A high-precision age estimate of the Holocene Plinian eruption of Mount Mazama, Oregon, USA

© The Author(s) 2015 The climactic eruption of Mount Mazama in Oregon, North America, resulted in the deposition of the most widespread Holocene tephra deposit in the conterminous United States and south-western Canada. The tephra forms an isochronous marker horizon for palaeoenvironmental, sedimentary and archaeological reconstructions, despite the current lack of a precise age estimate for the source eruption. Previous radiocarbon age estimates for the eruption have varied, and Greenland ice-core ages are in disagreement. For the Mazama tephra to be fully utilised in tephrochronology and palaeoenvironmental research, a refined (precise and accurate) age for the eruption is required. Here, we apply a meta-analysis of all previously published radiocarbon age estimations (n = 81), and perform Bayesian statistical modelling to this data set, to provide a refined age of 7682–7584 cal. yr BP (95.4% probability range). Although the depositional histories of the published ages vary, this estimate is consistent with that estimated from the GISP2 ice-core of 7627 ± 150 yr BP (Zdanowicz et al., 1999)

The ‘Little Ice Age’ in the Southern Hemisphere in the context of the last 3000 years : Peat-based proxy-climate data from Tierra del Fuego

DM’s research (at Department of Earth Sciences, Uppsala University) was supported through a European Community Marie Curie Fellowship (Contract HPMF-CT-2000-01056).Peer reviewedPostprin

Shieling activity in the Norse Eastern Settlement : palaeoenvironment of the 'Mountain Farm', Vatnahverfi, Greenland

Peer reviewedPostprin

High-resolution palynology reveals the land-use history of a Sami renvall in northern Sweden

Acknowledgements: This research was funded by the Leverhulme Trust through the Footprints on the Edge of Thule project, and was written under the auspices of the ERC-funded project Arctic Domus. Thanks are offered to Audrey Innes for laboratory assistance; Ian Foster for 210Pb dating; Gordon Cook for AMS radiocarbon analyses; and Martin Konert and the late Sjoerd Bohncke for assistance with LOI and related analyses. The comments of Tim Mighall, Jeff Blackford, Mari Kuoppamaa, two anonymous referees and the editor helped to improve the paper.Peer reviewedPublisher PD

The Effect of Climate Change on the Palaeohydrology of Subarctic Permafrost Peatlands in Kola Peninsula, Russia

Pohjoisilla soilla on merkittävä vaikutus globaaliin hiilen kiertoon suuren hiilivarastonsa sekä vuosittaisten hiilidioksidin (CO2) ja metaanin (CH4) virtausten myötä. Ihmisen aiheuttama ilmastonmuutos voi vaikuttaa soiden hiilidynamiikkaan muuttamalla esimerkiksi perustuotantoon liittyviä prosesseja ja kosteusoloja sekä sulattamalla ikiroutaa. Näiden muutosten vaikutusta pohjoisten soiden kykyyn toimia tulevaisuuden hiilinieluina ei vielä tarkoin tunneta, mutta erityisesti soiden kosteusolojen muutoksilla voi olla merkittävä vaikutus hiilinielun tehokkuuteen. Tässä pro gradu -tutkielmassa tarkastelen viime vuosisatojen paleohydrologiaa ja turpeen kertymistä Lovozeron ikiroutasuoalueella Kuolan niemimaalla Venäjällä. Käytän kuoriamebojen fossiileja historiallisten kosteusmuutosten indikaattoreina. Muita tutkimusmenetelmiä ovat detrended correspondence – analyysi sekä radiohiili 14C ja lyijyisotoopin 210Pb ajoitukset. Muiden tutkimusryhmän jäsenten tuottamat kasvimakrofossiili- ja hiilikertymäaineistot toimivat omia tuloksiani tukevina aineistoina. Tulokset osoittavat, että eri tutkimusalueiden hydrologiset muutokset ja turpeen kertymisen nopeus erosivat toisistaan menneiden ilmastovaihteluiden aikana. Tämä viittaa siihen, että muutokset johtuvat enemminkin soiden sisäisistä prosesseista kuin ilmastosta. Kuitenkin kaikissa kolmessa suokohteessa oli havaittavissa kuivumista ja turpeen kertymisen kiihtymistä viimeisen vuosisadan aikana. Lisäksi kaikissa kohteissa on tapahtunut muutos kosteampiin olosuhteisiin viimeisen vuosikymmenen aikana. Tämä kosteuden lisääntyminen voi mahdollisesti johtua ikiroudan sulamisen kiihtymisestä. Kuoriameba-aineistossa havaittiin myös miksotrofisten kuoriamebojen määrän lisääntyminen pintakerroksissa. Tämä on saattanut edistää nopeaa turpeen kertymistä suon pintaosissa. Lovozeron soiden toisistaan poikkeavat historiat sekä viime vuosisadan kehityskulku kohti kuivempia olosuhteita vastaavat muilta pohjoisilta soilta saatuja tuloksia. Viimeaikainen muutos kosteampiin olosuhteisiin poikkeaa kuitenkin muualta pohjoisilta alueilta tehdyistä havainnoista. Vaikuttaa siis siltä, että ilmastonmuutoksen aiheuttamat muutokset soiden hydrologiaan ja/tai turpeen ja hiilen kertymiseen eivät välttämättä ole kaikkialla yhteneviä. Näin ollen lisätutkimuksia edelleen tarvitaan erilaisten suovasteiden tarkempaan selvittämiseen.Northern peatlands have a major role in the global carbon cycle due to their carbon stocks and fluxes of carbon dioxide (CO2) and methane (CH4). Anthropogenic climate change may affect peatland carbon dynamics through changes in e.g. primary production, hydrology, and permafrost dynamics. It is uncertain whether these changes will lead to northern peatlands becoming significant sources of carbon to the atmosphere. Changes in moisture conditions especially can be an important factor in determining the carbon sink potential of northern peatlands. In this thesis I examine the palaeohydrology and peat accumulation over the past centuries in a permafrost peatland complex in Lovozero, Kola Peninsula, Russia. I used testate amoebae as a proxy of past changes in moisture conditions. Other study methods used here are detrended correspondence analysis (DCA) and 14C and 210Pb dating. The results were also supplemented with plant macrofossil and carbon accumulation data provided by other members of the research team. The results show varying responses of the peatland hydrology and peat accumulation to the past climatic shifts, suggesting that the changes have been driven more by autogenic factors rather than climate. However, all three sites indicated a drying trend and an increased peat accumulation for the last century. Yet, the last decade is charachterised by a wet shift. The wet shifts suggest that the peatlands may have crossed a threshold where increased evapotranspiration is exceeded by increased moisture due to thawing permfrost. The surface peat layers of all three sites were dominated by mixotrophic testate amoebae, which may have contributed to the high peat accumulation. The inconsistency of past successional pathways identified at Lovozero peatlands and the drying trend over the past century correspond to the previous studies from northern peatlands elsewhere. However, the most recent surface wetting during the last decade differs from what has been reported for the other northern sites. This suggests that the response mechanisms of peatlands to the anthropogenic climate change may not be uniform. Thus, further research is inevitably needed to increase our understanding of peatland-climate intercations

