A radiocarbon spike at 14 300 cal yr BP in subfossil trees provides the impulse response function of the global carbon cycle during the Late Glacial.

We present new 14C results measured on subfossil Scots Pines recovered in the eroded banks of the Drouzet watercourse in the Southern French Alps. About 400 new 14C ages have been analysed on 15 trees sampled at annual resolution. The resulting Δ14C record exhibits an abrupt spike occurring in a single year at 14 300-14 299 cal yr BP and a century-long event between 14 and 13.9 cal kyr BP. In order to identify the causes of these events, we compare the Drouzet Δ14C record with simulations of Δ14C based on the 10Be record in Greenland ice used as an input of a carbon cycle model. The correspondence with 10Be anomalies allows us to propose the 14.3 cal kyr BP event as a solar energetic particle event. By contrast, the 14 cal kyr BP event lasted about a century and is most probably a common Maunder-type solar minimum linked to the modulation of galactic cosmic particles by the heliomagnetic field. We also discuss and speculate about the synchroneity and the possible causes of the 14 cal kyr BP event with the brief cold phase called Older Dryas, which separates the Bølling and Allerød millennium-long warm phases of the Late Glacial period. This article is part of the Theo Murphy meeting issue 'Radiocarbon in the Anthropocene'.

A paleogenome from a Holocene individual supports genetic continuity in Southeast Alaska.

Many specifics of the population histories of the Indigenous peoples of North America remain contentious owing to a dearth of physical evidence. Only few ancient human genomes have been recovered from the Pacific Northwest Coast, a region increasingly supported as a coastal migration route for the initial peopling of the Americas. Here, we report paleogenomic data from the remains of a ∼3,000-year-old female individual from Southeast Alaska, named Tatóok yík yées sháawat (TYYS). Our results demonstrate at least 3,000 years of matrilineal genetic continuity in Southeast Alaska, and that TYYS is most closely related to ancient and present-day northern Pacific Northwest Coast Indigenous Americans. We find no evidence of Paleo-Inuit (represented by Saqqaq) ancestry in present-day or ancient Pacific Northwest peoples. Instead, our analyses suggest the Saqqaq genome harbors Northern Native American ancestry. This study sheds further light on the human population history of the northern Pacific Northwest Coast.

Ancient bears provide insights into Pleistocene ice age refugia in Southeast Alaska.

During the Late Pleistocene, major parts of North America were periodically covered by ice sheets. However, there are still questions about whether ice-free refugia were present in the Alexander Archipelago along the Southeast (SE) Alaska coast during the last glacial maximum (LGM). Numerous subfossils have been recovered from caves in SE Alaska, including American black (Ursus americanus) and brown (U. arctos) bears, which today are found in the Alexander Archipelago but are genetically distinct from mainland bear populations. Hence, these bear species offer an ideal system to investigate long-term occupation, potential refugial survival and lineage turnover. Here, we present genetic analyses based on 99 new complete mitochondrial genomes from ancient and modern brown and black bears spanning the last ~45,000 years. Black bears form two SE Alaskan subclades, one preglacial and another postglacial, that diverged >100,000 years ago. All postglacial ancient brown bears are closely related to modern brown bears in the archipelago, while a single preglacial brown bear is found in a distantly related clade. A hiatus in the bear subfossil record around the LGM and the deep split of their pre- and postglacial subclades fail to support a hypothesis of continuous occupancy in SE Alaska throughout the LGM for either species. Our results are consistent with an absence of refugia along the SE Alaska coast, but indicate that vegetation quickly expanded after deglaciation, allowing bears to recolonize the area after a short-lived LGM peak.

Olive shrub buried on Therasia supports a mid-16th century BCE date for the Thera eruption.

