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The paper presents isolation basin stratigraphy in bottom sediments from nine lakes in the Teriberka area on the Kola Peninsula, northwestern Russia. Isolation contacts in these basins, identified from lithological and diatom analysis, were used together with 25 radiocarbon dates, to construct a relative sea-level (RSL) curve for the Holocene. Records of marine water re-influx were found in the sediment sequence from one lake, located at c. 17 m a.s.l. The re-influx of marine water seems to be caused by the mid-Holocene (Tapes) transgression and tsunami event. The RSL curve indicates several phases in the postglacial evolution of the Kola coast. An early phase of rapid sea-level fall of c. 32 m around 11,500 cal yr BP, at a rate of c. 40 mm per year, corresponds to glacio-isostatically induced emergence following deglaciation at the Younger Dryas and beginning of the Holocene. In the time interval between c. 11,000 and 7600 cal yr BP, either a stillstand or a slight rise in relative sea level, cresting at about 21 m a.s.l., is suggested in the Teriberka area. This is followed, after c. 7300 cal yr BP to the present day, by a slow glacioisostatic emergence with an average rate of about 2–3 mm per year. [ABSTRACT FROM AUTHOR]

Although Rapa Nui has been proposed as a classic example of cultural collapse, this hypothesis has been repeatedly questioned. This paper investigates cultural continuity on Rapa Nui following the onset of deforestation through a study of red ochre pits. Red ochre pigments are well-known from various contexts on Rapa Nui, but until recently its origin and the extraction process involved in their production were not precisely understood. New excavations have revealed the presence of multiple pits used for pigment production and storage by the island's prehistoric culture. Previous geoarchaeological studies, including geomorphological, pedological, geochemical and micromorphological analyses, have shown that the pits contain fine layers of reddish iron oxides (ochre), which result from repeated intentional burning. The oxide layers alternate with thin layers of phytoliths, interpreted as the remains of plant material used as fuel, and diatoms. This paper presents new phytolith and diatom data from the previously described site of Vaipú East, complemented with data from similar pits at the new sites of Vaipú West and Poike. New 14C dates are also presented from these sites. The phytolith and diatom data provide crucial information about the chaîne opératoire of the ochre production and the formation processes associated with the pits. The evidence of pigment production and storage at Vaipú East shows that labour-intensive ochre production took place on Rapa Nui during at least two separate phases after deforestation, while the pits discovered at other sites indicate that Vaipú East did not stand alone. This provides a further line of evidence in favour of cultural continuity rather than collapse following deforestation in the island's late prehistory. [ABSTRACT FROM AUTHOR]

The paper is focused on changes in biodiversity, the environment, and human activity in the Uvs Nuur Basin during the last three millennia based on biological and geochemical proxies from the lake Bayan Nuur. Regions with high biodiversity and relatively low anthropogenic pressures are typically the most vulnerable to both climate change and human activities. One such area is the Uvs Nuur Basin located on the north of the Great Lake Depression of Mongolia. The main objective of this study is to assess changes in the past biodiversity of the lake's microflora and microfauna, and surrounding vegetation biodiversity in the Uvs Nuur Basin, and to determine the main drivers of diversity change. Based on the analysis of pollen and chironomids we conclude that the most humid and afforested phase was between 1400 and 1800 CE. We assume that the Little Ice Age in the Uvs Nuur Basin was humid with mean annual precipitation ca. 305 mm/year and mean July temperature about 13°C. Conversely, the warmest and most arid period was between 650 and 1350 CE with mean annual precipitation ca. 280 mm/year and mean July temperature of about 16°C, attributed to the Medieval Warm Period. The biodiversity of terrestrial plants, chironomids, and Cladocera positive react to changes in annual precipitation and July temperature, whereas diatoms do not correlate directly to the climatic factors. The diversity and the evenness of plants are strongly correlated with the change in the leading biomes. The calculated species turnover suggests no significant changes in plant and Cladocera taxa composition, but significant changes in diatom and chironomid communities. This may be explained by the instability of lake ecology due to the fluctuation of the salinity and acidity of the water. An additional aim was to assess if dung fungi in lacustrine sediments reflect changes in human population density around the lake. We found that neither historical sources of human presence nor the influx of coprophilous fungi are correlated with the inferred climate changes. Coprophilous fungi can be used as individual or additional sources of assessment for the peopling and human-related herbivore density including overgrazing of the studied area. [ABSTRACT FROM AUTHOR]

The climate variability and related sea-level changes during the Holocene are still under discussion, especially in a regional context. Very little information comes from the southern and south-eastern Baltic coast. The aim of the paper is to gain insight on the history of regional environmental changes, particularly sea-level and storminess, and their driving forces. The investigations were located on a peatland on the coast of Puck Lagoon (Gulf of Gdańsk, southern Baltic Sea). The analysis of peat core comprised: radiocarbon dating, analysis of stable isotopes 18O and 13C and chemical components, as well as palynological and diatomic studies. Results showed the 1.0 m peat section accumulated over 1500 years, with a time resolution of 100 years per sample. The average water level in the Puck Lagoon rose by ca. 0.85 m during the last 1500 years in a cyclic mode, with a period cycle of ca. 600–550 years and an amplitude not exceeding 0.5 m. The accelerated sea level rise and frequent storminess occurred during the first half of the Dark Ages (1500−1300 years b2k) and LIA (750−450 years b2k) and since the beginning of the 20th century. Recognized environmental changes are well correlated with both temperature changes in the North Atlantic and changes in total solar irradiance, suggesting synchronous Northern Hemisphere-wide fluctuations. The solar forcing was an important constituent of natural climate variability in the past and of forcing climate warming during modern times - after the Little Ice Age. [ABSTRACT FROM AUTHOR]

The hemispheric-scale climatic fluctuations during the Holocene have probably influenced the large Siberian rivers. However, detailed studies of the West Siberian Plain postglacial environmental change are scarce and the records of millennial-scale palaeohydrology are nearly absent. This paper presents the Holocene palaeoecological reconstruction based on the sedimentary record of Lake Svetlenkoye, located near the confluence of major Siberian rivers Ob and Irtysh. Postglacial history of flooding, dynamics of regional and local vegetation, sedimentation regime, geochemical changes and lake water pH were reconstructed based on multi-proxy studies. We used palaeobotanical (plant macrofossils, pollen, diatoms), geochemical (organic matter, total organic carbon and nitrogen content, carbon/nitrogen ratio) and chronological (14C dates, spheroidal fly-ash particle counts) methods. The studied sediment section started to accumulate ~11,400 cal. yr BP. The initial shallow water body was flooded by Ob River waters ~8100–8000 cal. yr BP as confirmed by a remarkable increase in the sedimentation rate and the accumulation rate of the aquatic vegetation proxies. The period of flooding coincides with the high humidity periods reconstructed from regional palaeobotanical records. About 6800–6700 cal. yr BP, the study site became isolated from the Ob River floodplain and remained a small lake until present. The diatom-based lake water pH estimates suggest fluctuations in the pH values during the Holocene, the recent decrease since 1960s being the most notable. The vegetation record revealed constant postglacial presence of tree taxa – Betula, Pinus and Picea – although in different pollen ratios and accumulation rates through time. The paludification of the surroundings occurred since ca. 8500 cal. yr BP. [ABSTRACT FROM AUTHOR]

In this paper, we summarize the Holocene environmental history of the lower Yangtze region, east China, based on the sedimentary records and microfossil diatom, pollen, fungal and charcoal data that were published in the past two decades. We then examine the linkage between changes in the coastal environment and the development of rice agriculture in the region, with reference to the available archaeological evidence and historical archives. Based on the sedimentary and archaeological evidence, we conclude that during the early Holocene sea-level movements and sedimentary processes significantly changed the region’s landscape from an open, brackish water environment to a largely enclosed, wetland system. This newly established freshwater marsh environment provided a habitat favourable to rice agriculture. The early Neolithic farmers took the opportunity presented to them and started rice cultivation in locations where freshwater wetland systems were established. During the middle Holocene, environmental conditions were largely stable, and the coastal wetlands evolved slowly. Environmental change was only a supportive player in the Neolithic cultural processes, because the Neolithic people were able to adapt to these changes and took advantages of the newly emerging marsh land for food collection and production. Around 4200 years ago, the prosperous Liangzhu society fell, but there is no evidence to suggest the fall was related to a significant environmental change. The coastal environment continued to evolve slowly during the late Holocene. But this period saw rapid technological development in irrigation and flood protection, and the environmental factor was reduced to background noise. Throughout the Holocene, the main strategy taken by the Neolithic people to cope with environmental change was migration to find better food sources. Along with this strategy was the development of technology in landscape management to ensure a more reliable food production in addition to food collection through hunting, gathering and fishing. [ABSTRACT FROM AUTHOR]

