Boron stable isotope ratios in biogenic calcium carbonate minerals are known to reflect the decreasing of seawater pH, and thus they can be a useful tracer to track the trend of the ocean acidification. While validation of boron isotopes as a tracer for seawater pH has mainly focused on foraminiferal and coral CaCO3, a few studies examined CaCO3 skeletons produced by sclerosponges. In this study, we investigated stable boron and carbon isotope ratios in two sclerosponge specimens (Acanthochaetetes wellsi), collected from Okinoerabu Island, Japan. Carbon isotope ratios in both specimens showed a continuous decrease over the estimated growth periods, indicating that the Suess effect is recorded in sclerosponge skeletons. In contrast, boron isotope ratios in one specimen decreased over time, but not in the other. These findings suggest further analysis of additional specimens is necessary to determine whether boron isotope ratios in sclerosponge skeletons are reliable recorder of ocean acidification.
Continue reading ‘Can sclerosponge skeletons record ocean acidification?: boron and carbon isotope ratios (δ11B and δ13C) in Acanthochaetetes wellsi from Okinoerabu Island, southwestern Japan’Posts Tagged 'paleo'
Can sclerosponge skeletons record ocean acidification?: boron and carbon isotope ratios (δ11B and δ13C) in Acanthochaetetes wellsi from Okinoerabu Island, southwestern Japan
Published 21 July 2025 Science ClosedTags: biological response, laboratory, methods, North Pacific, paleo, porifera
Ocean acidification at the Toarcian Anoxic Event captured by boron isotopes in the lime mud record
Published 16 July 2025 Science ClosedTags: biological response, brachiopods, chemistry, field, mollusks, paleo
The Toarcian Oceanic Anoxic Event (ca. 183 million years ago) marks a global mass extinction coincident with dramatic changes in climate and ocean circulation, likely driven by large igneous province emplacement. Rapid carbon dioxide release may have induced global warming, widespread ocean deoxygenation, and ocean acidification. To constrain the magnitude of ocean acidification, we present boron isotope data from three different carbonate components, lime mud (micrite), brachiopods, and bivalves, from two marine sections in SW Europe. Only data from micrite shows a temporary decrease in boron isotope composition during the Toarcian Oceanic Anoxic Event, recording an ocean acidification event, which we reproduce using a coupled biogeochemical model. The contrasting stability of boron isotope values shown by bivalves and brachiopods suggests that the investigated taxa may have been able to physiologically buffer changes in ocean pH, and are therefore poor targets for the interrogation of pH changes in Earth history.
Continue reading ‘Ocean acidification at the Toarcian Anoxic Event captured by boron isotopes in the lime mud record’Ocean acidification is erasing microscopic historians, as St. Pete scientists try to learn their secrets
Published 9 July 2025 Media coverage ClosedTags: paleo
Beneath the ocean floor, in layers of ancient sediment, lie microscopic storytellers, marine organisms called foraminifera, or “forams” for short. These single-celled protists, no larger than a grain of sand, hold within their calcium carbonate shells a detailed record of Earth’s climate history. But, rising carbon emissions and ocean acidification may be erasing their story before scientists can read it.
At the University of South Florida’s College of Marine Science in St. Petersburg, oceanographer Callie Crawford is at the forefront of a research effort to understand how ocean acidification, a direct result of human-caused climate change, is ultimately threatening the ocean’s ability to remember.
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Crawford, an early-career scientist with two degrees in marine science and a minor in chemistry, works in the Rafter Ocean, which is run by Patrick Rafter and Climate Lab. She and her team collaborate with other scientists and labs to study sediment cores pulled from the ocean floor, containing layers dating back tens of thousands of years; records that, when combined with research from other labs, help reconstruct Earth’s past climate.
Inside these cores, scientists find foraminifera shells that preserve the chemical conditions of the water they lived in, clues that help reconstruct ancient ocean temperatures, carbon levels, and other vital environmental data.
This field of study, called paleoceanography, is key to building climate models that help us predict the planet’s future.
