Palaeoclimate Reconstructions Research Articles

Lake sediments from southern Norway capture Holocene variations in flood seasonality

Owing to the combined impact of human encroachment and global climate change, river flood hazards have increased around the world. Over the past decades, rapid warming has augmented atmospheric moisture fluxes. The resulting intensification of the hydrological cycle, as evident from instrumental records, is linked to more frequent and severe flooding. However, this observational baseline is too short to adequately assess long-term flood variability under different climate conditions. Geological archives can fill this critical knowledge gap by providing long-term (millennia) empirical constraints on the magnitude and frequency of floods. To reconstruct the frequency of flood events over the last >8000 years, this study investigated the Holocene lacustrine sediments from Lake Lygne in southwestern Norway. The precipitation in this area is sourced from the North Atlantic Ocean and transported by the prevalent westerly winds. As such, reconstructions of flood frequency variability may shed light on past moisture flux and flood generating weather systems in this part of northwestern Europe. We applied a multiproxy approach to robustly fingerprint the flood sediment signatures using multiple independent lines of evidence. This approach included analysing the sediments using X-ray fluorescence (XRF), computed tomography (CT scanning), and magnetic susceptibility (MS). We identified two types of event beds that differed significantly from background sedimentation throughout the sedimentary archive, which we interpreted as river flood deposits: one type is minerogenic and coarse silt-dominated; the other is a composite of minerogenic sediments and macrofossils. By comparing the sediment record with instrumental water discharge data from the last 100 years, we argue that these differing flood signals represent two flood regimes: rainfall-triggered floods during autumn and snowmelt-triggered floods during spring. Conducting a rate of change (RoC) analysis, we found significant millennial- and centennial-scale variability in the frequency of flood events. Moreover, comparing our findings with palaeoclimate reconstructions in the North Atlantic region, we found that the warmer than present early-mid-Holocene was dominated by extreme precipitation-triggered floods, shifting towards more snowmelt-triggered floods in the late Holocene.

A terrestrial record of climate variation during MIS 11 through multiproxy palaeotemperature reconstructions from Hoxne, UK

AbstractA terrestrial (lacustrine and fluvial) palaeoclimate record from Hoxne (Suffolk, UK) shows two temperate phases separated by a cold episode, correlated with MIS 11 subdivisions corresponding to isotopic events 11.3 (Hoxnian interglacial period), 11.24 (Stratum C cold interval), and 11.23 (warm interval with evidence of human presence). A robust, reproducible multiproxy consensus approach validates and combines quantitative palaeotemperature reconstructions from three invertebrate groups (beetles, chironomids, and ostracods) and plant indicator taxa with qualitative implications of molluscs and small vertebrates. Compared with the present, interglacial mean monthly air temperatures were similar or up to 4.0°C higher in summer, but similar or as much as 3.0°C lower in winter; the Stratum C cold interval, following prolonged nondeposition or erosion of the lake bed, experienced summers 2.5°C cooler and winters between 5°C and 10°C cooler than at present. Possible reworking of fossils into Stratum C from underlying interglacial assemblages is taken into account. Oxygen and carbon isotopes from ostracod shells indicate evaporatively enriched lake water during Stratum C deposition. Comparative evaluation shows that proxy-based palaeoclimate reconstruction methods are best tested against each other and, if validated, can be used to generate more refined and robust results through multiproxy consensus.

Applying the UDA-ODA discrimination technique to a herpetological association: the case of the Middle Palaeolithic site of El Salt (Alcoi, Spain)

El Salt (Middle Palaeolithic; Alcoi, Spain) is a key site for understanding the disappearance of Neanderthals in the eastern Iberian Peninsula, a process that is observed along its stratigraphic sequence. To improve our understanding of the palaeoclimatic context in which this process took place, we applied the UDA-ODA discrimination technique to the fossil herpetological assemblages from Stratigraphic Units (SU) Xb (52.3 ± 4.6 ka) and V (45.2 ± 3.4/44.7 ± 3.4 ka). This method is based in the application of an ecological criterion, the maximum altitude of each species on each Iberian range, to discern and remove those areas that do not meet their ecological requirements (UDA) from those that do (ODA), which are included in its distribution from Atlases from which the common distribution species is going to be extracted. Results indicate the existence of an alternation between “cold and wet” moments with “warm and dry” ones, all of them in a more humid context than nowadays. Climate was slightly warmer than nowadays in SU Xb, whereas was cooler in SU V. Regarding MAP, our results show less variation between SUs than it has been provided by previous studies. These results do not fully agree with those provided by small mammals from the same SUs, which indicate an increase of the temperatures whereas rainfall experienced the contrary. These differences could be related with the wider distribution of the Iberian herpetofauna, and some differences in the applied ecological criterion. Furthermore, herpetofaunal palaeoclimatic reconstruction shows that the abandonment of the site by Neanderthals seems to have occurred during an arid phase.

