We used fossil Chironomidae assemblages and the transfer function approach to reconstruct summer air temperatures over the past 300 years from a High Arctic lake in Hornsund, Svalbard. Our aims were to compare reconstructed summer temperatures with observed (last 100 years) seasonal temperatures, to determine a potential climate warming break point in the temperature series and to assess the significance and rate of the climate warming trend at the study site. The reconstructed temperatures were consistent with a previous proxy record from Svalbard and showed good correlation with the meteorological observations from Bjørnøya and Longyearbyen. From the current palaeoclimate record, we found a significant climate warming threshold in the 1930s, after which the temperatures rapidly increased. We also found that the climate warming trend was strong and statistically significant. Compared with the reconstructed Little Ice Age temperatures in late eighteenth century cooling culmination, the present day summer temperatures are >4°C higher and the temperature increase since the 1930s has been 0.5°C per decade. These results highlight the exceptionally rapid recent warming of southern Svalbard and add invaluable information on the seasonality of High Arctic climate change and Arctic amplification.

The Lake Tilla crater lake in northeastern Nigeria (10°23′N, 12°08′E) provides a ca. 17,000 14C yr multiproxy record of the environmental history of a Sudanian savanna in West Africa. Evaluation of pollen, diatoms, and sedimentary geochemistry from cores suggests that dry climatic conditions prevailed throughout the late Pleistocene. Before the onset of the Holocene, the slow rise in lake levels was interrupted by a distinct dry event between ca. 10,900 and 10,500 14C yr B.P., which may coincide with the Younger Dryas episode. The onset of the Holocene is marked by an abrupt increase in lake levels and a subsequent spread of Guinean and Sudanian tree taxa into the open grass savanna that predominated throughout the Late Pleistocene. The dominance of the mountain olive Olea hochstetteri suggests cool climatic conditions prior to ca. 8600 14C yr B.P. The early to mid-Holocene humid period culminated between ca. 8500 and 7000 14C yr B.P. with the establishment of a dense Guinean savanna during high lake levels. Frequent fires were important in promoting the open character of the vegetation. The palynological and palaeolimnological data demonstrate that the humid period terminated after ca. 7000 14C yr B.P. in a gradual decline of the precipitation/evaporation ratio and was not interrupted by abrupt climatic events. The aridification trend intensified after ca. 3800 14C yr B.P. and continued until the present.

The diatom stratigraphy of a 23-m sediment core from Lake Tilo, a maar lake in the Ethiopian Rift Valley, provides a 10,000-yr record of lake salinity and trophic status. Until 5500 14C yr B.P., the phytoplankton was dominated by Aulacoseira granulata, with only minor changes in the abundance of other diatoms; the lake was over 50 m deep, eutrophic, and oligosaline. At 5500 yr B.P., geothermal groundwater inflow, inferred from calcite and silica deposition rates, declined abruptly, and the lake became more oligotrophic, as indicated by a rapid rise in Cyclotella stelligera. About 4500 yr B.P., lake salinity began to increase, reaching approximately its present state ca. 2500 yr B.P., but with a temporary reversal to lower salinity at 4000–3500 yr B.P. The record shows no evidence of salinity increases equivalent to early Holocene low stands of the larger river-fed Rift Valley lakes, probably because of high rates of geothermal groundwater influx. It responded to reduced rainfall at 4500 yr B.P., when levels of the larger lakes also fell, because geothermal groundwater flux had diminished 1000 year earlier, independently of climate. Because geothermal groundwaters can form a significant proportion of a crater lake's hydrological budget and dominate its salinity budget, these results show that variable geothermal groundwater flux can override lake hydrochemical response to climate change. Palaeoclimatic interpretation of palaeosalinity proxies from the sediments of volcanic crater lakes should be approached with caution.

Lake Bosumtwi is one of the most widely studied palaeoclimate archives in West Africa. Results from numerous AMS 14C dates of samples from four piston cores from Lake Bosumtwi show that an abrupt sedimentary transition from a mid-Holocene sapropel to calcareous laminated muds occurred at about 3200 cal yr B.P. High-resolution analyses of the nitrogen isotopic composition of organic matter across this transition confirm its abrupt nature, and suggest that the change may signal a step toward increased aridity and intensified surface winds that affected western equatorial Africa from Ghana to the Congo basin. Northern and Eastern Africa experienced a similar abrupt shift toward aridity during the late Holocene, but at about 5000 cal yr B.P., a difference in timing that illustrates the regional nature of climate changes during the Holocene and the importance of feedback mechanisms in regulating Holocene climate variability. Furthermore, an abrupt change at about 3000 cal yr B.P. occurs at several sites adjacent to the tropical and subtropical Atlantic, which may hint at major changes in the surface temperatures of the tropical Atlantic and/or Pacific at this time.

