Posts Tagged 'Antarctic'

« Previous Entries
Next Entries »

Harpagifer bispinis, but not Patagonotothen tessellata, appears robust to interactive effects of ocean warming and acidification in southern Patagonia

Published 11 April 2025 Science Closed
Tags: , , , , , ,

Highlights

  • Climate change stressors impaired the thermal physiology of P. tessellata and H. bispinis.
  • Their thermal tolerances were more affected by ocean warming than by acidification.
  • The interaction of both stressors altered the aerobic scope of P. tessellata.
  • H. bispinis appears to be more robust to ocean warming and acidification.

Abstract

Ocean warming and acidification challenge marine ectotherms with rapid, multiple and simultaneous environmental changes. As knowledge of these impacts on fish from the sub-Antarctic is scarce, this study seeks to explore the combined effects of warming and acidification on the thermal and metabolic responses of Patagonotothen tessellata and Harpagifer bispinis, two sympatric notothenioid fish from the Beagle Channel. Juveniles were exposed to present-day and near-future summer temperatures (∼10 and 13 °C) and pCO2 levels (∼500 and 1300 μatm) in a full factorial design. Their critical thermal minimum/maximum (CTmin/CTmax) were assessed and their partial thermal tolerance polygons were estimated. Oxygen consumption rates allowed us to calculate fish’ aerobic scope (AS) as the difference between the standard and maximum metabolic rates (SMR and MMR). The CTmin of both species were affected by temperature, pCO2 level and their interaction, while the CTmax of P. tessellata was affected by both factors and that of H. bispinis, only by temperature. The partial thermal tolerance polygon of P. tessellata significantly decreased with future pCO2 levels, while no changes were observed for H. bispinis. In P. tessellata, SMR and MMR were affected by temperature and pCO2 levels and the AS by their interaction. Conversely, H. bispinis showed no differences in SMR, MMR and AS under different conditions. The increase in SMR and decrease in AS of P. tessellata with future temperatures and pCO2 levels may explain the changes in its thermal tolerance, while for H. bispinis, either the species has a greater capacity to adapt its metabolic response to warming and acidification, or different physiological processes are responsible for the observed changes in its thermal tolerance. Overall, present information could be a valuable tool for forecasting shifts in habitat suitability across the distribution range of both species and other similar fish in the context of climate change.

Continue reading ‘Harpagifer bispinis, but not Patagonotothen tessellata, appears robust to interactive effects of ocean warming and acidification in southern Patagonia’

Decadal progress of ocean acidification over the Southern Ocean

Published 19 March 2025 Science Closed
Tags: , ,

The Southern Ocean (SO, south of 30°S) covers 30% of the global ocean surface area and is presumed to account for 40% of the whole ocean’s anthropogenic CO 2 (DICanth) absorption1. This may lead to intensive anthropogenic acidification in the SO. However, natural processes also influence the change of ocean pH. Distinguishing anthropogenic and natural components from the observed dissolved inorganic carbon (DIC) and pH is essential for clarifying the acidification in the SO. Here we separated the anthropogenic and natural components by combining new parameterization techniques with high-resolution grid data constructed based on ship-based observations. During the 1990s‒2010s, ocean acidification affected by the anthropogenic effect covered most of the surface and intermediate depths by 3500 m over the SO, and the maximum decreasing rate of anthropogenic pH was 0.004 pH year–1 as twice decreasing of the global average. This remarkable decline of pH in the SO must result from the increase in DICanth of 10.9 Pg-C. The increase of DICanth in the SO was comparable to 11% of the global emission amount of CO2, implying the SO absorbing half of the global ocean’s DICanth is the largest uptake region of atmospheric anthropogenic carbon into the ocean interior.

