Posts Tagged 'Antarctic'

Distinct biochemical profiles in Antarctic seaweeds reflect acclimation to polar and hydrothermal environments with implications for biomass nutritional value

Published 1 December 2025 Science Leave a Comment
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Highlights

  • Chlorophyll a content in some seaweed species increased with latitude along the Antarctic Peninsula.
  • Seaweeds from fumarole vent sites revealed variations in fatty acids and pigments.
  • Lower nutritional value in Antarctic seaweeds from fumarole sites suggests potential responses to ocean warming and acidification.
  • Species-specific biochemical shifts in Antarctic seaweeds are anticipated under global change scenarios.

Abstract

Global change is driving ocean warming (OW) and acidification (OA), impacting marine ecosystems worldwide, including polar regions. Seaweeds, as key primary producers in coastal ecosystems, synthesize a wide range of biochemical compounds that support higher trophic levels. Their biochemical composition is conditioned by local environmental factors, including seawater temperature, pH, and nutrient availability. However, how polar seaweeds respond to ongoing global change remains poorly understood. In this study, we examined the influence of local environmental changes on the biochemical composition – including fatty acids (FA), pigments, carbon, and nitrogen – of nine Antarctic brown and red seaweed species. Specifically, we considered a latitudinal gradient from the South Shetland Islands (⁓62°S) to Yalour Island (⁓65°S), and the presence of active fumarole vents at Deception Island. Our results reveal species-specific and location-dependent biochemical shifts in most species. While chlorophyll a concentrations tended to increase with latitude, specimens collected from fumarole vents exhibited a reduction in total FA content, PUFA:SFA (polyunsaturated to saturated fatty acid) ratios, PUFA omega-3, and pigment concentrations. These shifts under hydrothermal influence are likely driven by elevated seawater temperatures and acidic conditions, suggesting a potential decline in nutritional value under future global change scenarios. Additionally, higher magnesium content was found in the skeletons of crustose coralline algae from shallow waters than in those at 22 m depth. Our results highlight the species-specific nature of biochemical responses to environmental stressors, underlining the complexity of predicting the impacts of global change on seaweed physiology and the potential cascading effects on Antarctic food webs.

Continue reading ‘Distinct biochemical profiles in Antarctic seaweeds reflect acclimation to polar and hydrothermal environments with implications for biomass nutritional value’

Compound marine heatwaves and acidity extremes in the Southern Ocean

Published 21 November 2025 Science Leave a Comment
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Abstract

Compound extremes of temperature and acidity that extend over substantial fractions of the water column can be particularly damaging to marine organisms, as they experience not only additional stress by the potentially synergistic effects of these two stressors, but also a reduction in habitable vertical space. Here, we detect and analyze such column-compound extremes (CCX) in the Southern Ocean between 1980 and 2019, and characterize their duration, intensity, and spatial extent. To this end, we use daily output from a hindcast simulation of the Regional Ocean Modeling System (ROMS), coupled with the Biological Elemental Cycling (BEC) model. We first detect extremes in temperature and acidity ([]) within the top 300 m using a relative threshold of 95% and then identify CCX where conditions are extreme for both stressors for at least 50 m of the water column. When analyzed on a fixed baseline, positive trends in ocean warming and acidification caused CCX to last longer, intensify, and expand throughout the Southern Ocean. In the Antarctic zone, CCX expanded between 1980 and 2019 more than ten times in volume, lasted up to 120 days longer, and doubled in anomaly. Some of the largest and longest events occurred in Antarctic Marine Protected Areas (MPAs), covering more than 200,000 km2 and persisting for over 500 days. CCX in the Subantarctic and Northern zones quadrupled in volume and increased by more than 30% in anomaly. Across the Southern Ocean, the increasing occurrence of CCX exacerbates the risks to marine ecosystems from warming and acidification.

