Late Holocene Climate Variability Research Articles

Phytoliths in bamboos from eastern and north-eastern India: Implications in distinguishing different ecoclimatic conditions and in deciphering Late Holocene climate variability

To develop a phytolith (biogenic silica) reference and to understand the eco-climatic indicative values of some grass silica short cells (GSSCs) occurring in the bamboos (Bambusoideae grasses), one of the chief floral components of eastern and north-eastern parts of India, we studied 44 modern bambusoid grasses and 26 surface soils from different eco-climatic zones covering both the plains and mountainous regions. Of the diverse phytoliths retrieved from the bamboos, Saddle tall and Saddle collapsed were the most abundant types (except in Yushania maling) and these types were also common in surface soil phytolith assemblages of the eastern and north-eastern parts of India. To assess the environmental sensitivity of most consistent morphotypes, we categorized two commonly occurring GSSC morphotypes namely Saddle tall into three groups based on their length and Saddle collapsed into two groups based on their length to width ratio respectively. Pearson’s correlation analysis, principal component analysis (PCA), and redundancy analysis (RDA) were used to understand if these morphotypes could distinguish different eco-climatic conditions. Variability of Saddle tall and Saddle collapsed types (both morphometric and abundance) in bamboos growing in these parts of India is a function of mean precipitation of the wettest quarter (MPWeQ) and mean temperature of the driest quarter (MTDQ). The present results served as a baseline for reevaluating the interpretations of a Late-Holocene fossil phytolith record from the eastern Himalaya further validating the potential of Saddle tall and Saddle collapsed types in reconstructing past climate variability in a wide geographical region.

Evaluating middle to late Holocene climate variability from δ18O of aquatic invertebrate remains in southwestern Greenland

Holocene paleotemperature records from ice-free margins of Greenland suggest spatiotemporal heterogeneity in the timing of key climate transitions following retreat of the Greenland Ice Sheet. However, the paucity of high-resolution climate records from this region limits our understanding of the timing, spatial variation, and drivers of Holocene climate variability. Here, we present a middle to late Holocene climate reconstruction based on δ18O of aquatic invertebrate (chironomid and cladoceran) remains and sediment geochemistry from lake sediments to elucidate millennial to submillennial-scale drivers of climate in southwestern Greenland. We establish that our site, Arrowhead Lake, is a through-flowing basin with an integrated signal of annual meteoric water with no evidence of significant evaporative enrichment. Core sediment geochemistry captures the transition from minerogenic-dominated to organic-rich sediments ∼8 cal ka BP. Chitin-based δ18O measurements of both chironomid head capsules and ephippia exhibit similar temporal variability through the record, broadly decreasing from 8.2 cal ka BP to present, concurrent with decreasing summer insolation and regional Neoglacial cooling. A simplified assumption that temperature is the sole driver of changes in isotopes of precipitation yields an estimated average temperature change from the middle to late Holocene at Arrowhead Lake of 2.1–3.0 °C, comparable to existing estimates of middle to late Holocene temperature decline in western Greenland. Depleted δ18O values after 3.3 cal ka BP correspond to the onset of Neoglacial cooling and independent evidence for a slowdown of the West Greenland Current, and suggests that both temperature and sea-ice variability were important controls on isotopic variability at this site. Highly depleted isotopic values at 8.2 cal ka BP followed by high isotopic variability in the early part of the middle Holocene suggests that our record may capture regional 8.2 ka cooling. This new isotope record provides insight into climate influences during the middle and late Holocene along the western Greenland margin that are important for understanding how ongoing melt of the Greenland Ice Sheet and amplified warming in the Arctic may impact the climate system.

