14C Dates Research Articles

Natural and anthropogenic controls on environmental change during the Holocene based on a multi-proxy record obtained from subalpine peatland in southern China

The interactions between past climate, human activity and environmental change in subtropical mountainous areas are poorly understood due to the lack of reliable records in South China. In this study, the evolution of the East Asian summer monsoon (EASM) during the Holocene, and the interactions between regional human activity and environmental change, were studied using multi-proxy records from a subalpine peat core recovered from South China. The chronology of this peat core has been well-constrained by 10 AMS 14C dates of peat stems. A series of proxy indicators, including carbon isotopes (δ13C), loss on ignition (LOI), magnetic susceptibility (MS), the chemical index of alteration (CIA), and geochemical elements from the Shiwangutian (SWGT) peatland were used to reconstruct the palaeohydrological changes during the Holocene. Regional moisture levels showed a generally arid–wet–arid pattern, and three phases of climatic change were detected as follows. 1) Between 11,600 and 9000 cal yr BP, the EASM was weak and a relatively dry climate developed. 2) Between 9000 and 4000 cal yr BP, the prevalence of humid climatic conditions was associated with a strong summer monsoon. 3) After 4000 cal yr BP, the climate shifted to relatively dry conditions. Further comparisons and analysis suggested that solar insolation, migration of the Intertropical Convergence Zone (ITCZ), and El Niño-Southern Oscillation (ENSO) activity played an important role in determining the variations in Holocene EASM intensity. In addition, the increase in both MS and heavy metal concentrations over the last 1000 years is consistent with an increase in the population of Hunan Province. Therefore, it can be inferred that population growth and the associated expansion of cropland and mining led to an increase in soil erosion and metal tool use. These findings suggest that the impact of human activity generally outweighed the natural climatic controls on the environment and landscape in the mountainous region of southern China over the last 1000 years.

High-resolution sea-level fluctuations during the Mid-Holocene in the Ningshao Coastal Plain region, eastern China

Sea level changes during the Mid-Holocene directly influenced the Neolithic culture in the Yangtze River Delta region (YRD). However, the high-resolution sea level change characteristics for this period remain unclear. In this study, we performed a high-resolution palynological analysis, including pollen, Dinoflagellate cysts, and Foraminiferal organic linings, using a high-resolution sediment core from Shanglin Lake, in the North of Ningshao Plain (the south of Hangzhou Bay). 11 accelerator mass spectrometry 14C(AMS) datings indicate the age of the sediments range from 8 cal ka B.P. to 5.6 cal ka B.P. The results show that during the Mid-Holocene, Shanglin Lake evolved from an estuary – subtidal lagoon – semi-enclosed bay – semi-enclosed lagoon – semi-enclosed bay – enclosed lagoon to a modern freshwater lake. There was a period of no, or minimal, eustatic sea-level rise between 7733 and 7585 cal yr B.P. The Mid-Holocene high sea level comes in 7253–7082 cal yr BP. Between 7000 cal yr BP and 5502 cal yr BP, the sea level is close to modern value. The sea level change during this period had a significant impact on the local Neolithic human activity.

The progradational Curumim barrier in southern Brazil: An archive of sea-level changes, and cyclic aeolian activity in the Holocene

This paper discusses a model of coastal barrier progradation where the development of a prograded plain was a product of the successive formation of foredune ridges followed by their burial by transgressive sand sheets and dunefields. The results are based on direct lithological data from drill holes and geomorphological analyses, indirect geophysical data (GPR), and 14C and OSL dating. Barrier progradation started at 6.69 ka (OSL) or 7.2 ka (14C), under sea-level rise. At around 5.0 ka (OSL), or thereabouts, a forced regression condition started to operate, when sea-level started to fall after it reached a maximum of 2.34 ± 0.8 m. During barrier progradation sets of foredunes were formed, and at least some of them were buried by sands of transgressive dunefields (TDF), which later evolved to transgressive sand sheets (TSS). A total of 11+ phases of TSS and a modern phase of TDF were formed in a time span of 6.69 ka (OSL) or 7.2 ka (14C), corresponding to one phase formed at each 560 or 600 yrs. Two models of possible development of the surface of Curumim barrier are proposed.