Plain Language Summary

Extreme heat events in the ocean, known as Marine HeatWaves (MHW), are becoming more common due to climate change. These events can be even more harmful when they occur at the same time as Ocean Acidity eXtreme (OAX) events, synergistically causing stress for marine life. In this study, we looked at how often these combined events in the upper ocean, called Column-Compound eXtremes (CCX), occurred in the Southern Ocean between 1980 and 2019. We used a numerical model simulation to investigate changes in CCX during the study period. Compared to conditions in 1980, we find that CCX in the Antarctic zone have expanded more than 10 times in volume and lasted up to 120 days longer. In addition, expansive and intense CCX are found in Antarctic Marine Protected Areas (MPAs), posing a threat to vulnerable ecosystems. These events covered more than 200,000 km2 and lasted more than 500 days. The increasing occurrence of CCX across the Southern Ocean exacerbates the risks to marine ecosystems arising from ocean warming and acidification.

Key Points

  • In the Antarctic zone, Column-Compound eXtremes (CCX) occupied in 2019 relative to 1980 ten times more volume and doubled in anomaly
  • Marine Protected Areas in the Ross Sea and Antarctic Peninsula are disproportionately affected by the largest, longest, most intense CCX
  • More than 70% of surface marine heatwaves contain CCX in 2019, although up to 60% of CCX occur without any surface expression
Continue reading ‘Compound marine heatwaves and acidity extremes in the Southern Ocean’

Anthropogenic forcing and upwelling accelerate aragonite undersaturation in the Prydz Bay, East Antarctica

Published 18 November 2025 Science Closed
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Abstract

The Southern Ocean is one of the rapidly acidifying regions globally, yet direct observational constraints on its carbonate chemistry remain scarce. Here, we combine shipboard measurements of pH and aragonite saturation state (Ωarag) from the summer 2015 Chinese National Antarctic Research Expedition with reconstructed wintertime conditions to characterize acidification in Prydz Bay. We report the first observation-based occurrence of surface aragonite undersaturation (Ωarag < 1.0) in the northern basin—emerging nearly two decades earlier than model projections. Surface Ωarag undersaturation is primarily driven by accelerated uptake of anthropogenic CO2 and shoaling of the aragonite saturation horizon, fueled by persistent upwelling of CO2-rich Circumpolar Deep Water. In the ocean interior, organic matter remineralization, CaCO3 dissolution, and continued anthropogenic CO2 intrusion further lower pH and Ωarag. Our results demonstrate that Prydz Bay is at the forefront of Southern Ocean acidification, highlighting the urgent need to incorporate both anthropogenic and natural biogeochemical feedbacks into high-resolution models to better predict future ecological impacts.

Plain Language Summary

The Southern Ocean is acidifying faster than most of the oceans on Earth, but most of what we know comes from computer models rather than direct observations. In Prydz Bay, East Antarctica, we combine shipboard data collected in summer 2015 with reconstructed winter conditions to track changes in seawater acidity (pH) and aragonite saturation (Ωarag), a key factor for shell-building marine life. We discover that seasonal expansion of low pH and nearly undersaturated aragonite led to the unforeseen early emergence of surface aragonite undersaturation in the northern basin. Strikingly, conditions that models predicted would not occur until around year 2038 have appeared nearly 20 years earlier. This rapid shift is driven by increased uptake of atmospheric CO2 and the rising influence of deep CO2-rich waters. In deeper layers, ongoing CO2 intrusion and the breakdown of organic material make the water even more acidic. These findings reveal that Prydz Bay is on the front lines of ocean acidification, underscoring the urgent need to reduce CO2 emissions and to better understand natural feedbacks in order to protect Antarctic marine ecosystems.

Key Points

  • Surface near-undersaturated Ωarag emerged in Prydz Bay during summer, nearly two decades ahead of model predictions
  • Enhanced atmospheric CO2 uptake and rapid shoaling of the aragonite saturation horizon dominate surface Ωarag undersaturation
  • Persistent upwelling of CO2-rich deep water combined with anthropogenic CO2 penetration shoal the Ωarag saturation horizon
Continue reading ‘Anthropogenic forcing and upwelling accelerate aragonite undersaturation in the Prydz Bay, East Antarctica’

Effects of ocean acidification on fatty acid composition in the Antarctic snail Neobuccinum eatoni

Published 31 October 2025 Science Closed
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Introduction: Ocean acidification (OA), resulting from the absorption of increasing atmospheric CO2 by the oceans, represents a major threat to marine organisms. Despite growing concern, the biochemical responses of Antarctic species to OA remain poorly understood.

