogeochemistry, the increase in the sea surface CO2 partial pressure over the past decades is closely following the increase in atmospheric CO2, resulting in a decreasing pH and decreasing saturation states of calcite and aragonite minerals. Despite the increasing abundance of novel data interpolation tools, e.g. based on machine learning, the heterogeneous distribution of CO2 in the surface ocean requires a dense observing network to reconstruct global change.
Continue reading ‘CO2 in the surface ocean’Combined effects of ocean deoxygenation, acidification, and phosphorus limitation on green tide macroalga, Ulva prolifera
Published 29 June 2023 Science ClosedTags: algae, biogeochemistry, biological response, growth, laboratory, multiple factors, North Pacific, nutrients, oxygen, photosynthesis, physiology
Highlights
- Additive and antagonistic interactions between the three stressors were mainly observed.
- Ocean deoxygenation, acidification, and P limitation can dysregulate the Ulva prolifera of photosynthetic efficiency.
- Green tide macroalgal Ulva prolifera has a strong acclimation capacity to elevated CO2, low O2, and high N/P.
- Ulva prolifera could use organic P to support its growth under low inorganic phosphorus conditions.
- Increased CO2 levels can decrease the energy costs associated with CCM, and can support the growth of macroalgal cells.
Abstract
Ocean deoxygenation, acidification, and decreased phosphorus availability are predicted to increase in coastal ecosystems under future climate change. However, little is known regarding the combined effects of such environmental variables on the green tide macroalga Ulva prolifera. Here, we provide quantitative and mechanistic understanding of the acclimation mechanisms of U. prolifera to ocean deoxygenation, acidification, and phosphorus limitation under both laboratory and semi-natural (mesocosms) conditions. We found that there were significant interactions between these global environmental conditions on algal physiological performance. Although algal growth rate and photosynthesis reduced when the nitrogen-to‑phosphorus (N/P) ratio increased from 16:1 to 35:1 under ambient CO2 and O2 condition, they remained constant with further increasing N/P ratios of 105:1, 350:1, and 1050:1. However, the increasing alkaline phosphatase activities at high N/P ratios suggests that U. prolifera could use organic P to support its growth under phosphorus limitation. Deoxygenation had no effect on specific growth rate (SGR) but decreased photosynthesis under low N/P ratios of 16:1, 35:1, and 105:1, with reduced activities of several enzymes involved in N assimilation pathway being observed. Elevated CO2 promoted algal growth and alleviated the negative effect of deoxygenation on algal photosynthesis. The patterns of responses to high CO2 and low O2 treatments in in situ experiments were generally consistent with those observed in laboratory experiments. Our results generally found that the strong physiological acclimation capacity to elevated CO2, low O2, and high N/P could contribute to its large-scale blooming in coastal ecosystem.
Continue reading ‘Combined effects of ocean deoxygenation, acidification, and phosphorus limitation on green tide macroalga, Ulva prolifera’Simulated upwelling and marine heatwave events promote similar growth rates but differential domoic acid toxicity in Pseudo-nitzschia australis
Published 28 June 2023 Science ClosedTags: abundance, biogeochemistry, biological response, laboratory, multiple factors, North Pacific, nutrients, otherprocess, physiology, phytoplankton, temperature
Along the west coast of the United States, highly toxic Pseudo-nitzschia blooms have been associated with two contrasting regional phenomena: seasonal upwelling and marine heatwaves. While upwelling delivers cool water rich in pCO2 and an abundance of macronutrients to the upper water column, marine heatwaves instead lead to warmer surface waters, low pCO2, and reduced nutrient availability. Understanding Pseudo-nitzschia dynamics under these two conditions is important for bloom forecasting and coastal management, yet the mechanisms driving toxic bloom formation during contrasting upwelling vs. heatwave conditions remain poorly understood. To gain a better understanding of what drives Pseudo-nitzschia australis growth and toxicity during these events, multiple-driver scenario or ‘cluster’ experiments were conducted using temperature, pCO2, and nutrient levels reflecting conditions during upwelling (13 °C, 900 ppm pCO2, replete nutrients) and two intensities of marine heatwaves (19 °C or 20.5 °C, 250 ppm pCO2, reduced macronutrients). While P. australis grew equally well under both heatwave and upwelling conditions, similar to what has been observed in the natural environment, cells were only toxic in the upwelling treatment. We also conducted single-driver experiments to gain a mechanistic understanding of which drivers most impact P. australis growth and toxicity. These experiments indicated that nitrogen concentration and N:P ratio were likely the drivers that most influenced domoic acid production, while the impacts of temperature or pCO2 concentration were less pronounced. Together, these experiments may help to provide both mechanistic and holistic perspectives on toxic P. australis blooms in the dynamic and changing coastal ocean, where cells interact simultaneously with multiple altered environmental variables.