Mid-Holocene climate-glacier relationship inferred from landforms and relict lake sequence, Southern Zanskar ranges, NW Himalaya

The geomorphological disposition of (para/peri) glacial landforms, elemental geochemistry, and optical chronology of the relict lake sediment in the Southern Zanskar ranges, northwest Himalaya are used to understand the relationship between glacial dynamics and the lake sedimentation during the mid-Holocene climate variability. Following the Last Glacial Maxima (LGM), pulsating deposition of outwash gravels until the early Holocene overwhelmed the Zanskar valley. The obstruction of Tsarap Chu (chu = river) by alluvial fans during the mid-Holocene led to the development of Padum Lake. In the present study, cirque glacier moraines representing three minor glacial advances were mapped along with sedimentological details and dated using Optically Stimulated Luminescence (OSL) dating technique. The oldest cirque glacier advance - Padum Cirque moraine-3 (PDCm-3) is dated to 11.4 ± 0.9 ka. The succeeding advance (PDCm-2) is dated to 5.3 ± 0.6 and 4.8 ± 0.8 ka whereas, the younger cirque glacier advance (PDCm-1) remains undated. The mid to late Holocene climate variability inferred using major and trace element geochemistry of the relict Padum lake sediments supported by optical chronology indicates six centennial to millennial-scale climatic phases. The prominent warmer phases are represented by decreased mineralogical fine grain flux (low K/Ti, Fe/Si, and Al/Si) with a corresponding increased coarse grain flux (higher Ti/Al and Sr/Al ratios). These phases are dated between 5.9 and 5.5 ka (phase-I), 3.8 and 3.4 ka (phase-IV), and 2.8 and 2.5 ka (phase-VI). The increased mineralogical finer fraction (higher K/Ti, Fe/Si, and Al/Si) between 5.5 and 5.1 ka (phase-II) and 3.4 and 2.8 ka (phase-V) indicate reduced meltwater flux during cooler phases. The intervening phase-III (5.1–3.8 ka) is characterized by increased mineralogical coarse grain flux (decreasing K/Ti, Fe/Si, Al/Si) suggesting gradual warming. The oscillatory climate at millennial scale was further used to understand glacier dynamics. The PDCm-2 advance in the lake record corresponds to the first major cooling (5.5 and 5.1 ka; phase-II) and continued until ∼3.8 ka. Using geochemical data of lake record, a major recession is inferred after 3.8 ka that persisted until around 3.4 ka (phase-IV). Similarly, the undated younger cirque glacier advance (PDCm-1) is assigned to the second cooling event (3.4 and 2.8 ka; phase-V). Thereafter, the cirque glaciers receded, most likely under increasing dryness and fluctuating climate (2.8–2.5 ka, phase-VI). After ∼2.6 ka, the development of ice-wedge pseudomorphs indicates the onset of permafrost conditions that degraded after ∼2.5 ka implying an increase in air temperature. The lake sedimentation terminates with the deposition of multiple younger alluvial fan facies. The climate variability shows a close correspondence with regional climate records suggesting that marginal glacier advancements were triggered by enhanced moisture via atmospheric rivers and cooler winter temperatures. The study highlights the potential of relict lake sediment in association with para- and peri-glacial landforms to reconstruct the pattern of minor glacier responses to climate variability during the Holocene.

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).

Late Holocene climate variability and its impact on cultural dynamics in central India

Abstract An understanding of long-term climate variability may provide a valuable perspective on the possible response of human societies to modern climate change. The present study, based on geochemical and sedimentological analyses on well dated (using AMS 14 C and optically stimulated luminescence (OSL) dates) alluvial sediments from Sina River basin (in Maharashtra, central India), provides a detailed understanding of the complex interplay between climate and cultural dynamics during the Late Holocene. The radiocarbon dates of the organic residues from the potsherds represent the Medieval period ( c. 1.6–0.95 cal ka BP), whereas the OSL sample shows an age of c. 7.5 ± 0.4 ka. Further, several cultural objects (e.g. potsherds, shell bangles, and copper artefacts) available at the site were also investigated in order to understand the extent of human activity in the region. The temporal changes in the proxies along with the abundance of cultural materials in the fluvial section during the Medieval period suggest that the human population attempted to adapt against the fluctuating climate conditions. The regional comparison of geo-archaeological datasets shows that the pronounced weakening of the monsoonal rainfall during the Late Holocene coincides with the disruption, migration and resettlement of indigenous societies, deciphering the possible impact of climate on human settlement.

