Basal Peat Research Articles

Holocene initiation and expansion of the southern margins of northern peatlands triggered by the East Asian summer monsoon recession

Northern peatlands represent one of the largest biospheric carbon reservoirs in the world. Their southern margins act as new carbon reservoirs, which can greatly influence the global carbon dynamics. However, the Holocene initiation, expansion and climate sensitivity of these peatlands remain intensely debated. Here we used a compilation of basal peat ages across six isolated peatlands at the southern margins of northern peatlands to address these issues. We found that the earliest initiation event of these peatlands occurred after the Younger Dryas (YD, 12,800–11,700 years ago) period. The second initiation event and rapid expansion occurred since 5 ka cal. BP. The recession of East Asian summer monsoon (EASM) during the YD period and at around 5 ka cal. BP likely played a major role in controlling the initiation and expansion of these peatlands. The rapid expansion of these peatlands possibly contributed to the significant increases in atmospheric methane concentrations during the late Holocene because of the minerotrophic fens status and rapid expansion of them. These ecological processes are different from northern peatlands, indicating the special carbon sink and source implications of these peatlands in the global carbon cycle.

A revision of the British chronostratigraphy within the last glacial-interglacial cycle based on new evidence from Arclid, Cheshire UK

Of the 24 Greenland interstadials in the Last Glacial-interglacial cycle (LGIC) only five are conventionally recognised in Britain. This paper aims to improve understanding of the LGIC in Britain from a site at Arclid, Cheshire. Sediments were characterised and luminescence used to establish a chronology. This found that the Chelford Sand Formation spans 77-47 ka with sand deposited initially by aeolian but later by fluvial transportation. Coleoptera and Diptera from the basal peat lens provided a reconstruction for a heather-rich heathland environment grazed by large herbivores, with summer temperatures between 13 and 18 °C, and winter temperatures between −14 and 1 °C. Flies included the earliest records of the blood-sucking horsefly Haematopota pluvialis, and the soldierfly Chloromyia formosa. The overlying Stockport Sand Formation was deposited fluvioglacially between 47-41 ka with the upper Stockport Till formed by the advance of the last British icesheet after ∼33 ka. Stenothermic beetle analysis from Arclid indicate similarities with results from other British mid LGIC sites, some of which are at or beyond the limit of radiocarbon dating and may be of a similar age to Arclid. Basal organic sediments found at Arclid along with other reassigned sites are proposed as a new Arclid Interstadial. A revised British LGIC chronostratigraphy has the Wretton, Chelford and Brimpton Interstadials and the previously suggested but not widely recognised Cassington Interstadial. The Arclid Interstadial occurred after these, but prior to the Upton Warren Interstadial complex. This closes the previous gap in interstadials between the Brimpton Interstadial and the Upton Warren Interstadial complex within the British chronostratigraphy.

A 5000-year record of relative sea-level change in New Jersey, USA

Stratigraphic data from salt marshes provide accurate reconstructions of Holocene relative sea-level (RSL) change and necessary constraints to models of glacial isostatic adjustment (GIA), which is the dominant cause of Late-Holocene RSL rise along the U.S. mid-Atlantic coast. Here, we produce a new Mid- to Late-Holocene RSL record from a salt marsh bordering Great Bay in southern New Jersey using basal peats. We use a multi-proxy approach (foraminifera and geochemistry) to identify the indicative meaning of the basal peats and produce sea-level index points (SLIPs) that include a vertical uncertainty for tidal range change and sediment compaction and a temporal uncertainty based on high precision Accelerator Mass Spectrometry radiocarbon dating of salt-marsh plant macrofossils. The 14 basal SLIPs range from 1211 ± 56 years BP to 4414 ± 112 years BP, which we combine with published RSL data from southern New Jersey and use with a spatiotemporal statistical model to show that RSL rose 8.6 m at an average rate of 1.7 ± 0.1 mm/year (1σ) from 5000 years BP to present. We compare the RSL changes with an ensemble of 1D (laterally homogenous) and site-specific 3D (laterally heterogeneous) GIA models, which tend to overestimate the magnitude of RSL rise over the last 5000 years. The continued discrepancy between RSL data and GIA models highlights the importance of using a wide array of ice model and viscosity model parameters to more precisely fit site-specific RSL data along the U.S. mid-Atlantic coast.

