Refine
Year of publication
Language
- English (48)
Is part of the Bibliography
- yes (48)
Keywords
- Ostracoda (8)
- Tibetan Plateau (7)
- Holocene (6)
- Central Asia (3)
- Lake sediments (3)
- Late Pleistocene (3)
- Palaeolimnology (3)
- Paleolimnology (3)
- XRD (3)
- human impact (3)
- pollen (3)
- Arid Central Asia (2)
- Climate change (2)
- Diatoms (2)
- Lake level (2)
- Late Holocene (2)
- Levant (2)
- Mongolia (2)
- Monsoon (2)
- Near East (2)
- Ostracods (2)
- Paleohydrology (2)
- Pollen (2)
- Qaidam Basin (2)
- Westerlies (2)
- Wetlands (2)
- central Mongolia (2)
- grain size (2)
- lake eutrophication (2)
- n-alkanes (2)
- vegetation degradation (2)
- Acheulian (1)
- Aquatic macrophytes (1)
- Aragonite (1)
- Arid central Asia (1)
- Ashmura (1)
- Asian monsoon (1)
- Biomarker (1)
- Carbon isotopes (delta C-13) (1)
- Carbon preference index (CPI) (1)
- Central-western Mongolia (1)
- Chara/Characeae (1)
- China (1)
- Conductivity (1)
- Continental air masses (1)
- Corbicula (1)
- Depositional origin (1)
- Depositional setting (1)
- Eastern Mediterranean (1)
- Ecology (1)
- Electrical conductivity (1)
- Foraminifera (1)
- Gadot Formation (1)
- Gastropods (1)
- Geochemistry (1)
- Grain size (1)
- Grain-size end-member modelling (1)
- High Asia (1)
- Hominins (1)
- Hula Basin (1)
- Human impact (1)
- Hydrogen isotopes (delta D) (1)
- Inference model (1)
- Israel (1)
- Lake Bayan Nuur (1)
- Lake Kinneret (1)
- Last Glacial Maximum (1)
- Late Glacial and Holocene (1)
- Late pleistocene (1)
- Limnology (1)
- Lower Palaeolithic (1)
- Macerals (1)
- Marine Isotope Stage 3 (1)
- Metabarcoding (1)
- Microfossils (1)
- Middle Palaeolithic (1)
- Mineral composition (1)
- Mineralogy (1)
- Moisture-advection feedback (1)
- Mountain lake (1)
- Multi-proxy record (1)
- Multi-site study (1)
- Multivariate regression trees (1)
- Nianbaoyeze Mountains (1)
- Non-marine (1)
- Northeastern China (1)
- OSL dating (1)
- Ohalo Site (1)
- Organic matter (1)
- PCA (1)
- Palaeoecology (1)
- Palaeoenvironmental reconstruction (1)
- Paleo-ecology (1)
- Paleo-productivity (1)
- Paleoenvironmental change (1)
- Pamir Mountains (1)
- Pamir mountains (1)
- Plant macro-remains (1)
- Pollen record (1)
- Pollen-climate calibration (1)
- Potamogeton/Stuckenia (1)
- Precipitation (1)
- Procrustes rotation (1)
- Qinghai-Tibetan Plateau (QTP) (1)
- Radiocarbon and OSL dating (1)
- Salinity (1)
- Sclerochronology (1)
- Sea of Galilee (1)
- Sediment geochemistry (1)
- Sedimentology (1)
- Shell Bar (1)
- Solute evolution (1)
- Southern Levant (1)
- Sr-87/Sr-86 (1)
- Stable isotopes (1)
- Submerged vegetation composition (1)
- Substrate (1)
- TOC (1)
- Taphonomy (1)
- Tibet (1)
- Total organic carbon (1)
- Transfer function (1)
- Tree-ring (1)
- Vegetation change (1)
- WA-PLS (1)
- Water chemistry (1)
- Water depth (1)
- XRF (1)
- XRF data (1)
- Xinjiang (1)
- Younger Dryas (1)
- biomarker (1)
- carbonates (1)
- climate (1)
- climate change (1)
- compositional species turnover (1)
- delta O-18 (1)
- diatoms (1)
- geochemistry (1)
- hydrology (1)
- isotopic analysis (1)
- lake sediments (1)
- modelling (1)
- modern pollen (1)
- ordination (1)
- organic matter (1)
- palaeoclimate reconstruction (1)
- palaeoecology (1)
- paleoclimate (1)
- palynology (1)
- transfer functions (1)
- vegetation reconstruction (1)
A high resolution multi proxy (pollen, grain size, total organic carbon) record from a small mountain lake (Lake Khuisiin; 46.6 degrees N, 101.8 degrees E; 2270 m a.s.l.) in the south eastern Khangai Mountains of central Mongolia has been used to explore changes in vegetation and climate over the last 1200 years. The pollen data indicates that the vegetation changed from dry steppe dominated by Poaceae and Artemisia (ca AD 760-950), to Larix forest steppe (ca AD 950-1170), Larix Betula forest steppe (ca AD 1170-1380), meadow dominated by Cyperaceae and Poaceae (ca AD 1380-1830), and Larix Betula forest steppe (after similar to AD 1830). The cold-wet period between AD 1380 and 1830 may relate to the Little Ice Age. Environmental changes were generally subtle and climate change seems to have been the major driver of variations in vegetation until at least the early part of the 20th century, suggesting that either the level of human activity was generally low, or the relationship between human activity and vegetation did not alter substantially between AD 760 and 1830. A review of centennial scale moisture records from China and Mongolia revealed that most areas experienced major changes at ca AD 1500 and AD 1900. However, the moisture availability since AD 1500 varied between sites, with no clear regional pattern or relationship to present day conditions. Both the reconstructions and the moisture levels simulation on a millennium scale performed in the MPI Earth System Model indicate that the monsoon-westerlies transition area shows a greater climate variability than those areas influenced by the westerlies, or by the summer monsoon only.
