Early-mid Holocene Research Articles

A stalagmite δ18O record from Jinfo Cave, southern China reveals early-mid holocene variations in the East Asian Summer Monsoon

The stability of the East Asian Summer Monsoon (EASM) during the early Holocene and the timing of the Holocene optimum have been intensely debated. Both stalagmite and lake records from northern China imply that there was a millennium-scale monsoon weakening event during the early Holocene, but whether this phenomenon is common across the Asian monsoon region remains unclear due to a paucity of records from southern China. We present results from U–Th dating and 433 stable carbon and oxygen isotope datapoints in order to investigate variations in the EASM during the early-mid Holocene in southern China. The results show that stalagmite δ18O values are relatively low in the period of 10.1–9.6 ka BP, indicating enhanced monsoon activity in the early Holocene. The stalagmite δ18O values for the period of 9.1–8.1 ka BP are characterized by a “w" type oscillation, indicating that there was a period of monsoon recession. In contrast, the period of 8.0–6.0 ka BP is characterized by relatively low, implying a strong monsoon. The results of our study indicate there was a millennial-scale weakening of the monsoon during the early Holocene in southern China. This suggests that the early Holocene monsoon weakening events are widespread throughout the monsoon region of eastern China.

A Holocene paleoenvironmental record based on ungulate stable isotopes from Lukenya Hill, Kenya

Investigating the development of Holocene behavioral adaptations requires knowing how and why different human groups are distributed on the landscape. An expanded dataset of site-specific environmental and habitat reconstructions from eastern Africa are crucial contextual components necessary for pushing this line of inquiry forward. This paper provides localized paleoenvironmental data from Holocene deposits at the multi-site Lukenya Hill archaeological complex on the Athi-Kapiti Plains of Kenya. Lukenya Hill preserves two temporal units, an early-mid Holocene (~9.0–4.6 ka) and a late Holocene (~2.3–1.2 ka), which span the end of the African Humid Period and the onset of late Holocene aridification. Carbon isotope analysis of herbivore tooth enamel (n = 22) indicates an increase in open grasslands over time with the early-mid Holocene having a woodier signal than the late Holocene and Recent populations in the Athi ecosystem. This pattern deviates from local environmental sequences in the Lake Victoria and Lake Turkana basins, providing additional evidence of heterogeneous habitat conditions during the Holocene of eastern Africa. The expansion of locally specific paleoecological datasets in eastern Africa allows for an examination of the role climate and ecology played in human economic and behavioral development during the Holocene.

Linking Holocene vegetation dynamics, palaeoclimate variability and depositional patterns in coastal successions: Insights from the Po Delta plain of northern Italy

Mediterranean deltaic-coastal plains represent relatively underexplored depositional archives that record the Holocene response of vegetation and depositional systems to high-frequency climate changes. In this study, we examine a 25 m-thick succession of Holocene age (core EM2) recovered in the innermost portion of the Po delta plain of northern Italy, applying an integrated palyno-stratigraphic approach. The existence of a paludal, freshwater setting inland of the line of maximum marine transgression favoured a low degree of pollen transportation. Application of cluster analysis to this palynological record leads to the identification of pollen-derived biomes and seven (auto)ecological groups of taxa that discriminate environmental signal (depositional facies) and regional climate conditions within a well-dated coastal record. Percentage variations of hygrophytes, aquatics and pasture-meadow herbs reveal local environmental dynamics, enabling the detailed facies characterisation of the cored succession, especially in terms of water table conditions. Framed into a chronologically constrained, high-resolution facies context, the proportion of montane taxa (climate degradation indicator) relative to Mediterranean taxa and Quercus + other deciduous trees (climate optimum indicators) highlight a vegetation-climate variability in the plain that fits with Bond events, especially for the early-mid Holocene (i.e., Preboreal and Boreal Oscillation, 8.2 ka event), supporting a strong Mediterranean–North Atlantic climate connection. For the first time, pollen from a continental succession of the Adriatic area clearly depicts the effects of the 8.2 ka cooling event on vegetation patterns (progressive degradation in high altitude communities) and depositional dynamics (increased fluvial activity), assessing the major role played by climate changes in shaping coastal landscapes in addition to glacio-eustatic variations.