Chlorine-36 Surface Exposure Dating of Late Holocene Moraines and Glacial Mass Balance Modeling, Monte Sierra Nevada, South-Central Chilean Andes (38°S)

The development of robust chronologies of Neoglaciation from individual glaciers throughout the high-altitude Andes can provide fundamental knowledge of influences such as regional temperature and precipitation variability, and aid in predicting future changes in the Andean climate system. However, records of Late Holocene glaciation from the Central Chilean Andes are sparse, and often poorly constrained. Here, we present 36Cl surface exposure ages, dendrochronologic constraints, and glacial mass balance modeling simulations of Late Holocene glacier fluctuations in the Central-South Chilean Andes. A series of concentric moraine ridges were identified on Monte Sierra Nevada (38°S), where exposure dating of basaltic boulders was used to establish a chronology of ice recession. We infer that moraine abandonment of the most distal ridge in the valley commenced by ∼4.2 ka, and was followed by glacier margin retreat to an up-valley position. Exposure ages of the oldest Late Holocene boulders (∼2.5–0.8 ka) along the marginal extents of the moraine complex indicate fluctuations of the glacier terminus prior to ∼0.65 ka. A final expansion of the ice margin reoccupied the position of the 4.2 ka moraine, with abatement from the outermost composite moraine occurring by ∼0.70 ka, as constrained by tree-ring data from live Araucaria araucana trees. Finally, a series of nested moraines dating to ∼0.45–0.30 ka, formed from a pulsed ice recession during the latest Holocene when the lower reaches of the glacial snout was most likely debris mantled. A distributed temperature index model combined with a glacier flow model was used to quantify an envelope of possible climatic conditions of Late Holocene glaciation. The glacial modeling results suggest conditions were ∼1.5°C colder and 20% wetter during peak Neoglaciation relative to modern conditions. These records also suggest a near-coeval record of Late Holocene climate variability between the middle and high southern latitudes. Furthermore, this study presents some of the youngest 36Cl exposure ages reported for moraines in the Andes, further supporting this method as a valuable geochronologic tool for assessing Late Holocene landscape development.

Mangrove expansion at poleward range limits in North and South America: Late-Holocene climate variability or anthropocene global warming?

Mangroves are expanding poleward in North and South America, but it is unclear whether such ecotonal-shift is an Industrial-Era phenomenon, or a recurring occurrence tied to Holocene climate variability. Our multi-proxy and remote sensing data from the U.S. Gulf Coast and southeastern Brazil suggest that the Industrial Era is the first time throughout the Holocene when mangroves were able to extend their distributions to the current boreal and austral range limits. A mangrove expansion of ∼1.3 ha (from 0.002 to 1.33 ha), 103 ha (from 23 to 126 ha), and 1.42 ha (from 0.39 to 1.81 ha) are documented at Bolivar Flats (Texas, U.S.A.), Mississippi River Delta (Louisiana, U.S.A.), and Apalachicola (Florida, U.S.A.), respectively, since the early 2000s, suggesting that mangrove expansion in North America is a 21st -century phenomenon and likely governed by warming winters. In contrast, the relatively slow mangrove expansion (from 96.1 to 106 ha between 2003 and 2019) at the austral range limit is controlled primarily by available habitats with suitable salinity and sediment substrate.

Reconstruction of the late Holocene climate variability from the summer monsoon dominated Bhagirathi valley, western Himalaya