The precise date of the 2nd millennium BCE ("Minoan") eruption of Thera (Santorini) has long been a focus of controversy due to a discrepancy between archaeological and radiocarbon-based dating of materials from stratigraphic layers above and below tsunami, ash and pumice deposits resulting from the eruption. A critical, though controversial, piece of evidence has been four segments of a radiocarbon-dated olive tree branch, buried on Thera during the eruption. Here we report new radiocarbon evidence from an olive shrub found carbonized by the same eruption deposits on neighboring Therasia (Santorini). The Therasia olive shrub dates slightly younger than the previous olive branch. Calibrated results and growth increment counts indicate increased probabilities for a mid-16th century BCE date for the eruption, overlapping with multiple volcanic sulfate markers from ice core records.

Response to Comment on "A global environmental crisis 42,000 years ago".

Our study on the exact timing and the potential climatic, environmental, and evolutionary consequences of the Laschamps Geomagnetic Excursion has generated the hypothesis that geomagnetism represents an unrecognized driver in environmental and evolutionary change. It is important for this hypothesis to be tested with new data, and encouragingly, none of the studies presented by Picin et al. undermine our model.

Response to Comment on "A global environmental crisis 42,000 years ago".

Our paper about the impacts of the Laschamps Geomagnetic Excursion 42,000 years ago has provoked considerable scientific and public interest, particularly in the so-called Adams Event associated with the initial transition of the magnetic poles. Although we welcome the opportunity to discuss our new ideas, Hawks' assertions of misrepresentation are especially disappointing given his limited examination of the material.

An early dog from southeast Alaska supports a coastal route for the first dog migration into the Americas.

The oldest confirmed remains of domestic dogs in North America are from mid-continent archaeological sites dated approximately 9900 calibrated years before present (cal BP). Although this date suggests that dogs may not have arrived alongside the first Native Americans, the timing and routes for the entrance of New World dogs remain uncertain. Here, we present a complete mitochondrial genome of a dog from southeast Alaska, dated to 10 150 ± 260 cal BP. We compared this high-coverage genome with data from modern dog breeds, historical Arctic dogs and American precontact dogs (PCDs) from before European arrival. Our analyses demonstrate that the ancient dog belongs to the PCD lineage, which diverged from Siberian dogs around 16 700 years ago. This timing roughly coincides with the minimum suggested date for the opening of the North Pacific coastal (NPC) route along the Cordilleran Ice Sheet and genetic evidence for the initial peopling of the Americas. This ancient southeast Alaskan dog occupies an early branching position within the PCD clade, indicating it represents a close relative of the earliest PCDs that were brought alongside people migrating from eastern Beringia southward along the NPC to the rest of the Americas. The stable isotope δ13C value of this early dog indicates a marine diet, different from the younger mid-continent PCDs' terrestrial diet. Although PCDs were largely replaced by modern European dog breeds, our results indicate that their population decline started approximately 2000 years BP, coinciding with the expansion of Inuit peoples, who are associated with traditional sled-dog culture. Our findings suggest that dogs formed part of the initial human habitation of the New World, and provide insights into their replacement by both Arctic and European lineages.

A global environmental crisis 42,000 years ago.

Geological archives record multiple reversals of Earth's magnetic poles, but the global impacts of these events, if any, remain unclear. Uncertain radiocarbon calibration has limited investigation of the potential effects of the last major magnetic inversion, known as the Laschamps Excursion [41 to 42 thousand years ago (ka)]. We use ancient New Zealand kauri trees (Agathis australis) to develop a detailed record of atmospheric radiocarbon levels across the Laschamps Excursion. We precisely characterize the geomagnetic reversal and perform global chemistry-climate modeling and detailed radiocarbon dating of paleoenvironmental records to investigate impacts. We find that geomagnetic field minima ~42 ka, in combination with Grand Solar Minima, caused substantial changes in atmospheric ozone concentration and circulation, driving synchronous global climate shifts that caused major environmental changes, extinction events, and transformations in the archaeological record.

"It made me feel brighter in myself"- The health and well-being impacts of a residential front garden horticultural intervention.

