Holocene Hydrological Changes Research Articles

Holocene hydrological changes in Europe and the role of the North Atlantic ocean circulation from a speleothem perspective

Societal concerns about future hydroclimate changes urge a thorough understanding of the governing processes. Here, an analysis of Middle and Late Holocene speleothem-based hydroclimate reconstructions and paleoclimate model simulations reveals sub-millennial fluctuations in the spatiotemporal variability of precipitation in the European and Mediterranean regions, that complements previous dendrochronological and pollen-based reconstructions with an improved temporal resolution. Although insolation forcing is the primary driver of Holocene hydroclimate changes in Europe on a multimillennial scale, the evaluation of the principal component analysis of speleothem records and correlations with sea surface temperature data indicates that North Atlantic ocean circulation played a significant role in the sub-millennial variation of continental moisture transport, with an increasing importance during the Late Holocene. The combined evaluation of speleothem-based data, climate simulations and sea surface temperature records therefore advances our understanding of the governing processes of Holocene hydroclimate changes in the European and Mediterranean regions.

Variable Kuroshio Current intrusion into the northern South China Sea over the last 7.3 kyr

The branch intrusion of the Kuroshio Current (KC) into the northern South China Sea (SCS) has a significant effect on temperature, salinity, circulation, and eddy generation. However, the study of Holocene hydrological changes and the historical influence of the KC in this region is limited. Here, we report high-resolution sea surface temperature (SST) and δ18Osw (as a proxy for sea surface salinity, SSS) records based on paired Mg/Ca ratios and δ18O analyses of the planktonic foraminifera Globigerinoides ruber combined the Pulleniatina obliquiloculata and G. sacculifer/G. ruber ratios from core 05E306 (22°0.06′ N, 118°59.64′ E; water depth = 1440 m) in the northern SCS. By comparing these data with records from cores located within and outside of the main KC flow pathway, we evaluate the spatiotemporal evolution of the KC in this region over the last 7.3 kyr. The strongest influence was observed from 6.1 to 5.3 ka, recorded as an abrupt increase in SST and SSS with remarkably increased P. obliquiloculata abundance (37.4%) and G. sacculifer/G. ruber ratios (3.18). During the following period, 5–2.5 ka, SST decreased by 0.4–1.1 °C with an associated decrease in δ18Osw, indicating a weakened KC. After 2.5 ka, the influence of the KC on the northern SCS strengthened; however, the high SST record still exhibits a spatial constraint in the longitude distribution of the KC during this period of strongest intrusion. Moreover, the abundance of planktonic foraminifera in the study area more strongly correlates with SSS than SST. The δ18Osw records in core 05E306 show a freshening trend after 5.7 ka, which is inconsistent with the declining East Asian Summer Monsoon precipitation record but consistent with the Holocene freshening trend recorded in the Western Pacific. This suggests that hydrological variability of the northern SCS is mainly influenced by the Western Pacific Ocean.

Plant wax evidence for precipitation and vegetation change from a coastal sinkhole lake in the Bahamas spanning the last 3000 years

Plant wax hydrogen isotopic composition is commonly used to reconstruct the hydrogen isotopic composition of precipitation used by terrestrial vegetation. However, mangroves growing in coastal environments take up a mixture of freshwater and seawater. Biosynthetic fractionation (between source water and plant wax) differs between plant types and as a function of salinity, potentially complicating interpretations of past precipitation in coastal environments. In order to reconstruct Holocene hydrologic and ecologic changes archived within sediments from Blackwood Sinkhole on Abaco Island in The Bahamas, we adopt a multi-proxy approach using plant wax hydrogen isotopic composition (δ2H) to reconstruct paleohydrology, together with plant wax carbon isotopic composition (δ13Cwax), sterol biomarkers and pollen abundances to identify vegetation change. When pollen indicates a stable terrestrial plant community (2950–850 cal yrs BP), variations of δ2H values measured on the plant wax C28n-alkanoic acid are interpreted in terms of precipitation isotope (δ2Hprecip) changes, with 2H-depletion from 2950 to ∼2100 cal yrs BP and ∼1700 to 1000 cal yrs BP. However, interpretation is complicated at 850 cal yrs BP, when δ2H values decrease (−50‰) concurrent with increased Laguncularia racemosa (white mangrove) and Conocarpus erectus (buttonwood mangrove), and the mangrove-derived biomarker, taraxerol. We develop a pollen-based correction for mangrove inputs, yielding reconstructed precipitation isotope estimates (δ2Hprecip-corr). Low δ2Hprecip-corr values are synchronous with increased abundance of pine pollen, both of which may indicate wetter conditions from 850 cal yrs BP to present. This study provides additional evidence that mangroves can complicate hydrologic reconstructions from n-alkyl terrestrial plant wax biomarkers, and that such complication can be removed by pollen-based correction. After correcting for mangrove inputs, we obtain estimates of δ2Hprecip-corr from −33 to +25‰ throughout the last 2950 years, with uncertainties on the order of 10–20‰.

