Posts Tagged 'biogeochemistry'

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Interactions between ocean acidification and multiple environmental drivers on the biochemical traits of marine primary producers: a meta-analysis

Published 19 September 2024 Science Closed
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Highlights

  • OA acted interactively with other environmental drivers on marine primary producers.
  • Additive effects dominated, with smaller proportions of antagonism and synergism.
  • Interaction type depends on the specific type of the environmental driver.

Abstract

Ocean acidification (OA) interacts with multiple environmental drivers, such as temperature, nutrients, and ultraviolet radiation (UVR), posing a threat to marine primary producers. In this study, we conducted a quantitative meta-analysis of 1001 experimental assessments from 68 studies to examine the combined effects of OA and multiple environmental drivers (e.g., light, nutrient) on the biochemical compositions of marine primary producers. The results revealed significant positive effects of each environmental driver and their interactions with OA according to Hedge’s d analysis. The results revealed significant positive effects of multiple environmental drivers and their interactions with OA. Additive effects dominated (71%), with smaller proportions of antagonistic (20%) and synergistic interactions (9%). The antagonistic interactions, although fewer, had a substantial impact, causing OA and other environmental drivers to interact antagonistically. Significant differences were observed among taxonomic groups: haptophytes and rhodophytes were negatively affected, while bacillariophytes were positively affected by OA. Our findings also indicated that the interactions between OA and multiple environmental drivers varied depending on specific type of the environmental driver, suggesting a modulating role of OA on the biochemical compositions of marine primary producers in response to global change. In summary, our study elucidates the complex interactions between OA and multiple environmental drivers on marine primary producers, highlighting the varied impacts on biochemical compositions and elemental stoichiometry.

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Historic ocean acidification of Loch Sween revealed by correlative geochemical imaging and high-resolution boron isotope analysis of Boreolithothamniom cf. soriferum

Published 18 September 2024 Science Closed
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Highlights

  • The δ11B of coralline algae skeleton offer a means to reconstruct coastal pH.
  • 2D maps of trace element content and δ11B were collected on Boreolithothamniom cf. soriferum.
  • These images were aligned using correlated multimodal imaging techniques.
  • We reconstruct an ocean acidification trend of −0.018 pH units yr-1 in Loch Sween.
  • Loch Sween switched from being a substantial sink of CO2 to a source in ∼2008.

Abstract

Ocean Acidification (OA) arises from the increase in atmospheric carbon dioxide concentration following the industrial revolution. The ecological and socio-economic consequences of OA were first identified around 10–15 years ago but remain poorly understood. This is particularly true in coastal regions where local processes can have dramatic consequences on pH trends through time, obscuring and compounding the long-term effects from rising atmospheric CO2. Here we explore the possibility of generating long records of coastal ocean pH using the skeletons of widely distributed coralline algae (CA). The skeletons of these slow growing (<1 mm/year) taxa often contain micron-scale heterogeneities, making sampling for high-resolution climate reconstructions using bulk sampling techniques difficult. Here we use laser ablation coupled to inductively coupled plasma mass spectrometers to generate high-resolution 2D images of the element/calcium ratios and boron isotope composition (δ11B) of a sample of Boreolithothamniom cf. soriferum from Loch Sween in Scotland, UK where we have been monitoring temperature since 2004 and pH during 2014. By carefully correlating the geochemical images with a scanning electron microscopy image we can segment them to remove the marginal portions of the skeleton, isolating the central growth axis to generate an age model and growth rate. The δ11B-pH is significantly elevated above the seawater pH in Loch Sween (8.4 to 8.9 vs. 7.9 to 8.1) consistent with other CA that show internal pH elevation. On a seasonal scale, internal pH is negatively correlated with temperature and also exhibits a long-term decline. By removing this temperature effect, internal pH can be correlated to seawater pH during the 2014 monitoring period allowing us to reconstruct a seawater acidification trend from 2004 to 2018 of -0.018 pH units per year, 10x higher than open ocean trends but consistent with contemporaneous monitoring efforts of UK coastal waters. Reconstructed aqueous CO2 suggests that prior to ∼2008 Loch Sween was a sink of CO2 but after this date, particularly during the early summer, it was a substantial CO2 source. Comparison of reconstructed aqueous CO2 with a record of calcification rate of our sample of Boreolithothamniom cf. soriferum suggests this acidification and associated rise in local seawater pCO2 may have freed this sample from carbon limitation leading to a recent increase in calcification.

