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Sound knowledge of present-day diatom species and their environments is crucial when attempting to reconstruct past climate and environmental changes based on fossil assemblages. For the North Atlantic region, the biogeography and ecology of many diatom taxa that are used as indicator-species in paleoceanographic studies are still not well known. Using information contained in large diatom-environment calibration datasets can greatly increase our knowledge on diatom taxa and improve the accuracy of paleoenvironmental reconstructions. A diatom calibration dataset including 183 surface sediment samples from the northern North Atlantic was used to explore the distribution and ecology of 21 common Northern Hemisphere diatom taxa. We define the ecological responses of these species to April sea ice concentrations and August sea surface temperatures (aSSTs) using Huisman-Olff-Fresco (HOF)-response curves, provide distribution maps, temperature optima and ranges, and high-quality light microscope images. Based on the results, we find species clearly associated with cold, warm and temperate waters. All species have a statistically significant relationship with aSST, and 15 species with sea ice. Of these, Actinocyclus curvatulus, Fragilariopsis oceanica and Porosira glacialis are most abundant at high sea ice concentrations, whereas Coscinodiscus radiants, Shionodiscus oestrupii, Thalassionema nitzschioides, Thalassiosira angulata, Thalassiosira nordenskioeldii and Thalassiosira pacifica are associated with low sea ice concentrations/ice-free conditions. Interestingly, some species frequently used as sea ice indicators, such as Fragilariopsis cylindrus, show similar abundances at high and low sea ice concentrations with no statistically significant relationship to sea ice.

The reference model underlying the UK phytobenthos (diatom) tool for Water Framework Directive assessments is revisited and a new approach is proposed which uses quantile regression to predict the lowest values of the Trophic Diatom Index (equating to the best available condition) at any level of alkalinity . Whilst a reference model based on least disturbed or minimally impacted conditions would be preferable in theory, in practice the absence of lowland high alkalinity streams in a minimally impacted condition in the UK precludes the use of these approaches. Having proposed a revised reference model for phytobenthos, we then go on to examine the relationship between phytobenthos and macrophytes. These two groups respond to nutrients and other stressors in different ways with phytobenthos being more sensitive to nutrients whilst macrophytes better reflect the extent to which secondary effects are likely. We argue that averaging the two sub-elements of the “macrophytes and phytobenthos” biological quality element is a more realistic option than the current approach of taking the lower of the two assessments. It is, however, possible, to predict the value of the combined quality element from either sub-element, though we recognize that this also risks misclassifications.

Prediction of high latitude response to climate change is hampered by poor understanding of the role of nonlinear changes in ecosystem forcing and response. While the effects of nonlinear climate change are often delayed or dampened by internal ecosystem dynamics, recent warming events in the Arctic have driven rapid environmental response, raising questions of how terrestrial and freshwater systems in this region may shift in response to abrupt climate change. We quantified environmental responses to recent abrupt climate change in West Greenland using long-term monitoring and paleoecological reconstructions. Using >40 years of weather data, we found that after 1994, mean June air temperatures shifted 2.2 °C higher and mean winter precipitation doubled from 21 to 40 mm; since 2006, mean July air temperatures shifted 1.1 °C higher. Nonlinear environmental responses occurred with or shortly after these abrupt climate shifts, including increasing ice sheet discharge, increasing dust, advancing plant phenology, and in lakes, earlier ice out and greater diversity of algal functional traits. Our analyses reveal rapid environmental responses to nonlinear climate shifts, underscoring the highly responsive nature of Arctic ecosystems to abrupt transitions.

The transition from the last ice age to the present-day interglacial was interrupted by the Younger Dryas (YD) cold period. While many studies exist on this climate event, only few include high-resolution marine records that span the YD. In order to better understand the interactions between ocean, atmosphere and ice sheet stability during the YD, more high-resolution proxy records from the Arctic, located proximal to ice sheet outlet glaciers, are required. Here we present the first diatom-based high-resolution quantitative reconstruction of sea surface conditions from central-eastern Baffin Bay, covering the period 14.0–10.2 kyr BP. Our record reveals warmer sea surface conditions and strong interactions between the ocean and the West Greenland ice margin during the YD. These warmer conditions were caused by increased Atlantic-sourced water inflow combined with amplified seasonality. Our results emphasize the importance of the ocean for ice sheet stability under the current changing climate., We would like thank the captain and all members of the cruise MSM09/2. We also thank O. Hyttinen, University of Helsinki, for her help with grain size distribution analysis. Funding from the Finnish Graduate School in Geology is kindly acknowledged as is the funding from the Academy of Finland (A.E.K. Ojala, QUAL-project 259343). We are grateful to F.M. Nick, H. Machguth, T. Luoto, and K. Pauli for insightful discussions.

