Inference of abrupt changes in noisy geochemical records using transdimensional changepoint models

International audienceWe present a method to quantify abrupt changes (or changepoints) in data series, represented as a function of depth or time. These changes are often the result of climatic or environmental variations and can be manifested inmultiple datasets as different responses, but all datasets can have the same changepoint locations/timings. The method we present uses transdimensional Markov chain Monte Carlo to infer probability distributions on the number and locations (in depth or time) of changepoints, the mean values between changepoints and, if required, the noise variance associated with each dataset being considered. This latter point is important as we generally will have limited information on the noise, such as estimates only of measurement uncertainty, and in most cases it is not practical to make repeat sampling/measurement to assess other contributions to the variation in the data.Wedescribe themain features of the approach (and describe themathematical formulation in supplementary material), and demonstrate its validity using synthetic datasets, with known changepoint structure (number and locations of changepoints) and distribution of noise variance for each dataset.We show that when using multiple data, we expect to achieve better resolution of the changepoint structure than when we use each dataset individually. This is conditional on the validity of the assumption of common changepoints between different datasets.We then apply themethod to two sets of real geochemical data, both from peat cores, taken from NE Australia and eastern Tibet. Under the assumption that changes occur at the same time for all datasets, we recover solutions consistent with those previously inferred qualitatively from independent data and interpretations. However, our approach provides a quantitative estimate of the relative probability of the inferred changepoints, allowing an objective assessment of the significance of each change

Postglacial peatland vegetation succession in Store Mosse bog, south-central Sweden : An exploration of factors driving species change

Boreal peatlands are facing significant changes in response to a warming climate. Sphagnum mosses are key species in these ecosystems and contribute substantially to carbon sequestration. Understanding the factors driving vegetation changes on longer time scales is therefore of high importance, yet challenging since species changes are typically affected by a range of internal and external processes acting simultaneously within the system. This study presents a high-resolution macrofossil analysis of a peat core from Store Mosse bog (south-central Sweden), dating back to nearly 10 000 cal. a BP. The aim is to identify factors driving species changes on multidecadal to millennial timescales considering internal autogenic, internal biotic and external allogenic processes. A set of independent proxy data was used as a comparison framework to estimate changes in the bog and regional effective humidity, nutrient input and cold periods. We found that Store Mosse largely follows the expected successional pathway for a boreal peatland (i.e. lake -> fen -> bog). However, the system has also been affected by other interlinked factors. Of interest, we note that external nutrient input (originating from dust deposition and climate processes) has had a negative effect on Sphagnum while favouring vascular plants, and increased fire activity (driven by allogenic and autogenic factors) typically caused post-fire, floristic wet shifts. These effects interactively caused a floristic reversal and near disappearance of a once-established Sphagnum community, during which climate acted as an indirect driver. Overall, this study highlights that the factors driving vegetation change within the peatland are multiple and complex. Consideration of the role of interlinked factors on Sphagnum is crucial for an improved understanding of the drivers of species change on short- and long-term scales.Peer reviewe

New insights from XRF core scanning data into boreal lake ontogeny during the Eemian (Marine Isotope Stage 5e) at Sokli, northeast Finland

Biological proxies from the Sokli Eemian (Marine Isotope Stage 5e) paleolake sequence from northeast Finland have previously shown that, unlike many postglacial records from boreal sites, the lake becomes increasingly eutrophic over time. Here, principal components (PC) were extracted from a high resolution multi-element XRF core scanning dataset to describe minerogenic input from the wider catchment (PC1), the input of S, Fe, Mn, and Ca-rich detrital material from the surrounding Sokli Carbonatite Massif (PC2), and chemical weathering (PC3). Minerogenic inputs to the lake were elevated early in the record and during two abrupt cooling events when soils and vegetation in the catchment were poor. Chemical weathering in the catchment generally increased over time, coinciding with higher air temperatures, catchment productivity, and the presence of acidic conifer species. Abiotic edaphic processes play a key role in lake ontogeny at this site stemming from the base cation- and nutrient-rich bedrock, which supports lake alkalinity and productivity. The climate history at this site, and its integrated effects on the lake system, appear to override development processes and alters its long-term trajectory.Peer reviewe

Holocene atmospheric dust deposition in NW Spain

Acknowledgements The authors would like to extend their thanks to the students of the EcoPast research group (GI-1553, Universidade de Santiago de Compostela, Facultade de Bioloxía) and colleagues who helped with fieldwork and laboratory analyses. Funding The author(s) disclosed receipt of the following financial support for the research, authorship and/or publication of this article: This research was partially funded by Consiliencia network (ED431D2017/08 Xunta de Galicia) and Funding for Consolidation and Structuration of Research Units (ED431B2018/20 Xunta de Galicia).Peer reviewedPostprin

Human bones tell the story of atmospheric mercury and lead exposure at the edge of Roman World