• High resolution proxy data traced late Holocene climate events for western Himalaya. • Sites have traced dry (4.2 ka; Little Ice Age) phases and moist Medieval warm period . • Dry (weak summer monsoon) phases correspond well with decreased solar irradiance. • Traced dry events are more prominent in drier alpine site than moist temperate site. • LIA phase recorded asynchronous response time in Alpine and Temperate pollen data. This study presents a centennial to decadal scale late Holocene climate scenario from the Indian summer monsoon (ISM) dominated region of western Himalaya. The subsurface sediments analyzed for palynology, carbon isotope (δ 13 C org ) and magnetic susceptibility (χlf) were collected from the temperate and alpine meadows, respectively receiving high (low) and relatively low (high) amount of ISM (winter) precipitation. We could identify the dry and moist phases linked to respective weakening and strengthening of ISM. High frequency of steppe pollen ( Ephedra , Amaranthaceae, Asteraceae, Brassicaceae) between 4.4 and 3.8 ka represented a dry phase, coeval to 4.2 ka global dry event. Subsequent low δ 13 C values and high pollen frequency of moist vegetation (Geraniaceae, Cyperaceae, Apiaceae, Ranunculaceae and pteridophytes) till ca. 0.9 ka suggested moist phase but with an intermittent dry episode ca. 2.9–2.5 ka, allowing rise of steppe taxa. Climate ameliorated ca. 1.8 ka and moist conditions further enhanced between 1.5 and 0.9 ka, corresponding to Medieval Warm Period. Sharp increase in δ 13 C org values and steppe vegetation ca. 0.8 ka attributed to dryness that intensified between 0.6 and 0.2 ka and coincide with Little Ice Age (LIA) anomaly. The recorded dry (weak ISM) phases showed correspondence with the low solar irradiance and supported the teleconnection with north Atlantic circulations. Palynological data from both the valleys complement each other throughout late Holocene time. However, the valleys showed temporal inconsistency in their aridity peaks during LIA phase. This indicates response variability of the two physiographically different sites to summer and winter monsoon systems.

Late Holocene climate variability in central Korea indicated by vegetation, geochemistry, and fire records of the Yongneup moor

In many cases, proxy-based palaeoclimatic and palaeoenvironmental reconstructions in East Asia have shown mixed signatures of summer temperature and precipitation, driven by the predominant regional impact of the East Asian Summer Monsoon. Although these studies have contributed significantly to understanding the past variability in East Asian summer climate during the Holocene period, relatively little has been learned about climatic conditions in other seasons, such as winter and spring, and variations in the individual climatic elements of temperature and precipitation. To address these issues, in this study, we present a reconstruction of a 3000-year fire and vegetation history of the Yongneup moor, central Korea, during the late Holocene based on multi-proxy analyses of pollen, geochemistry, and macrocharcoal. Our data identify two fire episodes at Yongneup during ca. 2900–2700 and 2400–2300 cal yr B.P., possibly caused amid deteriorated climatic conditions not only in summer but also in winter–spring during contemporaneous grand solar minima. During the last two millennia, Yongneup likely experienced cold weather conditions at ca. 1420–1230 and 1000–590 cal yr B.P. and warm conditions at ca. 1850–1420 and 1230–1000 cal yr B.P., as well as wet conditions during ca. 1530–1400, 1220–1000, and 890–700 cal yr B.P. and drier conditions during ca. 1750–1530, 1400–1220, 1000–890, and 700–530 cal yr B.P. The dry periods were coincident with an increased El Niño–Southern Oscillation in the Tropical Pacific Ocean, which supports its role in controlling the hydroclimate of the Korean Peninsula. Our results also emphasise the potential value of further research on the “Millennium Eruption” of Mount Paektu/Changbaishan (946 CE), whose climatic consequences in the East Asian region remain poorly understood. • Late Holocene climate variability in Korea reconstructed from the Yongneup moor • Fire events coincident with solar minima at ca. 2900–2700 and 2400–2300 cal yr B.P. • Potential impact of climate deterioration on Mumun (Bronze Age) societies in Korea • Fluctuations in cold–warm and dry-wet conditions during the last two millennia • Implication on the volcanic impact of the “Millennium Eruption” of Mount Paektu

Sub-bottom and bathymetry sonar inspection of postglacial lacustrine infill of the alpine lakes (Tatra Mts., Slovakia)