Investigation of coastal environmental change at Ruddons Point, Fife, SE Scotland

Ruddons Point, on the Firth of Forth coastline, Scotland, is a laterally extensive terrace of glacial and marine sediment deposits raised above current sea-level, situated near to Kincraig Point, a key site that records a series of stepped erosional platforms carved into the local bedrock, interpreted as post Last Glacial Maximum palaeoshorelines. The deposits at Ruddons Point continue inland, with exposures of the raised sands and gravels cut by the local river, the Cocklemill Burn. The site provides an opportunity to examine the depositional history through the Late Devensian and Holocene. Geophysical survey aided in interpreting characteristics of subsurface sediments such as the transition between the younger saltmarsh sediments and older underlying sands and clays below, which slope in a northerly direction. A chronology obtained through optically stimulated luminescence (OSL) dating spans from c. 29 ka for sands and clays at an elevation of −0.66 mOD to surface windblown sands at <300 years, at an elevation of 8.45 mOD. A basal peat, dated by radiocarbon dating to the early Holocene at c. 9.2 ka, formed prior to the Main Postglacial Transgression. Dating of inland raised marine deposits along the Cocklemill Burn records dates ranging from c. 8.9 to c. 4.3 ka. The raised marine deposits of Ruddons Point range from c. 8.1 to c. 2.9 ka, deposited unconformably on glacial tills and clays. This multidisciplinary field study builds depositional scenarios utilizing two dating methods, spanning the last c. 29 ka, to better understand coastal evolution for a region which has experienced complex relative sea-level variations. Supplementary material : Supplementary data related to this research article is available at https://doi.org/10.6084/m9.figshare.c.6080999 Thematic collection: This article is part of the Early Career Research collection available at: https://www.lyellcollection.org/topic/collections/early-career-research

Early Holocene relative sea-level changes on the central east coast of the Yellow Sea

Paleo-relative sea level (paleo-RSL) records in the far-field are essential for constraining models for global sea level change. We compared the early Holocene RSL history on the central east coast of the Yellow Sea with those of Bohai Bay, the northernmost point, and Gunsan Bay, south of the study area. A multi-proxy approach, including lithostratigraphy, biostratigraphy, combined with radiocarbon and OSL dating, facilitated the generation of 28 sea level index points (SLIPs) using 11 borehole samples. Excavation of basal peat of the 10.3 ka in the study area established that the observed RSL of the transgression in the early Holocene was −14.88 m, which was much shallower than −27.9 m in Gunsan Bay at 9.8 ka and was similar to −17.3 m in Bohai Bay at 9.7 ka. The observed RSL and the prediction curves of the study area were compared with those of other areas. In Gunsan Bay, the early Holocene GIA prediction curves are consistent with those observed, which seems to be the result of a “low setting” of the crust thickness and mantle viscosity. Therefore, it is presumed that the significant difference in the elevations observed between the study area and Gunsan Bay is caused by the levering effect owing to the difference in the tectonic characteristics. Conversely, other observed groups during 7.6–6 ka have a similar slope to the prediction curve of the Early Holocene in the study site, and it is thought that the sediments of the early Holocene were eroded and re-deposited along the channel. These results are of great importance as data of sea level variability in the far field due to glacial collapse and as data for the GIA modeling process.

