Cal Kyr BP Research Articles

Variation of summer monsoon intensity in the North China Plain and its response to abrupt climatic events during the early-middle Holocene

Ningjinpo paleolake was the largest lake in the North China Plain during the Holocene, and its continuous sedimentary record has the potential to reconstruct the summer monsoon intensity and determine the limnological response to abrupt climatic events at a high resolution. Here we use AMS 14C dating and analyses of grain-size and major element contents, and the results show that: (1) During 11.5–10.0 cal kyr BP, the geochemical climate change index (C) (1.16), sediment accumulation rate (SAR) (0.007 cm/yr) and median particle diameter (Md) (20.6 μm) are the lowest within the section, while the geochemical drought index (0.0323), Fe/Mn ratio (0.0088) and clay content (17.3%) are the highest, which indicate that the North China Plain received less precipitation, and chemical weathering and erosional intensity in the Ningjinpo paleolake catchment were weak. (2) During 10.0–7.7 cal kyr BP, the C index (1.36), content of sand (19.1%) and silt (68.0%), Md (27.2 μm) and SAR (0.019 cm/yr) increase significantly. These characteristics indicate that the climate gradually became wetter, chemical weathering and erosion intensity increased, and there was increased runoff to the lake, which raised the lake level. (3) During 7.7–5.5 cal kyr BP, the C index (1.56), silt content (71.8%) and SAR (0.030 cm/yr) increase to the highest, while the Fe/Mn ratio (0.0068), sand content (14.4%) and Md (21.4 μm) decrease to their lowest levels. These suggest the climate was warm and humid, the runoff to the lake was large, chemical weathering in the catchment was strong, and the water level of the lake reached the maximum for the Holocene. (4) During 5.5–3.3 cal kyr BP, the C index (1.26) and SAR (0.011 cm/yr) decrease substantially, whereas the sand content (28.2%) and Md (18.3 μm) increase to the highest levels. These characteristics demonstrate that the climate gradually became arid, the runoff to Ningjinpo paleolake was reduced, the intensity of chemical weathering and erosion in the catchment weakened, and the lake level decreased, although the high frequency of floods in this period. (5) In addition to the globally-recorded abrupt climatic events at ~8.2 cal kyr BP, ~5.3 cal kyr BP and ~4.2 cal kyr BP, which were recorded in the northern monsoon region of China, an abrupt climatic event in the middle Holocene, at ~7.2 cal kyr BP, was also recorded. In the northern monsoon region of China, these events may have been amplified by unusually active ENSO since the middle Holocene.

Climate changes in the Qaidam Basin in NW China over the past 40 kyr

Little is known about the climate and environmental changes that have occurred in the extremely arid regions of China since MIS (Marine Isotope Stage) 3 (59–29 cal kyr BP), when most regions in northwestern China and the Tibetan Plateau featured warm and humid conditions. In this paper, we present a record of the climate changes in the Qaidam Basin in arid northwestern China over the past 40 kyr based on the mineralogy of a 35-m-long sediment core recovered from Qarhan Salt Lake. Our results show that the lake was a saline or hyper-saline lake saturated with respect to gypsum between 40 and 33 cal kyr BP. Beginning at 33 cal kyr BP, evaporite formation was dominated by halite precipitation, indicating that the lake salinity had increased extensively and that the climate became drier during 33–24.5 cal kyr BP. The lake salinity then increased continuously, resulting in the appearance of bischofite between 24.5 and 14.6 cal kyr BP. The disappearance of bischofite and the increase in gypsum indicate that the salinity of the water decreased slightly between 14.6 and 8.3cal kyr BP. However, during the last 8300 years, the lake has dried up and is now a playa. Generally, the climate was wet in late MIS 3, arid in MIS 2 (29–11.7 cal kyr BP), and hyperarid in the Holocene. The relatively humid conditions may have resulted from weak evaporation caused by the relatively low insolation and intense ice-albedo feedback in late MIS 3. The decreased insolation and dramatically increased Eurasian ice volume in MIS 2 may have led to limited precipitation, which resulted in persistent dry climate conditions in the Qaidam Basin. In the Holocene, the reduction in ice volume reduced the albedo, and this change, in conjunction with increased insolation, may have led to evaporation exceeding local precipitation, resulting in hyperarid climate conditions in the Qaidam Basin.