An acoustic survey using sub-bottom sonar (SBS) and Autonomous Underwater Vehicle EcoMapper (AUVEM) combined with coring was used for the investigation of bottom topography, thickness of the sediments, and geodynamic factors influencing the postglacial deposition in Tatra Mts. lakes. This combined study of seven lakes shows four basic acoustic units and four subunits that are interpreted in terms of stratigraphy and lithology.However, the presence of particular acoustic units may not be encountered in all the lakes due to the effects of local and internal lake processes. Thick horizontal reflections with high amplitude reflectors characterize the bedrock or the infill with a thickness of more than 6 m. Chaotic internal reflection configuration and high amplitude reflectors are common and reflect the glacigene deposits of unknown thickness in the bottom of the lakes. Above the signals of glacigene sediments lie reflections with weak to moderate amplitude reflectors, and with a parallel and chaotic configuration. They correspond to the glaciolacustrine laminated clay and silt and postglacial gyttja that contain clastic outwash from various mass movement deposits. The transition zone between these two SBS reflections is formed by a discontinuous, parallel and wavy configuration with the acoustic bottom. This type of signal is interpreted as a mixture of cobbles, boulders, and fine-grained sediments.The exact lithological content and the presence of the acoustic units are determined by other factors that may not be visible around the lakes and can cause stratigraphic hiatuses. As a prominent and un-recognized factor in the Tatra Mts. until now is the presence of the bottom springs (pockmarks) of the non-karstic origin, which effectively disturb the fine clastic and organic matter deposition and hence can limit the use of the lake deposit for palaeoclimatic and palaeoecological studies. The mass movement processes – debris flow, rockfall – forming the mountain geo-relief are frequent and their products are visible in the marginal facies. The sonar inspection also provides evidence of mass movement deposits, which have no indication on the terrestrial environment and thereby represent intralacustrine landslides as a result of bedrock instability due to the late Pleistocene deglaciation or Holocene climatic variability.

Climatic implications of late Holocene loess and intervening paleosols, Southern Zanskar range, northwestern Himalaya

ABSTRACT The loess-paleosol proxy records from mid-latitude Asia have been instrumental in the reconstruction of regional paleoclimate evolution and its relationship with global climatic changes. The present study explores the discrete occurrence of a loess and paleosol sequence (LPS) in the Southern Zanskar Range (SZR), NW Himalaya. Stratigraphic variations in sediment texture, supplemented with geochemical, organic and magnetic proxies, indicate two broad phases of loess accretion (L-1) and paleosol formation (PS-1). The older phase of loess accretion (L-1) is dated between 2.5 ± 0.3 ka and >2.0 ka, whereas the L-2, which fully transformed into the modern soil (MS) probably deposited during the Little Ice Age (LIA) phase. The textural attributes (high sand content) of loess indicate source proximal deposition, whereas the geochemical and magnetic proxies point towards the pre-depositional weathering (in the source area). The PS-1 dated to 2189 ± 296 cal yr BP indicates improved moisture conditions, whereas the MS is assigned to post LIA warm phase. These findings provide an important step towards better understanding the sensitivity of loess accretion and paleosol formation in the SZR linked to late Holocene climate variability.

Mid-to Late Holocene climatic and anthropogenic influences in Mpondoland, South Africa

Mpondoland on the South African east coast is a particularly dynamic region in terms of climate change as it is influenced by both temperate and tropical circulation and climate systems. We present a sediment record that indicates regional climatic change and anthropogenic influence during the last ∼5500 yr. Catchment data allow an understanding of signal transmission from the catchment to the site of the marine core. Plant-wax isotope distributions and elemental composition, as well as palynological, burned phytolith and micro-charcoal data, are used to infer paleoclimatic shifts and reconstruct past human activity. Whereas previous studies have often disregarded early anthropogenic drivers of environmental change, our study provides palynological evidence of human impacts and geochemical evidence of increased erosion starting as early as ∼1500 years ago. Downcore proxy analysis suggests that particularly humid conditions persisted from ∼900 to ∼300 cal yr BP, encompassing both the Medieval Climate Anomaly and the Little Ice Age. We suggest that humidity during the Medieval Climate Anomaly was sourced from a poleward shift of the Southern Hemispheric Westerlies and the South African high-pressure cell, allowing for the southward expansion of the Southern Indian Ocean Convergence Zone. During the Little Ice Age, the equatorward movement of the Southern Hemispheric Westerlies probably brought increased rainfall to areas that are normally beyond the northern limit of the Southern Hemispheric Westerlies. Comparison of our record to available regional archives of centennial-scale late Holocene climate variability in South Africa demonstrates that Mpondoland is located at a transition zone of tropical and sub-tropical climatic influences.

