Glacial and postglacial sedimentation in the Fryxell basin, Taylor Valley, southern Victoria Land, Antarctica

A 9.14 m long sediment sequence was recovered from Lake Fryxell, Taylor Valley, southern Victoria Land, Antarctica, and investigated for its chronology and sedimentological, mineralogical, and biogeochemical changes. The basal part of the sequence is dominated by coarse clastic matter, i.e., mainly sand. The sediment composition suggests that a lake existed in Fryxell basin during the Middle Weichselian by ca. 48,000 cal. year BP. After a short period of lake-level lowstand ca. 43,000 cal. year BP, lower Taylor Valley became occupied by the proglacial Lake Washburn, which was at least partly supplied by meltwater and sediments from the Ross Ice Sheet that was advanced to the mouth of Taylor Valley. Evaporation of Lake Washburn to lower levels started during the Last Glacial Maximum at ca. 22,000 cal. year BP, long before the Ross Ice Sheet retreated significantly. Lake-level lowering was discontinuous with a series of high and low stands. From ca. 4000 cal. year BP environmental conditions were similar to those of today and lower Fryxell basin was occupied by a small lake. This lake evaporated to a saline or hypersaline pond between ca. 2500 and 1000 cal. year BP and refilled subsequently.     

Glacial-interglacial changes in moisture balance and the impact on vegetation in the southern hemisphere tropical Andes (Bolivia/Peru)

A palynological investigation of the last glacial-interglacial cycle in the southern hemisphere tropical Andes reveals changes in the moisture balance as the main driver in vegetation change. Thirty accelerator mass spectrometry radiocarbon dates, biostratigraphy and tephra correlation reveal that a 119 m sediment core recovered from the Huiñaimarca sub-basin of Lake Titicaca (16.0° to 17.5° S, 68.5° to 70° W; 3810 masl) contains sediments covering > 151,000 years. Correlation of aridity indicators with precessional variations in insolation is used to fine tune the structure of the age-depth curve within this period.Variations in Isoëtes concentration (above/below 10,000 grains/cm³) identify the extent of shallow water environments. Examination of another palaeolimnological indicator (Pediastrum) and consideration of the bathymetry of the Huiñaimarca sub-basin allow the reconstruction of lake-level fluctuations. These data indicate five wet/dry cycles between c. 151,000 and 14,200 cal yr BP. High stands are suggested during the transition into (c. 134,000 cal yr BP), and out of (c. 114,000 and 92,000 cal yr BP), the last interglacial, and during full glacial conditions (c. 70,000 and 45,000 cal yr BP). These cycles are superimposed on a general trend of deepening lake levels through the glacial period.This interpretation is supported by correlation with sediments from Salar de Uyuni (20°S, 68°W; 3653 masl). The youngest wet episode is concurrent with palaeolake Minchin (c. 45,000 cal yr BP), with further evidence for an additional wet period commencing c. 28,000 cal yr BP, concomitant with palaeolake Tauca. The timing of lake level fluctuations is also supported by palaeoshoreline reconstructions from the Uyuni-Poopó region. However, our data do not suggest a major peak in lake level in Huiñaimarca during the Ouki lake cycle (c. 120,000–98,000 cal yr BP) as inferred from U–Th ages obtained from palaeoshorelines around Lago Poopó. The most extreme dry event occurs during the last interglacial period and resulted in a sedimentary hiatus tentatively dated to c. 121,000–129,000 cal yr BP.The observed wet/dry cycles are shown to have a marked and rapid impact on the vegetation. The aridity of the last interglacial promoted a community dominated by Chenopodiaceae/Amaranthacae, with no modern Andean analogue. Polylepis/Acaena pollen is also shown to fluctuate markedly (0–20%), particularly during the transitions into, and out of, the last interglacial. It is probable that this pollen taxon is primarily representative of the high altitude arboreal genus Polylepis, which is a key component of highly biodiverse Andean woodlands today. Rapid fluctuations indicate the sensitivity of this ecosystem to natural environmental pressure and potential vulnerability to future human impact and climate change.The 100,000 year (eccentricity) solar cycle is shown to be the major controlling factor in moisture balance and vegetation over the last glacial-interglacial cycle. However, significant fluctuations in moisture balance are also evident on timescales considerably shorter than the full glacial-interglacial cycle. We have linked these to precessional (21,000 year) forcing. Nevertheless, precise independent dating during the full glacial cycle is required to confirm the importance of this forcing mechanism.     