Hydrochemical and isotopic studies providing a new functional model for the coastal aquifers in Douala Coastal Sedimentary Basin (DCSB)/Cameroon

A new conceptual model of the hydrogeological systems in Cameroon's Douala Coastal Sedimentary Basin (DCSB) was constructed. The model is based upon the basin's known geology, plus data from recent field campaigns that allowed the collection of rainwater and groundwater samples for analyses of stable isotopes (δ2H, δ18O, δ13C), radiogenic isotopes (3H, 14C), and water chemistry. Aquifer characteristics that were thereby deciphered include recharge, isotopic distributions, residence times, and mixing processes. Rainfall samples (mean δ18O = −2.0 ‰; mean δ2H = −6.80 ‰; weighted mean = −2.4 ‰ δ18O, −9.85 ‰ δ2H) scatter along two distinct lines, thus indicating that local rainfall events undergo processes during convective events, variability in humidity, amount effects, and seasonal variations. Stable isotope values of river water samples are close to the weighted mean of local precipitation, with some downstream enrichment. The Quaternary/Mio-Pliocene superficial aquifer system (depth < 70 m) and the intermediate Oligocene/Upper Eocene aquifer system (depth: 70 to 200 m) exhibit evidence of similar fractionation processes through an enrichment gradient of δ-values. The enrichment is more pronounced at the top of the superficial aquifer, which is very exposed to direct rainfall water infiltration, evaporation, and amount effects. The depth profiles of δ-values coupled to water chemistry and tritium contents, evidence leakage between (i) the superficial system's Quaternary alluvium sands and Mio-Pliocene sands; and (ii) the superficial and intermediate systems. Thus, the aquifers that contain modern, post nuclear groundwater are characterized by flow exchanges and direct recharge from rainfall events. In contrast, the Upper Eocene system has depleted δ-values and lower bicarbonate contents, suggesting not only that this system was recharged by rapid infiltration (with limited effect of evaporation), but that this recharge occurred during a cooler time in the past. The residence times (computed from 14C dates) indicate uncorrected ages ranging from hundreds to thousands of years.

Climate and sea-level fluctuations on the western coast of Bohai Bay during the 4.2 ka event: Multi-proxy evidence from the Nandagang area of Cangzhou, China

The 4.2 ka event was an important climatic event during the mid–late Holocene, with significant effects on the ecological environment and climatic evolution of different regions. Coastal wetlands, as a transitional ecosystem between land and sea, are sensitive to changes in climate and sea level; hence, research on coastal wetlands is important for reconstructing past climate and sea-level changes and for predicting future changes. However, little research has been conducted on the characteristics of the 4.2 ka event on the western coast of Bohai Bay in China. We analyzed the pollen assemblages (214 samples), grain size, and geochemical element contents of a mid–late Holocene sedimentary sequence from the Nandagang (NDG) wetland on Bohai Bay, with the chronology based on 13 AMS 14C dates. The results revealed the history of climate and sea-level changes on the western coast of Bohai Bay during the interval of 5000–3600 cal yr BP. High sedimentary arboreal pollen concentrations indicated that the NDG area had a relatively dense cover and humid climate during 5000–4450 cal yr BP. During the 380-year interval of 4450–4070 cal yr BP, corresponding to the 4.2 ka event, the decreased representation of arboreal pollen indicated a decrease in the regional forest cover and an arid climate. The internal structure of the 4.2 ka event recorded in core NDG showed a dry-wet-dry temporal structure during the intervals of 4450–4290 cal yr BP, 4290–4170 cal yr BP, and 4170–4070 cal yr BP, respectively, together with a relatively low sea level. Comparison of the relative sea level (RSL) record of the NDG wetland with similar records from other coastal regions in East Asia during the 4.2 ka event revealed contrasting trends. During 4070–3600 cal yr BP, the tree pollen concentration increased again, indicating that the forest vegetation coverage increased and the climate became wetter. Overall, our results suggest that the 4.2 ka event, as recorded in Bohai Bay, was related to the reduced influence of the western Pacific Ocean Warm Pool and the more frequent occurrence of the El Niño–Southern Oscillation.