Continue reading ‘Decadal progress of ocean acidification over the Southern Ocean’

Impacts of ocean acidification on the palatability of two Antarctic macroalgae and the consumption of a grazer

Published 27 February 2025 Science Closed
Tags: , , , , , ,

Increases in atmospheric CO2 have led to more CO2 entering the world’s oceans, decreasing the pH in a process called ’ocean acidification’. Low pH has been linked to impacts on macroalgal growth and stress, which can alter palatability to herbivores. Two common and ecologically important macroalgal species from the western Antarctic Peninsula, the unpalatable Desmarestia menziesii and the palatable Palmaria decipiens, were maintained under three pH treatments: ambient (pH 8.1), near future (7.7) and distant future (7.3) for 52 days and 18 days, respectively. Discs of P. decipiens or artificial foods containing extracts of D. menziesii from each treatment were presented to the amphipod Gondogeneia antarctica in feeding choice experiments. Additionally, G. antarctica exposed to the different treatments for 55 days were used in a feeding assay with untreated P. decipiens. For D. menziesii, extracts from the ambient treatment were eaten significantly more by weight than the other treatments. Similarly, P. decipiens discs from the ambient and pH 7.7 treatments were eaten more than those from the pH 7.3 treatment. There was no significant difference in the consumption by treated G. antarctica. These results suggest that ocean acidification may decrease the palatability of these macroalgae to consumers but not alter consumption by G. antarctica.

Continue reading ‘Impacts of ocean acidification on the palatability of two Antarctic macroalgae and the consumption of a grazer’

Climate-driven shifts in Southern Ocean primary producers and biogeochemistry in CMIP6 models

Published 26 February 2025 Science Closed
Tags: , , , , , , , , ,

As a net source of nutrients fuelling global primary production, changes in Southern Ocean productivity are expected to influence biological carbon storage across the global ocean. Following a high-emission, low-mitigation pathway (SSP5-8.5), we show that primary productivity in the Antarctic zone of the Southern Ocean is predicted to increase by up to 30 % over the 21st century. The ecophysiological response of marine phytoplankton experiencing climate change will be a key determinant in understanding the impact of Southern Ocean productivity shifts on the carbon cycle. Yet, phytoplankton ecophysiology is poorly represented in Coupled Model Intercomparison Project phase 6 (CMIP6) climate models, leading to substantial uncertainty in the representation of its role in carbon sequestration. Here we synthesise the existing spatial and temporal projections of Southern Ocean productivity from CMIP6 models, separated by phytoplankton functional type, and identify key processes where greater observational data coverage can help to improve future model performance. We find substantial variability between models in projections of light concentration (>15 000 (µE m−2 s−1)2) across much of the iron- and light-limited Antarctic zone. Projections of iron and light limitation of phytoplankton vary by up to 10 % across latitudinal zones, while the greatest increases in productivity occurs close to the coast. Temperature, pH and nutrients are less spatially variable – projections for 2090–2100 under SSP5-8.5 show zonally averaged changes of +1.6 °C and −0.45 pH units and Si* ([Si(OH)4]–[NO3–]) decreases by 8.5 µmol L−1. Diatoms and picophytoplankton and/or miscellaneous phytoplankton are equally responsible for driving productivity increases across the subantarctic and transitional zones, but picophytoplankton and miscellaneous phytoplankton increase at a greater rate than diatoms in the Antarctic zone. Despite the variability in productivity with different phytoplankton types, we show that the most complex models disagree on the ecological mechanisms behind these productivity changes. We propose that a sampling approach targeting the regions with the greatest rates of climate-driven change in ocean biogeochemistry and community assemblages would help to resolve the empirical principles underlying the phytoplankton community structure in the Southern Ocean.

Continue reading ‘Climate-driven shifts in Southern Ocean primary producers and biogeochemistry in CMIP6 models’