Modern Pollen Assemblages From Lake Sediments and Soil in East Siberia and Relative Pollen Productivity Estimates for Major Taxa

Modern pollen–vegetation–climate relationships underpin palaeovegetation and palaeoclimate reconstructions from fossil pollen records. East Siberia is an ideal area for investigating the relationships between modern pollen assemblages and near natural vegetation under cold continental climate conditions. Reliable pollen-based quantitative vegetation and climate reconstructions are still scarce due to the limited number of modern pollen datasets. Furthermore, differences in pollen representation of samples from lake sediments and soils are not well understood. Here, we present a new pollen dataset of 48 moss/soil and 24 lake surface-sediment samples collected in Chukotka and central Yakutia in East Siberia. The pollen–vegetation–climate relationships were investigated by ordination analyses. Generally, tundra and taiga vegetation types can be well distinguished in the surface pollen assemblages. Moss/soil and lake samples contain generally similar pollen assemblages as revealed by a Procrustes comparison with some exceptions. Overall, modern pollen assemblages reflect the temperature and precipitation gradients in the study areas as revealed by constrained ordination analysis. We estimate the relative pollen productivity (RPP) of major taxa and the relevant source area of pollen (RSAP) for moss/soil samples from Chukotka and central Yakutia using Extended R-Value (ERV) analysis. The RSAP of the tundra-forest transition area in Chukotka and taiga area in central Yakutia are ca. 1300 and 360 m, respectively. For Chukotka, RPPs relative to both Poaceae and Ericaceae were estimated while RPPs for central Yakutia were relative only to Ericaceae. Relative to Ericaceae (reference taxon, RPP = 1), Larix, Betula, Picea, and Pinus are overrepresented while Alnus, Cyperaceae, Poaceae, and Salix are underrepresented in the pollen spectra. Our estimates are in general agreement with previously published values and provide the basis for reliable quantitative reconstructions of East Siberian vegetation.

Climatic reconstruction at the early Miocene La Rinconada mine (Ribesalbes-Alcora Basin, eastern Spain) based on Coexistence Approach, CLAMP and LMA analysis

The early Miocene La Rinconada mine from eastern Iberian Peninsula contains a rich megafloral assemblage with abundant leaf fossils from a single stratigraphic level of the sedimentary succession. This has provided a good opportunity to undertake detailed comparative quantitative palaeoclimate reconstruction using different approaches, namely the Coexistence Approach (CA), Climate Leaf Analysis Multivariate Programme (CLAMP) and Leaf Margin Analysis (LMA). Considering the results of all techniques used, the palaeoclimate estimates are the following: mean annual temperature (MAT) CA = 10–16.5 °C/CLAMP = 11.48 °C, warmest month mean temperature (WMMT) CA = 25–26.4 °C/CLAMP = 23.31 °C, coldest month mean temperature (CMMT) CA = 4.3–4.8 °C/CLAMP = 0.84 °C, mean annual precipitation (MAP) CA = 1217–1297 mm, mean precipitation of the wettest month (MPWet) CA = 116–164 mm and mean precipitation of the warmest month (MPWarm) CA = 118–131 mm. Temperature and precipitation values obtained through CLAMP, LMA and CA indicate the occurrence of a wet and warm climate the whole year around with marked seasonality for rainfall and temperature but without a summer-dry regime. The climatic values obtained in the La Rinconada mine are in well accordance with other Burdigalian and late Burdigalian–early Langhian sites from the Iberian Peninsula (e.g. S 141 Borehole) and Central-Southern Europe (e.g. Holedeč, Čermníky, Přívlaky, Bílina Delta, Manisa-Soma, Spanokhorion and the Evia Island), suggesting the absence of a clear latitudinal gradient in temperature and precipitation for this period in Europe. This climate is consistent with the plant communities described in the area from taxonomic studies and IPR analysis.

