Posts Tagged 'paleo'

Witness to ocean acidification

Published 20 August 2026 Science Closed
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Foraminifera inhabit coastal and deep-sea marine environments. These microscopic, single-celled organisms are widely used as proxies for relative age determination and reconstructing past climates. The ratio of calcium isotopes (44Ca/40Ca) in their calcium carbonate shells depends on the amount of carbon dioxide (CO2) and carbonate saturation in seawater at the time of the shells’ formation. On page 527 of this issue, Chen et al. (1) report geochemical evidence that a rise in atmospheric CO2 concentration and ocean acidification at the end of the Aptian Stage [~113 million years ago (Ma)] may have caused the largest extinction of planktic foraminifera of the Cretaceous Period (146 to 66 Ma) (2–4), which is second only to the extinction event at the end of the Cretaceous Period (66 Ma) (5–7). The findings could be important for understanding potential effects of present-day increases in atmospheric CO2 levels on marine organisms.

Paraticinella rohri collected from the South Atlantic is a species of planktic foraminifera that went extinct at the Aptian–Albian boundary. IMAGE: HUBER AND LECKIE (3)

Seafloor-dwelling benthic foraminifera appeared more than 500 million years ago. It took at least 350 million years for them to evolve into planktic species that float in the upper ocean (8–10). The earliest species of planktic foraminifera lacked morphological diversity and were minor constituents of marine sediments. The first major morphological diversification of planktic foraminifera occurred (2, 11) during the Aptian Stage (125 to 113 Ma) of the mid-Cretaceous Period. New species of planktic foraminifera arose, with elongated chambers (Leupoldina) and larger, more heavily calcified shells (Globigerinelloides and Hedbergella), and the first species with a peripheral keel (Pseudoplanomalina cheniourensis) appeared by the late Aptian. Large increases in atmospheric CO2 concentration caused by massive volcanic eruptions triggered substantial depletion of oxygen in the oceans, including Oceanic Anoxic Event 1a and other similar events. Atmospheric CO2 likely drove warming of the atmosphere and water; warmer waters hold less dissolved oxygen compared to cooler water.

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Calcium isotopes link ocean acidification to Aptian–Albian foraminiferal extinctions

Published 19 August 2026 Science Closed
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Editor’s summary

About three quarters of planktic foraminifera species disappeared in the Aptian-Albian extinction event. What role might ocean acidification (OA) have played in this die-out? Chen et al. measured calcium isotope ratios in foraminifera, using them as a proxy for biocalcification and carbonate saturation (see the Perspective by Leckie). Their data reveal a dramatic reduction in calcification rates accompanied by decreases in the size, abundance, and diversity of planktic foraminifera. These results are consistent with the hypothesis that ocean acidification drove the extinctions of these organisms at the Aptian-Albian boundary. —Jesse Smith

Abstract

The second-largest extinction event in the evolutionary history of planktic foraminifera occurred at the Aptian–Albian boundary. This extinction may reflect ocean acidification (OA) associated with Oceanic Anoxic Event 1b. As calcium isotope ratios (δ44/40Ca) can track how biocalcification rates respond to OA, we measured δ44/40Ca records for planktic and benthic foraminifera, bulk carbonates, and authigenic calcite across the Aptian–Albian boundary in the South Atlantic. Benthic and bulk δ44/40Ca data display a distinct sequence of negative and positive excursions, similar to δ44/40Ca variations across other OA events. Planktic δ44/40Ca values increase markedly, tracking a reduction in calcification rates coincident with decreases in the size, diversity, and shell thickness of planktic foraminifera. These results suggest that OA drove extinctions of planktic foraminifera at the Aptian–Albian boundary.