An ostracod-based calibration function for electrical conductivity reconstruction in lacustrine environments in Patagonia,Southern South America

In the Patagonian region (∼37–56°S) E of the Andes, the salinity and solute composition of lakes is strongly related to their location along the marked W-E decreasing precipitation gradient that is one of the main climatic features of the area. A calibration function (n = 34) based on 12 ostracod species (Ostracoda, Crustacea) was developed by WA-PLS to quantitatively reconstruct electrical conductivity (EC) values as a salinity proxy. The selected one component model had a r² = 0.74 and RMSEP and maximum bias equal to 16% and 31% of the sampled range, respectively, comparable to other published ostracod-based calibration functions. This model was applied to the ostracod record of the closed lake Laguna Cháltel (49°58′S, 71°07′W), comprising seven species and dominated by two species of the genus Limnocythere. In order to evaluate the calibration function’s robustness, the obtained EC values were compared with qualitative lake level and salinity variations inferred through a multiproxy hydrological reconstruction of the lake. Both reconstructions show good overall agreement, with reconstructed EC values in the oligo-mesohaline range (average: 11 060 ± 680 μS/cm) between 4570 and 3190 cal BP, corresponding to the ephemeral and shallow lake phases, and a marked decrease in EC concurrent with a lake level rise, reaching an average EC of 1140 ± 90 μS/cm during the deep lake phase (1720 cal BP to present). The variability in the reconstructed EC values for the ephemeral lake phase showed some inconsistency with the expected trend, which was attributed to time-averaging effects; for its part, the pace of the decrease in EC during the medium-depth phase (3190–1720 cal BP) differed from the expected, which could be due to autigenic effects (redissolution of salts) at the onset of this phase. This comparison not only lends support to the adequacy of the calibration function, but also suggests that its application in the context of a multiproxy study can greatly contribute to distinguish between autigenic and climatic-related controls of paleosalinity in closed lakes, allowing performing more accurate paleoenvironmental inferences on the basis of paleohydrological reconstructions.     

Holocene environmental changes as recorded by mineral magnetism of sediments from Anguli-nuur Lake,southeastern Inner Mongolia Plateau,China

Two cores, one 1141-cm long (An-S) and the other 885-cm long (An-A), were retrieved from Anguli-nuur Lake (41°18′–24′N, 114°20′–27′E, ～ 1315 masl), one of the largest lakes in the transition zone between a semi-humid and semi-arid climate parallel to the present limit of the southeast monsoon along the southeastern Inner Mongolia Plateau in north China. Mineral-magnetic parameters (χ_lf, ARM, IRM_300mT, SIRM and IRM_? 300mT) were measured on An-S and two additional parameters (χ_ARM and HIRM) and four inter-parametric ratios (χ_ARM/SIRM, IRM_300mT/SIRM, IRM_? 300mT/SIRM and SIRM/χ_lf) were calculated. Potential sources of these lake sediments (catchment soils and dune materials close to the lake and in a distant sand plain) were sampled, and the magnetic properties of the surface-material specimens were measured. A chronological model was developed for An-S by comparing and combining AMS¹⁴C dates of An-S with ¹³⁷Cs, ²¹⁰Pb and AMS¹⁴C dates of An-A. With the help of surface-material magnetism, the magnetic data of An-S in combination with particle size, TOC and C/N and pollen analyses indicate the environmental changes during the last ～ 10,000 years around this lake. Conditions began to ameliorate at 10,900 cal. yr BP (9600 ¹⁴C yr BP) and thus relatively wet and warm environments prevailed during 10,900–8900 cal. yr BP (9600–8000 ¹⁴C yr BP). The Holocene optimum or the wettest and warmest conditions, was during 8900–7400 cal. yr BP (8000–6500 ¹⁴C yr BP). The environment began to deteriorate from 7400 cal. yr BP (6500 ¹⁴C yr BP) and the driest and coolest conditions occurred during 2200–480 cal. yr BP. There may have been a minor amelioration after 480 cal. yr BP. The inferred changes in palaeoenvironmental conditions around Anguli-nuur Lake are broadly in agreement with those around most other sites on the Inner Mongolia Plateau.     