Impacts of climate change on members of shallow water Antarctic communities

Published 16 January 2025 Science Closed
Tags: , , , , , , , , , ,

Human-derived CO2 emissions have lowered the ocean’s pH and increased global temperatures. Low seawater pH can decrease the calcification, growth, and survival of calcifying invertebrates. Furthermore, low pH changes macroalgal growth and stress, possibly altering palatability to consumers. Global warming has decreased sea ice coverage, profoundly influencing photosynthetic organisms by altering subsurface irradiance. Shallow, hard-bottom communities along the Western Antarctic Peninsula are characterized by large macroalgal forests that shelter large numbers of mesograzers. Amphipods and macroalgae have a community-wide mutualistic relationship where macroalgae provide refuge from predatory fish while amphipods remove competing epiphytes. To understand how climate change could impact members of this relationship, macroalgal-associated mesograzers were collected near Palmer Station, Antarctica (64°46′S, 64°03′W) and maintained under three different pH treatments [ambient (pH 8.1), near-future (pH 7.7), and distant-future conditions (pH 7.3)] for 52 days. Total assemblage number and the relative proportion of each species were similar across the treatments, indicating possible resistance to short-term low pH exposure. The amphipods Djberboa furcipes, Gondogeneia antarctica, and Prostebbingia gracilis were maintained under the pH treatments for 8 weeks. No difference in biochemical composition or survival was found between the treatments for any of the species. However, each species decreased molt activity between the ambient and pH 7.3 treatment. These results suggest that amphipods may maintain their survival in decreased pH by reallocating energy into compensatory behaviors and away from energy-expensive processes like molting. The palatability of the unpalatable Desmarestia menziesii and the palatable Palmaria decipiens were maintained under three pH treatments and then presented to the amphipod Gondogeneia antarctica in a feeding choice assay. Decreased seawater pH generally lowered the consumption of both species, suggesting that acidification may decrease the palatability of these macroalgae to consumers. Finally, biochemical composition, carbon and nitrogen percentages, and C:N were correlated with sea ice indices for the macroalgae D. menziesii, Himantothallus grandifolius, Sarcopeltis antarctica, and Iridaea sp. from a sea ice gradient. Surprisingly, most of the chemical components were not correlated with sea ice cover, indicating sea ice coverage does not change the nutritional contributions of macroalgae to food webs.

Continue reading ‘Impacts of climate change on members of shallow water Antarctic communities’

Climate change and polar marine invertebrates: life-history responses in a warmer, high CO2 world

Published 10 January 2025 Science Closed
Tags: , , ,

Polar marine invertebrates serve as bellwethers for species vulnerabilities in the face of changing climate at high latitudes of the Earth. Ocean acidification, warming/heatwaves, freshening, sea ice retreat and productivity change are challenges for polar species. Adaptations to life in cold water with intensely seasonal productivity has shaped species traits at both poles. Polar species have life histories often characterised as K-strategist or K-selected (e.g. slow growth and development, larval hypometabolism) that make them sensitive to climate stress and altered seasonal productivity. Moderate warming results in faster development and can have positive effects on development, up to a limit. However, ocean acidification can retard development, impair skeletogenesis and result in smaller larvae. Given the fast pace of warming, data on the thermal tolerance of larvae from diverse species is urgently needed, as well as knowledge of adaptive responses to ocean acidification and changes to sea ice and productivity. Predicted productivity increase would benefit energy-limited reproduction and development, while sea ice loss negatively impacts species with reproduction that directly or indirectly depend on this habitat. It is critical to understand the interactive effects between warming, acidification and other stressors. Polar specialists cannot migrate, making them susceptible to competition and extinction from range-extending subpolar species. The borealisation and australisation of Arctic and Antarctic ecosystems, respectively, is underway as these regions become more hospitable for the larval and adult life-history stages of lower-latitude species. Differences in biogeography and pace of change point to different prospects for Arctic and Antarctic communities. In this Commentary, we hypothesise outcomes for polar species based on life history traits and sensitivity to climate change and suggest research avenues to test our predictions.

Continue reading ‘Climate change and polar marine invertebrates: life-history responses in a warmer, high CO2 world’

Microplastic hotspots mapped across the Southern Ocean reveal areas of potential ecological impact

Published 9 January 2025 Science Closed
Tags: , , , , , ,

Marine microplastic is pervasive, polluting the remotest ecosystems including the Southern Ocean. Since this region is already undergoing climatic changes, the additional stress of microplastic pollution on the ecosystem should not be considered in isolation. We identify potential hotspot areas of ecological impact from a spatial overlap analysis of multiple data sets to understand where marine biota are likely to interact with local microplastic emissions (from ship traffic and human populations associated with scientific research and tourism). Then we account for cumulative effects by identifying which areas with potential elevated microplastic-biota interaction are already subject to climate change related stresses (ocean warming and acidification). Our analysis indicates that biologically productive coastal areas in proximity to populated facilities are where microplastics pose most risk to the ecosystem, and that the northern Antarctic Peninsula is likely to be the main risk hotspot. This study is the first to map the threat of microplastics to the Southern Ocean ecosystem in a multi-stressor context, locating where microplastic monitoring programmes and mitigation measures may be considered a matter of urgency.