Continue reading ‘Ocean acidification is erasing microscopic historians, as St. Pete scientists try to learn their secrets’Brachiopods and forams reduced calcification costs through morphological simplification during mass extinction events
Published 3 July 2025 Science ClosedTags: biological response, brachiopods, field, morphology, paleo, protists
Environmental stressors have exacerbated the collapse of marine ecosystems during mass extinctions. However, the survival strategies of marine species during mass extinctions remain unclear. Here, we investigated morphological evolution of brachiopods across the Permian–Triassic mass extinction (PTME) using a database of 3,225 specimens representing 1,061 species and foraminifera across the PTME and early Toarcian oceanic anoxic event (T-OAE) using a database of 757 specimens representing 12 species. We found a significant reduction in the number and proportion (plicae length/shell length) of shell plicae of brachiopods (36.4% and 60.0%, respectively) across the PTME and a significant decrease in the shell thickness of foraminifera (18.9% and 42.4% across the PTME and 36.9–61.8% across the T-OAE). We calculated that these adaptive strategies could reduce the energetic costs of calcification by more than half for brachiopods across the PTME, and by ~20–62% for foraminifera across the PTME and T-OAE, to compensate for the elevated cost of calcification due to environmental and ecological pressures. We propose that simplification of morphological features, such as reduced shell ornamentation and shell thinning, serves as a potential economic strategy for calcifying organisms to cope with extinction events by reducing energy demands, but further studies with a broader range of taxa and extinction events are needed to confirm the generality of this bioenergetic strategy.
Continue reading ‘Brachiopods and forams reduced calcification costs through morphological simplification during mass extinction events’New study shows how ‘marine revolution’ shaped ocean life
Published 7 May 2025 Press releases ClosedTags: paleo
A scanning electron micrograph of Globorotalia tumida, a calcareous planktic foraminifera. This specimen was collected from IODP Site U1559 in the South Atlantic Ocean. Credit: Chris Lowery.
Between 252 and 66 million years ago, the ocean underwent a revolution.
That’s when plankton with calcium carbonate skeletons colonized the open ocean. When they died, their remains fell like snow over large parts of the seafloor. The abundance of their skeletons over time changed the marine landscape, leading to unique rock formations and vast deposits of carbonate rock.
This buildup of carbonate minerals was an important part of the Mesozoic Marine Revolution, or MMR — a period of transformation in Earth’s oceans that helped set the stage for today’s modern marine ecosystem.
According to a new study led by researchers at The University of Texas at Austin and published in the Proceedings of the Royal Society B: Biological Sciences, the change in calcium carbonate dynamics in the ocean appears to have influenced the evolutionary trajectory of tiny but mighty sea creatures: foraminifera.
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Forams can make their skeletons out of different materials, including sediments and organic matter. The researchers found that after the MMR, calcareous forams — which build their shells by secreting calcium carbonate — flourished, going on to become the dominant type of foram living today.
The study’s lead author Katherine Faulkner, who conducted the research when she was an undergraduate student at UT, said that in addition to shedding light on foram diversity through time, the findings could help researchers learn about how other forms of marine life responded to swings in ocean chemistry over geologic time.
Continue reading ‘New study shows how ‘marine revolution’ shaped ocean life’Record of foraminifera test composition throughout the Phanerozoic
Published 17 April 2025 Science ClosedTags: biological response, morphology, paleo, protists, review
Marine calcifiers produce calcareous structures (e.g. shells, skeletons or tests) and are therefore sensitive to ocean chemistry. Nevertheless, the long-term evolutionary consequences of marine carbonate changes are not well understood. This article compares calcareous and non-calcareous responses to ocean chemistry changes throughout the Phanerozoic Eon (541 million years ago to present). To accomplish this, we calculated proportional wall-type diversity, origination rates and extinction rates for 2282 benthic foraminiferal genera. Calcareous origination and extinction rates fluctuated throughout the Palaeozoic Era (541–251.9 million years ago), but during the Mesozoic Era (251.9–66 million years ago), calcareous origination and extinction rates stabilized following the evolution of pelagic calcifiers. Despite variations in Cenozoic Era (66–0 million years ago) foraminifera diversity, calcareous wall types maintained around 77% proportional diversity. Although calcareous wall-type extinction rates decline during the Mesozoic and Cenozoic, Phanerozoic foraminifera wall-type changes during individual events are largely contingent upon contemporaneous conditions rather than overarching trends. Of the Big Five mass extinction events, calcareous wall-type proportions only decreased at the end-Permian (73% to 26% diversity) and end-Triassic (56% to 50% diversity). These results suggest long-term ocean chemistry changes were not the main driver of foraminiferal wall-type diversity through time.