North Atlantic forcing of Indian Winter Monsoon intensification: Evidence from Holocene sediments from the tropical Indian Ocean Island of Sri Lanka

The teleconnection between the Asian monsoon system and North Atlantic forcing is an enduring prospect of the Earth’s climate. During the Holocene interstadial, the Indian summer monsoon showed asynchronous weakening links to ice rafting events documented in the North Atlantic region. However, the sensitivity of the Indian Winter Monsoon in response to North Atlantic cold spells is unclear due to a lack of compelling evidence. This study aims to extract the deglacial Indian Winter Monsoon signals using lithogenic tracers in coastal sediments and explore its association with the North Atlantic cooling episodes. A 5.1 m sediment core was retrieved from Pottuvil Lagoon in the southeastern coast of Sri Lanka, and the concentrations of K, Rb, Mg, Al, and Ti in 101 sub-sections were analysed using ICP-MS. The core- chronology was established by Bacon 2.2 age-depth modelling based on calibrated AMS 14C dates. The monsoon signal was reconstructed using element proxies and compared with the drift ice indices from the North Atlantic deep-sea sediments. Results revealed distinct phases of intense monsoon activity at 2553–2984 years BP, 3899–5021 years BP, and 5244–5507 years BP intervals with intermittent weak phases during 2253–2553, 2984–3899, and 5021–5244 years BP. The episodes of the intensified Indian Winter Monsoon coincided with Bond Events 2, 3, and 4, showing a strong coherence with the North Atlantic’s deglacial climate. Thus, on a millennial scale, North-Atlantic cooling has triggered intense winter monsoon conditions over the tropical Indian Ocean region from the mid to late Holocene. In comparison with regional monsoon archives, the Pottuvil winter monsoon record exhibits an anti-phase association with the Indian Summer Monsoon during Holocene ice-rafted debris events. The geochemical approach executed in this study could provide new insight into the millennial-scale pacing of the winter counterpart of the Indian monsoon links to climate extremes of high northern latitudes.

RADIOCARBON STEP-COMBUSTION OXIDATION METHOD AND FTIR ANALYSIS OF TRONDHEIM CaCO3 PRECIPITATES OF ATMOSPHERIC CO2 SAMPLES: FURTHER INVESTIGATIONS AND INSIGHTS

ABSTRACT Eight atmospheric carbon dioxide samples (as calcium carbonate—CaCO3—precipitates) from Lindesnes site (58ºN, 7ºE), belonging to 1963 and 1980 (four samples from each year) and stored at the National Laboratory for Age Determination (NTNU), have been reevaluated through radiocarbon (14C) analysis. Previous 14C results indicated the presence of a contaminant, which was not removed through different chemical cleansing procedures (e.g., hydrochloric acid—HCl and/or hydrogen peroxide—H2O2). Here, we present a follow up investigation using 14C step-combustion and Fourier-transform infrared spectroscopy (FTIR) analysis. Results from 14C data indicate unsuccessful removal of the contaminant, while further FTIR analysis displayed the presence of moisture. This finding alludes to the possibility that the contaminant is of ambient air-CO2 deeply embedded in CaCO3 powders (within clogged CaCO3 pores and/or bonded to the lattice). Samples were found exposed to air-CO2 and humidity. These conditions may have lasted for years, possibly even decades, leading to the 14C offsets detected here.

Western frontier of the Archaic Scythia: typo-chronology vs radiocarbon dating

One of the key issues in the chronology of Late Hallstatt period is the so-called Hallstatt plateau in the calibration curve extending the calibrated range of single dates to c. 800-400 BC. Analysis of the 14C dates of the ash-hill from the Chotyniec hillfort, indicate its dating to the time range, which does not exceed the interval of 780-469 BC. Typological analysis of the artefact collection allows us to date the ash-hill to the middle of the 7th – the first third of the 6th century BC (HaС2-HaD1). This dating corresponds to the Early Scythian timeand chronology of the Western Podillian group. The analysis of material culture allows us to indicate the immediate closeness of the Chotyniec agglomeration to the Western Podillian group.