Dating basal peat: The geochronology of peat initiation revisited

Attributing the start of peat growth to an absolute timescale requires dating the bottom of peat deposits overlying mineral sediment, often called the basal peat . Peat initiation is reflected in the stratigraphy as a gradual transition from mineral sediment to increasingly organic material, up to where it is called peat. So far, varying criteria have been used to define basal peat, resulting in divergent approaches to date peat initiation. The lack of a universally applicable and quantitative definition, combined with multiple concerns that have been raised previously regarding the radiocarbon dating of peat, may result in apparent ages that are either too old or too young for the timing of peat initiation. Here, we aim to formulate updated recommendations for dating peat initiation. We provide a conceptual framework that supports the use of the organic matter (OM) gradient for a quantitative and reproducible definition of the mineral-to-peat transition (i.e., the stratigraphical range reflecting the timespan of the peat initiation process) and the layer defined as basal peat (i.e., the stratigraphical layer that is defined as the bottom of a peat deposit). Selection of dating samples is often challenging due to poor preservation of plant macrofossils in basal peat, and the representativity of humic and humin dates for the age of basal peat is uncertain. We therefore analyse the mineral-to-peat transition based on three highly detailed sequences of radiocarbon dates, including dates of plant macrofossils and the humic and humin fractions obtained from bulk samples. Our case study peatland in the Netherlands currently harbours a bog vegetation, but biostratigraphical analyses show that during peat initiation the vegetation was mesotrophic. Results show that plant macrofossils provide the most accurate age in the mineral-to-peat transition and are therefore recommendable to use for 14 C dating basal peat. If these are unattainable, the humic fraction provides the best alternative and is interpreted as a terminus-ante-quem for peat initiation. The potential large age difference between dates of plant macrofossils and humic or humin dates (up to ∼1700 years between macrofossil and humic ages, and with even larger differences for humins) suggests that studies reusing existing bulk dates of basal peat should take great care in data interpretation. The potentially long timespan of the peat initiation process (with medians of ∼1000, ∼1300 and ∼1500 years within our case study peatland) demonstrates that choices regarding sampling size and resolution need to be well substantiated. We summarise our findings as a set of recommendations for dating basal peats, and advocate the widespread use of OM determination to obtain a low-cost, quantitative and reproducible definition of basal peat that eases intercomparison of studies. • We present three detailed radiocarbon sequences of the mineral-to-peat transition. • Basal peat needs to be clearly defined based on a quantitative reproducible parameter. • Peat initiation is a process of a certain timespan rather than an event. • Plant macrofossil dates are most accurate, humic/humin dates are likely too young. • A conceptual framework and recommendations for dating peat initiation are presented.

The influences of volcanic eruptions on the development of peatland: A case study from the Changbai Mountains, Northeast Asia

Peatlands often develop around active volcanoes. However, little research has been conducted on the impacts of volcanic eruptions on peatland development. Here, we investigated the impacts of Holocene volcanic eruptions of the Changbaishan Volcanic field on the development of Dongfanghong peatland by using basal peat ages, geochemical and palaeoecological data. Analytical results suggest that lateral expansion process of the Dongfanghong peatland was due to paludification. This process was mainly controlled by complex volcanic lava terrain rather than climatic changes. Volcanic rocks provided an impervious horizon for the establishment of peat plants. Thick tephra layers resulted in the retrogressive succession of vegetation community that changed from mesomoor community dominated by the mixture of herbs and Sphagnum into the lowmoor community dominated by herbs. The subsequent high carbon accumulation rates were induced through the phosphorus release from tephra layers and formation of a impervious horizon. These results suggest that volcanic eruptions can significantly influence peatland development.

