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To investigate past vegetation change and human activity at the highest elevations on Easter Island, this study examines pollen, phytoliths, diatoms, starch and arthropods preserved in sediment/soil profiles from Rano Aroi crater, and another, newly described wetland in the adjacent, much smaller Rano Aroi Iti depression. A Bayesian age–depth model for Rano Aroi provides adequate certainty for the Late Pleistocene and last ~1000 years, but is poorly constrained from 12,000 to 1000 cal BP. The occurrence of cf. Potamogeton and Lycopodium pollen types at this highland site (~425 m altitude), while absent or rare at lowland sites, could well be related to the cooler higher altitude conditions. Smaller quantities of Arecaceae (palm) pollen than at lowland sites indicate that this relatively high-altitude part of the island was near the altitudinal forest limit in the Late Pleistocene, with extensive Asteraceae-dominated shrubland. Arecaceae forest dominated the Holocene, for which there is evidence for a prolonged dry phase. The subsequent disappearance of charcoal and reappearance of diatoms, particularly Eunotia cf. pectinalis, suggest that the dry phase ended prior to human settlement. Polynesian activity is best constrained by abundant microscopic charcoal fragments beginning in a layer at 710 (2σ: 645–797) cal BP, and suggesting a period of forest clearance and burning, culminating at 339 (2σ: 177–428) cal BP. Thinner soils compared with lowland horticultural sites and 14C dates of macroscopic Sophora charcoal suggest that the site was occupied after 1670 CE. Newly described terraces, and pollen, phytoliths and starch of cf. Broussonetia papyrifera (paper mulberry), cf. Colocasia esculenta (taro) and Musa (banana) sp. identified in this study show the value of a combined microfossil approach and provide evidence for extension of cultivation of these Polynesian-introduced cultigens to this least accessible part of the island. Rano Aroi Iti yielded a Bayesian 14C age–depth chronology to a basal age of 1530–1314 cal BP, giving an unexpectedly old age for presumably introduced New World pollen of Sisyrinchium, which occurs throughout the core.

Taihu Lake has been recognized as a seriously contaminated waterbody with regard to Cd, Cu, Pb and Zn over the last two decades. The input of pollutants has increased due to economic and social development and population increase. Seventy percent of the pollutants in Taihu Lake comes from rivers, with the Yili River being a major source of pollutants. Lakes Xijiu and Dongjiu are connected to the Yili River and Taihu Lake and are sites where material is preferentially deposited because of hydrodynamic conditions. Sediment cores were collected from Xijiu Lake (core XJ-1) and Dongjiu Lake (core DJ-5) to investigate anthropogenic heavy metal contamination. Concentrations of Cu, Pb and Zn gradually increased since the late 1930s, peaked in 1970, and then dropped slightly. A sudden increase in concentrations of Cu, Pb and Zn occurred in 1991 and peaked again in 1996, then dropped markedly. Maximum concentration of Cd in core XJ-1 was 21.2 mg kg−1 and mean concentration was 12.1 mg kg−1. In core DJ-5, the maximum and mean concentrations were 6.9 and 5.4 mg kg−1, respectively. Cr showed a pattern of variation different from the other heavy metals, but its concentration also dropped after peaking in 1996. Enrichment factors and anthropogenic factors revealed that human activities in the catchment played a key role in the heavy metal contamination. Increases in Cd, Cu, Pb and Zn concentration were caused by industrial development, particularly from non-ferrous metal smelting industries. The recent drop in Cd, Cu, Pb and Zn concentrations is attributed to pollution reduction measures instituted by the government. Cr was influenced by both natural and anthropogenic processes.