Continue reading ‘Historic ocean acidification of Loch Sween revealed by correlative geochemical imaging and high-resolution boron isotope analysis of Boreolithothamniom cf. soriferum’

Morphological and physiological responses of the cosmopolitan marine diatom Thalassiosira rotula to acidification

Published 13 August 2024 Science Closed
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We investigated the effect of decreased pH on the morphology and nutrient physiology of the cosmopolitan marine diatom Thalassiosira rotula (CCMP3362) by acclimating unialgal cultures to two different CO2 gas concentrations under optimal light, temperature and nutrient conditions. At lower pH (higher CO2), T. rotula exhibited a reduction in cell diameter (7%), surface area (13%), and volume (20%), and an increase in surface area-to-volume ratio (7%). All measures of silicification in T. rotula, i.e., silica (SiO2) quota, rate of silicic acid (Si(OH)4) utilization, and elemental ratios of SiO2:C and SiO2:N, remained unchanged. Similarly, carbon (C) and nitrogen (N) quotas, ratios and utilization rates were mostly unaffected by pH. In contrast, the utilization rate of nitrate (ρNO3) was significantly lower at decreased pH when the rate was normalized by cell number instead of by cell volume. The changes in cell morphology found in this study under low pH were likely not large enough to significantly impact physiological processes and the role of this species in marine food webs and biogeochemical cycles. It is possible that the interactive effects of pH, temperature, light, and nutrient availability characteristic of different regions of the world ocean could result in stronger physiological and morphological responses in this widespread diatom. However, under constant optimal growth conditions, T. rotula was only mildly affected by changes in pH, and in particular the physiology and elemental stoichiometry of C, N and Si were not sensitive to acidification.

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Coupling effects of CO2-induced ocean acidification and nitrogen enrichment on growth, photosynthesis and nitrogen utilization of an invasive seaweed (Sargassum muticum)

Published 8 August 2024 Science Closed
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Highlights

  • Ocean acidification promotes growth of Sargassum muticum.
  • Both ocean acidification and enrichment of NO3−−N increase photosynthesis of Sargassum muticum.
  • Ocean acidification and NO3−−N enrichment non-synergistically enhance invasiveness of S. muticum.

Abstract

Sargassum muticum, an invasive seaweed, has colonized many parts of the world along the coast. Marine environment invaded by this species is aggravated the complexity by CO2-induced ocean acidification (OA) and coastal eutrophication. However, the coupling effects of seawater acidification and eutrophication on this invasive species remain unclear. In this study, we cultured Sargassum muticum at two concentrations of pCO2 (420 ppmv, LC and 1000 ppmv, HC) and nitrate (10 μM, LN and 200 μM, HN) for 16 days, to investigate the coupling effects of CO2-induced seawater acidification and nitrate enrichment on growth and photosynthesis of Sargassum muticum. The results showed that high CO2 increased the relative growth rate (RGR) of alga by 58.9% under LN condition, while such increment was not found under HN condition. Thus, the highest RGR was emerged in the HCLN treatment. The photosynthetic rate curve under different inorganic carbon concentrations (Psingle bondC curve) presented that high CO2 increased the maximum inorganic carbon utilization rate (Vmax) by 8.1% under HN condition; while inhibited it by 29.8% under LN condition. The affinity to inorganic carbon, reflected by the half-saturation constant (K0.5), was improved significantly by high CO2 and/or high nitrate, compared with LCLN treatment. The photosynthetic rate curves under different irradiances (Psingle bondI curve) suggested that the maximum photosynthetic rate (Pmax) of alga was enhanced remarkably by high N, and kept unaffected by high CO2. The lowest value of dark respiration rate (Rd) was found in HCLN treatment, and there was no significant difference among the other three treatments. Additionally, an increase chlorophyll a content caused by high N was only found in HC treatment. After 16 d culture, nitrate reductase activity (NRA) of algae in HN treatments decreased significantly, compared with those in LN treatments. Furthermore, high CO2 enhanced NRA dramatically only in algae grown at LN level. Correspondingly, the lowest nitrate uptake rate (NUR) was found in LCHN treatment, and there was no significant difference among the other three treatments. In conclusion, our results showed that elevated CO2 enhanced the RGR, and the coupling of high CO2 and nitrate affected the photosynthesis and NUR, however did not synergistically promote growth of S. muticum. Therefore, we speculate that the future OA may exacerbate the invasiveness of S. muticum; nevertheless, the eutrophication of seawater would not amplify this effect.

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Implications of ocean warming and acidification on heavy metals in surface seawater of the Bohai Sea

Published 26 July 2024 Science Closed
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Highlights

  • Most of the studied heavy metals declined from the three bays to the centre of the Bohai Sea;
  • The major risk agents in seawater were Pb and Hg across the whole Bohai Sea;
  • Rising temperature or pH decline significantly affected the dynamics of heavy metals;
  • Ocean warming and acidification will modify the speciation and nature of heavy metals.