Early to mid-Holocene vegetation history, regional climate variability and human activity of the Ningshao Coastal Plain, eastern China: New evidence from pollen, freshwater algae and dinoflagellate cysts

Palynological evidence of an Early-Mid Holocene around the Hemudu archaeological site have not been insufficiently discovered. Two sediment cores HMD1501 and HMD1502, respectively, from the Tianluoshan site, Zhejiang Province, eastern China, were examined in this study on certain palynological aspects, i.e. pollen, spores, freshwater algae and dinoflagellate cysts. The results show the information relating climate change, vegetation history and human activity over the Early-Middle Holocene. In the early Holocene, ca. 10 708–7193 cal yr BP, abundant arboreal pollen Pinus and Quercus (evergreen) and small amounts of herb pollen and fern spores were observed in this study, then it was considered that conifer mixed forest with broad-leaf trees flourished in the Tianluoshan site and the adjacent areas under consistent warm and humid climatic conditions that was in line with the Holocene Climate Optimum. And afterwards, an increase in the herb pollen component and temperate broad-leaf taxa, combining a decrease in the tropical and subtropical taxa suggested that relatively cold and dry climatic conditions occurred during the mid-Holocene (ca. 7193–5655 cal yr BP), in particular, a large amounts of cultivated Poaceae (Oryza comp.) pollen grains ≥40 μm, in addition to rice relics from the Hemudu Cultural Stage, supports the presence of extensive rice agriculture on the Ningshao Coastal Plain, eastern China, during the mid-Holocene (ca. 7193–5655 cal yr BP). Moreover, four sedimentary facies marine sub-tidal, shallow-marine, shore lacustrine environments and plow layer in the two sediment cores were also identified.

Late Pleistocene history of aggradation and incision, provenance and channel connectivity of the Zanskar River, NW Himalaya

The Zanskar River, one of the largest tributaries of the upper Indus catchment, drains transversely northward from the Higher Himalaya, dominated by the Indian summer monsoon, to flow through the arid, westerlies-dominated, highly folded and thrusted Zanskar ranges in Ladakh. The Doda and the Tsarap Lingti Chu join to form the Zanskar, which in turn joins the Indus at Nimu. With an average gradient of ~ 4 m/km, the Zanskar has a gradient ~2.5 times lower than that of rivers like the Ganga and Brahmaputra, which flow through the southern wet Himalaya. Based on Stream Length (SL) gradient index and valley width and height ratio, the Zanskar valley can be divided into upper and lower divisions, separated by a gorge of nearly 60 km length. The river channel in both the divisions is flanked by 10–30 m thick valley-fill deposits that in the upper part are amalgamated with fan and paleolake deposits. Using these fills and incorporating morpho-stratigraphy, Optically Stimulated Luminescence (OSL) dating and provenance analysis based on U—Pb Zircon chronology, the study show that the Zanskar valley aggraded in three phases: (i) the oldest phase during ~43 to ~32 ka (cool and wet MIS 3), (ii) during 20–12 ka, a climatic transition from the dry LGM to the wet early Holocene and (iii) the youngest aggradation phase commenced between 9 and 6 ka, corresponding with the strengthened monsoon phase of the early–mid Holocene. The study implies that, during the oldest aggradation phase, the wider Padam basin stored 3.25 ± 0.11 km 3 of sediment, which, in the present geomorphic setup is 0.96 ± 0.10 km 3 . The provenance analysis suggests that, despite the presence of the deep narrow gorge and a low gradient, the upper and lower Zanskar valleys remained connected throughout their aggradational history. Unlike in the southern wetter Himalaya, where catchment-wide exhumation is the main source of sedimentation, valley filling in the Zanskar basin has been overwhelmed by sediment derived from headward erosion. • The Zanskar valley, NW Himalaya, is studied for aggradation and incision history and climatic variability • Three aggradation phases: ~43–32 ka, ~20–12 ka, and ~9–6 ka. • The wider Padam valley, at present stores 0.96 ± 0. 10 km 3 of sediment, which during the oldest aggradation phase was 3.25 ± 0.11 km 3 • Zircon U-Pb ages point towards channel connectivity and that > 50% of fill sediments are derived from the headwaters