Long-term winter/summer warming trends during the Holocene revealed by α-cellulose δ18O/δ13C records from an alpine peat core from central Asia

Based on previously reported monitoring results from the alpine Sahara sand peatland (SSP) in the southern Altai Mountains, and modern observational δ18Op data from the Altai area, the new SSP peat α-cellulose δ18O (δ18Ocell) record spanning the last ∼11,000 years is determined to be an indicator of winter temperature. The record shows a long-term winter warming trend during the Holocene. Therefore, possibly for the first time, the SSP δ18Ocell record, combined with the reported SSP α-cellulose δ13C (δ13Ccell) record from the same peat core and supported by an independent modern-process study, provides records of Holocene winter and summer temperature. These signals demonstrate robust long-term winter/summer warming trends during the Holocene that are supported by independent records from nearby sites. Comparison of the SSP Holocene temperature records with those of winter/summer insolation and GHG (atmospheric greenhouse gas) forcing demonstrates a close link between temperature and insolation (a natural factor) prior to ∼5 cal kyr BP (1 kyr = 1000 years; BP = before present, where “present” is defined as AD 1950). However, there may be a close link between increased GHG forcing (a possible anthropogenic factor) and increased temperature after ∼5 cal kyr BP. We emphasize that, given the scarcity of high-quality, well-dated Holocene temperature records, the possible link between GHG forcing and temperature since the mid-Holocene needs to be further investigated. Thus we conclude that an increased number of reliable Holocene temperature records from other regions are urgently needed in order to determine the spatial extent (regional or global) of the Holocene warming trend.

Holocene dynamics of the southern westerly winds over the Indian Ocean inferred from a peat dust deposition record

The southern westerly winds (SWW) play a major role in climate variability in Southern Hemisphere mid- and high-latitudes, regulating rainfall, ocean circulation, and the Southern Ocean carbon sink. Despite their importance, little is known about millennial scale changes in the SWW and how they have influenced the climate system in the past and interacted with the Earth’s surface elements, such as dust, nutrients and carbon. Here we present a dust record from a 6.6 kyr old peat core in Amsterdam Island (AMS) situated at the northern edge of the SWW (37°S) in the Southern Indian Ocean. Mineral dust flux was used to track atmospheric dust production, long-distance transport and subsequent deposition. Dust provenance was determined from rare earth element (REE) and Nd isotopic signatures (εNd) in the peat core, compared with a reference dataset of Southern Hemisphere dust sources. Using a multi-proxy mixing model, the εNd and REE ratios show a relatively uniform mixture of ca. 40% local, 15% Southern African and 45% Southern South American dust sources since 6.6 cal kyr BP. However, from 1910 AD onwards, there is a doubling in the contribution from Southern Africa (32%). Two mineral dust flux minima occur at 6.2–4.9 cal kyr BP and 3.9–2.7 cal kyr BP, interpreted as periods with equatorward-shifted and/or strengthened SWW at the northern edge of the wind belt. Conversely, periods of higher dust flux at 6.6–6.2 cal kyr BP, 4.9–3.9 cal kyr BP, and 1.4 cal kyr BP onwards are interpreted as poleward-shifted and/or weakened SWW. These interpretations are based on the findings that higher (lower) wind speeds lead to enhanced (less) removal of distal dust on the way to AMS, by wet deposition and turbulence. Published Holocene SWW records at the northern edge of the wind belt (33–41°S) covering South-America, Southern-Africa and Australia, show much variability over the last 6.6 kyr. We suggest this reflects complex regional climate variability in the different SH longitudinal sectors, indicating that SWW are not zonally homogeneous at the northern edge of the wind belt. The recent shift in dust provenance is not accompanied by enhanced total dust deposition at AMS. We therefore suggest that human impact (e.g., land use changes) and drier climate conditions in Southern Africa have led to enhanced dust mobilization.

