Postglacial Period Research Articles

High Genetic Diversity of Hirudo verbana Carena, 1820 (Annelida: Hirudinea: Hirudinidae) in Romania Confirms That the Balkans Are Refugia Within Refugium

This study presents the first data on the distribution of the Mediterranean medicinal leech Hirudo verbana in Romania, as well as the first molecular characterization of the Romanian populations, using mitochondrial DNA markers. In total, 133 specimens from 19 populations in Romania were surveyed for mitochondrial COI and 12S markers. Available GenBank sequences from other localities throughout Europe were included to place the Romanian populations in a broader phylogeographical context. The Romanian H. verbana samples belong to 23 COI haplotypes, 4 of which are previously known from Serbia and Ukraine, while 19 haplotypes are herein reported for the first time. For 12S, the number of haplotypes identified was 12, from which only 5 are unique to Romania. The Romanian H. verbana cluster within the previously reported eastern phylogroup, known to occur from Serbia to North Caucasus, Turkey, and Uzbekistan. The mismatch distribution analysis and the results of neutrality tests suggest that the Romanian H. verbana currently undergoes a population dispersal. This study also revealed that the lower Danube basin is a hotspot of genetic diversity of H. verbana, where different lineages from the Balkan and Anatolian glacial refugia mixed in the postglacial period. Species Distribution Models (SDMs) indicated that the main ecological variables influencing the current distribution of H. verbana are wetland coverage and elevation. Following the IUCN Red List categories and criteria, the present conservation status of the Mediterranean medicinal leech H. verbana in Romania was assessed as Vulnerable (VU). Our study contributes towards a more refined understanding of the genetic diversity of H. verbana and of the factors that led to its current geographical distribution in Romania and Europe.

Radiocarbon age-offset measurements reveal shifts in the transport mechanism and age of permafrost-derived organic carbon from Burial Lake, arctic Alaska from MIS 3 to present

The stability of arctic permafrost and the carbon it contains are currently threatened by a rapidly warming climate. Burial Lake, situated in northwestern arctic Alaska, is underlain by continuous permafrost and has a uniquely rich set of paleoclimate proxy data that comprise a 40-ka record of climate and environmental change extending well into Marine Isotope Stage (MIS) 3. Here, we examine the relationship between erosion, subsurface hydrology, and primary productivity from the Burial Lake sediments to improve our understanding of the links between climate, hydrology, sediment transport, and carbon mobility. The record is developed with radiocarbon (14C) age-offsets from two independent methods used to date the lake sediments: 1) 14C measurements on paired bulk sediment and plant macrofossils from the same stratigraphic layer of lake sediment and 2) ramped pyrolysis-oxidation (RPO) 14C analysis that separates fractions of organic carbon (OC) from a single bulk sediment sample based on thermochemical differences through continuous heating. As lakes capture and archive OC transported from the watershed, changes in the amount and relative age of permafrost-derived OC mobilized during past climatic variations can be documented by examining how age-offsets change over time. The Burial Lake sediment revealed higher age-offsets during the cold Last Glacial Maximum (LGM; ∼29-17 ka) than the comparatively warmer post-glacial (∼17 ka-present) and the MIS 3 interstadial (∼40-29 ka) periods. The relatively warm, wet climate of the post-glacial period promoted both terrestrial and aquatic productivity, resulting in increased OC deposition, and it likely favored transport via subsurface flow of dissolved OC (DOC) sourced from soils. This resulted in a greater flux of contemporary OC relative to ancient OC into the lake sediment, lowering the average age offset to ∼2 ka. In contrast, the low-productivity conditions of the LGM resulted in slow soil accumulation rates, leaving ancient OC in a shallower position in the soil profile and allowing it to be easily eroded in the form of particulate OC (POC). Although the amount of total OC deposited in the lakebed during the LGM is small relative to post-glacial deposition, the majority is ancient, which leads to a relatively high average age offset of ∼9 ka. Finally, climate and environmental conditions of the MIS 3 interstadial were intermediate between those of the post-glacial and the LGM. As with post-glacial sediments, a relatively large amount of OC is present; however, the vast majority of it is ancient (more similar to the LGM), and it produces an average age offset of ∼6 ka. The Burial Lake radiocarbon record demonstrates the complexities of the thaw and mobilization of permafrost OC in arctic Alaska, including the balance between production, transport, deposition, remobilization, and preservation. This record highlights the importance of considering factors that both enhance and inhibit erosion (i.e. vegetation cover, lake level, precipitation) and the mechanisms of OC transport (i.e. subsurface flow or erosion) in predictions of future permafrost response to changes in climate.

