Boreas最新文献

In this study, we analysed a ~54-m sediment core consisting of Quaternary sediments overlying the Neoproterozoic Muhos Formation in central western Finland, adjacent to the Gulf of Bothnia. The sediments recovered were logged, and their sedimentological characteristics defined. Two fine-grained sediment units were subjected to biostratigraphical studies using pollen and diatom analyses. In addition, two sand-rich units and a wooden stick were dated by the optically stimulated luminescence (OSL) and ¹⁴C-AMS methods. The core sediments were divided into six units, where several diamicton, sand and gravel, and silt-and-clay-dominated beds were studied. The results indicate that the sediment succession of the core beneath the Holocene Litorina Sea and the Ancylus Lake sediments of the Baltic Basin were deposited in glacial and lacustrine environments that existed in the Oulu River valley during the time period between the Saalian glaciation (MIS 6) and the Holocene. The stratigraphical evidence, supported by the OSL ages, suggests that the Scandinavian Ice Sheet (SIS) entered the Muhos area during the Saalian glaciation, and at least during three separate time intervals in the Weichselian stage. Stratigraphically controlled and age-bracketed evidence shows that the first Weichselian SIS advance extended further south in the eastern part of Fennoscandia than previously estimated, and that this ice growth phase occurred during the Early Weichselian Herning Stadial (MIS 5d). The subsequent ice growth phases occurred during the Middle (MIS 4) and Late (MIS 2) Weichselian substages. The lacustrine and littoral sediments of the Muhos core were correlated with the late Eemian interglacial (MIS 5e) and two Weichselian interstadials (MIS 5c and MIS 3).

Eemian pollen records from central Europe describe a transition from thermophilous tree taxa in the early Eemian to boreal tree taxa in the late Eemian with forest opening in the subsequent stadial. Available summer-temperature reconstructions for the mid- to late Eemian transition show decreasing values during that time. We present a new chironomid record from southern Germany that covers the mid-Eemian to the end of the first Würmian stadial (c. 125–105 ka) and also parts of the late Rissian glaciation and early Brörup interstadial of the early Würmian glaciation. Based on this record we describe lake development in the former Füramoos palaeolake and quantitatively reconstruct July air temperature during the examined interval. Late Rissian sediments are dominated by two chironomid taxa, Sergentia coracina-type and Micropsectra radialis-type, indicating very cold conditions. Following an uncertain interval, probably including a hiatus at the late Rissian/Eemian transition, mid-Eemian sediments contain Tanytarsus glabrescens-type and Tanytarsus mendax-type suggesting relatively high July air temperatures. During the late Eemian, typically thermophilic taxa such as Tanytarsus glabrescens-type disappear, suggesting decreasing temperatures. Stadial A is associated with increases in Microtendipes pedellus-type suggesting more oligotrophic conditions. Early Brörup sediments contain Tanytarsus glabrescens-type, suggesting a slight increase in July air temperature. Reconstructed July air temperatures show temperatures of 7–8 °C during the late Rissian and a decline from ~15.5–12 °C during the mid- to late Eemian associated with decreasing Northern Hemisphere July insolation. July air temperature values vary between 12 and 14 °C in the late Eemian, while reconstructed temperatures remain within 12–13.5 °C during Stadial A. Our new chironomid-based temperature reconstruction provides valuable corroboration and new quantification of temperature development from the mid-Eemian to the early Brörup interstadial as well as for sections of the late Rissian from the alpine foreland of southern Germany.