The Acheulian site of Gesher Benot Ya‘aqov (GBY) in the Upper Jordan Valley revealed important data on environment and material culture, as well as evidence for hominin behavioural and cognitive patterns documented at the margins of the Hula Palaeo-lake. A 50 m long core (GBY#2) drilled at the archaeological site has provided a long Pleistocene geological, environmental and climatological record, which expands the existing knowledge of hominin-habitat relationships. Bracketed by two basalt flows dated by 40Ar/39Ar and based on the identification of the Matuyama-Brunhes Boundary (MBB) and correlation with the GBY excavation site, the sedimentary sequence provides the climatic history around the MBB. Multi-proxy data including pollen and non-pollen palynomorphs, macro-botanical remains, molluscs and ostracods provide evidence for lake and lake-margin environments during Marine Isotope Stages (MIS) 20 and 19. Semi-moist conditions were followed by a pronounced dry phase during MIS 20, and warm and moist conditions with Quercus-Pistacia woodlands prevailed during MIS 19. In contrast to the reconstructed climate change from relatively dry to moister conditions, the depositional environment developed from an open-water lake during MIS 20 to a lake margin environment in MIS 19. Generally shallower conditions at the core site in MIS 19 resulted from the progradation of the lake shore due to the filling of the basin. Micro-charcoal analysis suggests a likelihood of human-induced fire in some parts of the core, which can be correlated with artefact-containing layers of the GBY excavation site. The Hula Palaeo-lake region provided an ideal niche for hominins and other vertebrates during global glacial-interglacial climate fluctuations at the end of the Early Pleistocene.
In this paper we present the sedimentary features and the luminescence chronology for Nahal Mahanayeem Outlet (NMO), an archaeological open air site at the southern margin of the Hula Basin (Northern Jordan Rift Valley, Israel). The site is characterized by a lithic assemblage ascribed primarily to the Middle Paleolithic Mousterian tradition, and by an excellent preservation of floral and faunal remains.
Six geological units forming the stratigraphic sequence of the site were distinguished: (Unit 6) archaeologically sterile, light-colored limnic carbonates; (Unit 5) conglomerates of rounded basalt boulders and cobbles forming a hill-like topography; (Unit 4 and Unit 3) a sequence of similar dark silty sediments, attached to and overlaying the conglomerates, containing the archaeological horizons of the site; (Unit 2) a number of channels cutting into the top of Unit 3, filled with coarse sand and rounded basalt and limestone gravels of fluvial origin; and (Unit 1) a thin sand layer laid down by the present-day Jordan River covering another unconformity as a result of heavy machinery drainage operations in 1999.
The OSL age for Unit 6 yielded a minimum age older than 460 ka. Sedimentary features and the embedded fossils suggest that Unit 1 can be linked to the Early Pleistocene Gadot Chalk. Unit 5 represents a local geological feature and could be an indicator for a period of increased erosion with formation of coarse grained sediments. The archaeological horizons form the lower parts of Unit 4 and yielded OSL-ages between 55 and 65 ka, indicating an affiliation to the sediments called "Ashmura Formation" with an Upper Pleistocene age for the site. The channel fills of Unit 2 can be dated by the recovered artifacts. These range in age from the Upper Paleolithic (Aurignacian) to historic times. Unit 1 is recent.
The study of the complex NMO stratigraphy, combined with coherent OSL chronology, has enabled us to reconstruct parts of the geological history of the Hula Basin during the Late Pleistocene. It is this history that forms the background for the human migration and utilization of natural resources in the Upper Jordan Rift Valley. (C) 2013 Elsevier Ltd and INQUA. All rights reserved.