A key concern in the assessment of the recovery of acidified lakes from the effect of acid deposition is the reference pH of acidified lakes and how reference values can be used to establish targets for restoration. In this paper we evaluated the accuracy of three different, although overlapping, diatom-pH transfer functions using UK Acid Waters Monitoring Network (AWMN) data to compare inferred pH from diatoms collected in annually exposed sediment traps with measured water column pH for 11 acid-sensitive lakes. We then used these transfer functions to infer lake-water pH from approximately AD 1850 (taken as the reference date) to AD 1990 (the core-top date) for radiometrically dated sediment cores from each site. When applied to the sedimenttrap samples all three models tended to underpredict measured pH in the less acidic sites, with the SWAP model being the most biased. All three models were in good agreement in reconstructing pH for the AD 1850 reference period. Reference pH varied between sites from approximately 4.9 to 6.4, and was correlated with modern basecation status. In the acidification phases of the cores discrepancies in pH inference between models appear to be linked to differences in pH optima for a minority of taxa. Current (2006) diatom-inferred pH values from the most recent sediment traps, when compared with sediment core tops, provide evidence of recovery at most sites but its extent, so far, is slight when compared with the reference period. The substantial difference between sites in their reference conditions indicates clearly that recovery success can not be measured against a single target pH or, by inference, ANC value and must be assessed on a site-specific basis. [ABSTRACT FROM AUTHOR]

Dallund Sø, a lake on the island of Funen, Denmark, is positioned in a landscape that has been heavily impacted by human activities and land-use change over thousands of years. In 1998 a project was initiated to utilize a variety of palaeoecological analyses to investigate lake response to changing land use through the period of agricultural impact on the Danish landscape, i.e., the last 6000 years. This paper describes the overall aims of the study, the natural and cultural setting, sediment core collection, sampling and physical properties, the chronology and erosion history. The long-term changes in the terrestrial and aquatic ecosystem are assessed in the following papers in this Research set using (i) pollen, (ii) diatoms, macrofossils and Pediastrum and (iii) zooplankton. These papers are followed by a synthesis paper focusing on the linkage between land-use change and lake development. [ABSTRACT FROM AUTHOR]

This paper presents a multiproxy high-resolution study of the past 2600 years for Seebergsee, a small Swiss lake with varved sediments at the present tree-line ecotone. The laminae were identified as varves by a numerical analysis of diatom counts in the thin-sections. The hypothesis of two diatom blooms per year was corroborated by the [sup 210]Pb and [sup 137]Cs chronology. A period of intensive pasturing during the 'Little Ice Age' between AD 1346 and AD 1595 is suggested by coprophilous fungal spores, as well as by pollen indicators of grazing, by the diatom-inferred total phosphorus, by geochemistry and by documentary data. The subsequent re-oligotrophication of the lake took about 88 years, as determined by the timelag between the decline of coprophile fungal spores and the restoration of pre-eutrophic nutrient conditions. According to previous studies of latewood densities from the same region, cold summers around AD 1600 limited the pasturing at this altitude. This demonstrated the socio-economic impact of a single climatic event. However, the variance partitioning between the effects of land use and climate, which was applied for the whole core, revealed that climate independent of land use and time explained only 1.32% of the diatom data, while land use independent of climate and time explained 15.7%. Clearly land use influenced the lake, but land use was not always driven by climate. Other factors beside climate, such as politics or the introduction of fertilizers in the seventeenth and eighteenth centuries also influenced the development of Alpine pasturing. [ABSTRACT FROM AUTHOR]

Geological investigations of coastal sediment sequences play a key role in verifying earthquake and tsunami characteristics inferred from historical records. In this paper, we present a multi-proxy investigation of a coastal lowland site facing the Nankai-Suruga megathrust and appraise evidence for tsunamis and earthquake-triggered terrestrial mass movements occurring over the last 800 years. Combining a high-resolution chronology with X-ray computed tomography and analyses of particle size, diatoms, pollen, non-pollen palynomorphs and aerial photographs, we present the most compelling geological evidence of the 1361 CE Kōan (also known as Shōhei) tsunami reported to date from any site along the megathrust. This finding is consistent with either of two recent hypotheses: a single larger rupture of both the Nankai and Tōnankai regions or two smaller ruptures separated by a few days. Enhancing the site chronology using Bayesian age modelling, we verify evidence for inundation during the 1498 CE Meiō tsunami. While previous investigations identified evidence for historically recorded tsunamis in 1605, 1707 and 1854 CE and a storm surge in 1680 or 1699 CE, we encountered a thick sand layer rather than discrete extreme wave deposits in this interval. The overprinting of evidence highlights the potential for geological records to underestimate the frequency of these events. A terrestrial mass movement also deposited a sand layer at the site; radionuclide dating and aerial photographs provide independent confirmation that this may have been triggered by intense shaking in 1944 CE during the most recent great Nankai-Suruga megathrust earthquake. [ABSTRACT FROM AUTHOR]

Much geological evidence points to repeated plate-boundary earthquakes on the Cascadia subduction zone, Pacific Northwest USA. Current land motions, calculated using short-term (100 yr) tide gauge, repeat levelling and other geodetic data, record deformation during the present interseismic period. These short-term data form the basis of efforts to model longer-term plate-boundary deformation and assess seismic hazard in this region. In this paper we use relative sea-level (RSL) data from the last 4000 cal. yr BP to examine four aspects of these plate-boundary deformation models over several earthquake cycles: rates of isostatic rebound, the spatial pattern and magnitude of coseismic deformation, and rates of interseismic strain accumulation. Age/altitude plots of RSL data from a 300-km-long string of sites stretching from Copalis River (central Washington) to Alsea Bay (central Oregon) reveal a systematic north- south decline in the rate of isostatic rebound equal to c. 0.25 +- 0.02 mm yr1 100 km 1 . High precision microfossil and RSL data from Johns River (Washington) and Netarts Bay (Oregon) register repeated episodes of late-Holocene coseismic submergence. This is contrary to the coseismic uplift expected, based on differences in uplift rates calculated using late-Quaternary marine terrace data from the region. Moreover, the magnitudes of coseismic submergence inferred from these RSL data are typically half the modelled predictions based on current deformation rates. Lastly, we identify evidence from Netarts Bay for pre-seismic RSL rise of up to 0.4 mm yr1 in the decades immediately preceding each episode of marsh burial. Together, our findings shine new light on models of rapid relative sea-level rise in the Pacific Northwest, and highlight the need to strengthen further the dialogue between long-term geological and short-term geodetic studies in this region. [ABSTRACT FROM AUTHOR]

Micropalaeontological techniques play an important role in high-resolution studies of sea-level change. Salt-marsh foraminifera are among the most valuable groups of sea-level indicators as their distribution shows a narrow vertical zonation which can be accurately related to former sea level. This paper focuses on testate amoebae (`thecamoebians'), a closely related group of protozoans which have also been widely reported in salt marshes, but only in low numbers and diversities and only in the size fraction used in foraminiferal analyses (63 mum). A new preparation technique is described which is based on the analysis of the 63 mum fraction using high power light microscopy. This technique is applied to surface sediment samples from a salt marsh in the Taf estuary in south Wales. The results show that small testate amoebae (63 mum) are much more abundant and diverse in salt-marsh sediments than the larger testate amoebae (63 mum). Species diversity increases from 2 (63 mum) to 36 (63 mum) and the maximum abundance is 65 600 individuals per cm 3 . The assemblages display a distinct spatial zonation across the marsh surface which appears to be closely related to elevation and to tidal parameters. The surface distribution of the testate amoebae is compared with the distribution of foraminifera and diatoms at the same site. The implications of using 63-mum testate amoebae as a tool for sea-level reconstruction are discussed. [ABSTRACT FROM AUTHOR]

Sedimentary charcoal, diatom and phytolith records of the past 1500 years at Elk Lake, Minnesota, in combination with sediment trap studies and a transect of surface sediment samples, document the mechanisms by which previously deposited charcoal is redeposited and finally buried in this lake. The frequent correspon dence of high diatom concentrations and peaks of phytolith and charcoal fragments suggests that currents and turbulence related to lake circulation are responsible for winnowing charcoal and phytoliths from shallow water depositional sites to deeper areas of the lake. High diatom concentrations in the record relate to increased nutrient fluxes also supplied by circulation. Despite the fact that the watershed and area around Elk Lake has not been burned since AD 1922, charcoal continues to reach the profundal zone from littoral source areas in Elk Lake. The variable redeposition of within-lake charcoal requires evaluation before fire-history records can be related to global, regional or even local fire events. [ABSTRACT FROM PUBLISHER]