Mid to late Holocene hydrological and sea-level change reconstructions from La Mancha coastal lagoon, Veracruz, Mexico

We studied a 13-meter sediment core collected from La Mancha coastal lagoon, Veracruz, Mexico, to determine paleoenvironmental variations linked to the mid- to late Holocene sea-level rise. We examined modern and fossil benthic foraminiferal assemblages, isotopic values in tests of Ammonia tepida (δ18O-foram and δ13C-foram), δ13C in organic matter (δ13C-org), and sediment elemental ratios (Fe/Ca, Ca/Ti, and K/Rb) to reconstruct salinity variations, coastal processes, and the morphologic evolution of a partially closed coastal lagoon. We identified four main periods of environmental change: (1) From ~7800 to 6500 cal. yr. BP, the core site was an open lagoon with higher oceanic influence than today, through the presence of a southern mouth, as evidenced by the euryhaline assemblage Ammonia-Quinqueloculina-Bolivina-Nonionella. Low δ18O-foram and high δ13C values on foraminifera shells indicate greater inputs of seawater, and δ13C-org values reflect a lagoon environment. Elemental ratios of lower Fe/Ca, moderate Ca/Ti, and higher K/Rb suggest increased coastal weathering and reduced detrital deposits than today. (2) From ~6500 to 4600 cal. yr. BP., the lagoon experienced the progressive closure of the southern mouth, to the point that sedimentation restricted seawater entrance, as evidenced by variable δ13C-org values, a lowering trend in δ18O-foram and δ13C-foram values, low Fe/Ca, higher Ca/Ti but moderate K/Rb values. At this time, benthic foraminifera were dominated by the opportunistic Ammonia-Elphidium polyhaline assemblage. (3) From ~4600 to 1400 cal. yr. BP, the northern mouth was the only source of seawater to the lagoon, establishing the optimal environment for calcareous foraminifera of the polyhaline assemblage Ammonia-Elphidium. Lowest δ13C-org values indicate greater organic input by terrestrial plants. (4) At 1400 cal. yr. BP, modern conditions of a partially closed lagoon were established, while increased terrigenous inputs and freshwater runoff favored the growth of agglutinated foraminifera species. At millennial time scales, in addition to the sea level rise effects, the lagoon evolution fits in the paleoclimatic context that links insolation, the latitudinal change of ITCZ, ocean currents, longshore drift and moisture transport, as driving factors of morphological change in the western coast of the Gulf of Mexico.

Millennial-scale Holocene hydrological changes in the northeast Atlantic: New insights from ‘La Grande Vasière’ mid-shelf mud belt

A mid- to late-Holocene paleohydrological reconstruction from the northeast Atlantic is proposed through the study of a high-resolution sedimentary record from the northern continental shelf of the Bay of Biscay (BoB). Three foraminiferal species dominate the assemblages with Rosalina globularis showing an overall decrease in absolute and relative abundances from ~7 to 0.4 cal. ka BP, whereas the opposite trend is observed for Cibicides refulgens and Lobatula. These long-term patterns are interpreted as a response to the overall cooling trend and/or the progressive deepening of the water column because of the relative sea-level (RSL) rise. Foraminiferal δ18O and grain-size analyses show a significant shift around 3.5–2.5 cal. ka BP toward a heavier isotopic signature and finer sediments. We mainly link this change to enhanced contribution of continental freshwaters and fine sediments after the near-stabilization of the RSL rise. By reducing coastal accommodation spaces, this led to a better channelization of river outflows and probably to the formation of the modern winter thermohaline front. Superimposed on these long-term patterns, our data highlight strong millennial-scale variability (1250-year peak). Such cyclicity is consistent with several records tracing changes in rainfall and storminess regimes in northern Europe, and the dynamics of the subpolar gyre (SPG). We suggest a millennial time-scale control of a NAO-like (North Atlantic Oscillation) climatic process modulating continental humidity (and the associated river discharges) and SPG dynamics through wind stress. Spectral analyses reveal an additional 500-year frequency peak implying a possible solar forcing.