Radiocarbon Dating of the Nyixoi Chongco Rock Avalanche, Southern Tibet: Search for Signals of Seismic Shaking and Hydroclimatic Events

Landslides are important agents of the surface processes involved in the growth of mountainous topography. Dating prehistoric landslides is a prerequisite for establishing the relationships between prehistoric slope instability, and past climatic regimes and paleoseismic records. The Nyixoi Chongco rock avalanche (NCRA) is located in the Angang graben within the N–S trending rift zone in southern Tibet. It represents a giant prehistoric mass wasting event that was characterized by exceptional mobility and a large volume. However, the exact emplacement time and origin of the NCRA are still controversial. In this study, we conducted 14C dating of peat layers and snail shells to constrain the emplacement age of the NCRA. The 14C ages of the organic material and plant remnants in the basal peat layer are 1272–1389 and 1299–1404 cal AD, respectively. The 14C ages of aquatic snail shells and the bog overlying the rock avalanche are 425–565 and 1022–159 cal AD, respectively. These results indicate that the NCRA consisted of at least two separate and distinct events, instead of the single event suggested by previous studies. Based on field investigations and temporal correlations, we infer that there may be no paleoseismic records in the Angang graben that would corroborate a coseismic trigger for the NCRA. Therefore, we suggest that the 14C ages of the sediments below and above the landslide rocks should be interpreted carefully. The 14C ages alone do not provide sufficient evidence to infer the true trigger of the NCRA event.

Insights into Holocene relative sea‐level changes in the southern North Sea using an improved microfauna‐based transfer function

ABSTRACTIn light of global warming and rising relative sea level (RSL), detailed reconstructions of RSL histories and their controlling processes are essential in order to manage coastal‐protection challenges. This study contributes to unravelling Holocene RSL change on the East Frisian North Sea coast in high resolution and with a new approach for the German Bight. For the first time, a transfer function (vertical error: 29.7 cm ≙ ~11% of the mean tidal range) for RSL change based on a combined training set of benthic foraminifers and ostracods from the back‐barrier tidal basin of Spiekeroog is applied to the Holocene record of the back‐barrier tidal basin of Norderney. The resulting RSL curve for the Norderney tidal basin is corrected for decompaction and shows a deceleration in RSL rise between 6000 and 5000 cal bp.The smallest possible error envelope (~1 m) results from the good suitability of salt‐marsh layers between 5000 and 4000 cal bp.The RSL curve provides an approach towards the closure of the common data gap of peat‐based curves for the southern North Sea related to a lack of basal peats in the youngest age range, and verifies regional differences in glacial isostatic adjustment.

Middle Pleistocene to Holocene palaeoenvironmental evolution of the south-eastern Alpine foreland basin from multi-proxy analysis

The multidisciplinary analysis of two long sedimentary successions of continental and shallow marine deposits from the Venetian plain (NE Italy) provides new data on the stratigraphic architecture and the landscape evolution of the south-eastern Alpine foreland basin during the last 210–220 ka, with further evidences of a warm temperate phase older than MIS 8.We present and discuss a detailed multi-proxy data set from these successions (GER1 and CB cores). The results of stratigraphic, palynological and micropalaeontological analyses are cross-interpreted, showing the potentiality of building a composite section of two close continental successions within the same alluvial system, the Brenta megafan, with 15 km distance between cores along a downstream direction. The chronology of the upper part of the cores is supported by radiocarbon dating, showing the presence of Last Glacial Maximum (LGM) and post-LGM fluvial deposits. Lower down, the estimated chronology relies on the tight integration between palynostratigraphy and lithostratigraphy, on the recognition of main unconformities, as well as on the correlation with other regional biostratigraphic records and the Northern Hemisphere/global isotopic record.The only marine transgression recorded in the studied successions is attributed to the MIS 7.3 and represents the basal tiepoint for the correlation between the two cores. Below the MIS 7.3 transgressive marine surface there is a fluvial succession with weakly-developed palaeosoils and a poor pollen content suggesting cold climate (possibly MIS 8), that lies on top of a thick peat layer showing palynological evidence of a warm temperate climate. The occurrence of well-preserved Pterocarya and Carya pollen in the basal peat level (GER1 core) is compared to that of other pollen sequences in Europe, providing new insights for the chronological framing of the problematic last occurrence of these taxa in the southern alpine area.Whilst mixed temperate forest persisted throughout MIS 7c-7a, conifers spread during MIS 6. By this time, a glaciofluvial aggradation phase is recorded, highlighting the strong relationship between glacial maxima and alluvial aggradation in the Venetian plain. None of the drilling sites were reached by the Last Interglacial sea transgression. However, the Eemian forest signature is well recorded in CB core, and the following Early to Middle Würm stadial-interstadial sequence is clearly outlined thanks to the joint analysis of the two successions. Broad-leaved thermophilous forests disappeared at the end of the Early Würm and only Pinus and Betula persisted throughout the LGM, during which a chronologically well-constrained glaciofluvial aggradation occurred. The last depositional event corresponds to the post-LGM cut-and-fill of fluvial incised valleys in GER1 core, and to soil evolution and very thin burial by Brenta River fluvial deposits in CB core. The comparison between the results of this study with data of previous deep cores in the distal alluvial plain remarks an increasing long-term subsidence towards Venice area.