Continue reading ‘Microplastic hotspots mapped across the Southern Ocean reveal areas of potential ecological impact’

The Southern Ocean Time Series: a climatological view of hydrography, biogeochemistry, phytoplankton community composition, and carbon export in the subantarctic zone

Published 25 December 2024 Science Closed
Tags: , ,

The Southern Ocean Time Series (SOTS) provides highly temporally resolved observations of the physical, chemical and biological variability in the upper ocean, as well as the export of particulate carbon to the ocean interior, in the subantarctic region south of Australia. The SOTS observatory focuses on the subantarctic region because of its importance in the formation of mode water and the associated uptake and storage of anthropogenic heat and carbon. The region is also critical for the supply of oxygen to the interior and the export of nutrients to fuel primary production in broad areas of the low latitude global ocean. The SOTS observatory is the longest running multidisciplinary initiative in the open Southern Ocean, and has delivered high quality observations from the surface to the seafloor for more than a decade, and for some parameters, over two decades, using two deep-water moorings. The moorings are serviced annually, providing additional opportunities for shipboard sampling and sensor validation and calibration. Using observations collected at the SOTS site between 1997 and 2022, the seasonal variability in upper ocean hydrography, biogeochemistry, phytoplankton community composition, and biodiversity, along with carbon export to the ocean interior are presented. This climatological view of the region is complemented by a review of recent findings underpinned by observations collected by the SOTS observatory and highlighting the ongoing need for long time series to better understand the subantarctic ocean and its response to a changing climate.

Continue reading ‘The Southern Ocean Time Series: a climatological view of hydrography, biogeochemistry, phytoplankton community composition, and carbon export in the subantarctic zone’

Cascading tipping points of Antarctica and the Southern Ocean

Published 19 December 2024 Science Closed
Tags: ,

Antarctica and the Southern Ocean are key elements in the physical and biological Earth system. Human-induced climate change, and other human activities in the region, are leading to several potential interacting tipping points with major and irreversible consequences. Here, we examine eight potential physical, biological, chemical, and social Antarctic tipping points. These include ice sheets, ocean acidification, ocean circulation, species redistribution, invasive species, permafrost melting, local pollution, and the Antarctic Treaty System. We discuss the nature of each potential tipping point, its control variables, thresholds, timescales, and impacts, and focus on the potential for cumulative and cascading effects as a result of their interactions. The analysis provides substantial evidence of the need for more concerted and rapid action to limit climate change and to minimise the impacts of local human activities to avoid these cascading tipping points.

Continue reading ‘Cascading tipping points of Antarctica and the Southern Ocean’

Sensitivity of the Southern Ocean CO2 sink to a rapid increase and subsequent decrease of atmospheric CO2

Published 28 November 2024 Science Closed
Tags: , , ,

Despite the importance of the Southern Ocean carbon sink, its response to future atmospheric CO2 perturbations and warming remains highly uncertain. In this study, we use six state-of-the-art Earth system models to assess the response of Southern Ocean air-sea CO2 fluxes (FCO2) to a rapid atmospheric forcing increase and subsequent negative emissions in an idealized carbon dioxide removal reversibility experiment. We find that during positive emissions, the region north of the Polar Front only takes up atmospheric CO2 for 30-50 years before reaching equilibrium; surface stratification and reduction of CO2 solubility with warming diminishes ocean CO2 uptake in this region. In contrast, south of the Polar Front, the upper ocean continues to take up CO2 until the end of positive emissions at 140 years. Sea-ice loss and the accumulation of anthropogenic dissolved inorganic carbon in the upper ocean reduce the upwelling-driven seasonal CO2 outgassing, leading to a stronger Antarctic CO2 sink. CO2 removal triggers a CO2 uptake reduction that slowly converts the Southern Ocean into a CO2 source which persists for at least 50 years post-mitigation. Furthermore, we find that model sensitivity to atmospheric perturbation is closely linked to seasonal FCO2 dynamics. Specifically, models with a thermally dominated pCO2 seasonal cycle exhibit nearly twice the sensitivity to atmospheric perturbations compared to non-thermal models. Our findings further emphasize the necessity of accurate model representation of the seasonal CO2 dynamics for appropriately simulating the future Southern Ocean carbon sink.

Continue reading ‘Sensitivity of the Southern Ocean CO2 sink to a rapid increase and subsequent decrease of atmospheric CO2’

Skeletal magnesium content in Antarctic echinoderms along a latitudinal gradient

Published 4 October 2024 Science Closed
Tags: , , , , , , , , ,

Highlights

  • Skeletal structures presented high Mg content, except in echinoid spines.
  • Asteroids had the highest Mg content, followed by ophiuroids, holothuroids, and echinoids.
  • No local variability in skeletal Mg content was observed in asteroids and holothuroids.
  • Environmental parameters may have influenced the skeletal Mg in ophiuroids and echinoids.