The Role of Polyploidy in the Genetic Structure and Expansion of Lepisorus clathratus in the Qinghai-Tibetan Plateau and Hengduan Mountains.

Polyploidy plays a crucial role in plant evolution, particularly in shaping genetic diversity and geographic distribution. This study investigates the genetic diversity and distribution of Lepisorus clathratus (C. B. Clarke) Ching, a polyploid fern species endemic to the Qinghai-Tibetan Plateau and Hengduan Mountains. We sampled 586 individuals from 66 populations and identified three ploidy levels: diploid, tetraploid, and hexaploid. Flow cytometry and chloroplast DNA sequencing were used to assess ploidy variation and genetic structure. Tetraploid populations dominated the Hengduan Mountains and exhibited wider geographic ranges, while diploids were largely confined to the Qinghai-Tibetan Plateau. Molecular variance analysis revealed significant genetic differentiation among regions, with polyploid populations demonstrating higher cross-region migration rates compared with diploids, as evidenced by the historical gene flow analysis. Ecological niche modeling suggested that polyploids expanded more successfully in post-glacial periods, likely due to their greater ecological flexibility and capacity for long-distance colonization. These findings highlight the critical role of polyploidy in shaping genetic structure and species expansion, contributing to the understanding of plant adaptation in response to historical climatic changes.

Post-Marinoan paleoredox and paleoproductivity record in Puga cap carbonate: Implication for coastal life colonization at the Amazon Craton marginal Sea

The geochemical signatures in cap carbonate successions are critical records of paleoceanographic conditions following Snowball Earth events. These deposits offer insight into the shifts in redox conditions and the re-establishment of biogeochemical cycles during postglacial periods, providing a window into the evolving marine environments and potential drivers of early oxygenation. To track redox changes during this transition, we present improved high-resolution analyses of redox proxies across Puga cap carbonate (~635 Ma) on the Southern Amazon Craton, Brazil, allowing for the identification of temporal redox transitions during the post-Marinoan transgression. The depletion of trace elements, particularly redox-sensitive elements (RSEs), such as Mo, U, V, Cr, and Ni in microbialites formed in basal cap dolostone, was deposited under oxic conditions. Following the initial melting of Marinoan glaciers, microbial mats flourished and grew in a semi-restricted shallow marine environment in the coastal paleoenvironment along the Amazon cratonic margin, where nutrient-rich surface waters fueled primary productivity. In contrast, the increase in RSEs in upper wave-dominated dolostone facies indicates predominantly dysoxic conditions in continuous sea level rise, resulting in the drowning of these early microbial environments and the precipitation of cap limestones. The sequential oxic-dysoxic redox marks the transition from shallow sea to deepening CaCO3-oversaturated platform conditions. These results demonstrate an unequivocal synchronous relationship between the initial oxygenation of the Amazon margin and the local microbial mat flourishment shortly after the Marinoan glaciation.

