Mid-late Holocene Research Articles

Agricultural adaptations to mid-late Holocene climate change in western Türkiye

The period around the mid-late Holocene transition (c. 2200 bc) saw major societal developments across the eastern Mediterranean. At the same time, the region experienced a shift to more arid climatic conditions. This included punctuated episodes of rapid climate change such as the ‘4.2 ka event’, which has been implicated in widespread societal ‘collapse’ at the end of the Early Bronze Age. The ways in which societies adapted agricultural production to cope with a drying climate are poorly understood. We begin to rectify this through stable isotope analysis of archaeobotanical remains from the Aegean region of western Türkiye, conducted to reveal changes in agricultural decision making across the mid-late Holocene transition. We find that Bronze Age farmers adapted agricultural production strategies by investing in drought-tolerant cereals cultivated on drier fields with water management strategies redirected towards pulses. Despite this, we find no evidence for pronounced drought stress in cereals grown during the period of the 4.2 ka event. This raises the potential for alternative explanations for societal disruptions visible across the Anatolian Plateau during this time, such as the breakdown of long-distance trade networks.

Holocene coastal sedimentary evolution and neolithic human adaption in response to sea level changes in the Palaeo-Taihu valley, East China

The neolithic human-land relationship in the eastern coastal plain of China, interlinked sedimentary evolution and sea level changes, has been central to numerous studies. Here, we focus on the evolution of the sedimentary environment and its impacts on human activity in the Palaeo-Taihu valley (PTV) within the northern wing of Hangzhou Bay in response to post-glacial sea level rise. We employ multi-proxy analyses (lithology, AMS 14C, grain size, elements, TOC, and microfossil) on a new sediment core (WZ05) of comparatively analyze a series of previous radiocarbon-dated cores. Our results indicate that since the last deglaciation, the sedimentary environment of Core WZ05 has undergone the floodplain, upper tidal flat, estuary, upper tidal flat, coastal marsh, and fluvial plain, respectively. Regional cores comparisons display three stages: (1) A late Pleistocene incised valley (older than 9600 cal yr BP) dominated by terrestrial deposits accompanied by pottery sherds and rice phytoliths revealing that human activity on the floodplain can be dated to ca. 10600-10300 cal yr BP; (2) An early-mid Holocene transgression stage (9600-7800 cal yr BP) resulted from rapid sea level rise, causing widespread seawater inundation of the floodplain which interrupted early human activity. The transgression maximum during 8000-7800 cal yr BP was marked by the highest sedimentation rates and the coexistence of deep and shallow water species of foraminifera, corresponding to the appearance of a semi-enclosed estuary; (3) Finally, mid-late Holocene terrestrial deposits are the response to a slower sea-level rise and the seaward migration of the coast as the sediment supply exceeded sea level rise at 7800 cal yr BP. Tidal flats and coastal marshes dominated the PTV until 6500 cal yr BP, thereafter sediments continue to fill the PTV such that it develops into a subaerial plain. The reappearance of a freshwater environment since ∼ 7600 cal yr BP allowed the recovery of rice cultivation in the region. Saltwater deposits interspersed with terrestrial deposits between 7000-6500 cal yr BP probably reflect marine inundation during storm events and would have depressed rice domestication.

Terrestrial vegetation and lake aquatic community diversity under climate change during the mid–late Holocene in the Altai Mountains

Using pollen analysis and metabarcoding of plant sedimentary ancient DNA (sedaDNa), we infer the floristic diversity in the vicinity of Lake Balyktukel, Ulagan Plateau, the Altai Mountains, over the last 7 kyr. The SedaDNA method identified 200% more taxa than found by morphological pollen analysis. In particular, it revealed that the dominant tree for the last 7 kyr was Larix rather than Pinus, which was less frequent in the vicinity of Lake Balyktukel. About 7 ka, larch forest mixed with dwarf birch was widespread on the Ulagan Plateau. The period between 5.3 and 3.4 kyr BP was characterized by the maximal spread of larch forest with an understorey cover of Vaccinium vitis-idaea. Pollen-based annual precipitation reconstruction indicates the most humid phase was between 6.95 and 4.3 ka, and generally coincides with maximal phytodiversity. The most bioproductive period of the lake was from 7 to 6 ka. After that, the trophicity of the lake decreased until 4.5 ka. The appearance of Hippuris vulgaris and increase in Ranunculus subgen. Batrachium at about 5.3–5 ka may indicate the extension of shallow-water ecotopes. Between 3.7 and 3.5 ka, the cyanobacterium Anabaena – an indicator of increased organic matter and algal blooms – was widespread. A planktic thermophilic cladoceran Bosmina longirostris appeared after 1.8 ka and colonized the lake, suggesting an increase in lake trophicity. The last 100 years have been characterized by dramatic changes in the cladoceran community reflecting significant warming of climate.