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Study on the mechanical characteristics of the stress relaxation in the carbonate rock after high-temperature acidification

Published 3 July 2026 Science Closed
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To elucidate the mechanism by which acidification influences wellbore stability in deep reservoir formations, this study investigates the rheological and mechanical behaviors of the carbonate rock subjected to high-temperature acid etching. A novel experimental system was developed to characterize the stress relaxation behavior of the acid-etched carbonate rock, and the characteristics of the stress relaxation curves under various acid etching conditions and strain levels were systematically analyzed. Combined with Burgers model and the Levenberg–Marquardt algorithm, the evolution of rheological parameters of the carbonate rock under different acid etching regimes was quantitatively evaluated. The results indicate that the acid-etched carbonate rock exhibit significant rheological mechanical properties due to the presence of developed microcracks and complex pore structures. Under the identical acid etching duration and temperature, the initial stress, residual stress, and time required for stress relaxation stabilization all increase with increasing the strain level. Overall, the stress relaxation magnitude prior to the core fracture ranges from 15 to 25 MPa, and the stabilization time for the core stress relaxation falls between 5 and 7 h. The stress relaxation behavior of the acid-etched carbonate core is well described by the Burgers model. At fixed strain levels and temperatures, the instantaneous shear modulus  decreases linearly with extended acid etching time, whereas the instantaneous shear modulus  and the viscosity coefficients  and  exhibit exponential degradation. The final variation ranges of the key rheological parameters are determined as follows: instantaneous shear modulus  ranges from 5 × 103 to 2 × 104 MPa, instantaneous shear modulus  ranges from 6 × 105 to 2 × 106 MPa, viscosity coefficient  ranges from 2 × 107 to 8 × 107 MPa h, and viscosity coefficient  ranges from 1 × 105 to 1.2 × 106 MPa h. Furthermore, the evolutionary equations correlating the global model fitting parameters with the porosity of acid-etched samples are established, using acid etching time as an intermediate variable. The results of this study provide a theoretical basis for the analysis of wellbore stability after acidification and the selection of acid fracturing completion methods of deep reservoirs.

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Erosion-driven delayed warming and marine stress prior to the end-Permian mass extinction

Published 30 June 2026 Science Closed
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The end-Permian mass extinction (EPME) presents an anomaly: intense global warming lags the onset of the carbon isotope excursion (CIE) by ~50,000 years, challenging the presumed link between carbon cycle perturbations and climate warming. Using biogeochemical modeling, Bayesian inversion, and multiple proxies, here we show that incorporating continental erosion as a forcing term into the hyperthermal models can resolve this decoupling. Enhanced erosion, likely resulting from the terrestrial die-off of vegetation, accelerates continental weathering, which buffers early carbon release and delays global warming. This process also increases riverine phosphorus export to the oceans, fostering gradual marine anoxia and preconditioning the oceans for the extinction event. With these findings, we present a coherent unifying scenario for the EPME environmental dynamics. Furthermore, our study refines the hyperthermal paradigm, offering implications for future climate scenarios.

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Environmental, phylogenetic, and palaeogeographic impact on relative septal thickness in Devonian ammonoids from Morocco

Published 3 June 2026 Science Closed
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Building upon previous research, this study examines potential relationships between septal thickness in Devonian ammonoids from the Anti-Atlas of Morocco and isotopic proxy data from the literature for atmospheric CO2, sea surface temperature, oceanic pH, and weathering (δ18O, δ13C, δ11B, 87Sr/86Sr). Recent studies have demonstrated that various mollusc groups show some growth sensitive to environmental factors. Our results indicate no significant correlation between septal thickness and the examined proxies, except for significantly thinner septa in the genus Phoenixites following the environmental perturbations during the Kellwasser Event, which included anoxic conditions and possibly ocean acidification. This supports the hypothesis that a positive selection for reduced shell material occurred in response to changing seawater chemistry. Additionally, our results align with published data and may support a correlation between septal thickness and palaeolatitude. This study contributes to our understanding of the evolutionary impacts of environmental stressors such as ocean acidification on ammonoids and their adaptive strategies to changing environmental conditions.