The sampling skills of three common European fish species (Barbus barbus, Chondrostoma nasus and Squalius cephalus) were tested to assess their potential as biomonitors of past changes in river water quality through the analysis of diatoms in fish guts. The study was performed on three rivers with different chemical and physical conditions. Comparison of similarity indices revealed low diatom assemblage resemblance between epilithic samples and samples collected from fish guts at the same locality. In contrast, a mixed-effect linear model identified significant differences between locations through comparison of diatom-based water quality indices. Among fish species, diatom indices calculated from gut samples of B. barbus and C. nasus were in most cases not significantly different from those from epilithic samples while those from S. cephalus were often significantly different. The results of the study demonstrate that diatom analysis of fish guts provides a clear distinction between eutrophic and hypereutrophic rivers. Finer nutrient variations within hypereutrophic conditions were also found to be significant for some diatom indices. In this context, choice of appropriate diatom water quality index proved to be crucial in maximizing the sensitivity of the method.

A multi-proxy palaeoecological study of the lateglacial and early Holocene sediments of Jansvatnet, Hammerfest, northernmost Norway (70°39′ N) showed that cold and arid conditions prevailed in both the lateglacial interstadial and the Younger Dryas. Terrestrial proxies are macrofossils and pollen. Aquatic proxies are plant and invertebrate macrofossils, pollen, diatoms, and chironomids. Mean July temperatures were reconstructed using pollen and chironomid calibration functions and ecological knowledge of the fossil flora and fauna. Lake-water pH was reconstructed using a diatom pH-calibration function. Above sterile basal deglacial silts, biotic activity was detected around 14600 years ago in the interstadial (chronologically equivalent to the Bolling-Allerod in the Greenland Ice-Core Chronology). Catchment vegetation resembled polar desert and ultra-cold stenothermic chironomids lived in the lake. However, diatom assemblages were diverse and dynamic. In the Younger Dryas stadial, conditions deteriorated. In the early Younger Dryas chironomid-inferred air temperatures (CI-Tjul) fell about 1 °C. Pollen-inferred temperatures (PI-Tjul) did not fall and the terrestrial vegetation hardly changed because of the extreme aridity. The lake water was turbid from suspended clay which diminished aquatic life. Later in the Younger Dryas (ca 12400 cal yr BP) reconstructed mean July temperatures fell by a further 3 °C and were close to the minimum to support life, at around 3–4 °C. However, decreased turbidity allowed moss growth on the lake bottom that provided habitats for invertebrates and diatoms. In the last 200 years of the Younger Dryas temperatures increased by 2–3 °C and terrestrial and aquatic organisms responded quickly. At the start of the Holocene a rapid increase of more than 3 °C in PI-Tjul to 9.5 °C initiated the replacement of sparse arctic tundra by low-arctic dwarf-shrub heath. Simultaneously, a further 2 °C increase in CI-Tjul to 10–11 °C reflected a regime shift in the lake. Aquatic macrophytes rapidly replaced the moss carpet, diatom assemblages stabilised and diatom plankton developed, and cold stenotherm chironomids were replaced by cool-temperate taxa. Productivity increased as CI-Tjul reached a steady maximum of around 12 °C and PI-Tjul reached 10.5 °C at about 10000 cal yr BP. At this time, tree-birch arrived and woodland developed over the catchment. Birch could have immigrated from the south up the west coast or from the east along the Barents Sea coast. Acidophilous aquatic taxa increased as diatom-inferred pH gradually decreased from 7.3 to 6.6. After ca 9380 cal yr BP, the density and extent of birch woodland decreased and species of exposed rocky areas increased, reflecting increased windiness, precipitation, and possibly a small decrease in July temperatures. Birch now formed the arctic tree-line at Jansvatnet. The lateglacial climatic pattern at Jansvatnet resembles patterns detected elsewhere in northern Norway and Svalbard and in marine records from the Norwegian and Barents Seas but contrasts with patterns in southern Norway.