Fluvial Responses to Late Quaternary Climate Change in a Humid and Semi-Humid Transitional Area: Insights from the Upper Huaihe River, Eastern China

Research into river processes in different climatic and geomorphic areas is vital for a clearer understanding of the non-linear responses of rivers to climate change. The Huaihe River (HHR) Basin, located in China’s North–South Transition Zone (NSTZ), provides an ideal environment in which to explore river responses to climate change within a humid/semi-humid transitional area. Based on optically stimulated luminescence (OSL) and 14C dating, combined with sedimentary stratigraphic analyses, we reconstructed the river processes of three sedimentary sequences in the upper HHR since the Late Quaternary. Our results showed that the upper HHR was characterized by aggrading meandering channels from the Last Glacial Maximum (LGM) to 0.5 ka, and an aggrading wandering channel from 0.2 ka to the present. Two periods of downcutting occurred during 5.8–3.0 and 0.5–0.2 ka, respectively. The river incision is potentially linked to changes in the climate during the Mid–Late Holocene transition and the Little Ice Age (LIA). However, there have been no marked changes in channel patterns in the upper HHR since the LGM. This phenomenon reflects the influence of vegetation on channel patterns during climate change. Our results showed that the fluvial processes in different climatic and geomorphic areas are controlled by the local hydroclimatic regime.

Assessment the Impacts of Sea-Level Changes on Mangroves of Ceará-Mirim Estuary, Northeastern Brazil, during the Holocene and Anthropocene.

Predictions of the effects of modern Relative Sea-Level (RSL) rise on mangroves should be based on decadal-millennial mangrove dynamics and the particularities of each depositional environment under past RSL changes. This work identified inland and seaward mangrove migrations along the Ceará-Mirim estuary (Rio Grande do Norte, northeastern Brazil) during the mid-late Holocene and Anthropocene based on sedimentary features, palynological, and geochemical (δ13C, δ15N, C/N) data integrated with spatial-temporal analysis based on satellite images. The data indicated three phases for the mangrove development: (1°) mangrove expansion on tidal flats with estuarine organic matter between >4420 and ~2870 cal yrs BP, under the influence of the mid-Holocene sea-level highstand; (2°) mangrove contraction with an increased contribution of C3 terrestrial plants between ~2870 and ~84 cal yrs BP due to an RSL fall, and (3°) mangrove expansion onto the highest tidal flats since ~84 cal yr BP due to a relative sea-level rise. However, significant mangrove areas were converted to fish farming before 1984 CE. Spatial-temporal analysis also indicated a mangrove expansion since 1984 CE due to mangrove recolonization of shrimp farming areas previously deforested for pisciculture. This work mainly evidenced a trend of mangrove expansion due to RSL rise preceding the effects of anthropogenic emissions of CO2 in the atmosphere and the resilience of these forests in the face of anthropogenic interventions.

Centralization or decentralization? A spatial analysis of archaeological sites in northern China during the 4.2 ka BP event

The phenomenon of centralization or decentralization has been widely observed in archaeological research. Studies are usually related to the evolution and dynamics of culture or civilization, but less pertinent to the temporal–spatial pattern and variation of human settlement, especially the insufficient applications of statistics and spatial analyses; also, their relationship with climate change is unclear. In this study, using the one-way analysis of variance (one-way ANOVA) and standard deviational ellipse (SDE) with its parameters and frequency histogram, with thousands (>4,000) of document-based data on archaeological sites (the indicator of human settlement), two pairs of successive cultural types, i.e., Majiayao–Qijia cultures and Longshan–Yueshi cultures in both ends of northern China were compared as cross-regional cases to uncover whether the locations of prehistoric settlements with ended or started ages were (de-) centralized under the impacts of climate cooling and aridification during the well-known “4.2 ka BP event” (4200–3900 BP). The results illustrate that the “inherited” sites become more decentralized. Such a pattern embodies human resilience (including adaptation and migration) for pursuing better living conditions under the circumstances of climatic and environmental deterioration over the mid–late Holocene cultural transition, which provides some implications for the response to contemporary climate change.