We analysed photosynthetic pigments in annually laminated sediment of meromictic Lake La Cruz, Spain, to cope with the timing and characterisation of primary productivity changes over the last four centuries. The photosynthetic pigments identified included chlorophyll a and b (and its derivatives) and specific carotenoids of different algal groups, such as zeaxanthin, lutein, alloxanthin, diadinoxanthin and diatoxanthin among others. Marker pigments of phototrophic sulfur bacteria were also observed, including bacteriochlorophyll a derivatives, homologue series of bacteriophaeophytins d and bacterial carotenoids okenone and chlorobactene. We investigated the diagenetic processes of pigment alteration in anoxic sediments and the possible implications for paleoproductivity reconstruction and interpretation. The lack of systematic down-core changes in diagenetic indicators suggests that variability of sedimentary pigment concentrations is the result of changes in lake productivity. The lower concentration of algal photosynthetic pigments in the bottom of sediment sequence corresponds to the onset of meromictic conditions. Before that, sediment was not continuously anoxic and the preservation of pigments was reduced. Regarding photosynthetic bacteria, green sulfur bacteria derivatives indicate that population growth was limited until the settled organic matter was sufficient to provide enough sulphide. Moreover, the presence of bacterioviridine, an oxidised derivative of bacteriochlorophyll a, suggest the competitive relation among photosynthetic bacteria. The high relative abundance of zeaxanthin indicates the dominance of picocyanobacteria in the primary productivity over the last centuries. Fluctuations of the pigment signal observed in the sediment sequence during the meromictic period were well correlated with fluctuations of solar activity.

During the lake deep drilling campaign PASADO in 2008, more than 500 m of lacustrine sediment was recovered from the maar lake Laguna Potrok Aike, Argentina. The major element composition was assessed at high resolution with an ITRAX X-ray fluorescence core scanner. The sharp boundary between a carbonate-bearing and a carbonate-free depositional system occurs at 13.5 cal. ka BP and marks the transition from glacial to Late Glacial sediments. Holocene and Late Glacial sediments can be distinguished by elements that are indicative of organic matter (Br, Cl) or calcite (Ca). Glacial sediments are characterized by elements that represent terrigenous clastic input (Fe, Ti, K, Si). Trace elements (Mn, Rb, V, Ni) accumulate with the bulk of lithogenic elements indicating frequent oxic conditions and rare diagenetic remobilization. Based on principal component analysis we interpret the scores of the first principle component as a summarizing indicator for climate-related variations of depositional conditions. During the Holocene climate changes mirror the total inorganic carbon profile, which was used as a proxy for lake-level reconstructions of the past 16 ka in previous studies. High scores in the first principle component probably reflect periods of increased chemical over mechanical weathering and developing soils and vegetation cover limiting sediment availability for erosional processes. These intervals often also show increases in total organic carbon values and total organic carbon/total nitrogen ratios, which are associated with periods of Antarctic warming in the last glacial. Geochemical variations of the clastic glacial sediments are explored by excluding carbonate-bearing sediments from principal component analysis. Although, in this lake, Ca is a purely clastic signal in carbonate-free sediments, it does not correlate with the bulk of indicators for terrigenous input. Instead Ca dominates a second principal component together with Sr. This component mainly distinguishes coarse grained layers from the remaining sediment. The main provenance of this coarse-grained material is suggested to be a basalt outcrop at the western shore. Low lake levels, high waves and flash-flood events may have increased the availability of basaltic sand during extremely cold, arid and windy conditions. High wind speeds and lack of vegetation may have facilitated the increased transport of coarse-grained material into the center of Laguna Potrok Aike. Decreases in the second principal component can be observed during Oxygen Isotope Stage 2 when increased dust input has been found in cores from Laguna Potrok Aike, the Southern Ocean and Antarctica.

We present a design for a piston corer that can take a sediment core up to 1 m long, with an undisturbed sediment–water interface. The coring device possesses a tripod unit and a core-tube unit, the latter comprised of a core tube, a piston with a wire, a drive weight in which the core tube is mounted and a steel rod. The tripod stands on the sediment surface during coring, stabilizing the system and serving as an anchor point for the piston wire. A ball clamp, the critical component of the design, is mounted on top of the tripod. The steel rod runs through the ball clamp and at its lower end, holds the drive weight and the core tube. The ball clamp allows the core tube to slide downward, while the piston is held in a fixed vertical position by the wire connected to the tripod. When the corer is lifted, however, the ball clamp locks. This makes it possible to operate the corer with a single cable, because the piston is not subject to any lifting force when the corer is retrieved. The piston remains in position in the core tube even if the collected sediment core is very short. The piston corer can be deployed from a raft or a boat.