Abstract

At present, a clear dependency of the dynamics upon temperature and pH has not been established for many heavy metals (HMs), so making it difficult to project and quantify the impact of ocean warming and acidification on metal biogeochemistry in future scenarios. To understand the responses of HMs to future ocean warming and acidification, we estimated the spatial-temporal variations and pollution status of six dissolved HMs (i.e., Cu, Zn, Pb, Cd, Hg, and As) in surface seawater throughout the Bohai Sea during 2012–2014. The results showed that the average concentrations of Cu, Zn, Pb, Cd, Hg, and As in seawater of the Bohai Sea were between 2.01–3.18, 10.47–15.58, 0.85–2.31, 0.25–0.55, 0.05–0.13, and 1.24–1.98 μg L-1, respectively. Spatially, the average concentrations of the studied HMs generally decreased from the three bays towards the central area, except for Hg which was relatively high in the central Bohai Sea in some cases. This implied that, in addition to continental inputs, there may be other processes affecting the distribution pattern of Hg, such as cyclonic or anticyclonic gyres, benthic fluxes between surface and bottom layers, and some marine planktonic and microbial activities. The pollution assessments of six HMs in seawater revealed that the major risk pollutants were Pb and Hg across the Bohai Sea. Analyses of the local and interactive effects of temperature and pH on HMs showed that the interactive effect of changing temperature and pH on HMs is much more complex than a direct temperature/pH relationship with HMs. Altogether, the results suggested that future ocean warming and acidification will significantly influence the concentrations of dissolved HMs in seawater of the Bohai Sea, but with different relationships.

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Nitrogen input modulates the effects of coastal acidification on nitrification and associated N2O emission

Published 11 July 2024 Science Closed
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Highlights

  • N input influenced the response of nitrifying microbes to coastal acidification.
  • Elevated N input alleviated the inhibitory effect of acidification on nitrification.
  • Increase of N input intensified the production of N2O under coastal acidification.
  • Metatranscriptome data further provided microbial evidence at transcriptional level.

Abstract

Acidification of coastal waters, synergistically driven by increasing atmospheric carbon dioxide (CO2) and intensive land-derived nutrient inputs, exerts significant stresses on the biogeochemical cycles of coastal ecosystem. However, the combined effects of anthropogenic nitrogen (N) inputs and aquatic acidification on nitrification, a critical process of N cycling, remains unclear in estuarine and coastal ecosystems. Here, we showed that increased loading of ammonium (NH4+) in estuarine and coastal waters alleviated the inhibitory effect of acidification on nitrification rates but intensified the production of the potent greenhouse gas nitrous oxide (N2O), thus accelerating global climate change. Metatranscriptomes and natural N2O isotopic signatures further suggested that the enhanced emission of N2O may mainly source from hydroxylamine (NH2OH) oxidation rather than from nitrite (NO2−) reduction pathway of nitrifying microbes. This study elucidates how anthropogenic N inputs regulate the effects of coastal acidification on nitrification and associated N2O emissions, thereby enhancing our ability to predict the feedbacks of estuarine and coastal ecosystems to climate change and human perturbations.

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B(OH)4− and CO32− do not compete for incorporation into aragonite in synthetic precipitations at pHtotal 8.20 and 8.41 but do compete at pHtotal 8.59

Published 8 July 2024 Science Closed
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Coral skeletal B/Ca (effectively B/CO32–), in combination with boron isotopic composition (δ11B), has been used to reconstruct the dissolved inorganic carbon chemistry of coral calcification media and to explore the biomineralisation process and its response to ocean acidification. This approach assumes that B(OH)4−, the B species incorporated into aragonite, competes with dissolved inorganic carbon species for inclusion in the mineral lattice. In this study we precipitated aragonite from seawater in vitro under conditions that simulate the compositions of the calcification media used to build tropical coral skeletons. To deconvolve the effects of pH and [CO32–] on boron incorporation we conducted multiple experiments at constant [CO32–] but variable pH and at constant pH but variable [CO32–], both in the absence and presence of common coral skeletal amino acids. Large changes in solution [CO32–], from < 400 to >1000 µmol kg−1, or in precipitation rate, have no significant effect on aragonite B/Ca at pHtotal of 8.20 and 8.41. A significant inverse relationship is observed between solution [CO32–] and aragonite B/Ca at pHtotal = 8.59. Aragonite B/Ca is positively correlated with seawater pH across precipitations conducted at multiple pH but this relationship is driven by the effect of pH on the abundance of B(OH)4– in seawater. Glutamic acid and glycine enhance the incorporation of B in aragonite but aspartic acid has no measurable effect. Normalising aragonite B/Ca to solution [B(OH)4–] creates KDB(OH)4− which do not vary significantly between pH treatments. This implies that B(OH)4– and CO32– do not compete with each other for inclusion in the aragonite lattice at pHtotal 8.20 and 8.41. Only at high pH (8.59), when [B(OH)4–] is high, do we observe evidence to suggest that the 2 anions compete to be incorporated into the lattice. These high pH conditions represent the uppermost limits reliably measured in the calcification media of tropical corals cultured under present day conditions, suggesting that skeletal B/Ca may not reflect the calcification media dissolved inorganic carbon chemistry in all modern day corals.

