Late Holocene Moisture Research Articles

Alluvial-lacustrine record of Mid- to Late-Holocene moisture variations trend verified by multiple proxies in the middle and lower reaches of the Hutubi River, northwest China

Alluvial-lacustrine deposits are important carriers for studying paleo-hydrological information and the evolution of paleo-environments. In this study, a total of 6 optically stimulated luminescence (OSL) samples from 2 profiles in the lower and middle reaches of the Hutubi River in the North Tianshan Mountains were dated, and a comprehensive analysis was conducted by integrating sedimentary structures, grain sizes, and magnetic susceptibility characteristics to explore the sedimentary environment patterns and regional evolution processes during the Mid to late Holocene. The results revealed the following findings: (1) The OSL signal of quartz samples indicates the predominance of fast components, allowing reliable dating of regional fluvial sediments using the appropriate condition-tested coarse-grained quartz single-aliquot regenerative dose (SAR) protocol within the 90–125 μm range. (2) Analysis of sedimentary structures, grain sizes, and magnetic susceptibility characteristics reveals lithofacies of heterotopic synchronous or homotopic asynchronous in exposed profiles, with predominantly poorly sorted fine and very fine sand. Magnetic susceptibility is primarily controlled by the content of magnetic minerals in the coarse particles, while also being influenced by the combined effects of provenance input and depositional environment, indicating a complex regional sedimentary environment influenced by variable hydrodynamic conditions driven by fluvial processes. (3) Based on OSL dating results and the analysis of various environmental proxy indicators, it is determined that the climatic environment in the Middle and Late-Holocene in the downstream areas of the northern piedmonts of the Tianshan Mountains demonstrates a fluctuating pattern of wet and dry alternations. The sedimentary environment shifted from a stable state in the Mid-Holocene to an unstable state in the Late-Holocene. The intermittent appearance of wet records may be associated with increased river activity caused presumably by the release of high-altitude ice due to rising temperatures and warming conditions.

A prolonged dry Mid-Holocene recorded by Moon Lake in the Tengger Desert, arid and semiarid China

AbstractReconstructing the Mid-Holocene climate change in arid and semiarid areas can help predict regional moisture availability and resultant lake evolution and vegetation changes due to future warming. Here, we present a sediment core (YLH15A) from Moon Lake in the Tengger Desert, arid and semiarid China. Based on robust accelerator mass spectrometry 14C dating and multiproxy analyses (pollen, grain size, elements, and total organic carbon), we reconstructed regional climate changes since 7.6 cal ka BP. The climate was generally dry from 7.6 to 2.8 cal ka BP, as indicated by the dried-up lake, strong aeolian activities, and no vegetation, except for a short-term wet interval between 5.4 and 4.9 cal ka BP. The generally dry climate shifted after 2.8 cal ka BP, which is suggested by expanded steppe desert/steppe and increased vegetation cover; it was also accompanied by lake development, which was likely related to increased groundwater recharge originating from regional precipitation and temporary floods from adjacent mountain areas. Our results reveal a prolonged dry Mid-Holocene and relatively wet Late Holocene that are basically consistent with climatic records from the central–east Asian arid and hyperarid areas. The prolonged dry climate in the arid and hyperarid areas is likely to be related to high evaporation triggered by high temperatures during the Middle Holocene.

High-resolution luminescence chronology of loess-paleosols reveals East Asian summer monsoon and winter monsoon variation in Hexi Corridor during the past 25 kyr