Fourier transform near-infrared spectroscopy (FT-NIRS) together with partial least squares regression was used to produce calibrations between spectra and concentrations of total organic carbon (TOC) in marine sediments collected from widely varying depositional settings. Samples from ODP 664 (oxic Quaternary, low TOC, deep sea ooze) and ODP 959 (anoxic Cretaceous black shale) were analysed using standard instrumental techniques and with FT-NIRS. Unknown TOC concentrations in samples were then predicted using spectra and calibration equations, resulting in higher resolution data without additional time consuming and expensive traditional analyses. Good correlations were achieved between measured and FT-NIRS predicted concentrations ( r 2 > 0.8), providing evidence that FT-NIRS has a promising potential for the rapid and accurate determination of TOC in a wide variety of sediment types.

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 sediment-trap 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 base-cation 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.

Diatom dissolution in surface sediment samples from two regional lake datasets in the Northern Great Plains (NGP; n 5 64) and West Greenland (n 5 40) is assessed using a morphological approach categorizing valves during routine diatom analysis. Two dissolution indices are derived to parameterize diatom dissolution, and, when compared between two analysts in a blind test, show good correspondence and are closely correlated to diatom fragmentation. We explore the relationships between hydrochemical and physical lake parameters (including meromixis) on dissolution within both lake regions using multivariate methods and modeled with logistic regression. Salinity is the sole significant predictor of dissolution in West Greenland but salinity, carbonate concentration ([CO3 22 ]) and meromixis are significant predictors in the NGP. Limnological parameters explain 40–59% of variation in dissolution in both regions for both dissolution indices. The dissolution index methodology is applied to a short sediment sequence from Devils Lake (North Dakota), where diatom-inferred salinity inferences can be compared with a historical record of salinity fluctuations over the 20th century. Absolute errors in paleosalinity estimates are strongly correlated with diatom dissolution, with salinity overestimated in 8 out of 11 poorly preserved samples. Preservation does appear to constrain the reliability of the inferred paleosalinity at this site and may also affect the quality of diatom-based paleoenvironmental inferences elsewhere (including estimates of biogenic silica), where preservation state is often not explicitly considered.

A method for automatic identification of diatoms (single-celled algae with silica shells) based on extraction of features on the contour of the cells by multi-scale mathematical morphology is presented. After extracting the contour of the cell, it is smoothed adaptively, encoded using Freeman chain code, and converted into a curvature representation which is invariant under translation and scale change. A curvature scale space is built from these data, and the most important features are extracted from it by unsupervised cluster analysis. The resulting pattern vectors, which are also rotation-invariant, provide the input for automatic identification of diatoms by decision trees and k-nearest neighbor classifiers. The method is tested on two large sets of diatom images. The techniques used are applicable to other shapes besides diatoms.

The chronosequence approach, which infers temporal patterns of environmental change from a spatial array of modem sites, has been a major tool for studying successional processes. A model of early lake ontogeny in boreal landscapes, developed from a chronosequence of lakes in Alaska, suggests that long-term soil development and related hydrological change produce a loss of alkalinity and base cations, a decrease in pH, an increase in DOC and a transient increase followed by a decrease in lakewater nitrogen concentrations over time. We compare this model of lake ontogeny with patterns of change reconstructed from diatom assemblages in 10 sediment cores from the same region. Lakewater pH declined in the majority of lakes, but the pattern, rate and magnitude of decline varied considerably among sites, apparently related to local differences in hydrologic setting. Inferred trends in nitrogen concentration over time are not spatially uniform and appear to vary because of local differences in vegetation history. Thus, patterns of early lake ontogeny may be spatially heterogeneous over timescales of many hundreds of years, even within relatively small geographic areas.

Palaeolimnological data (diatoms, ostracods, foraminifera, molluscs, aquatic pollen and lithology) from a radiocarbon dated sediment core from a saline lake, the Laguna de Medina, provide the first complete record of Holocene lake-level change for southwest Spain for the last c. 9000 cal. years. The lake has always been relatively shallow but has exhibited marked fluctuations in salinity and water depth, especially in the earlier record when oscillations culminate in maximum lake levels from c. 6960-6680 cal. BP ( c. 6070-5830 BP), indicating enhanced early to mid-Holocene humidity and a mid-Holocene humidity maximum. Prolonged shallowing thereafter reflects in part increased aridity in the later Holocene. Lake desiccation followed by a c. 800-yr phase (zone 2) of major limnological change commencing at c. 8000 cal. BP ( c. 7200 BP), and a number of other abrupt desiccation events, are also noteworthy. The mid-Holocene maximum is consistent with widespread evidence for high lake levels around 6000 BP, but the underlying climatic mechanisms are uncertain; there is some evidence it may apply predominantly to the westerly (Atlantic) Peninsula, withi earlier maxima in the east. Phases of abrupt limnological change show affinities with African data; as in African lakes, the ′zone 2′ phase appears to be a response to global change centred on c. 8.1-8.2 cal. BP. Other correlations made are tenuous, due partly to the lack of preservation in the upper record of some of the proxies used. Other desiccation events currently appear to be of more local significance, reflecting high decadal- to century-scale climatic variability throughout the Holocene.