Methods: This study investigated the impact of OA (pH 7.70 ± 0.09) on the fatty acid (FA) composition of the Antarctic snail Neobuccinum eatoni over a two-month experimental period (December 2015–March 2016). Fatty acid profiles were analyzed in multiple tissues to assess potential alterations induced by low-pH (LpH) conditions.

Results: Significant tissue-specific changes in FA composition were detected, particularly in the mantle and gill. Under LpH exposure, notable modifications occurred in long-chain polyunsaturated fatty acids (LC-PUFAs) such as 22:5n-3, 22:6n-3, and 24:5n-6. Elevated LC-PUFA levels in the mantle suggested a compensatory response to oxidative stress, while shifts in the n-3/n-6 ratios in the gill pointed to potential alterations in immune and anti-inflammatory functions.

Discussion: Indicators of homeoviscous adaptation (HVA), including PUFA/SFA ratios and mean chain length (MCL), revealed biochemical strategies used by N. eatoni to maintain membrane fluidity under acidified conditions. This study provides the first evidence of FA-based responses to elevated pCO₂ in an Antarctic gastropod, highlighting the potential of fatty acids as sensitive biomarkers of physiological adaptation to environmental stressors.

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What recreating Scott’s Antarctic expedition reveals about our seas today

Published 14 August 2025 Media coverage Closed
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The research trip retraced the routes of Borchgrevik’s Southern Cross, Shackleton’s Discovery and Scott’s Terra Nova expedition in January. Photograph: Courtesy of Dr Hugh Carter

Three glass specimen jars full of satsuma-sized sea urchins sit on Dr Hugh Carter’s desk in the Natural History Museum. Each one, collected from the depths of the Southern Ocean by polar teams led by Sir Ernest Shackleton, Capt Robert Falcon Scott and the Norwegian Carsten Borchgrevink, tells a tale of heroic exploration and scientific endeavour.

Now, more than a century later, Carter, the Natural History Museum’s (NHM) curator of marine invertebrates, hopes the preserved Antarctic urchins, 50 in all, will help tell a different, increasingly urgent story of modern times: how changes in the world’s southernmost waters may be affecting marine life.

In January, the biologist undertook a six-week long research trip to visit the exact sites sampled by Borchgrevink’s Southern Cross, Shackleton’s Discovery and Scott’s ill-fated Terra Nova expedition between 1898 and 1913.

His voyage, part of a multidisciplinary expedition run by the National Institute of Water and Atmosphere (Niwa), supported by the Antarctic Science Platform in New Zealand, partly retraced the route made by Scott. Scott and four other explorers, including the chief scientist, Edward Wilson, perished in the ice around a month after the samples sitting on Carter’s desk were collected.

…

Carter’s theory is that comparing the “tests” or shell of the urchins (a type of invertebrate known as echinoderms, which include starfish and sea cucumbers) in the NHM’s collection with modern samples will help reveal more about the impact of ocean acidification, often called the “evil twin” of the climate crisis. Acidification is caused when carbon dioxide is rapidly absorbed into the ocean, where it then reacts with water molecules leading to a fall in the pH of the seawater.

Preliminary findings on Carter’s ship, the deep water research vessel the RV Tangaroa, appeared to confirm his worst fears.