A multi-proxy study including analyses of delta C-13(org) for the lake sediment core GN-02 and grain size, TOC. CaCO3 content, delta C-13(carb) and delta O-18(carb) of bulk carbonate, and the mineralogy of the parallel core GN-04 from Gun Nuur was performed to reconstruct the Holocene hydrology and climate on the northern Mongolian Plateau. The chronology was established using 40 C-14 dates of bulk organic matter in addition to nine previously published radiocarbon dates for core GN-02, and further five C-14 dates for the new core GN-04. A lake reservoir effect of 1060 C-14 years was determined as the intercept of the high-resolution GN-02 age-depth model at the modern sediment surface. The size of the reservoir effect is supported by the age of the core-top sample (1200 +/- 40 C-14 years) and the determined difference between a wood-derived radiocarbon age from the GN-02 core base and the age-model inferred age for bulk organic matter at the same stratigraphic level (1000 C-14 years). Low lake level and prevailing aeolian sediment deposition at Gun Nuur under dry conditions were recorded during the earliest Holocene (> 10,800-10,300 cal a BP). Gun Nuur expanded under significantly wetter conditions between 10,300 and 7000 cal a BP. Unstable climate conditions existed in the mid Holocene (7000-2500 cal a BP) and three periods of low lake-levels and significantly drier conditions were recorded between 7000-5700, 4100-3600 and 3000-2500 cal a BP. Intermediate lake levels were inferred for the intervening periods. Around 2500 cal a BP, the climate change and wetter conditions were established again. As a consequence, the lake level of Gun Nuur rose again due to higher effective moisture and the relatively wet present conditions were achieved ca. 1600 cal a BP. Our results suggest that the initial Holocene climate change on the northern Mongolian Plateau was not accompanied by a rapid increase in precipitation as on the Tibetan Plateau. The establishment of wetter conditions in northern Mongolia lagged behind the early Holocene moisture increase on the Tibetan Plateau by ca. 1000 years. Subsiding dry air in the north of the Tibetan Plateau resulted from the strengthened summer monsoon on the Tibetan Plateau during the period of maximum summer insolation and probably inhibited a significant precipitation increase in Mongolia. The significant moisture increase in the Gun Nuur region at ca. 10.3 cal ka BP is probably not related to the northward shift of the present summer monsoon boundary or the moisture delivery from the northern Atlantic through the westerlies. Instead, water from melting snow, ice and frozen ground and the generation of precipitation from the local recycling of moisture are discussed as possible moisture source for the early onset of wetter conditions on the Mongolian Plateau.
Sediments of a thermokarst system on the north-eastern Tibetan Plateau were studied to infer changes in the lacustrine depositional environment related to climatic changes since the early Holocene. The thermokarst pond with a length of 360 m is situated in a 14.5 x 6 km tectonically unaffected intermontane basin, which is underlain by discontinuous permafrost.
A lake sediment core and bankside lacustrine onshore deposits were analysed. Additionally, fossil lake sediments were investigated, which document a former lake-level high stand. The sediments are mainly composed of marls with variable amounts of silt carbonate micrite, and organic matter.
On the basis of sedimentological (grain size data), geochemical (XRF), mineralogical (XRD) and micropaleontological data (ostracods and chironomide assemblages) a reconstruction of a paleolake environment was achieved.
Lacustrine sediments with endogenic carbonate precipitation suggest a lacustrine environment since at least 19.0 cal ka BP. However, because of relocation and reworking processes in the lake, the sediments did not provide distinct information about the ultimate formation of the lake. The high amount of endogenic carbonate suggests prolonged still-water conditions at about 9.3 cal ka BP. Ostracod shells and chironomid head capsules in fossil lake sediments indicate at least one former lake-level high stand, which were developed between the early and middle Holocene. From the late Holocene the area was possibly characterized by a lake-level decline, documented by a hiatus between lacustrine sediments and a reworked loess or loess-like horizon. After the lake-level decline and the following warming period, the area was affected by thermally-induced subsidence and a re-flooding of the basin because of thawing permafrost.
The Central Asian Pamir Mountains (Pamirs) are a high-altitude region sensitive to climatic change, with only few paleoclimatic records available. To examine the glacial-interglacial hydrological changes in the region, we analyzed the geochemical parameters of a 31-kyr record from Lake Karakul and performed a set of experiments with climate models to interpret the results. delta D values of terrestrial biomarkers showed insolation-driven trends reflecting major shifts of water vapor sources. For aquatic biomarkers, positive delta D shifts driven by changes in precipitation seasonality were observed at ca. 31-30, 28-26, and 17-14 kyr BP. Multiproxy paleoecological data and modelling results suggest that increased water availability, induced by decreased summer evaporation, triggered higher lake levels during those episodes, possibly synchronous to northern hemispheric rapid climate events. We conclude that seasonal changes in precipitation-evaporation balance significantly influenced the hydrological state of a large waterbody such as Lake Karakul, while annual precipitation amount and inflows remained fairly constant.