Continue reading ‘Record of foraminifera test composition throughout the Phanerozoic’Quantitative reconstruction of intermediate water pH in the South China Sea based on branched tetraether lipids
Published 16 April 2025 Science ClosedTags: chemistry, field, North Pacific, paleo
The geochemical proxy of ocean pH is crucial for understanding the dynamics of ancient ocean carbon reservoirs. This study employs the cyclization index of branched glycerol dialkyl glycerol tetraether compounds (brGDGTs), widely used in terrestrial environments for paleo-pH reconstruction, to investigate the intermediate water pH in the South China Sea. The South China Sea, a semi-enclosed marginal sea in the western Pacific, serves as the study area. By collecting data including global soil datasets, subtropical soil data, samples with water depths less than 50 meters in the northern South China Sea, surface sediment samples in the South China Sea, and brGDGTs data from rock cores in the northern South China Sea, significant differences were found in the composition of brGDGTs in marine sediments compared to those in soils. This proves the in-situ self generation viewpoint of brGDGT in the ocean, mainly generated in the middle water column, providing a basis for reconstructing ocean acidification. The research materials for establishing a global formula include deep-sea sediment samples from the South China Sea, Western Pacific, Southeast Pacific, Northeast Atlantic, and Southwest Atlantic, all of which were collected at depths of over 300 meters to avoid terrestrial influence. Lipids were extracted using a modified Bligh-Dyer method and analyzed using high-performance liquid chromatography-atmospheric pressure chemical ionization-mass spectrometry(HPLC-APCI-MS). A positive correlation between brGDGTs indices (CBT’ and #Ringstetra)and seawater pH was established, allowing for the development of empirical formulas for reconstructing ancient midwater seawater pH. Utilizing published brGDGTs data from Holocene sediments in the northern South China Sea, the reconstructed pH values indicate a maximum of approximately 7.89 around 6.5 ka and a minimum of about 7.72 around 1.5 ka. The study validates that brGDGTs in deep-sea sediments are of marine origin. This research demonstrates that brGDGTs in marine sediments are autochthonous and can be employed to reconstruct intermediate water pH, providing significant insights into ocean acidification history.
Continue reading ‘Quantitative reconstruction of intermediate water pH in the South China Sea based on branched tetraether lipids’Calcification of planktonic foraminifer Neogloboquadrina dutertrei and its indicative significance for ocean acidification
Published 16 April 2025 Science ClosedTags: biological response, dissolution, field, morphology, paleo, protists
Planktonic foraminifera are widespread calcifying protozoa and represent a primary source of marine biogenic calcium carbonate. Elucidating the mechanisms underlying the calcification processes of planktonic foraminifera holds significant importance for understanding the marine biological pump and carbon cycling.
The present study investigated the controlling mechanisms of calcification in modern planktonic foraminifer Neogloboquadrina dutertrei by analyzing the foraminiferal shell weight data from 92 sets of surface sediments from different ocean areas, including the eastern tropical Indian, the western tropical Pacific, the eastern tropical Pacific, and the western tropical Atlantic. First, this study reveals that deep-ocean carbonate dissolution, which is related to deep-ocean carbonate ion saturation state (Δ[CO32-]), is the dominant factor influencing the shell weight of N. dutertrei in surface sediments. Then, by correcting the dissolution effect on the shell weight of N. dutertrei, we estimated the initial shell weight from which to assess secular changes in the degree of calcification of N. dutertrei. The initial shell weight results suggest that the calcification of N.dutertrei is mainly controlled by seawater carbonate system parameters such as pH, carbonate ion concentration ([CO32-]), and carbon dioxide concentration (pCO2). Calcification of N. dutertrei would decrease with ocean acidification.
Furthermore, we reconstructed initial shell weight of N.dutertrei at sites KX97322-4 and U1490 in the western tropical Pacific to evaluate the response of N. dutertrei calcification to climate changes over glacial-interglacial time scales. Calcification of N. dutertrei in the western tropical Pacific has increased during glacial periods in response to lower atmospheric pCO2 since 800 ka, confirming the dominant influence of ocean acidification on N. dutertrei calcification. We suggest that the shell weight of specific planktonic foraminiferal species may serve as a potential proxy for past seawater carbonate system reconstructions.
Continue reading ‘Calcification of planktonic foraminifer Neogloboquadrina dutertrei and its indicative significance for ocean acidification’Variations of coccolith morphology and their influencing factors in the northeastern South China Sea since the last glacial maximum
Published 15 April 2025 Science ClosedTags: biological response, chemistry, field, morphology, North Pacific, paleo, phytoplankton, sediment
Coccoliths are widely present in marine sediments of the South China Sea and closely associated with paleoenvironmental changes. This study investigates the morphological variations and driving factors of coccoliths since the Last Glacial Maximum(LGM) by analyzing the morphology and related indicators of Noelaerhabdaceae coccoliths in sediment samples from core MD18-3569 (0.01~12.41 m; 0.69~26.58 ka) in the northeastern South China Sea(22°09.30’N, 119°49.24’E at water depth 1320 m), and a total of 155 samples were collected, with a sampling resolution of approximately 167 years. Morphological attributes such as coccolith length, thickness, area, and mass were obtained through microscopic measurements and computational formulas. Coccolith morphological constants were used to evaluate preservation conditions. Based on these data, morphological divergence index and calcification index were calculated. Using the PyCO2SYS model, ocean carbonate system parameters were reconstructed to explore their impact on coccolith morphology.