Continue reading ‘Simulated upwelling and marine heatwave events promote similar growth rates but differential domoic acid toxicity in Pseudo-nitzschia australis’The roles of carbonate, borate, and bicarbonate ions in affecting zooplankton hatching success under ocean acidification
Published 27 June 2023 Science ClosedTags: biogeochemistry, biological response, individualmodeling, modeling, multiple factors, physiology, reproduction, respiration, review, temperature, zooplankton
Two ocean acidification studies about egg hatching success (HS) in geographically important marine copepods, Calanus finmarchicus and C. helgolandicus, were reanalyzed with improved statistical procedures. The new results at low and moderate levels of seawater acidification showed no HS inhibition at normal habitat temperatures but statistically significant inhibition at warmer and colder temperatures. These HS results were compared with seawater carbonate system and borate concentrations from precise seawater measurements. The temperature dependent differences in HS could not be directly explained by changes in the seawater concentrations of either H+, bicarbonate (HCO3−), or CO2* (CO2* being the sum of unhydrated CO2 and H2CO3). In contrast, HS differences did match trends in seawater carbonate (CO32−) concentrations. A numerical model was developed which evaluates the concentrations of O2 or CO2*, HCO3−, and CO32− at the cellular level across an egg and embryo by considering both gas diffusion with the seawater and respiration by the embryo. Again, temperature-dependent trends in HS could not be explained changes in intracellular CO2* or HCO3− concentrations, but HS did trend with the changes in intracellular CO32− concentrations. Carbonate ions form strong coordination complexes with metals, so acidification-driven decreases in external seawater carbonate concentrations, which are amplified at warmer temperatures, could release injurious metals, thus driving the HS inhibition at warmer temperatures. Increases in cytoplasmic carbonate concentrations at warmer temperatures caused by seawater acidification could complex with biochemically-needed nutrient-type metals within the cells, also causing the increased HS inhibition at warmer temperatures. Furthermore, boron is essential in chemically signaling within and between cells. Seawater borate concentrations were closely correlated with HS inhibition via Michaelis-Menton equations, suggesting that acidification-driven decreases in seawater borate concentrations may also inhibit HS. Finally, the acidification-driven increases in CO2 diffusion into cells dramatically increased intracellular bicarbonate concentrations. At mild levels of seawater acidification, an organism might compensate by exporting bicarbonate from the cells to the haemolymph and then to the seawater. Although the energetic cost, as percentage of ATP production, might be high, increased respiration rates at warmer temperatures might better allow the organism to survive. However, as temperature is lowered, the cellular respiration rate declines more rapidly with respect to temperature than does the gas diffusion coefficient. Consequently, bicarbonate accumulation driven by inward CO2 diffusion might overwhelm the egg’s bicarbonate export capacity at colder temperatures, explaining the colder temperature HS inhibition.
Continue reading ‘The roles of carbonate, borate, and bicarbonate ions in affecting zooplankton hatching success under ocean acidification’Influence of changes in pH and temperature on the distribution of apparent iron solubility in the oceans
Published 21 June 2023 Science ClosedTags: biogeochemistry, chemistry, field, North Atlantic, South Atlantic, South Pacific
Abstract
An insufficient supply of the micronutrient iron (Fe) limits phytoplankton growth across large parts of the ocean. Ambient Fe speciation and solubility are largely dependent on seawater physico-chemical properties. We calculated the apparent Fe solubility (SFe(III)app) at equilibrium for ambient conditions, where SFe(III)app is defined as the sum of aqueous inorganic Fe(III) species and Fe(III) bound to organic matter formed at a free Fe3+ concentration equal to the solubility of Fe hydroxide. We compared the SFe(III)app to measured dissolved Fe (dFe) in the Atlantic and Pacific Oceans. The SFe(III)app was overall ∼2–4-fold higher than observed dFe at depths less than 1,000 m, ∼2-fold higher than the dFe between 1,000 and 4,000 m and ∼3-fold higher than dFe below 4,000 m. Within the range of used parameters, our results showed that there was a similar trend in the vertical distributions of horizontally averaged SFe(III)app and dFe. Our results suggest that vertical dFe distributions are underpinned by changes in SFe(III)app, which are driven by relative changes in ambient pH and temperature. Since both pH and temperature are essential parameters controlling ambient Fe speciation, these should be accounted for in investigations of changing Fe dynamics, particularly in the context of ocean acidification and warming.