Vegetation history with implication of climate changes and human impacts over the last 9000 years in the Lake Nanyi area,Anhui Province,East China

Palynological analyses in combination with radiocarbon dating on a Holocene borehole from the Lake Nanyi, Anhui Province, East China demonstrate a well-documented local vegetation evolution since 9000 cal BP, which is the first record of Holocene climate change and human impact in this region. Since 9000 cal BP a mixed evergreen and deciduous broad-leaved forest dominated by Cyclobalanopsis and Quercus developed in this area, indicating a warm climate condition with enhanced insolation. A mixed evergreen and deciduous broad-leaved forest was fully developed between 6600–4500 cal BP, which corresponds to the Holocene Climate Optimum with the strong influence of East Asian summer monsoon (EASM). After 3000 cal BP the broad-leaved forest decreased rapidly, while land herbs and ferns increased. It seems that the climate condition in East China was similar to the present after Holocene Climate Optimum. Pollen results show a potential interface between environment changes and human activities. Pollen diagram demonstrates that human impacts on the natural vegetation remained weak at the early stage but significantly enhanced upwards. The distinctive fluctuations of the pollen contents among AP (trees and shrubs), and the possible agriculture indicators might infer the potential human behaviors for environment changes. Due to the enlargement of organized farming and increase in population, natural forest was eventually replaced by farmland since 3000 cal BP. This study would increase our knowledge of Holocene vegetation transition related to the monsoon dynamics on a long timescale in East China and provide an environmental background for more detailed studies on cultural developments in the middle and lower reaches of the Yangtze River region.     

Ostracods and the Holocene palaeolimnology of Lake Qarun, with special reference to past human–environment interactions in the Faiyum (Egypt)

We present an ostracod record covering the past two millennia from an 8.25-m core taken from Lake Qarun, in the Faiyum Depression of Egypt. The occurrence of ostracod species in the lake is controlled primarily by variations in solute composition, which are in turn related to shifts in catchment land use. At times when the Faiyum Depression supported thriving agriculture, lake water contained Na⁺–Cl^? brine, and Cyprideis torosa dominated the ostracod assemblage. When the Faiyum Depression experienced periods of environmental and economic decline, lake water contained Na⁺–HCO₃ ^? brine, and Limnocythere inopinata dominated. The relative abundance of other ostracod species provides additional information about past conditions in Lake Qarun including salinity and lake level changes. Overall, the ostracod assemblages provide evidence for human influences in the Faiyum, which extend back before instrumental or detailed observational records began.     

Environmental changes recorded in deposits of the Izyubrinye Salontsi Lake,Sikhote-Alin

Paleoecological changes during the development of Lake Izyubrinye Solontsi from the Solontsovskie (Shanduyskie) Lakes located in the midlands of the Eastern Sikhote-Alin have been reconstructed. Lake formation is related to landslides on the paleovolcano slopes. A complex study of the peat-bog section (botanical, diatom, spore-pollen, and radiocarbon analysis) allows reconstructing paleoenvironmental changes with high resolution. A considerable variability of lake and swamp environments highly responsive to climate changes in the late Holocene has been revealed. Peat accumulation began about 4000¹⁴С BP. The main peat-forming plants were Sphagnum mosses and herbs, except for the period 2330?1530 ¹⁴C BP (2360?1480 cal. BP), when a swamp overgrown by larch forests and predominantly woody peat accumulated. Forest ecosystems on the lake coasts were quite stable. The role of fir and broadleaved species increased in the composition of dark coniferous forests with Korean pine during the warm phases and the role of birch, in the cold phases; secondary forests occupied the low slopes during the last 1000 years. The age of paleofires has been determined.     