Assessing biotic response to anthropogenic forcing using mollusc assemblages from the Po–Adriatic System (Italy)

Abstract Preserving the adaptive capacities of coastal ecosystems in the Anthropocene requires an understanding of their natural variability prior to modern times. We quantified responses of nearshore molluscs assemblages to past environmental changes using 101 samples ( c. 57 300 specimens) retrieved from the subsurface Holocene succession and present-day seabed of the Po–Adriatic System (Italy). Present-day assemblages shifted in their faunal composition with respect to their mid-late Holocene counterparts. Major differences are observed in lower nearshore settings, where present-day samples show higher heterogeneity, reduced standardized richness, reduced relative abundance of Lentidium mediterraneum, and increased relative abundance of Varicorbula gibba , scavengers (genus Tritia ), and deposit feeders (nuculid bivalves). A dominance of infaunal opportunistic species and shifts towards detritus-feeding and scavenging are often associated with disturbed benthic habitats. Our results suggest that the ongoing anthropogenic stressors (mainly bottom trawling and non-native species) are currently shifting benthic communities into novel states outside the range of natural variability archived in the fossil record. Supplementary material: A document containing additional statistics, figures, and tables, also considering different filters applied to the molluscan dataset, is provided as a Word file. In addition, appendices concerning sample and taxa information and R-scripts are provided as .csv and .r files. These are available at https://doi.org/10.6084/m9.figshare.c.6351348

Holocene sea surface temperature and salinity variations in the central South China Sea

The South China Sea (SCS) is sensitive to the East Asian monsoon (EAM) and changes in the Western Pacific. However, because of the difficulty of sampling and lack of data in the central SCS, many uncertainties remain the primary driving force of paleoclimatic variations. Here, a sediment core JL136, from the central SCS, was used to evaluate variations of sea surface temperature (SST) and salinity (SSS) during the Holocene, and then the corresponding influencing factors were analyzed, based on measured Mg/Ca ratio and stable isotopic compositions (δ18O and δ13C) of planktonic foraminifera Globigerinoides ruber sensu stricto (s.s.). The results show that the Mg/Ca-SST change is consistent with the speleothem δ18O records across most Asian monsoon regions on the Holocene long-term trend, revealing that the central SCS record is a response to the East Asian Summer Monsoon (EASM) intensity changes induced by Northern Hemisphere summer insolation (NHSI) variation. During the early Holocene (11.6–8.8 ka), SSS was low with an average of 32.7 psu, which may be related to palaeogeographic variations with sea level changes and the increased coastal water due to the opening of the Taiwan Strait. During the mid-late Holocene, high salinity ocean water was fully exchanged with the SCS due to the influence of high sea level, with an overall higher salinity in the SCS compared with the early Holocene (average 33.8 psu). In addition, the SSS broadly showed an increasing trend, which may be mainly controlled by the weakening EASM intensity and the decreasing precipitation during the low NHSI.

Mid-late holocene accretional history of low-lying, coral-reef rim islets, South-Marutea Atoll, Tuamotu, central South Pacific: The key role of marine hazard events