Ecosystem changes of the coastal areas of the East China Sea (ECS) during the past 30 years have been characterized by increased productivity and increased occurrences of dinoflagellate red tides; both were commonly attributed to be caused by anthropogenic input of nutrients. However, climate-driven regime shifts were found in the Pacific, but they have not been observed in the ECS owing to the lack of continuous high resolution data. Hence, it is still a challenge to distinguish the influences of anthropogenic activities and climate changes on ECS shelf ecosystem. We compare phytoplankton biomarker (brassicasterol, dinosterol, and alkenones) data of five box cores from the coastal area of the ECS, which afford phytoplankton productivity and community structure records at decadal-scale resolution for the last 100 years. Phytoplankton productivity in all cores increased during the past 50 years, but community structure changes showed different trends. Relative diatom contribution revealed a decreasing trend during the past ca. 50 years in cores DH5-1 and CJ43 collected near the Changjiang Estuary, which were likely caused by increased N/Si and N/P ratios, providing conditions more favorable for dinoflagellates growth. In contrast, the relative diatom contribution increased in cores 32, 34, and DH6-3 further away and south of the Changjiang Estuary, suggesting limited influence of the Changjiang water. Instead, diatom increasing trend is likely caused by increased supply of phosphorus and silicate, as a result of larger Kuroshio intrusion flux and the corresponding strengthened coastal upwelling. Therefore, both anthropogenic activities and climate-driven coastal upwelling have contributed to increased productivities, but these two forcing mechanisms have resulted in contrasting community structure changes at different sites in the coastal area of the ECS. [ABSTRACT FROM AUTHOR]

The Peruvian coastal upwelling is one of the most productive systems in the global ocean, with important impacts on the carbon cycle. Primary productivity there displays strong variations at the interannual to decadal timescales. However, down-core investigations rarely reach sufficient temporal resolution to assess the response of productivity to climatic variations at these timescales beyond the instrumental and historical periods. We here analyzed diatom assemblages, sea-surface temperatures (SSTs), and nitrogen and organic carbon contents on a laminated sediment core from the Peruvian continental shelf to trace variations in regional productivity over the last 3000 years. Our record provides evidence for different climatic and oceanic conditions with more humid and less productive conditions older than 2500 cal. yr BP and drier and more productive conditions younger than 2500 cal. yr BP. The last 2500 years also present much stronger centennial-scale variability with the occurrence of six intervals with higher total diatom abundances and stronger percentages in upwelling-related diatom species, representative of intensified productivity, congruent to lower percentages in benthic diatoms, indicative of reduced rainfall. These six periods were synchronous to intervals of enhanced Walker circulation, suggesting a strong imprint of the Pacific zonal circulation on productivity variations off Peru. Our record also demonstrates that SSTs did not vary in phase with productivity, arguing against the idea of regional SSTs controlled by the upwelling intensity, but were rather in agreement to SST records off southern Chile, suggesting that Peruvian SST variations were largely controlled by oceanic currents at southern high latitudes. [ABSTRACT FROM AUTHOR]

A paleolimnological record from the central Messenian plain (southwestern Peloponnese, southern Greece) indicates rapid changes in the water level and chemistry of a transient lake on the flanks of the Taygetos Mountains during the last c. 6000 years. The analyses are based on diatoms as well as carbon and nitrogen isotopes from bulk sediments in a 7.5-m-long sediment core retrieved from the drained fen of Agios Floros, at the northern banks of the ancient River Pamisos. The sequence consists of fen peat in the uppermost section underlain by lacustrine sediments, which are punctuated by two layers of clay with diatomaceous silt bands. High accumulation rate is recorded in the oldest part of the section (up to 23 mm/yr), particularly during two decadal-long periods centered at c. 5700 and c. 5300 cal. BP. The diatom record reveals pronounced peaks in the planktonic taxon Cyclotella distinguenda, which correspond to the laminated sequences, reflecting the rapid development of a deep lake with an open water environment during these two time periods. Another two events with intermediate water levels are inferred at c. 5200 and c. 4600 cal. BP. These short-lived phases were probably, to a large extent, caused by local tectonic processes and the consequent hydrological anomalies of the nearby karst springs, although abrupt climatic changes with enhanced precipitation might have also played a role. At c. 4500 cal. BP, our data suggest the development of terrestrial conditions in this area, which can be attributed to the decreasing activity/dry up of springs, probably associated with more arid climate. After c. 2500 cal. BP, the diatom record infers a return to wetter conditions, probably as a response to more humid climate with marked seasonality and human activities, developing the present-day environment with cultivated and seasonally semi-flooded fields. [ABSTRACT FROM AUTHOR]

Sediments from Lake Petit (2200 m a.s.l., Southern Alps) are particularly relevant for analysis of coupled landscape palaeoecology and palaeolimnology. Diatom assemblages, organic matter composition of sediments (total nitrogen and organic carbon) and Pediastrum boryanum concentrations were obtained from a 144-cm-long core, enabling the reconstruction of the aquatic ecosystem over nearly the last 5000 cal. BP. From 4800 to 4300 cal. BP, Lake Petit was a stable diatom-productive water body dominated by alkaliphilous diatoms (Staurosirella pinnata). During this period, nutrients and cations were supplied by the chemical weathering of podzols that developed under conifer woodlands. This overall stability was suddenly interrupted at 4200 cal. BP by a major detrital pulse that was probably climate linked (4200 cal. BP event) and that triggered a drop in diatom productivity and diversity. From 4100 to 2400 cal. BP, diatom productivity progressively decreased, whereas Pediastrum developed. Diatom assemblages were more diversified (predominance of Pseudostaurosira robusta, P. brevistriata and P. pseudoconstruens) and reflected a regime of continuous erosion, whereas slopes were colonised by grazed grasslands. Finally, from 2400 cal. BP to the present day, diatom assemblages reveal a slight acidification and nutrient enrichment of waters concomitant with increasing human pressure in the catchment. These results demonstrate the close links between ecosystems and the ready propagation of disturbances throughout watersheds that might lead to abrupt regime shifts in such alpine environments. [ABSTRACT FROM AUTHOR]

Central Chile is heavily exploited for mineral and water resources, with agriculture and large urban populations all creating intensive landscape use. Few records of past environmental and climate change are available that afford a broader context. To aid in this assessment, we present a 700-year reconstruction from Laguna del Maule (LdM) in the high Andes of central Chile based on sedimentological, geochemical, diatom and pollen analyses. The age model is based on 210Pb/137Cs and 14C dating tied into known volcanic eruptions. Sedimentology consists of organic-rich sediments and diatom oozes with several interspersed volcanic-rich facies and two tephra deposits. Sediment geochemistry exhibits increased productivity (high Br/Ti, biosilica) and more dominant oxic conditions (high Fe/Mn) from AD 1300 to 1400 and from AD 1650 to 1850, likely during periods of relatively lower lake levels and better development of littoral environments. However, during this later period, high elevation vegetation was dominant, indicative of regional cooler/wetter conditions. In contrast, sediments deposited from AD 1850 to 1930 evidence decreased productivity and increased anoxic lake bottom conditions. The ‘Little Ice Age’ (LIA) in LdM is characterized by significant variations in lake dynamics and hydrology with cooler/wetter conditions (AD 1570–1700), major environmental changes in the 18th century and ending at ca. AD 1850. LdM record documents the impact of the LIA in the southern hemisphere and stresses the global nature of this climate period. Large changes in lake dynamics and diatoms assemblages during the 20th century could be related to anthropogenic impacts, but recent changes in climate patterns cannot be excluded. [ABSTRACT FROM AUTHOR]