Continue reading ‘What recreating Scott’s Antarctic expedition reveals about our seas today’

Antarctic fishes in a changing climate: a comparative approach to predicting species-specific futures

Published 12 August 2025 Science Closed
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The polar regions are experiencing climate change at the fastest rates on Earth and serve as bellwethers for the profound threats facing species, ecosystems, and physical processes worldwide due to uncurbed anthropogenic greenhouse gas emissions. My dissertation research focuses on early life stages of Antarctic fishes, which are thought to be particularly vulnerable to climate change due to their unique evolutionary history and specialization to their stenothermal habitat. I used a comparative framework, examining four closely related species in the Nototheniidae family – Trematomus bernacchii, Trematomus pennellii, Trematomus nicolai, and Pagothenia borchgrevinki – to understand how subtle interspecific variation in traits may impact species-specific performance under projected future ocean conditions. I first measured basal characteristics across the four species, as very little is known about Antarctic fishes at young life stages, focusing on metabolic traits and the exploration-avoidance axis of behavior, two key dimensions of species fitness and drivers of niche differentiation. While basal metabolic demands appeared relatively conserved across species at the juvenile life stage, I found divergent behavioral strategies that could be a critical driver of niche differentiation in Antarctic fish assemblages. T. bernacchii and T. pennellii showed risk-prone behavior, T. nicolai showed avoidant behavior, and P. borchgrevinki showed cautious exploratory behavior. I also observed a potentially conserved freezing strategy in response to novelty, which, when paired with in situ observations, indicates that freezing may be an important predator avoidance strategy in these fishes. I then focused on the two ‘risky’ species – Trematomus bernacchii and Trematomus pennellii – to explore how acclimation to projected future ocean warming and ocean acidification conditions may impact their risk-prone behavior. While acclimation to warming and elevated pCO₂ affected behavior in both species, the effect sizes of pCO₂ were small, and warming was the driving force behind behavioral modifications. In both species, fishes acclimated to ocean warming conditions demonstrated reduced exploratory activity and showed indications of neophilia. These responses amplified over time, and T. pennellii demonstrated a stronger response (i.e., effect sizes) in both behaviors. Consistent with previous physiological and behavioral studies, while limited, our results support the inference that T. pennellii have a particularly risk-prone strategy when faced with novelty that is amplified when acclimated to warming. My final chapter proposes a novel ‘ice reef’ framework and emphasizes how three-dimensional ice habitat formed by platelet, anchor, and brinicle ice may function as critical nursery and refugia habitats for young polar fishes. Drawing on in situ observations and the literature, I discuss the recurring behavioral, physiological, and morphological features across a diversity of polar fishes, suggesting ice-associated and ice-obligate life history strategies may be much more widespread than previously acknowledged. As climate change rapidly alters ice phenology and stability, the loss of ice reefs could jeopardize fish recruitment, community resilience, and key ecosystem services. This perspective underscores the urgent need to study ice reefs before they disappear altogether.

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Responses of the natural phytoplankton assemblage to Patagonian dust input and anthropogenic changes in the Southern Ocean

Published 10 July 2025 Science Closed
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Abstract

The cumulative effects of multi‐faceted changes on the phytoplankton community of the Southern Ocean (SO) are not yet known, which is a major limitation to predicting the future direction of the biological carbon pump. Thus, our study aimed to estimate the effects of intensified Patagonian dust inputs, warming and acidification on the growth, composition and production of phytoplankton assemblages in the Polar Frontal Zone (PFZ) and the High‐Nutrient Low‐Chlorophyll (HNLC) region of the Indian sector of the SO during the austral summer 2022. Natural phytoplankton communities were incubated for 5‐day under 4 scenarios (present and future conditions, and 2 intermediate scenarios). In the PFZ, +3°C and acidification stimulated the growth of phytoplankton, mainly cyanobacteria, while intensified dust inputs alone did not have notable impact. Conversely, in HNLC waters, the addition of Fe‐dust alone increased the total chlorophyll a of diatoms (mainly F. kerguelensis), whereas the negative effect of acidification and +3°C counteracted the positive impact of dust input on the diatoms. In these waters, future conditions benefited smaller species (haptophytes and cyanobacteria). The net particulate organic carbon production (POC) was also unaltered by future conditions, suggesting that primary production may not change in the future SO. However the increase in the length and number of long‐chain diatoms under future HNLC conditions may indicate that POC export could intensify in the future.

