Turf and surf

The recent publication of the summary for policy makers by Working Group I of the Intergovernmental Panel on Climate Change (IPCC) [1] has injected a renewed sense of urgency to address climate change. It is therefore timely to review the notion of preventing 'dangerous anthropogenic interference with the climate system' as put forward in the United Nations Framework Convention on Climate Change (UNFCCC). The article by Danny Harvey in this issue [2] offers a fresh perspective by rephrasing the concept of 'dangerous interference' as a problem of risk assessment. As Harvey points out, identification of 'dangerous interference' does not require us to know with certainty that future climate change will be dangerous—an impossible task given that our knowledge about future climate change includes uncertainty. Rather, it requires the assertion that interference would lead to a significant probability of dangerous climate change beyond some risk tolerance, and therefore would pose an unacceptable risk.

The Paleocene–Eocene transition at Mead Stream, New Zealand: a southern Pacific record of early Cenozoic global change

Interpreting the impact of climate change on vertebrates in the fossil record can be complicated by the effects of potential biotic drivers on morphological patterns observed in taxa. One promising area where this impact can be assessed is a high-resolution terrestrial record from the Bighorn Basin, Wyoming, that corresponds to the Paleocene–Eocene thermal maximum (PETM), a geologically rapid (~170 kyr) interval of sustained temperature and aridity shifts about 56 Ma. The PETM has been extensively studied, but different lines of research have not yet been brought together to compare the timing of shifts in abiotic drivers that include temperature and aridity proxies and those of biotic drivers, measured through changes in floral and faunal assemblages, to the timing of morphological change within mammalian species lineages. We used a suite of morphometric tools to document morphological changes in molar crown morphology of three lineages of stem erinaceid eulipotyphlans. We then compared the timing of morphological change to that of both abiotic and other biotic records through the PETM. In all three species lineages, we failed to recover any significant changes in tooth crown shape or size within the PETM. These results contrast with those documented previously for lineages of medium-sized mammals, which show significant dwarfing within the PETM. Our results suggest that biotic drivers such as shifts in community composition may have also played an important role in shaping species-level patterns during this dynamic interval in Earth history.

The Paleocene-Eocene Thermal Maximum (PETM; ∼55.9 Ma) was a hyperthermal event associated with large carbon cycle perturbations, sustained global warming, and marine and terrestrial environmental changes. One possible trigger and/or source of the carbon release that initiated the PETM is the emplacement of the North Atlantic Igneous Province (NAIP). This study focuses on an expanded section of marine clays and diatomite on Fur Island in northern Denmark, where the entire PETM sequence has been identified by a negative ∼4.5‰ δ13CTOC excursion. This remarkably well-preserved section also contains >180 interbedded ash layers sourced from the NAIP, making it an ideal site for investigating the correlations between large-scale volcanism and environmental changes. This study provides a new and complete high-resolution TEX86-derived sea-surface temperature (SST) reconstruction over the entire PETM and the post-PETM section (up to about 54.6 Ma). The palaeothermometry record indicates an apparent short-lived cooling episode in the late Paleocene, followed by a pronounced temperature response to the PETM carbon cycle perturbations with a ∼10°C SST increase during the PETM onset (up to ∼33°C). Extreme SSTs fall shortly after the PETM onset, and continue to decrease during the PETM body and recovery, down to anomalously cool SSTs post-PETM (∼11–23°C). Both phases of potential cooling coincide with proxies of active NAIP volcanism, suggesting a causal connection, although several overprinting non-thermal factors complicate interpretations of the TEX86 values. Indices of effusive and explosive NAIP volcanism are largely absent from the Danish stratigraphy during the PETM body, though a re-emergence toward the end of the PETM suggest NAIP volcanism might have played a role in the PETM termination in the North Sea. This new SST record completes the previous fragmented view of climate changes at this globally important PETM site, and indicates large temperature variations in the North Sea during the earliest Eocene that are possibly linked to NAIP volcanism.