The variability and interaction of the East Asian summer monsoon (EASM), East Asian winter monsoon (EAWM) and Westerlies dominate mid-latitude Asian hydroclimate and influence over a billion lives in Asia. However, how variation in the EASM, EAWM and Westerlies influences climate change in their transition zones in NW China remain unclear. Specifically, how these atmospheric systems interact during strong-weak phases variation over different timescales is still hotly debated. This study investigates four loess-paleosol sequences in the transition zone between EASM and Westerlies-influenced areas along the central Hexi Corridor of NW China, and presents 63 quartz optically stimulated luminescence (OSL) ages to generate the most detailed chronology for any loess record within the Hexi Corridor. In combination with sedimentology, proxy indexes of magnetic parameters (χlf, χfd, χARM/SIRM) and grain size of these loess-paleosol sequences, and TraCE-21 ka climatic modelling, the loess deposition and climatic changes at central Hexi Corridor regions over the past 25 ka are reconstructed. Our results indicate that: (1) loess deposition initiated by at least 25 ka at Hexi Corridor. Loess depositional rates decrease from late last glacial into the Holocene, with maximum accumulation rates (140–180 g/cm3/ka) occurring during the Last Glacial Maximum. Depositional hiatuses up to 8 ka are recognized in late Quaternary Hexi Corridor loess, which suggests that high-resolution chronologies are necessary for robust paleoclimatic reconstructions from loess records in the region. (2) Over glacial-interglacial cycles, climate in the Hexi Corridor demonstrates a cold-dry glacial and a warm-moist interglacial, consistent with moisture changes observed in the monsoonal Chinese Central Loess Plateau and Westerlies-dominated Central Asia. However, moisture in central Hexi Corridor increased from the early Holocene to mid-Holocene, with a wettest period at 8–7 ka, and followed by a relatively wet late Holocene. These changes are most consistent with the EASM-dominated Chinese Central Loess Plateau and suggests that Westerlies influence in the central Hexi Corridor is minor over at least the past 25 kyr. (3) EAWM intensities demonstrate an anti-phase relationship to EASM intensities over the past 25 kyr in the Hexi Corridor, with decreasing EAWM intensity into the early-mid Holocene and an increase into the late Holocene. (4). EASM precipitation variability in the Hexi Corridor appears to not to be a direct nor singular response to changes in 30°N summer insolation. EASM lags insolation by 3 kyr during the Holocene, supporting the idea that high-latitude forcing through changes in ice volume, greenhouse gases, and/or meltwater input to North Atlantic and Southern oceans can effectively modulate EASM intensity and critically influence Hexi Corridor paleoclimatic conditions.

Mid to Late Holocene moisture evolution of semi-arid Mongolia and its anti-phase relationship with monsoonal Asia

The spatial and temporal interaction of the Westerlies and the Asian Summer Monsoon (ASM) are often suggested to drive the Holocene moisture evolution of semi-arid Mongolia and Central Asia, but so far, it has remained a controversial topic of debate. In this context, we established a high-resolution 7.4 cal ka paleohydrological record from Shireet Naiman Nuur in the central Mongolian Khangai Mountains using compound-specific biomarker δ2H analyses. Our results suggest that drier conditions from 7.4 to 3.6 cal ka BP and wetter conditions since 3.6 cal ka BP until present are indeed related to changes in atmospheric circulation pattern. A strong anti-phasing between our record and records in monsoonal Asia shows that ASM intensification during the Mid Holocene shifted the ASM limit and adjacent subsidence dry-zones northwards, leading to increased dryness at Shireet Naiman Nuur. Overall wetter conditions during the Late Holocene are related to negative North Atlantic Oscillation phases advecting moisture into central Mongolia and Shireet Naiman Nuur by southerly-displaced Westerlies.

Multimillennial fire history of northern Finland along a latitude/elevation gradient

In boreal environments, wildfires are expected to decrease in frequency and/or size with latitude/elevation, mainly in response to climate, as well as fuel availability and type. Furthermore, fire frequency and biomass burned are supposed to have been higher during warm and dry periods of the Holocene (last ∼ 11,000 years). We tested these assumptions in northern Finland by using charcoal analysis to reconstruct Holocene regional fire regimes from eight lake sediment sequences sampled within four different environments in terms of elevation, latitude and vegetation type: (1) low latitude/mid elevation coniferous forests (Pinus sylvestris and Picea abies); (2) mid latitude/low elevation pine forests (Pinus sylvestris); (3) mid-high latitude/elevation transitional mixed forests (Pinus sylvestris and Betula pubescens subsp. tortuosa); and (4) high latitude/elevation birch woodlands (Betula pubescens subsp. tortuosa). As expected, fire frequency decreased with increasing latitude/elevation. Contrary to expectations, fire frequency was not significantly higher in the warm and dry mid-Holocene than in the cool and wet late Holocene, except in transitional mixed forests. Biomass burned was higher in the mid- than in the late Holocene, but only in pine and pine-spruce forests. The opposite was observed in transitional mixed forests and birch woodlands, suggesting that factors other than climate controlled fire regimes in these environments. While climate warming will likely result in more biomass burned in low latitude/elevation coniferous forests, other disturbances (such as insect outbreaks) might play a more important role in high latitude/elevation birch-pine forests and birch woodlands.