Residential gardens make up 30% of urban space in the UK, yet unlike many other green space typologies, their role in the health and well-being agenda has largely been overlooked. A horticultural intervention introduced ornamental plants to 38 previously bare front gardens (≈ 10 m2) within an economically deprived region of North England, UK. Measures of perceived stress and diurnal cortisol profiles (as an indicator of health status) were taken pre- and post-intervention (over 3 months). Residents reported significant decreases in perceived stress post-intervention. This finding was aligned with a higher proportion of 'healthy' diurnal cortisol patterns post-intervention, suggesting better health status in those individuals. All residents derived one or more reported socio-cultural benefits as a result of the front garden plantings, although overall scores for subjective well-being did not increase to a significant level. Further qualitative data suggested that the gardens were valued for enhancing relaxation, increasing positive emotions, motivation, and pride of place. The results indicate that adding even small quantities of ornamental plants to front gardens within deprived urban communities had a positive effect on an individual's stress regulation and some, but not all, aspects of subjective well-being. The research highlights the importance of residential front gardens to human health and well-being, and thus their contribution to the wider debates around city densification, natural capital and urban planning.

Extended dilation of the radiocarbon time scale between 40,000 and 48,000 y BP and the overlap between Neanderthals and Homo sapiens.

The new radiocarbon calibration curve (IntCal20) allows us to calculate the gradient of the relationship between 14C age and calendar age over the past 55 millennia before the present (55 ka BP). The new gradient curve exhibits a prolonged and prominent maximum between 48 and 40 ka BP during which the radiocarbon clock runs almost twice as fast as it should. This radiocarbon time dilation is due to the increase in the atmospheric 14C/12C ratio caused by the 14C production rise linked to the transition into the Laschamp geomagnetic excursion centered around 41 ka BP. The major maximum in the gradient from 48 to 40 ka BP is a new feature of the IntCal20 calibration curve, with far-reaching impacts for scientific communities, such as prehistory and paleoclimatology, relying on accurate ages in this time range. To illustrate, we consider the duration of the overlap between Neanderthals and Homo sapiens in Eurasia.

Machine learning as a diagnostic decision aid for patients with transient loss of consciousness.

BACKGROUND: Transient loss of consciousness (TLOC) is a common reason for presentation to primary/emergency care; over 90% are because of epilepsy, syncope, or psychogenic non-epileptic seizures (PNES). Misdiagnoses are common, and there are currently no validated decision rules to aid diagnosis and management. We seek to explore the utility of machine-learning techniques to develop a short diagnostic instrument by extracting features with optimal discriminatory values from responses to detailed questionnaires about TLOC manifestations and comorbidities (86 questions to patients, 31 to TLOC witnesses). METHODS: Multi-center retrospective self- and witness-report questionnaire study in secondary care settings. Feature selection was performed by an iterative algorithm based on random forest analysis. Data were randomly divided in a 2:1 ratio into training and validation sets (163:86 for all data; 208:92 for analysis excluding witness reports). RESULTS: Three hundred patients with proven diagnoses (100 each: epilepsy, syncope and PNES) were recruited from epilepsy and syncope services. Two hundred forty-nine completed patient and witness questionnaires: 86 epilepsy (64 female), 84 PNES (61 female), and 79 syncope (59 female). Responses to 36 questions optimally predicted diagnoses. A classifier trained on these features classified 74/86 (86.0% [95% confidence interval 76.9%-92.6%]) of patients correctly in validation (100 [86.7%-100%] syncope, 85.7 [67.3%-96.0%] epilepsy, 75.0 [56.6%-88.5%] PNES). Excluding witness reports, 34 features provided optimal prediction (classifier accuracy of 72/92 [78.3 (68.4%-86.2%)] in validation, 83.8 [68.0%-93.8%] syncope, 81.5 [61.9%-93.7%] epilepsy, 67.9 [47.7%-84.1%] PNES). CONCLUSIONS: A tool based on patient symptoms/comorbidities and witness reports separates well between syncope and other common causes of TLOC. It can help to differentiate epilepsy and PNES. Validated decision rules may improve diagnostic processes and reduce misdiagnosis rates. CLASSIFICATION OF EVIDENCE: This study provides Class III evidence that for patients with TLOC, patient and witness questionnaires discriminate between syncope, epilepsy and PNES.