Geoarchaeology of Holocene oasis formation, hydro-agricultural management and climate change in Masafi, southeast Arabia (UAE)

AbstractOases are subject to decreasing resources and changing human activities. Fully aware of their rich heritage, the United Arab Emirates (UAE) have undertaken work to preserve and revitalize these oases. However, there is a clear lack of understanding of the dynamic links between climate change, hydraulic and agricultural management, and socioeconomic activities. To clarify these links, our team conducted a systematic geoarchaeological, geophysical, spatial, and chronological study of the Masafi oasis, UAE. Results indicate the existence of a natural humid area as early as the late Pleistocene (~18 cal ka BP). These conditions persist during the early-mid Holocene with drainage activation and soil development (~12–6.3 ka). During the late Holocene, after the emergence of the “artificial” oasis around ~3250 cal yr BP, cycles of intense management suggesting water availability (~3250–2380 cal yr BP; 550 cal yr BP) alternate with episodes of fluvial detritism (~2380–1870 cal yr BP; >550 cal yr BP) and scattered evidence of farming activities with complex hydroclimatic signatures (~2300–550 cal yr BP). These results, together with regional environmental data, indicate that water and soil resources were available and exploited strategically throughout the Holocene despite adverse climatic conditions, and the oasis of Masafi could have acted as a desertrefugium.

The impact of environmental change on Palaeolithic and Mesolithic plant use and the transition to agriculture at Franchthi Cave, Greece.

The multi-period (~38,000–6000 cal BP) site of Franchthi Cave, located in the Argolid peninsula of southern mainland Greece, is unique in the Eastern Mediterranean for preserving a long archaeological sequence extending from the Upper Palaeolithic through to the end of the Neolithic period. In this paper, we present new anthracological (carbonized fuel wood waste) evidence from Franchthi Cave with which we reconstruct the changing ecology of woodland vegetation in its environs during the late Pleistocene and the early-mid Holocene. The integrated archaeobotanical record (charred wood and non-wood macro-remains) demonstrates that in the Lateglacial the now-submerged coastal shelf of the southern Argolid peninsula was covered by steppe grassland vegetation dominated by junipers, almonds, cereals and legumes. The rapid climatic amelioration that marked the start of the Holocene brought about the disappearance of juniper and the expansion of deciduous woodland, cereals and lentils. This woodland-grassland biome bears no analogues in the modern and historical vegetation ecology of the Aegean basin. Instead, it is directly comparable to the steppe woodland biomes exploited by late Pleistocene and early Holocene hunter-gatherers in Southwest Asia, and points to the convergent evolution of late Pleistocene and early Holocene plant exploitation strategies between the two regions. Continuous sea-level rise during the early Holocene led to the gradual extinction of this unique palaeohabitat, which acted as the catalyst for the selective introduction of domesticated cereal crops at Franchthi Cave in the early 9th millennium cal BP. Our meta-analysis of the non-wood archaeobotanical data puts into question the concept of the wholesale introduction of a crop “package” by pioneer settler groups arriving from the East. It is proposed instead that selective cereal crop introduction formed part of a complex pattern of sociocultural interactions that brought together indigenous and immigrant groups into new communities.

Palynological record of Holocene vegetation and climate changes in a high-resolution peat profile from the Xinjiang Altai Mountains, northwestern China

