Explore the vast range of titles available.

Mass loss from the Amundsen Sea sector of the West Antarctic Ice Sheet has increased in recent decades, suggestive of sustained ocean forcing or an ongoing, possibly unstable, response to a past climate anomaly. Lengthening satellite records appear to be incompatible with either process, however, revealing both periodic hiatuses in acceleration and intermittent episodes of thinning. Here we use ocean temperature, salinity, dissolved-oxygen and current measurements taken from 2000 to 2016 near the Dotson Ice Shelf to determine temporal changes in net basal melting. A decadal cycle dominates the ocean record, with melt changing by a factor of about four between cool and warm extremes via a nonlinear relationship with ocean temperature. A warm phase that peaked around 2009 coincided with ice-shelf thinning and retreat of the grounding line, which re-advanced during a post-2011 cool phase. These observations demonstrate how discontinuous ice retreat is linked with ocean variability, and that the strength and timing of decadal extremes is more influential than changes in the longer-term mean state. The nonlinear response of melting to temperature change heightens the sensitivity of Amundsen Sea ice shelves to such variability, possibly explaining the vulnerability of the ice sheet in that sector, where subsurface ocean temperatures are relatively high.

The lithostratigraphic characteristics of the iconic Blue Lias Formation of southern Britain are influenced by sedimentation rates and stratigraphic gaps. Evidence for regular sedimentary cycles is reassessed using logs of magnetic susceptibility from four sites as an inverse proxy for carbonate content. Standard spectral analysis, including allowing for false discovery rates, demonstrates several scales of regular cyclicity in depth. Bayesian probability spectra provide independent confirmation of at least one scale of regular cyclicity at all sites. The frequency ratios between the different scales of cyclicity are consistent with astronomical forcing of climate at the periods of the short eccentricity, obliquity and precession cycles. Using local tuned time scales, 62 ammonite biohorizons have minimum durations of 0.7 to 276 ka, with 94% of them <41 ka. The duration of the Hettangian Stage is ≥2.9 Ma according to data from the West Somerset and Devon/Dorset coasts individually, increasing to ≥3.7 Ma when combined with data from Glamorgan and Warwickshire. A composite time scale, constructed using the tuned time scales plus correlated biohorizon limits treated as time lines, allows for the integration of local stratigraphic gaps. This approach yields an improved duration for the Hettangian Stage of ≥4.1 Ma, a figure that is about twice that suggested in recent time scales.

Lower Jurassic marine basins across the northwest European epicontinental shelf were commonly marked by deposition of organic-rich black shales. Organic-carbon burial was particularly widespread during the Toarcian Oceanic Anoxic Event (T-OAE: also known as the Jenkyns Event) with its accompanying negative carbon-isotope excursion (nCIE). Lower Toarcian black shales in central and southern Germany are known as the Posidonia Shale Formation (Posidonienschiefer) and are thought to have formed during the T-OAE nCIE. Here, we present stratigraphic (carbon-isotope, Rock–Eval, calcareous nannofossil) data from the upper Pliensbachian and lower Toarcian strata from a core drilled on the northern flank of the Lower Saxony Basin, north–west Germany. The bio- and chemostratigraphic framework presented demonstrates that (i) the rock record of the T-OAE at the studied locality registered highly condensed sedimentation and/or multiple hiatuses and (ii) the deposition of organic-rich black shale extended significantly beyond the level of the T-OAE, thereby contrasting with well-studied sections of the Posidonia Shale in southern Germany but showing similarities with geographically nearby basins such as the Paris Basin (France). Prolonged and enhanced organic-carbon burial represents a negative feedback mechanism in the Earth system, with locally continued environmental perturbance accelerating the recovery of the global climate from T-OAE-associated hyperthermal conditions, whilst also accelerating a return to more positive δ 13 C values in global exogenic carbon pools. Graphical abstract