Continuous terrestrial records of paleoclimate and paleovegetation that extend to the late Pleistocene are rare for the circum-Caribbean uplands. In this study we analyzed the bulk and compound-specific carbon isotope composition of lake sediments spanning this period from Lago de las Morrenas 1 (LM1), a glacial lake in the highlands of southern Costa Rica, for evidence of climate and vegetation changes that may not have been apparent in previous analyses. The stable carbon isotope ratios of n-alkanes typically derived from terrestrial plants (δ13CC27–C33) indicate an increased abundance of C4 plant taxa during the late Pleistocene and earliest Holocene that may be related to decreased atmospheric carbon dioxide concentrations, increased aridity, or habitat availability. These n-alkane isotope ratios also provide evidence of more arid conditions during the early and late Holocene, and more mesic conditions during the middle Holocene, a pattern prevalent in other paleoclimate records from the region that is thought to be related to millennial-scale dynamics of the intertropical convergence zone (ITCZ). The sensitivity of the LM1 paleorecord to trade wind dynamics provides further support for the role of millennial-scale shifts in ITCZ dynamics in driving neotropical environmental change, and indicates that the effects of ITCZ migration were not limited to the lowlands.

Sediment lithology and mineralogy, as well as ostracode, plant macrofossil and stable isotope stratigraphies of lake sediment cores, are used to reconstruct late Holocene hydrologic changes at Kenosee Lake, a relatively large, hyposaline lake in southeastern Saskatchewan. Chronological control is provided by AMS radiocarbon ages of upland and shoreline plant macrofossils. All indicators outline an early, low-water, saline phase of lake history (4100–3000 BP), when the basin was occupied by a series of small, interconnected, sulfate-rich brine pools, as opposed to the single, topographically-closed lake that exists today. A rapid rise in lake-level (3000–2300 BP) led to the establishment of carbonate-rich, hyposaline lake conditions like those today. Lithostratigraphic data and ostracode assemblages indicate peak salinities were attained early in this period of lake infilling, suggesting that the lake-level rise was initially driven by an influx of saline groundwater. Lake-level and water chemistry have remained relatively stable over the last 2000 years, compared to earlier events. Because of a lack of datable organic material in sediments deposited during the last 2000 years, the chronology of recent events is not well resolved. Plant macrofossil, lithostratigraphic and ostracode evidence suggests that lake draw-down, accompanied by slightly higher than present salinites, occurred sometime prior to 600 BP, followed by peak lake-level and freshwater conditions. This most recent high lake stand, indicative of a high water table on the surrounding upland, may also have led to the establishment of an extensive cover of Betula in the watershed, possibly in response to paludification. Ostracode assemblages indicate that peak freshwater conditions occurred within the last 100 years. Since historically documented lake-level fluctuations correlate with decadal scale climatic fluctuations in the meteorological record, and late-Holocene hydrologic dynamics correspond to well documented climatic excursions of the Neoglacial and Little Ice Age, Kenosee Lake dynamics offer insight into the susceptibility of the region's water resources to climate change.

We utilized paleoecological techniques to reconstruct long-term changes in lake-water chemistry, lake trophic state, and watershed vegetation and soils for three lakes located on an elevational gradient (661–1150 m) in the High Peaks region of the Adirondack Mountains of New York State (U.S.A.). Diatoms were used to reconstruct pH and trophic state. Sedimentary chrysophytes, chlorophylls and carotenoids supplied corroborating evidence. Pollen, plant macrofossils, and metals provided information on watershed vegetation, soils, and biogeochemical processes. All three lakes were slightly alkaline pH 7–8 and more productive in the late-glacial. They acidified and became less productive at the end of the late-glacial and in the early Holocene. pH stabilized 8000–9000 yr B.P. at the two higher sites and by 6000 yr B.P. at the lowest. An elevational gradient in pH existed throughout the Holocene. The highest site had a mean Holocene pH close to or below 5; the lowest site fluctuated around a mean of 6. The higher pH and trophic state of the late-glacial was controlled by leaching of base cations from fresh unweathered till, a process accelerated by the development of histosols in the watersheds as spruce-dominated woodlands replaced tundra. An apparent pulse of lake productivity at the late-glacial-Holocene boundary is correlated with a transient, but significant, expansion of alder (Alnus crispa) populations. The alder phase had a significant impact on watershed (and hence lake) biogeochemistry. The limnological changes of the Holocene and the differences between lakes were a function of an elevational gradient in temperature, hydrology (higher precipitation and lower evapotranspiration at higher elevation), soil thickness (thinner tills at higher elevation), soil type (histosols at higher elevation), vegetation (northern hardwoods at lower elevation, spruce-fir at higher), and different Holocene vegetational sequences in the three watersheds.