Diatom-based reconstruction of Holocene hydrological changes along the Colorado River floodplain (northern Patagonia, Argentina)

Diatom assemblages recovered from a Colorado River delta core in northern Patagonia, Argentina were analyzed in order to assess past environmental conditions. A total of 35 samples were selected from a 172-cm core extracted 37 km from the mouth (39°36′19.6″S; 62°29′26.1″W). One-hundred and thirty-eight taxa were recognized and grouped according to life forms. Two diatom zones were identified by cluster analysis. At the base of the sequence, the Diatom Zone I (DZI; 4132 ± 35 − 2919 ± 27 14C yr BP), consisted of clays, and was characterized by assemblages dominated by aerophilous and benthic taxa and chrysophyte stomatocysts, which led to inferences of a sedimentary environment corresponding to a pond experiencing dry periods. The upper section (DZII) was dominated by fine sands and silts encompassing the last ~ 150 yr with abundant planktonic and tychoplanktonic diatoms. Benthic diatoms were abruptly replaced by planktonic forms in this zone indicating a shift to deeper waters. These results characterize the meandering dynamics of a deltaic system. During the Mid-Holocene, more arid periods would have favored the deactivation of meanders and the formation of riverine and oxbow wetlands. In Late-Holocene and historical times, more humid conditions and the hydrological system across the floodplain reactivated the paleochannel. Today, the dominant diatom species are brackish/freshwater fragilaroids. A non-multidimensional scaling analysis showed a lack of analogy between fossil and modern samples. The change in diatom floras in recent historical times was attributed to anthropogenic disturbances, a consequence of the regulation of the river flow. This regulation is evidenced by less discharge, morphological modifications in the floodplain and increased salinity in the last decade.

Mineralogy and carbonate geochemistry of the Dali Lake sediments: Implications for paleohydrological changes in the East Asian summer monsoon margin during the Holocene

Hydrological variations in individual plateau lakes respond from both local hydrological processes and regional climatic changes. This study presents high resolution, absolutely-dated records of minerals in bulk samples and elements and stable isotopes of endogenic calcites from a sediment core from Dali Lake in Inner Mongolian Plateau, aiming to investigate the patterns and mechanisms of Holocene hydrological and climatic changes in the modern northern margin of the East Asian summer monsoon (EASM). Increases in the percentages of allogenic minerals (quartz, microcline and albite) and decreases in the percentages of endogenic/authigenic minerals (calcite, Mg-calcite and gypsum), together with decreases in the values of Ca and Mg concentrations and δ18O and δ13C of endogenic calcites indicate an excess of water input to the lake over evaporative losses, and vice versa. These data suggest that the hydrological balance of Dali Lake was controlled by strong evaporation before 9800 cal yr BP, and then the lake was supplied by significantly increased inflowing water between 9800 and 5900 cal yr BP. From 5900 to 4850 cal yr BP, the water input to the lake significantly decreased. Since 4850 cal yr BP, the inflowing water maintained a low level. In addition, the distinct characteristics of mineralogy and carbonate geochemistry of the Dali Lake sediments during the periods of high lake level between 9800–7700 and 7700–5900 cal yr BP imply that the lake was mainly fed by snow/ice melt water in the former period and then by regional precipitation in the latter period, which was further supported by the pollen records from the same sediment core. These results suggest that Holocene hydrological variations in the EASM margin were closely related to changes in regional temperature and precipitation which were ultimately controlled by changes in the Northern Hemisphere summer insolation, northern high latitude ice sheets, global sea level and physicochemical conditions of the North Atlantic and western tropical Pacific on orbital and millennial timescales. The datasets in this study support that the maximum EASM intensity occurred during the middle Holocene in the northern EASM regions.