The results show that coccolith length ranged from 2.69 μm to 3.86 μm(mean: 3.20 μm) since the LGM, with significant variability but no clear trend. Thickness ranged from 0.07 μm to 0.17 μm(mean: 0.13 μm) and exhibited a decreasing trend since the LGM. Coccolith mass varied between 2.31 pg and 9.02 pg(mean: 5.61 pg), also showing a decreasing trend since the LGM. Coccolith morphological constants indicate good preservation and high data reliability. Morphological divergence index results suggest a decline in coccolith size diversity, reflecting reduced seasonal variation and regional productivity. Calcification intensity metrics indicate a weakening of calcification since the LGM.
By comparing temperature, salinity, and ocean carbonate system parameters, the study identifies rising atmospheric CO2 concentrations and resultant ocean acidification as the primary factors contributing to reduced coccolith calcification. The impacts of temperature and salinity were relatively minor. These findings demonstrate the complex response of Noelaerhabdaceae coccoliths to environmental changes and highlight the significant roles of regional climate variations and carbonate system evolution in shaping coccolith morphology.
Continue reading ‘Variations of coccolith morphology and their influencing factors in the northeastern South China Sea since the last glacial maximum’Boron proxies: from calcification site pH to Cenozoic pCO2
Published 14 April 2025 Science ClosedTags: calcification, chemistry, paleo
The atmospheric partial pressure of CO2 (pCO2) is the key driver of climate variability. Boron isotopic compositions (δ11B) of marine calcium carbonates reveal pCO2 of the geologic past because boron isotope incorporation is sensitive to seawater pH, which closely reflects atmospheric pCO2. Biocarbonate δ11B values record environmental pH through a metabolic prism (so called “vital effects”), sometimes complicating interpretations. However, biocarbonate boron isotopes, coupled with boron concentrations (B/Ca), can also reveal the processes of calcification. Here, we review the link between seawater pH and the effective pH recorded by marine organisms via biomineralisation and summarise pCO2 reconstructions from boron isotopes for the Cenozoic (≈70 Ma to modern times), arguably the most significant contribution of this proxy system to date.
Continue reading ‘Boron proxies: from calcification site pH to Cenozoic pCO2 ‘Combined uranium-series and trace elements analysis in cold seep bivalves: possibility in hundred-year-scale reconstruction of deep-sea temperature and acidification
Published 17 March 2025 Science ClosedTags: chemistry, North Pacific, paleo
Despite the pivotal role of deep-sea in the global climate system, effective technology is still limited for reconstructing the key parameters of deep-sea environment such as temperature and acidification, especially at the hundred-year scale. In this study, we assessed the robustness and reliability of using bivalve shells in reconstructing cold seep environments. A significant heterogeneous distribution of trace elements was observed in the shells of clams and mussels from Formosa and Haima cold seeps even if they were collected from the same site, which was caused mainly by the environmental variables rather than physiological characters. The results of the principal component analysis revealed different trace elements ratios in the shell were associated with seepage. In particular, Sr/Ca was identified as a reliable proxy for temperature reconstruction, which performed better than oxygen isotopes. Na/Ca and U/Ca are potential proxies for cold seep acidification, but further validation is needed before their practical application. The age bias using the U-series dating method resulted from high 232Th and low initial 230Th/232Th rather than from alpha-recoil processes. The median ages assigned to mussels from the F and Haima cold seeps were 229.5 and 323.5 years, respectively. The lifespan of clams from the Haima cold seep was too short to date accurately. We proposed to conduct feasibility verification and error correction to enhance the method performance in reconstructing the hundred-year evolution of cold seep environment in the South China Sea.