Holocene relative sea-level data for the East Frisian barrier coast, NW Germany, southern North Sea

AbstractCollecting sea-level data from restricted coastal areas is essential for understanding local effects on relative sea level. Here, a revised relative mean sea-level curve for the area of the East Frisian island Langeoog, northwestern Germany, for the time period from 7200 cal BP until Recent is presented. The revision is based on the reinterpretation of previously published and unpublished data following the HOLSEA standardisation of data handling. Altogether 68 sea-level data taken from 32 cores and outcrops from Langeoog, its back-barrier and the adjacent mainland, which have been collected since the 1950s for mapping and landscape reconstruction purposes, are presented. The age constraints, derived from radiocarbon ages of basal peat, intercalated peat and molluscs and optical dating of tidal deposits, were evaluated in terms of the HOLSEA sea-level protocol and their stratigraphic context. For 7200 cal BP until modern times, 30 sea-level index points with different uncertainty ranges were defined. Additionally, a factor of decompaction was estimated for the remaining basal peat samples as well as for the underlying sediments of intercalated peat samples.The comparison of the Langeoog relative sea-level curve with the relative sea-level curve from the western Netherlands shows that the Langeoog curve lies up to 0.80 m lower than the Dutch curve and diverges for the time before 6000 cal BP. Though the offset coincides with the overall predicted trend of glacial-isostatic adjustment, it is less than predicted.Our study provides a useful assessment of legacy data and contributes to an improved sea-level index dataset for the southern North Sea coast.

From dust till drowned: the Holocene landscape development at Norderney, East Frisian Islands

AbstractWithin the multidisciplinary WASA project, 160 cores up to 5 m long have been obtained from the back-barrier area and off the coast of the East Frisian island of Norderney. Thirty-seven contained basal peats on top of Pleistocene sands of the formerGeestand 10 of them also had intercalated peats. Based on 100 acclerator mass spectrometry (AMS)14C dates and analyses of botanical as well as zoological remains from the peats, lagoonal sediments and the underlying sands, a variety of distinct habitats have been reconstructed. On the relatively steep slopes north of the present island, a swampy vegetation fringe several kilometres wide with carrs of alder (Alnus glutinosa) moved in front of the rising sea upwards of theGeestas it existed then until roughly 6 ka, when the sea level reached the current back-barrier region of Norderney at around −6 m NHN (German ordnance datum). From then on for nearly 4000 years a changing landscape with a mosaic of freshwater lakes and fens existed within this area. It was characterised by various stands ofCladium mariscus(fen sedge), alternating with brackish reed beds withPhragmites australis(common reed) and salt meadows withAster tripolium(sea aster),Triglochin maritima(sea arrowgrass),Juncus gerardii(saltmarsh rush) as well as mudflats withSalicornia europaea(common glasswort). As far as shown by our cores, this highly diverse, and for humans potentially attractive landscape was at least some 4 km wide and followed the coast for about 10 km. Before the rising sea caused diversification of habitats, wet heath as well as dry and dusty sand areas existed. In the course of time, parts of the wet heath turned into raisedSphagnumbogs under an oceanic precipitation regime before this diverse landscape was drowned by the rising sea and finally covered by marine sediments, while the earlier sediments and peats were partly eroded and redeposited.