Key Points
- Apparent iron solubility is driven by ambient pH, temperature (T) and dissolved organic carbon (DOC) and showed a 6-fold variation between surface (pH = 8.05 on the total scale, DOC = 71.8 μmol L−1, T = 20.4°C) and deep oceanic waters (pH = 7.82, DOC = 38.6 μmol L−1, T = 1.1°C)
- Higher values of apparent iron solubility were determined for deep Atlantic and Pacific waters, with lower values in subtropical gyres
- Calculated apparent iron solubility showed a similar trend in vertical distribution to dissolved iron, highlighting the importance of considering the impact of changes in ambient physico-chemical conditions on seawater iron chemistry
Coccolithophores and diatoms resilient to ocean alkalinity enhancement: a glimpse of hope?
Published 20 June 2023 Science ClosedTags: biogeochemistry, biological response, growth, laboratory, mitigation, North Pacific, physiology, phytoplankton, primary production
It is increasingly apparent that adequately mitigating anthropogenic climate interference will require ocean carbon dioxide removal (CDR) strategies. Ocean alkalinity enhancement (OAE) is an abiotic ocean CDR approach that aims to increase the ocean’s CO2 uptake capacity through the dispersal of pulverized mineral or dissolved alkali into the surface ocean. However, OAE’s effect on marine biota is largely unexplored. Here, we investigate the impacts of moderate (~700 μmol kg−1) and high (~2700 μmol kg−1) limestone-inspired alkalinity additions on two biogeochemically and ecologically important phytoplankton functional group representatives: Emiliania huxleyi (calcium carbonate producer) and Chaetoceros sp. (silica producer). The growth rate and elemental ratios of both taxa showed a neutral response to limestone-inspired alkalinization. While our results are encouraging, we also observed abiotic mineral precipitation, which removed nutrients and alkalinity from solution. Our findings offer an evaluation of biogeochemical and physiological responses to OAE and provide evidence supporting the need for continued research into how OAE strategies affect marine ecosystems.
Continue reading ‘Coccolithophores and diatoms resilient to ocean alkalinity enhancement: a glimpse of hope?’Increased biogenic calcification and burial under elevated pCO2 during the Miocene: a model-data comparison
Published 15 June 2023 Science ClosedTags: biogeochemistry, chemistry, modeling, North Pacific, paleo, regionalmodeling, review, South Pacific
Abstract
Ocean acidification due to anthropogenic CO2 emission reduces ocean pH and carbonate saturation, with the projection that marine calcifiers and associated ecosystems will be negatively affected in the future. On longer time scale, however, recent studies of deep-sea carbonate sediments suggest significantly increased carbonate production and burial in the open ocean during the warm Middle Miocene. Here, we present new model simulations in comparison to published Miocene carbonate accumulation rates to show that global biogenic carbonate production in the pelagic environment was approximately doubled relative to present-day values when elevated atmospheric pCO2 led to substantial global warming ∼13–15 million years ago. Our analysis also finds that although high carbonate production was associated with high dissolution in the deep-sea, net pelagic carbonate burial was approximately 30%–45% higher than modern. At the steady state of the long-term carbon cycle, this requires an equivalent increase in riverine carbonate alkalinity influx during the Middle Miocene, attributable to enhanced chemical weathering under a warmer climate. Elevated biogenic carbonate production resulted in a Miocene ocean that had carbon (dissolved inorganic carbon) and alkalinity (total alkalinity) inventories similar to modern values but was poorly buffered and less saturated in both the surface and the deep ocean relative to modern.