An 11?000-year lithostratigraphic and paleohydrologic record from Equatorial Africa: Lake Edward, Uganda-Congo

Sedimentologic and geochemical analyses of four cores from Lake Edward, Uganda-Congo, document a complex record of moisture balance in the Edward basin from 11?000 cal yr BP to present. Highly organic, diatomaceous muds provide evidence for shifts in wind intensity and stratification within an early Holocene wet phase. Lake level variations within this period may have shifted due to tectonic lowering of the lake’s outlet level. The onset of mid-Holocene aridity, as documented by the appearance of authigenic calcite at 5200 cal yr BP, initiated a period of falling lake levels that culminated in a late Holocene lowstand between 4000 and 2000 cal yr BP. This lowstand is documented by coarse sediments whose fabric and mineralogy depend on the core site. Although different cores yield different ages for this regression, it appears that declining lake levels culminated in a maximum lake lowstand of −14 m. Lake levels then rose rapidly, attaining modern positions by 1700 cal yr BP. This lake level history suggests that although many paleoclimatic changes in Africa are apparently synchronous throughout northern hemispheric Africa, other events may be spatially heterogeneous. These patterns highlight the need for a well-dated network of paleoclimate sites within the African continent.     

Coastal evolution and Holocene ostracods in Melides lagoon (SW Portugal)

A multidisciplinary study covering sedimentology (texture, carbonate and organic matter content, clay mineralogy), geochemistry (major, minor and trace elements, isotopes), palaeoecolgy (ostracods) and isotopic dating (¹⁴C) has been carried out on two long cores (MB-40.0 m and MIGM-34.0 m) retrieved from the barrier and the alluvial plain margining the Melides lagoon (south-western coast of Portugal). The interpretation of the whole data set allowed the establishment of an evolutionary model for this lowland since the Late Glacial. This model includes four stages. It starts with a fluvial terrestrial environment, replaced by an estuarine to fully marine one (circa 9500 cal BP), due to the rapid rise in sea level recorded during the first phase of the Holocene transgression. The deceleration of sea level rise favoured the emplacement of a sandy barrier (circa 5900 cal BP) that promoted the differentiation of a coastal lagoon which has been progressively filled with fluvial sediments.The ostracod fauna in both locations includes 38 species of littoral to sublittoral/phytal marine forms (mainly Urocythereis britannica, Carinocythereis whitei, Loxoconcha rhomboidea, Pontocythere elongata, Semicytherura sella, Semicytherura acuta, Basslerites cf. berchoni, Hiltermannicythere emaciata) and brackish water forms (Cyprideis torosa, Loxoconcha elliptica), which clearly characterize the signature of both the marine and lagoonal episodes, respectively.     

Ostracod distribution in Ulungur Lake (Xinjiang,China) and a reassessed Holocene record

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.     

The Lake Superior varve stratigraphy and implications for eastern Lake Agassiz outflow from 10,700 to 8900 cal ybp (9.5-8.0 C ka)

Glaciolacustrine rhythmites within sediment cores from Lake Superior record the regional recession of the Laurentide Ice Sheet (LIS) from 10,700 to 8900 cal ybp [ca. 9.5-8.0 ¹⁴C ka]. LIS retreat from Superior opened eastern Lake Agassiz outlets so that the rhythmites reflect the combined impacts of sediment-laden meltwater and Lake Agassiz discharge. Multiple rhythmite stratigraphies, a time series analysis of the thickness measurements, and high-resolution inorganic carbonate data demonstrate that this is an annual record (varved). The varve thickness records primarily document regional ice margin dynamics; correlative thick varve sequences at 9100 cal ybp [∼ 8.1 ¹⁴C ka] and 10,400-10,200 cal ybp [∼ 9.2-9.0 ¹⁴C ka] record two periods of enhanced glaciofluvial discharge, most likely moraine formation (the Nakina and Nipigon). General varve cessation is associated with the circumvention of Lake Agassiz and glacial meltwater into Lake Ojibway at 9040 cal ybp [∼ 8.1 ¹⁴C ka], although adjacent to the inlets from Lake Nipigon, rhythmic sedimentation persisted for 200 years.Positively identifying Lake Agassiz catastrophic discharge events remains speculative but seems feasible. Following retreat of Marquette ice that had re-advanced to fill the basin, the initial influx of Lake Agassiz water is expected at around 10,600 cal ybp [∼ 9.4 ¹⁴C ka], but at this time, most of northeastern Lake Superior was covered by ice. Three sets of thick-thin varves in western Lake Superior perhaps record influxes of Lake Agassiz at around 10,630, 10,600, and 10,570 cal ybp [∼ 9.4 ¹⁴C ka]. Varve formation in Superior coincides with high lake levels in Lake Huron, suggesting that high lake levels in Huron correspond to periods of high Agassiz and/or meltwater flow into Lake Superior.     