Modern pollen–vegetation relationships along an altitudinal transect in the Western Higher Himalaya, India: Palaeoclimatic and anthropogenic implications

Palynology is one of the most reliable tools for the reconstruction of past vegetation and climate and modern pollen analogues are important for the calibration of fossil pollen assemblages. The present study analyses the pollen–vegetation relationships along a steep altitudinal gradient (2700–3680 m), in the western Higher Himalayan region. On the basis of altitude, three vegetation zones were demarcated: Zone I (2700–3100 m) is composed of mixed-temperate forest vegetation, dominated by Quercus semecarpifolia and Rhododendron arboreum; Zone II (3100–3250 m) is marked by sub-alpine forest vegetation, characterised by R. campanulatum and R. barbatum, along with Abies spectabilis and Q. semecarpifolia; Zone III (3250–3680 m) is above the tree-line (3250 m) and represented by alpine-scrub and meadows. Thirty-five surface soil samples (twenty, seven and eight from each zone, respectively) were analysed along the altitudinal transect to decode the representation of the extant vegetation in the pollen-rain. The pollen–vegetation relationship is non-linear due to the over-representation of extra-local Pinus pollen in each zone. Nonetheless, the modern pollen assemblages show a general correlation with the local broad-leaved taxa and the herbaceous elements; with the exception of Rhododendron pollen, which is under-represented. Among the non-pollen palynomorphs (NPPs), the presence of coprophilous fungal spores is compatible with the grazing activities in the area. Multivariate statistical analyses performed on the surface pollen data indicate that the dataset can efficiently distinguish the different vegetation zones across the altitudinal gradient. This work provides the modern analogues for pollen-based palaeoclimatic reconstructions for the Western-Higher Himalayan region, and would also help to decipher the inception and intensification of anthropogenic activities in the region.

Ancient DNA reveals a southern presence of the Northeast Arctic cod during the Holocene.

Climate change has been implicated in an increased number of distributional shifts of marine species during the last century. Nonetheless, it is unclear whether earlier climatic fluctuations had similar impacts. We use ancient DNA to investigate the long-term spawning distribution of the Northeast Arctic cod (skrei) which performs yearly migrations from the Barents Sea towards spawning grounds along the Norwegian coast. The distribution of these spawning grounds has shifted northwards during the last century, which is thought to be associated with food availability and warming temperatures. We genetically identify skrei specimens from Ruskeneset in west Norway, an archaeological site located south of their current spawning range. Remarkably, 14C analyses date these specimens to the late Holocene, when temperatures were warmer than present-day conditions. Our results either suggest that temperature is not the only driver influencing the spawning distribution of Atlantic cod, or could be indicative of uncertainty in palaeoclimate reconstructions in this region. Regardless, our findings highlight the utility of aDNA to reconstruct the historical distribution of economically important fish populations and reveal the complexity of long-term ecological interactions in the marine environment.

Long-term floristic and climatic stability of northern Indochina: Evidence from the Oligocene Ha Long flora, Vietnam

The antiquity of the tropical Asian flora is being revealed by recent detailed work on a number of Cenozoic plant megafossil sites, some of which have been radiometrically dated for the first time, but our knowledge of how the highly diverse modern biota came into being remains poor due to a sparsity of records. In this paper, we describe fossil plant assemblages from the Oligocene Dong Ho Formation of the Ha Long region, northern Vietnam. The Oligocene Ha Long megafossil flora has so far yielded 38 species, including conifers and angiosperms mainly belonging to Fagaceae, Lauraceae and Dipterocarpaceae, all with significant tropical Asian kinship. The Ha Long flora is similar to other Paleogene floras from southern China, especially those from the Pan Gulf of Tonkin region. The Ha Long floral composition is typical of a tropical-subtropical ecotone and the vegetation is reconstructed as a lowland tropical evergreen forest mixed with calcicole (limestone-loving) taxa. These taxa and the vegetation type they comprise still exist in this area. Palaeoclimate reconstruction made using both the Coexistence Approach and the Climate Leaf Analysis Multivariate Program indicate a mean annual temperature of ~20 °C, a coldest month mean temperature around 10 °C, and yearly precipitation averaging almost 2000 mm. These results suggest a warm and humid peripheral tropical environment. Floristic and climatic comparison within the Ha Long and other southern China palaeofloras reveals a long-term environmental, floristic and vegetational stability in this region since the Paleogene. This long-maintained plant diversity also provided a source for populating the East Asian flora and vegetation after the late Paleogene East Asian arid belt retreat.