Coastal response to global warming during the Paleocene-Eocene Thermal Maximum

Seismic geomorphology and stratigraphic analysis can reveal how source-to-sink systems dynamically respond to climatic and tectonic forcing. This study uses seismic reflection data from the Norwegian Sea to investigate the stratigraphic response to a short-lived (0.2 Myr) period of climate change during the Paleocene-Eocene Thermal Maximum (PETM), superimposed on a long-lived (∼8 Myr) period of hinterland uplift. The data show that long-term uplift resulted in ∼300 m of relative sea-level fall, forced regression and formation of incised valleys during the latest Paleocene-earliest Eocene. The short-lived PETM climate perturbation at ∼56 Ma changed the transport dynamics of the system, allowing sediment to be bypassed to wide channel complexes on the basin floor, feeding a large mud-rich basin-floor fan more than 50 km into the basin. Our analysis also suggest that sediment supply was up to four times higher during the PETM compared to earlier and later periods. Maximum regression at ∼55.5 Ma resulted in the formation of a subaerial unconformity. The style of subaerial incision was dictated by shelf accommodation and proximity to the area of direct sediment input. Out-of-grade shelves and slopes sourced by littoral drift were prone to incision, but direct-fed and graded shelves and slopes were not. Despite maximum regression, sediments were not transported significantly beyond the toe-of-slope aprons, suggesting that rapid climate change was more efficient in bypassing sediment to the deep-water than low stands of sea level. As long-term accommodation increased after the PETM, deltas were still able to reach shelf edge, but periods of maximum regression were not associated with deep incisions along the outer shelf and only smaller canyons and gullies formed. The shelf-slope wedge was finally transgressed at ∼51 Ma. The age of deep valley incisions overlaps with the time of subaerial erosion in the East Shetland and Faroe-Shetland basins, suggesting a common mechanism for North Atlantic uplift around 55–56 Ma. Other seismic stratigraphic surfaces do not seem to be regionally time-equivalent, highlighting the importance of local controls on internal architecture of shelf-slope wedges. This study demonstrates the high-resolution stratigraphic response to long- and short-term external forcing together with intrinsic processes and can help identify similar relationships in other areas.

Beyond methane: Towards a theory for the Paleocene–Eocene Thermal Maximum

Rock magnetic properties can be useful determining paleonvironmental changes. A dramatic climate change as occurred in the PETM modified the environment and hence the magnetic properties recorded in the sediments. New paleomagnetic data from the marine record of the PETM in the Southern Pyrenean Zone shows the variation on the magnetic parameters in four different sections. The magnetic signal reveals a positive excursion of magnetic values starting before the onset of the marly interval of La Faja de las Flores Mb (beginning of the PETM record, Ilerdian) in the Carriata section with a maximum value in the marly interval. A similar magnetic signal is observed in Bujaruelo section (~10 km south of Carriata at PETM times) directly related to the marly interval of Faja de las Flores Mb. However more to the south, the PETM interval does not appear in the sedimentary record, therefore in the southern Gallisue section no magnetic excursion occurs, and in the southernmost studied Entremon section a magnetic positive excursion occurs in a thin marly interval unrelated to the PETM, and in two lower intervals of the column. All sections were subjected to later deformation during the pyrenean orogeny and the three northernmost are in the regional cleavage front where pressure-solution and remagnetizations have been described. A postfolding remagnetization component is found in the three northern sections.

The Initial Eocene Thermal Maximum (IETM) at c . 55 Ma represents a period of rapid global warming that lasted less than 200 ka. The response of vegetation to such an event, and particularly warm-adapted highly diverse vegetation types, is poorly understood. Using pollen floral, clay mineral and stable carbon isotope analyses of sediments from the upper Tuscahoma Formation on the eastern US Gulf Coast (eastern Mississippi and western Alabama), we document paratropical floral changes across the Palaeocene–Eocene boundary from the Wahalak #2 and lower Harrell cores. Data indicate strong changes in the abundance of kaolinite that correlate with changes in relative abundance of native pollen taxa. There is no evidence for a transient, extra-tropical flora on the US Gulf Coast that may characterize the IETM. Immigration and extinction are not associated with this event. Instead, Early Eocene plant immigration occurs in pulses and therefore is not associated directly with climate change during the IETM. The two cores share the same regional species pool but compositional differences are stronger between cores than they are either through changes in environment, increased soil erosion or chemical weathering, or through the introduction of non-native plants. Our data suggest that vegetation change across the Palaeocene–Eocene boundary is not a single event but rather a sequence of cascading events.