Linkages between surface and deep circulations in the southern Japan Sea during the last 27,000 years: Evidence from planktic foraminiferal assemblages and stable isotope records

We analyzed planktic foraminiferal assemblages, oxygen and carbon isotope records, and the presence or absence of laminations to reconstruct the paleoenvironments of the southern Japan Sea since the last glacial period. Data were collected from two well-dated cores. One core (water depth 999 m) included thinly laminated mud layers, the other (water depth 283 m) contained nonlaminated sediments. Tephrochronology and accelerator mass spectrometry ¹⁴C dating of 14 horizons revealed that the two cores contained continuous records of the last 27 cal kyr. A total of 13 planktic foraminiferal species belonging to six genera were identified in down-core samples. The typical indicators of the Tsushima Current water, Globigerinoides ruber, Neogloboquadrina dutertrei, Pulleniatina obliquiloculata, Globigerinoides tenellus, and Globigerinita glutinata occurred since 9.3 cal kyr BP. Neogloboquadrina incompta, which was the dominant species in the Tsushima Current region of the modern Japan Sea, first occurred at 8.2 cal kyr BP and dominated the assemblage since 7.3 cal kyr BP. These results clearly indicate that the warm Tsushima Current started to inflow into the Japan Sea at 9.3 cal kyr BP, and the modern surface conditions in the southern Japan Sea were essentially established at 7.3 cal kyr BP. Our data and comparison of the presence or absence of laminated sediments in three locations from the southern Japan Sea suggest that deep circulation during the deglacial period was weaker than that at present. In addition, deep circulation in the modern Japan Sea, which supplies oxygen-rich water to the entire basin, started probably in association with the first inflow of the Tsushima Current beginning at 9.3 cal kyr BP.     

Transition from shallow lake to a wetland: a multi-proxy case study in Zalavári Pond,Lake Balaton,Hungary

Lake Balaton, the largest shallow lake in Central Europe, has no natural outlet, therefore, underwent water level changes during its 15,000–17,000 years of history. The lake is very sensitive to both climate changes and human impacts. Surroundings have been inhabited since the Stone Age; however, heavy human impact can be recognized during the past 6000 years. In this study, we established three different stages for and reconstructed water level changes of Lake Balaton by geochemical data, subfossil Cladocera and diatom remains in the sediments of the Zalavári Pond, a part of the Kis-Balaton wetland. In 9900–8600 cal. year BP, climate was dry, water level was low, and there was a wetland in this area. Although organic matter content was low in the sediment, the ratio of Fe/Mn was high. Between 5600 and 5000 cal. year BP, water level increased, Fe/Mn ratio shows that oxygen conditions of sediments was improved in agreement with the relatively low number of diatom remains and dense chydorid remains. About 5000 cal. year BP, water level of Lake Balaton decreased as indicated by high organic content with low carbonate and high Fe/Mn ratio in the sediments (oxygen depletion). At the bottom of this section, high Fe and S concentrations showed accumulation of pyrite (FeS₂) that is common in wetlands with very low redox potential. Low abundance of Cladocera remains together with rich and diverse diatom flora confirm the low water level hypothesis. Our data support that the water level of Lake Balaton was higher between 8600 and 5000 cal. year BP than it is at present.     

Assessment of the ecological status of European surface waters: a work in progress