Recent peat slide in Co. Antrim extends the known range of weak basal peat across Ireland

Peat instability and failure became an important topic of study following a series of damaging landslides in 2003. A peat slide in August 2014 at Croaghan, in the Orra Mountains of Co. Antrim, Northern Ireland, provided the first opportunity to compare directly estimates of peat shear strength from direct simple shear and tensile strength testing. Physical properties of peat from throughout the depth profile were obtained to provide reference characteristics for the strength test results and to facilitate comparisons with results from locations where detailed botanical compositions have been analysed. Both methods showed that the basal peat at the study site had a shear strength much lower than 6 kPa. The physical properties are the same as at sites 150 km further south-west, so the composition of the peat at the study site is inferred to be dominated by sedges (particularly Eriophorum vaginatum) with some heathers (Ericaceae) and mosses (including Sphagnum). The weak basal layer appears to be similarly lacking fibres, which allowed failure to occur in response to adverse water pressures arising from extreme rainfall. Basal shear strength of <5 kPa is a reasonable starting assumption for planned engineering works on intact blanket peat in Ireland.

How Old Are Marshes on the East Coast, USA? Complex Patterns in Wetland Age Within and Among Regions

AbstractSea‐level dynamics, sediment availability, and marine energy are critical drivers of coastal wetland formation and persistence, but their roles as continental‐scale drivers remain unknown. We evaluated the timing and spatial variability of wetland formation from new and existing cores collected along the Atlantic and Gulf coasts of the United States. Most basal peat ages occurred after sea‐level rise slowed (after ~4,000 years before present), but predominance of sea‐level rise studies may skew age estimates toward older sites. Near‐coastal sites tended to be younger, indicating creation of wetlands through basin infilling and overwash events. Age distributions differed among regions, with younger wetlands in the northeast and southeast corresponding to European colonization and deforestation. Across all cores, wetland age correlated strongly with basal peat depth. Marsh age elucidates the complex interactions between sea‐level rise, sediment supply, and geomorphic setting in determining timing and location of marsh formation and future wetland persistence.

O SIGNIFICADO PALEOGEOGRÁFICO DAS TURFEIRAS COSTEIRAS DO RIO GRANDE DO SUL

Na Planície Costeira do Rio Grande do Sul (PCRGS) depósitos de turfas afloram ao longo do litoral indicando os setores onde as barreiras costeiras exibem uma natureza transgressiva. Ao longo das últimas décadas várias causas foram apontadas para explicar o processo erosivo nestes setores, todas associadas a fenômenos naturais. Estas turfas aflorantes são tidas como elemento chave no entendimento da evolução costeira de longo termo deste litoral. O processamento químico das amostras foi realizado a frio com HCl (5%) e KOH (5%) e separação entre partículas orgânicas e inorgânicas com solução aquosa de ZnCl2. Este estudo se baseou em amostras de turfas obtidas de sondagens geológicas, afloramentos e perfilagens com Georradar nas praias de Itapeva e Hermenegildo. Os resultados indicam que o estrato basal que recobre os sedimentos pleistocênicos é formado por turfas, sinalizando cronologicamente o início da sedimentação holocênica na PCRGS em torno de 10.000 anos AP, quando ainda prevaleciam condições essencialmente lacustres, nas posições que viriam a se desenvolver os sistemas de barreiras costeiras holocênicas. Uma vez instaladas, estas barreiras criaram condições para o desenvolvimento de uma segunda geração de ambientes paludiais, desta vez, vinculados à redução das profundidades dos sistemas lagunares em processo de colmatação, por volta de 710 anos AP. Este estudo fornece evidências de que a linha de costa atual da PCRGS encontra-se num processo contínuo de reorientação, conduzido por um déficit sedimentar nos setores costeiros onde as barreiras retrogradantes migram para o continente e no sentido N-NO, expondo depósitos turfáceos sistematicamente ao longo do litoral.