Key Points
- Pelagic carbonate production during the warm Middle Miocene was approximately doubled relative to present-day values
- Net pelagic carbonate burial of the Middle Miocene was likely ∼30%–45% higher than modern values
- The decreases in [
]sw and carbonate production toward the present kept Neogene dissolved inorganic carbon and total alkalinity nearly constant despite a global pCO2 decrease
Ocean afforestation’s effect on deep-sea biogeochemistry
Published 8 June 2023 Science ClosedTags: biogeochemistry, chemistry, individualmodeling, mitigation, modeling
If climate change is left unchecked it will lead to unprecedented deterioration of human health, economy and ecology. According to the IPCC, in order to avoid severe consequences, global warming will need to be limited to 1.5°C. However, the 1.5°C warming will be exceeded if current trends continue, which is why the need for Carbon Dioxide Removal (CDR) has become increasingly apparent. Ocean afforestation is currently one of the most promising CDR approaches, with the least competition for space, high carbon sequestration potential and high technical feasibility. Ocean afforestation approaches attempt to sequester carbon by sinking seaweed to deep-sea areas. This research looks at the consequences of the seaweed input to deep-seafloor. An early diagenetic model called RADI is used to predict the fate of the carbon and the effect on biogeochemistry. The model was adapted to include new sources of sedimentary organic matter, such as seaweed (Sargassum, Saccharina, Macrocystis) and Sugarcane bagasse, which are currently considered potential candidates for ocean afforestation purposes. Sargassum, an invasive free-floating species, has a large sequestration potential and is readily available. Sinking Sargassum in pulse, large amounts over short times, leads to high carbon retention in the sediment (up to 25% after two years) but leads to hypoxic conditions in the sediment for at least two years after addition. Continuous Sargassum sinking also leads to carbon sequestration but with a much less invasive impact on the seafloor. The carbon from continuous sinking does not remain in the sediment but is remineralized and flows out to the bottom water as inorganic carbon. Saccharina, an edible coastal species, could be used to grow on free floating organic buoy. Having the additional sequestration benefit from the carbon fixed in the organics. Carbon retention is highest for the pulse addition of this seaweed (33% after two years), compared to a continuous approach (30%) in which the seaweed is added over longer timescales in small amounts. Since this pulse input also leads to hypoxic conditions in the sediment, the continuous approach is more favourable for this approach. Macrocystis, the giant kelp known for forming ecosystems, is a fast-growing coastal species. This species requires harvesting and baling for use in carbon sequestration. Carbon retention is much higher for pulse addition (30%). Sugar cane bagasse is an agricultural residue with high carbon content. Sinking this residue to anoxic basins, has been proven to retain more carbon than in oxygenated bottom waters. This can be confirmed with the results which showed a carbon retention of up to 50% after two years. The effect on the benthic biome is also less intense since the low oxygen conditions already necessitate a specialized microbiome. Sugarcane bagasse is furthermore the only addition capable of increasing bottom water pH. Whereas all seaweed approaches had higher dissolved inorganic carbon than alkalinity flow to the bottom water, resulting in net acidification. This research provides a first look into the effects of ocean afforestation on deep sea biogeochemistry, and illustrates the importance of the composition, quantity and input duration of the seaweed used.
Continue reading ‘Ocean afforestation’s effect on deep-sea biogeochemistry’Risk assessment of a coastal ecosystem from SW Spain exposed to CO2 enrichment conditions
Published 8 June 2023 Science ClosedTags: abundance, biogeochemistry, biological response, BRcommunity, community composition, crustaceans, echinoderms, laboratory, mesocosms, mollusks, morphology, mortality, North Atlantic, otherprocess, physiology, sediment
The Weight-of-Evidence (WOE) approach uses multiple lines of evidence to analyze the adverse effects associated with CO2 enrichment in two stations from the Gulf of Cádiz (Spain) with different contamination degrees. Sediment contamination and metal (loid) mobility, toxicity, ecological integrity, and bioaccumulation from the samples exposed to different acidification scenarios (pH gradient from 8.0 to 6.0) were used in the WOE. The experiments were conducted under laboratory conditions using a CO2-bubbling system. Different integration approaches such as multivariate analyses were used to evaluate the results. The results indicated that the adverse biological effects under pH 6.5 were related to the mobility of dissolved elements (As, Fe, Cu, Ni, and Zn). Furthermore, the pH reduction was correlated to the increase of bioaccumulation of As, Cr, Cu, Fe, and Ni in the tissues of mussels at pH 7.0. The noncontaminated sediment showed environmental degradation related to the acidification at pH values of 7.0; whereas the sediment moderately contaminated showed both environmental risks, caused by acidification and the presence and the increase of the bioavailability of contaminants. The WOE approach supposes an effective tool to identify and distinguish the causes of adverse effects related to the enrichment of CO2 in marine environments.