Palaeoenvironmental changes in the Khuran Estuary of SE coastal Iran during the last two millennia, based on the analysis of a sediment core

Late Holocene palaeoenvironments of the northern Strait of Hormoz and the palaeohydrology of the SE Zagros were reconstructed using multi-proxy analysis (e.g. magnetic susceptibility (MS), grain size analysis, total organic matter %, CaCO3%, C/N ratio, and foraminiferal assemblage) of a radiocarbon-dated sediment core (KHU) from the Khuran Estuary. High sedimentation rate (1.23 cm yr−1) and elevated grain size, MS, C/N ratio, as well as the abundance of porcelaneous foraminifers (Quinqueloculina sp.), revealed that during the first three centuries CE, sediments settled in a relatively high accommodation space with strong tidal currents and raised terrigenous sediment input from the SE Zagros. About four centuries later, the gradual disappearance of porcelaneous taxa and the dominance of agglutinated and hyaline ones, besides the increasing C/N ratio, indicated that geomorphological conditions became favourable for mangroves. MS reduction and negative correlation between MS and grain size showed that during this period the relative proportion of terrigenous particles in sediment decreased which, in turn, confirms a reduction of river discharge. Afterwards, the abundance of mud aggregates, low C/N ratio and a dramatic reduction of foraminifers showed that a < 1 m thick sediment unit representing a relatively long period (1.4 cal kyr BP onwards; sedimentation rate: 0.06 cm yr−1) was deposited within a high marsh environment being mostly above mean high water. Generally, correlations between proxy records of the core KHU with Zagros lakes and other archives from African lakes and Greenland re-inforce the reconstruction of atmospheric teleconnection between the North Atlantic and the interior of West Asia during the late Holocene.

Paleoproduction and environmental change at Mono Lake (eastern Sierra Nevada) during the Pleistocene-Holocene transition

The late Quaternary limnological history of Mono Lake (~16.6–4.3 cal kyr BP), a hydrologically closed basin in the eastern Sierra Nevada (California), is inferred based on a multi-indicator analysis of a long (~10.8 m) composite sediment core constructed from overlapping deepwater piston cores. The composite core, dated by 14C and tephra correlation, shows variations in sedimentology, magnetic susceptibility, elemental geochemistry and stable isotopes through time, consistent with changes in aquatic productivity, hydroclimate, and volcanism. In the late Pleistocene, deepwater stratigraphy was influenced by high-amplitude water-level changes and runoff from a glaciated watershed. In contrast, Mono Lake's elevation was lower in the Early to Middle Holocene; low-amplitude water-level changes, wave reworking of the shoreline, and water-column stratification were important controls on facies during that time. The data suggest that the chief controls on organic facies development in Mono Lake – productivity, preservation, and dilution dynamics – are sensitive to climate changes that influence lake-level elevation, water chemistry, and the position of deltas. The study shows that deepwater sediments from certain locales in Mono Lake are well-preserved, continuous, and can be reliably dated with 14C applied to terrestrial materials. When paired with precisely dated paleoshoreline data, these sediments provide a high-resolution archive of deglacial and Holocene environmental information for the eastern Sierra Nevada.

Северо-западные берега Онежского полуострова Белого моря в голоцене: условия развития, динамика, хронология

According to detailed geomorphological studies, radiocarbon dating and Stolbovoe Lake sediments and terrace sedimentary cover diatom analysis three different stages of coastal zone development in the northwest of the Onega Peninsula had been identified and dated. The abrasion coastlines at elevations of 18.5–30 m were formed earlier ~9.5–8.5 cal kyr BP, during the Late Glacial transgression and the glacio-isostatic regression of the Early Holocene. A well-defined predominantly abrasion coastline at elevations of 14–18.5 m was formed ~8.2–5.8 cal kyr BP during the mid-Holocene Tapes transgression with insignificant fluctuations of the sea level with hydrodynamic activity greater than present. A short-term episode (~6.0–5.8 cal kyr BP) of the relative sea level rise on the shore of the Dvina Bay has been identified, probably associated with storm surges. Abrasion-accumulative coastlines at elevations up to 14–15 m were formed after ~5.8 cal kyr BP in the conditions close to modern. At all stages of development, the shores were dynamically young. The leading role of the postglacial uplift in the extension of the coast contour, and of the structure of the glacial relief–in the morpho- and lithodynamics of the coastal zone is shown. During the Tapes transgression, the rates of uplift of adjacent morphostructural blocks differed (~0.5 and 2.1–2.2 mm/year); then the uplift became uniform (~2.8–2.9 mm/year). The structure of the coastal forms indicates the constant prevailing directions of the waves and sediment transport, starting from the middle Holocene.