Synchronous or Not? The Timing of the Younger Dryas and Greenland Stadial-1 Reviewed Using Tephrochronology

The exact spatial and temporal behaviour of rapid climate shifts during the Last Glacial–Interglacial Transition are still not entirely understood. In order to investigate these events, it is necessary to have detailed palaeoenvironmental reconstructions at geographically spread study sites combined with reliable correlations between them. Tephrochronology, i.e., using volcanic ash deposits in geological archives as a dating and correlation tool, offers opportunities to examine the timing of events across wider regional scales. This study aims to review the posited asynchrony of the Younger Dryas stadial in comparison with Greenland Stadial-1 by correlating new proxy data from southernmost Sweden to previous palaeoclimate reconstructions in Europe based on the presence of the Hässeldalen Tephra, the Vedde Ash, and the Laacher See Tephra. μ-XRF core-scanning data were projected using a recently published age–depth model based on these tephras and several radiocarbon dates, and compared to previous findings, including by adapting previous chronologies to the recently proposed earlier date of the Laacher See Tephra (13,006 ± 9 cal. a BP). Although the results to some extent support the idea of a more synchronous Younger Dryas event than previously assumed, this issue requires further high-resolution proxy studies to overcome limitations of temporal precision.

Investigation of the possible role of the Central Paratethys as a migration route and speciation area of the ancestors of Mediterranean Larroussius, Paraphlebotomus and Phlebotomus species

The Oligocene and Miocene tectonic and biogeographical alterations of the peri-Mediterranean area could strongly impact the speciation processes and migrations of Mediterranean sandfly species. To understand the possible former role of this palaeobiogeographic factor on ancestral sandfly species, the potential suitability values of five Larroussius, two Paraphlebotomus and one Phlebotomus species were modelled from the Rupelian to the Tortonian stage in the Central Paratethys. The bioclimatic extrema of this sandfly species and the Coexistence Approach-based palaeoclimatic reconstructions made the basis of hypothesis testing. In the case of the Tortonian stage, a georeferenced climatic model was created. The models indicate that the suitability values could notably vary by species and periods. The monsoon-influenced humid subtropical climate of the Oligocene epoch could be less suitable for the ancestors of Mediterranean sandfly taxa than the later, drier humid subtropical climates-characterised Miocene stages. The Central Paratethys area could be less suitable for ancestors of the extant Paraphlebotomus, and Phlebotomus in the Miocene epoch compared to Larroussius species. It may indicate that the Central Paratethys formed a barrier against the east-to-west migration of the ancestors of Phlebotomus and Paraphlebotomus species. In contrast, Larroussius species could prefer the Miocene climate of the Central Paratethys. In the Tortonian stage, mainly the coastal areas of the sea could be colonised by sandflies. These results indicate that the coasts of the Central Paratethys should be not only considered as a potential former migration route but could be a part of the speciation area of Larroussius sandflies.

Late Holocene glaciers in western Scotland?

ABSTRACT In this paper we use a numerical glacier-climate model, a detailed photogrammetric survey and lichenometry to reconstruct small palaeoglaciers on Ben Nevis and surrounding mountains in western Scotland. These glaciers would have been sustained under a climate where the mean annual air temperature was –1.0°C to –2.0°C compared to present-day values either with or without a decrease in precipitation amount of 10–30%. Historical meteorological data show that these air temperatures were reached on Ben Nevis in the latter part of the 19th century. Although we have no data on the age of these small glaciers, palaeoclimate reconstructions suggest that such conditions almost certainly existed several times during the Holocene in Scotland; the last time being the Little Ice Age of the 16th to 19th Centuries. We argue from this that small Scottish glaciers may have been able to develop in high sheltered cirques at many times during the Holocene and that the glacial history of Scotland therefore requires revision.