Deep-water circulation changes lead North Atlantic climate during deglaciation.

Constraining the response time of the climate system to changes in North Atlantic Deep Water (NADW) formation is fundamental to improving climate and Atlantic Meridional Overturning Circulation predictability. Here we report a new synchronization of terrestrial, marine, and ice-core records, which allows the first quantitative determination of the response time of North Atlantic climate to changes in high-latitude NADW formation rate during the last deglaciation. Using a continuous record of deep water ventilation from the Nordic Seas, we identify a ∼400-year lead of changes in high-latitude NADW formation ahead of abrupt climate changes recorded in Greenland ice cores at the onset and end of the Younger Dryas stadial, which likely occurred in response to gradual changes in temperature- and wind-driven freshwater transport. We suggest that variations in Nordic Seas deep-water circulation are precursors to abrupt climate changes and that future model studies should address this phasing.

Annual radiocarbon record indicates 16th century BCE date for the Thera eruption.

The mid-second millennium BCE eruption of Thera (Santorini) offers a critically important marker horizon to synchronize archaeological chronologies of the Aegean, Egypt, and the Near East and to anchor paleoenvironmental records from ice cores, speleothems, and lake sediments. Precise and accurate dating for the event has been the subject of many decades of research. Using calendar-dated tree rings, we created an annual resolution radiocarbon time series 1700-1500 BCE to validate, improve, or more clearly define the limitations for radiocarbon calibration of materials from key eruption contexts. Results show an offset from the international radiocarbon calibration curve, which indicates a shift in the calibrated age range for Thera toward the 16th century BCE. This finding sheds new light on the long-running debate focused on a discrepancy between radiocarbon (late 17th-early 16th century BCE) and archaeological (mid 16th-early 15th century BCE) dating evidence for Thera.

Deglaciation of the Pacific coastal corridor directly preceded the human colonization of the Americas.

The route and timing of early human migration to the Americas have been a contentious topic for decades. Recent paleogenetic analyses suggest that the initial colonization from Beringia took place as early as 16 thousand years (ka) ago via a deglaciated corridor along the North Pacific coast. However, the feasibility of such a migration depends on the extent of the western Cordilleran Ice Sheet (CIS) and the available resources along the hypothesized coastal route during this timeframe. We date the culmination of maximum CIS conditions in southeastern Alaska, a potential bottleneck region for human migration, to ~20 to 17 ka ago with cosmogenic 10Be exposure dating and 14C dating of bones from an ice-overrun cave. We also show that productive marine and terrestrial ecosystems were established almost immediately following deglaciation. We conclude that CIS retreat ensured that an open and ecologically viable pathway through southeastern Alaska was available after 17 ka ago, which may have been traversed by early humans as they colonized the Americas.

Target-distractor synchrony affects performance in a novel motor task for studying action selection.

The study of action selection in humans can present challenges of task design since our actions are usually defined by many degrees of freedom and therefore occupy a large action-space. While saccadic eye-movement offers a more constrained paradigm for investigating action selection, the study of reach-and-grasp in upper limbs has often been defined by more complex scenarios, not easily interpretable in terms of such selection. Here we present a novel motor behaviour task which addresses this by limiting the action space to a single degree of freedom in which subjects have to track (using a stylus) a vertical coloured target line displayed on a tablet computer, whilst ignoring a similarly oriented distractor line in a different colour. We ran this task with 55 subjects and showed that, in agreement with previous studies, the presence of the distractor generally increases the movement latency and directional error rate. Further, we used two distractor conditions according to whether the distractor's location changes asynchronously or synchronously with the location of the target. We found that the asynchronous distractor yielded poorer performance than its synchronous counterpart, with significantly higher movement latencies and higher error rates. We interpret these results in an action selection framework with two actions (move left or right) and competing 'action requests' offered by the target and distractor. As such, the results provide insights into action selection performance in humans and supply data for directly constraining future computational models therein.