Mid- and low latitude effects on eastern South African rainfall over the Holocene

Climate variability and its forcings in eastern South Africa during the late Quaternary remain poorly understood with data suggesting temporal variability and spatial heterogeneity. To constrain the variability and the drivers of past climate, we explore vegetation (C3/C4) and hydrological change using stable carbon and hydrogen isotopes of plant-waxes and X-ray fluorescence (XRF) analysis in marine core GeoB20610-2 offshore the Limpopo River. We find evidence for two climatic phases: an initial arid phase (c. 7–3 cal kyr BP), followed by a wetter phase (c. 3–0 cal kyr BP). To put our findings into a regional context, we investigate a latitudinal transect of sites along eastern South Africa and divide the region into three distinct hydro-climatic zones, with significantly different climate drivers. During the last c. 3 cal. ka BP, wet climatic conditions dominated the northern summer rainfall zone (SRZ) and the southern South African zone (SSAZ), whereas arid conditions prevailed in the central and eastern SRZ. In the northern SRZ the climate was driven by local insolation, where heightened insolation resulted in more precipitation. The aridity during the last c. 3 cal. ka BP in the central and eastern SRZ and the increased humidity in the SSAZ are attributed to an equatorward displacement of the southern hemisphere westerlies, the South African high-pressure cell and the South Indian Ocean Convergence Zone (SIOCZ). For the Holocene we find little evidence for an Indian Ocean SST control on climate. The results for the Limpopo River catchment region highlight the spatial heterogeneity of Holocene climate conditions in eastern South Africa and indicate significant latitudinal differences in climate drivers.

The deficiency of organic matter 14C dating in Chinese Loess-paleosol sample

Abstract In the absence of reliable charcoal, wood or plant macrofossils, organic matter in loess-paleosols is often used for 14C dating. However, organic matter can be contaminated by a variety of carbon sources within the sediments, and this may affect the radiocarbon dating results. Specific chemical pretreatments can be applied to minimize such effects, and comparisons with optically stimulated luminescence (OSL) dates from the same sediments allows us to assess potential open system effects on organic matter. Here we present comparisons of the two geochronometers from loess-paleosol deposits in the Chinese Loess Plateau. Our results show that loess -paleosol samples from the past 25 cal kyr BP generally yield reliable 14C dates, however, beyond this range, specifically ~25–59 cal kyr BP, we observe a steady increase in OSL ages with depth, but no consistent increase in corresponding AMS 14C ages. We suggest that relatively old samples from loess-paleosols should be studied using techniques such as compound-specific radiocarbon dating, ramped pyrolysis or stepped-temperature combustion.

Central Iberia in the middle MIS 3. Paleoecological inferences during the period 34–40 cal kyr BP

The environmental conditions that existed during the period between 45 and 30 ka are of vital importance for addressing the transition between the Middle and Upper Paleolithic. It seems to be a hiatus of Paleolithic populations, a “no (hu)man’s land” in Central Iberia, coinciding with the mid part of Marine Isotope Stage (MIS) 3, between 42 and 28 cal kyr BP. This break in the archaeological record makes it difficult to address this period paleoecologically. Here we present a new cave site, Portalón del Tejadilla (Segovia), dated to a period roughly between ∼34.2 and 40.4 cal kyr BP in which cold-adapted faunas, such as woolly rhinoceros and giant deer, have been recovered in a hyena den site context. This site is located in Central Iberia, and more specifically, on the southern edge of the northern Plateau, an unexpected region for the presence of these faunas during the MIS 3. These new findings extend the geographical distribution of several species, including Coelodonta antiquitatis and Megaloceros giganteus. Furthermore, they document a climatic deterioration (colder and dryer) during the mid MIS 3 in Central Iberia in one of the coldest and driest episodes of the Late Pleistocene. Portalón del Tejadilla fills this temporal gap and provides valuable paleoecological information about the transition between the Middle to Upper Paleolithic.