Abstract

Ocean warming and acidification driven by anthropogenic CO2 emissions may impact the mineral composition of marine calcifiers. Species with high skeletal Mg content could be more susceptible in polar regions due to the increased solubility of CO2 at lower temperatures. We aimed to assess the environmental influence on skeletal Mg content of Antarctic echinoderms belonging to Asteroidea, Ophiuroidea, Echinoidea and Holothuroidea classes, along a latitudinal gradient from the South Shetland Islands to Rothera (Adelaide Island). We found that all skeletal structures, except for echinoid spines, exhibited high Mg content, with asteroids showing the highest levels. Our results suggest that asteroids and holothuroids exert a higher biological capacity to regulate Mg incorporation into their skeletons. In contrast, the variability observed in the skeletal Mg content of ophiuroids and echinoids appears to be more influenced by local environmental conditions. Species-specific differences in how environmental factors affect the skeletal Mg content can thus be expected as a response to global climate change.

Continue reading ‘Skeletal magnesium content in Antarctic echinoderms along a latitudinal gradient’

Antarctic benthic ecological change

Published 4 September 2024 Science Closed
Tags: ,

The benthic community around Antarctica is diverse and highly endemic. These cold-adapted species are under threat from local and global drivers, including warming, acidification and changes to the cryosphere. In this Review, we summarize observed, experimental and modelled Antarctic benthic ecological change. Warming, glacial melt and retreat, and reduced ice cover are causing regional benthic biomass to increase or decrease, depending on the additional influences of ice scour, turbidity and freshening. Additionally, the dominance of previously cold-restricted or light-restricted taxa is increasing, and several ecological tipping points have already been breached, leading to ecological phase shifts in some habitats. The largest changes have been observed in communities in the shallows of the West Antarctic Peninsula, notably change to distribution, biodiversity, biomass and trophic structure. Models based on observational and experimental evidence indicate that these changes will spread deeper and eastwards throughout this century. Available data are primarily limited to a handful of shallow-water taxa; thus, future work will need to involve multispecies observations and experiments encompassing multiple drivers to understand community and ecosystem responses, and autonomous monitoring techniques to fill geographical, bathymetric, seasonal and taxonomic gaps; advances in environmental DNA and artificial-intelligence-based techniques will help to rapidly analyse such data.

Continue reading ‘Antarctic benthic ecological change’

The Southern Ocean carbon sink has been overestimated in the past three decades

Published 29 July 2024 Science Closed
Tags: , , , ,

Employing machine learning methods for mapping surface ocean pCO2 has reduced the uncertainty in estimating sea-air CO2 flux. However, a general discrepancy exists between the Southern Ocean carbon sinks derived from pCO2 products and those from biogeochemistry models. Here, by performing a boosting ensemble learning feed-forward neural networks method, we have identified an underestimation of the surface Southern Ocean pCO2 due to notably uneven density of pCO2 measurements between summer and winter, which resulted in about 16% overestimating of Southern Ocean carbon sink over the past three decades. In particular, the Southern Ocean carbon sink since 2010 was notably overestimated by approximately 29%. This overestimation can be mitigated by a winter correction in algorithms, with the average Southern Ocean carbon sink during 1992-2021 corrected to −0.87 PgC yr−1 from the original −1.01 PgC yr−1. Furthermore, the most notable underestimation of surface ocean pCO2 mainly occurred in regions south of 60°S and was hiding under ice cover. As the surface ocean pCO2 under sea ice coverage in the winter is much higher than the atmosphere, if sea ice melts completely, there could be a further reduction of about 0.14 PgC yr−1 in the Southern Ocean carbon sink.