Stratigraphic hiatuses of variable time intervals within the Rhuddanian to early Aeronian (Llandovery, Silurian) are identified in the area bordering East Chongqing, West Hubei and Northwest Hunan in central China. Their distribution suggested the existence of a local uplift, traditionally named the Yichang Uplift. The diachronous nature of the basal black shale of the Lungmachi Formation crossing different belts of this Uplift signifies the various developing stages during the uplifting process. The present paper defines the temporal and spatial distribution pattern of the Yichang Uplift, which might be one of the important controlling factors for the preservation and distribution of the shale gas in this region, as it has been demonstrated that the shale gas exploration is generally less promising in the areas where more of the basal part of the Lungmachi Formation is missing. Therefore, better understanding of the circumjacent distribution pattern developed throughout the uplifting process may provide the important guidance for the shale gas exploration. The present work is a sister study to the published paper, “Stage-progressive distribution pattern of the Lungmachian black graplolitic shales from Guizhou to Chongqing, Central China”. These two studies thus provide a complete Ordovician-Silurian black shale distribution pattern in the Middle and Upper Yangtze, a region with the major shale gas fields in China.

In global warming experiments, the majority of global climate models warm faster in the eastern equatorial Pacific than in the west and produce a weakening of the Walker circulation. In contrast, GFDL-ESM2M is an exception that exhibits a La Niña–like mean-state warming with a strengthening of the Walker circulation. This study explores the cause of this exceptional response and proposes a new mechanism, the nonlinear ENSO warming suppression (NEWS), where the transient heating rate difference between the atmospheric and oceanic reservoirs annihilates extreme El Niños, causing a suppression of mean-state warming in the east. Heat budget analyses of GFDL-ESM2M robustly show that nonlinear dynamical heating, which is necessary for extremely warm El Niños, becomes negligible under warming. An idealized nonlinear recharge oscillator model suggests that, if the temperature difference between the atmospheric and oceanic reservoirs becomes larger than some threshold value, the upwelling becomes too efficient for El Niño–Southern Oscillation (ENSO) to retain its nonlinearity. Therefore, extreme El Niños dissipate but La Niñas remain almost unchanged, causing a La Niña–like mean-state warming. NEWS is consistent with observations and GFDL-ESM2M but not with the majority of state-of-the-art models, which lack realistic ENSO nonlinearity. NEWS and its opposite response to atmospheric cooling, the nonlinear ENSO cooling suppression (NECS), might contribute to the Pacific multidecadal natural variability and global warming hiatuses.

The boreal bivalve Arctica islandica is an important fishery in the United States (US), yet very little is known about the resiliency of this species to fishing activity due to limited understanding of localized population demographics. Demographics including age frequency, recruitment patterns, mortality rates, and sexual dimorphism were evaluated for a population sampled off Long Island (LI, 40.09658°N 73.01057°W) and compared with samples from Georges Bank (GB, 40.72767°N, 67.79850°W) collected in 2015 and 2017, where GB was described in a previous study. This study supports evidence that this species is sexually dimorphic. Earlier assumptions of prolonged lapses in recruitment were not substantiated for either the GB or LI populations; yearly cohorts were observed for the past century, and both populations presented recruitment pulses in approximately 8-y periods. Estimated ages from this study are older than previously reported for the US Mid-Atlantic with the oldest animal represented by a 310-year-old male collected from LI. Simulated total mortality was higher at GB than LI, and higher for GB females than GB males, with simulated mean longevity estimates greater at LI than GB. The population sex ratio at GB was 1:1.1 (female:male), whereas the LI ratio was 1:1.4 and relatively deficient in large females. Recruitment into the populations occurs routinely with substantial hiatuses being rare and substantive year classes occurring at least decadally with lesser, but contributing, recruitment in most years in between. Routine recruitment may insulate this species from risks posed by overfishing to an extent not typical for other long-lived species.