Late Holocene high-resolution paleoenvironmental reconstruction from Beaver Lake in the northwest lowlands of the Olympic Peninsula, Washington (USA)

Fire is an essential component of the landscapes and forests of the Pacific Northwest, including the temperate rainforests of the Olympic Peninsula. Previous fire history reconstructions from the peninsula show that fire return intervals varied throughout the postglacial period, primarily in response to climatic changes and corresponding shifts in vegetation. However, much less is known about the fire history of the low-elevation forests of the Olympic Peninsula and the role of cultural fire regimes in these environments. The purpose of this study was to reconstruct the paleoenvironmental history of a low-elevation study site, Beaver Lake, located in the northwestern part of the peninsula. Using macroscopic charcoal, pollen, and sedimentological analyses of a ca. 3440-year-long record, we reconstructed a high-resolution record that shows fire activity was remarkably high during the late Holocene for an area considered part of a temperate rainforest. However, patterns of burning varied throughout the record, with the first third (ca. 3440 to 2350 cal yr BP) and last third (ca. 800 cal yr BP to the present day) recording much higher amounts of fire activity compared to the middle portion (ca. 2350 to 800 cal yr BP), which recorded very little fire activity. Larger and/or more severe fires that likely burned during multi-year droughts correlate with peaks in magnetic susceptibility and pollen trends that indicate substantial geomorphic responses and successional changes in forest structure following these events. Cooler temperatures and a wetter climate, indicated by nearby glacial advancements, may have staved off fire activity during the period of low fire activity. Cultural burning by the Indigenous tribes of the Olympic Peninsula likely contributed to the observed fire activity at Beaver Lake as nearby prairies were managed for resource procurement, indicated in particular by an increase in herbaceous morphotype charcoal during the past 800 years.

Evidence of conservative range in mountain grasses during past climate change: Only contractions or local expansions possible

The ongoing biodiversity crisis associated with anthropogenic global warming has especially severe effects on mountain and cold-adapted species. The lesson from the postglacial period can provide examples for future predictions, but scenarios of the range shift of mountain species are not fully explored. Different stories could happen if a species achieved long-distance dispersal and reached lowland locations or if survived only in mountains, during the ice age. In the case of grasses, a key role in range dynamics is played also by polyploidy. Due to their enhanced genetic and physiological plasticity, polyploids are thought to be less likely to become extinct during global changes.The present study explores the postglacial range shifts in two Festuca species, which differ in range size (endemic vs widespread) and in ploidy level (diploid vs mixed-ploidy). We used phylogeography and distribution models to analyze changes in potential range during global warming. We achieved a sophisticated prediction by using modeling based on climate and edaphic factors.Our findings indicate a low level of gene flow between populations, irrespective of variation in distance, range size and ploidy. Slightly shorter genetic distances were observed between the tetraploid populations compared to the diploids. Our data indicates that diploids adapted to cold conditions were restricted to mountains during glaciations, while polyploids spread more widely during cold periods. Nevertheless, since the LGM it appears that all studied ranges have been rather conservative, with maybe some local contractions and expansions, especially in tetraploids. Moreover, tetraploids demonstrated the most stable potential range during climate warming.The studied cases are characterized by individual and complex range dynamics dependent on local conditions and cytotype behaviour. However, generally speaking, studied mountain species demonstrate a conservative range, which places them at risk of extinction during global warming due to the lack of effective means of escape.

Genetic divergence and ecological adaptation of an eastern North American spring ephemeral Sanguinaria canadensis

AbstractAimDescription of the driving forces for genetic divergence is important for understanding spatial pattern of biodiversity and development of conservation plans. Paleo‐climate, geographical barriers and habitat heterogeneity are considered to be the main influential factors; however, an integrative study is still lacking to reveal their interactions.LocationEastern North America.MethodsHere, we generated MIG‐seq SNPs of 403 Sanguinaria canadensis samples and seven plastome data. The methods of phylogeography and landscape genomics were applied to infer their genetic divergence, demography, species distribution modelling, ecological differentiation and local adaptation.ResultsWe identified three distinct genetic lineages corresponding to geographical distributions isolated by the Appalachian Mountains and the Mississippi River. Ecological niche modelling and population demographic inference demonstrated that the response of S. canadensis to Pleistocene climate changes was consistent with the pattern of southward contraction during the ice age and northward recolonization during the inter−/postglacial period. Isolation in multiple southern refugia was a key factor resulting in the genetic divergence, whereas secondary contact triggered by repeated range shifts allowed gene flow among different lineages. A greater effect of isolation‐by‐environment than isolation‐by‐distance was founded, which suggested heterogeneous environment was also a promotor of genetic differentiation. Candidate adaptive loci related to transposable elements were identified under the influence of divergent environmental selection. Ecological niche divergence also reflected adaptation to different environments.Main ConclusionsThis study revealed that genetic divergence has occurred within S. canadensis populations under the combined effect of paleo‐climate, geographical barriers and habitat heterogeneity, and emphasized the necessity of establishing different conservation units in future biological conservation and management work.