Radiocarbon dates from the Netherlands and Doggerland as a proxy for vegetation and faunal biomass between 55 and 5 ka cal bp

ABSTRACTThree hundred forty‐one radiocarbon dates from the Groningen radiocarbon database are compiled in this study. They show for the first time that organic sediment samples from the eastern Netherlands and mammal bones from Doggerland reflect shifts in the presence and the density of vegetation (food for herbivores) and mammal biomass during the last ice age (Weichselian Stage, ~119–14.7 ka cal bp). Comparison with oxygen isotope curves of Greenland ice cores and geomorphological data shows that cold climate, in particular during the younger part of the Weichselian Middle Pleniglacial and during the Late Pleniglacial, and related scarcity or even absence of vegetation, were limiting factors for the carrying capacity of the landscape and thus for the population density of large herbivores during the period covered by 14C dating (last ca. 55 000 years). A ‘fossil gap’ during the Late Pleniglacial lasted ca. 13 000 years from ca. 28 to 15 ka cal bp. Previous research from the nearby Eifel region in Germany shows that environmental conditions were less extreme (‘refugium conditions’) than in the Netherlands, taking into account the continuous presence of spores of coprophilous fungi in the Eifel, indicating uninterrupted food supply for herbivores.

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A SUMMARY OF RADIOCARBON MEASUREMENTS OF FLUVIAL AND COLLUVIAL DEPOSITS IN CATCHMENTS OF SOUTH-CENTRAL ONTARIO, CANADA

ABSTRACTFluvial and colluvial deposits of Late Holocene age in South-Central Ontario catchments have provided few 14C dates, most by conventional methods registering century-old ages. Other young deposits, dated by conventional and accelerator mass spectrometry radiocarbon (AMS 14C), have yielded bomb-affected post-1950 ages over variable time limits. Attempts to date the base of Ah and lower-in-section soil horizons, in Early to Late Holocene stream terrace deposits, have yielded atomic bomb effects. Comparing bomb contamination in Late Holocene fluvial deposits, using both conventional and AMS methods, identifies a mix of bomb-affected beds juxtaposed with dated beds, the latter yielding ages with narrow standard deviations. Colluvial deposits overlying key glacial sections in the Rouge Catchment, while rare, yield bracketed AMS ages for an Ahbk horizon that refines weathering times relative to previously obtained conventional 14C dates. Bomb-affected sediment appears variably distributed within floodplain soils and in the ground soil of a colluvial section. Mass wasted deposits, with AMS 14C ages spread over the last few centuries, appear related to Little Ice Age (LIA) changes in climate, corroborated by pollen records. Further, these AMS-14C dated beds calibrate weathering of secondary Fe-Al oxihydroxides over the first half a millennium of weathering time.

FIRST RESULTS OF COMPLEX DATING AND GROWTH RATE ESTIMATION OF SPELEOTHEM FROM VORONTSOVSKAYA CAVE (KRASNODAR REGION, RUSSIA)

Speleothems are unique archives of information about climate, geomagnetism, and ecological conditions of past epochs of the Earth, and over the past two decades have been successfully used for paleoclimatic and paleomagnetic studies. The uniqueness of these geological objects lies in the peculiarities of their formation and preservation in them of a wide range of geochemical, geological and geophysical proxies, and, most importantly, in the ability to obtain time series of these proxies in an unprecedentedly accurate resolution using 230Th/U, 14C and some other geochronological methods, as well as incremental chronology. This paper presents the first results of dating the Vor speleothem from the Vorontsovskaya Cave (Krasnodar region), which preserved a record of the geomagnetic excursion, obtained by 230Th/U α-spectrometry, 14C dating, and incremental chronology. Such studies have been carried out in Russia for the first time. Despite the limitations of using the methods of isotope geochronology, it was possible to obtain a limit on the age of the excursion, which probably occurred no earlier than 5500–6000 years ago. At the same time, the incremental chronology made it possible to determine with great accuracy the duration of the main phase of the excursion, which equals 871 ± 16 years, during which the virtual geomagnetic pole was in the southern hemisphere, and also to obtain the upper limit on the age of the excursion, which probably occurred no later than 5.5–6 thousand years ago.