1. Priority question exercises are becoming an increasingly common tool to frame future agendas in conservation and ecological science, used to identify research foci which are relevant to the needs of the scientific community and which also have high policy and conservation relevance. 2. To date there has been no coherent synthesis of key questions and priority research areas for palaeoecology, which combines biological, geochemical and molecular techniques in order to reconstruct ecological and environmental systems far into the past. 3. We adapted a well-established methodology to identify 50 priority research questions in palaeoecology. We used a set of criteria that were designed to identify realistic and achievable research goals, and selected questions from a pool submitted by the international palaeoecology research community and relevant policy practitioners. Questions are not ranked by priority but are grouped thematically, and are generally focussed on the late Cenozoic onwards (past c. 65 Ma). 4. The major difference in our methodology compared to other, similar exercises was the integration of online participation both before and during the workshop, representing an important development for increasing engagement and visibility. 5. The questions selected are structured around six themes: human-environment interactions in the Anthropocene; biodiversity, conservation, and novel ecosystems; biodiversity over long timescales; ecosystem processes and biogeochemical cycling; comparing, combining and synthesising information from multiple records; and methodological approaches to palaeoecology. 6. Future opportunities in palaeoecology are related to improved incorporation of uncertainty into reconstructions, an enhanced understanding of ecological and evolutionary dynamics and processes, and the continued application of long-term data for better-informed landscape management. 7. SYNTHESIS: The 50 priority questions selected in this exercise present palaeoecological science as a vibrant and thriving discipline, and highlight its vast potential for resolving both pure (e.g. theoretical) and applied (e.g. environmental) research questions directly related to ecological science and global change.

Davis, B.A.S. et al., Modern pollen samples provide an invaluable research tool for helping to interpret the quaternary fossil pollen record, allowing investigation of the relationship between pollen as the proxy and the environmental parameters such as vegetation, land-use, and climate that the pollen proxy represents. The European Modern Pollen Database (EMPD) is a new initiative within the European Pollen Database (EPD) to establish a publicly accessible repository of modern (surface sample) pollen data. This new database will complement the EPD, which at present holds only fossil sedimentary pollen data. The EMPD is freely available online to the scientific community and currently has information on almost 5,000 pollen samples from throughout the Euro-Siberian and Mediterranean regions, contributed by over 40 individuals and research groups. Here we describe how the EMPD was constructed, the various tables and their fields, problems and errors, quality controls, and continuing efforts to improve the available data.

To obtain more accurate reconstructions of past salinities and climate it is necessary to merge regional datasets of saline lake diatoms and water chemistry; a prerequisite of which is to standardize taxonomic practice. To illustrate this process, an investigation of the identity of a small Cyclotella species, frequently observed in the diatom community of saline lakes, is described. This taxon, which has been referred to in earlier literature as Cyclotella caspia, is of interest because it is present in fossil African assemblages, yet is absent from the modem flora of this region. Uncertainties over its correct identification prevented material in a North American dataset from being used as an analogue in salinity reconstructions. LM and SEM investigations reveal that there are no significant differences between Recent North American and Holocene sub-fossil North American and African material which suggests that the salinity optimum calculated from the North American water chemistry data can be used for ...

The Climate and Salinity (CASPIA) Project is concerned with diatoms as environmental indicators in inland waters and their use in reconstructing salinity and major ion composition from fossil diatom assemblages in lake sediments. By comparing saline lake diatom floras from around the world the project aims to establish a common, harmonised approach to sample collection, diatom identification and nomenclature, and to develop techniques for numerical analysis and data storage.

Spheroidal carbonaceous particles (SCPs) produced by high temperature combustion of coal and oil are found in significant concentrations in the surface sediments of lakes in areas of high acid deposition. The sediment record of these particles showing the onset of industrialisation correlates well with the record of acidification as indicated by diatom analysis. The surface sediments from 146 lakes in Scotland, U.K., were analysed for SCPs. The results show a pattern very similar to that of modelled sulphur deposition. However, within a region particle concentrations can vary quite considerably and this is generally assumed to be due to lake and catchment factors. A data set containing SCP concentration, sulphur deposition, lake altitude, area, maximum depth, volume, catchment area, catchment area: lake area ratio, residence time, and annual rainfall for the 146 lakes was compiled. Exploratory analysis of the data set using principal components analysis (PCA) indicated that sulphur deposition, lake size, altitude and annual rainfall were important in explaining SCP concentrations. Stepwise multiple regression confirmed this showing that sulphur deposition explained 32.6% of the variance in the SCP data and altitude, lake area and rainfall, selected sequentially, explained a further 9.8, 3.6 and 2.1%, respectively. We conclude that although there is a clear spatial correlation between SCP deposition and sulphur deposition, the relationship is not sufficiently strong for SCP concentration to be used quantitatively as a predictor of sulphur deposition at a lake site.