South-Marutea Atoll is located in the Gambier Island Group, at the south-eastern end of the Tuamotu Archipelago, French Polynesia, central South Pacific. Understanding the modalities of islet building from low-lying atolls over the mid to late Holocene, in relation to sea-level changes and cycles of marine hazard events, is a prerequisite for better anticipate future geomorphic changes to which the islets will likely be faced in the next decades under global climate warming. Herein is presented the depositional history of two selected atoll islets, based on chronostratigraphic analysis of sedimentary, coral-dominated sequences from six excavations. Identified as Motu Aramu and Motu Vainono, these islets are located respectively in north-north-east and due south of the atoll rim. Additional surficial sampling was conducted on modern ocean-facing shingle ridges, respectively on north-north-west (Motu Oire), west (Motu Aranui) and east (Motu Tekava) rim areas, in order to date the latest ridge-emplacement stages. Oire and Aranui sites, located along the leeward atoll sites, are protected from trade winds, Aramu, Vainono and Tekava are located on the windward sides, directly exposed to northeasterly and southeasterly storm swells respectively. A total of 88 coral clasts were collected to be U/Th dated. The excavated sequences range between 2.50 ​m and 0.90 ​m in thickness, from the outer islet sides lagoonwards. Five lithofacies, including two subfacies, were recognized based on texture and biological composition: a coral boulder-cobble-dominated, a coral pebble-dominated – pebble-supported and sand-supported subfacies – and a foraminifera-rich, sand-dominated and an organic-rich, pebble to sand facies. These facies tend to be distributed from ocean sides landwards according to a decreasing grain-size gradient. A model of atoll-island accretion emerges in relation with changes in frequency and intensity of marine hazard events. The islet foundations consist of conglomerate platforms, locally up to 1.0 ​m thick, deposited from about 5,000 to 1,000 ​calendar year (cal yr) BP. Islets began to accrete from 5,000 ​yr cal BP. While at Motu Vainono, islet building occurred continuously over the last 5,000 years, at Motu Aramu, there is an apparent non-depositional episode, from 4,000 to 2,000 ​yr cal BP, interpreted as caused by a marked decreased in enso-related cyclone activity. The outer shingle ridges in all studied sites were regularly reshaped during the last millennium. During the last 5,000 years, the major accretion-islet episodes occurred irrespective of the course of sea level, indicating that sea-level change was not a driver of islet accretion. Periodical, marine high-energy events clearly appear to be the key controls of islet shaping. Shifts of cyclone source areas further south and increasing cyclone intensity, but lower frequency, due to enhanced enso variability throughout the 21st century, is postulated to expose the Gambier island Group to stronger, but fewer disturbance events when compared to the last millennia.

Peat sequence diatoms from Kedarnath, Central Himalaya, used to reconstruct mid-late Holocene hydroclimatic conditions

Diatoms preserved in peat can preserve valuable evidence of palaeoenvironmental changes due to their sensitivity to climatic changes and their crucial role in high productivity and nutrient cycling. We present total diatom concentrations and diatom community composition preserved in a high-altitude peat deposit located in the headwaters of the Mandakini River, Central Himalaya, India, to reconstruct the hydroclimatic conditions which prevailed during the mid-late Holocene. Since diatom productivity is associated with water table height/elevation, the high diatom concentrations during ∼5656–5307 cal yr BP, ∼4310–4264 cal yr BP, ∼3515–3024 cal yr BP and ∼ 1679–988 cal yr BP are inferred to have been periods of relatively high water table, denoting improved hydrological conditions. Conversely, low concentrations of diatoms occurred during ∼8077–5866 cal yr BP, ∼5263–4332 cal yr BP, ∼4241–3570 cal yr BP, ∼2970–1715 cal yr BP, and ∼ 697–370 cal yr BP. The temporal changes in the diatom suggest stressed hydrological conditions. The water table fluctuations inferred from diatom concentration variability show a positive correlation with the Indian summer monsoon (ISM) intensity and a negative correlation with the westerlies. The observed low concentrations of diatoms was associated with the relatively dry climatic conditions, which is detrimental to the peat environment and therefore suggests the need for in-situ data monitoring for the Indian peat deposits. As dry conditions can result in the deterioration of peat deposits, which may prove a significant source of atmospheric carbon dioxide in a changing climate, their conservation strategies will help limit carbon emissions.