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Darkness and body size shaped end-Cretaceous marine extinction patterns

Published 29 May 2026 Science Closed
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The Chicxulub asteroid impact at the Cretaceous–Paleogene (K–Pg) boundary (66 Ma) is thought to have caused the extinction of around 75% of species in the fossil record by triggering catastrophic environmental changes1. However, despite decades of research, the mechanisms linking the environmental changes to the selective extinction patterns observed in the marine fossil record remain unresolved. Here we use a global trait-based ecosystem model2,3 to establish this causality for the marine plankton community beyond the fossilized groups. Our model simulates diversity dynamics during the initial 100 years after the K–Pg boundary and represents explicitly extinction based on biomass thresholds that scales with body size. Under K–Pg climatic forcings, the model reproduces successfully key observed extinction patterns, including the high vulnerability of planktic foraminifera and other zooplankton, the survival of small mixotrophs4 and phytoplankton5,6, and potential for reduced diversity loss in high-latitude settings7. Our analysis suggests that impact-driven darkness and body-size-dependent extinction thresholds drove most of the observed extinction patterns. These results suggest that plankton ecologies enhance survival through differences in energy demand and acquisition. Our study bridges the gap between fossil evidence of extinction patterns and the K–Pg impact winter hypothesis, highlighting the value of trait-based models for understanding past biodiversity crises.

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Ca C code for Stable Ca and Sr isotope responses to ocean acidification during Oceanic Anoxic Event 2

Published 20 May 2026 Science Closed
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Ca – C model for Stable Ca and Sr isotope responses to ocean acidification during Oceanic Anoxic Event 2 published in Chemical Geology.

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Stable Ca and Sr isotope responses to ocean acidification during Oceanic Anoxic Event 2

Published 20 May 2026 Science Closed
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Volcanism-driven ocean acidification has repeatedly disrupted Earth’s carbon cycle and ecosystems. Calcium isotopes (δ44/40Ca) provide a potential means of tracking these perturbations, since both the weathering and burial of CaCO3 and the isotopic compositions associated with these fluxes are sensitive to changes in seawater pH. However, the use of δ44/40Ca to reconstruct acidification and infer biocalcification stress is often complicated from overprinting by diagenetic processes. In this paper, we investigate stable Ca (δ44/40Ca) and Sr (δ88/86Sr) isotope responses to ocean acidification during Oceanic Anoxic Event 2 (OAE 2) in a pelagic marine carbonate succession from the Western Interior Seaway. The records are reconstructed using the Iona-1 core in Texas, which fully captures Os isotope evidence for the onset of LIP volcanism that is missing from a previously published Ca isotope record in the Western Interior Seaway in Colorado. Here we show that a negative Ca isotope excursion occupies the missing part of the previously published Western Interior Seaway record, and that it the begins with the onset of large igneous province volcanism as represented by the abrupt shift to lower initial 187Os/188Os isotopic ratios in the core. Box-model simulations show that the negative Ca isotope excursion could be produced through reduced Ca isotope fractionation affecting pelagic carbonate production under conditions of transient acidification stress, followed by rapid recovery through carbonate alkalinity feedback. δ88/86Sr values broadly covary with δ44/40Ca values but deviate from the expected kinetic slope, instead defining a mixing array consistent with seawater-buffered recrystallization. Together, the coupled stable Ca-Sr isotope systematics distinguishes primary acidification-driven signals from diagenetic modification and demonstrate the utility of dual-isotope approaches for tracing volcanism-induced perturbations to the marine carbon cycle.

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Extending planktic foraminiferal Mg/Ca palaeothermometry into polar temperature ranges: crust- and lamellae specific calibrations and non-thermal controls