Holocene hydrological and sea surface temperature changes in the northern coast of the South China Sea

In order to reconstruct the Holocene environmental history of a coastal site in the northern South China Sea, this study analysed the organic carbon isotope ratios (δ13Corg) and alkenone unsaturation ratios (UK′37) from a 36.5m-long sediment core drilled at seabed in the mouth region of the Pearl River estuary and generated a coupled hydrological and temperature record. This record reveals changes of monsoon-induced sediment discharge and sea surface temperature of the Holocene in four stages. In Stage I, the site was under fluvial conditions prior to postglacial marine transgression. Stage II saw an increase of sea surface temperature from c. 23.0°C to 27.0°C, associated with a strengthened summer monsoon from c. 10,350 to 8900cal. years BP. This was also a period of rapid sea-level rise and marine transgression, during which the sea inundated the palaeo-incised channel, i.e. the lower part of the T-shape accommodation space created by the rising sea. In these 1500years, fluvial discharge was strong and concentrated within the channel, and the high sedimentation rate (11.8mm/year) was very close to the rate of sea-level rise. In the subsequent 2000years (Stage III) sea level continued to rise and the sea flooded the broad seabed above the palaeo-incised channel, resulted in fluvial discharge spreading thinly across the wide accommodation space and a much reduced sedimentation rate (1.8mm/year). Sea surface temperature in this stage reached 27.3°C initially, but dropped sharply to 26.1°C towards c. 8200cal. years BP. The final stage covers the last 7000years, and the site was under a stable sea level. Sedimentation in this stage varied a little, but averaged at 1.8mm/year. Whilst fluvial discharge and sea surface temperature didn’t change much, two short periods of hydrological and temperature change were observed, which are related to the climatic cooling events of c. 4200cal. years ago and the Little Ice Age.

Cyanobacteria and testate amoeba as potential proxies for Holocene hydrological changes and climate variability: Evidence from tropical coastal lowlands of SW India

Cyanobacteria and thecamoebians are the two major constituents of Non Pollen Palynomorphs (NPP) found in the palynological preparations. The former is well represented in the sediment archives while the latter has restricted occurrence in the Holocene sequence apart from the conventional organic matter of pollen and spores. Well preserved morphotypes of Gleotrichia and Rivularia are the best forms of cyanobacteria found in almost all the studied profiles and their abundance towards Early to Middle Holocene coincides with the heavy rainfall and wet climate conditions during the Holocene climate optimum (HCO). Contrary to cyanobacterial diversity, thecamoebians are restricted to Late Holocene in most of the studied profiles and their occurrence is correlated with the prevailing dry and stressful environmental conditions. The major elements of thecamoebians identified belong to Arcellaceans, Centropyxids and Cucurbitella types. Abundance of Centropyxids and Arcellaceans in Varapuzha, West Kadungallur, Koonamavu, Pachcha and Ernakulam indicates low humidity and low precipitation. However, the relative abundance of Centropyxids in Mid Holocene at Ernakulam and Koonamavu reflects the early colonization of this type competing with the cyanobacteria, whereas, Arcellaceans are essentially confined to Late Holocene. Dominance of cyanobacteria and its proliferation is directly related to freshwater influx of the rainfall as well as the local hydrological regimes associated with the active aquifers controlled by the geomorphological features of the region in which the wetland system sustained. Considering the signatures of cyanobacteria and thecamoebians observed in the sediment archives their occurrence in the wetlands during the Holocene corresponds to the hydrodynamic regimes brought in by the freshwater influx as a result of monsoon variability. The well preserved cyanobacterial signatures in sediment archives of Kerala coast and their scarcity or even absence elsewhere along the west coast of India indicates that they are exclusively adapted to the wetland habitats where the hydrodynamic regimes are regularly controlled by fresh water influx in the form of extended rainy days of the monsoon system.