Continue reading ‘Risk assessment of a coastal ecosystem from SW Spain exposed to CO2 enrichment conditions’Explosive volcanism periodicity past cycles record within the last 0.8 Mya evidenced by tephra and benthic foraminifera of IODP Hole U1485AA (Exp. 363 WPWP)
Published 5 June 2023 Science ClosedTags: abundance, biogeochemistry, biological response, BRcommunity, community composition, field, otherprocess, paleo, protists, sediment, South Pacific
Volcanic eruptions with increase in the amount of carbon dioxide (CO2) and other gases are responsible for the extinction of many species because of decreased pH and carbonate availability which creates ocean acidification. Here we show how benthic foraminifera have evolved, by studying sediments from U1485A (1145 m water depth) core in the Papua New Guinea (PNG) collected during IODP Expedition 363 in the Western Pacific Warm Pool (WPWP), one of the warmest marine waters of the world. High-stressed environments dominated by low diversity of opportunistic species after volcanic activity was detected by the presence of tephra and volcanic ashes within the last 0.8 Mya. The decrease in the diversity patterns show an inverse correlation to the presence of tephra and ash right after Pleistocene volcanic eruptions in the past. Deep-water fauna is dominated by Cibicidoides pachiderma, from the early Oligocene through the Pleistocene, Uvigerina hispida from early Miocene through Pleistocene, U. prosbocidae from late Oligocene through Pleistocene, and an outer neritic upper bathyal Uvigerina mediterranea from high salinities, warm waters, low dissolved oxygen, and high organic matter. Bolivinita quadrilatera characteristic of 200-500m depth, Bolivina robusta from 3 to 900m, and the Rotalinoides compressiusculus, a shallow warm water species, from 2-37m depth show higher diversity peaks in interglacial cycles. High-stress conditions with mass extinction after volcanic eruptions leads to enhanced weathering, global warming and cooling afterwards, and ocean acidification, resulting in a crisis in the marine environment in terms of carbonate. Diversity gradients suggested that foraminiferal species responded to the cyclic pulses of volcanic eruptions, and its unstable ecological conditions created by the increase in the temperature and CO2. Here we show that tephra layers and ash record a periodicity of explosive volcanism within the last 0.8 Myr maintaining a strong 100 kyr periodicity, and that earth’s orbital cycles might trigger peaks of volcanic eruptions 41,000-year cycle.
Continue reading ‘Explosive volcanism periodicity past cycles record within the last 0.8 Mya evidenced by tephra and benthic foraminifera of IODP Hole U1485AA (Exp. 363 WPWP)’Coastal acidification alters estuarine sediment nitrous oxide and methane fluxes
Published 2 June 2023 Science ClosedTags: biogeochemistry, laboratory, North Atlantic, sediment
Abstract
The impact of coastal acidification on sediment nitrous oxide (N2O) and methane (CH4) fluxes is largely unknown. We exposed temperate estuarine sediments to moderate (pH 7.3) and extreme (pH 6.3) acidification. Sediments were collected from two sites—one exposed to high and the other to low nitrogen loading. We demonstrate that low pH has a strong effect on greenhouse gas fluxes. The response, in terms of both magnitude and direction, was site specific. Sediments from the high nitrogen loading site exhibited increased N2O fluxes and decreased CH4 fluxes under moderate and extreme acidification. In contrast, sediments from the low nitrogen loading site exhibited decreased N2O fluxes under moderate and extreme acidification while CH4 fluxes both decreased (moderate) and increased (extreme). This study highlights the dynamic response of sediment N2O and CH4 fluxes to low pH and emphasizes the need for deeper understanding of ofcoastal acidification impacts on sediment biogeochemistry.
Scientific Significance Statement
Estuaries are increasingly exposed to low pH conditions (i.e., coastal acidification) largely driven by rising temperatures, increased precipitation, and excess nutrient loading. The impact of coastal acidification on sediment biogeochemical processes, including those responsible for the production or consumption of greenhouse gases (GHGs) are largely unknown. Here, we show that sediment fluxes of two powerful GHGs (nitrous oxide: N2O and methane: CH4) respond rapidly to low pH conditions. In addition, the magnitude and direction of this response varies within an estuary, even at sites with similar pH exposure histories. Overall, this study highlights the need to incorporate current and future pH conditions in forecasting models and in the development of coastal GHG budgets.
Continue reading ‘Coastal acidification alters estuarine sediment nitrous oxide and methane fluxes’