ABSTRACTThe rate of coral reef degradation from climate change is accelerating and, as a consequence, a number of interventions to increase coral resilience and accelerate recovery are under consideration. Acropora spathulata coral colonies that survived mass bleaching in 2016 and 2017 were sourced from a bleaching-impacted and warmer northern reef on the Great Barrier Reef (GBR). These individuals were reproductively crossed with colonies collected from a recently bleached but historically cooler central GBR reef to produce pure and crossbred offspring groups (warm–warm, warm–cool and cool–warm). We tested whether corals from the warmer reef produced more thermally tolerant hybrid and purebred offspring compared with crosses produced with colonies sourced from the cooler reef and whether different symbiont taxa affect heat tolerance. Juveniles were infected with Symbiodinium tridacnidorum, Cladocopium goreaui and Durusdinium trenchii and survival, bleaching and growth were assessed at 27.5°C and 31°C. The contribution of host genetic background and symbiont identity varied across fitness traits. Offspring with either both or one parent from the northern population exhibited a 13- to 26-fold increase in survival odds relative to all other treatments where survival probability was significantly influenced by familial cross identity at 31°C but not 27.5°C (Kaplan–Meier P=0.001 versus 0.2). If in symbiosis with D. trenchii, a warm sire and cool dam provided the best odds of juvenile survival. Bleaching was predominantly driven by Symbiodiniaceae treatment, where juveniles hosting D. trenchii bleached significantly less than the other treatments at 31°C. The greatest overall fold-benefits in growth and survival at 31°C occurred in having at least one warm dam and in symbiosis with D. trenchii. Juveniles associated with D. trenchii grew the most at 31°C, but at 27.5°C, growth was fastest in juveniles associated with C. goreaui. In conclusion, selective breeding with warmer GBR corals in combination with algal symbiont manipulation can assist in increasing thermal tolerance on cooler but warming reefs. Such interventions have the potential to improve coral fitness in warming oceans.This article has an associated First Person interview with the first author of the paper.

An Integrated Risk Assessment for Climate Change (IRACC) is developed and applied to assess the vulnerability of sharks and rays on Australia's Great Barrier Reef (GBR) to climate change. The IRACC merges a traditional climate change vulnerability framework with approaches from fisheries ecological risk assessments. This semi‐quantitative assessment accommodates uncertainty and can be applied at different spatial and temporal scales to identify exposure factors, at‐risk species and their key biological and ecological attributes, critical habitats a`nd ecological processes, and major knowledge gaps. Consequently, the IRACC can provide a foundation upon which to develop climate change response strategies. Here, we describe the assessment process, demonstrate its application to GBR shark and ray species, and explore the issues affecting their vulnerability to climate change. The assessment indicates that for the GBR, freshwater/estuarine and reef associated sharks and rays are most vulnerable to climate change, and that vulnerability is driven by case‐specific interactions of multiple factors and species attributes. Changes in temperature, freshwater input and ocean circulation will have the most widespread effects on these species. Although relatively few GBR sharks and rays were assessed as highly vulnerable, their vulnerability increases when synergies with other factors are considered. This is especially true for freshwater/estuarine and coastal/inshore sharks and rays. Reducing the impacts of climate change on the GBR's sharks and rays requires a range of approaches including mitigating climate change and addressing habitat degradation and sustainability issues. Species‐specific conservation actions may be required for higher risk species (e.g. the freshwater whipray, porcupine ray, speartooth shark and sawfishes) including reducing mortality, preserving coastal catchments and estuarine habitats, and addressing fisheries sustainability. The assessment identified many knowledge gaps concerning GBR habitats and processes, and highlights the need for improved understanding of the biology and ecology of the sharks and rays of the GBR.