Palaeoclimatic reconstructions from lake sediment biological records can be challenging, due to variation in non-climatic factors, which alter ecosystem responses. To consider this, it is important to replicate a study regionally, so as to gain information on spatial variability of ecosystem response and the influence of site-specific conditions. Previous pollen-based palaeoclimatic records from three well-dated Arctic lake sites highlight the response of regional Scots Pine (Pinus sylvestris) and Mountain Birch (Betula pubescens ssp. czerepanovii) forest-tundra transition to Holocene climatic variability and suggest the northernmost Peninsulas of Finnmark to be climatically sensitive. This study analysed dated sediment sequences between c. 3970 and c. 6200 cal. yr BP from these three previously published shallow lakes: Liten Čap’pesjav’ri (LCJ), over Gunnarsfjorden (OGF) and over Kobbkrokvatnet (OKV), for freshwater diatoms. Diatom assemblages showed an increase in the planktonic diatoms relative to benthic diatoms, with an onset towards higher abundances of small centric planktonic diatoms at OGF (between c. 5270 and 5350 cal. yr BP) and OKV (between c. 5280 and 5350 cal. yr BP). Additionally, a diatom compositional shift was detected at LCJ between c. 5180 and 5300 cal. yr BP. Trend analysis found the main diatom compositional change at all three sites to occur at 5300 cal. yr BP. However, this synchronous diatom shift during the mid-Holocene varies in magnitude within the three Finnmark lakes. The abrupt planktonic:benthic diatom ratio changes are independent of the Pinus:Betula ratios and are likely to be a result of lake ice-cover changes, allowing longer growing seasons, greater water column stability and higher nutrient concentrations from surrounding catchments. This study highlights the significant differences in aquatic ecosystem and terrestrial vegetation response to climatic changes, with diatom assemblages at these sites either responding before the regional tree-line shift or to a separate climatic event within the mid-Holocene. [ABSTRACT FROM AUTHOR]

Peatlands in northern Ontario, Canada, archive multiple biological indicators, including macrofossils, algae, testate amoebae, and pollen. These proxies can provide insights concerning the timing and nature of long-term climatic and environmental changes. The Hudson Bay Lowlands (HBL) of central Canada contain one of Earth’s largest continuous peatland complexes, and thus comprehensive spatial and temporal studies are needed to understand the implications of climate change on carbon cycling. Diatom assemblages were examined in three cores retrieved from ombrotrophic bogs across two Canadian terrestrial ecozones. Comparisons were made with testate amoebae and macrofossil data previously analyzed from these cores, as well as with regional pollen records from surrounding peatlands. From ~2000 to ~600 cal. BP, changes in diatom composition likely reflect hydrosere succession within the peatland, including fluctuations in connectivity to the water table and pH changes. From ~600 cal. BP to present, the synchronous timing of changes in diatoms and testate amoebae are tracking drying conditions and subsequent microhabitat variations that occur within bogs. It is possible that diatoms are tracking subtle changes in the stability of peat microforms including bog hollows and hummocks, highlighting their sensitivity to small chemical change, whereas testate amoebae are tracking the lowering of a peatland water table and subsequent drying of the peatland. The use of multiple proxies provides a more holistic approach to interpreting past ecological succession and responses to climate within peatlands. When present and well preserved, diatoms can be applied to track drying conditions in bogs, in terms of both hydrosere succession and present climatic change. [ABSTRACT FROM AUTHOR]

A multiproxy study of a 7 m long sedimentary sequence from Lake La Parra (39°50.948′, 1°52′, 1014 m a.s.l.) supported by 11 14C AMS and 210Pb/137Cs dates provides a robust, high-resolution hydrological and environmental variability record for the last 1600 years of the Las Torcas sinkhole Complex in the Central Iberian Range. The succession of depositional environments in Lake La Parra sinkhole is controlled by both changes in the regional water table and by the balance between sedimentary input through ephemeral creeks and in-lake production of carbonates and organic matter. Although synergetic links with climate are likely, phases of increased sediment delivery to the lake at c. ad 500–700, c. ad 1000, ad 1450–1500, ad 1550–650 and since 1700 till recent times are driven primarily by human impact in the watershed. Prior to c. ad 300, the sinkhole was dry, then became a lake at the end of the Roman Period (ad 350) when the doline was flooded, and it has not dried out during the last 1600 years. Moderate lake levels with deposition of coarser clastic facies dominated up to the 12th century (ad 400–1200), and relatively higher levels with deposition of laminated facies during the 13th–15th centuries (ad 1200–1600). The pattern of palaeohydrological evolution at a centennial scale is roughly coherent with most Iberian lacustrine records; however, the ‘La Parra’ sequence indicates that increased humidity during Iberian–Roman times was restricted to southern Spain and the humid phases of the ‘Little Ice Age’ (‘LIA’) starting and ending earlier in the central Iberian Range compared with the Pyrenean Domain and southern Spain. This new sequence highlights the heterogeneity through space and time of the main dry and wet climatic periods at shorter scales, emphasizing the impact of latitudinal climate gradients on the Iberian Peninsula climate variability. [ABSTRACT FROM AUTHOR]

We analyzed diatoms, lithology, and stable isotopes in a sediment core from the Ciénaga Grande de Santa Marta lagoon to reveal the history of late Holocene relative sea level rise and the ontogeny of the lagoon on the Caribbean coast of Colombia. At ~5300 cal. yr BP, the area was characterized by shallow, freshwater ponds that were prone to seasonal flooding. From ~4250 to ~2060 cal. yr BP, these ponds became brackish as relative sea level began to rise, and since ~2060 cal. yr BP, marine conditions have prevailed. In addition to tracking relative sea level rise, we also investigated periods of greater and lesser precipitation during times of brackish and marine conditions, respectively, as indicated by diatom-inferred changes in water salinity and shifts in the source of sediment organic matter. Comparisons with other regional paleoenvironmental records suggest that humid climate conditions prevailed in the Caribbean until about 4000 cal. yr BP. After that time, climate became more variable, with drier conditions registered from ~ 4000 to 2000 cal. yr BP. Wetter conditions returned after ~2000 cal. yr BP. [ABSTRACT FROM PUBLISHER]

Sedimentary diatom profiles from saline lakes are frequently used to reconstruct lakewater salinity as an indicator of drought. However, diatom-inferred salinity (DI-salinity) reconstructions from geographically proximal sites in the Great Plains (USA) have yielded disparate results. This study explores how physical changes in lake habitat resulting from drought may affect climate inferences from salinity reconstructions. Differences in relationships among drought, lake-level change, and diatom community structure over the last century were examined for three saline lakes in the northern Great Plains with dissimilar DI-salinity records. At each site, models were developed relating available planktic:benthic (P:B) habitat area to lake-level change, and models were compared with instrumental drought records and fossil diatoms to understand how drought conditions were recorded in sedimentary diatom assemblages. The degree to which DI-salinity tracked drought variation was affected by site-specific physical characteristics that influenced the relationship between lake-level change and P:B habitat zonation within each lake. Moon Lake showed the strongest correlation between drought and DI-salinity, although this relationship was weaker during wetter conditions, as highstands resulted in a larger influx of benthic diatoms. At Coldwater Lake, a dual-basin system, P:B varied depending on lake level, which apparently reduced the correlation between DI-salinity and drought. At Lake Cochrane, the simplest and freshest of the three basins, the P:B of fossil diatoms was a better proxy for drought than DI-salinity. The integration of additional ecological characteristics into interpretations of paleoclimate records, particularly for biologically-based proxies, may improve reconstructions of regional patterns of climate variation. [ABSTRACT FROM AUTHOR]

Postglacial paleoenvironmental changes and landscape development in the Hudson Bay Lowlands in subarctic Canada were inferred using sediment properties and diatom and pollen assemblages in the sediments of a lake raised above the surrounding peatlands in an ice-marginal landform. Coarse-grained, inorganic sediments at the base of the Lake AT01 core suggest a high-energy periglacial environment, following isostatic emergence from Hudson Bay around 6840 cal. BP. Initial diatom assemblages dominated by Fragilaria spp., and pollen of Shepherdia canadensis, indicate early successional conditions in a recently deglaciated environment. Around 6200 cal. BP, tychoplanktonic Fragilarioid diatoms are replaced by large benthics. Coincident increases in Equisetum spores, Cyperaceae pollen and sediment organic matter suggest the establishment of a more productive macrophyte-rich shallow lake. While the Holocene Thermal Maximum and subsequent Neoglacial may have contributed to these shifts, pollen and diatom records suggest only subtle responses to Holocene climatic changes. A core chronology inferred from radioisotopes suggests a hiatus in sediment accumulation between 3650 and 200 cal. BP. Peaks in carbonate inferred from loss-on-ignition and increases in bulk density in that section of the core suggest some effect of erosional or thermokarst processes, or the breaching of a sandbar, now a remnant island in the lake, in the drainage of the lake and ensuing hiatus. Sediment accumulation resumed within the past two centuries; diatom assemblages in the uppermost section are characterized initially by benthic diatoms of smaller valve size compared with the pre-hiatus assemblages. More recently, increases in the planktonic diatom Cyclotella stelligera are recorded, signaling significant environmental changes. [ABSTRACT FROM AUTHOR]