Pastoralism increased vulnerability of a subalpine catchment to flood hazard through changing soil properties

Soil erosion is strongly linked to both precipitation patterns and land-use. We examine the effects of erosion and its drivers (i.e. human or/and climate) on soil evolution from the study of lacustrine archives in the northern French Alps. Multi-proxy analyses of the Lake Gers sediment sequence combined with the study of soils and rocks of its catchment allowed to reconstruct its evolution over the past 4.6 kyr. This included 14C dating, short-lived radionuclides, geochemistry, loss on ignition, grain-size analyses, as well as plant and mammal DNA analyses. A total of 127 instantaneous deposits were identified among the continuous sedimentation in the lake and 93 were interpreted as flood deposits. Erosion was quantified for the whole catchment considering both the continuous sedimentation and the flood deposit thicknesses.The catchment is mainly formed by andesitic sandstones over which Andosols and Podzols can develop. However, low weathered materials from colluviation constitute the main input to the lake.Four main phases of changes in soil weathering were recorded by increases in K2O/TiO2 ratios, associated with an increase in both erosion and flood-frequency. Two phases were associated with climate cooling in the Western Alps, from 2.65 to 2.5 and from 1.45 to 1.3 cal kyr BP. The two others (1.9–1.75 and 0.9–0.4 cal kyr BP) were triggered with deforestation, with cow grazing during the Roman period, and with grazing of cows, sheep and goats during the Medieval period, amplified by the onset of the Little Ice Age. The increase in erosion and flood frequency after 950 cal yr BP indicates substantial damages to soils of the catchment including increase of their erodibility over the last millennia.

The first AMS radiocarbon dates of organic matter microinclusions in the ice wedge of the upper part of the Batagay yedoma megaslump, Yakutia

Microinclusions of organic matter were dated using acceleration mass spectrometry in seven samples from the upper part of the thick Pleistocene syngenetic ice wedges uncovered in the outcrop of the Batagay yedoma located in northern Yakutia along the upper Yana River (67,58 N, 134,77 E). The dated fragment of ice wedge was formed within 22 760-20 010 radiocarbon years BP (or 27 100-33 800 cal BP). Using detailed isotope data, the January average air temperature in the Late Pleistocene (25-30 cal kyr BP) was calculated for the Batagay section along with a series of reference sections in northwestern Yakutia. It was shown that the minimum January average air temperature (-51 C) was characteristic at that time for the area of the Batagaika crater, with values 4-5 higher in areas 500-600 km further north. This effect was caused by the occurrence of the Yakutian anticyclone in winter during the Late Pleistocene, which was just as pronounced as that at the present time.

Evidence of cooling in the tropical South Atlantic off southeastern Brazil during the last 50 kyr

The tropical Atlantic has been considered as a huge energy source, contributing to the tremendous heat and moisture that can be delivered from the equatorial region towards the high latitudes through ocean current circulation. However, there is still debate whether the cold waters from the south ever had an influence on the tropical Atlantic off southeastern Brazil during glacial times. This study aims to reconstruct the tropical Atlantic environmental conditions off southeastern Brazil, to investigate whether this area had been influenced by cold waters from the south during the last glacial maximum (LGM), and to correlate the marine environmental changes with the climate and vegetation changes on the continent. This study provides the first long dinocyst record off southeastern Brazil of the last ca. 50 kyr. In combination with the freshwater algae and pollen records, it contributes to a better understanding of marine and terrestrial environmental changes in tropical regions of southeastern Brazil. The study indicates a relatively low sea surface temperature (SST), more eutrophic and unstable sea surface conditions in tropical South Atlantic off southeastern Brazil from 50 to 45 cal kyr BP. From 45 to 25 cal kyr BP, SST was relatively high, stable and less eutrophic conditions occurred, indicating a stable influence by the Brazil Current (BC). From 25 to 12 cal kyr BP, in particular during the LGM, SST decreased markedly, suggesting the occurrence of colder water masses from the south. Since the Lateglacial, SST increased and became relatively stable.

Coastal landscape evolution of Corsica island (W. Mediterranean): palaeoenvironments, vegetation history and human impacts since the early Neolithic period