Published 15 May 2026 Science Closed
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The rapidity of climate change in the polar regions underscores the need for improved understanding of its impacts on ocean circulation at both regional and global scales. Reconstructions of past polar ocean-cryosphere interactions can provide this context, but large uncertainties in existing proxies limit the utility of such studies. For instance, there are currently no low-temperature (<9 °C) culture-based Mg/Ca-calibrations for planktic foraminifera, a key tool for reconstructing past changes in ocean temperatures. There is also limited understanding of non-thermal influences on Mg/Ca in Neogloboquadrina pachyderma, the only modern polar planktic foraminifera. Moreover, this species exhibits considerable levels of heterogeneity in composition precipitating a thick lower-Mg/Ca outer crust over higher Mg/Ca inner lamellae calcite; specimens with predominantly, albeit variable crust–lamellae proportions, are thus thought to introduce substantial uncertainty into high-latitude palaeotemperature reconstructions. Here, we used N. pachyderma cultured across a range of temperatures, salinities, and carbonate chemistry conditions including experiments in which pH and [CO32-] either covaried or were decoupled. By using a laser ablation approach to analyse crust and lamellae separately, we present new Mg/Ca-temperature calibrations for each component that extend culture-based calibrations in N. pachyderma down to the lower temperature-range (2–9 °C). The crust-specific calibration is of particular importance in high-latitude downcore records where N. pachyderma are commonly observed to preserve predominantly or only crust. Our results show significant carbonate chemistry influence on Mg/Ca with opposite influences from pH and carbonate ion concentration, when these variables changed in isolation. Additionally, we show that environmental conditions regulate crust-lamellar proportions, where increased salinity and temperature, and lower pH lead to less crust formation with implications for future ocean acidification and Arctic Atlantification, and for downcore reconstructions.

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Ordovician sedimentary processes and related driving forces: Jordan, Arabian Plate

Published 7 May 2026 Science Closed
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The Ordovician-Lower Silurian siliciclastics deposited on the Jordanian Platform represent a transitional sedimentary system between their granitoid Gondwana source area and the Paleo-Tethys. While fluvial fining upward cycles (FUCs) of quartz arenite dominate braid plain deltas/upper shore face environments of the Lower Ordovician, arkosic tempestite and oxygen-deficient bituminous pelite/tuffite cycles cover upper/lower shore face environments of the Sandbian and Katian. The mineral deficit (feldspar, unstable heavy minerals) relates to acid sturz-rain events during volcanic degassing (SO2, HCl, HF, NOx) sourced in an Infracambrian/Cambrian Large Igneous Province (LIP) around S Sinai/Wadi Araba Rift-Zone. The change of sedimentary architectural elements/lithofacies types during the Upper Darriwilian took place after an L-chondrite of the Main Asteroid Belt (MAB) crossed the Earth’s orbit (~470 Ma), which resulted in some small meteorite craters (i.e., Lockne). Through the Sandbian and Katian, this insignificant impact series was accompanied by massive tephra production during worldwide explosive subduction-related volcanic arc magmatism. During the Upper Ordovician High Stand-System Tract (HST), the glass-bearing tephras were transformed under marine conditions into montmorillonite (K-bentonite), contributing to green tuffitic pelite interbedded with storm-generated arkosic clastics. Transtensional tectonics (pull-apart type) caused the main Ordovician-Silurian unconformity (“paleovalleys”) in SE Jordan and Saudi Arabia. Their sedimentary fills expose arkosic FUCs originated by shallow-water turbidites during the Hirnantian. The intensive explosive volcanism generated almost continuously negative climate forcing (“cosmic winter”) by tephra, aerosols, smog, and clouding that led to regional glaciation in the S Hemisphere. The abrupt 87Sr/86Sr-ratio decrease accompanies, at the Sandbian base, the onset of magmatism, while δ13C excursions follow a Transgressive System Tract (TST) and three T-maxima indicating increasing phytoplankton growth. The undulation—0% mirrors a cyclicity of volcanic events, climate forcing, Eh, and pH conditions. The δ18O rise shows a continuous CO2 assimilation until its stop (~1200 ppm CO2) and the following formation of black-shale facies.

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Millennial-scale changes in marine lithofacies during the Paleocene-Eocene Thermal Maximum: a deep-time analog for Anthropocene hydrologic and acidification impacts

Published 30 March 2026 Science Closed
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Highlights

  • Global marine sediment changes during the PETM were quantitatively reconstructed.
  • Sediment changes controlled by sea level and latitudinal hydrology.
  • Acidification influenced pelagic sediment composition, especially in the Atlantic.
  • Carbonate “overshoot” occurred during the PETM recovery.