Three washover sand beds, ranging from 15 to 34 cm in thickness, were recorded in a lagoonal mud sequence on the Shizuoka coast of central Japan, which faces the Suruga Trough. The sand beds were composed of well-sorted and well-rounded beach sand derived by a marine inundation. The basal erosion surface, mud clasts, and presence of both inverse and normal grading suggest that the sand beds formed as a result of high-energy deposition. The sand beds are multilayered, with fine alternations of sand sheets and mud drapes, which are consistent with deposition from a long-period wave train. Radiocarbon dates obtained from the three washover deposits are around ad 1000, 3565–3486 cal. yr BP, and 4000 cal. yr BP. Vertical changes in the diatom assemblages suggest a gradually increasing inflow of seawater up to the second sand bed, followed by a rapid change to freshwater conditions just above the bed. The gradual increase of seawater inflow begins again just above the second sand bed. We conclude that this series of sequential environmental changes indicates interseismic subsidence and coseismic uplift. The study area experienced around 1 m of uplift during the ad 1854 Ansei Tokai earthquake (Mw 8.4). In contrast, the area has subsided gradually (c. 6 mm/yr) during the present interseismic period. The youngest sand bed may be correlated with the ad 1096 Eicho earthquake, which caused severe damage along the Shizuoka coast. [ABSTRACT FROM AUTHOR]

Holocene paleoclimate records from Greenland help us understand the response of the Greenland Ice Sheet and regional oceanic and atmospheric circulation systems to natural climate variability in order to place recent changes in a longer-term perspective. Here biogeochemical analysis of a lake sediment core from southeast Greenland is used to define changes in moisture balance and runoff during the Holocene in a catchment near the margin of the Greenland Ice Sheet. A 1.6 m sediment core that spans the last 8.8 ka was recovered from Flower Valley Lake on Ammassalik Island. Magnetic susceptibility, diatoms, bulk biogeochemical properties (TOC, C/N, δ13Corg), and lipid biomarkers (n-alkanes; C16–C31) reveal changes in clastic sedimentation and the relative input of terrestrial- and aquatic-derived organic matter. Hydrogen isotope values (δD) of mid- (n-C25) and long-chain (n-C29, n-C31) n-alkanes allow reconstruction of δD of precipitation and summertime evaporation of lake water. Following a period of early lake ontogeny and landscape stabilization after deglaciation from 8.4 to 7.0 ka, the mid Holocene, 8.4–4.1 ka, is characterized by greater evaporative enrichment of the lake water as indicated by δD records. After 4.1 ka, there is a decrease in evaporative enrichment of the lake water. There is also an abrupt transition to more variable sedimentation marked by sharp increases in magnetic susceptibility, C/N, δ13Corg, and the concentration of long-chain n-alkanes, showing periodic delivery of terrestrial organic matter and clastic sediment to the lake. Higher insolation during the mid Holocene resulted in a warmer and drier climate with longer ice-free periods in the summer and enhanced evaporation of lake water. The reduction in insolation and colder temperatures during the late Holocene caused a reduction in evaporation of lake water over the last 4.1 ka and was accompanied by periodic increases in surface runoff, which correspond with intervals of cold Greenland Ice Sheet surface temperatures. [ABSTRACT FROM PUBLISHER]

Pollen assemblages, diatom assemblages, and sedimentology, from Cumbres Bog in the southeastern San Juan Mountains of Colorado, provide a record of climate and environmental change since the end of the last glacial maximum (LGM). Cumbres Bog is unusually deep (basal sediments extend 12 m below the surface) for its altitude (~3050 m a.s.l.) and we extracted 7 m core of continuous sediment below ~5 m of water and peat. The resulting record provides strong evidence of: a period of warming immediately after the LGM (~18–13 cal. kyr BP), a cool interval coinciding with the Younger Dryas (~12.8–11.5 cal. kyr BP), a warm stable period from 10 to 6 cal. kyr BP, and a cooler and highly variable climate interval after 6 cal. kyr BP. More specifically, pollen ratios and fossil diatoms indicate that cold periods generally match with previously identified periods of rapid climate change that occurred at 10.6, 8.7–7.9, 7.0–6.9, 5.4–5.2, 3.3–3.0, 2.3, 2.0 and 1.5 cal. kyr BP. This record also adds resolution to previous regional records and indicates that the periodicity of climate variability changed from 2000–3000 years to 700–1100 years around 6 cal. kyr BP and to <500 years after 3.5 cal. kyr BP. Overall, our record provides important, relatively high-resolution paleoclimatic information for this remote region of the southern Rockies. [ABSTRACT FROM AUTHOR]

This study presents relative sea-level (RSL) change from 11,200 to 500 cal. BP in the Toyooka Basin, western Japan. Diatom assemblage and sedimentary sulfur analyses were performed for 32 sediment cores obtained from thick Holocene fluvial and marine deposits. An age model was constructed based on tephrochronology and 31 radiocarbon ages from elevations of −46.85 to +1.51 m in 19 cores. The RSLs in the Toyooka Basin are −31.05 m in elevation at 10,000 cal BP, above −4.00 m at 7900 cal. BP, −0.47 m at 6700 cal. BP and +0.15 m at 3300 cal. BP. A rapid sea-level rise, at a rate of about 23 mm/yr, is observed during the period from 10,600 to 10,300 cal. BP. Relative sea-level rose at a rate of about 12 mm/yr between 10,000 and 7900 cal. BP. The rate of sea-level rise decelerated at 7900 cal. BP, from about 12 mm/yr (10,000–7900 cal. BP) to 3 mm/yr (7900–6700 cal. BP). The mid-Holocene sea-level highstand probably occurred between 7000 and 6000 cal. BP, but it remains difficult to constrain its elevation. These RSL features described here may provide a typical example of Holocene sea-level changes resulting from both eustatic and hydro-isostatic components for the Japanese islands. [ABSTRACT FROM AUTHOR]

The Winnipeg River Drainage Basin (WRDB), within the boreal forest region of northwest Ontario, is a region that is expected to be negatively affected by climate warming. Inferences of droughts over the past two millennia from Little Raleigh Lake were based on two nearshore sediment cores. The core locations were from depths of ~12 and 15 m and were based on sufficient nearshore sediment accumulation and distance from the modern benthic-to-planktonic diatom boundary, where a distinct shift from dominance of benthic taxa changed to dominance of planktonic taxa in surficial sediments at ~11.8 m. Diatom-inferred depth was based on a model developed from 60 surficial sediments within the study lake. Depth inferences indicate that prolonged periods of aridity occurred from ~ad 950 to 1300 (corresponds to ‘Medieval Climate Anomaly’) and from ~ad 1625 to 1750 (aridity during ‘Little Ice Age’). We found that the core collected from a depth closer to the benthic-to-planktonic diatom boundary was more sensitive to changes in lake level than the deeper core where planktonic diatoms dominated the assemblage. The inferred low-water stands of the past two millennia are well outside of the range of the past ~100 years, suggesting that recent drought history may not be a good estimate of future extremes. [ABSTRACT FROM PUBLISHER]

This study combined multiple aquatic and terrestrial proxies, including diatoms, pollen, grain size, and bulk-sediment chemistry to reconstruct the history of three lake sites located in the central Sand Hills of Nebraska, USA. Long-term changes in effective moisture are evident at all sites, with significant changes occurring at ~6000, ~4000, and ~ 2000 cal. yr BP. Both aquatic and terrestrial indicators suggest that effective moisture was low between 10,000 and ~6000 cal. yr BP, and that this time interval was the driest period of the Holocene. The dominance of benthic and tychoplanktic diatom taxa indicates relatively shallow lake-level, high sand influx indicates moderately high eolian activity, and the pollen assemblage suggests xeric grasslands with abundant mud flats. About 6000 cal. yr BP, all three sites experienced an increase in effective moisture. Lake-level rise is indicated by increases in planktic and tychoplanktic diatoms relative to benthic taxa, while greater abundance of grass pollen and charcoal, and decreased eolian flux indicate stabilized dunes with dense vegetation sufficient to fuel local fires. A significant hydrologic shift recorded at all sites occurred at ~4000 cal. yr BP. This event was characterized by substantial lake-level rise, yet decreased grass cover and fire frequency, and increased eolian activity. Water-table rise may have been caused by a combination of factors including: (1) formation of dune-dams that blocked old drainage channels, (2) reduced grass cover and hence reduced evapotranspiration, and (3) changes in the frequency and duration of drought. The most likely cause(s) of the differential response of the terrestrial and aquatic systems at this time is not clear, none-the-less the late Holocene was not nearly as dry as the interval prior to 6000 cal. yr BP. The last ~2000 yr were characterized by several short-term fluctuations in lake level, including an interval of drought between 950 and 750 cal. yr BP, coincident with increased eolian activity during the latter part of the Medieval Climatic Anomaly. [ABSTRACT FROM PUBLISHER]