Tracing human impact on a mountainous plant landscape in Rhodopi Mt (N. Greece) during the last 1100 years

Mediterranean mountain ecosystems have been attractive to human societies due to their valuable resources, but are also susceptible to environmental and climate changes. The Rhodope Mountain Range hosts one of the least disturbed natural forests of Europe and is a conservation priority area in the Southern Balkans. Located in the borderlands of the plain of Macedonia, the forest ecosystem development of Rhodope Mountains was shaped not only by Late Holocene climatic variability, but also by changes in human activities since Byzantine times. Palynological and microscopic charcoal analysis of the Livaditis ombrotrophic bog record offers unique insights into vegetation and landscape evolution under the influence of human land-use practices in the south Rhodope area during the last c.a. 1100 years. The findings show a forested landscape, with well-developed Pinus and Abies forests of in the montane zone and mixed deciduous oak forests below that flourished in the area until 900 AD. The expansion of human activity in mountainous areas during the period of Byzantine economic growth (ca. 1000 AD) is evidenced by forest clearance through fire, affecting mainly the Abies populations. The Livaditis record bears evidence about both, arboriculture and cereal cultivation as well as animal husbandry during the first period of human activities in the uplands, while a shift towards pastoralism is most likely associated with the establishment of the Vlach population in the region (ca. 1200 AD). Subsequently, a short-lived expansion of the Pinus percentages could be attributed to the afforestation of abandoned pasture land during the Little Ice Age. Finally, a further intensification of pastoralism is most likely concurrent with the population expansion documented during the Ottoman period (after 1500 AD). The Livaditis pollen record shows significant vegetation shifts in the upland area of southern Rhodope Mountains that could be associated with changes in climate, population mobility and density, as well as evolving land-use practices.

Late-Holocene climate response and glacial fluctuations revealed by the sediment record of the monsoon-dominated Chorabari Lake, Central Himalaya

We studied a periglacial lake situated in the monsoon-dominated Central Himalaya where an interplay of monsoonal precipitation and glacial fluctuations during the late Holocene is well preserved. A major catastrophe occurred on 16–17 June 2013, with heavy rains causing rupturing of the moraine-dammed Chorabari Lake located in the Mandakini basin, Central Himalaya, and exposed 8-m-thick section of the lacustrine strata. We reconstructed the late-Holocene climatic variability in the region using multi-parametric approach including magnetic, mineralogical and chemical (XRF) properties of sediments, paired with grain size and optically simulated luminescence (OSL) dating. The OSL chronology suggests that the lake was formed by a lateral moraine during the deglaciation phase of Chorabari Glacier between 4.2 and 3.9 ka and thereafter the lake deposited about 8-m-thick sediment sequence in the past 2.3 ka. The climatic reconstruction of the lake broadly represents the late-Holocene glacial chronology of the Central Himalaya coupled with many short-term climatic perturbations recorded at a peri-glacial lake setting. The major climatic phases inferred from the study suggests (1) a cold period between 260 BCE and 270 CE, (2) warmer conditions between 900 and 1260 CE for glacial recession and (3) glacial conditions between ~1370 and 1720 CE when the glacier gained volume probably during the ‘Little Ice Age’ (LIA). We suggest a high glacial sensitivity to climatic variability in the monsoon-dominated region of the Himalaya.