Fired shards from selected ancient Anatolian ceramics: a brief review of their mineralogical nature and pedological?microstructural evolution

This review is concerned with some key features observed within grouped samples of ancient ceramics that provide important evidence concerning the selection of appropriate raw materials and the evolution of the firing technologies employed in their production. It also demonstrates the importance of distinguishing and accounting for the mineralogical and microstructural attributes and identifying the processes responsible for the microstructural evolution of these ancient ceramics. The mineralogy largely reflects both the nature of the raw materials used and the maximum temperatures achieved during firing, deduced from the presence of specific high temperature minerals (HTMs). The microstructural evolution processes, deduced by the micromorphology of these ancient ceramics and displayed in specific features, observed in both the matrix and the slip of these ceramics, are largely controlled by the firing methods used in manufacturing. Thus, we conclude that the application of micromorphological principles, methods, and observations derived from the broad sphere of ?pedology? to the study of ancient ceramics, provides valuable insights into the independent evolution of ceramic production methods in ancient societies. Thus, most of the observations recorded here concern identification of the raw materials used to make ancient ceramics and the firing processes used in their manufacture. Our data demonstrate that these ancient potters made use of a variety of temper materials (quartz and chaff, together with fragments of locally available rocks and minerals) that are now preserved in the matrix. Furthermore, analyses of the micromorphological attributes displayed by these ancient ceramics are helpful in determining and explaining the shrinkage features (stress coatings or poro-striated b-fabrics) and the preferred orientation of the elongated pores that have developed after firing in poorly controlled and slow-fired furnaces. In this regard, we finally seek to develop a useful data library ultimately targeting the enhancement of simulated ancient ceramic/pottery production, with an overall objective to apply the mineralogical and pedological properties of Anatolian ceramics researched in this work to globally selected shard specimens. Postburial processes, such as the illuviation-deposition of clay minerals to form the observed clay coatings, probably operated during the wet-dry cycles associated with mid-late Holocene climatic fluctuations. Accompanying calcification-decalcification processes, which may result from an intra cramic leaching-deposition of carbonate present in the source material of the pottery, are also consistent with the known wet-dry cycles of the mid to late Holocene pedogenesis (soil formation) episode and is reflected in the clay coatings and further attested by coeval changes in the soil-faunal activity.

A comprehensive analysis of Holocene extraordinary flood events in the Langxian gorge of the Yarlung Tsangpo River valley

Increasing extreme temperature, precipitation and rapid meltwater events have added stress to the Himalaya's hydrological sensitivity and major flood risks, however, current extreme hydrological dataset and their genesis are insufficient to assess future flood discharge extremes in High Asian’ rivers. Here, Holocene extreme floods in the Yarlung Tsangpo River valley were reconstructed by using physic-chemical analysis, optically stimulated luminescence dating and palaeohydraulic techniques. Palaeoflood slackwater deposits (SWDs) were identified by means of palaeohydrological criteria and comparison with SWDs from large flood that occurred in 2018. Palaeoflood SWDs consist of well-sorted silt and sand with a consistent geochemical composition, implying a similar sedimentary source. Such results suggest that these SWDs were transported in suspension over long distances during flood events. The chronological analysis indicates that there are three palaeoflood events, dated to 5.7, 3.9 and 2.9–1.2 ka, during the mid-late Holocene. Palaeoflood peak discharges in the bedrock reach and meandering channel were estimated to be 27,600–35,000 m3/s using one-dimensional and two-dimensional hydrodynamic modelling. The simulation results clearly show the potential palaeoflood depositional range in the lower–velocity and eddy backwater environments between Jiacha and Langxian gorge. The palaeoflood magnitudes redefine the regional largest flood discharge, and fit well with global maximum flood curves. And mid-late Holocene extreme flood magnitudes were generally 2.5–3.5 times larger than the current maximum gauged flood, but lower than the Jiedexiu glacial lake outburst floods. Comprehensive analysis highlights the three extraordinary floods were possibly induced by monsoon rains and glacial meltwater. Site-specific palaeoflood information advances our knowledge of rare and extraordinary floods in the highest and largest river in the southern Tibetan Plateau.

Responses of Caribbean Mangroves to Quaternary Climatic, Eustatic, and Anthropogenic Drivers of Ecological Change: A Review.