Plain Language Summary

Phytoplankton in the Southern Ocean (SO) play a critical role in absorbing atmospheric carbon dioxide and supporting marine ecosystems, however their response to future environmental changes remains unclear. This study examined how increased dust inputs, warming, and acidification affect the phytoplankton community in two contrasted biogeochemical domains of the SO, the Polar Frontal Zone (PFZ) and the High‐Nutrient Low‐Chlorophyll (HNLC) region. In the PFZ, warming and acidification favored the smaller phytoplankton species, while in the HNLC region, iron‐rich dust stimulated diatom species, though this effect was attenuated by warming and acidification. While overall the production of organic carbon by phytoplankton remained unchanged, diatoms may enhance carbon export to deeper waters under future conditions due to increased number and length of chain‐forming species. These findings highlighted the complexity of phytoplankton responses, which vary across regions and are influenced by interactive environmental factors. Understanding the impact of these environmental factors on phytoplankton is critical to predicting how future changes will shape the role of the SO in the global carbon cycle.

Continue reading ‘Responses of the natural phytoplankton assemblage to Patagonian dust input and anthropogenic changes in the Southern Ocean’

Ocean acidification decreases molting but not survival of Antarctic amphipods Djerboa furcipes, Gondogeneia antarctica, and Prostebbingia gracilis

Published 10 July 2025 Science Closed
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Ocean acidification refers to a decrease in the pH of the world’s oceans from the oceanic uptake of human-derived atmospheric CO2. Low pH is known to decrease the calcification and survival of many calcifying invertebrates. Shallow, hard bottom communities along the Western Antarctic Peninsula often have incredibly large numbers of invertebrate mesograzers that shelter on and are mutualists with the dominant brown macroalgae. The common amphipod species Djerboa furcipes, Gondogeneia antarctica, and Prostebbingia gracilis were collected from the immediate vicinity of Palmer Station, Antarctica (64°46′S, 64°03′W) in January–February 2023 and maintained under three different pH treatments simulating ambient conditions (approximately pH 8.0), near-future conditions for 2100 (pH 7.7), and distant future conditions (pH 7.3) for 8 weeks. Molt number and mortality were monitored throughout the course of the experiment. After the 8 week exposure, amphipods were analyzed for their biochemical compositions including the Mg/Ca ratio of their exoskeletons. There was no significant difference in biochemical composition or survival among the pH treatments for any of the amphipod species. All three species, however, had significantly fewer total numbers of molts in the pH 7.3 treatment than in the ambient treatment. These results suggest that amphipods may be able to maintain their survival in decreased pH by reallocating energy into compensatory behaviors, such as acid–base regulation, and away from energy expensive processes like molting.

Continue reading ‘Ocean acidification decreases molting but not survival of Antarctic amphipods Djerboa furcipes, Gondogeneia antarctica, and Prostebbingia gracilis’

Spatial variability of marine carbonate system along the Drake Passage and northern Antarctic Peninsula during the austral summer

Published 27 June 2025 Science Closed
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Highlights

  • Sea surface pCO2, O2 and hydrographic parameters were measured, whereas Alk was estimated through different approaches.
  • In Drake Passage, photosynthesis drives carbonate variability north of the Polar Front and upwelling dominates to the south.
  • Photosynthesis reduces pCO2 and increases pH and carbonate concentration at enclosed coastal Antarctic areas.
  • Lowest pH in the northern Antarctic Peninsula likely results from mixing of waters rich in natural and anthropogenic carbon.
  • Calcite and aragonite are mostly supersaturated though aragonite undersaturation occurs under Dense Shelf Water influence.