Because of decreasing sea-ice extent and increasingly frequent Arctic storms, low-lying coastal ecosystems are at heightened risk from marine storm surges. A major Arctic storm event originating in the Beaufort Sea in September 1999 resulted in the flooding of a large area of the outer alluvial plain of the Mackenzie Delta (Northwest Territories, Canada), and has been previously shown to have caused unprecedented impacts on the terrestrial ecosystems on a regional scale. We use diatoms preserved in lake sediment cores to gain a landscape perspective on the impact of the storm on freshwater systems, and to determine if other such events have occurred in the recent past. Our results indicate that five lakes located at the coastal edge of the low-lying Mackenzie Delta show strong, synchronous, and previously unobserved increases in the relative abundance of brackish-water diatom taxa coincident with the timing of the 1999 storm surge. These changes were not observed at a control site located farther inland. The degree to which the storm surge impacted the chemical and biological limnology of the lakes varied, and was not explained by measured physical variables, suggesting the degree of impact is likely related to a combination of factors including distance from the coast, the size:volume ratio of the lake and its catchment, and water residence time. We show that the 1999 storm surge resulted in unmatched broadscale impacts on the freshwater ecosystems of the outer Mackenzie Delta, and that while minimal recovery may be occurring in some of the systems, the lakes studied remain chemically and biologically impacted more than a decade after the inundation event. [ABSTRACT FROM AUTHOR]

A multiproxy sedimentary record from Lake Igaliku in southern Greenland documents 1450 years of human impacts on the landscape. Diatoms, scaled chrysophytes, and C and N geochemistry show perturbations consistent with recent agricultural activities (post-ad 1980), superimposed upon long-term environmental variability. While the response to Norse agriculture (~ad 986–1450) is weak, the biological response to the last 30 years of modern sheep farming is marked, with drastic changes in diatom taxa, δ13C and δ15N isotopic ratios, and a sharp increase in scaled chrysophytes. Indeed, current conditions in the lake during the last 30 years are unprecedented in the context of the last 1450 years. The dominant driver for recent changes is likely an intensification of agricultural practices combined with warming summer temperatures. Warm temperatures and agricultural disturbance together during Norse Landnám did not lead to the marked changes seen in the modern lake environment over the last 30 years. The synergistic response between increased climate warming and agriculture will likely have unanticipated effects. These findings confirm the sensitivity of Arctic lakes to external anthropogenic forcing and are the first analyses of their kind for the effects of agriculture in Greenland. [ABSTRACT FROM AUTHOR]

Laminated sediments are unique archives of palaeoenvironmental and palaeoceanographic conditions, recording changes on seasonal and interannual timescales. Diatom-rich laminated marine sediments are examined from Dumont d’Urville Trough, East Antarctic Margin, to determine changes in environmental conditions on the continental shelf from 1136 to 3122 cal. yr BP. Scanning electron microscope backscattered electron imagery (BSEI) and secondary electron imagery are used to analyse diatom assemblages from laminations and to determine interlamina relationships. Diatom observations are quantified with conventional assemblage counts. Laminae are primarily classified according to visually dominant species identified in BSEI and, secondarily, by terrigenous content. Nine lamina types are identified and are characterized by: Hyalochaete Chaetoceros spp. resting spores (CRS); CRS and Fragilariopsis spp.; Fragilariopsis spp.; Corethron pennatum and Rhizosolenia spp.; C. pennatum; Rhizosolenia spp.; mixed diatom assemblage; Stellarima microtrias resting spores (RS), Porosira glacialis RS and Coscinodiscus bouvet; and P. glacialis RS. Formation of each lamina type is controlled by seasonal changes in sea ice cover, nutrient levels and water column stability. Quantitative diatom assemblage analysis revealed that each lamina type is dominated by CRS and Fragilariopsis sea ice taxa, indicating that sea ice cover was extensive and persistent in the late Holocene. However the lamina types indicate that the sea ice regime was not consistent throughout this period, notably that a relatively warmer period, ~3100 to 2500 cal. yr BP, was followed by cooling which resulted in an increase in year round sea ice by ~1100 cal. yr BP. [ABSTRACT FROM PUBLISHER]

Diatom assemblages from Holsteinsborg Dyb on the West Greenland shelf were analysed with high temporal resolution for the last 1200 years. A high degree of consistency between changes in frequency of selected diatom species and instrumental data from the same area during the last 70 years confirms the reliability of diatoms (particularly sea-ice species and warm-water species) for the study of palaeoceanographic changes in this area. A general cooling trend with some fluctuations is marked by an increase in sea-ice species throughout the last 1200 years. A relatively warm period with increased influence of Atlantic water masses of the Irminger Current (IC) is found at ad 750–1330, although with some oceanographic variability after ad 1000. A pronounced oceanographic shift occurred at ad 1330, corresponding in time to the transition from the so-called ‘Medieval Warm Period’ (MWP) to the ‘Little Ice Age’ (LIA). The LIA cold episode is characterized by three intervals with particularly cold sea-surface conditions at ad 1330–1350, ad 1400–1575 and ad 1660–1710 as a result of variable influence of Polar waters in the area. During the last 70 years, two relatively warm periods and one cold period (the early 1960s to mid-1990s) are indicated by changes in the diatom components. Our study demonstrates that sedimentary records on the West Greenland shelf provide valuable palaeoenvironment data that confirm a linkage between local and large-scale North Atlantic oceanographic and atmospheric oscillations. [ABSTRACT FROM AUTHOR]

The response of diatom assemblages to changes in climate and nutrients over a 1200 year timescale was investigated by means of a multiproxy sediment core study involving radiometric dating, diatoms, grain size, loss on ignition and geochemical analysis. Four stages of environmental change were defined, each being consistent with changes in documented human activity and known climate patterns. From ad 750 to 880 relatively high nutrient status and a cold, unstable climate was inferred based on the high abundance of Aulacoseira subarctica and high Na/K and Na/Al values. In the following 1000 years (ad 880–1880) diatom assemblages were dominated by Cyclotella comensis, Cyclotella radiosa and Achnanthidium minutissimum, suggesting a long period of relatively low productivity and, by implication, that climate was the main control on the community during this period. Two climatic phases, namely the ‘Medieval Warm Period’ (MWP) and the ‘Little Ice Age’ (LIA), were apparent. According to shifts in the diatom assemblages and other proxies, it was proposed that the MWP was initiated from ~ad 880 and was terminated by the LIA at ~ad 1350. After ad 1880 the palaeoecological data revealed a period of strong human impact in the catchment and hence higher productivity. This work illustrates the complexity of climate–nutrient interactions and the roles of the two drivers on different timescales and at various stages of the lake’s history: climate impacts were more pronounced when nutrient concentrations were relatively stable prior to ~ad 1880; while nutrients appeared to play a more important role in regulating diatom communities from the mid-eighteenth century. [ABSTRACT FROM PUBLISHER]

Sediment records from closed-basin lakes in the Northern Great Plains (NGP) of North America have contributed significantly to our understanding of regional paleoclimatology. A high-resolution (near decadal) fossil diatom record from Kettle Lake, ND, USA that spans the last 8500 cal. yr BP is interpreted in concert with percent abundance of aragonite in the sediment as an independent proxy of groundwater flow to the lake (and thus lake water level). Kettle Lake has been relatively fresh for the majority of the Holocene, likely because of the coarse substrata and a strong connection to the underlying aquifer. Interpretation of diatom assemblages in four groups indicative of low to high groundwater flow, based on the percent of aragonite in sediments, allow interpretations of arid periods (and probable meromictic lake conditions) that could not be detected based on diatom-based salinity reconstructions alone. At the centennial–millennial scale, the diatom record suggests humid/wet periods from 8351 to 8088, 4364 to 1406 and 872 to 620 cal. yr BP, with more arid periods intervening. During the last ~ 4500 years, decadal–centennial scale periods of drought have taken place, despite the generally wetter climate. These droughts appear to have had similar impacts on the Kettle Lake hydrology as the ‘Dust Bowl’ era droughts, but were longer in duration. [ABSTRACT FROM PUBLISHER]