A high-resolution pollen record in a peat sequence from the Altai Mountains of Xinjiang, China, allows reconstruction of the regional vegetation and climate changes that occurred during the Holocene. Pollen distributions from the sequence indicate that the vegetation community in the Altai Mountains region transitioned through five general phases: forest and desert steppe, wet steppe, desert steppe, steppe, and finally forest and desert steppe. These vegetative phases imply that the regional climate changed from a cold and dry early Holocene to a warmer and wetter early-mid Holocene and then to a cold and rather dry mid-Holocene that was followed by a cool and wet late Holocene and finally by warm and dry conditions for the last millennium. These regional changes in climate are roughly consistent with local changes previously reconstructed from organic geochemical paleoclimate proxies in the same peat sequence by Zhang et al. (2016), but with some minor but important differences that reflect local factors.Regional comparisons reveal that the Holocene climate changes in the Altai Mountains are generally consistent with those of most arid central Asian regions that are influenced mainly by westerlies. However, they are out-of-phase with the climate histories of regions controlled by the Asian monsoons, indicating that the Asian monsoons did not extend to the high-altitude mountain regions of arid central Asia during the Holocene. We postulate that the regional Holocene moisture variations have been mainly modulated by NAO variations that affected transport of water vapor from the North Atlantic Ocean by the westerlies. Moreover, local factors that include topography of the mountains and glacial meltwater events in the high-altitude regions also contributed to the climate changes in the Altai Mountains. In addition, air temperatures related to summer insolation of the Northern Hemisphere might have played an important role in modulating moisture in the region, but only after the local montane ice-sheets had disappeared by the mid-Holocene.

Continuous Holocene input of river sediment to the Indus Submarine Canyon

Sediment supply and sea level interact to control sediment flux to deep-water submarine fans. Although some fans continue to be active during times of rising sea level, the source of sediment is not always clear and may be dominated by reworking in high energy coastal areas rather than reflecting erosional signals directly from the source drainage basin. We present new age and geochemical provenance data from cores covering the last ~20 ka that show continuous deep-water sedimentation through the Indus submarine canyon since at least ~11 ka, despite the cessation of sedimentation on the upper fan around that time. Large turbidity flows mantled terraces >200 m above the thalweg throughout the Holocene and their deposits show trends in grain size and geochemistry that we interpret to record direct supply from the river mouth and little reworking of older deposits eroded by longshore currents, storm waves, slumping, or sliding, at least at 4.7–9.0 ka. We use Nd–Sr isotope compositions to show that sediments within the canyon and in the shelf clinoform to the east of the canyon are similar to the Holocene river mouth, suggesting direct supply from the Indus River to the eastern clinoform and into the canyon. The sediment storage time on the shelf before redeposition would be no more than ~8 k.y., and likely much less during the Early-Mid Holocene (4.7–9.0 ka). Sr–Nd isotopes also indicate that significant reworking of sediment older than 8 ka during sea level rise is excluded. Thus, coherent erosional pulses (signals) in the river, likely caused by climatic disturbances, are communicated to the canyon at least since ~9.0 ka, suggesting that sediment supply, modulated by climate in the Indus basin, dominates over sea level in controlling canyon sedimentation in high sediment supply settings, although the vast majority of the sediment supply is stored on the shelf and in the delta. Our study for the first time allows the differentiation between reworking within the canyon and direct supply from the river in a major submarine canyon.

Quantifying variable rates of postglacial relative sea level fall from a cluster of 24 isolation basins in southern Norway

Sediment sequences obtained from 24 isolation basins located on the Skagerrak coastline are used to develop new sea level index points for southern Norway. The basins are located near a common shoreline isobase and extend from marine limit at c. 83 m asl. to present sea level. The abundance of bedrock isolation basins within the small study area enables a high-resolution reconstruction of postglacial relative sea-level change. For most of the basin records, 3–5 samples of terrestrial plant macrofossils were radiocarbon dated across the biostratigraphically-defined isolation boundary. Eight of the isolation events were further constrained by Bayesian modelling of the radiocarbon age results. The overall reconstructed sea-level history is as expected for a formerly glaciated coastline; consisting of a rapid regression from marine limit followed by a slower pace of relative sea level fall from early-mid Holocene to present. The new dataset of sea level index points, however, further delineates century-scale oscillations in rates of sea level regression, which record past changes in sea surface height and vertical land motion (glacial isostatic adjustments, GIA). Results provide new constraints for future numerical models aimed at reducing uncertainty in century-scale relative sea-level projections for Fennoscandia.