Holocene vegetation dynamics of the Yamal Peninsula based on palaeobotanical data from relict peat bog deposits

We have performed a comprehensive paleoecological study of the peat bog deposits from six localities of the Seyakha, Yuribey and Khadytayakha rivers in the subarctic tundra zone on the Yamal Peninsula. Radiocarbon dating, as well as pollen and plant macrofossil analyses were used to track the chronological changes of the plant communities on the peninsula along the North-South transect in the Late Glacial and Postglacial periods. It was found that open woodland with tree birch and spruce existed in the Yuribey river valley during the Bölling-Allerød interstadial (between 14.7 and 12.7 cal. ka BP). Shrub tundra with Betula nana was widespread in this area during the Younger Dryas, between 12.6 and 11.7 cal. ka BP, under climatic conditions similar to modern ones. The spread of arboreal species (Betula sect. Betula, Picea obovata, Larix sibirica) and associated boreal herbaceous plants began later (between 10.2 and 9.7 cal. ka BP) as climatic conditions improved. The most favorable conditions for tree birch and larch existed in the Seyakha river valley between 10.2 and 8.7 cal. ka BP, whereas the best conditions for the same species and spruce in the Yuribey river valley were observed between 10.2 and 4.4 cal. ka BP. It was much warmer than it is today, and open woodland or even closed forests were widespread. Forest degradation and spread of open landscapes with tundra communities occurred in the Seyakha river valley after 8.7–8.5 cal. ka BP and in the Yuribey river valley after 4.7–4.3 cal. ka BP. Climatic conditions became similar to modern ones. Today, arboreal species grow in the Khadytayakha river valley, forming extrazonal forest communities in the subarctic tundra zones.

New digital bathymetric model of Lake Onego (Verhne-Svirskoe reservoir): development, verification, application

A new digital bathymetric model of Lake Onego (Verhne-Svirskoe Reservoir) has been developed based on navigation charts. Verification of the model was carried out by comparing the modeled bathymetry with the cartographic materials, echo sounder measurements, and previous bathymetric models. Spatial resolution of the developed model is 50 m in plane and 2 m in depth. Despite these identified deviations in depth, the model has a good agreement between raster values and measured depth, which can be considered sufficient to calculate the main morphometric characteristics of the lake and solve other applied tasks. Morphometric characteristics of the water body (within the boundaries of the lake and reservoir separately) and its limnic regions were updated based on the developed digital model. In particular, values of the water area, water volume, average and maximum depth, littoral area (up to isobaths 2, 5, and 10 m) of limnic regions were specified for the first time based on the developed bathymetric model. The Central and South Onego are the largest regions by water area, while the Large Onego, the Central part of the lake and the Povenets Bay are the deepest. The largest areas of the lake in terms of the littoral area value are the Central part and the South Onego, while the maximum percentage of the littoral area was observed in the Kizhi skerriesand for most of thenorthern bays of the lake. The digital bathymetric model was applied to reconstruct the lake development in the post-glacial period, as well as in mapping the Quaternary deposits of the lake basin. The digital model can also be used as a basis for 3D modeling of geomorphologic, thermo-hydrodynamic and sedimentation processes.