Small mammals of the Holocene sequence of Postes Cave (SW Spain): biogeographic and palaeoenvironmental implications for southwestern Iberia

ABSTRACT Postes Cave in SW Spain (Extremadura) displays a Holocene archaeostratigraphic sequence radiocarbon-dated to between c. 8.5–4 cal kyr BP (Mesolithic-Chalcolithic). The sediments collected at two areas within the cave yielded small mammal remains belonging to eleven species of rodents, ‘insectivores’, lagomorphs and chiropterans. This small mammal fossil assemblage is one of the few known to date in the southwest of the Iberian Peninsula. Preliminary taphonomic analysis and previously published data suggest that the remains were accumulated by the predatory activity of Eurasian eagle owls and small to medium-sized carnivores such as red foxes. The palaeoenvironmental and palaeoclimatic reconstructions performed show stable conditions with slight variations during its time span, suggesting an initial scenario of open forested habitats during the Mesolithic and Neolithic which progressively decreased in favour of more open habitats during the Chalcolithic coinciding with human-induced changes of the landscape and with the aridification trend of this period. The presence of Microtus cabrerae and Crocidura suaveolens in the assemblage is noteworthy since they are now extinct in this region. The plausible causes and the processes of these extirpations are discussed.

Isotopic analysis of otolith carbonates using laser heating: A fast method for obtaining high-resolution climate signal.

The stable isotopic compositions of biogenic carbonates like fish otoliths (ear bones) are widely used for palaeoclimatic reconstruction. The conventional method using acid-digestion of micro-milled samples is a multi-step time-consuming process. Here we report a fast method based on laser heating of otolith carbonates to obtain accurate and high-resolution stable isotopic compositions. Otoliths of catfish from the Gulf of Kutch were analysed to check the precision, accuracy and time-resolution of the isotope ratios. The CO2 , generated by heating otoliths with a 50 W CO2 laser, was analysed for its oxygen and carbon isotope ratio [δ18 O and δ13 C, with precision: 0.12 and 0.17‰ (1σ), accuracy: 0.13 and 0.25‰, respectively] using a continuous-flow isotope ratio mass spectrometer. The effect of laser power (0.7-2W) was assessed for reproducible data. Samples were roasted and analysed to account for the effect of the inherent organic matter on the isotopic values. Roasting did not alter the δ18 O of the otoliths but increased the δ13 C slightly. High-resolution (125 μm) analysis of the right and left otolith of a fish yielded similar δ18 O and δ13 C values, suggesting the suitability of either of them for deriving the climate signal. An increase in δ18 O values from ~ -2‰ to ~ -1‰, observed across the ontogeny, is consistent with the known migratory behaviour of the catfish between freshwater and the sea. The otolith δ18 O value of an adult fish records the sea surface temperature (with ~3°C uncertainty) on a monthly scale. The otolith δ13 C values, with the knowledge of dietary δ13 C, provide the mean annual δ13 C value of dissolved inorganic carbon. The study provides a rapid method for retrieving high-resolution seasonal climate data from otoliths found aplenty in geological/archaeological records.

Palaeoecological significance of the “wolf event” as revealed by skull ecometrics of the canid guilds

Members of the mammalian order Carnivora are rarely considered as proxies for palaeoecological reconstructions due to their broad phenotypic plasticity and high climatic tolerance. However, palaeontologists have traditionally interpreted the appearance of some particular carnivoran species in relation to major climatic events. The ‘wolf event’ characterised the inset of climatic deterioration for continental Eurasian fauna, ca 2.0 million years ago. It was defined as the dispersal of cursorial wild canids from East Asia to Europe consequently to the spread of the steppe environment. Anecdotal interpretations were never supported by rigorous testing about the palaeoecological significance of these canid taxa. Here, we employ two dimensional geometric morphometrics of canid skulls to characterise and interpret the structure of extant guilds and its relationship with climate and provide inferences on the early Pleistocene Valdarno community. Averaged skull size and shape of canid guilds are currently associated with climatic parameters that reflect annual mean temperature, seasonality and precipitation. The canid guild from Valdarno showed a clustered phylogenetic structure and its average shape resembles those of communities characterised by relatively high seasonal environments. This study supports the use of canid community structure for palaeoclimatic reconstructions and validate the early Pleistocene as a period of climatic deterioration for Eurasian large mammal fauna.