LAGOA SALGADA: AN OVERVIEW OF A BRAZILIAN HYPERSALINE LAGOON ENVIRONMENTAL STUDIES OVER THE LAST 5000 YEARS USING RADIOCARBON DATE CORRECTIONS

ABSTRACTThe Lagoa Salgada is located in the Paraíba do Sul river delta plain on the coast of Rio de Janeiro state, Brazil, and is one of the few lagoons in the world that have well-developed recent stromatolites. Lagoa Salgada is a hypersaline lagoon formed in a very complex environmental system subjected to terrestrial and oceanic influences under different sea level regimes and climate variations. In addition, sediment and stromatolites are characterized by unusually positive inorganic δ13C VPDB values. For this reason, it has been the target of several geological and paleoenvironmental studies, which, in their great majority, require a geochronological technique in order to determine the changes in the environment over time. When radiocarbon (14C) dating is used, it is necessary to consider some details as the source of 14C in the environment and perform 14C ages calibration accordingly. In the present paper, a bibliographic survey was carried out in order to review the data treatment and improve the environmental evolution discussion based on accurate calibration. Using the Marine20 curve and an undetermined ΔR, we generated growth and depositional models to establish an overview of the formation of this lagoon.

Coupling of Dye Analysis and Compound Specific Radiocarbon (14C) Analysis (CSRA) in Heritage Sciences

Natural organic dyes and pigments have been used for millennia to bring colour into our daily lives. Being sourced from a variety of natural sources, they form an extremely varied and large class of compounds, all of which retain the atmospheric 14CO2 of their year of growth. As such these compounds represent ideal candidates for radiocarbon (14C) dating, allowing the identification of or providing information towards the period in which the coloured artefact was created. However, up to now no such analysis has ever been conducted solely on organic colourants within an object. The complex nature of the samples and the sample size limitations with respect to precious and rare art artefacts requires innovative inter- and multidisciplinary approaches. Here we discuss preliminary results in the development of a compound-specific radiocarbon analysis (CSRA) methodology for the analysis of anthraquinone derived red dyes extracted from dyed wool yarns. The aim of this research project is to introduce new routes to date cultural heritage objects, in particular to overcome their intrinsic complexity through the development of CSRA strategies.

Sesame use in Turpan during the Tang dynasty: Evidence from the Astana Cemetery

Three concentrations of sesame seed remains have been discovered from the Astana Cemetery of Turpan, Xinjiang, China. 14C dating and unearthed documents indicate that they approximately belong to the 7th–8th centuries, which represent the earliest reliable archaeobotanical evidence of sesame in China. In addition to plant macrofossil method, pyrolysis–gas chromatography/mass spectrometry (Py-GC/MS) analyses were also employed to investigate two sesame samples and characterized its special biomarkers (sesamol & sesamin & sesamolin). Based on the preserved condition and concomitantly unearthed plant remains, these sesame remains were considered to be used as cereal and/or oilseed crops and pillow fillers. Furthermore, combined with the record of unearthed documents from the Astana Cemetery, it is assumed that sesame has been extensively cultivated and used by the indigenous people during the Tang dynasty (approximately the 7th–9th centuries). This paper offers new insights into the role of sesame in the economic and social life of Turpan inhabitants.