Radiocarbon dating peatland development: Key steps in reconstructing past climate in the central Appalachian Mountains

Canaan Valley in West Virginia contains a greater area of peatlands than any other locality in the mid-Atlantic Highlands. Extensive fieldwork focused on peat stratigraphy, combined with high-resolution radiocarbon dating, was used to evaluate five peatlands within Canaan Valley National Wildlife Refuge (CVNWR). One hundred soil cores were profiled and described, 30 with laboratory analysis, including 52 radiocarbon dates. Calibrated basal peat dates from the five peatlands indicate the onset of peat genesis ranged from ∼18,600 to ∼15,200 cal yr BP. Basal peat dates on the two oldest cores are 1800 to 2200 years older than published dates on peat initiation in any other Appalachian Mountain peatlands. Peat accumulation rates varied from 0.02 mm/yr to 1.34 mm/yr, with a mean of 0.14 mm/yr. Results of age-depth profiles for six well-dated cores consistently exhibit: rapid accumulation during the late Pleistocene (Heinrich Stadial 1, Bølling-Allerød interstadial, and Younger Dryas cold stadial), lower accumulation rates in the early Holocene (Greenlandian Age), even lower accumulation rates during the mid-Holocene (Northgrippian Age), and the most rapid peat accumulation at the onset of the late Holocene (early Meghalayan Age). A paucity of shallow peat dating younger than 2000 BP may reflect a reduction in peat accumulation, or mixing of surface vegetation into near-surface soil horizons. Soil cores from CVNWR suggest a somewhat different peat development history than the process of terrestrialization previously proposed for other peatland ecosystems in the region.

Saltmarsh sustainability throughout the Holocene in Boston Harbor: A new sea-level curve for the lower Gulf of Maine and implications of recent anthropogenic alteration

Saltmarsh evolution is closely linked to sea-level rise (SLR) and sediment supply. In a regime of accelerating SLR, saltmarsh survival depends on the ability of the marsh platform to grow vertically through organic and inorganic accumulation, and laterally via transgression over adjacent uplands. In formerly glaciated settings, the formation and maintenance of a saltmarsh are complicated by steep uplands, low sediment availability, isostatic rebound, changes to tidal amplitudes, and anthropogenic alteration. While much work has examined the development of large saltmarshes in New England since the mid-Holocene and Anthropocene, little is known about the smaller isolated saltmarshes that form in pockets along the glaciated coastline. We use radiocarbon dates from newly uncovered index points (basal peat) within Boston Harbor to date one of the oldest saltmarshes in the region (∼4.2 ka), and calculate the polynomial relative sea-level curve (RSLR) for the lower Gulf of Maine taking into account tidal amplification throughout the Holocene. This study informs the historical persistence of isolated saltmarshes under varying rates of sea-level rise (magnitude as much as 2 mm yr−1). Additionally, we refine the timing and rates of the mid-Holocene sea-level deceleration in this region: between 2.8 and 3.3 ka, slowing from 2.1 mm yr−1 to 0.5 mm yr−1. RSLR determined from the past century of tide gauge data is 2.86 mm yr−1, five times greater than historic rates over the past 2000 years. Recent vertical accretion rates (determined from marker horizons and 210Pb data) indicate that portions of Boston Harbor’s saltmarshes are able to keep pace with current RSLR. However, historical diking and ditching practices appear to have resulted in elevation loss and conversion from high saltmarsh platforms to low saltmarsh platforms, largely influencing the amount of inorganic sediment needed to help maintain marsh surfaces. These results highlight that knowledge of historical anthropogenic modifications and changes in hydroperiod are critical when interpreting vertical accretion results. More importantly, anthropogenic modification within sediment starved saltmarshes may be the cause for cannibalization of marsh shorelines, whereby inorganic sediment eroded from marsh edges is recycled and delivered to the surface, facilitating vertical accretion that offsets RSLR. Under modern accelerated sea-level rise and decreased sediment supply, this cannibalization process may now be the only pathway for saltmarsh survival.