Loess transportation surfaces in west-central Wisconsin, USA

Abstract The concept of a loess transportation surface portends that saltating sands deflate silt/dust and send them into suspension. This process continues until a topographic barrier stops the saltating sand, allowing loess deposits to accumulate downwind. This paper reports on loess transportation surfaces in west-central Wisconsin, USA. During the postglacial period, cold, dry conditions coincided with strong northwesterly winds to initiate widespread saltation of freely available sands, deflating any preexisting loess deposits. Large parts of the study area are transportation surfaces, and lack loess. Loess deposits were only able to accumulate at “protected” sites—downwind from (east of) topographic barriers, such as isolated bedrock uplands and the north-to-south flowing Black River. Loess in locations from these barriers is thicker (sometimes >5 m) than would be expected, and in places has even accumulated above preexisting loess deposits. For example, downwind (east) of the Black River, most of the low-relief landscape is covered with ≈40–70 cm of silty loess, even though it is many tens of kilometers from the initial loess source. Upwind of the river, on the transportation surface, the low-relief landscape is only intermittently mantled with thin, scattered deposits of silty-sandy eolian sediment, and generally lacks loess.

The history of dryland and wetland vegetation in the Russian-Finnish Friendship Nature Reserve in the Post-Glacial period

The history of dryland and wetland vegetation in the Russian-Finnish Friendship Nature Reserve in the Post-Glacial period

An 8500-year history of climate-fire-vegetation interactions in the eastern maritime black spruce–moss bioclimatic domain, Québec, Canada

ABSTRACT The eastern, maritime portion of the black spruce – moss bioclimatic domain in Québec (Canada) is characterized by large wildfires with low occurrence. However, it is still poorly understood how climate–fire interactions influenced long-term vegetation dynamics in the boreal forest of eastern Québec. The long-term historical climate–fire–vegetation interactions in this region were investigated using a multiproxy (chironomids, charcoal, and pollen) paleoecological analysis of an 8500-year sediment core. Chironomid-inferred August air temperatures suggest that the warm Holocene Thermal Maximum (HTM; between ca. 7000–4000 cal yr BP) shifted to the cooler Neoglacial period (4000 cal yr BP to present), consistent with other temperature reconstructions across Québec. The shift to spruce-moss forest dominance around 4800 cal yr BP occurred nearly a thousand years before the climatic shift to the Neoglacial period and rather coincided with a shift from frequent low-severity small fires to infrequent but large and severe fire events. Our results suggest that long-term changes in the summer temperature are probably not the main factor controlling fire and vegetation dynamics in eastern Québec. It seems that, throughout the postglacial period, summer temperatures never fell below a threshold that could have induced a significant vegetation response.

Increasing terrigenous input into the continental margin seawater during the late Ediacaran, North China

The late Ediacaran period encompasses widespread glacial deposits and early animal radiation. The temporal and spatial context of these events is not well established. The possible links between the glacial deposits and late Ediacaran fossils are critical for understanding the co-evolution of early animals and marine environments. This study presents a detailed geochemical reconstruction from the Tuerkeng Formation on the western margin and the Dongpo Formation on the southern margin along the North China Craton (NCC). The two fossiliferous late Ediacaran formations cover a critical interval between the end of the Zhengmuguan-Luoquan glaciation and the occurrence of late Ediacaran tubular fossils (e.g., Shaanxilithes). The two formations' similar and intermediate CIA values indicate moderate weathering under a warm and humid climate. Stratigraphic covariation of water-insoluble elements in samples from Tuerkeng and Dongpo formations suggest a rapid input of terrestrial materials at the beginning of deglaciation, and these terrestrial materials continued to be input into the shallow marine environment along the western and southern margins of NCC during the deposition of the two formations. Accompanied by the continental weathering and erosion of fresh rocks during the postglacial period of late Ediacaran, abundant nutrients as well as the terrigenous materials would be continuously transported into the continental margin seawater, which may ultimately lead to the rise of the Ediacaran biota. Our results provide new insights into paleoenvironment conditions along the continental margin of NCC and highlight the critical role of the postglacial terrigenous input in the evolution of early animals.