Abstract

Extreme climatic events can significantly alter marine lithofacies. However, global oceanic sediment patterns during deep-time hyperthermal events, which are potential analogues for the hydrologic and climatic impacts of modern anthropogenic warming, remain poorly constrained. Here, we compile 162 marine stratigraphic records to track millennial-scale sediment dynamics during the Paleocene–Eocene Thermal Maximum (PETM). We find that sedimentation was primarily controlled by hydrologic intensification (resulting in ∼36% carbonate platform demise), eustatic fluctuations (resulting in ∼52% siliciclastic shelf retrogradation), and ocean acidification (resulting in ∼41% deep-sea calcareous sediment replacement). Lithofacies changes along continental margins show distinct latitudinal zonation, reflecting variations in hydrologic intensity and carbonate productivity. The impact of eustatic sea-level change is strongest in region where hydrologic effects are muted. Deep-sea acidification was widespread, with the strongest expression in the Atlantic, and weaker effects in the Pacific and Indian oceans. Widespread carbonate “overshoot” following PETM recovery suggests enhanced continental weathering. This study implies that ongoing anthropogenic warming could rapidly reorganize marine sedimentation through intensified hydrological cycle, accelerated sea-level rise, and ocean acidification on centennial timescales, much faster than during the PETM and potentially with greater magnitude.

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Individual foraminiferal analysis: a promising tool for high-resolution temperature and pH reconstruction

Published 27 March 2026 Science Closed
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Compared with traditional bulk foraminiferal analysis methods, in situ analysis of individual foraminiferal tests (individual foraminiferal analysis or IFA) offers several advantages over traditional bulk methods, including enhanced temporal resolution where fossiliferous sample material is limited as well as potentially resolving seasonal-scale climate variability in deep time. Despite these advantages, applications of element-to‑calcium (El/Ca) ratios and δ11B in benthic foraminifera using IFA remain limited, and the biogeochemical drivers of intra-test and inter-test geochemical variability are poorly constrained. In this study, we systematically evaluate El/Ca ratios and δ11B in individual benthic foraminifera. By analysing Holocene epifaunal benthic foraminiferal species Cibicidoides wuellerstorfi from a deep ocean core site (ODP Site 999), we conclude that intra- and inter-test variabilities are regulated by ontogenetic effects resulting in inter-test variabilities of ±0.14 mmol/mol Mg/Ca, ± 14 μmol/mol B/Ca, and ± 0.18 ‰ δ11B. Application of the IFA method to epifaunal benthic foraminifera species Cibicides lobatulus from a box core in the English Channel, UK reveals ~0.1 pH units acidification and ~ 1 °C warming since the mid-19th century. By demonstrating that individual-level variability in reconstructed temperature and pH tracks seasonal trends in the available contemporaneous water-column instrumental measurements at the same site, we provide a ground-truthing to our multi-proxy IFA methodology, and also demonstrate the potential for benthic IFA to provide seasonal-scale reconstructions of ocean climate over hundreds to millions of years.

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Seawater pH fluctuations during the Ordovician to Silurian transition: insights from δ11B records in carbonates

Published 26 February 2026 Science Closed
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Highlights

  • A positive δ11Bcarb excursion has been observed during the Hirnantian coinciding with Gondwana glaciation.
  • Seawater pH fluctuations during the OST are caused by declining atmospheric pCO₂, sea level fall and carbonate weathering.
  • The fluctuation of seawater pH exerted a crucial role in the climatic changes and biotic evolutions during the OST.

Abstract

Environmental changes during the Ordovician to Silurian transition (OST) and the cause of Late Ordovician Mass Extinctions (LOMEs) remain a subject of debate. This study presents the first continuous seawater pH record spanning the Late Ordovician and Early Silurian, based on carbonate boron isotope (δ11Bcarb) data obtained from a carbonate-dominated section in South China. Our results reveal predominantly stable δ11Bcarb values throughout the Late Ordovician and Early Silurian, punctuated by a positive δ11Bcarb excursion during the Hirnantian coinciding with Gondwana glaciation. The calculated seawater pH pattern indicates a generally low pH baseline across the OST, temporarily interrupted by a transient increase in surface ocean pH coinciding with the glacial episode. These pH fluctuations are interpreted to result from a combination of factors, including declining atmospheric pCO₂ levels, sea level changes, weathering of carbonate rocks, and decomposition of organic matter. This study suggests that the fluctuation of seawater pH exerted a crucial role in the climatic changes and biotic evolution during the OST. The enhanced carbonate weathering and increased seawater pH, together with sea level fall and a reduction in shelf area, likely contributed to the decreased net accumulation of carbonates and represented a negative feedback for the development of glaciation and cooling climate. Given that the living of organisms (e.g. brachiopod, conodont, sponge and radiolarian) was sensitive to the changes in seawater pH, if and how the seawater pH fluctuations affected the LOMEs still needs more detailed work in the future.