Abstract

The influence of physical and biogeochemical processes on the variability of the carbonate system in the Southern Ocean remains poorly constrained. Understanding this influence is crucial to distinguish natural variations from anthropogenic impacts and accurately interpret observed trends. Here, we investigate how physical and biogeochemical processes influence the spatial distribution of summer carbonate system variables along the Drake Passage and northern Antarctic Peninsula. Continuous, high-frequency surface partial pressure of CO2 (pCO2), dissolved oxygen (O2) and essential hydrographic variables were collected during the austral summer of 2019, whereas other carbonate system variables were estimated after the reconstruction and evaluation of total alkalinity. Our findings show that in the Drake Passage, Circumpolar Deep Water upwelling increases the pCO2 (> 400 μatm) and dissolved inorganic carbon (> 2175 μmol kg−1), leading to reduced pH (< 7.99) south of the Polar Front. North of the Polar Front, photosynthesis lowers pCO2 (< 390 μatm), while increasing pH (> 8.00) and carbonate ions (> 110 μmol kg−1), with enrichment occurring in the Subantarctic coccolithophore growth region. Along the northern Antarctic Peninsula, including Gerlache Strait, Antarctic Sound, and Admiralty Bay, photosynthesis and sea ice/glacial melt are the main drivers of pCO2 reductions to levels below 350 μatm. The mixing of Circumpolar Deep Water with Weddell Sea Dense Shelf Water can naturally and anthropogenically raise pCO2 and decrease pH in northern Antarctic Peninsula waters, where pH is generally lower (as low as 7.90) compared to adjacent areas. Nevertheless, most environments remain supersaturated with respect to carbonate minerals calcite and aragonite, although signs of aragonite undersaturation have occur in surface waters influenced by Dense Shelf Water. These findings offer new insights into carbonate system processes across a large Southern Ocean region, improving understanding of spatial variability in marine carbon dynamics.

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Antarctic macroalgal-associated amphipod assemblages exhibit long-term resistance to ocean acidification

Published 19 June 2025 Science Closed
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The pH of the world’s oceans has decreased since the Industrial Revolution due to the oceanic uptake of increased atmospheric CO2 in a process called ocean acidification. Low pH has been linked to negative impacts on the calcification, growth, and survival of calcifying invertebrates. Along the Western Antarctic Peninsula, dominant brown macroalgae often shelter large numbers of diverse invertebrate mesograzers, many of which are calcified. Mesograzer assemblages in this region are often composed of large numbers of amphipods which have key roles in Antarctic macroalgal communities. Understanding the impacts of acidification on amphipods is vital for understanding how these communities will be impacted by climate change. To assess how long-term acidification may influence the survival of different members in these assemblages, mesograzers, particularly amphipods, associated with the brown alga Desmarestia menziesii were collected from the immediate vicinity of Palmer Station, Antarctica (S64°46′, W64°03′) in January 2020 and maintained under three different pH treatments simulating ambient conditions (approximately pH 8.1), near-future conditions for 2100 (pH 7.7), and distant future conditions (pH 7.3) for 52 days then enumerated. Total assemblage number and the relative proportion of each species in the assemblage were found to be similar across the pH treatments. These results suggest that amphipod assemblages associated with D. menziesii may be resistant to long-term exposure to decreased pH.

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Antarctic krill habitat suitability changes: historical trends and future projections under climate scenarios

Published 17 June 2025 Science Closed
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Highlights

  • Sea temperature and pH are key environmental factors affecting krill habitats.
  • Krill habitat suitability shows spatiotemporal heterogeneity across regions.
  • Under low emission scenario, krill habitat suitability will recover by 2100.
  • Under high emission scenario, highly suitable habitat may be lost by 2100.

Abstract

Antarctic krill plays a crucial role in the Southern Ocean ecosystem. However, data limitations leave a significant gap in understanding the changes in krill habitat suitability. This study integrated data from Chinese Antarctic research expeditions and KRILLBASE database, using Maxent model to assess spatiotemporal shifts in krill suitable habitat from 1991 to 2100 across the eastern and western Antarctic under SSP-RCP scenarios. The results reveal regional differences in climate and environmental impacts on krill habitats. Sea temperature and pH are dominant environmental factors affecting habitat suitability. With climate changes, the suitable habitats are shifting toward higher latitudes, and the latitudinal shift of habitats in CCAMLR Areas 48 and 58 is in the opposite direction. Under high-emission scenarios, krill habitats face severe contraction and loss, whereas low-emission scenarios suggest partial recovery by 2100. Coordinated global action to protect krill habitats is essential to address the biodiversity crisis in the Southern Ocean.