A multiproxy analysis of a sediment core from Glukhoye Lake in the southern Kuril Islands indicates that the basin originated c. 8.2 cal. ka BP as a brackish lagoon with the subsequent development of a freshwater lake (c. 4.0 to 3.3 cal. ka BP), a bog (c. 3.3 to 2.4 cal. ka BP) and a second lake (c. 2.4 cal. ka BP to present). The basin history primarily reflects local coastal dynamics and is not related to proposed Archipelago-wide changes in sea level. Between c. 8.2 and 8.0 cal. ka BP, the vegetation of southern Kunashir Island was characterized by Betula–Quercus forest with a secondary component of temperate broadleaf trees. Quercus broadleaf forest established c. 8.0 to 6.5 cal. ka BP and represents the Holocene thermal maximum. The remainder of the record shows a gradual decrease in temperate and an increase in conifer taxa, indicating a gradual cooling from the Holocene thermal maximum to c. 2.3 cal. ka BP. Maxima in Picea and Abies pollen between c. 2.3 and 1.1 cal. ka BP suggest conditions that were slightly cooler than present. Palaeovegetation changes in the Kuril Islands as inferred from lake and section data differ in the timing and/or composition of the vegetation communities, although results from the two types of sites become more similar as the number of sections increases. The lake results do not support a previous conceptual model developed for the southern Russian Far East, which linked changes in sea levels to Holocene climate fluctuations. Rather the depositional environments in the lake cores seem more related to coastal dynamics that are independent of fluctuations in sea levels or climate. The difficulty in developing accurate age models for sites with multiple depositional environments may be the most important obstacle for documenting and understanding the Archipelago’s vegetation and climate histories.

With this short editorial I would like to update you about some forthcoming changes in the mode of production of Boreas. Following in-depth considerations and a recommendation by our Publisher, the Administrative Board decided to convert the journal from the traditional subscription-based model to full Open Access as of 2022, which already came into effect for all new submissions from August 2021. In practical terms, this move means that all forthcoming articles published in Boreas will be freely available to everybody across the world generating a high potential for increased circulation and impact, also where the journal was inaccessible previously. All new articles will be immediately free to download and share, helping to increase research dissemination. Furthermore, all articles published from 1997 will be free to read for everybody online. We continue to see many institutions and global funders creating Open Access policies for their authors, and we are hereby making it easier for authors to fulfil their funders’ mandates regarding Open Access publication. With this move Boreas is joining other high impact journals in the Wiley Open Access portfolio, and will benefit from a number of advantages that this confers.

But Open Access carries also a change in the financial model whereby the accepted articles will be charged a publication fee. Typically, this fee is covered by the bilateral agreements between the publishers and the authors’ home institutions, based on country-wide agreements, which are currently increasing significantly and paving the way for Open Access to become the main science publication model in the future. Individual authors not covered by these licences and not having other funding will be able to request fee waivers.

Another change concerns the production of Boreas on paper. Since its first volume in 1972, the journal has been disseminated as printed copies, later supplemented and gradually replaced by the online edition. Following recent trends, from 2022 Boreas will no longer be printed on paper but remain as an online journal only. Most of you will hardly notice it. The traditional walk to the hardcopy library has long been replaced by the more convenient electronic access, which is clearly reflected by the dropping subscriptions of printed copies of journals worldwide. In doing so, we are not only addressing the global shortages of library space but also saving substantial hardcopy and hardware production flow, with benefit to the environment. This book is thus the last issue of Boreas appearing in the printed version.

Last but not least, Karen Luise Knudsen will be retiring as Assistant Editor at the end of 2021. Karen Luise has held this post since 2000 and I would like to use this opportunity to convey my most sincere thanks for all her dedicated work for Boreas, her professionalism in co-editing it, and enthusiasm in co-managing all relevant adm