A multi-proxy investigation of sediment cores has enabled us to reconstruct the coastal environmental evolution of East-Central Corsica (the sites of Saint Florent, Piantarella-Bonifacio and Palo-Solenzara) for the last 8000 years. The analytical methods comprise pollen (five original pollen diagrams), weight loss-on-ignition measurements, laser granulometry, and ostracod identification. In addition, 26 radiocarbon dates are used to provide a robust chronostratigraphy for the sedimentary sequences. The assessment of coastal landscape dynamics enables us to define the major morphological changes and to evaluate the complex interplay between climatic forcing and anthropogenic activity on the vegetation history of Corsica, within an archaeological context, since the early Neolithic period (∼7.4 cal kyr BP). The major findings are that the first farmers reached Corsica by sea, and they encountered a coastal environment mainly composed of freshwater ponds located close to the shoreline. This specific paleoenvironmental feature offered a favourable location for agriculture and for the development of permanent settlements where a subsistence economy was developed. Since the Middle Holocene, postglacial sea-level rise has caused major changes in local coastal environments, often characterized by salt intrusion into freshwater bodies. At the transition between the Mid and Late Holocene (∼4.0 cal kyr BP), an increase in both salinity and aridity caused substantial landscape changes, mainly characterized by a further expansion of saline marshland, mainly occupied by Chenopodiaceae. The results also provide new insights into the role of Erica in the original Holocene vegetation of Corsica. Our data clearly indicate that an Erica arborea - Quercus ilex forest transition occurred before 6.3 cal kyr BP, significantly earlier than previously proposed. Finally, the earliest evidence of cereal cultivation is at ∼7350 cal kyr BP, and in addition we are better able to constrain the role of humans in the landscape dynamics of Corsica since the early Neolithic.

Warm Younger Dryas summers and early late glacial spread of temperate deciduous trees in the Pannonian Basin during the last glacial termination (20-9 kyr cal BP)

This paper focuses on the last glacial termination vegetation and climate reorganization of the Eastern Pannonian Plain via the multi-proxy paleoecological analysis of Kokad mire in Eastern Hungary. Grains size, sediment chemistry and magnetic susceptibility records are compared with the pollen and plant macrofossil records on the basis of which biome and quantitative summer mean temperature reconstructions are provided and discussed with other climate records of the region. Biome assignments indicated (graminoid and forb) tundra vegetation from 19,440 cal yr BP with the local presence of Betula pendula, B. pubescens, B. nana, and Pinus sylvestris. A rapid biome shift to cool coniferous forest took place at 16,200 cal yr BP, and a second biome shift was identified at 14,740 cal yr BP when cool mixed forest developed and persisted into the Early Holocene. The most prominent feature of the record was the early post last glacial maximum (LGM) establishment (17,700 cal yr BP) and expansion (14,700 cal yr BP) of elm (Ulmus) and hazel (Corylus) supporting the phylogeographical evidence for extra-Mediterranean refugia in the Pannonian Basin. The fungal spore record indicated the presence of large grazing mammals locally after the LGM until ∼16,780 cal yr BP. Their disappearance predated the biome shift to cold coniferous forest and the final increase of forest fires. Pollen based summer temperature reconstruction suggested relatively warm summers (∼14.5 °C) by 19,440 cal yr BP, and buffered July mean temperature fluctuations throughout the last glacial termination in this region with < 1 °C decrease in summer mean temperatures during the Younger Dryas stadial, and ∼2.2 °C warming in the Early Holocene. Our comprehensive summary of the basin’s Late Pleniglacial (24,000–14,600 cal yr BP) and late glacial paleoenvironmental and paleoclimate records showed a partially wooded landscape with higher woody cover in Western Hungary. Several loess and lake archives confirmed that in this region of Europe the warming after Heinrich event 1 (around 16,200 cal yr BP) had similar amplitude to the late glacial warming.

A 16,000-year record of climate, vegetation and fire from Wallacean lowland tropical forests

The tropical forests of Sulawesi represent some of the most diverse, biogeographically significant ecosystems globally. However, long-term ecological data for the region are scarce, making it difficult to predict vegetation response to future climatic and anthropogenic drivers of change. This is problematic as gauging the acclimation thresholds of forests within tropical Asia has been identified as an IPCC policy imperative.This study uses palynological and geochemical analysis of sediments from a tectonic basin – Lake Lantoa – to reconstruct the hydroclimatic, fire, and tropical rainforest dynamics of south Sulawesi over 16,000 years, and reveal the response of lowland ultramafic forest to large-scale environmental change. Our results show that the Late Pleistocene was characterised by a drier, more seasonal climate and persistent fire in the landscape. These conditions supported a slightly open, Gymnostoma-rich, semi-seasonal forest, and constrained the available habitat range for hydrophilic tropical conifers. Increased effective moisture in the Holocene, interpreted from the onset of periodic lake stratification under deeper conditions, appears to have precluded forest burning, and facilitated the expansion of a lowland ultramafic rainforest and upland tropical coniferous forest. An increase in garden/secondary forest taxa and ground ferns from ∼2 cal kyrs BP implies increased human management of the landscape. While these data highlight the compositional dynamism of lowland forest in Wallacea to seasonality, fire, and reduced precipitation, they demonstrate biome-scale resilience to glacial-scale environmental change. This contrasts with interpretations of forest sensitivity to climatic change drawn from analysis of leaf wax isotopes from adjacent lake basins, highlighting the value of adopting multi-proxy, taxonomically high-resolution techniques for reconstructing floristic histories.