Ecological stability of Late Pleistocene-to-Holocene Lesotho, southern Africa, facilitated human upland habitation

Investigation of Homo sapiens’ palaeogeographic expansion into African mountain environments are changing the understanding of our species’ adaptions to various extreme Pleistocene climates and habitats. Here, we present a vegetation and precipitation record from the Ha Makotoko rockshelter in western Lesotho, which extends from ~60,000 to 1,000 years ago. Stable carbon isotope ratios from plant wax biomarkers indicate a constant C3-dominated ecosystem up to about 5,000 years ago, followed by C4 grassland expansion due to increasing Holocene temperatures. Hydrogen isotope ratios indicate a drier, yet stable, Pleistocene and Early Holocene compared to a relatively wet Late Holocene. Although relatively cool and dry, the Pleistocene was ecologically reliable due to generally uniform precipitation amounts, which incentivized persistent habitation because of dependable freshwater reserves that supported rich terrestrial foods and provided prime locations for catching fish.

Evidence of Mid-Holocene (Northgrippian Age) Dry Climate Recorded in Organic Soil Profiles in the Central Appalachian Mountains of the Eastern United States

Peatlands in Canaan Valley National Wildlife Refuge hold a pedomemory of Pleistocene and Holocene climatic fluctuations in the central Appalachian Mountains of the eastern United States. A field investigation profiling 88 organic soil profiles, coupled with 52 radiocarbon dates and peat accumulation rates, revealed a distinct sequence of organic soil horizons throughout five study areas. The dominantly anaerobic lower portions of the organic soil profiles consist of varied thicknesses of hemic and sapric soil materials, typically layered as an upper hemic horizon, underlain by a sapric horizon, underlain by another hemic horizon. Peat deposition began after the Last Glacial Maximum with relatively high Heinrich Stadial 1 accumulation rates to form the lowest hemic horizon. Peat accumulated at significantly slower rates as the climate continued to warm in the early Holocene Greenlandian Age. However, between 10,000 and 4200 cal yr BP peat accumulation decreased further and the decomposition of previously deposited peat prevailed, forming the sapric horizon. This interval of greater decomposition indicates a drier climatic with dates spanning the late Greenlandian Age through the Northgrippian Age. The upper hemic horizon within the anaerobic portion of the soil profile formed from high peat accumulation rates during the wetter late Holocene Meghalayan Age.

Increasing effective moisture during the Holocene in the semiarid regions of the Yili Basin, Central Asia: Evidence from loess sections

The evolution of Holocene moisture in semiarid and arid regions of Central Asia is key to understanding changes in current and future water resources, and has been a hotly debated topic in the past few decades. Central Asian loess deposits have shown potential as records of past moisture changes, particularly during the Holocene. Here, the variations in effective moisture during the Holocene in the semiarid regions of the Yili Basin, Central Asia, are obtained from three loess sections. Reliable chronologies were constructed using 26 quartz optically stimulated luminescence (OSL) ages. The strengthening pedogenesis, steady increases in magnetic susceptibility, and continuous decreases in mean grain size in the three loess sections all suggest that effective moisture continuously increased throughout the Holocene, indicating a dry early Holocene, a moderately humid middle Holocene, and a wet late Holocene. Rainfall carried by the Asian summer monsoon and the Westerlies contributes to the moisture changes in Central Asia. However, considering the dominance of evaporation over rainfall in controlling aridity-humidity shifts in this region, the continuous weakening of evaporation caused by a decrease in Northern Hemisphere summer insolation and associated atmospheric temperatures is primarily responsible for the wetting trend throughout the Holocene in the semiarid regions of the Yili Basin.