Pacific Southwest United States Holocene Droughts and Pluvials Inferred From Sediment δ18O (calcite) and Grain Size Data (Lake Elsinore, California)

Records of past climate can inform us on the natural range and mechanisms of climate change. In the arid Pacific southwestern United States (PSW), which includes southern California, there exist a variety of Holocene records that can be used to infer past winter conditions (moisture and/or temperature). Holocene records of summer climate, however, are rare from the PSW. In the future, climate changes due to anthropogenic forcing are expected to increase the severity of drought in the already water stressed PSW. Hot droughts are of considerable concern as summer temperatures rise. As a result, understanding how summer conditions changed in the past is critical to understanding future predictions under varied climate forcings. Here, we present a c. 10.9 kcal BP δ18O(calcite) record from Lake Elsinore, California, interpreted to reflect δ18O(lake water) values as controlled by over-water evaporation from summer-to-early fall. Our results reveal three millennial scale intervals: (1) the highly evaporative Early Holocene (10.55–6.65 kcal BP), (2) the less evaporative Mid-Holocene (6.65–2.65 kcal BP); and (3) the evaporative Late Holocene (2.65–0.55 kcal BP). These results are coupled with an inferred winter precipitation runoff (sand content) record from Kirby et al. (2010). Using these data together, we estimate the duration and severity of centennial-scale Holocene droughts and pluvials (e.g., high δ18O(calcite) values plus low sand content = drought and vice versa). Furthermore, the coupled δ18O(calcite) and sand data provide a generalized Holocene lake level history. The most severe, long-lasting droughts (i.e., maximum summer-to-early fall evaporation and minimum winter precipitation runoff) occur in the Early Holocene. Fewer, less severe, and shorter duration droughts occurred during the Mid-Holocene as pluvials became more common. Droughts return with less severity and duration in the Late Holocene. Notably, the Little Ice Age is characterized as the wettest period during the Late Holocene

Hydrological changes during the last millennium in three subarctic permafrost peatlands and their link to climate shifts