Mangroves are among the world's most threatened ecosystems. Understanding how these ecosystems responded to past natural and anthropogenic drivers of ecological change is essential not only for understanding how extant mangroves have been shaped but also for informing their conservation. This paper reviews the available paleoecological evidence for Pleistocene and Holocene responses of Caribbean mangroves to climatic, eustatic, and anthropogenic drivers. The first records date from the Last Interglacial, when global average temperatures and sea levels were slightly higher than present and mangroves grew in locations and conditions similar to today. During the Last Glaciation, temperatures and sea levels were significantly lower, and Caribbean mangroves grew far from their present locations on presently submerged sites. The current mangrove configuration was progressively attained after Early Holocene warming and sea level rise in the absence of anthropogenic pressure. Human influence began to be important in the Mid-Late Holocene, especially during the Archaic and Ceramic cultural periods, when sea levels were close to their present position and climatic and human drivers were the most influential factors. During the last millennium, the most relevant drivers of ecological change have been the episodic droughts linked to the Little Ice Age and the historical developments of the last centuries.

Mid- to late Holocene vegetation response to relative sea-level fluctuations recorded by multi-proxy evidence in the Subei Plain, eastern China

Reconstructing Holocene changes in regional sea level is useful for understanding future sea-level scenarios. In this paper we examined the sedimentology, pollen, foraminifera, and organic matter properties of a well-dated profile from the Subei Basin that spans the last 6.7 ka. By integrating our findings with the archaeological record, we investigated mid- to late Holocene vegetation responses to relative sea-level fluctuations and considered the impact of climatic variations on cultural development. In the middle Holocene, the rapid and abrupt expansion of salt marsh vegetation (Chenopodiaceae, Cyperaceae, and Poaceae) suggests a relative rise in sea level. From 5.7 to 4.2 cal ka BP, lowland swamps were settled by Neolithic communities, as indicated by peak levels of microscopic charcoal and a significant rise in herbaceous pollen species, such as Cyperaceae, Typha, Myriophyllum, and Poaceae. From 4.2 to 3.7 cal ka BP, a major increase in Chenopodiaceae abundance and a δ13C excursion were observed along with a decrease in Cyperaceae and Poaceae levels, which revealed that human activity significantly decreased following the 4.2 ka climate event. Evidence suggests that the area under investigation experienced a relatively high sea level between 6.7 and 6.0 ka, a relative decrease in sea level between 6.0 and 5.7 ka, a steady sea-level condition between 5.7 and 4.2 ka, and gradual replacement by a freshwater marsh between 5.7 and 4.2 ka. The pollen and δ13 C records demonstrate that the relative sea level rose quickly from 4.2 to 3.7 ka, which could correspond to the 4.2 ka event. Enhanced El Niño-Southern Oscillation (ENSO) variance and intense climatic events in eastern China were the driving forces behind the mid-late Holocene relative sea-level shift. The rise in relative sea level eventually led to the collapse of the Qingdun and Jiangzhuang sites in the Subei Basin. Our results provide independent vegetation evidence of the simultaneous changes in relative sea level and variations in climate.

Deciphering the role of late Quaternary sea level fluctuations in controlling the sedimentation in the Brahmaputra Plains

Continent-continent collision between Eurasian and the Indian plate during the Cenozoic period lead to the formation of the Himalayan Mountain chain and the development of the Indus-Ganga-Brahmaputra foreland basin to the south. Complex climate-tectonic interactions in this orogenic belt are responsible for the rapid erosion and filling of the Indus-Ganga-Brahmaputra foreland basin with the eroded materials. This study based on geomorphic mapping, lithofacies analysis, and geochemical (Strontium-Neodymium i.e., SrNd analysis) provenance characterization, as well as optically stimulated luminescence (OSL) ages, provides a dated sedimentation framework for the western Assam lowland areas. The dated relict fan surface lies ~40 m above mean sea level (msl), is incised and forms a regional valley terrace T1 composed of meandering channel deposits. Modern braided rivers flow on the T0 surface. The findings suggest that the alluvial fan is composed of three distinct lithofacies associations and aggraded during 27 to 3 ka. The bottom-most gravelly-sandy facies indicates progradation of the fan during the last glacial maximum (LGM), owing to the increased gradient of the Himalaya bound rivers. The middle facies is a sheet flood deposit which formed during the Latest Pleostocene-early Holocene period with rising sea level and increasing precipitation. During the Mid-Late Holocene, the uppermost facies is deposited as rivers lost their gradient in response to high sea level stand, resulting in inland sedimentation within muddy meandering channels. Our analysis found that falling sea level during the late Holocene was associated with greater precipitation and allowed the river to incise, to form gullies over the fan surface and form the valley terrace T1. The SrNd isotope fingerprints have been used to identify varying fan sediment sources in the Himalaya's southern front (i.e., Lesser and Higher Himalaya) as a function of changing monsoon conditions.