Paleo surface wind for southern Quebec was inferred quantitatively for the past 9500 years from diatom assemblages archived in the sediment of the shallow mountain Lac du Sommet using biweekly sediment trap samples along an elevation gradient in the study area. The wind reconstruction was compared with diatom-inferred dissolved organic carbon concentration, chironomid-inferred mean August air temperature, pollen, grain size and loss-on-ignition. Increased lake circulation, interpreted as indicating stronger surface winds, was inferred from diatoms around 8700, 4500, 3000 to 2000 cal. yr BP and during the past 250 years. Increased lake stratification was diatom-inferred from 7500 to 5000 cal. yr BP and between 1500 and 500 cal. yr BP. Diatom-inferred paleowinds were congruent with the regional fire history. In general, diatom production was significantly correlated with diatom-inferred lake circulation. Diatom-inferred lake circulation and diatom production were not correlated with the pollen assemblage changes, diatom-inferred dissolved organic carbon and chironomid-inferred August air temperature, which were highly intercorrelated. After the disappearance of the meltwater in the St Lawrence River valley, the chironomids reflected a warming trend that lasted until about 5000 cal. yr BP, trees replaced shrubs and diatom-inferred dissolved organic carbon increased from 4 mg/l to 6 mg/l. Diatom-inferred lake circulation exhibited periodicities of 200 and 900 years, whereas chironomid-inferred August air temperatures indicated a distinct (significant) 200 year periodicity. [ABSTRACT FROM AUTHOR]

The diatom flora from a high-resolution core collected from Disko Bugt, central West Greenland, records variations in surface water temperature for the late Holocene (1600-300 cal. BP). Our data support the existence of a previously identified anti-phase relationship between the surface water temperature from West Greenland and climate events recorded in the NE Atlantic and between surface and subsurface waters (identified from benthic foraminifera) of the West Greenland Current (WGC). The diatom flora record relatively cool surface water conditions during the end of the 'Roman Warm Period' and 'Medieval Warm Period' (MWP), and relatively warmer surface water conditions during the 'Dark Ages Cold Period' and 'Little Ice Age' (LIA). This is particularly pronounced during the MWP, experiencing the coldest conditions, and the LIA experiencing the warmest conditions through the whole sequence studied. The most likely explanation for this anti-phase relationship is linked to the flux of meltwater delivered to the WGC from sea ice and the Greenland ice sheet off the West Greenland margin. The generally warmer conditions of the MWP resulted in increased melting of sea ice and the Greenland ice sheet producing an increased meltwater flux and cooling of the surface waters of the WGC. In contrast, reduced meltwater flux during the relatively cold LIA resulted in reduced meltwater flux to the WGC, producing a relative warming of the surface waters recorded by the diatom flora. [ABSTRACT FROM AUTHOR]

A peat-sequence covering the last 16 ka (16 000 cal. yr BP) from Braamhoek wetland, eastern South Africa, was analysed in terms of phytolith and diatom composition. The fossil peat was rich in phytoliths, while diatoms were less prominent, probably as a result of degradation during wetland plant growth associated with silica uptake. With this study we present the first continuous phytolith and diatom record from South Africa covering the Late Pleistocene and Holocene period. The phytolith assemblages indicate a clear dominance of C3-grasses within the wetland throughout the sequence. The fossil diatom record infer changes in past moisture conditions. Unlike the modern wetland, which is dominated by benthic and aerophilic diatoms, the Late Pleistocene-early Holocene wetland favoured growth of planktonic species. Abundance of planktonic diatoms suggests three main phases when water depth was deeper than today; at c.13.6 ka, 11.3 ka and 10.4-10.0 ka. These indications of past fluctuations in humidity mostly provide confirmation of previously published indications of pollen, charcoal fragments and isotopes in the same core, but the siliceous microfossil data also help to refine the paleo-environmental interpretation of the sequence. [ABSTRACT FROM AUTHOR]

Analyses of a 12 m marine sediment core from Neny Fjord, Marguerite Bay, Antarctic Peninsula (68.2571°S, 66.9617°W), yield a high-resolution record of Holocene climate variability. The sediments preserve signals of past glacial and marine environments and offer a unique insight into atmospheric and oceanic forcings on the western Antarctic Peninsula climate. Dating of basal material reveals that deglaciation of the fjord occurred prior to 9040 cal. yr BP and provides a minimum constraint on the timing of deglaciation close to the southern Antarctic Peninsula ice-divide. Continuous deposition of ice-distal sediments and seasonally open-water diatoms indicates that the site has not been over-ridden by glacier ice during the Holocene. A facies of sand-rich material offers the only evidence of a localized glacier advance, during the mid Holocene. Statistical analysis of diatom assemblage data reveals several climatic episodes of varying magnitude and duration. These include an early-Holocene warm period (∼9000 and ∼7000 cal. yr BP), potentially associated with influx of Circumpolar Deep Water onto the continental shelf and coinciding with widespread glacial retreat and Holocene collapse of the George VI Ice Shelf. The mid-Holocene (∼7000 to ∼2800 cal. yr BP) sediments are characterized by diatom assemblages indicative of less pervasive sea-ice cover and prolonged growing seasons with evidence of increased meltwater discharge from ∼4000 cal. yr BP. The youngest sediments (∼2800 cal. yr BP to present) contain a record that is consistent with the widely documented 'neoglacial' period followed by an abrupt reversal and climate amelioration from sometime after ∼200 cal. yr BP. [ABSTRACT FROM AUTHOR]

A high-resolution, independent pollen-inferred paleoclimate record and direct algal seasonality data from the actual time of sediment deposition are used to interpret the high-resolution diatom and chrysophyte record of varved Lake Mina, west-central Minnesota, USA during AD 1116-2002. This direct algal seasonality information was obtained by splitting varves into constituent winter-spring and summer lamina, and separately analyzing the siliceous algae in each layer. Analyses of integrated, continuous four-year diatom and chrysophyte samples from a sedimentary sequence show that the time period AD 1116-1478 (ie, the Atlantic-centered 'Medieval Climate Anomaly' (MCA)) was characterized by periods of vigorous and prolonged spring mixing, suggesting that ice-out occurred early. However, the warm summer temperatures in the MCA, particularly in a massive drought spanning AD 1300-1400, frequently caused the lake to stratify strongly, leading to nutrient depletion. During AD 1478-1870 (ie, the Atlantic-centered 'Little IceAge' (LIA)), Lake Mina was characterized by weak spring circulation and increasing nutrient depletion, suggesting late ice-out conditions. Strong summer stratification and/or nutrient depletion in both time periods is shown by the occurrence of the nutrient-poor oligotrophic taxon Cyclotella pseudostelligera. The diatom and chrysophyte assemblages of the period of Euro- American settlement AD 1870-2002 show higher nutrient availability and increased spring mixing intensity, as a result of forest clearance and increasingly earlier ice-out (documented in regional historical records). [ABSTRACT FROM AUTHOR]

A series of monoliths collected from Ambra Crater in the Upper Wahgi valley, Papua New Guinea have been subject to multiproxy (pollen, microcharcoal and diatom) palaeoecological investigation. The palaeoecological record enables a relatively high-resolution reconstruction from c. 4000-500 cal. BP. Throughout the sequence, the valley floor and crater area were continuously deforested and carpeted with a grassland-disturbance taxa mosaic. Vegetation communities in the valley were largely unaffected by successive tephra deposition events, although some muted effects occurred. Tephra deposition did have considerable local effects on soil water conditions and hydrology in the base of the crater. The Ambra Crater record is consistent with longer chronologies from wetlands in the Upper Wahgi valley, which document extensive disturbance to dryland forests and their replacement with grasses and other disturbance taxa from the mid Holocene. The Ambra Crater record, taken in conjunction with previously published multisite data, enables critique and discrimination of different interpretations of agricultural history in the highlands during the late Holocene. [ABSTRACT FROM AUTHOR]

A palaeolimnological investigation of changes in water quantity and quality in Lake 239, Experimental Lakes Area, in northwestern Ontario indicates marked changes in limnological conditions during the Holocene. Water quantity changes are based on the analysis of diatoms and inferences of lake-level changes from a nearshore sediment core. Changes in water quality are based on the analysis of diatom assemblages and associated quantitative inferences of total phosphorus (TP) from a deep central core, as well as changes in diatom accumulation rates, the proportion of chrysophyte scales to diatoms and changes to organic matter content. Lake levels at least 8 m lower than today were inferred from the nearshore core and were concurrent with an increase in nutrient-rich diatom assemblages, an increase in diatom accumulation and a decrease in the chrysophytes relative to diatoms in the central core. Fragilaria crotonensis and Aulacoseira subarctica were two of the dominant nutrient-rich taxa that contributed to an increase in diatom-inferred TP during the mid Holocene. Results from this study provide strong empirical evidence that water levels much lower than today can dramatically change trophic status, as occurred during the dry mid Holocene, and may provide a good analogue for understanding future impacts of climatic changes due to anthropogenic activities. [ABSTRACT FROM AUTHOR]