As guest editors for the 2023 Edition of Frontiers in Earth Science featuring the article collection titled "Curbing Carbon Emissions: Insight from the Ecosystem Evolution During Ancient Hyperthermal Events," we express our immense satisfaction with the caliber of contributions from international experts. We extend our gratitude for their valuable insights into this research theme. The collection encompasses comprehensive reports on deep-time extreme hydrothermal events, notably the Early Triassic Extreme Heat Event and the Paleocene-Eocene Thermal Maximum. These contributions significantly enhance our comprehension of the repercussions of hydrothermal events on marine productivity, the marine ecosystem, and lacustrine environments. Beyond the scientific discourse on hydrothermal events, the collection includes research articles focusing on technology designed to mitigate carbon emissions while ensuring sustainable energy supply.Woods et al. delve into the well-documented hydrothermal event at the Permian-Triassic boundary, revealing a rapid 5 ℃ increase in surface seawater temperature within 0.5 million years (Sun et al., 2012). Their study of the Ursula Creek deepwater section in western British Columbia analyzes productivity and redox conditions. Findings indicate that the Early Triassic witnessed anoxic conditions and subdued productivity due to ocean stagnation or weak circulations during the greenhouse period. This regime was overturned by reestablishing coastal upwelling until a cooling event at the end of the Early Triassic. The persistent anoxia significantly impacted the marine ecosystem, delaying recovery from the end-Permian mass extinction. Traditional concepts are challenged by recent findings of Dai et al. (2023), which suggest a faster recovery in overarching anoxic conditions.Li et al. contributed to the reconstruction of the Eocene to Miocene palaeoclimate of the Qaidam Basin by the collection of carbon and oxygen isotopes. Utilizing geochemical data extracted from lacustrine carbonate, they identified three aridity events at 40-32 Ma, 22-20 Ma, and 13 Ma. These events, closely tied to variations in carbon and oxygen isotope composition, are attributed to the regression of the Paratethys Sea, Tibetan Plateau uplift, global cooling, and tectonic events. This case study sheds light on climate changes in a lacustrine lake following the Paleocene-Eocene Thermal Maximum, coupled with a subsequent continuous cooling event.Addressing the contemporary challenge of balancing carbon emissions and energy security, understanding the geochemical characteristics of this deep natural gas would contribute valuable knowledge for the energy sector, offering a potential solution in the pursuit of cleaner energy during the ongoing energy transition. Studies on natural gas preserved in diverse geological formations, such as marine gypsum-salt strata, terrestrial shales, and marine-terrestrial transitional shales, are presented in this special issue. Shi et al. explore deep natural gas trapped in Ordovician gypsum-salt strata in China's Ordos Basin. The study identifies the gas hydrocarbon-dominated source with minor non-hydrocarbon contributions. Crucially, sub-salt natural gas is concentrated in moderately mature cracks, holding promising reserves. The research provides insights into the Ordovician subsalt natural gas genesis and its potential as a significant energy resource. Wang et al. focus on the Upper Triassic Xujiahe Formation in the Sichuan Basin, China, examining its terrestrial shales. The study reveals significant thickness, high maturity, and substantial gas generation potential. This exploration of source rocks sheds light on the promising shale gas reserves in the Sichuan Basin. The findings underscore the importance of understanding the geochemical characteristics of source rocks in diverse geological formations, contributing to the broader discussion on reliable energy sources amid the ongoing global transition. Chen et al. investigate the geochemical and gas-bearing characteristics of the Late Permian Longtan Formation in southern Sichuan, China. The study reveals the dominance of vitrinite in organic matter, exhibiting high maturity and gas generation potential. The findings underscore the promising reserves of shale gas in the marine-continental transitional shales of the Longtan Formation. Understanding the geochemical properties of these shales contributes to the assessment of reliable energy sources during the ongoing energy transition. The research emphasizes the significance of shale gas exploration in diverse geological formations for sustainable energy solutions.Highlighting the pivotal role of technology in shale gas exploration and development, Jiao et al. introduce a quantitative method for characterizing microcrack networks, crucial reservoirs for shale gas. Their findings emphasize the substantial impact of microcrack degree on reservoir quality, highlighting the correlation between a high degree of microcracks and initial productions.In the broader context of the current global challenges, notably the sixth mass extinction linked to greenhouse warming and anthropogenic activities, this special issue aims to stimulate interest in global warming and energy transition. By doing so, we aspire to deepen our understanding of the driving forces behind the sixth mass extinction and foster informed responses to mitigate its impact. We anticipate that this collection will catalyze further exploration and dialogue in these critical areas.