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Regionally distinct drivers of the carbonate system dynamics in the Drake Passage and northern Antarctic Peninsula

Published 4 June 2025 Science Closed
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Highlights

  • AT and CT in the DP and NAP were influenced by salinity, terrestrial inputs, and coastal upwelling.
  • Oceanic regions of the DP were significantly influenced by phosphate levels and high eddy kinetic energy.
  • AT and CT in the DP and NAP exhibited both conservative (coastal regions) and non-conservative (oceanic regions) behaviors.
  • The highest risk for carbonate undersaturation was observed in the NAP.

Abstract

The Drake Passage (DP) and the adjacent northern Antarctic Peninsula (NAP) are highly dynamic regions within the Southern Ocean where physical and biogeochemical processes simultaneously influence the CO2 system. Ocean total alkalinity (AT) and total dissolved inorganic carbon (CT) serve as valuable early indicators of calcium carbonate undersaturation and help evaluate the buffering capacity of the ocean. However, significant uncertainty remains in predicting carbonate system dynamics in the DP and NAP due to a lack of seasonal representation and the spatial variability. To address this uncertainty, we identified factors affecting the carbonate system at a regional level using unprecedented surface data from two consecutive austral summer and early fall periods (February–April 2003 and 2004). The data revealed that the dynamics of AT and CT in the DP and NAP exhibited both conservative and non-conservative behaviors influenced by the position of the Polar Front (PF), and the proximity to land. In coastal regions, salinity and terrestrial influence were major determinants, while in oceanic regions, nutrients and phytoplankton productivity played a more prominent role. The position of the PF creates a latitudinal edge in nutrient ratios, establishing a new hierarchy of carbonate chemistry drivers where silicate gains prevalence toward the southern DP and NAP. The results highlight significant regional variability in the carbonate system, with increasing AT and CT from north to south, making NAP the most vulnerable region due to accelerated acidification and ice melt-growth. Susceptibility to ocean acidification and seasonal fluctuations in the carbonate system indicate a higher risk to calcareous structures in the southernmost region.

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Ocean acidification and elevated temperatures alter the behavior of a sub-Antarctic fish

Published 3 June 2025 Science Closed
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Highlights

  • Climate change stressors impair the behavoir of subantarctic fish.
  • Activity levels of E. mclovinus increased with higher temperatures.
  • Future pCO2 levels increased fish’s boldness.
  • Implications of behavioral changes on the species’ fitness remain unknown.

Abstract

The interaction of multiple climate change stressors can affect the behavior of marine fish. While these effects have been reported in tropical and temperate species, much less is known for fish inhabiting high latitudes. We analyzed the combined effects of ocean acidification and the highest and lowest seasonal temperatures on the activity level and boldness of Eleginops maclovinus, an ecologically and commercially important notothenioid fish from the subantarctic area. Juveniles were acclimated for one month to two temperatures (T = 4 and 10 °C) and two pCO2 levels (∼500 and ∼1800 μatm) in a full factorial design. In an open field test, the time spent active was significantly affected by temperature, with fish at 10 °C 1.63 times more active than those at 4 °C, but not by pCO2 or the interaction (T × pCO2). No differences were observed in the average swimming velocity measured when active, nor in the time spent in the inner zone of the tank. A refuge emergence test indicated increased boldness under near-future pCO2 levels with fish emerging 2.06 (4 °C) and 1.23 (10 °C) times faster than those acclimated to present-day pCO2 levels. The disruptions of these fundamental behaviors by these climate-driven stressors could have consequences for foraging and predator-prey interactions, with likely detrimental effects on the interactions among sympatric subantarctic fishes under projected climate change scenarios.

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Fatty acid response of calcifying benthic Antarctic species to ocean acidification and warming

Published 22 May 2025 Science Closed
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Highlights

  • None of the species showed changes in the immune function in response to OA or OW.
  • FA associated with cell membrane fluidity wasn’t affected in both species.
  • 20:5n-3 and 20:1n-9 FA were negatively impacted in A. eightsii under OW.
  • Both species appear capable of maintaining stable FA levels in these conditions.