This paper aims to highlight the potential of using elemental and stable isotope analyses of aquatic macrophytes in palaeolimnological studies. Potamogeton pectinatus material was collected from modem plants (n=68) and from late glacial and Holocene-aged sediments from Koucha Lake (northeastern Tibetan Plateau; 34.0 degrees N; 97.2 degrees E; 4540 m a.s.l.). It was analyzed for delta C-13(Potamogeton) (modern: -23 to 0 parts per thousand, fossil: -19 to -4 parts per thousand) and delta N-15(Potamogeton) (modern: -11.0 to +13.8 parts per thousand, fossil: -9.5 to +6.7 parts per thousand) in addition to elemental carbon and nitrogen (modem C/N-Potamogeton: 7 to 29; fossil: 13 to 68) and sulfur (fossil: 188-899 mu mol/g dry weight). Fossil data were interpreted in terms of palaeo-nutrient availability and palaeo-productivity based on the modem relationships between various proxies and certain environmental data. Productivity of Potamogeton pectinatus mats at Koucha Lake as indicated by palaeo-epsilon(Potamogeton-TIC) (i.e. the enrichment of delta C-13(Potamogeton) relative to the delta(CTIC)-C-13) was reduced during periods of high conductivity, especially between 10.3 and 7.4 cal kyr BP. Potamogeton pectinatus material from these periods was also characterized by high S-Potamogeton indicating high sulfide concentrations and anoxic conditions within the sediments. However, C/N- Potamogeton ratios and delta N-15(Potamogeton) from the lower core section were found to have been altered by decompositional processes. A pronounced shift in the aquatic productivity of Lake Koucha occurred at similar to 7.4 cal kyr BP when the hydrological conditions shifted towards an open lake system and water depth increased. At this time a strong increase in productivity led to a strong decrease in the water HCO3- concentration as inferred from the application of a epsilon-(Potamogeton-TIC)-InHCO3- transfer function. A comparison of reconstructed productivity changes from Koucha Lake with further environmental proxies suggests that primary productivity changes are probably a function of internal lake dynamics and were only indirectly triggered by climate change.
Sediments of Lake Donggi Cona on the northeastern Tibetan Plateau were studied to infer changes in the lacustrine depositional environment, related to climatic and non-climatic changes during the last 19 kyr. The lake today fills a 30x8 km big and 95 m deep tectonic basin, associated with the Kunlun Fault. The study was conducted on a sediment-core transect through the lake basin, in order to gain a complete picture of spatio-temporal environmental change. The recovered sediments are partly finely laminated and are composed of calcareous muds with variable amounts of carbonate micrite, organic matter, detrital silt and clay. On the basis of sedimentological, geochemical, and mineralogical data up to five lithological units (LU) can be distinguished that document distinct stages in the development of the lake system.
The onset of the lowermost LU with lacustrine muds above basal sands indicates that lake level was at least 39 m below the present level and started to rise after 19 ka, possibly in response to regional deglaciation. At this time, the lacustrine environment was characterized by detrital sediment influx and the deposition of siliciclastic sediment. In two sediment cores, upward grain-size coarsening documents a lake-level fall after 13 cal ka BP, possibly associated with the late-glacial Younger Dryas stadial. From 11.5 to 4.3 cal ka BP, grain-size fining in sediment cores from the profundal coring sites and the onset of lacustrine deposition at a litoral core site (2 m water depth) in a recent marginal bay of Donggi Cona document lake-level rise during the early to mid-Holocene to at least modern level. In addition, high biological productivity and pronounced precipitation of carbonate micrites are consistent with warm and moist climate conditions related to an enhanced influence of summer monsoon. At 4.3 cal ka BP the lake system shifted from an aragonite- to a calcite-dominated system, indicating a change towards a fully open hydrological lake system. The younger clay-rich sediments are moreover non-laminated and lack any diagenetic sulphides, pointing to fully ventilated conditions, and the prevailing absence of lake stratification. This turning point in lake history could imply either a threshold response to insolation-forced climate cooling or a response to a non-climatic trigger, such as an erosional event or a tectonic pulse that induced a strong earthquake, which is difficult to decide from our data base.