Continue reading ‘The Southern Ocean carbon sink has been overestimated in the past three decades’

Anthropogenic CO2, air–sea CO2 fluxes, and acidification in the Southern Ocean: results from a time-series analysis at station OISO-KERFIX (51° S–68° E)

Published 24 June 2024 Science Closed
Tags: , , ,

The temporal variation of the carbonate system,air–sea CO2 fluxes, and pH is analyzed in the southern Indian Ocean, south of the polar front, based on in situ data obtained from 1985 to 2021 at a fixed station (50°400 S–68°250 E) and results from a neural network model that reconstructs the fugacity of CO2 (fCO2) and fluxes at monthly scale. Anthropogenic CO2 (Cant) is estimated in the water column and is detected down to the bottom (1600 m) in 1985, resulting in an aragonite saturation horizon at 600 m that migrated up to 400 m in 2021 due to the accumulation of Cant. At the subsurface, the trend of Cant is estimated at +0.53 ± 0.01 µmol kg−1 yr−1 with a detectable increase in the trend in recent years. At the surface during austral winter the oceanic fCO2 increased at a rate close to or slightly lower than in the atmosphere. To the contrary, in summer, we observed contrasting fCO2 and dissolved inorganic carbon (CT) trends depending on the decade and emphasizing the role of biological drivers on air–sea CO2 fluxes and pH inter-annual variability. The regional air–sea CO2 fluxes evolved from an annual source to the atmosphere of 0.8 molC m−2 yr−1 in 1985 to a sink of −0.5 molC m−2 yr−1 in 2020. Over 1985–2020, the annual pH trend in surface waters of −0.0165 ± 0.0040 per decade was mainly controlled by the accumulation of anthropogenic CO2, but the summer pH trends were modulated by natural processes that reduced the acidification rate in the last decade. Using historical data from November 1962, we estimated the long-term trend for fCO2, CT, and pH, confirming that the progressive acidification was driven by the atmospheric CO2 increase. In 59 years this led to a diminution of 11 % for both aragonite and calcite saturation state. As atmospheric CO2 is expected to increase in the future, the pH and carbonate saturation state will decrease at a faster rate than observed in recent years. A projection of future CT concentrations for a high emission scenario (SSP5-8.5) indicates that the surface pH in 2100 would decrease to 7.32 in winter. This is up to −0.86 lower than pre-industrial pH and −0.71 lower than pH observed in 2020. The aragonite undersaturation in surface waters would be reached as soon as 2050 (scenario SSP5-8.5) and 20 years later for a stabilization scenario (SSP2-4.5) with potential impacts on phytoplankton species and higher trophic levels in the rich ecosystems of the Kerguelen Islands area.

Continue reading ‘Anthropogenic CO2, air–sea CO2 fluxes, and acidification in the Southern Ocean: results from a time-series analysis at station OISO-KERFIX (51° S–68° E)’

Diverse inorganic carbon uptake strategies in Antarctic seaweeds: revealing species-specific responses and implications for ocean acidification

Published 21 June 2024 Science Closed
Tags: , , , , ,

Highlights

  • Antarctic seaweeds exhibited diverse CO2 concentrating mechanisms (CCMs) which vary between algal phyla and a depth gradient.
  • Red Antarctic seaweeds represent the highest percentage of non-CCM species, while brown seaweeds represent the highest percentage of CCM species.
  • Green Antarctic seaweed demonstrate the loss of CCMs in response to depth.
  • Ocean acidification: OA may cause cascade effects in Antarctic ecosystems due to changes in seaweeds abundance patterns (non-CCMs species > CCM species).

Abstract

Seaweeds are important components of coastal benthic ecosystems along the Western Antarctic Peninsula (WAP), providing refuge, food, and habitat for numerous associated species. Despite their crucial role, the WAP is among the regions most affected by global climate change, potentially impacting the ecology and physiology of seaweeds. Elevated atmospheric CO2 concentrations have led to increased dissolved inorganic carbon (Ci) with consequent declines in oceanic pH and alterations in seawater carbonate chemistry, known as Ocean Acidification (OA). Seaweeds possess diverse strategies for Ci uptake, including CO2 concentrating mechanisms (CCMs), which may distinctly respond to changes in Ci concentrations. Conversely, some seaweeds do not operate CCMs (non-CCM species) and rely solely on CO2. Nevertheless, our understanding of the status and functionality of Ci uptake strategies in Antarctic seaweeds remains limited. Here, we investigated the Ci uptake strategies of seaweeds along a depth gradient in the WAP. Carbon isotope signatures (δ13C) and pH drift assays were used as indicators of the presence or absence of CCMs. Our results reveal variability in CCM occurrence among algal phyla and depths ranging from 0 to 20 m. However, this response was species specific. Among red seaweeds, the majority relied solely on CO2 as an exogenous Ci source, with a high percentage of non-CCM species. Green seaweeds exhibited depth-dependent variations in CCM status, with the proportion of non-CCM species increasing at greater depths. Conversely, brown seaweeds exhibited a higher prevalence of CCM species, even in deep waters, indicating the use of CO2 and HCO3−. Our results are similar to those observed in temperate and tropical regions, indicating that the potential impacts of OA on Antarctic seaweeds will be species specific. Additionally, OA may potentially increase the abundance of non-CCM species relative to those with CCMs.