This paper presents a study of changes in eutrophication over the past 100 years in a fertile estuary. The Danish estuary Mariager Fjord is a long, narrow sill-fjord with a permanently anoxic basin. In 1997 anoxia spread from the basin to the entire inner estuary, killing almost all eukaryotes and prompting debate on the causes. This paper reports a multi-proxy survey of 210Pb-dated sediment cores from the anoxic basin. Analyses of diatoms, dinoflagellates, pigments and geochemical proxies were used to determine changes in ecosystem structure over the past 100 years. The aim was to establish ‘base-line conditions’, for management purposes, of the biological structure prior to 1900, and to examine possible causes of changes observed. Geochemical proxies total nitrogen (TN), total carbon (TC) and biogenic silica (BSi) were consistently high throughout the sediment record. Increased concentrations of pigments and natural isotopes (δ13C, δ15N) suggested increasing production and nutrient loading. The main changes in the biological proxies occurred between 1915 and the 1940s, and indicated that the estuary has been somewhat eutrophic since 1900, but that the eutrophication process increased over the past 100 years. A reconstruction of TN concentration by a diatom-based transfer function supports this interpretation, with inferred TN ca. 1900 around 60 μmol l−1, and an increase in TN concentration over the past century to ca. 130 μmol l−1 by 1995. Inferred TN decreased to ca. 100 μmol l−1 by 2001, similar to present day monitoring data.

Climate change during the late Pleistocene is dominated by periodicities on millennial time scales as documented by ice cores and sedimentary marine and terrestrial records of global distribution. Interannual to decadal variations have also been demonstrated in dust concentrations in Greenland ice cores but there is lack of comparable detail in sedimentary records. An 8.5 m long multiproxy record from Lake Albano (central Italy) spanning the time interval between B15.0 and 28.0 cal kyr BP reveals a high temporal resolution window into climate change during the Last Glacial Maximum (LGM). Distinct warm/cold cycles of millennial to centennial duration indicate a major response of the lake to climate-induced environmental changes. Flickering interannual to interdecadal variations within these cycles are interpreted to reflect oscillations of the North Atlantic (NAO) implying shifts in temperature, wind strength, source of moisture and atmospheric circulation pattern. r 2004 Elsevier Ltd and INQUA. All rights reserved.

As newly formed landscapes evolve, physical and biological changes occur that are collectively known as primary succession. Although succession is a fundamental concept in ecology, it is poorly understood in the context of aquatic environments. The prevailing view is that lakes become more enriched in nutrients as they age, leading to increased biological production. Here we report the opposite pattern of lake development, observed from the water chemistry of lakes that formed at various times within the past 10,000 years during glacial retreat at Glacier Bay, Alaska. The lakes have grown more dilute and acidic with time, accumulated dissolved organic carbon and undergone a transient rise in nitrogen concentration, all as a result of successional changes in surrounding vegetation and soils. Similar trends are evident from fossil diatom stratigraphy of lake sediment cores. These results demonstrate a tight hydrologic coupling between terrestrial and aquatic environments during the colonization of newly deglaciated landscapes, and provide a conceptual basis for mechanisms of primary succession in boreal lake ecosystems.

Unfortunately, the list of authors contains a number of duplications, omissions and other errors in the original publication of the article. The correct list appears in this erratum.

A diatom transfer function based on data from 152 lakes in northwest Europe is derived using the technique of weighted-averaging partial least squares (WAPLS) and applied to Lake Sobygard, a shallow, hypertrophic Danish lake, to infer past changes in epilimnetic total phosphorus (TP) concentrations since the 1930s. The results show that the two-component WAPLS model has low prediction errors (RMSEP = 0.21 log10 TP units) and is applicable to lakes distributed throughout northwest Europe, covering a TP range 10−1000 μg TP L-1. The example shows how the method can provide an estimate of baseline conditions and rates of enrichment, allowing managers to set realistic targets for lake restoration.