Reduced visual exploration when viewing photographic scenes in individuals with autism spectrum disorder.

Individuals with autism spectrum disorder (ASD) often display enhanced attention to detail and exhibit restricted behavior. However, due to a lack of comprehensive eye-movement modeling techniques, it is currently unknown whether these behavioral effects are also evident during scene viewing (i.e., detailed visual inspection and restricted visual exploration). Free-viewing eye-tracking data from observation of everyday photographic scenes were recorded during 2 experiments involving high-functioning adolescents with ASD and matched typically developing (TD) controls (Experiment 1, ASD n = 14; TD n = 22; Experiment 2, ASD n = 16; TD n = 23). Data from both experiments were combined and analyzed using 5 novel methods of eye-tracking, time-course analysis, enabling detailed characterization of viewing strategies. Participants' verbal descriptions of scenes were also assessed. Scenes either contained a centrally positioned person whose face was in full view or contained no centrally positioned face. For both types of scene, ASD participants displayed significantly less exploration of new areas over time compared with their TD peers. Analyses of scan-path length and recursion suggested a greater tendency to explore areas close to the current fixation in the ASD group, termed visual persistence. Differences were not accounted for by fixation rate. Significantly more areas within the scenes were also missing from the verbal descriptions in the ASD group. Differences were observed for both scene types, suggesting a domain-general difference rather than a specific impairment related to face processing. The observed characteristic viewing patterns may explain relative superior processing of local level information in individuals with ASD.

Attitudes towards the sharing of genetic information with at-risk relatives: results of a quantitative survey.

To investigate public attitudes towards receiving genetic information arising from a test on a relative, 955 University of Sheffield students and staff were surveyed using disease vignettes. Strength of attitude was measured on whether, in the event of relevant information being discovered, they, as an at-risk relative, would want to be informed, whether the at-risk relative's interest should override proband confidentiality, and, if they had been the proband, willingness to give up confidentiality to inform such relatives. Results indicated considerably more complexity to the decision-making than simple statistical risk. Desire for information only slightly increased with risk of disease manifestation [log odds 0.05 (0.04, 0.06) per percentage point increase in manifestation risk]. Condition preventability was the primary factor increasing desire [modifiable baseline, non-preventable log odds -1.74 (-2.04, -1.44); preventable 0.64 (0.34, 0.95)]. Disease seriousness also increased desire [serious baseline, non-serious log odds -0.89 (-1.19, -0.59); fatal 0.55 (0.25, 0.86)]. Individuals with lower education levels exhibited much greater desire to be informed [GCSE log odds 1.67 (0.64, 2.66)]. Age did not affect desire. Our findings suggest that attitudes were influenced more by disease characteristics than statistical risk. Respondents generally expressed strong attitudes demonstrating that this was not an issue which people felt ambivalent about. We provide estimates of the British population in favour/against disclosure for various disease scenarios.

Isotopic evidence for the occurrence of biological nitrification and nitrogen deposition processing in forest canopies.