Continue reading ‘Diverse inorganic carbon uptake strategies in Antarctic seaweeds: revealing species-specific responses and implications for ocean acidification’

Archival records of the Antarctic clam shells from Marian Cove, King George Island suggest a protective mechanism against ocean acidification

Published 21 February 2024 Science Closed
Tags: , , , , , , , ,

Abstract

Continuous emissions of anthropogenic CO2 are changing the atmospheric and oceanic environment. Although some species may have compensatory mechanisms to acclimatize or adapt to the changing environment, most marine organisms are negatively influenced by climate change. In this study, we aimed to understand the compensatory mechanisms of the Antarctic clam, Laternula elliptica, to climate-related stressors by using archived shells from 1995 to 2018. Principal component analysis revealed that seawater pCO2 and salinity in the Antarctic Ocean, which have increased since the 2000’s, are the most influential factors on the characteristics of the shell. The periostracum thickness ratio and nitrogen on the outermost surface have increased, and the dissolution area (%) has decreased. Furthermore, the calcium content and mechanical properties of the shells have not changed. The results suggest that L. elliptica retains the mechanism of protecting the shell from high pCO2 by thickening the periostracum as a phenotype plasticity.

Highlights

  • We analyzed archival shells of the Antarctic clams in response to climate change.
  • Seawater pCO2 and salinity in the Antarctic Ocean have increased since the 2000’s.
  • Shell dissolution decreased over time while total shell thickness remained constant.
  • The calcium content and mechanical properties of the shell remained unchanged.
  • Shell integrity was retained by thickening the organic layer enriched with nitrogen.
Continue reading ‘Archival records of the Antarctic clam shells from Marian Cove, King George Island suggest a protective mechanism against ocean acidification’

Transport of anthropogenic carbon from the Antarctic shelf to deep Southern Ocean triggers acidification

Published 2 February 2024 Science Closed
Tags: , ,

Abstract

Flow of dense shelf water provide an efficient mechanism for pumping CO2 to the deep ocean along the continental shelf slope, particularly around the Antarctic bottom water (AABW) formation areas where much of the global bottom water is formed. However, the contribution of the formation of AABW to sequestering anthropogenic carbon (Cant) and its consequences remain unclear. Here, we show prominent transport of Cant (25.0 ± 4.7 Tg C yr−1) into the deep ocean (>2,000 m) in four AABW formation regions around Antarctica based on an integrated observational data set (1974–2018). This maintains a lower Cant in the upper waters than that of other open oceans to sustain a stronger CO2 uptake capacity (16.9 ± 3.8 Tg C yr−1). Nevertheless, the accumulation of Cant can further trigger acidification of AABW at a rate of −0.0006 ± 0.0001 pH unit yr−1. Our findings elucidate the prominent role of AABW in controlling the Southern Ocean carbon uptake and storage to mitigate climate change, whereas its side effects (e.g., acidification) could also spread to other ocean basins via the global ocean conveyor belt.

Key Points

  • We show evidence for the accumulation of Cant along the Antarctic shelf-slope into the deep ocean
  • The process of AABW formation drives Cant downward transport at 25.0 ± 4.7 Tg C yr−1, sustaining the CO2 uptake in the surface ocean
  • This further triggers acidification of AABW at a rate of −0.0006 ± 0.0001 pH unit yr−1, which is faster than in other deep oceans
Continue reading ‘Transport of anthropogenic carbon from the Antarctic shelf to deep Southern Ocean triggers acidification’

A synthesis of ocean total alkalinity and dissolved inorganic carbon measurements from 1993 to 2022: the SNAPO-CO2-v1 dataset (update)