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Y/Ho ratios in marine sediments unveil Neoproterozoic ocean acidification

Published 28 January 2026 Science Closed
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Understanding Precambrian seawater pH is critical for unraveling Earth’s early marine environments and biospheric evolution. Yet, quantitative constraints remain elusive due to the lack of robust proxies. Here, we demonstrate that yttrium/holmium (Y/Ho) fractionation during adsorption onto marine sediments serves as a novel and reliable pH proxy. Experimental results reveal that Y/Ho fractionation in ferruginous sediments follows a pH-dependent power-law relationship, while in argillaceous sediments, it is jointly controlled by pH and salinity at low salinities (< 29‰) but stabilizes (KdY/Ho ≈ 0.4) at higher salinities (≥ 29‰). Temperature exerts a negligible influence, ensuring broad applicability across geological timescales. Leveraging these relationships, we develop a quantitative method to reconstruct paleo-seawater pH using Y/Ho ratios from coexisting ferruginous and argillaceous sediments. Validation against modern and Phanerozoic records confirms the proxy’s accuracy (e.g., pH 8.21 ± 0.22 for modern Pacific sediments). Application to Neoproterozoic meta-pelites and iron formations reveals prolonged oceanic acidification (pH 5.9–6.4), deviating from previous model-based neutral-to-alkaline estimates. This acidic state, likely sustained by CO2 outgassing from carbonatite-alkaline volcanism during Rodinia’s breakup, challenges conventional views of Precambrian ocean chemistry. Our findings provide a transformative tool for probing early Earth’s environmental dynamics and highlight the interplay between tectonics, magmatism, and marine pH evolution.

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Ecological stability of late Maastrichtian benthic foraminifera amidst Deccan volcanism

Published 29 December 2025 Science Closed
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Highlights

  • Benthic foraminifera assemblage at Bidart reveal a stable, mesotrophic late Maastrichtian seafloor.
  • K/Pg boundary at Bidart shows signs of ecological stress and taphonomic dissolution.
  • Deccan-induced calcification stress was restricted to surface ocean and had minimal impact on benthic foraminifera.
  • Robust test ratio and fragmentation index together serve as effective taphonomic proxies.

Abstract

The late Maastrichtian witnessed profound disruptions in biogeochemical cycles, leading to the fifth mass extinction at the Cretaceous–Paleogene (K/Pg) boundary. At Bidart section (France), the final ∼60 kyr of the Maastrichtian coincide with mercury (Hg) peaks, low magnetic susceptibility, evidence of biological stress and taphonomic alteration in planktic foraminifera, indicative of an ocean acidification event. While this event primarily appears to be a surface-ocean phenomenon, previous studies also documented a minor rise in benthic foraminiferal test fragmentation beginning 0.5 m below the K/Pg boundary, with a pronounced spike at the boundary itself.

A detailed investigation of benthic foraminifera in biozone CF1 at Bidart section (France) reveals a diverse and balanced assemblage preceding the K/Pg boundary, with minimal taphonomic alterations. At the K/Pg boundary, infaunal populations diminished, diversity declined sharply, test fragmentation intensified, yet paradoxically, the absolute abundance of genera rose markedly. Preferential preservation is evident in the dominance of robust taxa (Cibicidoides spp., Coryphostoma spp.), while a high fragmentation index reflects strong taphonomic dissolution and time-averaging. A plausible explanation for this could be CO2-rich waters mixing into the ocean interior over 100–1,000 years, driving dissolution during the ∼10,000-year deposition of the K/Pg boundary red clay. The stark contrast between the planktic and benthic census and morphometric data at Bidart section clearly constrains any Deccan-related calcification stress to the surface mixed layer. Lastly, the integrated planktic and benthic considerations re-emphasize a need to carefully separate taphonomic signals from true ecological stress.