Continue reading ‘Combined uranium-series and trace elements analysis in cold seep bivalves: possibility in hundred-year-scale reconstruction of deep-sea temperature and acidification’Coral skeletal isotopes (δ¹³C and δ¹¹B) as indicators of seawater light attenuation and pH chemistry in the Singapore Strait
Published 4 February 2025 Science ClosedTags: biological response, chemistry, corals, field, paleo, physiology
This study investigates the interaction between δ¹³C and δ¹¹B with terrigenous carbon dynamics in the Singapore Strait, a region characterized by distinct monsoon patterns and significant terrigenous input from surrounding peatlands. We hypothesized that elevated levels of colored dissolved organic matter (CDOM) during the Southwest Monsoon would decrease light penetration, leading to more negative δ¹³C values in coral skeletons. Additionally, we expected that remineralization of terrigenous dissolved organic matter (tDOM) would acidify seawater, resulting in more negative δ¹¹B values in corals. Analysis of Porites spp. corals from two plug cores (KUK and KUL) and seawater data from Kusu Island (2017-2020) revealed no significant correlation between CDOM and coral δ¹³C anomalies— deviations between coral skeletal δ¹³C values and the δ¹³C values of dissolved inorganic carbon (DIC) in seawater— contradicting our hypothesis. Instead, variations in coral δ¹³C appear to be related to a reservoir effect associated with negative δ¹³C in seawater DIC, influenced by tDOC remineralization. Although not statistically significant, the positive correlation pattern observed between δ¹¹B and seawater pH in the KUL core suggests that δ¹¹B might serve as a useful proxy for historical seawater pH and acidification. This finding also supports the idea that Porites corals may regulate their internal pH in response to changes in seawater acidity, potentially influenced by tDOC remineralization. Inconsistencies in the KUK core could be attributed to data offsets from our age-depth model. Further research with extended sampling is needed to confirm δ¹¹B’s sensitivity to pH changes and understand its impact on coral physiology. This study highlights the complex interplay between seasonal changes, carbon dynamics, and coral isotopic records.
Continue reading ‘Coral skeletal isotopes (δ¹³C and δ¹¹B) as indicators of seawater light attenuation and pH chemistry in the Singapore Strait’Delayed onset of ocean acidification in the Gulf of Maine
Published 23 January 2025 Science ClosedTags: biogeochemistry, chemistry, North Atlantic, paleo
The Gulf of Maine holds significant ecological and economic value for fisheries and communities in north-eastern North America. However, there is apprehension regarding its vulnerability to the effects of increasing atmospheric CO2. Substantial recent warming and the inflow of low alkalinity waters into the Gulf of Maine have raised concerns about the impact of ocean acidification on resident marine calcifiers (e.g. oysters, clams, mussels). With limited seawater pH records, the natural variability and drivers of pH in this region remain unclear. To address this, we present coastal water pH proxy records using boron isotope (δ11B) measurements in long-lived, annually banded, crustose coralline algae (1920–2018 CE). These records indicate seawater pH was low (~ 7.9) for much of the last century. Contrary to expectation, we also find that pH has increased (+ 0.2 pH units) over the past 40 years, despite concurrent rising atmospheric CO2. This increase is attributed to an increased input of high alkalinity waters derived from the Gulf Stream. This delayed onset of ocean acidification is cause for concern. Once ocean circulation-driven buffering effects reach their limit, seawater pH decline may occur swiftly. This would profoundly harm shellfisheries and the broader Gulf of Maine ecosystem.
Continue reading ‘Delayed onset of ocean acidification in the Gulf of Maine’Ocean acidification signals through deep time: a review of proxies
Published 8 January 2025 Science ClosedTags: biological response, paleo, protists, review
Highlights
- A comprehensive review of multiple ocean acidification proxies from the geologic past.
- Proxies classified by data type, time, and required facilities: observational or analytical.
- Observational: shell weight, dwarfism, carbonate size, fragmentation, preservation.
- Analytical: calcium carbonate, magnetic susceptibility, isotopes, and trace elements.
- Proxy use depends on calibration, diagenesis, timescale, and conditions it reflects.
Abstract
Anthropogenic CO₂ levels have increased by nearly 40% from preindustrial levels, with about 30% absorbed by the ocean leading to ocean acidification (OA). The associated carbonate undersaturation can critically affect marine calcifying communities. Major disruptions in the marine carbonate cycling are common throughout the Phanerozoic stratigraphic record, and often coincide with major mass extinctions and faunal turnover events. The anthropogenic OA is progressing at a rate nearly ten times faster than similar events of the past 300 million years. This makes OA research of high priority, and entails a rigorous evaluation of OA events from deep time for perspective. Such efforts are contingent upon reliable proxies. This review compiles geochemical and foraminifera-based proxies, offering a critical assessment of their fidelity, ease of use, and application scope.
This study evaluates the scope and utility of documented observational and analytical proxies based on factors like the nature of data, and the time, effort and advanced analytical facilities involved. Foraminifera-based observational proxies like morphological and community responses to OA are effective but demand taxonomic expertise. They are further complicated by vital effects, metabolic trade-offs, the influence of stressors other than ocean acidification, and paleogeographic variability in both the magnitude of stress and the organisms’ response to it. Well-calibrated analytical (geochemical) proxies offer the potential for rapid, high-resolution records across various sites. All proxies face challenges from diagenetic alterations, which can affect their reliability. However, this review offers the pros/cons and practical recommendations for proxy utility, emphasing the need for a multi-proxy approach to enhance accuracy and cross-verification. Future research must urgently address plankton community responses, OA-tolerant taxa, and localized calcification environments to grasp the full impact of acidification. It is critical to refine lesser-known proxies (e.g., S/Ca) and to rapidly expand datasets on carbonate system parameters across Phanerozoic OA events to advance our understanding and mitigation strategies.