Branched glycerol dialkyl glycerol tetraether (GDGT) distributions observed in a sediment core from Lake McKenzie were utilized to quantitatively reconstruct the pattern of mean annual air temperature (MAAT) from coastal subtropical eastern Australia between 37 and 18.3 cal ka BP and 14.0 cal ka BP to present. Both the reconstructed trend and amplitude of MAAT changes from the top of the sediment core were nearly identical to a local instrumental MAAT record from Fraser Island, providing confidence that in this sediment core branched GDGTs could be used to produce a quantitative record of past MAAT. The reconstructed trend of MAAT during 37 to 18.3 cal ka BP and timing of the Last Glacial Maximum (LGM) in the Lake McKenzie record were in agreement with previously published nearby marine climate records. The amplitude of lower-than-present MAAT during the LGM potentially provides information on the latitude of separation of the Tasman Front from the East Australian current in the subtropical western Pacific. The Lake McKenzie record shows an earlier onset of near modern day warm temperatures in the early Holocene compared to marine records and the presence of a warmer than present day period during the mid-Holocene.

The equatorial peatlands of the Kutai lowland of eastern Kalimantan are generally 4–10 m in thickness but some sections exceed 16 m in depth. The deposition of peat commenced about 8000 yrs ago after shallow flooding of the basin by the Mahakam River. The earliest vegetation is a Pandanus swamp which grades upwards to swamp forest dominated by dipterocarps. The peatland has expanded laterally and rivers have maintained narrow levee-channel tracks through the swamp, which has grown vertically in balance with river accretion. Historical fires are associated with extreme El Niño years of drought, but human agency is important. The fires of 1982–1983 and 1997–1998 burnt up to 85% of the vegetation on the peatland. Although charcoal analyses show that fire has occurred throughout the history of the peatland, it is rare in forests remote from rivers until the last 3000 years and only common within the last millennium. Fires are earlier and more frequent in sites accessible from waterways, and floodplains have been widely burnt down to water table or below, forming extensive lakes.

Up to 2.3 m long sediment sequences were recovered from the deepest part of Lake Hoare in Taylor Valley, southern Victoria Land, Antarctica. Sedimentological, biogeochemical, and mineralogical analyses revealed a high spatial variability of these parameters in Lake Hoare. Five distinct lithological units were recognized. Radiocarbon dating of bulk organic carbon samples from the sediment sequences yielded apparently too old ages and significant age reversals, which prevented the establishment of reliable age-depth models. However, cross correlation of the sedimentary characteristics with those of sediment records from neighbouring Lake Fryxell indicates that the lowermost two units of the Lake Hoare sediment sequences were probably deposited during the final phase of proglacial Lake Washburn, which occupied Taylor Valley during the late Pleistocene and early Holocene. High amounts of angular gravel and the absence of fine-grained material imply a complete desiccation with subaerial conditions in the Lake Hoare basin in the middle of the Holocene. The late Holocene (< c. 3300 calendar yr bp) is characterized by the establishment of environmental conditions similar to those existing today. A late Holocene desiccation event, such as proposed in former studies, is not indicated in the sediment sequences recovered.

A 270 cm long sediment sequence was recovered with a piston corer from east lobe Bonney, Taylor Valley, Antarctica, and characterized according to its sedimentological, mineralogical, and geochemical properties. It is the first record of such length recovered from east lobe Bonney. The sediment core is mainly composed of halite crystals of different sizes, water, and a relatively low and stable proportion of clastic particles. Although the sediment surface was probably disturbed by the coring process and absence or low contents of organic material or carbonates hampers the establishment of a robust chronology by radiocarbon dating, the core probably contains at least several hundred years of information about the history of the lake and the Bonney basin. Variations in halite crystal sizes and amount as well as variations in the composition of clastic material can be related to past lake level changes and evaporation cycles.