Late glacial and Holocene climate variability, southernmost Patagonia

A Late glacial – Holocene palaeoecological record, constrained by a robust chronology, from a peat bog near Punta Burslem (54°54′S, 67°57′W) on Isla Navarino, southernmost Patagonia documents the shifts in intensity and focus of the Southern Westerly Winds (SWWs) at these high latitudes. Such long-term records are required to reconstruct and better understand the likely regional impacts of a poleward shift and intensification of the SWWs predicted under global warming scenarios. Deglaciation at Punta Burslem occurs sometime before c. 17,000 cal a BP, and the post glacial landscape is dominated by cold tolerant pioneer species. Nothofagus woodland is established by c. 12,250 cal a BP, this moisture sensitive vegetation type retreats in the early to mid-Holocene from c. 9700 to 7050 cal a BP reflecting an intense and sustained drier phase associated with a prolonged poleward contraction of the SWWs. After c. 6000 cal a BP there is a regional trend to cooler and wetter climate. However, we identify at least five periods of rapid climate change (RCC) leading to drier conditions at this southern extreme of Patagonia: c. 5350-4750 cal a BP, c.4300-3300 cal a BP, c. 2600-1850 cal a BP, c. 1350-1100 cal a BP and c. 550-350 cal a BP. From a synthesis of our Isla Navarino records and a latitudinal spread (34°-64°S) of multiproxy records it is proposed that these periods of RCC and relatively drier conditions indicate latitudinal shifts in the location and intensity of the SWWs in response to climatic warming leading to reduced precipitation at the southern margins of Patagonia.

Schmidt-hammer exposure-age dating (SHD) performed on periglacial and related landforms in Opplendskedalen, Geirangerfjellet, Norway: Implications for mid- and late-Holocene climate variability

Schmidt-hammer exposure-age dating (SHD) was applied to a variety of boulder-dominated periglacial landforms in an attempt to establish a local mid-/late-Holocene chronology for the Geirangerfjellet in South Norway. Landform ages were obtained by application of a local calibration curve for Schmidt hammer R-values based on young and old control points comprising fresh road cuts and a bedrock surface in proximity to the study area, respectively. The area was deglaciated ~11.5 ka ago according to independent age information. Investigation of age, formation and stabilization of the periglacial landforms and processes involved allowed assessment of the underlying Holocene climate variability and its relationship to landform evolution. Our SHD ages range from 7.47 ± 0.73 ka for glacially abraded bedrock at the valley bottom to 2.22 ± 0.49 ka for surface boulders of a rock-slope failure. All landforms shared negative skewness and largely have narrow tailed frequency distributions of their R-values. This points to either substantial reworking of the boulders within a landform or continuous debris supply. Our results show that most landforms stabilized during the Holocene Thermal Maximum (~8.0–5.0 ka). The findings do not support the hypothesis that rock-slope failures predominately occur shortly after local deglaciation. Instead, it appears that they cluster during warm periods due to climate-driven factors, for example, decreasing permafrost depth or increasing cleft-water pressure leading to slope instabilities. Periglacial boulder-dominated landforms in the western maritime fjord region seem to react sensitively to Holocene climate variability and may constitute valuable but to date mostly unexplored sources of palaeoclimatic information.

Late Holocene climatic variability in Subarctic Canada: Insights from a high-resolution lake record from the central Northwest Territories.

We examined late Holocene (ca. 3300 yr BP to present-day) climate variability in the central Northwest Territories (Canadian Subarctic) using a diatom and sedimentological record from Danny’s Lake (63.48ºN, 112.54ºW), located 40 km southwest of the modern-day treeline. High-resolution sampling paired with a robust age model (25 radiocarbon dates) allowed for the examination of both lake hydroecological conditions (30-year intervals; diatoms) and sedimentological changes in the watershed (12-year intervals; grain size records) over the late Holocene. Time series analysis of key lake ecological indicators (diatom species Aulacoseira alpigena, Pseudostaurosira brevistriata and Achnanthidium minutissimum) and sedimentological parameters, reflective of catchment processes (coarse silt fraction), suggests significant intermittent variations in turbidity, pH and light penetration within the lake basin. In the diatom record, we observed discontinuous periodicities in the range of ca. 69, 88–100, 115–132, 141–188, 562, 750 and 900 years (>90% and >95% confidence intervals), whereas the coarse silt fraction was characterized by periodicities in the >901 and <61-year range (>95% confidence interval). Periodicities in the proxy data from the Danny’s Lake sediment core align with changes in total solar irradiance over the past ca. 3300 yr BP and we hypothesize a link to the Suess Cycle, Gleissberg Cycle and Pacific Decadal Oscillation via occasional inland propagation of shifting air masses over the Pacific Ocean. This research represents an important baseline study of the underlying causes of climate variability in the Canadian Subarctic and provides details on the long-term climate variability that has persisted in this region through the past three thousand years.