Continue reading ‘Ocean acidification signals through deep time: a review of proxies’From holocene to anthropogenic impact: surpassing coral’s pH up-regulation capacity under ocean acidification
Published 1 January 2025 Science ClosedTags: biological response, corals, laboratory, North Pacific, paleo, physiology
Highlights
- Coral calcifying fluid chemistry during the past ∼5500 years.
- No clear responses of coral CF chemistry to pre-industrial climate shifts.
- Declines in coral pHcf and [CO32−]cf during the CWP.
- A pantropical compilation of δ11B-pHcf matches atmospheric CO2 since Mid-Holocene.
- Limits of corals’ pHcf up-regulation to counteract ocean acidification.
Abstract
Corals’ regulation of internal calcifying fluid (CF or cf) chemistry is crucial for their extraordinary calcification capacity, endowing them with a certain ability to cope with environmental changes such as anthropogenic ocean acidification (OA) and warming. However, it remains unclear whether the impacts of these changes on corals have substantially surpassed their regulation capacity, particularly in comparison to the CF chemistry responses to natural climate variability with minor or no human perturbation. In this study, we reconstructed the pH, dissolved inorganic carbon, and carbonate ion concentrations in coral CF (pHcf, DICcf, and [CO32−]cf) during the Mid- to Late-Holocene, by analyzing the skeletal δ11B and B/Ca of 80 Porites spp. from eastern Hainan Island in the South China Sea (SCS). Our records indicate considerable inter-colony variations in CF chemistry, with maximum disparities reaching 0.18 units for pHcf and 1664 μmol/kg for DICcf. With this in mind, we found no clear responses of coral DICcf to the climate fluctuations during the past ∼5500 years, nor evident differences in pHcf and [CO32−]cf across pre-industrial natural epochs. However, pHcf and [CO32−]cf of modern corals have significantly declined compared to fossil corals. Further analyzes compiling global data on Porites spp. also confirm this pronounced pHcf decrease in modern corals, suggesting the limitations of pantropical corals to counteract OA by up-regulating pHcf. Importantly, these fossil and modern corals reveal a clear long-term pHcf descending trend parallel to atmospheric CO2 changes, supporting the reliability of coral δ11B in recording long-term changes in seawater pH (pHsw).
Continue reading ‘From holocene to anthropogenic impact: surpassing coral’s pH up-regulation capacity under ocean acidification’Marine biological responses to abrupt climate change in deep time
Published 24 December 2024 Science ClosedTags: biological response, paleo, review
Non-technical Summary
Paleobiology can offer diverse insights into how climate change has affected past species and ecosystems. Timely and important areas of research focus on the potential of paleobiology to contribute to solutions for climate impacts on natural ecosystems. But how far can past responses to abrupt climate change be generalized to derive predictions for the modern and future worlds? The long timescales over which biological responses are observed in the deep time past hamper the applicability of paleontological observations, but by how much? To address these questions, we review paleontological evidence for the impacts of geologically rapid climatic change. Fruitful avenues for future research lie in (1) characterizing the relationship between the magnitude of warming and extinction toll, (2) using physiology to bridge timescales, and (3) assessing the role of long-term climate history to predict the impact of short-term climate change. Identifying how consistent and robust paleontological signals are across timescales will help to make deep-time observations more useful for the modern world.