The response of flood-plain ecosystems to the Late Glacial and Early Holocene hydrological changes: A case study from a small Central European river valley

We use a range of environmental variables to explore the possible drivers influencing the biota, especially the composition of aquatic invertebrates, during the Younger Dryas (YD) and Early Holocene (EH) in different river valley sites: a well-developed meandering river and the confluence zone of headwater streams. Using pollen, macrofossil, cladoceran, and chironomid as well as geochemical and lithological data as proxies for environmental factors (i.e., water depth and temperature), we attempt to show that these different sites display similar hydroclimatic signals (especially floods). The geochemical records in the studied valley are correlated with environmental factors, such as the evolution of the vegetation, the intensification phase of slope processes, and fluvial activities. Cladocerans and chironomids potentially play important roles in the recognition of flood episodes in the study sites, and any shift in their diversity and, especially, the co-occurrence of planktonic, sediment-associated cladocerans with rheophilic chironomids could be valuable indicators of floods and flow episodes. The variable changes in water levels at the sites reconstructed by the cladoceran-based water-depth model were positively associated with changes in lithophilic elements (K, Na, Al, Mg, and Ti), SiO2(biog+ter) and Fe/Mn, and our estimates of the paleohydraulic parameters for the study sites are generally consistent with changes in the composition of aquatic invertebrates. The recorded YD floods appear to be synchronous, regardless of the size and the different geological and geomorphological settings of each part of the river catchment. Our investigation demonstrates that flood magnitude increases in the downstream direction along the valley. The common increases in the water level at all study sites from the Grabia River valley are significant from 12,400 to 12,200 and from 11,900 to 11,800 cal BP and are comparable with those from elsewhere in Poland and Europe.

Holocene hydrological changes in the Rhône River (NW Mediterranean) as recorded in the marine mud belt

Abstract. Expanded marine Holocene archives are relatively scarce in the Mediterranean Sea because most of the sediments were trapped in catchment areas during this period. Mud belts are the most suitable targets to access expanded Holocene records. These sedimentary bodies represent excellent archives for the study of sea–land interactions and notably the impact of the hydrological activity on sediment accumulation. We retrieved a 7.2 m long sediment core from the Rhône mud belt in the Gulf of Lions in an area where the average accumulation rate is ca. 0.70 m 1000 yr−1. This core thus provides a continuous and high-resolution record of the last 10 ka cal BP. A multiproxy dataset (XRF core scan, 14C dates, grain size and organic-matter analysis) combined with seismic stratigraphic analysis was used to document decadal to centennial changes in the Rhône hydrological activity. Our results show that (1) the early Holocene was characterized by high sediment delivery likely indicative of local intense (but short-duration) rainfall events, (2) important sediment delivery around 7 ka cal BP presumably related to increased river flux, (3) a progressive increase in continental/marine input during the mid-Holocene despite increased distance from river outlets due to sea-level rise possibly related to higher atmospheric humidity caused by the southward migration of the storm tracks in the North Atlantic, (4) multidecadal to centennial humid events took place in the late Holocene. Some of these events correspond to the cold periods identified in the North Atlantic (Little Ice Age, LIA; Dark Ages Cold Period) and also coincide with time intervals of major floods in the northern Alps. Other humid events are also observed during relatively warm periods (Roman Humid Period and Medieval Climate Anomaly).

Holocene vegetation and climate variability between winter and summer rainfall zones of South Africa

To better understand Holocene vegetation and hydrological changes in South Africa, we analyzed pollen and microcharcoal records of two marine sites GeoB8331 and GeoB8323 from the Namaqualand mudbelt offshore the west coast of South Africa covering the last 9900 and 2200 years, respectively. Our data corroborate findings from literature that climate developments apparently contrast between the summer rainfall zone (SRZ) and winter rainfall zone (WRZ) over the last 9900 years, especially during the early and middle Holocene. During the early Holocene (9900–7800 cal. yr BP), a minimum of grass pollen suggests low summer rainfall in the SRZ, and the initial presence of Renosterveld vegetation indicates relatively wet conditions in the WRZ. Toward the middle Holocene (7800–2400 cal. yr BP), a rather moist savanna/grassland rich in grasses suggests higher summer rainfall in the SRZ resulting from increased austral summer insolation and a decline of fynbos vegetation accompanied by an increasing Succulent Karoo vegetation in the WRZ, which possibly suggests a southward shift of the Southern Hemisphere westerlies. During the last 2200 years, a trend toward higher aridity was observed for the SRZ, while the climate in the WRZ remained relatively stable. The ‘Little Ice Age’ (ca. 700–200 cal. yr BP) was rather cool in both rainfall zones and drier in the SRZ while it was wetter in the WRZ.