Continue reading ‘B(OH)4− and CO32− do not compete for incorporation into aragonite in synthetic precipitations at pHtotal 8.20 and 8.41 but do compete at pHtotal 8.59’

Marine Roseobacter clade bacteria decelerate the conversion of dimethylsulfoniopropionate under ocean acidification

Published 2 July 2024 Science Closed
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Ocean acidification has been an alarming issue that is jeopardizing the marine environment and ecology. Marine Roseobacter clade bacteria mediate important biogeochemical cycles in the ocean and are an indispensable sector of marine ecology. However, seldom has research attempted to unveil the effects of ocean acidification on bacteria in the Roseobacter clade, leaving a gap in understanding the environmental and ecological impacts of global climate change and ocean acidification. Here, we evaluated the effects of acidification on Roseovarius nubinhibens, a representative strain in the marine Roseobacter clade. We found that a marginal decrease in pH was influential enough to inhibit cell growth and induce cellular responses at the system level. We determined the essential role of glutathione metabolism in response to a lower pH via combined RNA sequencing, biochemical analysis, and CRISPR-Cas genome editing. Finally, we observed that a lower pH decelerated the metabolism of dimethylsulfoniopropionate, a key precursor for the global sulfur cycle and the formation of clouds, which would probably hasten global climate changes. Taking together, we believe that our study provides a missing puzzle piece toward a comprehensive understanding of the effects of global climate change and ocean acidification on our planet.

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Ocean acidification in the tropical Indian Ocean over the past 37 years: insights from 𝛿11B and B/Ca records in a Maldives coral

Published 1 July 2024 Science Closed
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Highlights

  • This is the first coral’s carbonate chemistry record in the tropical Indian Ocean.
  • Porites calcification pH is sensitive to ocean acidification, but the transfer function to seawater pH needs re-evaluation.
  • A different internal energy/dissolved inorganic carbon (DIC) supply might explain the lower [DIC] CF observed in Maldives corals.
  • Data from a wider geographic range is required to constrain the impacts of ocean acidification on corals.

Abstract

Boron isotopes (𝛿11B) in coral skeletons of Porites have been widely applied to reconstruct past seawater pH (pHSW) on decadal to centennial timescales. However, due to biological regulation within corals, an additional transfer function is required to estimate ambient seawater chemistry during the skeleton growth under the calcification site fluid pH. Temperature may also interfere with coral calcification fluid pH (pHCF) due to changes in kinetics of coral aragonite precipitation, or buffering capacity in coral calcification fluid. To decipher how coral Porites adjusts pHCF in response to pHSW from complex environmental controls, long-term records from sites with least fluctuations in environmental conditions other than pHSW are essential. Here we present a 37-year record of coral 𝛿11B and B/Ca ratios derived from a coral core collected from southern Maldives, the tropical Indian Ocean. Our results show no clear seasonality in the coral 𝛿11B and B/Ca ratios between monsoons, but a long-term decline in coral pHCF is evident across the entire record. When applying different existing transfer functions, we also observe discrepancies among the calculated pHCF values, model results and short-term instrumental data. Calculated calcification fluid dissolved inorganic carbon concentration ([DIC]CF) values are relatively low compared to literature, suggesting that coral calcification fluid carbonate chemistry may be under different levels of control, even within the same coral taxa. Thus, coral records from a wider geographic range are required to better quantify coral response to ocean acidification, and our results can serve as a baseline for future comparisons.

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Freezing-induced acidification of sea ice brine

Published 28 June 2024 Science Closed
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Highlights

  • Brine in sea ice acidifies progressively with decreasing temperature.
  • Sea water salinity controls the sea ice brine acidity more than the original pH.
  • The minerals’ precipitation causes the reduced buffering capacity and acidification.
  • In-situ probe method assessing microscopic (sea) ice brine acidity is introduced.