Abrupt shifts of productivity and sea ice regimes at the western Barents Sea slope from the Last Glacial Maximum to the Bølling-Allerød interstadial

Advanced knowledge of spatio-temporal constraints on the Barents Sea Ice Sheet during the late Weichselian glaciation overshadows relatively limited understanding of seasonal sea ice (experiencing an annual advance-retreat cycle) and primary productivity trends accompanying massive, abrupt climate changes during glacial-deglacial cycles. Such paleo-reconstructions are crucial prerequisites for improved comprehension and prediction of current and future climate change. Here, we investigate sea ice and phytoplankton biomarker distributions in a Barents Sea sediment core covering ca. 25.8–15.4 cal kyr BP to elucidate abrupt shifts of spring–summer sea ice concentrations and relative sympagic–pelagic productivity trends at the southwestern continental slope. Despite significant presence of seasonal sea ice, the Last Glacial Maximum (LGM) and initial shelf edge deglaciation (SEDG) at the core site are characterised by occurrence of productive coastal polynya adjacent to the maximum ice sheet extent. The onset of perennial (i.e. multi-year) ice cover and near-zero productivity during Heinrich Stadial 1 (HS1; ca. 18.0–16.3 cal kyr BP) accompanies significant meltwater fluxes from ice sheet debuttressing and the consequent stagnation of thermohaline circulation. Rapid sea ice retreat and unprecedented pelagic productivity observed after 16.3 cal kyr BP coincides with areal ice sheet deglaciation and is potentially linked to the release of sub-surface heat and nutrient reservoirs, together with reinvigorated deep water circulation following millennial heating of the deep ocean during HS1. We find that a multivariate fingerprinting approach involving assessment of both downcore and surface biomarker distributions is able to distinguish relative ice-algal and pelagic diatom productivity driven by sea ice dynamics.

Lipid biomarkers in lacustrine sediments of subtropical northeastern Mexico and inferred ecosystem changes during the late Pleistocene and Holocene

Evolution of ecosystems in the northeastern Mexico since the Last Glacial Maximum (LGM) and through the Holocene are yet to be fully characterised, creating a gap in our understanding of the ecological response to climate change in this water scarce region. Here we explore the response of lacustrine and surrounding terrestrial habitats of this region to hydrological changes of the late Pleistocene and especially the Holocene. Biomarker-based proxy data from the El Potosi Basin indicates dynamic and variable input of organic matter (OM) into the basin, with sources being the surrounding vegetation, bacterial biomass and aquatic microfauna. Changes in these inputs reveal distinct stages of ecosystem development over the last 20,000 years. Overall low lipid abundances (as a proportion of TOC) from 20 to 19 cal kyr BP, mainly from aquatic/in-situ microbial biomass and degraded terrestrial OM, are attributed to relatively low runoff. Increasing lipid proportions during the deglaciation, from 19 to 15 cal kyr BP, were mostly derived from terrestrial sources like woodland vegetation, soil and wetland vegetation, and we attribute them to more rainfall and runoff. Subsequently, the wetland biomarkers disappeared, and woodland input began to dominate the OM assemblage from 15 to 11.7 cal kyr BP. During the early- and mid-Holocene, after about 11.7 cal kyr BP, putative woodland and grass inputs decreased and the dominant vegetation appeared to shift to subtropical desert shrub, which could have been due to increasing regional aridity. The onset of the dry late Holocene was characterised by gradual environmental transition and ecosystem adaption, especially from 4.2 to 2.8 cal kyr BP. The terrestrial vegetation comprised increasing proportions of C4 grasses, documented by changes in leaf wax carbon isotopic compositions, and potentially more open-vegetation, while the in-lake bacterial production increased. With increasing desertification from 2.8 cal kyr BP, the terrestrial productivity decreased substantially, the lake became shallower/ephemeral, and the surrounding soils became more alkaline. Changes of the limnic habitat from algal towards microbial communities occurred ~300 years after the onset of terrestrial habitat changes. During the last millennium, the C3 components of the vegetation again dominated. This implies an enhanced moisture supply, possibly from agricultural activities. Overall, this work reveals the marked sensitivity of northeastern Mexico ecosystems to the climatic shifts that occurred since the LGM, and this perhaps indicates their vulnerability to future global warming.