Medicine Lake is a small (165 ha), relatively shallow (average 7.3 m), intermediate elevation (2,036 m) lake located within the summit caldera of Medicine Lake volcano, Siskiyou County, California, USA. Sediment cores and high-resolution bathymetric and seismic reflection data were collected from the lake during the fall of 1999 and 2000. Sediments were analyzed for diatoms, pollen, density, grain size (sand/mud ratio), total organic carbon (TOC), and micro-scale fabric analysis. Using both ¹⁴C (AMS) dating and tephrochronology, the basal sediments were estimated to have been deposited about 11,400 cal year BP, thus yielding an estimated average sedimentation rate of about 20.66 cm/1,000 year. The lowermost part of the core (11,400–10,300 cal year BP) contains the transition from glacial to interglacial conditions. From about 11,000–5,500 cal year BP, Medicine Lake consisted of two small, steep-sided lakes or one lake with two steep-sided basins connected by a shallow shelf. During this time, both the pollen (Abies/Artemisia ratio) and the diatom (Cyclotella/Navicula ratio) evidences indicate that the effective moisture increased, leading to a deeper lake. Over the past 5,500 years, the pollen record shows that effective moisture continued to increase, and the diatom record indicates fluctuations in the lake level. The change in the lake level pattern from one of the increasing depths prior to about 6,000 cal year BP to one of the variable depths may be related to changes in the morphology of the Medicine Lake caldera associated with the movement of magma and the eruption of the Medicine Lake Glass Flow about 5,120 cal year BP. These changes in basin morphology caused Medicine Lake to flood the shallow shelf which surrounds the deeper part of the lake. During this period, the Cyclotella/Navicula ratio and the percent abundance of Isoetes vary, suggesting that the level of the lake fluctuated, resulting in changes in the shelf area available for colonization by benthic diatoms and Isoetes. These fluctuations are not typical of the small number of low-elevation Holocene lake records in the region, and probably reflect the hydrologic conditions unique to Medicine Lake.     

Annually laminated lake sediments and environmental changes in Bashang Plateau, North China

Angulinuo Lake is the biggest lake on the Bashang Plateau, North China, and is 47.6 km² in area and 2-6 m in depth. A core from the inner part of Angulinuo Lake was sliced and the sediment was observed by Scanning Electronic Microscope (SEM). Annual laminations characterized by variable color and grain size were found and interpreted as recording the cyclic deposition of lacustrine clay and aeolian dust. The results of chemical analysis of coarse grains conducted by SEM-EDAX, and grain size analysis of modern aeolian dust in the ice on Angulinuo Lake, support an aeolian origin for the light coarse layers. Image analysis technique was used to calculate the size and number of coarse grains in each layer. The coarse grains were fractionated into four classes: > 42 μm, 14-42 μm, 14-4.2 μm and 1.4-4.2 μm. In general, the abundance of the four classes shows similar temporal variation patterns. Around Angulinuo Lake, the winter monsoon is strong and transports aeolian dust into the lake. When the winter monsoon is strong, the size and amount of coarse grains are expected to increase. We infer that the winter monsoon was weaker during 8430-5440 year BP, and was unstable in the later part of this period. From 5440 year BP, the winter monsoon became stronger, and then weaker from 3250 to 2490 year BP. During 2490-1170 year BP, the winter monsoon was slightly stronger, but since 1170 year BP, it has become weaker again. The changes of the winter monsoon intensity recorded in the annual laminations in Angulinuo Lake sediments correspond well to environmental changes in North China and to changes in sea level during the same period. Periods of weaker winter monsoon correspond to times of higher sea levels while the periods of stronger winter monsoon correspond to the Neoglaciation stage in China and the periods of lower sea levels.     

Early to mid-Pleistocene ostracod δO and δC in the central Tibetan Plateau: Implication for Indian monsoon change

As one of the pioneering projects of the Chinese Environmental Scientific Drilling (CESD) Program, a 206.5 m long sediment core (CE) was retrieved from Co Ngoin (Co = lake) Basin in the central Tibetan Plateau. Limnic records of the abundance of ostracod shells and their oxygen and carbon isotope measurements, together with the geochemical and the sedimentological investigations, were carried out on the interval between 143 and 52 m core depths, corresponding to ca. 2.01–0.84 Myr. Distinct oscillations of the abundance and the chemical compositions of ostracod shells have yielded the original information about variations in lakewater chemistry in association with the change in the Indian monsoon over the period of 2.01 to 0.84 Myr. The climate conditions during the Early Pleistocene were characterized by frequent oscillations and the ostracod records had expressed its synchronous response to these oscillations. A major climate change occurred in the Co Ngoin area at about 0.93 Myr. A pronounced fluctuation in ostracod δ¹⁸O and δ¹³C during the Mid-Pleistocene transition (MPT) is possibly associated with an increase in continental ice sheets. The compositional and the sedimentological characters of the immediately overlying sediments imply a shallow aquatic environment and also a harsh (salinity?) condition beyond the tolerance limits for ostracod survival, resulting in the disappearance of the Qinghaicypris crassa Huang 1979 around 0.84 Myr.     