Abstract

The acidity of sea ice and snow plays a key role in the chemistry of the cryosphere; an important example lies in the photochemical catalytic release of reactive bromine in polar regions, facilitated at pHs below 6.5. We apply in-situ acid-base indicators to probe the microscopic acidity of the brine within the ice matrix in artificial sea water at a range of concentrations (0.35–70 PPT) and initial pHs (6–9). The results are supported by analogous measurements of the most abundant salts in seawater: NaCl, Na2SO4, and CaCO3. In the research herein, the acidity is expressed in terms of the Hammett acidity function, H2−. The obtained results show a pronounced acidity increase in sea water after freezing at −15 °C and during the subsequent cooling down to −50 °C. Importantly, we did not observe any significant hysteresis; the values of acidity upon warming markedly resembled those at the corresponding temperatures at cooling. The acidity increase is attributed to the minerals’ crystallization, which is accompanied by a loss of the buffering capacity. Our observations show that lower salinity sea water samples (≤ 3.5 PPT) reach pH values below 6.5 at the temperature of −15 °C, whereas higher salinity ices attain such values only at −30 °C. The ensuing implications for polar chemistry and the relevance to the field measurements are discussed.

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Taphonomy and aleoecology of lycoptera: a case study from the lower jehol group in Western Liaoning, Northeastern China

Published 27 June 2024 Science Closed
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Taphonomy and paleoecology (biological behavior) of the Early Cretaceous fish fossils are poorly described. This study reports for the first time a detailed taphonomical and paleoecological study on Lycoptera in the Mesozoic strata of western Liaoning Province, NE China. The XRD analysis shows that gismondine is the dominant clay minerals that could have contributed to the preservation of Lycoptera fossils and microbial mat fragments in the fossil-bearing horizon. Gismondine may have formed under volcanism-related hydrothermal regime that was transformed from crystal and lithic fragments. The μ-XRF imaging analysis shows a dominant chemical composition of Al, Si, P, S, Rh, K, Ca, Ti, C, Cr, Mn, Fe, Ni, among which P, Ca, C and S are enriched in the fish skeleton in comparison to the matrix. This suggests a dominant apatite composition for the fish skeleton. Hydrothermal influence did not smear off these organic signals probably because of protection of gismondine. The coexistance of C and S with Ni is assumed to represent recovered primary productivity following volcanic explosions and toxic gas emissions. The head of juvenile fish stays close to the body of adult fish. Pending further discoveries, such phenomenon is interpreted to suggest that adult fish actively protected juvenile fish in the presence of environmental pressures such as anoxia and deterioration of water quality induced by volcanism. Ocean acidification and hypoxia in association with volcanism created a harmful environment causing mass extinction of fish. The adult Lycoptera protected their juveniles by its body at the moment before death. Such biological behavior will be increasingly reported given the wide occurrence of Lycoptera in Mesozoic strata.

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Sulphate reduction and carbonate precipitation in a high-energy algal rim framework

Published 24 June 2024 Science Closed
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Algal ridges are protective features for coral reefs that form through the accretion and encrustation of reef rubble and debris by crustose coralline algae (CCA) and processes of diagenetic cementation. Carbonate precipitation and dissolution dynamics on and within algal ridge frameworks are poorly understood. We studied the surface and subsurface geochemistry of the algal ridge framework at One Tree Island, Australia. Measurable quantities of hydrogen sulphide were detected in most porewater samples collected from bores, indicating a largely anoxic ridge framework. Total alkalinity (TA) and pH measurements indicate that the precipitation of carbonate minerals within the interior of the ridge framework occurs under largely anoxic conditions and is likely to be driven by TA changes associated with sulphate-reducing bacteria. Modelling of porewater hydrogen sulphide concentrations in combination with TA and dissolved inorganic carbon (DIC) indicates anoxic respiration processes produce alkalinity within the algal ridge framework. However, significantly more TA is removed via the precipitation of mineral carbonate, resulting in porewater TA concentrations falling below the open seawater values. The precipitation of mineral carbonate also lowers interstitial water pH, such that pH changes are not solely from organic carbon diagenesis. The simultaneous precipitation and dissolution of carbonate minerals within the algal ridge framework are key to forming and cementing algal ridges, which are important physical protective features for coral reefs.

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How much can riverine biogeochemical fluxes affect the arctic ocean acidification?

Published 19 June 2024 Science Closed
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Abstract

Arctic rivers carry not only large amounts of freshwater but also biogeochemical materials into the ocean and play important roles in Arctic ocean acidification (OA). This study quantitatively evaluated the effects of riverine biogeochemical fluxes (R-BGC; carbon and nutrients) on the Arctic marine carbonate system and OA using multi-decadal experiments (1979–2018) with a pan-Arctic sea ice–ocean model. Improved initial and lateral boundary conditions of carbonate properties, observation-based riverine biogeochemical data, and land model-based interannually varying riverine freshwater discharge were adopted to enable more realistic experiments. The model simulated negative trends in aragonite saturation state (Ω) and pH in most regions of Arctic Ocean regardless of R-BGC. The increased riverine freshwater promoted more OA through the higher dilution effect. Compared to the experiment with riverine discharge of only freshwater, the inclusion of R-BGC caused positive anomalies in Ω and pH (by ∼0.14 and ∼0.03 in central basins, and by ∼0.15 and ∼0.06 in shelf seas, respectively). In the central basins, these anomalies were caused mostly by carbon (total alkalinity and dissolved inorganic carbon) of the R-BGC. In the shelf seas, nutrient (nitrate and silicate) fluxes also contributed ∼14% and ∼32% of the anomalies owing to the enhanced primary production and a corresponding reduction in seawater pCO2. R-BGC mitigated OA (ΔΩ = −1.53 × 10−3 year−1 and ΔpH = −0.56 × 10−3 year−1) in regions where riverine freshwater was accumulated (i.e., the Canada Basin, Chukchi Cap, Eurasian Basin, and East Siberian Sea). This study stressed the importance of including R-BGC for OA model projection.