Ikiroutasoilla on suuri hiilensidontakapasiteetti, jonka ansiosta ne ovat tärkeitä ilmaston säätelijöitä. Noin 14% planeettamme maaperän orgaanisesta hiilestä on varastoituneena subarktisen alueen ikiroutasoihin, jotka ovat herkkiä ilmastonmuutoksille pohjoisesta sijainnistaan johtuen. Ikiroutasuot toimivat myös elinympäristönä lukuisille kosteuden muutoksille herkille lajeille, kuten sammalille ja kuoriameboille. Näitä lajeja voidaan käyttää aikojen kuluessa tapahtuvien hydrologisten muutosten tutkimiseen, joka mahdollistaa tulevan ilmastoresponssin mallintamisen. Tässä pro gradu -tutkielmassa tutkitaan hydrologian muutoksia kolmelta ikiroutasuolta pohjoisRuotsin Taavavuomasta ja Abiskosta kerätyissä kairanäytteissä kuoriamebojen lajistokoostumusta apuna käyttäen. Lajistokoostumukset yhdistettiin radiohiili- (14C) ja lyijyajoitusten (210Pb) tuloksiin menneiden aikojen vedenpinnan korkeuden rekonstruoimiseksi. Tulokset ulottuivat neljän eri ilmastovaiheen ajalle. Rekonstruktioita verrattiin menneisiin kuoriameboista tehtyihin tutkimuksiin ymmärtääksemme, kuinka ikiroutasuot ja niiden lajisto reagoivat soiden aktiivisessa turvekerroksessa tapahtuviin hydrologian muutoksiin. Kolmesta tutkimuskohteestamme vain Taavavuomasta kerätyt kairanäytteet ulottuivat niin kutsutulle Dark Age Cold Periodille sekä keskiajan lämpökaudelle. Molempien kairanäytteiden lajistokoostumukset viittasivat vedenpinnan vaihdelleen Dark Age Cold Periodin aikana, mutta keskiajan lämpökauden aikana tulokset olivat keskenään ristiriitaisia, toisen kohteista osoittaessa kosteampaan ja toisen kohteista kuivempaan keskiajan lämpökauteen. Tutkimustulokset viittaavat kosteampaan pieneen jääkauteen sekä kuivempaan teollistumisen jälkeiseen lämpökauteen kahdessa kolmesta kohteesta, tukien menneitä tutkimuksia. Yhdessä kohteessa tulokset olivat päinvastaisia. Tulokset osoittavat kuoriamebakoostumuksen vaihdelleen runsaasti aikojen kuluessa. Tämä viittaa siihen, että soiden hydrologia voi vaihdella nopeasti ja huomattavan paljon jopa paikallistasolla. Kuoriamebojen huonosti tunnettu ekologia hankaloittaa tulosten tulkintaa, ja siksi erilaisten, toisiaan tukevien indikaattorien käyttäminen on välttämätöntä luotettavien tulevaisuuden ennusteiden tekemiseksi.Permafrost peatlands have the capacity to store significant amounts of carbon, and thus they act as important controllers of the climate. Approximately 14% of the world’s soil organic carbon pool is stored in permafrost peatlands, which are sensitive to climatic fluctuations due to their location in the high latitudes of the subarctic zone. Permafrost peatlands also act as a habitat for a large number of moisture-sensitive organisms, such as bryophytes and testate amoebae, which can be used to study how the hydrology of peatlands has changed and will continue to change throughout time, giving us an opportunity to predict the future of peatlands under a changing climate. In this Master’s Thesis I examined the testate amoebae composition and used these species as indicators to study hydrological fluctuations from three subarctic permafrost peatland cores extracted from Taavavuoma and Abisko in northern Sweden. The species compositions were combined with radiocarbon (14C) and lead (210Pb) dates to reconstruct the past water table levels for the late Holocene, spanning four climatic periods. The reconstructions were then compared to past studies on testate amoebae to understand how permafrost peatlands and their species assemblages respond to changes in the hydrology of the active layer of the peat. Out of the study sites only the Taavavuoma cores spanned the Dark Age Cold Period (DACP) and Medieval Climate Anomaly (MCA). Species compositions in both cores indicated fluctuating water tables during the DACP, but during the MCA the results began to contradict with one site showing a wetter, and the other a drier MCA. Two out of three study sites indicated a wetter Little Ice Age and a drier Post-Industrial Warming, supporting past studies indicating similar results, whereas one study site gave opposite results. The results indicated large variability in testate amoebae assemblages throughout time, indicating that the hydrology of peatlands can change very abruptly and vary considerably even on a local scale. Modelling is however complicated by the poorly known ecology of testate amoebae, which is why a multi-proxy approach is essential to reliably predict the future fate of permafrost peatlands

Were last glacial climate events simultaneous between Greenland and France? A quantitative comparison using non-tuned chronologies

Author Posting. © The Author(s), 2009. This is the author's version of the work. It is posted here by permission of John Wiley & Sons for personal use, not for redistribution. The definitive version was published in Journal of Quaternary Science 25 (2010): 387-394, doi:10.1002/jqs.1330.Several large abrupt climate fluctuations during the last glacial have been recorded in Greenland ice cores and archives from other regions. Often these Dansgaard-Oeschger events are assumed to have been synchronous over wide areas, and then used as tie-points to link chronologies between the proxy archives. However, it has not yet been tested independently whether or not these events were indeed synchronous over large areas. Here, we compare Dansgaard-Oeschgertype events in a well-dated record from southeastern France with those in Greenland ice cores. Instead of assuming simultaneous climate events between both archives, we keep their age models independent. Even these well-dated archives possess large chronological uncertainties, that prevent us from inferring synchronous climate events at decadal to multi-centennial time scales. If possible, comparisons between proxy archives should be based on independent, non-tuned time-scales.BW acknowledges support from the Swedish Research Council (VR)