Palaeoecological Interpretation of a Late Holocene Sediment Sequence from the Alpine Belt of the Southern Mongolian Altai Mountains

The climate in the Altai Mountains is determined by two major climate systems whose dominance has varied over time, leading to significant spatio-temporal changes in temperature and precipitation during the Holocene. This study aimed at the reconstruction of the local to regional moisture and temperature conditions in an alpine belt of the southern Mongolian Altai during the Late Holocene. It thereby contributes to a more comprehensive understanding of the region’s palaeoclimate in the Holocene. Our reconstruction is based on palynological and sediment analyses as well as radiometric age determinations of samples from a 130 cm exposed soil/sediment profile within the alpine belt. Largely supported by sedimentological and geochemical observations, the pollen assemblages indicate a warm and dry period between about 2600 and 2250 cal a BP, a subsequent cold and humid phase extending to about 130 cal a BP, and a return to warm and dry conditions lasting to present. Our data support the results of recent studies on the regional climate variability and the observation of significant differences in the mode of climate changes and its temporal sequence within the Altai Mountains. Although the pollen assemblages in the profile reflected a continuous anthropo-zoogenic influence on the study site’s vegetation climatic signals were clearly detectable, underlining the indicator value of the pollen data from the Alpine sediments for regional palaeoclimatic reconstruction.

Evidence for the Little Ice Age in upland northwestern Europe: Multiproxy climate data from three blanket mires in northern England

The Little Ice Age (LIA) is a well-recognised palaeoclimatic phenomenon, although its causes, duration and severity have been matters of debate and dispute. Data from a wide range of archives have been used to infer climate variability before, during and after the LIA. Some published proxy-climate data from peatlands imply that two particularly severe episodes within the LIA may be contemporaneous between hemispheres; these echo a previous climatic downturn ca. 2800 cal BP of similar severity but lesser duration. Here, we present palaeoclimate data from the mid- to late-Holocene, reconstructed from three blanket peats in Yorkshire: Mossdale Moor, Oxenhope Moor and West Arkengarthdale. Multiproxy techniques used for palaeoclimatic reconstruction were plant macrofossil, pollen and humification analyses. Dating was provided by a radiocarbon-based chronology, aided by spheroidal carbonaceous particles (SCPs) for all sites, and 210Pb dates for one. The LIA presents as a distinct climatic event within each palaeoenvironmental record at the three sites. These indications are compared with terrestrial datasets from northwest Europe and elsewhere. A broad degree of synchronicity is evident, signifying that the LIA is one of the most pronounced downturns in global climate in the last ca. 6000 years, and arguably the most routinely recorded within the Holocene.

Depositional timing and palaeoclimate interpretation of the Tamala Limestone aeolianites in Shark Bay, Western Australia

• AAR dating shows an aging of the Tamala Limestone aeolianites towards the east. • The Tamala Limestone aeolianites are landward-advancing (i.e., transverse) dunes that have migrated from west to east. • Dune accumulation occurred during dry/cold glacials of the Pleistocene period. • Dune activity in the region is strongly linked to a weak Leeuwin Current. • Dune accumulation occurred during a northward shift of both the Hadley and Ferrel cells. The carbonate units grouped under the name “Tamala Limestone” outcrop for a thousand kilometres along the coast of Western Australia. The extensive Zuytdorp Cliffs shaping the northern half of the coastline up to Shark Bay expose and offer an exceptional access to the stratigraphy of this formation. The regional survey of the Shark Bay region, which combines both stratigraphic and sedimentological analyses, reveals that the Tamala Limestone is a dry accumulating aeolian system composed of large transverse dunes migrating parallel to the prevailing winds. Accordingly, the amino acid-data show an aging of the units towards the east. Episodes of carbonate aeolian sedimentation correlate with the successive glacial intervals of the Pleistocene whilst paleosols are correlated with breaks in the sedimentation during interglacial intervals. Palaeoclimate reconstructions reveal that sea level and sea surface temperature of the Indo-Pacific Warm Pool were lower during glacial intervals. The weakened Leeuwin Current, which flows along the western coast of Australia and is the main source of precipitation, contributed to the aridification of the region. Consequently, and associated with a northward migration of the Hadley and Ferrel cells, periods of glaciation were drier. By contrast, paleosols developed through dissolution of the carbonate units during more humid interglacial intervals.