Origin of the Badar Sand Field and the late pleistocene tectonic movements in the Tunka depression, the Baikal Rift Zone, Eastern Siberia

The Badar Sand Field is a geomorphological phenomenon representing a dome structure that dominates the topography of the subsiding Tunka Depression in the SW Baikal Rift. Many interpretations of its origin, including tectonic uplift, have been proposed, but the question remains open. We propose a new model to explain its genesis, based on a thorough analysis of both new and previously published geomorphological and sedimentological data. We suggest that the accumulation of the Badar Sand Field occurred in two stages: aquatic and aeolian. The lower part of the sandy deposits accumulated during the long-term existence of a landslide-dammed paleolake within the Tunka Depression. The upper part was formed after the drainage of the paleolake due to aeolian redeposition of sands. New results of OSL-dating from the vertical 40-m geological cross-section “Badar” showed that the accumulation of lake sediments occurred in the period 24–15 thousand years ago (MIS2). Based on the analysis of satellite images, we modeled the paleolake and determined that it arose as a result of landslides that dammed the antecedent section of the Irkut river valley in the Elovsky Spur. The analysis of the Irkut river terraces showed the absence of tectonic uplift within the Tunka Depression in the Holocene. The incision of the Irkut River at 40–90 m into the Badar dome occurred as a result of the restoration of equilibrium in the longitudinal profile of the river due to changes in sedimentation conditions in the post-glacial period.

Subalpine ”pinification”: Early signs of a pending and distinct biogeographic shift in the Swedish Scandes: Review and updates

This study focuses, by in situ records and long-term observations, on recent (post-Litte Ice Age), arboreal change in a mountain birch dominated (Betula pubescens ssp. czerepanovii) valley in the Swedish Scandes. During the early Holocene thermal optimum and up to the onset of the mid-Holocene Neoglaciation, Scots pine (Pinus sylvestris) dominated the tree cover of this valley and formed the treeline ecotone adjacent to the early alpine tundra. Subsequently, and consistent with progressive cooling until the late 19th century, prevailing pine stands demised and opened for landscape-level expansion of birch and spruce (Picea abies). A short and distinct break in that process took place by the Medieval Climate warming phase, about 1000-800 years before present. Subsequently, during pre-industrial time, temperatures reached their lowest levels of the entire post-glacial period. This was the so-called Little Ice Age, which ended the long-term Holocene cooling. That cold-climate epoque was broken by the late-19th and early 20th century. Thereafter and up to the present-day, temperatures in the study region (summer and winter) have increased by slightly less than 2 °C. As a consequence, treelines of all species have advanced by a maximum of more than 200 altitudinal meters. Pine displays the most persistent expansion, particularly over the past few decades. “Falangist” occurrences appear in the pure birch forest, tens of kilometers and hundreds of meters, respectively, beyond and above the outposts by the early 20th century. Occasionally, scattered young pine trees now grow close to the birch forest limit and somewhat above. In particular, at sites where pine stands demised during the Little Ice Age, c. AD. 1300-1850, prolific regeneration and insignificant winter mortality are recorded over the past 15 years. In comparison, birch and spruce provide no analogous signs of recent expansion. It may be hypothesized that unabated climate warming and corresponding arboreal progression will profoundly transform the plant cover of this valley, and others alike, into the same pine-dominated state that prevailed during the early Holocene. In other words, a new biogeographic zonation pattern may be on the rise, with pine back as the dominant subalpine species. This option is focused by continued monitoring.