Holocene hydrologic and hydrochemical changes of the South Basin of Lake Manitoba, Canada, inferred from ostracode shell chemistry and autoecology

Holocene record of ostracode shell chemistry from the South Basin of Lake Manitoba shows how isostatically and climatically induced changes in the surface and groundwater input to the overall hydrologic budget affected the hydrochemistry. The shallow South Basin experienced periods of extensive shell transport from isolated pools and groundwater seeps, as suggested by disparate chemistry of Fabaerformiscandona rawsoni shells from the same 1-cm-thick sediment sample. Temporal changes reconstructed from ostracode species and F. rawsoni shell chemistry include, for some depth intervals, shells of individuals that were not living at the same time or were not living at the core site. Shell chemistry before the South and North Basins became connected at 1850 BP broadly show a hydrologically closed-basin behavior with alternating periods of a more and less stressful environment to ostracodes. F. rawsoni with high δ 18O and low Mg/Ca or low δ 18O and high Mg/Ca were likely transported from marginal evaporated pools or groundwater seeps. Overall δ 18O and δ 13C values increase over time, but at levels for which multiple analyses were made, the values show a wide range, and indicate a highly variable hydrochemical environment both spatially and temporally (over one summer or multiple summers).

Holocene hydrological changes in SE Iran, a key region between Indian Summer Monsoon and Mediterranean winter precipitation zones, as revealed from a lacustrine sequence from Lake Hamoun

Core sediments from the dry lake bed of Hamoun were subdivided into 3 main sedimentary units using a multi-proxy approach (e.g. petrography, grain size analysis, total organic matter % and CaCO3% determination) to reconstruct the palaeoenvironment of the Sistan Basin (SE Iran) as a transition zone between the monsoon summer precipitation zone of south Asia and the Mediterranean winter precipitation zone of the Iranian plateau during the Holocene. Data revealed that during the late-glacial to early Holocene, the lake and its catchment area, western Hindu Kush, were under a more prominent influence of the Indian Ocean monsoon and formed a moist and productive environment with less wind action, as shown by the provenance of high organic matter lacustrine sediments together with the lack of an aeolian fraction. Due to southward migration of the Inter Tropical Convergence Zone during the mid Holocene, arid climate manifested by an interplay of seasonal aeolian and fluvial deposition became dominant. These conditions were due to reinforcement of subtropical anticyclones on the Iranian plateau. The presence of green to brownish green moderate organic matter lacustrine sediments showed that during the late Holocene, Mediterranean-type winter precipitation dominated in the area. During the initial part of this period, the Shahr-i Sukhteh civilization was close to the lake. The environment was relatively similar with that of today. Some palaeostorms can also be detected during this time interval, shown by occurrences of high aeolian inputs in the basin.

The Holocene environmental changes in boreal fen peatland of northern Mongolia reconstructed from diatom assemblages

The Holocene hydrological changes of fen peatland in northern Mongolia were reconstructed using diatom fossils with an aid of Sphagnum leaf fossils. Analyses were conducted on three cores taken across the basin and reconstructed water environments were compared to find basin-wide hydrological changes and climate anomalies. The peatland has been covered by sedges during most of its 10 thousand years history, but all cores showed common peatland hydrosere processes from fluvial environment in the early Holocene period, shallow marsh to present acidic fen peatland. The establishment of fen peatland at 6.8–6.4 cal ka BP was marked synchronously by the shift of diatom and Sphagnum taxa assemblages and this period was inferred as the onset of the mid-Holocene dry climate which is widely observed around Mongolia. The dry environment lasted until around 2.8 cal ka BP with a temporal wetter condition at 4.4–3.5 cal ka BP. Short term diatom trend shifts indicated temporal wetter environments at 8.7–8.4, 8.0–7.6, 2.4–2.1, 1.2–0.5 cal ka BP and a dry environment at 0.4–0.2 cal ka BP. These periods of hydrology changes were correlative with other studies in Mongolia and East Siberia, so they would represent climate-induced hydrological changes, and those regions might share the same response to long term insolation changes or global climate anomalies. However, disagreements of climate data even within northern Mongolian region suggest large influence of regional geography and the balance of evapotranspiration on climate behaviors as shown by recent dendrological paleoenvironment researches. Coherent differences of main taxa compositions between three cores were attributed to core site-specific local hydrology mainly in terms of relative wetness from wettest core site accompanied by abundant planktonic diatom taxa to driest site with acidic peat indicator taxa. Timings and manners of temporal diatom trend shifts were also largely different between cores suggesting significant difference in each core site sensitivity to basin-wide hydrology changes, confirming the necessity of using multiple cores and proxies in peatland sediments to detect climate-induced environmental changes.