Climate change is predicted to alter temperature, carbonate chemistry and oxygen availability in the oceans, which will affect individuals, populations and ecosystems. We use the fossil record of benthic foraminifers to assess developmental impacts in response to environmental changes during the Palaeocene–Eocene Thermal Maximum (PETM). Using an unprecedented number of µ-computed tomography scans, we determine the size of the proloculus (first chamber), the number of chambers and the final size of two benthic foraminiferal species which survived the extinction at sites 690 (Atlantic sector, Southern Ocean, palaeodepth 1900 m), 1210 (central equatorial Pacific, palaeodepth 2100 m) and 1135 (Indian Ocean sector, Southern Ocean, palaeodepth 600–1000 m). The population at the shallowest site, 1135, does not show a clear response to the PETM, whereas those at the other sites record reductions in diameter or proloculus size. Temperature was similar at all sites, thus it is not likely to be the reason for differences between sites. At site 1210, small size coincided with higher chamber numbers during the peak event, and may have been caused by a combination of low carbonate ion concentrations and low food supply. Dwarfing at site 690 occurred at lower chamber numbers, and may have been caused by decreasing carbonate saturation at sufficient food levels to reproduce. Proloculus size varied strongly between sites and through time, suggesting a large influence of environment on both microspheric and megalospheric forms without clear bimodality. The effect of the environmental changes during the PETM was more pronounced at deeper sites, possibly implicating carbonate saturation.This article is part of a discussion meeting issue ‘Hyperthermals: rapid and extreme global warming in our geological past’.

Providing empirical evidence about the response of tropical shallow-water organisms to past warming and hyperthermal events is particularly important considering that they are severely threatened by current global warming. Stratigraphic resolution in shallow-water sections cannot be as precise as in pelagic environments and the empirical evidence is usually limited to a “before-and-after” comparison to assess the biological effects of events.During the early Paleogene, the Neothetyan circum-Mediterranean region was the global center of reef coral diversity. Our compilation of Paleocene to Eocene reef coral occurrences allows for an analysis of reef coral responses to the major climatic changes of this time interval in unprecedented temporal detail, including the Paleocene-Eocene Thermal Maximum (PETM), when global mean temperatures reached more than 5°C above pre-industrial levels.Reef corals were negatively affected by the PETM as we document a small decrease in diversity at both species and genus level and an increase of extinction rate across the hyperthermal event. During the onset of the Early Eocene Climate Optimum (EECO), diversity gradually increased as also documented by a peak of origination rate. The EECO diversity high is mainly related to the rich coral fauna recently described from NE Italy where the EECO and post-EECO phases are characterized by an accurate specimen-based systematic revision of museum collections associated to a detailed biostratigraphic calibration.The Late Eocene cooling was accompanied by an increase in diversity, with the origination of several Oligocene coral taxa and the extinction of Eocene ones. The Late Eocene is also the time when coral reefs started to flourish again after the crisis of Late Paleocene-Early Eocene. This study was funded by the Italian Ministry of Education and Research (MIUR), funds PRIN 2017: project “Biota resilience to global change: biomineralization of planktic and benthic calcifiers in the past, present and future” (prot. 2017RX9XXY).

Sediment routing systems (SRSs) are a critical element of the global response to ongoing climate change. However SRS response to climate forcing is complex, fragmentary, and obscured when viewed over short, human time scales (10(-1)-10(2) yr). Over long time scales (>10(2)-10(3) yr), the aggregated, system-wide response of SRSs to climate forcing can be gleaned with more confidence from the sedimentary record, but the nature and time scales of this aggregated response to abrupt climate change are still poorly understood. Here, we investigate the aggregated temporal response of a SRS in northern Spain to abrupt climate warming at the Paleocene-Eocene thermal maximum (PETM). Our results show that terrestrial sites in northern Spain record a temporal lag of 16.5 +/- 7.5 k.y. between the onset of the PETM, defined by an abrupt negative excursion in the delta C-13 profile, and the onset of coarse-grained deposition. Within the same SRS at a deep marine site 500 km to the west, we observe a temporal lag of 16.5 +/- 1.5 k.y. using an age model that is independent of that used for the terrestrial sites. These results suggest that the aggregated, system-wide response of SRSs to present-day global warming-if we take the PETM as an appropriate modern-day analogue-may persist for many millennia into the future.