Fagus diversification in China in relation to East Asian monsoon evolution

When and how the extraordinary species diversity in subtropical East Asia formed is intensely debated, and the available evidence is often inconsistent. In this study, we evaluate the effects of pre- and post- Quaternary events on the evolutionary and biogeographic history of Chinese beech (Fagus species that now occur in China) to gain new insights into the historical establishment and future fate of the East Asian subtropical forest (EASF). A series of approaches and datasets were used to reconstruct biogeographic and evolutionary history of the Chinese beech. They include phylogeography based on the polymorphisms of the complete chloroplast genomes, species distribution models, and a large palaeobiogeographic dataset including 59 pre-Quaternary fossil records, 296 Quaternary fossil records and 3515 modern pollen records. Our multidisciplinary approach suggests that (i) Chinese beech has dispersed to subtropical East Asia and diversified in the early Miocene when the Asian monsoon (AM) intensified; (ii) the last post-glacial warming resulted in limited poleward displacement but significant contraction at southern and lower elevations; (iii) the poleward dispersal of Chinese beech was limited by drought in the early growing season in temperate China, controlled by the East Asian summer monsoon. Our results support the hypothesis that the establishment of the EASF is closely related to the evolution of the AM. More importantly, we suggest that with continued climate warming (e.g., during the last post-glacial period or under current climate change), the monsoon probably hindered rather than promoted the persistence of deciduous beech species, resulting in a decline in species richness.

Vertical leaching of paleo-saltwater in a coastal aquifer–aquitard system of the Pearl River Delta

Marine transgressive and regressive processes have promoted the formation of deltas and estuaries from the postglacial period, and the coastal aquifer-aquitard system can be identified based on the complicated sedimentary environments in the river delta. The groundwater system is usually composed of freshwater and paleo saltwater, and the vertical leaching of paleo saltwater from aquitard to fresh aquifer occurs due to density difference and gravity effect. In this study, radium quartet and radon were used as the tracers for groundwater due to their different half-lives. We constructed a radium reactive transport model considering the vertical leaching of paleo saltwater in a deltaic aquifer-aquitard system and then applied it in the Pearl River Delta (PRD). The activity ratio of 224Ra to 228Ra was used to characterize whether the groundwater system was controlled by α-recoil or sufficient 232Th under fully weathered condition, and results showed that the deltaic system was well weathered and the vertical leaching of paleo saltwater inhibited the α-recoil input and increased the decay of the sorbed parent nuclide in the aquifer. After incorporating the vertical leaching of saltwater in the model, the value of retardation factor in the shallow aquitard evidently increased, meaning that the leaching of salty porewater into the aquifer greatly affected the adsorption–desorption process of radium isotopes in the aquitard, and the value of retardation factor reduced to the lower limit in the basal aquifer, indicating that the desorption process was determined by the vertical leaching of saltwater here. After considering the effect of vertical leaching, the estimated water transit time in the aquifer was decreased and the groundwater discharge rate was increased, and the converse results were obtained in the aquitard. The proposed radium reactive transport model advances the understanding of the salinization process in coastal aquifers through vertical migration and facilitates the understanding of freshening process of paleo saltwater in the river delta with similar hydrogeological settings.

Incised-valley filling sedimentation in a small river valley of a wave-dominated, embayed coast in response to Holocene sea level rise, Yeongil Bay, Southeastern Korea

Incised-valley infill deposits are closely related to sea level changes during the post-glacial period of the late Quaternary and are an important topic in sea level history. In Asia, there are many large river basins that receive large amounts of sediment from the land, and the infilling deposits of incised valley systems have been well studied. Yeongil Bay is a semi-enclosed, funnel-shaped topographic feature on the east coast of the Korean Peninsula, located in the southwestern part of the East Sea (Sea of Japan). The Hyeongsan River, a small river flowing into Yeongil Bay, is flows perpendicular to the East sea. During the last glacial maximum (LGM), when the sea level was >120–130 m lower than at present in the Korea Strait, inflowing river processes are thought to have formed incised valleys. In this study, the sediment depositional patterns of incised valley fill since the LGM were examined by analyzing the sedimentary facies, optically stimulated luminescence (OSL) dates, and radiocarbon dates by accelerated mass spectrometry (AMS) of three sediment cores in Yeongil Bay. The infilling sequence consists of sediments from channel lag (>12 ka) and meandering river (12–10 ka), wave-dominated estuary (12–7.8 ka), and wave-dominated delta (7.8–0 ka) systems in ascending order. The barrier appear only in the outer part of Yeongil Bay. The barrier emerged from eroding estuary systems at 8.5 ka. Millennial-scale isochrons based on OSL and radiocarbon dates showed that fluvial and estuary systems were deposited in retrogradation and delta systems were deposited in progradation since LGM. The modern delta of the Asian large rivers were initiated by a decreasing rate of sea level rise during the mid-Holocene, and consideration of this is important for RSL. This study emphasizes the importance of accommodation capacity as much as sediment discharge as a factor in the timing of delta initiation. This study provides important insights into the incised-valley infill deposits and past environmental conditions, and may help to gain a better understanding of how coastal environments have changed with sea level changes.