Mid to late Holocene climate variability, forest fires and floods entwined with human occupation in the upper Ganga catchment, India

The present study attempts to understand the geomorphic response in the upper Ganga catchment to the mid-late Holocene (neoglacial) climate variability. The study infers five major phases of millennial-scale climate variability with centennial-scale inversions using geochemical and magnetic proxies from relict Lesser Himalayan Lake sediments. Phase-1 (6–4 ka) is marked by enhanced precipitation/runoff (increased allochthonous contribution) under a stronger Indian Summer Monsoon (ISM). The prominent reversal in the trend between ∼5 and 4 ka includes global arid events such as 4.2 ka. Phase-2 (4–2.2 ka) shows a declining precipitation/runoff (decreased allochthonous input) under declining ISM with a prominent dip after ∼3 ka. After phase-2 the climate reversals are distinct and of shorter (centennial) duration. For example, in Phase-3 (2.2–1.4 ka) improved ISM is inferred; Phase-4 (1.4–1.0 ka) is marked by a sharp decline in the ISM, and Phase-5 (<1.0 ka) includes centennial-scale events of Medieval Climate Anomaly (MCA) and the onset of Little Ice Age (LIA). The relative increase (decrease) in the concentration of geochemical and magnetic proxies is indicative of strengthened (weakened) ISM where relatively drier phases are in sync with the North Atlantic climate perturbations. We observed clustering of optically dated flood events around 6.5, 4.5, 2.6, 1.4, 0.8, and 0.4 ka which corresponds to periods of moderate ISM thus, suggesting a coupling between warm-humid monsoon and relatively dry westerlies. The relatively higher concentration of micro-charcoal in the lake sediments indicates widespread forest fires around 5.9–5.3, 4.5–4.3, 3.4–3.0, 2.0–1.5 and ∼1 ka. Given the archaeological evidence of sedentary settlements since ∼3 ka in the upper Ganga catchment, the study speculatively argues anthropogenic forcing for forest fires after 3 ka. Further, the highest probability flood phases succeed the fire events and may be indicative of enhanced vulnerability of the catchment to floods due to vegetation loss (enhanced erosion and surface runoff).

Evolution of a single incised valley related to inherited geology, sea level rise and climate changes during the Holocene (Tirso river, Sardinia, western Mediterranean Sea)

We performed a morpho-stratigraphic study of the Tirso River incised valley (Sardinia Island, western Mediterranean Sea), an erosional feature crossing the Sinis fault, a major normal fault bordering the Campidano basin between the Gulf of Oristano and the western Sardinia shelf. High-resolution seismic reflection profiles and multibeam echosounder data, integrated by age-constrained stratigraphic logs derived from 9 sediment cores enabled us to reconstruct the valley evolution during the Holocene. We found that the Tirso valley is the result of a single event of incision and infill during the last eustatic cycle, strongly controlled by the presence of the Sinis fault. In fact, this structure represents a geological threshold that marks an abrupt change in substrate lithology and seabed slope, which controlled the valley morphology, narrow when downcutting early Pliocene formations along the steeper open shelf, and wider inside the Gulf, in the Pleistocene alluvial deposits of the flatter Gulf of Oristano. The sedimentary record starts with alluvial sediments filling the valley along the shelf during the initial phase of sea level rise, i.e., over 10 ka. During the last ~9.0 ka, a bay head delta developed, with the formation of barriers at the gulf entrance. In the mid-late Holocene, the progressive sea-level rise led to rapid drowning of the barrier system, recorded by marine and estuarine sediments filling the valley. Analysis of ecological associations in the cores, collected along a valley-normal transect, allowed for a detailed reconstruction of the paleo-environmental conditions during the latest phase of the incised valley filling controlled by global climatic variations in the Mediterranean region between ~9.0 and ~ 4.5 ka. Together with eustasy, our work reveals that the evolution and sedimentary infill of the Tirso incised valley was strongly controlled by inherited geological constraints, which influenced the morphology of the valley and the stratigraphic pattern.