Holocene atmospheric circulation in the central North Pacific: A new terrestrial diatom and δ18O dataset from the Aleutian Islands

The North Pacific is a zone of cyclogenesis that modulates synoptic-scale atmospheric circulation, yet there is a paucity of instrumental and paleoclimate data to fully constrain its long-term state and variability. We present the first Holocene oxygen isotope record (δ18Odiatom) from the Aleutian Islands, using siliceous diatoms preserved in Heart Lake on Adak Island (51.85° N, 176.69° W). This study builds on previous work demonstrating that Heart Lake sedimentary δ18Odiatom values record the δ18O signal of precipitation, and correlate significantly with atmospheric circulation indices over the past century. We apply this empirical relationship to interpret a new 9.6 ka δ18Odiatom record from the same lake, supported by diatom assemblage analysis. Our results demonstrate distinct shifts in the prevailing trajectory of storm systems that drove spatially heterogeneous patterns of moisture delivery and climate across the region. During the early-mid Holocene, a warmer/wetter climate prevailed due to a predominantly westerly Aleutian Low that enhanced advection of warm 18O-enriched Pacific moisture to Adak, and culminated in a δ18Odiatom maxima (33.3‰) at 7.6 ka during the Holocene Thermal Maximum. After 4.5 ka, relatively lower δ18Odiatom indicates cooler/drier conditions associated with enhanced northerly circulation that persisted into the 21st century. Our analysis is consistent with surface climate conditions inferred from a suite of terrestrial and marine climate-proxy records. This new Holocene dataset bridges the gap in an expanding regional network of paleoisotope studies, and provides a fresh assessment of the complex spatial patterns of Holocene climate across Beringia and the atmospheric forces driving them.

Timing and duration of the East Asian summer monsoon maximum during the Holocene based on stalagmite data from North China

We present a continuous C-O isotope series that shows the detailed variability of East Asian summer monsoon (EASM) since 11.0 ka BP. The series is based on two stalagmites, namely, DSY1 and LM2, which were, respectively, obtained from Dongshiya and Laomu caves. The δ18O profiles of stalagmite excurse negatively in early Holocene and gradually become positive after around 6.9 ka BP, tracking the change in Northern Hemisphere summer insolation. Moreover, the ‘early-Holocene maximum’ supported by stalagmite δ18O records differs from the ‘mid-Holocene maximum’ indicated by geological archives, such as lake sediments and loess. This difference may be caused by different definition indicators of monsoon intensity. Stalagmite δ18O is relative to EASM intensity, but irrelative to precipitation in the East Asian monsoon region. The time intervals of EASM maximum and Holocene climatic optimum are desynchronized, which is confirmed by the variation in the stalagmite δ13C series. Stalagmite δ13C and δ18O have different variation tendencies. The tendency of δ13C in early mid-Holocene was generally light, but it was discontinuity and disrupted by rapid positive shift between 8.2 and 7.7 ka BP. We conclude that a rapid shift of about 8 ka BP is a turning point, before and after which δ13C acquires different controlling factors. Stalagmite δ13C showed no signs of positive excurse in late Holocene but it exhibited another characteristic, namely, millennial time scale oscillations. The few changes in stalagmite δ13C is attributed to weakened insolation during summer in the northern hemisphere, which leads to low evaporation rate, thereby modulating effective humidity change. The edge of the seasonal monsoonal front in northern China during monsoon recession is sensitive to the rain belt and causes the δ13C of the stalagmite to fluctuate greatly. This phenomenon shows that the climate in the study area is unstable in the late Holocene

Mass balance implies Holocene development of a low-relief karst patterned landscape

We constructed mass balances of both calcium and phosphorus for two watersheds in Big Cypress National Preserve in southwest Florida (USA) to evaluate the time scales over which its striking landscape pattern developed. This low-relief carbonate landscape is dotted with evenly spaced, evenly sized, shallow surface depressions that annually fill with surface water and thus support wetland ecosystems (e.g. cypress domes) embedded in a pine-dominated upland matrix with exposed bedrock. Local and landscape scale feedbacks between hydrology, ecological dynamics and limestone dissolution are hypothesized to explain this karst dissolution patterning. This hypothesis requires the region to be wet enough to initiate surface water storage, which constrains landscape formation to interglacial periods. The time scale therefore would be relatively recent if creation of the observed pattern occurred in the current interglacial period (i.e. Holocene), and older time scales could reflect inherited patterns from previous inter-glacial periods, or from other processes of abiotic karstification. We determined phosphorus stocks across four landscape compartments and estimated the limestone void space (i.e., wetland depression volume) across the landscape to represent cumulative calcium export. We calculated fluxes in (e.g., atmospheric deposition) and out (i.e., solute export) of the landscape to determine landscape denudation rates through mass balance. Comparing stocks and annual fluxes yielded independent estimates of landscape age from the calcium and phosphorus budgets. Our mass balance results indicate that the landscape began to develop in the early-mid Holocene (12,000–5000 ybp). Radiocarbon dating estimates implied similar rates of dissolution (~1 m per 3000–3500 years), and were in agreement with Holocene origin. This supports the hypothesis that ecohydrologic feedbacks between hydrology and vegetation occurring during the present interglacial period are sufficient to shape this landscape into the patterns we see today, and more broadly suggests the potential importance of biota in the development of macro-scale karst features.