Three‐fold nature of coastal progradation during the Holocene eustatic highstand, Po Plain, Italy – close correspondence of stratal character with distribution patterns

AbstractAlthough general trends in transgressive to highstand sedimentary evolution of river‐mouth coastlines are well‐known, the details of the turnaround from retrogradational (typically estuarine) to aggradational–progradational (typically coastal/deltaic) stacking patterns are not fully resolved. This paper examines the middle to late Holocene eustatic highstand succession of the Po Delta: its stratigraphic architecture records a complex pattern of delta outbuilding and coastal progradation that followed eustatic stabilization, since around 7·7 cal kyr bp. Sedimentological, palaeoecological (benthic foraminifera, ostracods and molluscs) and compositional criteria were used to characterize depositional conditions and sediment‐dispersal pathways within a radiocarbon‐dated chronological framework. A three‐stage progradation history was reconstructed. First, as soon as eustasy stabilized (7·7 to 7·0 cal kyr bp), rapid bay‐head delta progradation (ca5 m year−1), fed mostly by the Po River, took place in a mixed, freshwater and brackish estuarine environment. Second, a dominantly aggradational parasequence set of beach‐barrier deposits in the lower highstand systems tract (7·0 to 2·0 cal kyr bp) records the development of a shallow, wave‐dominated coastal system fed alongshore, with elongated, modestly crescent beaches (ca2·5 m year−1). Third, in the last 2000 years, the development of faster accreting and more rapidly prograding (up toca15 m year−1) Po delta lobes occurred into 30 m deep waters (upper highstand systems tract). This study documents the close correspondence of sediment character with stratal distribution patterns within the highstand systems tract. Remarkable changes in sediment characteristics, palaeoenvironments and direction of sediment transport occur across a surface named the ‘A–P surface’. This surface demarcates a major shift from dominantly aggradational (lower highstand systems tract) to fully progradational (upper highstand systems tract) parasequence stacking. In the Po system, this surface also reflects evolution from a wave‐dominated to river‐dominated deltaic system. Identifying the A–P surface through detailed palaeoecological and compositional data can help guide interpretation of highstand systems tracts in the rock record, especially where facies assemblages and their characteristic geometries are difficult to discern from physical sedimentary structures alone.

Anatomy of a transgressive tidal inlet reconstructed through high-resolution seismic profiling

Although the morphology and morphodynamics of modern tidal inlets have been analysed in a wealth of studies, these systems can be considered representative only for highstand conditions, while little is known about the characteristics and evolution of their transgressive counterparts. Through the analysis of high-resolution seismo-acoustic profiles, this work investigates a rare example of a preserved filled tidal inlet formed during the early Holocene on the continental shelf of the northern Adriatic Sea. The quantity and quality of the available data allowed a detailed reconstruction of the morphology and internal architecture of this feature. This 1.2 km-long, 17 m-thick channelized scour formed in a microtidal environment between 9.0 and 9.5 kyr cal BP. The tidal prism is estimated to have been ca. 4.4 × 107 m3. The internal geometry of the filling material shows no evidence of migration of the inlet, which lasted only for a few centuries and was soon after drowned by the sea transgression. This rapid evolution is in contrast with the millennial-scale lifespan of most of the modern highstand lagoon systems. This work provides a new outlook on the evolution of tidal inlets during phases of marine transgression and in relation to variable rates of sea-level rise. In many cases, paleo tidal inlets are the only witnesses of the presence of transgressive barrier-lagoon systems which had been completely eroded by the wave action after their submersion. These features represent therefore an important proxy to infer the position of the related coastline and to constrain the past relative sea level.