Effects of late Holocene climate variability and anthropogenic stressors on the vegetation of the Maya highlands

Climate variability and human activities have shaped the vegetation communities of the Maya region of southern Mexico and Central America on centennial to millennial timescales. Most research efforts in the region have focused on the lowlands, with relatively little known about the environmental history of the regional highlands. Here we present data from two sediment sequences collected from lakes in the highlands of Chiapas, Mexico. Our aim was to disentangle the relative contributions of climate and human activities in the development of regional vegetation during the late Holocene. The records reveal a long-term trend towards drier conditions with superimposed centennial-scale droughts. A declining moisture trend from 3400 to 1500 cal yr BP is consistent with previously reported southward displacement of the Intertropical Convergence Zone, whereas periodic droughts were probably a consequence of drivers such as El Niño. These conditions, together with dense human occupation, converted the vegetation from forest to more open systems. According to the paleoecological records, cultural abandonment of the area occurred ca. 1500 cal yr BP, favoring forest recovery that was somewhat limited by low moisture availability. About 600 cal yr BP, wetter conditions promoted the establishment of modern montane cloud forests, which consist of a diverse mixture of temperate and tropical elements. The vegetation types that occupied the study area during the last few millennia have remained within the envelope defined by the modern vegetation mosaic. This finding highlights the importance of microhabitats in the maintenance biodiversity through time, even under scenarios of high climate variability and anthropogenic pressure.

한반도 홀로세 후기 기후와 적도 태평양 해수면 온도 간의 연관성

한반도 홀로세 후기 기후와 적도 태평양 해수면 온도 간의 연관성

Late Holocene stable isotopic (δ13C and δ15N) records of lacustrine organic matter in Guangdong Province, south China, and their palaeoenvironmental implications

This study presents the results of TOC/TN (C/N) ratio, δ13C and δ15N analyses of lake sedimentary organic matter (OM) from the Hedong section, western Guangdong Province in south China, with the objective to reveal the history of hydrological and ecological variations in the region influenced by both the Indian summer monsoon (ISM) and East Asian summer monsoon (EASM). Variations in δ13C and δ15N of sedimentary OM may be closely related to past climatic conditions, which results in variations in surface runoff, lake level, allochthonous and autochthonous sources of OM, and lake productivity. Based on the interpretation of these proxies, four periods, i.e. 4370–4100, 3700–2900, 2400–2100 and 1900–900 cal. a BP, are characterized by low lake level, weakened surface runoff and deteriorated status of terrestrial and aquatic ecosystems, whereas the periods 4100–3700, 2900–2400, 2100–1900 and 900–600 cal. a BP are dominated by high lake level, strengthened surface runoff, and flourishing terrestrial and aquatic plants. A remarkable positive correlation between the δ13C values of the section and the ENSO number record obtained from the tropical Pacific implies that the impact of the ISM is greater than that of the EASM in the study area. The abnormal correspondence between the δ13C and solar activity reconstructed from 10Be and 14C records in GRIP ice‐core occurred from 1500–800 and particularly from 4200–4000 cal. a BP, suggesting that these two cool and dry intervals may be caused by stronger volcanic activities that are recorded in the GISP2 and Dome C ice‐cores. This study reveals that changes in solar insolation and solar activity, as well as changes in oceanic–atmospheric circulation (e.g. the ENSO intensity) and intensive volcano eruptions may have exerted influence on late Holocene climate variability in the study area.