A general mean annual temperature increase accompanied with substantial glacial retreat has been noted on the Tibetan Plateau during the last two centuries but most significantly since the mid 1950s. These climate trends are particularly apparent on the southeastern Tibetan Plateau. However, the Tibetan Plateau (due to its heterogeneous mountain landscape) has very complex and spatially differing temperature and precipitations patterns. As a result, intensive palaeolimnological investigations are necessary to decipher these climatic patterns and to understand ecological responses to recent environmental change. Here we present palaeolimnological results from a (210)Pb/(137)Cs-dated sediment core spanning approximately the last 200 years from a remote high-mountain lake (LC6 Lake, working name) on the southeastern Tibetan Plateau. Sediment profiles of diatoms, organic variables (TOC, C:N) and grain size were investigated. The (210)Pb record suggests a period of rapid sedimentation, which might be linked to major tectonic events in the region ca. 1950. Furthermore, unusually high (210)Pb supply rates over the last 50 years suggest that the lake has possibly been subjected to increasing precipitation rates, sediment focussing and/or increased spring thaw. The majority of diatom taxa encountered in the core are typical of slightly acidic to circumneutral, oligotrophic, electrolyte-poor lakes. Diatom species assemblages were rich, and dominated by Cyclotella sp., Achnanthes sp., Aulacoseira sp. and fragilarioid taxa. Diatom compositional change was minimal over the 200-year period (DCCA = 0.85 SD, p = 0.59); only a slightly more diverse but unstable diatom assemblage was recorded during the past 50 years. The results indicate that large-scale environmental changes recorded in the twentieth century (i.e. increased precipitation and temperatures) are likely having an affect on the LC6 Lake, but so far these impacts are more apparent on the lake geochemistry than on the diatom flora. Local and/or regional peculiarities, such as increasing precipitation and cloud cover, or localized climatic phenomena, such as negative climate feedbacks, might have offset the effects of increasing mean surface temperatures.
(Paleo-)climatologists are challenged to identify mechanisms that cause the observed abrupt Holocene monsoon events despite the fact that monsoonal circulation is assumed to be driven by gradual insolation changes. Here we provide proxy and model evidence to show that moisture-advection feedback can lead to a non-linear relationship between sea-surface and continental temperatures and monsoonal precipitation. A pollen record from Lake Ximencuo (Nianbaoyeze Mountains) indicates that vegetation from the eastern margin of the Tibetan Plateau was characterized by alpine deserts and glacial flora after the Last Glacial Maximum (LGM) (21-15.5 cal kyr BP), by alpine meadows during the Late Glacial (15.5-10.4 cal kyr BP) and second half of the Holocene (5.0 cal kyr BP to present) and by mixed forests during the first half of the Holocene (10.4-5.0 cal kyr BP). The application of pollen-based transfer functions yields an abrupt temperature increase at 10.4 cal kyr BP and a decrease at 5.0 cal kyr BP of about 3 degrees C. By applying endmember modeling to grain-size data from the same sediment core we infer that frequent fluvial events (probably originating from high-magnitude precipitation events) were more common in the early and mid Holocene. We assign the inferred exceptional strong monsoonal circulation to the initiation of moisture-advection feedback, a result supported by a simple model that reproduces this feedback pattern over the same time period. (C) 2014 Published by Elsevier B.V.
Pollen records from large lakes have been used for quantitative palaeoclimate reconstruction, but the influences that lake size (as a result of species-specific variations in pollen dispersal patterns that smaller pollen grains are more easily transported to lake centre) and taphonomy have on these climatic signals have not previously been systematically investigated. We introduce the concept of pollen source area to pollen-based climate calibration using the north-eastern Tibetan Plateau as our study area. We present a pollen data set collected from large lakes in the arid to semi-arid region of central Asia. The influences that lake size and the inferred pollen source areas have on pollen compositions have been investigated through comparisons with pollen assemblages in neighbouring lakes of various sizes. Modern pollen samples collected from different parts of Lake Donggi Cona (in the north-eastern part of the Tibetan Plateau) reveal variations in pollen assemblages within this large lake, which are interpreted in terms of the species-specific dispersal and depositional patterns for different types of pollen, and in terms of fluvial input components. We have estimated the pollen source area for each lake individually and used this information to infer modern climate data with which to then develop a modern calibration data set, using both the multivariate regression tree (MRT) and weighted-averaging partial least squares (WA-PLS) approaches. Fossil pollen data from Lake Donggi Cona have been used to reconstruct the climate history of the north-eastern part of the Tibetan Plateau since the Last Glacial Maximum (LGM). The meanannual precipitation was quantitatively reconstructed using WA-PLS: extremely dry conditions are found to have dominated the LGM, with annual precipitation of around 100 mm, which is only 32% of present-day precipitation. A gradually increasing trend in moisture conditions during the Late Glacial is terminated by an abrupt reversion to a dry phase that lasts for about 1000 yr and coincides with "Heinrich event 1" in the North Atlantic region. Subsequent periods corresponding to the Bolling/Allerod interstadial, with annual precipitation (P-ann) of about 350 mm, and the Younger Dryas event (about 270 mm P-ann) are followed by moist conditions in the early Holocene, with annual precipitation of up to 400 mm. A drier trend after 9 cal. ka BP is followed by a second wet phase in the middle Holocene, lasting until 4.5 cal. ka BP. Relatively steady conditions with only slight fluctuations then dominate the late Holocene, resulting in the present climatic conditions. The climate changes since the LGM have been primarily driven by deglaciation and fluctuations in the intensity of the Asian summer monsoon that resulted from changes in the Northern Hemisphere summer solar insolation, as well as from changes in the North Atlantic climate through variations in the circulation patterns and intensity of the westerlies.