A growing body of literature is using sclerochronological information to infer past climates. Sclerochronologies are based on series of skeletal growth records of molluscs that have been correctly aligned in time. Incremental series are obtained from a number of shells to assess the temporal control and improve the climate signal in the final chronology. Much of the sclerochronological theory has been adopted from tree-ring science, due to the longer tradition and more firmly established concepts of chronology construction in dendrochronology. Compared to tree-ring studies, however, sclerochronological datasets are often characterized by relatively small sample size. Here we evaluate how effectively palaeoclimatic signal can be extracted from such a suite of samples. In so doing, the influences of the very basic methods that are applied in nearly every sclerochronological study to remove the non-climatic growth variability prior to palaeoclimatic interpretations, are ranked by their capability to amplify the desired signal. The study is performed in the context of six shells that constitute a bicentennial growth record from annual shell increments of freshwater pearl mussel. It was shown that when the individual series were detrended using the models set by the mean or the median summary curves for ageing (that is, applying Regional Curve Standardization, RCS), instead of fitting the ageing mode statistically to each series, the resulting sclerochronology displayed more low-frequency variability. Consistently, the added low-frequency variability evoked higher proxy–climate correlations. These results show the particular benefit of using the RCS method to develop sclerochronologies and preserve their low-frequency variations. Moreover, calculating the ageing curve and the final chronology by median, instead of mean, resulted in an amplified low-frequency climate signal. The results help to answer a growing need to better understand the behaviour of the sclerochronological data. In addition, we discuss the pitfalls that may potentially disrupt palaeoclimate signal detection in similar sclerochronological studies. Pitfalls may arise from shell taphonomy, water chemistry, time-variant characters of biological growth trends and small sample size.

This study is the first published survey of diatom-environment relationships on sub-Antarctic Macquarie Island. Fifty-eight sites in 50 coastal and inland lakes were sampled for benthic diatoms and water chemistry. 208 diatom species from 34 genera were identified. Multivariate analyses indicated that the lakes were distributed along nutrient and conductivity gradients. Conductivity, pH, phosphate (SRP), silicate and temperature all explained independent portions of the variance in the diatom data. Transfer functions provide a quantitative basis for palaeolimnological studies of past climate change and human impacts, and can be used to establish baseline conditions for assessing the impacts of recent climate change and the introduction of non-native plants and animals. Statistically robust diatom transfer functions for conductivity, phosphate and silicate were developed, while pH and temperature transfer functions performed less well. The lower predictive abilities of the pH and temperature transfer functions probably reflect the broad pH tolerance range of diatoms on Macquarie Island and uneven distribution of lakes along the temperature gradient. This study contributes to understanding the current ecological distribution of Macquarie Island diatoms and provides transfer functions that will be applied in studies of diatoms in lake sediment cores to quantitatively reconstruct past environmental changes.

New evidence regarding the origins of the Crustacea of Antarctic lakes is reviewed. Palaeolimnological data indicates that the cladoceran Daphniopsis studeri has been present in Lake Reid, Larsemann Hills, for over 120 000 yr. This is the first direct evidence of a continental lacustrine refugium during the last glacial maximum. There are strong indications that the calanoid copepod Boeckella poppei maintained populations over the same period in lakes of the Amery Oasis, and the rapid post-glacial colonization by this species of newly formed lakes on the Antarctic Peninsula and Signy Island argues for a local rather than an extra-continental source. Evidence for the entry of marine-derived species into the longer term fauna of the continent is also presented. It is concluded that many of the Crustacea in Antarctic lakes are likely to have had a long association with the continent.

Lake sediment cores from Midge Lake, Livingston Island, South Shetland Islands and Sombre Lake, Signy Island, South Orkney Islands were analysed for volcanic tephra using light microscopy and magnetic susceptibility. Cores were dated using published 14C and 210Pb chronologies. Electron probe microanalyses of discrete tephra glass shards were undertaken to characterise the tephra geochemically in order to identify possible source volcanoes and refine tephrochronological data for the region. Results identified five tephra horizons in a core from Midge Lake. Four of these tephra at 3–4 cm, 8–9 cm (c. 450 yr BP), 15–16 cm (c. 755 ± 105 yr BP) and 21–22 cm (c. 1340 ± 100 yr BP) consisted of sodic basaltic to basalticandesitic glasses, containing abundant labradoritic feldspar inclusions, and a single ‘acidic’ tephra was found at 2–3 cm. Seven tephra horizons were identified in the Sombre Lake core including three basaltic tephra at 3–9 cm (30 ± 4 yr BP to 125 ± 25 yr BP), 31–32 cm and 44–46 cm (1325 ± 50 14C yr BP) and four acidic tephra at 21–22 cm and 24–25 cm, 33–36 cm (c. 1021 14C yr BP) and 54–56 cm (c. 1450 14C yr BP). These are the first tephra to be identified from the South Orkney Islands. Geochemical and grain size analysis indicated that the analysed Midge Lake tephra were derived from the Quaternary Deception Island volcano. Smaller grain sizes, congruent geochemical data and prevailing wind directions also indicate this volcano as the likely source of Sombre Lake tephra. Results highlight the importance of establishing geochemical consistency between tephra deposited across wide geographical areas, during apparently synchronous time periods, if they are to be used in a regional tephrochronology.