The far-reaching impact of the Sun on Earth's climate and on people's health and well-being is a poorly understood and non-consensual scientific issue, with empirical literature stressing the need to expand the knowledge of such relationships. Here, the interplay between solar activity (SA) and climate, and its likely cascading effects on all-cause mortality, were examined at several time scales. To this end, the parish records of Braga (1700–1880) and Torre de Moncorvo (1700–1850), in two different geographical locations of northern Portugal (Iberia, SW Europe), were used. Crude mortality rate (CMR) and winter–summer ratio (W/S) values were computed to characterize mortality patterns/trends and couple them with potential relevant drivers: total solar irradiance (TSI) as a proxy of SA, the North Atlantic Oscillation (NAO), and key historical events. What emerged, albeit incomplete, was a complex picture of death deeply embedded in people’s physical and socioeconomic environments, at a time when ubiquitous poverty (and co-morbid malnutrition) was the most inveterate cause of ill health. After identifying the positive mortality episodes in both municipalities, their incidence was found to be higher in periods of weakened SA (normal/grand minima). Standard inference statistics were used to estimate the significance of the observations. The highest CMR peaks matched not only with wars but also with known wide-ranging mortality crises, which seem to have been triggered by major agricultural production shortfalls, followed by substantial increases in food prices, driven, in turn, by climate deterioration, including extreme weather occurrences. The outcome was social unrest, famines, and outbreaks of infectious diseases, heightening the death toll. The influence of prominent solar/climate variations was investigated using wavelet transform coherence analysis (WTC). The results showed (multi)decadal oscillations in both (TSI and NAO) somehow regulating mortality. But the WTC analysis also estimated SA signals in low-frequency mortality dynamics disguised by time-varying determinants, where distinct players of space weather might have been implicated.

Developing a long-term understanding of the cryosphere is important in the study of past climatic change. Here we used a nested approach combining diverse instrumental (monthly meteorological data from four weather stations, as well as gridded data) and proxy data (based on blue intensity measurements from local tree ring records) to create a reconstruction of past summer temperature for the central Jotunheimen area in southern Norway. This record was then used to reconstruct annual glacier mass balance from 1962, the start of the yearly measurements, back to 1722, immediately prior to the regional Little Ice Age maximum. Our reconstruction of the ‘average’ Jotunheimen cumulative glacier mass balance is based on three representative glaciers (Storbreen, Hellstugubreen and Gråsubreen) that were synthesized into one composite record which we term ‘Gjennomsnittsbreen’ (‘mean glacier’ in Norwegian) to filter out localized controls on the behaviour of individual glaciers. While not ignoring the role of precipitation on glacier mass balance, our reconstruction demonstrates that glaciers in this region exhibit a strong summer temperature control and appear to have been declining more or less continuously since the mid-18th century. However, it also shows that this long-term trend of overall retreat in Jotunheimen is punctuated by relatively short-lived periods of neutral or occasionally positive glacier mass balance, signifying periods of stillstand or small-scale glacier advance. These periods or ‘events’ in our reconstruction were compared with an independent record of 12 moraine-building events developed using lichenometry. A minimum of 10 of the moraine-building events identifiable in our reconstruction were also identifiable in the lichenometric data which affords confidence in the performance of our interrogative model. A critical implication of this successful glacier mass balance reconstruction based on just summer temperature is that for Jotunheimen – in contrast to Norwegian maritime glaciers further to the west – there is no need (as was proposed in some previous studies) to invoke large, prolonged increases in winter snowfall to explain glacier advances, not even for events such as the Little Ice Age.

The Pacific Decadal Oscillation (PDO), the Pacific-North American Pattern (PNA) and the Northern Annular Mode (NAM) influence the Northern Hemisphere climate over all sorts of time scales, from days to decades. This study evaluates these climate modes under drastically modified conditions. It is found that in Marine Isotope Stage 31 (MIS 31), an interglacial with enhanced seasonal amplitude, the PDO, PNA and NAM are completely different in their temporal and spatial patterns with respect to current conditions. Moreover, the MIS 31 boundary conditions induce an amplification of the interannual variability, but a suppression of the decadal peak. It is found that changes in the air–sea interaction in the NH, in particular due to a weaker Aleutian low, are responsible for the absence of the decadal periodicity. However, no large changes are verified in terms of explained variance of those modes with respect to CTR. However, the amplitude of response related to the PDO, NAM and PNA is weaker in the MIS 31 experiment, very likely due to a reduced meridional thermal gradient. The results presented here are useful for palaeoreconstruction interpretation because proxies may reproduce dominant characteristics of temperature and precipitation related to the persistence of those modes of variability. Thus, their ability to reproduce long-term environmental conditions in some situations can be related to a preferential phase of the PDO, PNA and NAM.