Ostracod distribution and habitat relationships in the Kunlun Mountains, northern Tibetan Plateau
(2013)
Surface sediment samples were collected from the lakes Heihai, Kusai, Haiding Nuur and Yan Hu, and from streams and ponds in the Kunlun Mountains at the northern margin of the Tibetan Plateau to investigate the sub-fossil ostracod (micro-crustacean) fauna of the region. Among 65 collected samples, 46 ostracod shell-rich samples were used to study the relationship between the ostracod distribution and specific conductivity (SC) of the water, which ranged from 0.6 to 53.0 mS cm(-1). A total of eleven ostracod species was identified from this region, with about half of the species restricted to the Tibetan Plateau and its adjacent mountain areas, and the other half representing Holarctic taxa. Tonnacypris cf. estonica and Tonnacypris tonnensis are reported from the Tibetan Plateau for the first time. Leucocythere sp. is the dominant species and Ilyocypris cf. bradyi is also relatively abundant. The other seven species were recorded with limited abundances apparently due to lower SC tolerances. Leucocythere sp. was recorded over the full SC range from 0.6 to 53 mS cm(-1). Eucypris mareotica is a typical brackish and saline water species, which was found at sample sites with high SC (2.8-53.0 mS cm(-1)). In contrast, Leucocythere dorsotuberosa, Candona candida and Eucypris afghanistanensis prefer freshwater to slightly oli-gohaline waters with SC < 1.8 mS cm(-1). The SC optimum and tolerance range for each species were determined and compared to earlier reported data from other regions of Central Asia. The results indicate that species assemblage data from fossil ostracod shells have a large potential to provide information on past SC levels and more general climate-determined moisture conditions. (C) 2013 Elsevier Ltd and INQUA. All rights reserved.
Ostracod shells in surface sediments from Ulungur Lake (Xinjiang, China) belong mainly to Limnocythere inopinata as the dominant species, and Candona neglecta and Darwinula stevensoni as accompanying, less abundant taxa. Shells of an additional nine species were recorded only sporadically. The three most abundant ostracods have wide tolerance ranges in terms of salinity, substrate and water depth. The similarly recorded bivalve Pisidium subtruncatum, and the gastropods Gyraulus chinensis and Radix auricularia belong to the most tolerant representatives of the genera. The bivalve and gastropods, in addition to the ostracod assemblage, reflect the fact that Ulungur Lake has experienced strong lake level and salinity variations due to water withdrawal in the catchment and the counteracting diversion of river waters to the lake in recent decades. The substrate in Ulungur Lake is typically fine-grained, apart from the delta region of the Ulungur River channel, which is marked by relatively coarse-grained detrital sediments barren of ostracod shells. This channel was created 40 years ago to divert water to Ulungur Lake and support its local fisheries and recreational facilities. A reassessed Holocene ostracod record from the lake shows that a significantly higher salinity and lower lake level existed in the early Holocene before 6.0 ka in response to the regional climate. In contrast, a higher lake level and lowest salinity is inferred for the late Holocene period between ca. 3.6 and 1.3 ka before present. Afterwards, the lake level declined and salinity increased in response to regional moisture reduction, although conditions similar to the early Holocene lake status were not re-established. Our surface-sediment-derived data provide a baseline for analysis of future environmental variations due to global climate change and regional water management.