Abstract
Ancient changes in the biosphere, from organismic traits to wholesale ecosystem changes, can be aligned with climate forcing across the Phanerozoic. Clear examples of abrupt climate warming causing biodiversity crises are primarily found between the Permian and Paleogene periods. During these times, catastrophic events occurred, resembling the extreme climate scenarios projected for the near future. The paleobiologic literature around these events generally supports the hypothesis that abrupt climate change was a dominant trigger of extinction and/or ecological crisis. When climate change and climate history are considered, virtually all post-Paleozoic global biotic events can be confidently attributed to climatic change, with abrupt warming (hyperthermal events) leaving the most consistent fingerprint. The combined stress of deoxygenation and warming are sufficient to explain marine extinction patterns across most hyperthermal events. Although ocean acidification may have contributed, the direct role of pH on the extinction toll of organisms is not consistently demonstrated. Future research can enhance the correspondence between the magnitudes of climatic changes and their biological impacts, even though observed rates of change cannot currently be compared across different timescales. Mimicking multi-scale approaches in modern ecology, paleontological approaches to climate impact research will benefit from specifically targeting scaling relationships
Rhodolith beds in a shifting world: a palaeontological perspective
Published 16 December 2024 Science ClosedTags: algae, biological response, paleo, review
The occurrence of rhodolith beds in the stratigraphic record from the Cretaceous to the Pleistocene was analysed from published papers. Most data refer to low-mid latitude records of rhodolith beds described in the Tethyan-Paratethyan-Mediterranean domain. The first putative rhodolith beds are from Albian (uppermost Lower Cretaceous) deposits. These rhodolith beds are made up mostly of unattached loose branching corallines as well as of nodular structures. From the Coniacian (Upper Cretaceous) to the Langhian (Middle Miocene), abundance of rhodolith beds shows a generally increasing fluctuating trend with two significant expansions in the Priabonian (late Eocene) and during the Aquitanian-Langhian (Early-Middle Miocene). After the Langhian maximum, rhodolith beds sharply declined to a minimum in the Zanclean (Early Pliocene). During the Pleistocene, they recovered to values similar to those reached in the Langhian. The general increase in rhodolith beds up the Langhian maximum correlates well with global temperature and pCO2 declines and with an ocean pH increase. The tectonic activity leading to important palaeogeographic changes in the Tethyan-Parathetyan-Mediterranean realm might account for the Serravallian-Zanclean downfall of rhodolith-dominated deposits. The Cretaceous-Pleistocene record of rhodolith beds shows that these ecosystems withstood successfully a highly changing world. The rapid acclimation of particular taxa to environmental changes and the variable reaction of taxa distributed at different water depths can be crucial to understand their success. In this regard, it would be interesting to analyse how different taxa in modern deep rhodolith beds respond to changing oceanic conditions.
Continue reading ‘Rhodolith beds in a shifting world: a palaeontological perspective’Paleo-atmospheric CO2 reconstructions from deep-ocean sediments
Published 22 November 2024 Science ClosedTags: paleo, sediment
Biological remains in ocean sediments document the remarkable history of atmospheric CO2 and its fundamental control on Earth’s climate. Higher resolution studies are needed to better understand the short-term processes that inform imminent anthropogenic climate changes.
Human activities have increased the concentration of carbon dioxide in our atmosphere from 280 ppm before industrialization to 424 parts per millin (ppm) in 2024. Without reductions in emissions, CO2 is projected to rise to >800 ppm by the end of this century, driving warming well in excess of the 1°C already recorded (IPCC 2021). How warm it will get can be projected by complex numerical climate models whose skills are validated using the detailed relationship between atmospheric CO2 and global climate in Earth’s history. Instrumental measurements of CO2 have been collected since 1958 (Lan et al. 2024), and ancient air trapped in Antarctic ice documents Earth’s atmospheric composition over hundreds of thousands of years prior (Bereiter et al. 2015; Yan et al. 2019). However, CO2 during this geologically recent past was generally lower than today, and global temperatures colder. Much warmer intervals occurred in the distant past, but because the atmosphere of that time cannot be sampled directly, paleo-CO2 reconstructions rely on indirect proxies preserved in the sedimentary record.
Reconstructing CO2 from ocean sediments
Deep-sea sediments are key to paleoreconstructions; they are globally distributed and gradually accumulate biogenic and inorganic proxy materials over tens of millions of years, thereby providing excellent age stratigraphy. Uniquely useful in documenting past surface-ocean temperatures and the partial pressure of CO2 (PCO2) are the mineralized and organic remains left behind by organisms that once inhabited the ancient surface ocean. This is because gas exchange at the air-sea interface drives PCO2 in seawater towards equilibrium with PCO2 in the atmosphere. Once absorbed in seawater, CO2 reacts with water (H2O) and forms a suite of carbon species whose abundances are controlled by well-understood chemical equilibrium reactions that also determine seawater acidity (i.e. pH).
Not all oceanic regions are appropriate for paleo-CO2 studies because vigorous photosynthesis can diminish sea-surface CO2 while upwelling of deeper waters delivers respired CO2 to the surface, disturbing the air–sea equilibrium. Therefore, paleo-CO2 studies focus on off-shore regions such as subtropical gyres, where photosynthesis is weak and downwelling of surface waters allows air–sea equilibrium to be established.