Carbon and nutrient pools and fluxes in unmanaged mountain Norway spruce forests, and losses after natural tree dieback

Forest areas infected by insects are increasing in Europe and North America due to accelerating climate change. A 2000–2020 mass budget study on major elements (C, N, P, Ca, Mg, K) in the atmosphere-plant-soil-water systems of two unmanaged catchments enabled us to evaluate changes in pools and fluxes related to tree dieback and long-term accumulation/losses during the post-glacial period. A bark-beetle outbreak killed >75 % of all trees in a mature mountain spruce forest in one catchment and all dead biomass was left on site. A similar forest in a nearby catchment was only marginally affected. We observed that: (1) the long-term (millennial) C and N accumulation in soils averaged 10–22 and 0.5–1.1 kg ha−1 yr−1, respectively, while losses of Ca, Mg, and K from soils ranged from 0.1 to 2.6 kg ha−1 yr−1. (2) Only <0.8 % and <1.5 % of the respective total C and N fluxes entering the soil annually from vegetation were permanently stored in soils. (3) The post-disturbance decomposition of dead tree biomass reduced vegetation element pools from 27 % (C) to 73 % (P) between 2004 and 2019. (4) Tree dieback decreased net atmospheric element inputs to the impacted catchment, and increased the leaching of all elements and gaseous losses of C (∼2.3 t ha−1 yr−1) and N (∼14 kg ha−1 yr−1). The disturbed catchment became a net C source, but ∼50 % of the N released from dead biomass accumulated in soils. (5) Despite the severe forest disturbance, the dissolved losses of Ca and Mg represented 52–58 % of their leaching from intact stands during the peaking atmospheric acidification from 1970 to 1990. (6) Disturbance-related net leaching of P, Ca, Mg, and K were 4, 69, 16, and 114 kg ha−1, respectively, which represented 7–38 % of the losses potentially related to sanitary logging and subsequent removal of the aboveground tree biomass.

Implications of population changes among the Arvicolinae (Rodentia, Mammalia) in El Mirón Cave (Cantabria, Spain) for the climate of the last c. 50,000 years

The El Mirón Cave site in Spain has one of the most complete archaeological and palaeontological records of the Late Pleistocene in the Iberian Peninsula, encompassing most of the last c. 50,000 years. Among other studies, the fossiliferous record has allowed the development of various interpretations of faunal and climatic changes during this period of time in the northern Atlantic region of the Iberian Peninsula. The addition of more radiocarbon dates from El Mirón Cave make it possible to revise some of the interpretations of the micromammal sequence carried out earlier for this major site. The record of small mammals is one of the most used tools to study the climate of the past, and among them the several Arvicolinae species are of great importance for the study of Quaternary climatic variations, due to their adaptations to a great diversity of habitats. New methodologies such as ancient DNA and geometric morphometric analyses now permit us to conduct a review of the Arvicolinae species previously described at this site and better to differentiate between species with similar morphologies, like Microtus arvalis and M. agrestis. We also identified the presence of a species not recorded before in El Mirón, Terricola pyrenaicus. With the study of the Arvicolinae species associations, we reaffirm the climate variations originally described in this deposit, indicating in detail how the successive changes in temperature and environment took place throughout the course of the late Last Glacial and early Postglacial periods (Marine Isotope Stages 3–1).