Ostracod shells from the archaeological site Gesher BenotYa'aqov (GBY) in the upper Jordan River Valley (Israel) were investigated to improve the understanding of the environmental conditions of the Acheulian occupation site during the early-mid Pleistocene transition (0.78 Ma). The diverse ostracod assemblage consists of 28 species. The distribution of most of the recorded species in the region today shows that the hydrological conditions at the early-mid Pleistocene transition were not fundamentally different from the modern ones. However, the predominance of Candona neglecta shells in the GBY sequence probably indicates cooler climatic conditions than today. Shells of Candona angulata in the artefact-richer upper half of the sequence suggest a slight salinity increase in the ancient Hula Lake from pure freshwater to slightly oligohaline conditions. This shift probably resulted from wetter conditions and a more stable lake environment with increased residence time of the lake water and stronger influence of evaporation. Shells of the brackish water ostracod Cyprideis torosa and the slightly halophilic Heterocypris sauna and Plesiocypridopsis newtoni were recorded only rarely suggesting that the lake maintained an outlet through the entire period represented by the GBY sequence. Shells of Gomphocythere ortali in GBY cycles 1 and 2 imply that a permanent freshwater stream existed close to the site. Humphcypris subterranea shells in cycles 3-5 provide further evidence that a tributary entered the lake from the south in contrast to the modern setting with the north-south flowing Jordan River at GBY. Statistical analysis of the quantitative ostracod data from GBY identified a group of samples from layers containing more abundant stone artefacts and another group of samples from layers with scarce artefacts. Samples from layers containing more abundant artefacts have relatively high abundances of C. angulata, Darwinula stevensoni and Physocypria kraepelini shells and include rare shells of Ilyocypris hartmanni, Ilyocypris salebrosa, Heterocypris incongniens and Pseudocandona sp. 2 which do not occur in the other samples. The presence of P. kraepelini and H. incongruens shells in artefact-richer sediments possibly indicates poor bottom water oxygenation in the ancient Hula lake sometimes during the periods of Acheulian occupation. However, more detailed studies are required to assess whether lower dissolved oxygen levels in the lake resulted from a slight lake level rise and possibly higher nutrient flux to the lake during wetter conditions or whether hominins already impacted lake's nutrient status by butchering at its shore or by burning of near-shore vegetation. (c) 2014 Elsevier B.V. All rights reserved.
A 352 cm long sediment core from Hersek Lagoon (Gulf of Izmit) was investigated for its ostracod species composition in order to evaluate the potential of ostracods to detect tsunami deposits in coastal environments. The Gulf of Izmit is the eastern bay of the Marmara Sea which is tectonically controlled by the North Anatolian Fault. Ostracod shells are rare in the lower third of the core, which probably represents a coastal wetland environment. According to radiocarbon dating of terrestrial plant remains, this unit was deposited between AD 500 and AD 800. Above, ostracod shells are abundant and dominantly monospecific, composed almost exclusively of the widespread brackish water ostracod Cyprideis torosa. This almost monospecific occurrence indicates the establishment and maintenance of the Hersek Lagoon after AD 800. Three distinct layers of mollusc shells and fragments contain ostracod shells of marine and to a lesser extent non-marine origin in addition to those of C. torosa. The shell layers are further characterized by significant maxima in total ostracod shell numbers. The high concentration of ostracod shells, the higher species numbers and the mixture of marine, lagoonal and non-marine ostracod shells shows that shell layers were formed as high-energy deposits resulting from tsunamis or large storms in the Marmara Sea. The partial occurrence of non-marine ostracod shells in the shell layers possibly indicates that tsunamis with extensive run-ups and significant backwash flows caused the high-energy deposits rather than large storms. The investigated sediments show that lagoonal ostracods can serve as good proxies for tsunamis or large storms through significant variations in total shell numbers, species numbers and the mixing of shells of different origin.
Ostracods from water bodies in hyperarid Israel and Jordan as habitat and water chemistry indicators
(2012)
The hyperarid region of Israel and Jordan covers a large area where numerous sites of Pleistocene lake sediments suggest that climate conditions were significantly wetter during the Pleistocene. This region experienced a significant increase in aridity in recent decades and the number of existing surface waters is diminishing rapidly. We studied ostracod shells from 49 pond and stream sites to determine the species distribution and to infer ecological preferences especially with respect to general differences in water movement, conductivity and ion composition. Twenty-two ostracod species were identified in total of which 12 taxa occur at three or more sites. Among the rarer species. Cyprinotus scholiosus was identified for the first time after two records from Plio- and Pleistocene sites in Yemen and Saudi Arabia. Further, Paracypretta amati was recorded and its ecological preferences discussed for the first time following the description of the species from its type locality in Sudan. Cypridopsis elongata is the only typical inhabitant of lotic habitats, strictly preferring freshwater conditions and waters with an alkalinity/Ca ratio around 1 and cations dominated by Ca(2+) and anions by HCO(3)(-). In contrast, Cyprideis torosa, Limnocythere inopinata and Heterocypris incongruens apparently prefer waters dominated by Na(+) associated with cations and Cl(-) associated with anions. Heterocypris salina and C. torosa occur over a wide conductivity (or salinity) range and in waters with alkalinity/Ca ratios around 1 and with significant alkalinity depletion. Humphcypris subterranea, Ilyocypris spp. and H. sauna are the only taxa which do not show any preference with respect to both the cation and anion dominance of the waters. The ecological preferences of the ostracod species from water bodies in the study area are discussed in detail and can be used for a qualitative assessment of the hydrodynamical and hydrochemical conditions of former water bodies in the presently hyperarid environment based on ostracod species composition analysis of Pleistocene aquatic sediments.