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Exploring structural integrity of coralline algae in response to the environmental changes associated with the PETM: a tale of functional resistance

Published 11 December 2025 Science Closed
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Coralline algae are key benthic components of shallow-marine ecosystems globally and as habitat-formers they support high biodiversity levels. Experiments on living coralline algae show internal growth changes in response to warming and higher CO2. These growth changes are leading to weakened structural integrity and increased breakage impacting their ecological function of habitat formation. Short-term experiments, though, raise questions about long term acclimation over multiple generations. Coralline algae have an extensive fossil record across the Cenozoic. Analysing growth changes within the geological record, specifically across hyperthermals, geologically abrupt environmental changes in the Earth’s history characterized by rapid ocean warming, acidification and sea level rise, can complement modern experiments. This allows us to quantify the vulnerability and response of habitat formers, such as coralline algae, to long-term environmental change. We evaluated cellular structure and structural integrity in species of the genera Sporolithon and Lithothamnion from Meghalaya, NE India (Eastern Tethys) before and during the Paleocene-Eocene Thermal Maximum, PETM (~55.8 Ma), the most pronounced hyperthermal of the Cenozoic. Cellular structural changes were not uniform between species, some species showed increased stress and strain due to larger cell sizes during the PETM, while other species revealed negligible changes in cell sizes. Unexpectedly, stresses and strains experienced by these Palaeogene taxa are comparable to contemporary species of the study genera. These findings suggest a resilience to long term warming and lower pH conditions resulting in a resistance to breakage. However, species differences in environmental change responses potentially highlight variations in phenotypic plasticity.

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Carbon-rich waters are becoming even more acidic as atmospheric CO2 levels rise

Published 20 November 2025 Press releases Closed
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The waters bordering North America could soon be inhospitable to critical marine creatures if the Northeastern Pacific Ocean continues to acidify at the current rate, a new study shows.

Earth’s oceans have become approximately 30% more acidic since the industrial revolution began more than 200 years ago. Acidification changes marine chemistry and depletes key minerals that calcifying organisms, such as corals and clams, need to build their skeletons and shells. The Northeastern Pacific is naturally more acidic than other oceans, fueling debate about how much its chemistry will change in the coming decades.

The study, published Nov. 13 in Nature Communications, shows that high baseline acidity makes the water more sensitive to additional carbon dioxide from human activities. Analyses of coral skeletons from the past century revealed that CO2 has been accumulating in North American waters faster than in the atmosphere, driving rapid acidification.

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“The findings implicate not only marine ecosystems, but all of the people who depend on them as well,” added lead author Mary Margaret Stoll, a UW doctoral student of oceanography.

The ocean becomes more acidified when carbon dioxide dissolves to form an acid that releases hydrogen and bicarbonate ions, lowering the water’s pH level. In North America, a powerful current system — the California Current — transports cool water south along the coast. The combination of current flow and wind creates optimal conditions for upwelling, a process that cycles deep water to the surface.

Organic matter — dead plants and animals — sinks to the bottom of the ocean, where it decomposes and releases carbon dioxide back into the water. Upwelling surfaces this CO2 rich water, increasing the acidity of subsurface and surface zones. These natural fluctuations complicate researchers’ efforts to predict how much acidification will occur from human activities.

This study helps resolve these questions with records kept by centuries old corals.