The role of climate-fuel feedbacks on Holocene biomass burning in upper-montane Carpathian forests

Abstract Over the past few decades, mean summer temperatures within the Carpathian Mountains have increased by as much as 2 °C leading to a projected increased forest fire risk. Currently, there are no paleofire records from the Western Carpathians that provide the long-term range of natural variability to contextualise the response of upper-montane forests to future environmental change and disturbance regimes. We present the first high-resolution Holocene fire history record from the upper-montane ecotone from the High Tatra Mountains, Slovakia, as well as provide a regional synthesis of pan-Carpathian drivers of biomass burning in upper-montane forests. Our results illustrate that forest composition and density both greatly influence biomass burning, creating two different climate-fuel feedbacks. First, warmer conditions in the early Holocene, coupled with generally higher abundances of Pinus sp., either P. cembra and/or P. mugo/sylvestris, created a positive climate-fuel relationship that resulted in higher amounts of biomass burning. Second, cooler and wetter late Holocene conditions led to denser Picea abies upper-montane forests, creating a negative climate-fuel feedback that reduced biomass burning in upper-montane forests across the Carpathians. Given that warmer and drier conditions are expected across the entire Carpathian region in the future, our results illustrate how future climate change could potentially create a positive climate-fuel relationship within upper-montane forests dominated by Picea abies and Pinus cembra and/or P. mugo/sylvestris.

Late Holocene Moisture Changes in the Core Area of Arid Central Asia Reflected by Rock Magnetic Records of Glacier Lake Kalakuli Sediments in the Westernmost Tibetan Plateau and their Influences on the Evolution of Ancient Silk Road

AbstractThe evolution of Ancient Silk Road (ASR) was deeply influenced by late Holocene moisture changes in Arid Central Asia (ACA). Nevertheless, controversies in Holocene moisture change pattern of ACA and poorly–constrained age models of related studies have made the discussion about late Holocene moisture changes in ACA and their influences on the evolution of ASR difficult. Recently, a high–resolution age model during the late Holocene was established for Kalakuli Lake, a small glacier lake located in the core area of ACA. A thorough rock magnetic investigation was carried out on Kalakuli Lake sediments based on this age model. The magnetic mineral assemblage of Kalakuli Lake sediments is still dominated by primary magnetite despite minor diagenetic effects. Comparisons of rock magnetic records to parameters previously used as indicator of glacier fluctuations suggest that clastic input to Kalakuli Lake was high (low) and magnetic grain size is relatively larger (smaller), when glaciers on Muztagh Ata advanced (retreated). The ARM/SIRM ratio, a magnetic grain size proxy, is directly related to lake hydrodynamics, which are ultimately controlled by glacier fluctuations on Muztagh Ata as the result of regional moisture changes. Late Holocene moisture changes indicated by the ARM/SIRM ratio are consistent with cool/wet and warm/dry oscillations indicated by the unweighted average of biomarker hydrogen isotopic data of the C26 and C28 n–alkanoic acids in a previous study about Kalakuli Lake, most moisture change records of the core area of ACA and winter insolation of the Northern Hemisphere, but opposite to Asian monsoon evolution. Given Asian monsoon and the westerlies are mutually inhibited, we propose that late Holocene moisture changes in the core area of ACA were controlled by the intensity of Asian monsoon versus the westerlies under the governance of solar insolation. Generally increased moisture since the late Holocene indicated by the ARM/SIRM ratio favored cultural exchange and integration between the western and the eastern Eurasia, which paved the way for the formation of ASR. Coincidence between significant increase in moisture at ~200 BC suggested by the ARM/SIRM ratio and the formation of ASR indicates moisture as an important factor that facilitated the formation of ASR. The onsets of three prosperity periods of ASR in the history generally correspond to periods when moisture was relatively high, nevertheless, stagnant periods of ASR do not coincide with periods when moisture was relatively low in the core area of ACA. Disorganized correlations between stagnant periods of ASR and moisture changes in the core area of ACA suggest that moisture is not the decisive factor influencing the evolution of ASR.

Holocene moisture variations in the Arid Central Asia: New evidence from the southern Altai Mountains of China

A continuous peat sequence collected in the southern Altai Mountains provides a new opportunity to reconstruct the Holocene vegetation and moisture history in the Arid Central Asia. Based on pollen data of 190 samples with a chronologic support of eight AMS dates from a 380-cm core at Tuolehaite (TLHT) Peat, the Holocene moisture variations in the southern Altai Mountains of China were reconstructed. The reconstruction revealed a wet early Holocene (~10,600–~8500cal. yr BP), a considerably dry middle Holocene (~8500–~4000 cal. yr BP) and a resumed wet late Holocene (~4000–0 cal. yr BP). The Holocene moisture reconstruction is generally corroborated by other reviewed sequences from the southern Altai Mountains and the surrounding areas. According to the analysis of modern sources of precipatable water vapor for the southern Altai Mountains, the Holocene moisture variations in the southern Altai Mountains were proposed to have been causally associated with the variations in the sea surface temperature (SST) in the North Atlantic Ocean and also with the variations in the strength of Siberian High Pressure in the core of the Eurasian continent.