Published 31 January 2024 Science Closed
Tags: , , , , , , , ,

Total alkalinity (AT) and dissolved inorganic carbon (CT) in the oceans are important properties with respect to understanding the ocean carbon cycle and its link to global change (ocean carbon sinks and sources, ocean acidification) and ultimately finding carbon-based solutions or mitigation procedures (marine carbon removal). We present a database of more than 44 400 AT and CT observations along with basic ancillary data (spatiotemporal location, depth, temperature and salinity) from various ocean regions obtained, mainly in the framework of French projects, since 1993. This includes both surface and water column data acquired in the open ocean, coastal zones and in the Mediterranean Sea and either from time series or dedicated one-off cruises. Most AT and CT data in this synthesis were measured from discrete samples using the same closed-cell potentiometric titration calibrated with Certified Reference Material, with an overall accuracy of ±4 µmol kg−1 for both AT and CT. The data are provided in two separate datasets – for the Global Ocean and the Mediterranean Sea (https://doi.org/10.17882/95414, Metzl et al., 2023), respectively – that offer a direct use for regional or global purposes, e.g., AT–salinity relationships, long-term CT estimates, and constraint and validation of diagnostic CT and AT reconstructed fields or ocean carbon and coupled climate–carbon models simulations as well as data derived from Biogeochemical-Argo (BGC-Argo) floats. When associated with other properties, these data can also be used to calculate pH, the fugacity of CO2 (fCO2) and other carbon system properties to derive ocean acidification rates or air–sea CO2 fluxes.

Continue reading ‘A synthesis of ocean total alkalinity and dissolved inorganic carbon measurements from 1993 to 2022: the SNAPO-CO2-v1 dataset (update)’

Severe 21st-century ocean acidification in Antarctic Marine Protected Areas

Published 25 January 2024 Science Closed
Tags: , , , ,

Antarctic coastal waters are home to several established or proposed Marine Protected Areas (MPAs) supporting exceptional biodiversity. Despite being threatened by anthropogenic climate change, uncertainties remain surrounding the future ocean acidification (OA) of these waters. Here we present 21st-century projections of OA in Antarctic MPAs under four emission scenarios using a high-resolution ocean–sea ice–biogeochemistry model with realistic ice-shelf geometry. By 2100, we project pH declines of up to 0.36 (total scale) for the top 200 m. Vigorous vertical mixing of anthropogenic carbon produces severe OA throughout the water column in coastal waters of proposed and existing MPAs. Consequently, end-of-century aragonite undersaturation is ubiquitous under the three highest emission scenarios. Given the cumulative threat to marine ecosystems by environmental change and activities such as fishing, our findings call for strong emission-mitigation efforts and further management strategies to reduce pressures on ecosystems, such as the continuation and expansion of Antarctic MPAs.

Continue reading ‘Severe 21st-century ocean acidification in Antarctic Marine Protected Areas’

Skeletal Mg content in common echinoderm species from Deception and Livingston Islands (South Shetland Islands, Antarctica) in the context of global change

Published 17 January 2024 Science Closed
Tags: , , , , , ,

Highlights

  • This is the first assessment of the Mg content in echinoderms from Deception and Livingston Islands.
  • Echinoderms showed interclass as well as inter- and intraspecific differences in their Mg content.
  • The sea stars displayed the highest Mg content levels, followed by the brittle stars and sea urchins.
  • The Mg content of echinoderms inhabiting Deception Island may be influenced by local environmental conditions.

Abstract

Echinoderms with high levels of magnesium (Mg) in their skeletons may be especially sensitive to ocean acidification, as the solubility of calcite increases with its Mg content. However, other structural characteristics and environmental/biological factors may affect skeletal solubility. To better understand which factors can influence skeletal mineralogy, we analyzed the Mg content of Antarctic echinoderms from Deception Island, an active volcano with reduced pH and relatively warm water temperatures, and Livingston Island. We found significant interclass and inter- and intraspecific differences in the Mg content, with asteroids exhibiting the highest levels, followed by ophiuroids and echinoids. Specimens exposed to hydrothermal fluids showed lower Mg levels, which may indicate local environmental effects. These patterns suggest that environmental factors such as seawater Mg2+/Ca2+ ratio and temperature may influence the Mg content of some echinoderms and affect their susceptibility to future environmental changes.

Continue reading ‘Skeletal Mg content in common echinoderm species from Deception and Livingston Islands (South Shetland Islands, Antarctica) in the context of global change’

Subscribe

Search

  • Reset

OA-ICC Highlights

Resources