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Deep Pacific carbonate chemistry since the Last Glacial Maximum

Published 19 November 2025 Science Closed
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Quantitative constraints on deep ocean carbonate chemistry are critical for understanding the processes responsible for glacial-interglacial changes in atmospheric pCO2 and the ocean feedbacks that amplify carbon cycle change. Here, we present a new, high-resolution, B/Ca-based record of carbonate ion concentration (Δ[CO32−]) from central equatorial Pacific site ML1208-16BB spanning the last 35 kyr. This site, bathed by Pacific Deep Water, reveals a ∼24 ± 7 μmol/kg rise in deep ocean [CO32−] between ∼20 and 10 kyr, a larger change than previously reconstructed from sites in the western equatorial Pacific and those in the central equatorial Pacific bathed by Lower Circumpolar Deep Water. Our new reconstruction permits estimation of deep Pacific calcite saturation state (Ω), quantifying the degree of deep water undersaturation during the Last Glacial Maximum and implying a critical role for sedimentary porewater saturation state in resolving the Pacific carbonate preservation paradox. Finally, we pair our Δ[CO32−] reconstruction with previously-published benthic δ13C to present a process-oriented understanding of late glacial, deglacial, and Holocene deep Pacific carbonate chemistry changes. Our data suggest a larger role for glacial and deglacial alkalinity changes than previously suggested by records from the equatorial Pacific Ocean.

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A century of change in the California Current: upwelling system amplifies acidification

Published 19 November 2025 Science Closed
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Predicting the pace of acidification in the California Current System (CCS), a productive upwelling system that borders the west coast of North America, is complex because the anthropogenic contribution is intertwined with other natural sources. A central question is whether acidification in the CCS will follow the pace of increasing atmospheric CO2, or if climate effects and other biogeochemical processes will either amplify or attenuate acidification. Here, we apply the boron isotope pH proxy to cold-water orange cup corals to establish a historic level of acidification in the CCS and the Salish Sea, an associated marginal sea. Through a combination of complementary modeling and geochemical approaches, we show that the CCS and Salish Sea have experienced amplified acidification over the industrial era, driven by the interaction between anthropogenic CO2 and a thermodynamic buffering effect. From this foundation, we project future acidification in the CCS under elevated CO2 emissions. The projected change in pCO2 over the 21st century will continue to outpace atmospheric CO2, posing challenges to marine ecosystems of biological, cultural, and economic importance.

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Insights from a changing ocean: evolving biogeochemistry and its impacts on marine ecosystems and climate

Published 13 October 2025 Science Closed
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Marine biogeochemistry integrates chemical, biological, geological, and physical processes that are fundamental to Earth’s climate and ecosystems. As elements cycle through the ocean, atmosphere, and biosphere, they leave behind biogeochemical fingerprints that serve as proxies to track environmental change. Over the industrial era, anthropogenic CO2 emissions and other human activities have caused the oceans to change rapidly, perturbing this biogeochemical landscape. Characterizing biogeochemical shifts is critical to advance our understanding of climate-driven impacts, assess marine ecosystem health, and evaluate climate solutions. Recent advancements in biogeochemical tools and technologies have deepened our insights into oceanic change. The development of high-precision paleoproxies has extended records of ocean conditions into the pre-industrial era, while the Argo float array has enabled four-dimensional monitoring of biogeochemistry globally. High-resolution numerical modeling has also improved our ability to capture complex interactions at fine spatial and temporal scales, offering a holistic framework to understand anthropogenic impacts from past to future. Together, these technologies provide a comprehensive toolkit to characterize shifts in ocean biogeochemistry in unprecedented detail and advance our understanding of global environmental change. This thesis weaves together applications of novel biogeochemical tools to examine the drivers, impacts, and mitigation strategies of a rapidly changing ocean. Each chapter leverages diverse datasets and multiple tools to provide new insights on ocean change based on marine biogeochemistry. In Chapter 2, I combine boron-isotope measurements from cold-water corals with a biogeochemical model to reconstruct and investigate subsurface acidification trends over the industrial era in the California Current System. In Chapter 3, I combine Argo-based biogeochemical data products, archival tagging records, and machine learning methods to develop a four-dimensional species distribution model for an economically important fishery species, revealing biogeochemical constraints on its migration. In Chapter 4, I employ a high-resolution biogeochemical model of the Salish Sea to evaluate the detectability of ocean alkalinity enhancement, a marine carbon dioxide removal strategy for climate mitigation. These studies provide new frameworks and tools to investigate, monitor, and respond to a changing ocean.

Continue reading ‘Insights from a changing ocean: evolving biogeochemistry and its impacts on marine ecosystems and climate’

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