The Age of Peatlands and Peatland Formation Stages in Polesie Landscapes of the East European Plain

This paper presents the results of a study on peat deposits and radiocarbon dating of basal peat horizons in 43 peatlands located on three key sites within Meshchera Lowlands and Moksha Polesie. Peatlands formed by upland paludification processes and located on watersheds and terraces rising above floodplains were selected for the analysis. The obtained data indicate that the peatland formation process has been ongoing in these regions throughout the entire Holocene epoch and that this process has been affected by the fire regime in the area. In periods with higher wildfire frequencies (8800–5800 and 4200–3200 calendar years BP), changes in the water balance on flat and poorly drained plains occurring after the destruction of forest stands intensified the waterlogging processes.

South African peatlands: A review of Late-Pleistocene-Holocene dvelopments using radiocarbon dating

South Africa has a limited number of peatlands and most of them are relatively small compared to those in cooler temperate regions in the northern hemisphere. We gathered 40 basal peat samples representative of South Africa’s peatlands to explore their development during the Late Pleistocene and Holocene. Depth profiles of nine of them were also investigated using radiocarbon dating, which yielded information on past environmental changes affecting South African peatlands. The data showed three peaks in the frequency of peatland initiation, which are consistent with available climatic and sea level fluctuation data: one after the Last Glacial Maximum (LGM) and two during the Mid to Late Holocene. Inland peatlands in mountain valleys showed optimal growing conditions during the glacial-interglacial transition, continuing until the Early-Holocene. This is due to the switch to the wet and warm interglacial climate. In contrast, coastal peatlands showed optimal initiation conditions over two phases during the Holocene, which is consistent with sea level rise peaks that led to optimal moist conditions occurring ca. 6,000–3,000 and 1,000 years ago. Sea level rise reduced groundwater drainage, which led to a rise in the primary groundwater table. However, data from some of the coastal peatlands indicate independence from the sea level fluctuation, and that they are rather controlled by climatic conditions and their local hydrogeomorphic setting, e.g. perched groundwater aquifers. Some peatland complexes show a pattern of phased initiation with peat initiation consistent with altitude difference, which could be due to a positive feedback of blocking caused by peat accumulation in lower reaches, reducing groundwater drainage to the sea.

From natural to cultural mires during the last 15 ka years: An integrated approach comparing 14C ages on basal peat layers with geomorphological, palaeoecological and archaeological data (Eastern Massif Central, France)

This paper studies mire initiation modalities from the Late-Glacial to the Holocene by comparing radiocarbon ages on basal peat layers (112 sites from the Eastern French Massif Central – EFMC) with long-term land cover changes. We developed a semi-quantitative method based on the degree of openness and on Anthropogenic Impact Factors (AIF scores) from palaeoecological data (mire and lake records). Archaeological information was also considered to evaluate human impact. We compared regional mire development trends with datasets from Northern Europe, Siberia, Alaska and Canada, and with global CH4 emission. Heterogenous cases of mire initiation were highlighted during the last 15 ka years in the EMFC. From 15 to 11.7 ka cal. BP, some mires and histic horizons occurred, although further research is needed to better understand these peat accumulation phases. Related to the Early Holocene warming, a mire generation established by terrestrialization, in the southern EFMC where geomorphology favoured fens. Bogs also formed by paludification in the whole area between 10 and 7 ka cal. BP. Then, various cases of mire initiation were found from 4.4 to 2.4 ka cal. BP. The high number of mires established since 2.4 ka cal. BP could be related to major anthropogenic changes, indirectly favouring fens (in former ponds for instance) or small bogs (at the back of roads, walls or in abandoned drainage systems). This last generation was typical of Western European mountains and implied that moderate human impact may also produce socio-ecosystems with high ecological value.