Using an energy budget approach to understanding decadal temperature trends, this study highlights that observational uncertainty exceeds energy–flux deviations that affect such trends. Thus the origin of recent warming slowdown is unidentifiable. During the first decade of the twenty-first century, the Earth’s surface warmed more slowly than climate models simulated 1 . This surface-warming hiatus is attributed by some studies to model errors in external forcing 2 , 3 , 4 , while others point to heat rearrangements in the ocean 5 , 6 , 7 , 8 , 9 , 10 caused by internal variability, the timing of which cannot be predicted by the models 1 . However, observational analyses disagree about which ocean region is responsible 11 , 12 , 13 , 14 , 15 , 16 . Here we show that the hiatus could also have been caused by internal variability in the top-of-atmosphere energy imbalance. Energy budgeting for the ocean surface layer over a 100-member historical ensemble reveals that hiatuses are caused by energy-flux deviations as small as 0.08 W m −2 , which can originate at the top of the atmosphere, in the ocean, or both. Budgeting with existing observations cannot constrain the origin of the recent hiatus, because the uncertainty in observations dwarfs the small flux deviations that could cause a hiatus. The sensitivity of these flux deviations to the observational dataset and to energy budget choices helps explain why previous studies conflict, and suggests that the origin of the recent hiatus may never be identified.

A new stratigraphic survey of the pyroclastic deposits blanketing Pompeii ruins shows departures from prior reconstruction of the events that occurred inside the town during the two main phases (pumice fallout and pyroclastic density currents) of the ad 79 Vesuvius eruption. We document the depth and distribution of subaerial erosion surfaces in the upper part of the pyroclastic sequence, formed during two short-lived breaks occurring in the course of the second phase of the eruption. These pauses could explain why 50% of the victims were found in the streets during the pyroclastic density currents phase.

The pace of climate change can have a direct impact on the efforts required to adapt. For short timescales, however, this pace can be masked by internal variability (IV). Over a few decades, this can cause climate change effects to exceed what would be expected from the greenhouse gas (GHG) emissions alone or, to the contrary, cause slowdowns or even hiatuses. This phenomenon is difficult to explore using ensembles such as CMIP5, which are composed of multiple climate models and thus combine both IV and inter-model differences. This study instead uses CanESM2-LE and CESM-LE, two state-of-the-art large ensembles (LE) that comprise multiple realizations from a single climate model and a single GHG emission scenario, to quantify the relationship between IV and climate change over the next decades in Canada and the USA. The mean annual temperature and the 3-day maximum and minimum temperatures are assessed. Results indicate that under the RCP8.5, temperatures within most of the individual large ensemble members will increase in a roughly linear manner between 2021 and 2060. However, members of the large ensembles in which a slowdown of warming is found during the 2021–2040 period are two to five times more likely to experience a period of very fast warming in the following decades. The opposite scenario, where the changes expected by 2050 would occur early because of IV, remains fairly uncommon for the mean annual temperature, but occurs in 5 to 15% of the large ensemble members for the temperature extremes.

Over the last century, the global mean surface air temperature (SAT) has experienced two periods of warming slowdown (hiatuses), namely 1940–1975 and 1998–2012, as well as showing well-defined interdecadal oscillations. Previous studies have focused mainly on the most recent hiatus, and little is known about the period between 1940 and 1975. From the point of view of the sea surface temperature (SST), there are two aspects of interest; i.e., the climatological SST and SST variability. In this paper, observational and modelling evidence is used to show that, compared with the climatological SST, SST variability has been the main cause of the slowdown in rate of increase in SAT since 1940. In addition, the observational data and simulation results show that SST variability had a greater impact on the slowdown in rate of increase in SAT from 1940 to 1975 (− 1.2 × 10 −3  °C/year) than from 1998 to 2012 (− 5.7 × 10 −3  °C/year). The SAT change over the period 1940–1975 (1.0 × 10 −4  °C/year) was less affected by the climatological SST forcing experiment than that over the period 1998–2012 (− 5.0 × 10 −4  °C/year). Comparing with 1940–1975, the SAT change over the period 1998–2012 was much affected by the global SAT long-term warming. The distributions of wind stress and atmospheric pressure both indicate that, although the eastern Pacific Ocean played an important role in influencing the global SAT trend between 1998 and 2012, it made little contribution to changes in global SAT between 1940 and 1975. In addition, from the perspective of seasonality, the interdecadal variation of SAT over these two periods was a seasonally dependent phenomenon. Over the period 1940–1975, the annual SAT trend essentially followed the summer SAT trend, whereas between 1998 and 2012, winter was the dominant season of annual SAT change.