Understanding climate resilience in Scandinavia during the Neolithic and Early Bronze Age

Mid and late-Holocene climate shifts are considered to have profoundly shaped demographic developments and adaptive responses of communities globally. Yet their onset, duration, and impact on Neolithic and Early Nordic Bronze Age communities in the high-latitude ranges of southern and north-western Scandinavia remain a major research gap. Here, we built on an emerging body of archaeological and paleoclimate data, encompassing 20,908 anthropogenic 14C dates and 49 climate records from the Holocene. Additionally, we gathered and correlated a new archaeological dataset of 3649 houses from southern Scandinavia and southern Norway. In this study, we utilised 6268 reliable 14C dates and 2519 dwellings to generate time series and socio-economic trends from ∼4100 to 1100 BCE.Our study revealed three key findings: (1) A distinct lateral zonation, with variations in the duration and timing of the Holocene Thermal Maximum (∼7050–2050 BCE). In Southern Scandinavia, a warmer climate may have facilitated the spread of crop cultivation (3820–3790 BCE), coinciding with significant population growth. Neolithic communities settled in permanent two-aisled houses 90–160 years later (3700–3660 BCE). (2) The 2250 BCE (4.2 ka BP) cooling trend marked the beginning of a climate regime shift with varying duration and timing (∼3450–1450 BCE). This period coincided with demographic growth, migration, crop cultivation diversity, and the development of houses with crop storage facilities (2290–2215 BCE). (3) Severe abrupt cooling periods (∼1850–1450 BCE) corresponded to short-term demographic decline including disruptions in trade networks with continental Europe. However, repopulation and redistribution of wealth (∼1450 BCE), along with the development of stable three-aisled houses (1475–1450 BCE), underscore the resilience of food-producing economies in mitigating environmental disturbances.

EXPERIMENTAL OBSERVATIONS ON PROCESSING LEATHER, SKIN, AND PARCHMENT FOR RADIOCARBON DATING

ABSTRACT Skin-based samples (leather, skin, and parchment) in archaeological, historic and museum settings are among the most challenging materials to radiocarbon (14C) date in terms of removing exogenous carbon sources—comparable to bone collagen in many respects but with much less empirical study to guide pretreatment approaches. In the case of leather, the 14C content of materials used in manufacturing the leather can vary greatly. The presence of leather manufacturing chemicals before pretreatment and their absence afterward is difficult to demonstrate, and the accuracy of dates depends upon isolating the original animal proteins and removing exogenous carbon. Parchments differ in production technique from leather but include similar unknowns. It is not clear that lessons learned in the treatment of one are always salient for treating the other. We measured the 14C content of variously pretreated leather, parchment, skin samples, and extracts, producing apparent ages that varied by hundreds or occasionally thousands of years depending upon sample pretreatment. Fourier Transform Infrared Spectroscopy (FTIR) and C:N ratios provided insight into the chemical composition of carbon reservoirs contributing to age differences. The results of these analyses demonstrated that XAD column chromatography resulted in the most accurate 14C dates for leather and samples of unknown tannage, and FTIR allowed for the detection of contamination that might have otherwise been overlooked.

Estimating extinction time using radiocarbon dates

The extinction of a species is a key demographic event often signalling major climatic, ecological and/or evolutionary shifts that can be investigated using the fossil record. In that context, radiocarbon (14C) dating has become a popular tool to time and test for scenarios of extinction that can inform on how species respond to past and future ecosystem changes. We develop CRIWM, a method for estimating extinction (and arrival) time from time series of 14C dates while accounting for probability density functions (PDF) deriving from 14C calibration. The sister method GRIWM assumes normal chronometric errors and is inappropriate for 14C chronologies as PDFs are often non-Gaussian and multi-modal. Compared to GRIWM, CRIWM reduces by 4-fold the gap between true and estimated extinction times and the width of the confidence intervals, and is less sensitive to sample size, dating errors and the temporal distribution of specimens in a species’ fossil record. We build the R package Rextinct with three user-friendly functions for computing CRIWM and GRIWM, and the PDF moments, modes and intercepts of 14C calibrations. CRIWM and GRIWM accept time series comprising only 14C dates or observations (fossils, sightings) dated by multiple chronometric methods, and calibration curves for fossils sampled in the Northern and Southern Hemispheres and marine environments. For both methods, we implement two different estimators of extinction time whether they are reliant on a p-value (original conceptualization) or not (novel). CRIWM and Rextinct are robust tools to time extinction and arrival events using 14C chronologies spanning the entire Holocene to 50,000 calendar years Before Present, and can be used to investigate demographic phenomena queried through the fossil record such as migrations, domestications and extirpations.