Reconstructing Terrestrial Paleoclimates: A Comparison of the Co‐Existence Approach, Bayesian and Probability Reconstruction Techniques Using the UK Neogene

AbstractNeogene sediments in the UK are ideally situated for understanding the early development of hydrological dynamics and atmospheric circulation that led to the modern oceanic climate of northwest Europe. Onshore Neogene fossiliferous deposits in the UK are limited to the solution pipe fills at Trwyn y Parc in Anglesey (Middle Miocene), the Brassington Formation of Derbyshire (Serravallian‐Tortonian), and the Coralline Crag Formation (latest Zanclean‐earliest Piacenzian) and Red Crag Formation (Piacenzian‐Gelasian) in southeast England. Palynoflora from these localities can be used to provide snapshots into the climate at the time of deposition, however, palaeobotanical‐based reconstructions are typically lacking in their poor estimation of error. Therefore, we present the first pre‐Quaternary application of two terrestrial climate reconstruction techniques: CREST (Climate Reconstruction SofTware) and CRACLE (Climate Reconstruction Analysis using Coexistence Likelihood Estimation), that use Bayesian and likelihood estimation probability respectively to generate a new palaeoclimate reconstruction, and compare this to Co‐existence Approach reconstructions from the UK and continental Europe. Our study shows how Mean Annual Temperature (MAT) declines by 3°–6°C, Mean Annual Precipitation (MAP) declines by 480–600 mm and Precipitation Seasonality approximately halves throughout the Neogene. CREST and CRACLE reconstructions overlap with the Co‐exisence Approach and have the advantage of providing uncertainty, rather than ranges. The UK appears to have had a milder, wetter, and less seasonal climate than continental Europe. This is likely due to the buffering effects of the Atlantic Ocean and North Sea ameliorating the UK Neogene climate despite regional and global changes in atmospheric and oceanic circulation.

A high-altitude calibration set of modern biotic proxies from the Western Himalaya, India: Pollen–vegetation relation, anthropogenic and palaeoclimatic implications

We analysed the pollen composition, non-pollen palynomorphs (NPPs) and stable carbon isotope data (δ13C values) of surface sediments (soil), from the proglacial deposits (outwash plain and the two levels of kame-terraces) of the Chorabari Glacier, Kedarnath, India. The main objective was to develop the modern-proxy analogues, for the calibration of fossil records, for use in palaeoclimatic reconstructions. The pollen–vegetation relation is incompatible (non-linear) with the present vegetation, as the pollen assemblages are marked by the prolific over-representation of extra-local pollen, especially Pinus, over the local herbaceous taxa. Multivariate principal component analysis (PCA) was applied on the palynological data to ascertain the major groups of pollen in relation to the vegetation types and reveal variations in the pollen records between the kame-terraces and the outwash plain. δ13C values of the soil organic matter (SOM) show an average of − 27.0‰, indicating a C3 dominant vegetation. The pollen records have also revealed the anthropogenic activities in the form of degradation of tree-line and over-grazing by the domesticated animals. The NPPs reflect the prevalence of grazers in the present times, and would be useful in tracing the advent and intensification of grazing in the region. The modern pollen analogues show a good correlation with the fossil pollen data. The present study provides the much needed modern biotic analogues for vegetation-based past climatic reconstructions from the alpine regions of the Western Himalaya.

Palaeoecologic and Palaeoclimatic Inferences from Calcareous Nannofossils in Western Lobe Offshore, Niger Delta

In support of the ongoing temporal palaeoenvironment and palaeoclimatic reconstructions of the Neogene sediments, this study attempts to detail the paleo-proxies recovered from DEL-1 Well, western offshore Niger Delta. The standard smear slide method enabled the recovery of well-preserved calcareous nannofossils that depict early to mid–Miocene (NN4–NN5) sediments. The up-hole relationships between the nannofossil accumulation rate (NAR), the relative abundance of Discoaster and coccolith size of Reticulofenestra show step by step collapse of sea surface stability from early to middle Miocene. The lower horizons (8000–9460 ft) exhibit a low NAR, relatively high Discoaster abundance and relatively large Reticulofenestra size to suggest a deep thermocline and nutricline that characterise oligotrophic conditions in less warm-water induced climate. Conversely, upper horizons (5225–6550 ft) exhibit a high NAR, relatively low Discoaster abundance and relatively small Reticulofenestra size to suggest a shallow thermocline and nutricline that characterise eutrophic conditions in warm-water induced climate. The relative abundance of Helicosphaera carteri within the mid-NN5 suggests mesotrophic conditions within a stressed environment, with the possible occurrence of carbonate crash events. The combined parameters indicate gradual eutrophication and collapse of sea surface stability favouring nutrients and influx of terrestrial sediments in the ocean water as it progressed from early to middle Miocene. The abundance of the palaeo-proxies assemblages suggests hyposaline waters in a neritic environment that prevailed during the warm climatic condition.