Millennial-Scale Climate and Human Drivers of Environmental Change and Fire Activity in a Dry, Mixed-Conifer Forest of Northwestern Montana

Warmer temperatures and longer fire seasons are promoting larger, and in some cases, more severe fires in low- and mid-elevation, dry mixed-conifer forests of the Northern Rocky Mountains. Long-term historical fire conditions and human influence on past fire activity are not well understood for these topographically and biophysically heterogeneous forests. We developed reconstructions of millennial-scale fire activity, vegetation change, and human presence at Black Lake, a small closed-basin lake on the Flathead Indian Reservation in the Mission Valley, northwestern Montana, USA. Fossil pollen, charcoal, and biomarkers associated with human presence were used to evaluate the interaction between climate variability, fire activity, vegetation change and human activity for the past seven thousand years. Multi-proxy comparisons suggest climate variability acted as the primary control on fire activity and vegetation change from the early Holocene until the late Holocene when records suggest fire activity and climate variability decoupled. Specific biomarkers (5β-stanols including coprostanol and epi-coprostanol) associated with human presence indicate humans were present within the Black Lake watershed for thousands of years, although the inferred intensity of human presence was highly variable. A strong relationship between climate variability and fire activity during the early and mid-Holocene weakens during the last few thousand years, suggesting possible increased influence of humans in mediating fire activity in recent millennia. Human-set fires during the cooler and wetter late Holocene may have been aimed at maintaining important cultural resources associated with the heterogeneous mosaic of mixed conifer forests within the Black Lake watershed. The paleoenvironmental reconstruction at Black Lake provides one of the first independent records of human presence in the NRM, and suggests humans were present within the Black Lake watershed for over 7000 years. Further research is needed to evaluate the evidence for this continuous presence and the possible role that people played in shaping fire regimes and vegetation within low- to mid-elevation mixed-conifer ecosystems of the NRM.

Inconsistency between records of δ18O and trace element ratios from stalagmites: Evidence for increasing mid–late Holocene moisture in arid central Asia

The interpretation of trace element/calcium ratios of speleothems as indicators of local hydroclimatic variability in the vicinity of caves has led to controversy in reconstructing the evolution of moisture conditions in arid central Asia (ACA) during the Holocene. Here we present records of Mg/Ca, Sr/Ca, Ba/Ca, and U/Ca from precisely dated stalagmites from Baluk cave in Xinjiang (northwest China), spanning the past 9370 years. The co-variations of the trace element ratios, together with the slopes of the regression lines of the corresponding logarithmically transformed data, suggest that they are dominated by prior calcite precipitation (PCP) and thus can be used as reliable proxies of changes in moisture/precipitation. The trace element ratios are relatively high during ~9 to 5 ka and lower from 5 ka to the present, indicating a trend of increasing mid–late Holocene moisture in ACA. The long-term trend of variation of the trace element ratios is correlative with two other records of speleothem trace element ratios from caves in ACA: Kesang cave (western Xinjiang) and Ton cave (Uzbekistan). This spatial coherency of the trend of inferred moisture conditions from three caves that are separated by hundreds of kilometers demonstrates that speleothem trace element ratios are indicative of large spatial scale rather than local hydroclimatic variability in ACA during the Holocene. However, the long-term trend of variation of the trace element ratios is the inverse of the corresponding oxygen isotope (δ18O) records from the same cave sites, which implies that Holocene speleothem δ18O records do not represent changes in the precipitation amount in ACA; rather, they most likely reflect moisture sources and related water vapor transport controlled by Northern Hemisphere summer insolation (NHSI). Our findings provide new evidence for a ‘westerlies-dominated climatic regime’, which influenced hydroclimatic changes in ACA during the Holocene.

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.