There are two main frameworks for marine-based CO2 reconstructions: the stable carbon isotopic composition of organic phytoplankton (δ13Cphytoplankton) remains and the boron isotopic composition (δ11B) of fossilized CaCO3 shells. Briefly, the δ13Cphytoplankton proxy assumes CO2 passively diffuses into an algae cell, and the CO2-fixing enzyme RuBisCo preferentially takes up 12C over 13C during oxygenic photosynthesis. When CO2 is abundant, 12C is preferentially incorporated into organic matter (resulting in relatively lower δ13Cphytoplankton). The opposite occurs at low CO2 (Fig. 1). Although first applied to bulk organic matter (Popp et al. 1989), selective preservation and mixed organic sources imposed problems. These challenges have been resolved by using: (1) specific compounds produced by select algae (e.g. alkenones from Haptophytes); (2) specific compounds produced by the broader phytoplankton community (e.g. chlorophyll), enabling greater spatial and temporal diversity of reconstructions; and (3) organic carbon bound to mineral or organic exteriors of e.g. coccolithophores, diatoms or dinoflagellates. The detailed systematics of these approaches are reviewed in Hollis et al. (2019).
Figure 1: Basic systematics of the two marine CO2 proxies. Fossil organic compounds and CaCO3 shells are preserved in layered ocean sediments that can be extracted by deep-ocean drilling
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Continue reading ‘Paleo-atmospheric CO2 reconstructions from deep-ocean sediments’Coupled decline in ocean pH and carbonate saturation during the Palaeocene–Eocene Thermal Maximum
Published 20 November 2024 Science ClosedTags: chemistry, methods, modeling, paleo, sediment
The Palaeocene–Eocene Thermal Maximum, a climate event 56 million years ago, was characterized by rapid carbon release and extensive ocean acidification. However, our understanding of acidification and the evolution of ocean saturation states continues to be hindered by considerable uncertainties, primarily stemming from the limited availability of proxy data. Under such conditions, data assimilation allows for an internally consistent assessment of atmospheric CO2 changes, ocean acidification and carbonate saturation state during this period. Here, we present a reconstruction of the Palaeocene–Eocene Thermal Maximum carbon cycle perturbation by assimilating seafloor sediment CaCO3 and sea surface temperature proxy data with simulations from an Earth system model, which includes a comprehensive carbonate system. Our reconstructions indicate a substantial increase in atmospheric CO2 from 890 ppm (95% credible interval: 680–1,170 ppm) to 1,980 ppm (1,680–2,280 ppm), coupled with a notable decline in pH (0.46 units, ranging from 0.31 to 0.63 units) and surface-water calcite saturation state, decreasing from 10.2 (7.5–12.8) in the pre-event period to 3.8 (2.8–5.1) during the thermal maximum. Carbonate undersaturation intensified substantially in high-latitude surface waters during the Palaeocene–Eocene Thermal Maximum, paralleling the current decline in Arctic aragonite saturation driven by anthropogenic CO2 emissions.
Continue reading ‘Coupled decline in ocean pH and carbonate saturation during the Palaeocene–Eocene Thermal Maximum’Correlation of sub-centennial-scale pulses of initial Central Atlantic Magmatic Province lavas and the end-Triassic extinctions
Published 30 October 2024 Science ClosedTags: paleo
Significance
During the initial phase of eruptions, Central Atlantic Magmatic Province (CAMP) basalts spewed more than 500 times the amount of sulfur released during the Laki historic eruption in Iceland. The repeated injections of sulfate aerosols, constrained by paleosecular variation data, occurred in rapid succession. The resulting severe [albedo-induced] volcanic winters may have been the proximal cause for the well-resolved end-Triassic mass extinction in the continental realm. However, in the less temporally constrained marine realm, longer-term cumulative release of carbon dioxide from CAMP eruptive and intrusive activity may have played an important albeit somewhat diachronous role in the extinctions through ocean acidification and longer-term warming.
Abstract
The end-Triassic extinction (ETE) on land was synchronous with the initial lavas of the Central Atlantic Magmatic Province (CAMP) and occurred just after the brief 26 thousand year (kyr) reverse geomagnetic polarity Chron E23r that can be used for global correlation. Lava-by-lava paleomagnetic secular variation data, previously reported from Morocco and northeastern United States combined with our data for the North Mountain Basalt from the Fundy Basin of Canada show that the initial phase of CAMP volcanism occurred in only five directional groups or pulses each occupying less than a century. The first four directional groups occur during a ~40 kyr period based on available astrochronology and U-Pb geochronology. The coincidence of the initial major pulse of CAMP volcanism with the ETE points to short-lived volcanic winters albedo-induced by sulfate aerosols as a plausible key agent of the extinctions in the tropical continental realm, whereas looser correlations allow prolonged CO2 emissions to contribute to more long-ranging effects in the marine realm via ocean acidification and longer-term warming.
Continue reading ‘Correlation of sub-centennial-scale pulses of initial Central Atlantic Magmatic Province lavas and the end-Triassic extinctions’