Key Points

  • Simulations with only riverine freshwater overestimate Arctic ocean acidification and negative trends in aragonite saturation state and pH
  • Addition of riverine biogeochemical fluxes, especially total alkalinity and dissolved inorganic carbon, can reduce this overestimation
  • Riverine nutrient fluxes can also reduce ∼14% and ∼32% of the overestimation in aragonite saturation state and pH in shelf seas

Plain Language Summary

Ocean acidification (OA) is caused primarily by atmospheric CO2 absorption at the sea surface. In the Arctic Ocean, riverine biogeochemical inputs (R-BGC; carbon and nutrients carried by riverine water), in addition to freshwater discharge, affect OA. This study quantified the effects of R-BGC on OA using a couple of model simulations for 1979–2018. Advancing from previous studies, this study conducted more realistic experiments by using improved initial and lateral boundary conditions of carbonate properties, observation-based riverine biogeochemical data, and the land model-based interannually varying riverine freshwater discharge data. R-BGC impacts on OA were found mainly in the surface waters of the Arctic, especially in coastal regions close to the river mouths. During 1989–2018, negative trends in carbonate saturation state and pH (both indicating OA) were simulated regardless of R-BGC in most regions of Arctic Ocean. Compared to a simulation with riverine input of only freshwater, R-BGC mitigated the simulated OA in the regions with increased riverine freshwater content. This study stressed the importance of R-BGC for model-based OA estimation and future projections. It will improve the understanding of OA under climate change and aid in informing marine ecosystem-based management.

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Impact of climate change on carbon and nitrogen balance in Zostera Marina L. (Eelgrass)

Published 14 June 2024 Science Closed
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Seagrasses face vulnerability to both global stressors like Ocean Acidification (OA) and climate warming compounded by local stressors such as eutrophication that reduces light availability, leading to a complex dynamic of positive and negative effect on their growth and survival. Increased dissolved aqueous CO2 (CO2(aq)) benefits seagrasses by enhancing photosynthetic and growth rates, but it may increase nutrient demand, potentially depleting nutrient supply, especially in oligotrophic environments. In this study, the long-term impact of CO2 on Zostera marina L. (eelgrass) were investigated across a gradient of CO2(aq) concentrations (55 – 2200 µM CO2(aq)) and leaf area indices (LAI). The focus was on quantify changes in carbon (C) and nitrogen (N) content, composition, and metabolism in response to CO2-stimulated photosynthesis and growth. Absolute growth rates, shoot sizes, leaf density, sucrose concentrations, and carbon and nitrogen growth demands increased with increasing CO2(aq) availability. However, there was no notable decline in biomass-specific N content of leaf at higher CO2(aq) concentrations primarily due to dilution effects caused by carbon accumulation in thicker leaves, rather than N-limitation. Rather than increasing plant survival in the context of CO2(aq) enrichment, this study found that nutrient enrichment of the sediment reduced plant survival as a result of NH4 +toxicity. In contrast, the high H2S concentrations reaching millimolar levels in sediment, which was stimulated by organic carbon addition, was not particularly toxic to eelgrass. CO2 effects on N uptake were complicated by changes in canopy architecture due to increasing leaf area index (LAI), affecting N uptake patterns of leaves and roots. Combining a nutrient uptake model with the radiative transfer GrassLight (v2.14) model, this study explored how CO2-driven photosynthesis affected N uptake patterns and requirements for growth. Model predictions across varying LAIs and CO2(aq) concentrations indicated low N demand for eelgrass under all CO2(aq) conditions, with roots playing a key role in N acquisition as CO2(aq) concentrations increased. Overall, my results highlight the importance of photosynthesis in regulating N metabolism and acquisition between the above- and belowground components, and suggest that most eelgrass meadows are unlikely to experience N limitation, even in high CO2(aq) environments.