Summer moisture changes in the Lake Qinghai area on the northeastern Tibetan Plateau recorded from a meadow section over the past 8400 yrs

Abstract Holocene climatic and environmental changes on the northeastern Tibetan Plateau (TP) have been widely discussed based on the climatic records from sedimentary cores. However, differences in the reconstructed climatic history from various studies in this region still exist, probably due to influence of climatic proxies from multiple factors and the chronological uncertainties in lacustrine sediments. Here we present records of terrestrial plant δ13C, soil color and total organic carbon content over the past 8400 years from a well-dated meadow section on the northeastern TP. The terrestrial plant δ13C value serves as a good summer precipitation/moisture indicator in the studied region. Soil color property and TOC content are also able to disentangle the moisture evolution history. All the data show much wet climates at 8400–7400 cal yr BP, dry climates at 7400–6000 cal yr BP and then wet conditions with fluctuation at 6000–3200 cal yr BP. Late Holocene moisture appears to be comparable with moist conditions from 6000 to 3200 cal yr BP. By further comparing the climatic variations in the Lake Qinghai area with records of the reconstructed summer temperature and the Asian Monsoon precipitation, we believe that the pattern of moisture/precipitation evolution in the Lake Qinghai area was not completely consistent with regions around Lake Qinghai, probably due to complicated interaction between the East Asian Summer Monsoon and the Indian Summer Monsoon.

Late Holocene Records of Changing Moisture Regime from Wetlands in Southwestern Nova Scotia, Canada: Implications for Wetland Conservation and Restoration

An understanding of the morphological stability and succession of open water and wetland ecosystems in Nova Scotia is a priority for informing the conservation management of critical habitats for a complex of nationally listed, rare, disjunct wetland species. Baltzer Bog and Big Meadow Bog in southwestern Nova Scotia contain stratigraphic records of late Holocene moisture variability. Baltzer Bog is a shrub bog that formed in an elevated, enclosed kettle basin. Excavated sections exposed by peat mining revealed 2 distinct wood-rich horizons that are located above a well-developed soil and wood horizon that yielded a radiocarbon-dated age of 3260 cal. BP from an upright stump. The overlying wood-rich horizons were dated at 1640 and 1045 cal. BP and were overlain by Sphagnum species transitions indicative of increasing wetness. At Big Meadow Bog, a thin wood mat in Sphagnum at 90 cm depth was dated at 1760 cal. BP. These records are broadly correlative with pollen and stratigraphic data from Pleasant River Fen in central Nova Scotia that indicate periods of high and low productivity and a fluctuating water table from 1950 cal. BP until present. Though other high-resolution paleoclimate records from the region indicate that the late Holocene was a time of increasing precipitation and cooler air temperatures, these wetland records demonstrate that in Nova Scotia this time period was characterized by rapid variations in effective moisture and that significant and sustained dry periods likely occurred. This record of late Holocene moisture variability and its influence on habitat structure serves to better establish the potential for long-term residency of threatened and endangered species at wetland sites.

The mid to late Holocene transition in Barrancas, Jujuy, Argentina: Regional climate change, local environments and archaeological implications

This paper presents the preliminary results of a multiproxy analysis of the Cruces 2 record (PCC2), located in the area of Barrancas, Dpt. of Cochinoca, Province of Jujuy, Argentina. Our studies included geomorphology, organic matter and carbonate content, magnetic properties of sediments, diatoms and pollen analysis, with the purpose of exploring the environmental characteristics of the locality from the mid- to late Holocene transition (ca. 4500 BP) to 1000 BP. This research contributes to an ongoing effort to model resource structure during the Holocene in the South-central Andes highlands of Argentina, thus allowing a more informed debate regarding the availability, distribution and characteristics of human habitats in this region, contributing to predict and explain patterns in the archaeological record both at regional and local scales.The PCC2 record indicates that the mid- to late Holocene transition in the locality implied a change from more regionally dry and mostly stable conditions to more humid but unstable conditions. During the regionally wetter late Holocene the energy of the Barrancas hydrological system increased, including frequent torrential events, but these conditions were punctuated by discrete, recurrent and/or intense regionally dry episodes. Locally, these dry events manifested as episodes of paludization/paleosoil formation in Barrancas and other localities of the dry Puna, which took place at 3260, 3000, 2500, 2100, 1490/1460, and 1050cal BP.The consolidation of a group of cultural traits locally known as “the Formative Period” in the South-central Andes – village settlements, pottery, agriculture and/or pastoralism - may have been part of a sociocultural strategy to cope with resource uncertainty and economic risk brought on by late Holocene environmental instability from ca. 3500 BP on.