We thank Museo de Pontevedra and Dirección Xeral de Patrimonio Xuntade Galicia for providing access to skeletal collections. OLC is funded by ED481D 2017/014Xunta de Galicia. This work was supported bythe projects: Galician Paleodiet (ED481D 2017/014), Consiliencia network (ED 431D2017/08), GPC (ED431B 2018/20) all funded by Xunta de Galicia.Peer reviewedPublisher PD

Hässeldala – a key site for Last Termination climate events in northern Europe

The Last Termination (19 000–11 000 a BP) with its rapid and distinct climate shifts provides a perfect laboratory to study the nature and regional impact of climate variability. The sedimentary succession from the ancient lake at Hässeldala Port in southern Sweden with its distinct Lateglacial/early Holocene stratigraphy (>14.1–9.5 cal. ka BP) is one of the few chronologically well‐constrained, multi‐proxy sites in Europe that capture a variety of local and regional climatic and environmental signals. Here we present Hässeldala's multi‐proxy records (lithology, geochemistry, pollen, diatoms, chironomids, biomarkers, hydrogen isotopes) in a refined age model and place the observed changes in lake status, catchment vegetation, summer temperatures and hydroclimate in a wider regional context. Reconstructed mean July temperatures increased between c. 14.1 and c. 13.1 cal. ka BP and subsequently declined. This latter cooling coincided with drier hydroclimatic conditions that were probably associated with a freshening of the Nordic Seas and started a few hundred years before the onset of Greenland Stadial 1 (c. 12.9 cal. ka BP). Our proxies suggest a further shift towards colder and drier conditions as late as c. 12.7 cal. ka BP, which was followed by the establishment of a stadial climate regime (c. 12.5–11.8 cal. ka BP). The onset of warmer and wetter conditions preceded the Holocene warming over Greenland by c. 200 years. Hässeldala's proxies thus highlight the complexity of environmental and hydrological responses across abrupt climate transitions in northern Europe

Industrial-era lead and mercury contamination in southern Greenland implicates North American sources

We would like to thank Jesús R. Aboal (Universidade de Santiago de Compostela) and Kjell Billström (Naturhistoriska Riksmuseet) for access to the laboratory facilities; Antonio Rodríguez López helped with laboratory work. This research was done under the framework of the projects CGL2010-20672 (Plan Nacional I+D+i, Spanish Ministerio de Economía y Competitividad), R2014/001 and GPC2014-009 (Dirección Xeral I+D, Xunta de Galicia). The authors gratefully acknowledge the financial support of the UK Leverhulme Trust Footprints on the Edge of Thule programme award for core collection and associated environmental research.Peer reviewedPostprin

Abrupt high-latitude climate events and decoupled seasonal trends during the Eemian

The Eemian (the Last Interglacial; ca. 129-116 thousand years ago) presents a testbed for assessing environmental responses and climate feedbacks under warmer-than-present boundary conditions. However, climate syntheses for the Eemian remain hampered by lack of data from the high-latitude land areas, masking the climate response and feedbacks in the Arctic. Here we present a high-resolution (sub-centennial) record of Eemian palaeoclimate from northern Finland, with multi-model reconstructions for July and January air temperature. In contrast with the mid-latitudes of Europe, our data show decoupled seasonal trends with falling July and rising January temperatures over the Eemian, due to orbital and oceanic forcings. This leads to an oceanic Late-Eemian climate, consistent with an earlier hypothesis of glacial inception in Europe. The interglacial is further intersected by two strong cooling and drying events. These abrupt events parallel shifts in marine proxy data, linked to disturbances in the North Atlantic oceanic circulation regime.Peer reviewe

Early atmospheric metal pollution provides evidence for Chalcolithic/Bronze Age mining and metallurgy in Southwestern Europe

Although archaeological research suggests that mining/metallurgy already started in the Chalcolithic (3rd millennium BC), the earliest atmospheric metal pollution in SW Europe has thus far been dated to ~ 3500–3200 cal. yr. BP in paleo-environmental archives. A low intensity, non-extensive mining/metallurgy and the lack of appropriately located archives may be responsible for this mismatch. We have analysed the older section (> 2100 cal. yr. BP) of a peat record from La Molina (Asturias, Spain), a mire located in the proximity (35–100 km) of mines which were exploited in the Chalcolithic/Bronze Age, with the aim of assessing evidence of this early mining/metallurgy. Analyses included the determination of C as a proxy for organic matter content, lithogenic elements (Si, Al, Ti) as markers of mineral matter, and trace metals (Cr, Cu, Zn, Pb) and stable Pb isotopes as tracers of atmospheric metal pollutionThis work was funded by the projects CGL2010-20672 and HAR2008-06477-C03-03/HIST (Plan Nacional I + D + i, Spanish Ministerio de Economía y Competitividad), 10PXIB200182PR (General Directorate of I + D, Xunta de Galicia), and CDS-TCP (CSD2007-00058, Programa Consolider-Ingenio 2010). We are grateful to José Antonio López-Sáez, Fernando Gil Sendino, Carmen Fernández Ochoa and Roberto Zapico for their collaboration and assistance during the fieldwork, to José Rodríguez Racedo for helping with the geochemical analyses, and to Suzanne Leroy for perceptive comments on an earlier draftS