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Spatio-temporal dynamics of the carbonate system during macroalgae farming season in a semi-closed bay in southeast China

Published 11 June 2024 Science Closed
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Ocean Negative Carbon Emission (ONCE) involves utilizing natural marine chemistry and biology, along with mariculture, to achieve carbon sink goals. Growing awareness of the interplay between aquaculture and the coastal carbonate system has drawn researchers’ attention amid ring CO2 concentrations and the negative impacts of aquaculture on the environment. In this study, twelve sites representing different maricultural types were selected, including macroalgae, shellfish, fish, and non-farming areas. The environmental factors, dissolved inorganic carbon (DIC), total alkalinity (TA), and pCO2, were measured monthly during kelp farming periods. Nitrate is a major component of total nitrogen, and the NO3-N concentration in the macroalgal culture zone was lower than others, indicating effective nitrogen removal by macroalgae aquaculture. TA and DIC in non-farmed areas demonstrated larger variation ranges than in farming areas, probably due to the effects of precipitation on salinity. Aquaculture activities effectively maintained TA and DIC, with macroalgae cultivation playing an important role in TA stability, potentially resisting acidification. The pCO2sea-air of macroalgae culture areas in spring was slightly negative, suggesting carbon sink potential. However, further research is needed to assess the full extent of this “fourth type” of blue carbon, including accurate carbon footprint calculation and the contributions of particulate organic carbon and recalcitrant dissolved organic carbon. This study provided insight into the comprehensive contribution of different aquaculture types to the fishery environment and carbonate system, which can help guide aquaculture management and facilitate the carbon-neutral transition of aquaculture.

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The impact of aragonite saturation variability on shelled pteropods: an attribution study in the California Current System

Published 11 June 2024 Science Closed
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Observations from the California Current System (CalCS) indicate that the long-term trend in ocean acidification (OA) and the naturally occurring corrosive conditions for the CaCO3 mineral aragonite (saturation state Ω < 1) have a damaging effect on shelled pteropods, a keystone group of calcifying organisms in the CalCS. Concern is heightened by recent findings suggesting that shell formation and developmental progress are already impacted when Ω falls below 1.5. Here, we quantify the impact of low Ω conditions on pteropods using an individual-based model (IBM) with life-stage-specific mortality, growth, and behavior in a high-resolution regional hindcast simulation of the CalCS between 1984 and 2019. Special attention is paid to attributing this impact to different processes that lead to such low Ω conditions, namely natural variability, long-term trend, and extreme events. We find that much of the observed damage in the CalCS, and specifically >70% of the shell CaCO3 loss, is due to the pteropods’ exposure to naturally occurring low Ω conditions as a result of their diel vertical migration (DVM). Over the hindcast period, their exposure to damaging waters (Ω < 1.5) increases from 9% to 49%, doubling their shell CaCO3 loss, and increasing their mortality by ~40%. Most of this increased exposure is due to the shoaling of low Ω waters driven by the long-term trend in OA. Extreme OA events amplify this increase by ~40%. Our approach can quantify the health of pteropod populations under shifting environmental conditions, and attribute changes in fitness or population structure to changes in the stressor landscape across hierarchical time scales.

Continue reading ‘The impact of aragonite saturation variability on shelled pteropods: an attribution study in the California Current System’

A global monthly field of seawater pH over 3 decades: a machine learning approach

Published 20 May 2024 Science Closed
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The continuous uptake of anthropogenic CO2 by the ocean leads to ocean acidification, which is an ongoing threat to the marine ecosystem. The ocean acidification rate was globally documented in the surface ocean but limited below the surface. Here, we present a monthly four-dimensional 1°×1° gridded product of global seawater pH, derived from a machine learning algorithm trained on pH observations at total scale and in-situ temperature from the Global Ocean Data Analysis Project (GLODAP). The constructed pH product covers the years 1992–2020 and depths from the surface to 2 km on 41 levels. Three types of machine learning algorithms were used in the pH product construction, including self-organizing map neural networks for region dividing, a stepwise algorithm for predictor selection, and feed-forward neural networks (FFNN) for non-linear relationship regression. The performance of the machine learning algorithm was validated using real observations by a cross validation method, where four repeating iterations were carried out with 25 % varied observations for each evaluation and 75 % for training. The constructed pH product is evaluated through comparisons to time series observations and the GLODAP pH climatology. The overall root mean square error between the FFNN constructed pH and the GLODAP measurements is 0.028, ranging from 0.044 in the surface to 0.013 at 2000 m. The pH product is distributed through the data repository of the Marine Science Data Center of the Chinese Academy of Sciences at http://dx.doi.org/10.12157/IOCAS.20230720.001 (Zhong et al., 2023).

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Temperature and nutrients drive distinct successions between diatoms and dinoflagellates over the past 40 years: Implications for climate warming and eutrophication

Published 6 May 2024 Science Closed
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Highlights

  • We analyzed a 44-year dataset for diatoms (dia) and dinoflagellates (dino).
  • Dia dominance seasonally and ecologically changed to dia-dino co-dominance.
  • Temperature and nutrients drove these distinct successions respectively.
  • Future warming and eutrophication may promote dinoflagellates over diatoms.