Vegetation changes and associated climatic changes in the southern Altai Mountains within China during the Holocene

The location of the Altai Mountains at the limits of both the Pacific and Atlantic influences implies that this mountain range is an important climatic boundary. Based on pollen data of 188 samples of a 390-cm core from Narenxia Peat in the southern Altai with a chronologic support of 11 accelerator mass spectrometry (AMS) dates, we reconstructed the Holocene climatic change at Narenxia Peat. The reconstruction revealed five stages of climatic change: a cold and dry latest deglacial (prior to ~11,500 cal. yr BP), a warm and wet early-Holocene (~11,500 to ~7000 cal. yr BP), a considerably cooled and dried middle Holocene (~7000 to ~4000 cal. yr BP), a resumed warm and wet late-Holocene (~4000 to ~1200 cal. yr BP), and a relatively cool and dry latest Holocene (past ~1200 years). The reconstructions of mean annual temperature (MAT) and mean annual precipitation (MAP) from Narenxia Peat well resemble the reconstructions of North Atlantic Oscillations (NAO) and El Niño–Southern Oscillations (ENSO). The resemblance implies that the Holocene millennial-scale changes in MAT and MAP in the Altai might have been causally associated with the variations in NAO and ENSO.

Multiple drivers of Holocene lake level changes at a lowland lake in northeastern Germany

Many German lakes experienced significant water level declines in recent decades that are not fully understood due to the short observation period. At a typical northeastern German groundwater‐fed lake with a complex basin morphology, an acoustic sub‐bottom profile was analysed together with a transect of five sediment cores, which were correlated using multiple proxies (sediment facies, μ‐XRF, macrofossils, subfossil Cladocera). Shifts in the boundary between sand and mud deposition were controlled by lake level changes, and hence, allowed the quantification of an absolute lake level amplitude of ~8 m for the Holocene. This clearly exceeded observed modern fluctuations of 1.3 m (AD 1973–2010). Past lake level changes were traced continuously using the calcium‐record. During high lake levels, massive organic muds were deposited in the deepest lake basin, whereas lower lake levels isolated the sub‐basins and allowed carbonate deposition. During the beginning of the Holocene (>9700 cal. a BP), lake levels were high, probably due to final melting of permafrost and dead‐ice remains. The establishment of water‐use intensive Pinus forests caused generally low (3–4 m below modern) but fluctuating lake levels (9700–6400 cal. a BP). Afterwards, the lake showed an increasing trend and reached a short‐term highstand at c. 5000 cal. a BP (4 m above modern). At the transition towards a cooler and wetter late Holocene, forests dominated by Quercus and Fagus and initial human impact probably contributed more positively to groundwater recharge. Lake levels remained high between 3800 and 800 cal. a BP, but the lake system was not sensitive enough to record short‐term fluctuations during this period. Lake level changes were recorded again when humans profoundly affected the drainage system, land cover and lake trophy. Hence, local Holocene water level changes reflect feedbacks between catchment and vegetation characteristics and human impact superimposed by climate change at multiple temporal scales.

El Niño controls Holocene rabbit and hare populations in Baja California

The El Niño/Southern Oscillation (ENSO) is a major source of climatic variation worldwide, with significant impacts on modern human and animal populations. However, few detailed records exist on the long-term effects of ENSO on prehistoric vertebrate populations. Here we examine how lagomorph (rabbit and hare) deposition rate, population age structure and taxonomic composition from Abrigo de los Escorpiones, a well-dated, trans-Holocene vertebrate fauna from northern Baja California, Mexico, vary as a function of the frequency of wet El Niño events and eastern Pacific sea-surface temperatures (SSTs) derived from eastern Pacific geological records. Faunal indices vary significantly in response to El Niño-based precipitation and SST, with substantial moisture-driven variability in the middle and late Holocene. The late Holocene moisture pulse is coincident with previously documented changes in the population dynamics of other vertebrates, including humans. As the frequency and intensity of ENSO is anticipated to vary in the future, these results have important implications for change in future vertebrate populations.