Palaeolimnology of the last crater lake in the Eastern Carpathian Mountains: a multiproxy study of Holocene hydrological changes

A multi-proxy investigation (loss-on-ignition, major and trace elements, pollen, plant macrofossil and siliceous algae) was carried out on the sediment of a crater lake (Lake Saint Ana, 950 m a.s.l.) from the Eastern Carpathian Mountains. Diatom-based transfer functions were applied to estimate the lake’s trophic status and pH, while reconstruction of the water-depth changes was based on the plant macrofossil and diatom records. The lowest Holocene water depths were found between 9000 and 7400 calibrated BP years, when the crater was occupied by Sphagnum-bog. Significant increases in water depth were found from 5350(1), 3300(2) and 2700 cal yr BP. Of these, the first two coincided with major terrestrial vegetation changes, namely (1) the establishment of Carpinus betulus on the crater slope and (2) the replacement of the lakeshore Picea abies forest by Fagus sylvatica. The chemical record indicated significant soil changes along with the canopy changes (from coniferous to deciduous) that led to increased in-lake productivity and pH. A further increase in water depth around 2700 cal yr BP resulted in stable thermal stratification and hypolimnetic anoxia that via P-release further increased in-lake productivity and eventually led to phytoplankton blooms with large populations of Scenedesmus. High productivity was depressed by anthropogenic lakeshore forest clearances from ca. 1000 cal yr BP that led to the re-establishment of P. abies on the lakeshore and consequent acidification of the lake water. On the whole, these data suggest that Lake Saint Ana is a vulnerable ecosystem: in-lake productivity is higher under deciduous canopy and litter, and considerably repressed by coniferous canopy and litter. The lake today subsists in a managed environment that is far from its natural state. This would be a dense F. sylvatica forest supplying more nutrients and keeping up a more productive in-lake flora and fauna. Guest editors: K. Buczkó, J. Korponai, J. Padisák & S. W. Starratt Palaeolimnological Proxies as Tools of Environmental Reconstruction in Fresh Water     

An example of the consequences of human activities on the evolution of subalpine landscapes

A pollen study at Survilly (2235m asl, 06° 49′ 12″ E, 45° 59′ 24″ N), a small peatbog located on the Anterne mountain (Upper-Arve Valley, French north-western Alps) highlights the local role of human activities in Holocene vegetation dynamics of the currently treeless subalpine belt and the consecutive resumption of erosion. As early as 8890 cal. years BP (± 122), Pinus cembra grew close to the site. Grasslands without shrubs were established at around 4624 ± 86 cal. years BP. Due to human activities, spruces extended little after 3600 cal. BP. The intense grazing that resulted in the current alpine meadows goes back to 1436 cal. years BP (± 81). After 4624 cal. BP three clay layers show that from this period, the erosion became as active as during the first steps of the colonization of the vegetation prior to 10,050 cal. BP. During peat growth only a millimetre of clay at the end of the 9400–9050 cal. BP climatic event was recorded.     

A late glacial to present diatom record from Lake Euramoo, wet tropics of Queensland, Australia

A new diatom record from Lake Euramoo on the Atherton Tableland, north Queensland, Australia is used to assess regional climate change and variability and their links to forcing at a local to global scale. The major factor driving diatom composition in the approximately fifteen thousand-year record appears to be regional moisture availability. Patterns of diatom preservation and other indicators, particularly sediment organic content, suggest that permanent deep water formed at the site from ca. 15,000 cal. yr BP. However, between 13,800 and 11,500 cal. yr BP, there was a notable phase of lower lake levels and effective precipitation. The timing and duration of this phase does not correspond to large-scale climate phenomena such as the Antarctic Cold Reversal or the Younger Dryas and supports emerging evidence for a variable climate regime in the south-west Pacific during the late glacial transition.The Early to Mid Holocene record is one of remarkable stability with 5000 years of sustained dominance by the planktonic diatom Aulacoseira ambigua. Conversely, the Mid to Late Holocene record is marked by distinct diatom variability superimposed on a series of sustained shifts in composition. Accentuated Late Holocene climate variability may aid in explaining intensified land use in indigenous populations and also suggests that Europeans may have arrived in the landscape at the time it was most vulnerable to perturbation.