Abstract

Ocean acidification (OA) and ocean warming (OW) are likely to alter the biochemical composition of certain organisms as a physiological response to these changing environmental conditions. Given the importance of fatty acids (FA) in energy transfer within marine food webs, this two-month laboratory study examines the response of two calcifying species from Potter Cove (Antarctica) – the bivalve Aequiyoldia eightsii and the coral Malacobelemnon daytoni – to predicted OA and OW, focusing on their FA profiles. Neither species showed significant changes compared to the control group in the composition of FA ratios associated with immune function and cell membrane fluidity in response to either OA or OW. Additionally, the FA composition related to inflammatory responses remained largely unaffected by the stressors, although the 20:5n-3 FA was negatively impacted in A. eightsii under high-temperature conditions. Overall, the FA composition in these species appears robust to near-future environmental changes.

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Pteropods as early-warning indicators of ocean acidification

Published 6 May 2025 Science Closed
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Aragonite undersaturation (Ωar < 1) events are projected to rapidly increase in frequency and duration in the Antarctic Weddell Sea by 2050. Thecosome pteropods (pelagic snails) are bioindicators of ocean acidification (OA) because their aragonite shell dissolves easily at low Ωar saturation states. Here, we describe the shell dissolution state of the pteropod Limacina helicina antarctica in relation to the water column Ωar in the southern Weddell Sea during austral summer 2018 as benchmark for future monitoring of ongoing OA. Ωar depth profiles at the sampling sites were consistently close to or in the range of threshold levels (Ωar ~ 1.1–1.3) for pteropod shell dissolution. Pteropods contributed up to 69% of total mesozooplankton biomass, and their distribution correlated positively with Ωar and chlorophyll a concentration. When analyzed with scanning electron microscopy, 78% of the investigated shells exhibited dissolution, and 50–69% showed the more severe Type II dissolution exceeding current projections of pteropod shell dissolution for the Southern Ocean. But importantly, in our study, only two specimens had the most severe Type III dissolution. Dissolution often co-occurred with and occurred in scratch marks of unclear origin supporting notions that an intact periostracum protects the shell from dissolution. Where dissolution occurred in the absence of scratches or absence of evidence of periostracum breaches, microscale/nanoscale breaches may have been an important pathway for dissolution commencement supporting recent findings of a reduction of the organic shell content caused by low Ωar/low pH. The dissolution benchmark we provide here allows future application of pteropods as early-warning indicators of presumably progressing OA in the Weddell Sea.

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Compound marine heatwaves and acidity extremes in the Southern Ocean

Published 5 May 2025 Science Closed
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Compound extremes of temperature and acidity that extend over substantial fractions of the water column can be particularly damaging to marine organisms, as they experience not only additional stress by the potentially synergistic effects of these two stressors, but also a reduction in habitable vertical space. Here, we detect and analyse such column-compound extremes (CCX) in the Southern Ocean between 1980 and 2019, and characterise their duration, intensity, and spatial extent. To this end, we use daily output from a hindcast simulation of the Regional Ocean Modeling System (ROMS), coupled with the Biological Elemental Cycling (BEC) model. We first detect extremes in temperature and acidity ([H+]) within the top 300m using a relative threshold of 95% and then identify CCX where conditions are extreme for both stressors for at least 50m of the water column. When analysed on a fixed baseline, positive trends in ocean warming and acidification caused CCX to last longer, intensify, and expand throughout the Southern Ocean. In the Antarctic zone, CCX expanded between 1980 and 2020 by more than 10 times in volume, lasted up to 120 days longer, and doubled in anomaly. Some of the largest and longest events occurred in Antarctic Marine Protected Areas (MPAs), covering more than 200 000 km2 and persisting for over 500 days. CCX in the Subantarctic and Northern zones quadrupled in volume and increased by more than 30% in anomaly. Across the Southern Ocean, the increasing occurrence of CCX exacerbates the risks to marine ecosystems from warming and acidification.

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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
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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.

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Decadal progress of ocean acidification over the Southern Ocean

Published 19 March 2025 Science Closed
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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.

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

Published 27 February 2025 Science Closed
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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.

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

Published 26 February 2025 Science Closed
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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.

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