This study examines the role of tree canopies in processing atmospheric nitrogen (Ndep ) for four forests in the United Kingdom subjected to different Ndep : Scots pine and beech stands under high Ndep (HN, 13-19 kg N ha(-1)  yr(-1) ), compared to Scots pine and beech stands under low Ndep (LN, 9 kg N ha(-1)  yr(-1) ). Changes of NO3 -N and NH4 -N concentrations in rainfall (RF) and throughfall (TF) together with a quadruple isotope approach, which combines δ(18) O, Δ(17) O and δ(15) N in NO3 (-) and δ(15) N in NH4 (+) , were used to assess N transformations by the canopies. Generally, HN sites showed higher NH4 -N and NO3 -N concentrations in RF compared to the LN sites. Similar values of δ(15) N-NO3 (-) and δ(18) O in RF suggested similar source of atmospheric NO3 (-) (i.e. local traffic), while more positive values for δ(15) N-NH4 (+) at HN compared to LN likely reflected the contribution of dry NHx deposition from intensive local farming. The isotopic signatures of the N-forms changed after interacting with tree canopies. Indeed, (15) N-enriched NH4 (+) in TF compared to RF at all sites suggested that canopies played an important role in buffering dry Ndep also at the low Ndep site. Using two independent methods, based on δ(18) O and Δ(17) O, we quantified for the first time the proportion of NO3 (-) in TF, which derived from nitrification occurring in tree canopies at the HN site. Specifically, for Scots pine, all the considered isotope approaches detected biological nitrification. By contrast for the beech, only using the mixing model with Δ(17) O, we were able to depict the occurrence of nitrification within canopies. Our study suggests that tree canopies play an active role in the N cycling within forest ecosystems. Processing of Ndep within canopies should not be neglected and needs further exploration, with the combination of multiple isotope tracers, with particular reference to Δ(17) O.

Isotopic Fingerprint for Phosphorus in Drinking Water Supplies.

Phosphate dosing of drinking water supplies, coupled with leakage from distribution networks, represents a significant input of phosphorus to the environment. The oxygen isotope composition of phosphate (δ(18)OPO4), a novel stable isotope tracer for phosphorus, offers new opportunities to understand the importance of phosphorus derived from sources such as drinking water. We report the first assessment of δ(18)OPO4 within drinking water supplies. A total of 40 samples from phosphate-dosed distribution networks were analyzed from across England and Wales. In addition, samples of the source orthophosphoric acid used for dosing were also analyzed. Two distinct isotopic signatures for drinking water were identified (average = +13.2 or +19.7‰), primarily determined by δ(18)OPO4 of the source acid (average = +12.4 or +19.7‰). Dependent upon the source acid used, drinking water δ(18)OPO4 appears isotopically distinct from a number of other phosphorus sources. Isotopic offsets from the source acid ranging from -0.9 to +2.8‰ were observed. There was little evidence that equilibrium isotope fractionation dominated within the networks, with offsets from temperature-dependent equilibrium ranging from -4.8 to +4.2‰. While partial equilibrium fractionation may have occurred, kinetic effects associated with microbial uptake of phosphorus or abiotic sorption and dissolution reactions may also contribute to δ(18)OPO4 within drinking water supplies.

Examining the uncertain origin and management role of martens on Prince of Wales Island, Alaska.

Conservation biologists are generally united in efforts to curtail the spread of non-native species globally. However, the colonization history of a species is not always certain, and whether a species is considered non-native or native depends on the conservation benchmark. Such ambiguities have led to inconsistent management. Within the Tongass National Forest of Alaska, the status of American marten (Martes americana) on the largest, most biologically diverse and deforested island, Prince of Wales (POW), is unclear. Ten martens were released to POW in the early 1930s, and it was generally believed to be the founding event, although this has been questioned. The uncertainty surrounding when and how martens colonized POW complicates management, especially because martens were selected as a design species for the Tongass. To explore the history of martens of POW we reviewed other plausible routes of colonization; genetically and isotopically analyzed putative marten fossils deposited in the late Pleistocene and early Holocene to verify marten occupancy of POW; and used contemporary genetic data from martens on POW and the mainland in coalescent simulations to identify the probable source of the present-day marten population on POW. We found evidence for multiple routes of colonization by forest-associated mammals beginning in the Holocene, which were likely used by American martens to naturally colonize POW. Although we cannot rule out human-assisted movement of martens by Alaskan Natives or fur trappers, we suggest that martens be managed for persistence on POW. More generally, our findings illustrate the difficulty of labeling species as non-native or native, even when genetic and paleo-ecological data are available, and support the notion that community resilience or species invasiveness should be prioritized when making management decisions rather than more subjective and less certain conservation benchmarks.