Palynological implications for paleoenvironmental changes over the past 81,000 years on the Jeju Strait shelf, off southwestern Korea

Age-controlled palynostratigraphy has revealed changes in the depositional environment, vegetation, and climate of the southwestern Korean Peninsula since marine isotope stage (MIS) 5a. During MIS 5a (ca. 74–81 ka), the Jeju Strait shelf was an inner shelf with deposition influenced by the Jeju Warm Current (JWC), surrounded by land covered by mixed conifer and deciduous broadleaf forests under warm temperate conditions. The paleoenvironment during MIS 4 (57–71 ka) remains unknown due to a lack of palynomorphs from this stage. During mid–late MIS 3 (ca. 29–50 ka), the Jeju Strait shelf was an inner shelf influenced by cold-water masses from the Korean Coastal Current combined with weaker influences by the JWC, and the surrounding land was covered by mixed conifer and deciduous broadleaf forests that were less dense than in MIS 5a under warm and relatively dry conditions. A cold, slightly wet climate during MIS 2 (ca. 12–29 ka) led to the extension of predominantly cold-tolerant conifer forests due to lowstand sea levels, although inland East Asia remained cold and dry. During MIS 1 (ca. 0–12 ka), cold-tolerant conifer forests persisted into the early Holocene, and were subsequently replaced by mixed conifer and deciduous broadleaf forests as a warm climate was restored in the mid–late Holocene, when the depositional environment became an outer shelf due to highstand sea levels, as it remains today.

Mid-late Holocene vegetation history of the Argive Plain (Peloponnese, Greece) as inferred from a pollen record from ancient Lake Lerna.

This study provides a high-resolution reconstruction of the vegetation of the Argive Plain (Peloponnese, Greece) covering 5000 years from the Early Bronze Age onwards. The well dated pollen record from ancient Lake Lerna has been interpreted in the light of archaeological and historical sources, climatic data from the same core and other regional proxies. Our results demonstrate a significant degree of human impact on the environments of the Argive Plain throughout the study period. During the Early Bronze Age evidence of a thermophilous vegetation is seen in the pollen record, representing the mixed deciduous oak woodland of the Peloponnesian uplands. The plain was mainly used for the cultivation of cereals, whereas local fen conditions prevailed at the coring site. Towards the end of this period an increasing water table is recorded and the fen turns into a lake, despite more arid conditions. In the Late Bronze Age, the presence of important palatial centres modified the landscape resulting in decrease of mixed deciduous oak woodland and increase in open land, partly used for grazing. Possibly, the human management produced a permanent hydrological change at Lake Lerna. From the Archaic period onwards the increasing human pressure in association with local drier conditions caused landscape instability, as attested by a dramatic alluvial event recorded in the Pinus curve at the end of the Hellenistic Age. Wet conditions coincided with Roman times and favoured a forest regeneration pattern in the area, at the same time as we see the most intensive olive cultivation in the pollen record. The establishment of an economic landscape primarily based on pastures is recorded in the Byzantine period and continues until modern times. Overgrazing and fires in combination with arid conditions likely caused degradation of the vegetation into garrigue, as seen in the area of the Argive Plain today.

Mid-Late Holocene climate variabilities in the Bransfield Strait, Antarctic Peninsula driven by insolation and ENSO activities

The Antarctic Peninsula (AP) is sensitive to global climate changes. Diatom composition was investigated in a sediment core recovered from the Bransfield Strait, in order to reconstruct the changes in surface water conditions over the past ca. 5.8 kyr (mid-late Holocene) in the AP region. A relatively stable mid-Holocene (5.8–3.8 ka) with persistent presence of sea ice was punctuated by a cooling episode at 4.9–4.2 ka, followed by a cooling trend with stronger sea-ice variability during the late Holocene (since 3.8 ka), which enhanced the surface water stratification in the study area. Frequency analysis reveals centennial- to millennial-scale cyclicities resembling the characteristics of solar irradiance and El Niño-Southern Oscillation (ENSO). In particular, the increasing ENSO activities during the late Holocene resulted in intensified cold Weddell Sea outflow to the Bransfield Strait that increased sea ice presence and duration. This pattern is in contrast to a northerly warm air intrusion induced glacial meltwater discharge to the western AP region, leading to similar sea ice variability to that in the east AP region.