Human occupation of South Eastern Altai highlands (Russia) in the context of environmental changes

Multidisciplinary investigations including geomorphological and geoarchaeological approaches, litho-stratigraphic and pedogenetic analysis accompanied by radiocarbon dating show the contrasting human environmental changes within the highlands of the Russian Altai since the late Paleolithic. Radiocarbon ages of fossil soils formed at 1,475–1,730 m a.s.l. indicate draining of the ice-dammed lake in the Kurai basin before the beginning of the Holocene and disintegration of the Chuya lake into several shallow but quite spacious reservoirs by 8,223 ± 181 cal. BP. Using archaeological sites as spatio-temporal markers allows reconstructions to be specified based on geological data. Archaeological site distribution in the Chuya valley between the Chuya and Kurai basins indicates that all cataclysmic flood events related to the Holocene hydrological changes occurred before the Scythian epoch. Due to the redeposition of most Paleolithic finds in the region, they should be carefully examined before they are utilized for any reconstructions. Using fossil and contemporary soils as an independent informative climatic proxy archive supports the conception of generally more humid and warmer climate conditions in the first half of the Holocene within the SE Altai and a more arid and cold climate in the second one. The repeated climate deteriorations that caused glacier expansion and the progressive aridity intensification in the region along with the sociopolitical reasons are the major factors that controlled the habitat of nomadic communities and cultures shifting within the SE Altai in the second half of the Holocene. Anthropogenic impact together with the progressive aridization led to the deforestation of the eastern part of the Chuya depression.

Biomarker-based reconstructions of Holocene lake-level changes at Lake Gahai on the northeastern Tibetan Plateau

Holocene hydrological changes in regions dominated by the westerlies significantly differ from those by the Asian summer monsoon. The high-elevated northeastern Tibetan Plateau, located in between, is likely influenced by the interactions of both circulation systems. Here, we attempt to use biomarkers, n-alkanes and alkenones, to reconstruct Holocene lake-level changes at Lake Gahai in the Qaidam Basin. We choose a sediment core drilled at the lake shore, where biomarkers would be sensitive to lake-level changes. The n-alkane records show high average chain length (ACL), high carbon preference index (CPI), and low proportion of aquatic macrophyte (Paq) values at 7–2 kyr (thousand calibrated years ago) with peaked values around 6 kyr, whereas low ACL, low CPI, and high Paq values occurred after 2 kyr and before 7 kyr. No alkenones were detected at 7–2 kyr, suggesting that lake level at this period was incapable of constantly reaching to the coring site. Therefore, combined results provide unambiguous evidence of relatively low lake level at 7–2 kyr, probably lowest at ~6 kyr. Holocene lake-level changes in this marginal region thus display a different pattern from either of the core regions dominated by the westerlies (anti-phase) and the Asian summer monsoon (out-of-phase). We suggest that in the arid marginal region, temperature-induced evaporation could significantly affect regional hydrological balance, resulting in the discrepancy with the Holocene long-term precipitation decreasing trend in Asian monsoon-dominated regions.

Late Holocene hydrologic changes in northern New Zealand inferred from stable isotope values of aquatic cellulose in sediments from Lake Pupuke

Isotopic records of aquatic cellulose are becoming increasingly important for palaeohydrolog- ical reconstructions, but widespread application of this climate proxy is hampered by minerogenic contami- nation that affects oxygen isotope measures in cellu- lose. Few records of isotopes in aquatic cellulose are available from palaeoclimate archives in the Southern Hemisphere. In this study, we used a new bulk cellulose extraction method and determined the oxy- gen (d 18 O) and carbon (d 13 C) isotope values in

Holocene hydrological change in western Mongolia inferred from the lake record of Achit Nuur

Holocene hydrological change in western Mongolia inferred from the lake record of Achit Nuur

Pollen and diatom inferred Late Holocene hydrological changes in Central Florida

Pollen and diatom inferred Late Holocene hydrological changes in Central Florida