Speculative Volcanology

In 2009, exploratory drilling of geothermal wells in Iceland’s Krafla volcanic caldera unexpectedly struck magma. The fact that the encounter didn’t have catastrophic consequences has excited considerable interest - and an international research facility is now being set up to explore energy generation and other possibilities of closer engagement with magma. We take this event as an incitement to explore how the Earth-changing `violence’ of volcanic or igneous processes might be seen not simply as happening in time, but as both generative and destructive of time itself. We approach volcanism through the construct of a `speculative geology’ that draws on a recent return to metaphysical themes in philosophy as well as a growing interest in geological processes in the arts, humanities and popular culture. In this way, alongside cause-effect relations, we explore the more enigmatic processes through which subterranean geological forces offer an excessive potentiality from which humans and other life forms select and actualise a narrower range of creative or generative possibilities. The paper explores three significant volcanic episodes: a series of massive magma extrusions around 1.9 billion years ago linked to the ascendance of multicellular life, volcanism present in the East African Rift during pivotal phases of human evolution and the volcanic activity of the early-mid Holocene viewed as a contextual factor in the emergence of ancient practices of artisanal pyrotechnology. Our reading of the dynamic and violent interchange between the inner and outer Earth in these examples points to a non-self-identical planetary condition, on which the very structure of temporality emerges through a play of destruction and generativity. In this light, we circle back on the Krafla project to consider questions of risk, uncertainty and responsibility that attend the potential new interface with the underworld of magma.

Storm and tide influenced depositional architecture of the Pliocene–Pleistocene Chad Formation, Chad Basin (Bornu Sub–basin) NE Nigeria: A mixed fluvial, deltaic, shoreface and lacustrine complex

Lithofacies analyses of the upper part of the Chad Formation (Bama Ridge Complex) in the Bornu Sub–basin of the Chad Basin indicated four facies associations; fluvial, deltaic, shoreface and lacustrine sequences. The fluvial sequences are composed of fining upward cycles with successive occurrence of planar crossbedded sandstone facies displaying unimodal paleocurrent system and rare mudstone facies typical of braided river system. The deltaic succession consists of both fining and coarsening upwards cycles with the former depicting fluvial setting of an upper delta plain while the later suggestive of mouth–bar sequences. The setting displays a polymodal current system of fluvial, waves, storms and tides that were primarily induced by complex interactions of seiches and lunar tides. Similar current systems devoid of fluvial patterns were reflected in the coarsening upward packages of the shoreface sequences. Lacustrine succession composed of thick bioturbated mudstone facies generally defines the base of these coarsening upward profiles, giving a fluvio–lacustrine geomorphic relief where complex interaction developed the deltaic and shoreface facies along its shorelines. Clay mineral fractions of the formation are dominantly kaolinitic, indicating a predominantly humid tropical–subtropical climatic condition during their deposition. This climatic regime falls within the African humid period of the early–mid Holocene that led to the third lacustrine transgression of the Lake Mega-Chad, whereas the subordinate smectite mineralization points to aridification that characterizes most of the post humid period to recent.