The Tibetan Plateau (TP), including its surrounding mountain ranges, represents the largest store of ice outside the polar regions. It hosts numerous lakes as well as the head waters of major Asian rivers, on which billions of people depend, and it is particularly sensitive to climate change. The moisture transport to the TP is controlled by the Indian and Pacific monsoon and the Westerlies. Understanding the evolution of the interaction of these circulation systems requires studies on climate archives in different spatial and temporal contexts. The objective of this study is to learn more about the interannual variability of precipitation patterns across the TP and how different hydrologic systems react to different climatic factors.
Aragonite shells of the aquatic gastropod Radix, which is widely distributed in the region, may represent suitable archives for inferring hydrologic and climatic signals in particularly high resolution. Therefore, sclerochronological studies of delta O-18 and delta C-13 ratios in Radix shells from seven lakes were conducted, each representing a different hydrologic and climatic setting, on a transect from the Pamirs across the TP.
The shell patterns exhibit an increasing influence of precipitation and a decreasing influence of evaporation on the isotope compositions from west to east. delta O-18 values of shells from lakes on the eastern and central TP (Donggi Cona, Yamdrok Yumco, Tarab Co) mirror monsoon signals, indicated by more negative values and higher variabilities compared to the more western lakes (Karakul, Bangong/Nyak, Manasarovar). In Yadang Co, located on the central southern TP, the monsoon rains did not reach the lake in the sampling year, although it is located in a region which is usually affected by monsoon circulation. The delta O-18 values are used to differentiate the annual hydrological cycle into ice cover period, melt water period, precipitation period and evaporation period. delta C-13 compositions in the shells particularly depend on specific habitats, which vary in biological productivity and in carbon sources. delta O-18 and delta C-13 patterns show a positive covariance in shells originating from large closed basins. The results show that Radix shells mirror general climatic differences between the seven lake regions. These differences reflect both regional and local climate signals in sub-seasonal resolution, without noticeable dependence on the particular lake system.
Sedimentological, palaeontological and mineralogical analyses of sediments from the endorheic Al Jafr Basin were conducted to better understand the depositional and hydrological conditions on the southern Jordan Plateau in the late Quaternary. Surficially exposed carbonate-rich sediments in the western part of the basin contain ostracod (micro-crustacean) shells of Ilyocypris cf. bradyi, Candona neglecta, Heterocypris salina, Fabaeformiscandona fabaeformis, Pseudocandona sp. and Herpetocypris brevicaudata. The shells of these and other more rare species, and charophyte and mollusc remains indicate that the sediments were formed in a wetland setting of shallow freshwater to slightly oligohaline ponds, streams and swamps. The present more northern distribution of some of the recorded taxa implies that climate conditions were probably cooler during the wetland formation. Radiocarbon age data for biogenic carbonate from two locations suggest that the wetland setting existed during the second half of Marine Isotope Stage (MIS) 3 or possibly earlier. A significantly higher water table must have existed in the basin during wetland formation; and wetter climate conditions are inferred for the catchment or at least for its highest and most humid westernmost part. Deflation and local sediment accumulation by wind and occasional sheet-wash events apparently prevailed in the region since MIS 2. Our newly presented data and inferences do not support the reconstruction of a previously reported large and relatively deep Pleistocene lake in the Al Jafr Basin. However, more extensive studies are certainly required for a detailed assessment of the Quaternary hydrological conditions in southern Jordan. (C) 2014 Elsevier Ltd and INQUA. All rights reserved.
A geological feature in the Qaidam Basin known as the "Shell Bar" contains millions of freshwater clam shells buried in situ. Since the 1980s, this feature in the now hyper-arid basin has been interpreted to be lake deposits that provide evidence for a warmer and more humid climate than present during late marine isotope stage 3 (MIS 3). Global climate during late MIS 3 and the last glacial maximum, however, was cold and dry, with much lower sea levels. We re-investigated the feature geomorphologically and sedimentologically, and employed optically stimulated luminescence (OSL) dating to verify the chronology of the sediments. We interpret the Shell Bar to be a remnant of a river channel formed by a stream that ran across an exposed lake bed during a regressive lake phase. Deflation of the surrounding older, fine-grained lacustrine deposits has left the fluvial channel sediments topographically inverted, indicating the erosive nature of the landscape. Luminescence ages place the formation of the Shell Bar in MIS 5 (similar to 113-99 ka), much older than previous radiocarbon ages of < 40 ka BP, but place the paleoclimatic inferences more in accord with other regional and global climate proxy records. We present a brief review of the age differences derived from C-14 and OSL dating of some critical sections that were thought to represent a warmer and more humid climate than present during late MIS 3. We attribute the differences to underestimation of C-14 ages. We suggest that C-14 ages older than similar to 25 ka BP may require re-investigation, especially dates on samples from arid regions.