Abstract

Diatoms and dinoflagellates are two typical functional groups of phytoplankton, playing important roles in ecosystem processes and biogeochemical cycles. Changes in diatoms and dinoflagellates are thought to be one of the possible mechanisms for the increase in harmful algal blooms (HABs), due to changing hydrological conditions associated with climate change and human activities. However, little is known about their ability to adapt to changing ocean environments, thus making it difficult to know whether and how they are adapting. By analyzing a 44-year monitoring dataset in the central Bohai Sea during 1978–2021, we found that the abundance ratio of diatoms to dinoflagellates showed a decreasing trend seasonally and ecologically, indicating that the phytoplankton community underwent distinct successional processes from diatom dominance to diatom-dinoflagellate co-dominance. These processes exhibited varying responses to temperature, nutrient concentrations and ratios, and their interactions, of which temperature primarily drove the seasonal succession whereas nutrients were responsible for the ecological succession. Specifically, diatoms showed a preference for lower temperatures and higher DIP concentrations, and were able to tolerate lower DIN at lower temperatures. In contrast, dinoflagellates tended to prevail at conditions of warming and high N/P ratios. These different traits of diatoms and dinoflagellates reflected the fact that warming as a result of rising temperature and eutrophication as a consequence of nutrient input would favor dinoflagellates over diatoms. Moreover, the increasing dominance of dinoflagellates indicated that dinoflagellate blooms were likely to become more frequent and intense in the central Bohai Sea.

Continue reading ‘Temperature and nutrients drive distinct successions between diatoms and dinoflagellates over the past 40 years: Implications for climate warming and eutrophication’

Effect of ocean outfall discharge volume and dissolved inorganic nitrogen load on urban eutrophication outcomes in the Southern California Bight

Published 18 April 2024 Science Closed
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Climate change is increasing drought severity worldwide. Ocean discharges of municipal wastewater are a target for potable water recycling. Potable water recycling would reduce wastewater volume; however, the effect on mass nitrogen loading is dependent on treatment. In cases where nitrogen mass loading is not altered or altered minimally, this practice has the potential to influence spatial patterns in coastal eutrophication. We apply a physical-biogeochemical numerical ocean model to understand the influence of nitrogen management and potable wastewater recycling on net primary productivity (NPP), pH, and oxygen. We model several theoretical management scenarios by combining dissolved inorganic nitrogen (DIN) reductions from 50 to 85% and recycling from 0 to 90%, applied to 19 generalized wastewater outfalls in the Southern California Bight. Under no recycling, NPP, acidification, and oxygen loss decline with DIN reductions, which simulated habitat volume expansion for pelagic calcifiers and aerobic taxa. Recycling scenarios under intermediate DIN reduction show patchier areas of pH and oxygen loss with steeper vertical declines relative to a “no recycling” scenario. These patches are diminished under 85% DIN reduction across all recycling levels, suggesting nitrogen management lowers eutrophication risk even with concentrated discharges. These findings represent a novel application of ocean numerical models to investigate the regional effects of idealized outfall management on eutrophication. Additional work is needed to investigate more realistic outfall-specific water recycling and nutrient management scenarios and to contextualize the benefit of these management actions, given accelerating acidification and hypoxia from climate change.

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Ocean acidification offsets the effect of warming on sediment denitrification and associated nitrous oxide production

Published 16 April 2024 Science Closed
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Rates of denitrification and associated nitrous oxide (N2O) production are expected to increase with global warming, leading to positive climate feedback. However, previous studies have not considered the combined effect of ocean acidification (OA, pCO2 ~ 900 µatm) and warming on denitrification rates and N2O production. Here we used a series of whole core incubation studies to assess the combined impact of warming and OA on estuarine sediment denitrification rates and N2O production. Strong warming (+5 °C over mean in situ conditions) increased N2O production by ~4.2 µmol-N m−2 d−1 and denitrification by ~43 µmol-N m−2 d−1, fuelled by water column nitrate (Dw), but decreased rates of nitrification-coupled denitrification in the sediment (Dn) by ~82 µmol-N m−2 d−1. While Dn was not affected by OA, Dw decreased significantly by 51 µmol-N m−2 d−1 when OA was coupled with warmer temperatures. We estimate that OA may offset the increase in estuarine sediment denitrification and N2O production expected from warming alone by up to 64% and reduce a potential positive climate feedback loop by inhibiting denitrification pathways.

Continue reading ‘Ocean acidification offsets the effect of warming on sediment denitrification and associated nitrous oxide production’

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