Precession and atmospheric CO2 modulated variability of sea ice in the central Okhotsk Sea since 130,000 years ago

Recent reduction in high-latitude sea ice extent demonstrates that sea ice is highly sensitive to external and internal radiative forcings. In order to better understand sea ice system responses to external orbital forcing and internal oscillations on orbital timescales, here we reconstruct changes in sea ice extent and summer sea surface temperature (SSST) over the past 130,000 yrs in the central Okhotsk Sea. We applied novel organic geochemical proxies of sea ice (IP25), SSST (TEXL86) and open water marine productivity (a tri-unsaturated highly branched isoprenoid and biogenic opal) to marine sediment core MD01-2414 (53°11.77′N, 149°34.80′E, water depth 1123 m). To complement the proxy data, we also carried out transient Earth system model simulations and sensitivity tests to identify contributions of different climatic forcing factors. Our results show that the central Okhotsk Sea was ice-free during Marine Isotope Stage (MIS) 5e and the early-mid Holocene, but experienced variable sea ice cover during MIS 2–4, consistent with intervals of relatively high and low SSST, respectively. Our data also show that the sea ice extent was governed by precession-dominated insolation changes during intervals of atmospheric CO2 concentrations ranging from 190 to 260 ppm. However, the proxy record and the model simulation data show that the central Okhotsk Sea was near ice-free regardless of insolation forcing throughout the penultimate interglacial, and during the Holocene, when atmospheric CO2 was above ∼260 ppm. Past sea ice conditions in the central Okhotsk Sea were therefore strongly modulated by both orbital-driven insolation and CO2-induced radiative forcing during the past glacial/interglacial cycle.

A multiproxy study of the ocean-atmospheric forcing and the impact of sea-level changes on the southern Cape coast, South Africa during the Holocene

A multiproxy approach, focusing on biological proxies, was undertaken to determine the influence of sea-level changes along the southern Cape coast and the variability of water masses over the central Agulhas Bank region during the Holocene. A 30.47 m sedimentary core extracted from the coastal lake, Eilandvlei, shows continuous deposition for the last 9000 years. Microfossils were classified based on salinity and habitat, diatoms were further defined by their temperature preferences as either warm- or cold-water species. The composition of the assemblages is strongly linked to fluctuations in marine inflow into the system and the extent of freshwater inputs to the lake as recorded at the core site. Paleoproductivity improved during periods of equatorward migration of the westerlies, notably from 5800 to 5000 cal yr B.P., when surface water mixing increased. Spectral analysis revealed periodicities associated with solar cycles, namely Gleissberg and De Vries. The system remained predominantly marine and submerged in response to an early-mid Holocene transgression until 4700 cal yr B.P., when sea-level fluctuations and landscape modification restricted marine incursions, modified the exposed landscape and shifted the system toward a lagoon state. This multiproxy record provides insights into oceanic exchanges, surface water conditions and the mechanisms that govern them during the Holocene.

A high-resolution Holocene record of the East Asian summer monsoon variability in sediments from Mountain Ganhai Lake, North China

A high-resolution environmental magnetic records from a sediment profile in Mountain Ganhai Lake, has provided new insights into modulation of the East Asian summer monsoon (EASM) on climatic changes in North China from the final period of last deglacial stage to Holocene. Large pseudo-single-domain (PSD) to multidomain (MD) detrital magnetite grains are identified in the lake samples. The upwards decreasing magnetic susceptibility (χ) and anhysteretic remanent magnetic susceptibility (χARM) are consistent with the dominant vegetation changes: grassland (~13.0–10.5 ka) under dry and cold conditions, shrub-forest-grassland (~10.5–5.8 ka) in a warm and humid climate, and forest where the Pinus trees increase rapidly to be the dominant taxa, indicating the climate changes from warm and humid to cooler but drier between ~5.8 ka and ~4.0 ka. The lower S-100mT and S-300mT ratios coincide with the higher degree of soil stability and a stable lake stage at ~11.8–6.5 ka. Changes in magnetic anisotropy are also linked to environmental and climatic changes, with T parameters showing higher values during warm/interglacial periods. The anisotropy patterns indicate three different stages of the lake evolution: (1) an early stage of the lake, accompanied by a disturbed high-energy flow, a coarse average mineral particle diameter (MPD) distribution (>16.28 μm) and scattered subvertical minimum direction (K3) at ~13.0–11.8 ka; (2) a fairly stable lake environment between ~11.8 ka and 6.5 ka, indicated by a low-energy flow, finer MPD (~9.69 μm) and subvertical K3 axes; (3) an unstable, high-energy flow and coarse MPD (~20.03 μm) with tilted K3 axes, thus indicating a transition from lake-center to lakeside (~6.5–4.0 ka). These multi-proxy records reveal a weak EASM activity in the final period of the last deglaciation (~13.0–11.8 ka), a high EASM intensity in the early-mid Holocene (~11.8–4.8 ka), an EASM maxima in the mid-Holocene (~8.0–5.8 ka), which then generally weakens at ~4.3–4.2 ka. Overall, this study suggests the anisotropy and climatic changes in the alpine lake are significantly affected by the insolation-driven EASM.