Climatic controls on the dynamic lateral expansion of northern peatlands and its potential implication for the ‘anomalous’ atmospheric CH4 rise since the mid-Holocene

Understanding the dynamic changes in peatland area during the Holocene is essential for unraveling the connections between northern peatland development and global carbon budgets. However, studies investigating the centennial to millennial-scale process of peatland expansion and its climate and environmental drivers are still limited. In this study, we present a reconstruction of the peatland area and lateral peatland expansion rate of a peatland complex in northern Sweden since the mid-Holocene, based on Ground Penetrating Radar measurements of peat thickness supported by radiocarbon (14C) dates from four peat cores. Based on this analysis, lateral expansion of the peatland followed a northwest-southeast directionality, constrained by the undulating post-glacial topography. The areal extent of peat has increased non-linearly since the mid-Holocene, and the peatland lateral expansion rate has generally been on the rise, with intensified expansion occurring after around 3500 cal yr BP. Abrupt declines in lateral expansion rates were synchronized with the decreases in total solar irradiance superimposed on the millennial ice-rafted debris events in the northern high latitudes. Supported by the temporal evolution of peatland extent in four other Fennoscandian peatlands, it appears that the northern peatland areal extent during the early to middle Holocene was much smaller compared to previous empirical model reconstructions based on basal age compilations. Interestingly, our reconstruction shows the increments of peat area since the mid-Holocene coincide with the rise in atmospheric CH4 concentration, and that abrupt variations in atmospheric CH4 on decadal to centennial timescales could be synchronized with peatland lateral expansion rates. Based on our analysis we put forward the hypothesis that lateral expansion of northern peatlands is a significant driver of dynamics in the late Holocene atmospheric CH4 budget. We strongly urge for more empirical data to quantify lateral expansion rates and test such hypotheses.

Holocene vertical velocity fields in the Calabrian Arc (southern Italy): New insights from uplifted sea-level markers in the Crotone Peninsula

The study of fossil coastlines is one of the most widely used methods to unravel the vertical movements of the Earth's solid surface. All along the coast of the Calabrian Subduction Arc, well preserved Pleistocene marine terrace sequences document a protracted uplift history. Although Pleistocene vertical movements have been extensively explored, the Holocene history is not well understood. Numerous uplifted coastlines of the Holocene period have been studied along the Tyrrhenian side of Calabria, but the Ionian coastal sector is considerably under-studied. Our new data from the coast of the Crotone Peninsula fill this crucial data-gap. AMS 14C dating of seventeen sea level markers, elevated above the current mean sea level, show ages between 2300 and 7000 Cal. Yr BP. The elevation of the markers was corrected for the paleo sea level using the most updated GIA models ICE-6G (VM5a) and ICE-7G (VM7). We found that a coastline dated to 7 ka shows uplift rates of 0.8 mm/yr, consistent with late Pleistocene uplift rates (≈0.8 mm/yr). In contrast, a 2.3 ka coastline was uplifted by only 1 m, resulting in lower uplift rates of ≈0.5 mm/yr. However, there are clues that the abandonment of this younger coastline may have occurred with a rapid uplift pulse. Reconstructing the past vertical movements of the Crotone Peninsula reveals an unsteady uplift history. At some times fast uplift rates are required, while for other periods, lasting as long as 3–4 kyr, the uplift rate is slower or zero. An uplift history consisting of periods of accelerated uplift, or even coseismic pulses, would also explain the difference in uplift rates between short term (<5 ka) and long term (>5 ka) markers through a metric we have defined as uplift rate sensitivity. Understanding the details of this uplift history has social relevance. The co-seismic uplift hypothesis requires further investigation but if confirmed would likely affect the seismic and tsunami hazard of the Crotone Peninsula. Similarly, the unsteady uplift rate would cause a risk given the current rapid rate of global sea level rise. Periods of sustained vertical stability would increase the risk of flooding even in areas characterized by long-term uplift and thus considered safe.