Borg Indrepollen is a coastal lake on the island of Vestvågøy, Lofoten, NW Norway. A sedimentary sequence spanning the last 4500 cal. yr BP was analysed for diatom, C/N and stable isotopes (δ13C and δ15N). The record provides clear evidence of glacio-isostatic rebound in the Lofoten region. Five distinct lithostratigraphic- geochemical zones (I-V) and four major diatom zones (A-D) were identified. The early record (I-III, A-Biii; 4500-550 cal. yr BP) contains coarse sedimentary material and diatoms indicative of more marine conditions. The correlation between the isotopic data (high δ13C and low C/N) and trends in the biological data (marine/brackish flora) suggest the marine influence on the Indrepollen basin is a controlling factor of the source of organic material. The latter part of the record (IV, C; 550 cal. yr 550-226) indicates a transitional phase from marine-dominated diatom to brackish taxa and is coincident with a section of microlaminations in the core. The youngest zone (V, D; 226 cal. yr BP-present) is indicative of an isolated basin, with the deposition of fine sediments; freshwater diatom taxa dominate the biological record and δ13C are indicative of freshwater conditions. C/N suggests a shift to a terrestrial source of organic matter. The proxies show a transition from full marine conditions, when Indrepollen was a submerged fjord, to more freshwater, lacustrine conditions in the last 200 years. The record of land uplift from Borg Indrepollen mirrors changes in sedimentary records from across Northern Norway and relative sea-level curves for the region. [ABSTRACT FROM AUTHOR]

Precipitation on the South American Altiplano varies at a range of temporal scales. A long-term secular increase in moisture availability from the early/mid Holocene to the present, driven by increasing summer insolation resulting from precessional changes in the Earth's orbit, has been documented in earlier studies. However, higher frequency Holocene variability is not yet understood. Here we present high-resolution diatom assemblage data from two small Altiplano lakes, Lago Lagunillas and Lago Umayo, indicating changes in effective moisture in the southern tropical Andes at decadal, centennial and millennial timescales throughout the mid to late Holocene. A strong millennial-scale component, similar in pacing to periods of increased icerafted debris flux in the North Atlantic, is observed in both lake records, which suggests that regional precipitation and North Atlantic climate variability are coupled at these scales. The interpretation of the higher frequency variability is hampered by the small number of high-resolution continental and marine records for comparison. [ABSTRACT FROM AUTHOR]

This study documents an extensive aeolian sand sheet buried in the salt marshes of the Ho Bugt embayment in western Denmark. The extent of the sand sheet was mapped from c. 60 cores and sections, which were also used to reconstruct late-Holocene changes in relative sea level based on diatom analyses. Chronology was provided by optically stimulated luminescence (OSL) and radiocarbon dating. Our study shows that since 2000 cal. yr BP relative sea level in Ho Bugt has risen by approximately 1.5 m. The overall rise was punctuated by two periods with higher than average rates of sea-level rise, the first between 2000 and 1400 cal. yr BP and the second commencing c. 500 cal. yr BP. Around 700 cal. yr BP the evolution of the Skallingen Spit may have been responsible for a reduction in the local tidal range and the formation of an extensive 'black layer' in the western part of the embayment. OSL analyses date the sand sheet to between AD 1460 ± 40 and AD 1550 ± 30 (490 ± 40 and 400 ± 30 cal. yr BP), consistent with a period of increased storminess, coastal dune building, saltmarsh formation and increased relative sea-level rise during the early part of the LIA. Other studies have ascribed formation of coastal dunes along western European coastlines during the 'Little Ice Age' (LIA) to a combination of increased storminess and low relative sea level. In contrast, we conclude that during the LIA in western Denmark, storminess, transgressive conditions and relative sea-level rise, rather than a sea-level low stand, were important contributing factors to coastal sand movement and dune formation. [ABSTRACT FROM AUTHOR]

Geochemical analyses (x-ray fluorescence, δ13C and C/N ratios) were used to reconstruct early Holocene environments (between 10 685 and 7260 cal. yr BP) at a small lake near Holebudalen, southern Norway. Results show a period of increasing stability, with reduced catchment inwash (shown by titanium and potassium minerals), vegetation stabilization and increasing aquatic productivity (C/N ratios). However, periods of instability (loss on ignition (LOI) decrease) are also seen (most notably at c. 9060 cal. yr BP). Chironomid-inferred July temperature (CI-T) reconstructions show a cooling of c. 2°C (RMSEP = 1.0°C) between c. 8400 and 8000 cal. yr BP and so high-resolution (5 mm; c. 20 yr) diatom analyses were conducted between 8675 and 7830 cal. yr BP in order to further investigate this change. Between c. 8270 and 8000 cal. yr BP there were large reductions (> 50%) in the abundance of tychoplanktonic diatoms (eg, Aulacoseira species) and absolute increases in periphytic diatom communities (eg, Navicula pupula, Pinnularia mesolepta). The multiproxy analyses suggest a period of increased lake ice cover with associated reductions in turbulence during this time. Diatom flora changes are concomitant with a fall in percent LOI and increased catchment erosion at the site and other evidence of regional climatic perturbations in the early Holocene. Therefore, superimposed upon an early Holocene warming trend at Holebudalen, there are climatic perturbations, for example reflected between c. 8200 and 8000 cal. yr BP by diatom communities. [ABSTRACT FROM AUTHOR]

We report on Holocene surface-level variations of Lake Fryxell, Antarctica, as determined from multiproxy analyses of 18 sediment cores. During this time accumulating sediments were predominantly aeolian sand with algal and carbonate laminae. Based on stratigraphy, mineralogy and diatom assemblages we suggest some carbonate laminae were deposited when lake level dropped, leading to concentration and subsequent precipitation of salts. Although lake level appears to have remained relatively stable throughout the Holocene, minor (<4.5 m below present) lowstands occurred at approximately 6400, 4700, 3800 and ~ 1600 cal. yr BP. The stability of Lake Fryxell during the Holocene contrasts with large-scale variability at other Dry Valleys lakes (eg, Lake Vanda) and with suggestions from chemical diffusion models of a near-desiccation at ~ 1200 cal. yr BP. The reason for the comparative stability of Lake Fryxell is uncertain, but may be the result of basin morphology and the number, aspect and proximity of meltwater sources. [ABSTRACT FROM AUTHOR]

Sandy deposits of marine origin underlie the floor of Suijin-numa, a coastal lake midway along the subduction zone marked by the Japan Trench. The deposits form three units that are interbedded with lacustrine peat and mud above a foundation of marine, probably littoral sand. Unlike the lacustrine deposits, all three sandy units contain marine and brackish diatoms. The middle unit (B) contains, in addition, graded beds suggestive of multiple waves of long wavelength and period. The uppermost unit (C) probably dates to a time in the area's written history when the lake was separated from the sea by a beach-ridge plain at least 0.5 km wide and several metres high. Units A and B postdate AD 540-870, and unit C postdates AD 1030-1640 as judged from radiocarbon dating of leaves and seeds. Unit B pre-dates AD 915 and unit C postdates that year as judged from a tephra within the peat that separates units B and C. The age constraints permit correlation of unit B with a tsunami in AD 869 that reportedly devastated at least 100 km of coast approximately centred on Sendai. Unit C may represent a later catastrophic tsunami in 1611, or perhaps a storm surge that inundated much of Sendai. The lake lacks obvious signs of tsunamis from the region's largest twentieth-century earthquakes, which were centred to the north in 1933 (M 8.1) and directly offshore in 1936 (M 7.5), and 1978 (Mw 7.6). [ABSTRACT FROM AUTHOR]

The recent growth in the use of microfossil-based transfer functions in late-Quaternary sea-level reconstructions reflects their potential to accurately quantify palaeo sea-level changes. This study details the development of a diatom-based sea-level transfer function for the Severn Estuary, southwest England, a macrotidal setting that experiences the second highest tidal range in the world. This setting presents difficulties in representing the full tidal range from mean sea level (MSL) to highest astronomical tide (HAT). However, two separate transects were merged successfully and a statistically significant relationship between contemporary diatom assemblages and altitude (m O.D.) was established. A diatom-based transfer function for palaeoaltitude was developed using weighted averaging (WA), tolerance downweighted weighted averaging (WA-Tol) and weighted averaging partial least squares (WA-PLS). WA-Tol produced the lowest prediction errors for altitude and the transfer function was applied to a fossil diatom data set from Gordano Valley, a site adjacent to the Severn Estuary. [ABSTRACT FROM AUTHOR]