An 8000-year multi-proxy peat-based palaeoclimate record from Newfoundland: Evidence of coherent changes in bog surface wetness and ocean circulation

Energy carried by warm tropical water, transported via the Atlantic Meridional Overturning Circulation (AMOC), plays a vital role in regulating the climate of regions bordering the North Atlantic Ocean. Previous phases of elevated freshwater input to areas of North Atlantic Deep Water (NADW) production in the early to mid-Holocene have been linked with slow-downs in the AMOC and changes in regional climate. Newfoundland’s proximity in the North Atlantic region to the confluence of the Gulf Stream and the Labrador Current and to an area of NADW production in the Labrador Sea makes it an ideal testing ground to investigate the influence of past fluctuations in ocean circulation on terrestrial ecosystems. We use multi-proxy peat-based records from the east coast of Newfoundland to derive a proxy-climate signal for the past 8000 years, which we have compared with changes in ocean circulation. Prominent shifts towards near-surface bog water-table levels, reflecting cooler/wetter climatic conditions, are evident in the early mid-Holocene at c. 7830, 7500, 7220 and 6600 cal. BP with minor changes occurring at c. 6340 and 6110 cal. BP. These events are coherent with evidence of meltwater injections into the N. Atlantic and of reduced NADW production. More recent increases in bog surface wetness in the mid- to late Holocene at c. 4290 and c. 2610 cal. BP are also consistent with reported periods of reduced NADW production. Coherence between the bog-derived palaeoclimate record developed from Newfoundland and evidence of fluctuations in ocean current strength is apparent in the early mid-Holocene.

Quartz and K-feldspar luminescence dating of sedimentation in the North Bohai coastal area (NE China) since the late pleistocene

In this study, luminescence dating of core sediments from the North Bohai Coast (China) was applied to provide a high-resolution chronological constraint, on a better understanding of the Holocene marine-terrestrial interaction. The studied sedimentary sequence contains a terrigenous deposit, a transgressive deposit and a prograding deltaic succession; all are believed to have formed during the late Pleistocene. To establish a reliable luminescence chronology, the luminescence signals of ten samples were investigated in order to quantify the degree of bleaching. This approach involved the use of quartz OSL, K-feldspar infrared stimulated luminescence (IRSL) and post-IR IRSL (pIRIR) ages. The resulting data were then compared with radiocarbon ages. The quartz OSL signals were well-bleached for all the samples, and the feldspar pIRIR150 and pIRIR225 signals yielded reliable ages for the pre-Holocene deposits but overestimated ages for late Holocene deposits (<1000 years). Radiocarbon data appeared to slightly overestimate the age of the young Holocene samples, therefore the chronological framework was established using quartz OSL ages. The early-mid Holocene transgressive deposits are relatively thin, which was attributed to the low-gradient relief and weak riverine fluvial input. Rapid deltaic progradation with high sedimentation rates over the last millennia, was revealed by the quartz OSL age results. This was supported by historical records for this section of the coastline. Episodic deposition around 700 years ago most likely triggered by frequent flooding events, was highlighted by the clustered OSL ages. While the sediment increment was 2.7 × 104 m3 a−1 for the period of ∼6–1 ka, this increased considerably to 9.1 × 106 m3 a−1 during the rapid progradation of the last millennium. The increase appears related to winter monsoon enhancement and human activity during the last 1000 years.