Two sediment cores taken from Jaw lake (Bunger Hills, East Antarctica) were analysed for diatom composition and abundance. A diatom-salinity transfer function developed for the nearby Vestfold Hills was used to determine palaeosalinity reconstructions from the assemblages preserved in each of the cores. There is a large step-wise decrease in salinity in the second core from at least c. 4000 to c. 2000 uncorrected 14C yr BP. The salinity record from the first core starts at c. 3000 uncorrected 14C yr BP and is comparable with the salinity of the second core between c. 3000 and c. 2000 uncorrected 14C yr BP. Sudden lake water dilution in both cores at c. 1900 uncorrected 14C yr BP is followed by brief increases in lake water salinity between c. 1900 and c. 500 uncorrected 14C yr BP, after which gradual dilution to present occurs. This analysis of the local environmental history of this saline lake reveals a mid–late Holocene evolution of the lake basin similar to that documented from earlier marine and freshwater lacustrine sediments in the Bunger Hills. The high coherence of the independent sediment records suggests a robust general palaeosalinity reconstruction of the lake is achieved in addition to providing evidence for the fidelity of single sediment cores as useful and adequate representation of the palaeolimnological histories of Antarctic lakes.

Contemporary phytoplankton and palaeolimnological studies were made of the algal response to acidification and liming in three lakes in Hälsingland, central Sweden (Njupfatet, Sjösjön, Djuptjärn). Surveys and experimental studies of the phytoplankton response to liming were undertaken at Njupfatet, together with an experiment designed to determine the possible role of lake sediments as an inoculum for any new species arriving in the water column. Liming had little quantitative or qualitative effect on the phytoplankton diversity at Njupfatet, but did result in the loss of the dominant contributor to algal biomass, Merismopedia tenuissima. None of the four new species recorded in the lake following liming was hatched from the sediment inoculum experiment. A freeze core from Njupfatet was dated by 210Pb and carbonaceous fly-ash particle profiles were also determined for Njupfatet and Sjösjön, which provided an approximate chronology for the latter lake. Diatom analyses were made of the three lakes and pH and dissolved organic carbon inferred using weighted averaging methodology. Njupfatet had no planktonic diatoms over the last 200–300 years, and was dominated by benthic diatoms, but the diatom-inferred pH suggests that the lake was acidified to pH < 5 prior to liming in 1989. Both Djuptjärn and Sjösjön were dominated by planktonic diatoms, and were acidifying from (c. 1970) prior to liming, Sjösjön from pH 6 to ∼ 5 and Djuptjärn from 6·5 to ∼ 5·5. These pH inferences suggest that at least some lakes in this region are susceptible to atmospheric acidification. The response of the diatoms to liming is discussed, in particular the rapid expansion at Njupfatet, of Cyclotella glomerata a diatom which was also present in Sjösjön for a period prior to acidification, and at other lakes in south-west Sweden. Possible reasons for the expansion of this small centric diatom are discussed.

Two sediment cores from acid lake Store Hovvatn were analysed for chironomid head capsule remains over a sequence spanning from about 1730 A.D. to the late 1970s. Up to 30 taxa were identified from one (0.5 cm) level in the cores. Principal component analysis of taxon relative abundances showed a gradient corresponding more or less to the sediment sample chronology. Redundancy analysis with some chemostratigraphical variables, and with pH values inferred from diatoms, indicated that chironomid community change could be explained as a response to acidification. However, most of the taxa that declined or disappearedup-core are known to occur in acid lakes and pH sensitivity per se does not seem to explain the response of individualspecies. The relative abundance of Orthocladiinae increased up-core and the long term change may be conceived in terms of a retarded productivity or oligotrophication. The most conspicuous change in the chironomid community appears to coincide with decreasing aluminium concentrations in the sediments and may indicate toxic effects from labile aluminium in the water column.