Short Sediment Cores Research Articles

Origin and transport of trace metals deposited in the canyons off Lisboa and adjacent slopes (Portuguese Margin) in the last century

Submarine canyons play an important role in the transfer of contaminated sediments from shelf areas to the deeper ocean. To evaluate the importance of submarine canyons adjacent to the Tagus and Sado estuaries (Portuguese Margin) as sediment pathway major and trace elements, 210Pb radionuclides, organic carbon, calcium carbonate and grain size were analyzed in fifteen short sediment cores from the Cascais and Lisboa–Setúbal submarine canyons and neighbor slopes at the Estremadura Spur and off Sines. Mass accumulation rates (MAR) vary between 0.02 and 0.40 g cm −2 y −1 with the highest values in the upper Cascais and Lisboa canyons. Mercury and Pb enrichment factors exceed 2 and show a continuously increasing trend since 1950 AD in the upper sections of the Cascais Canyon and in the Lisboa–Setúbal Canyon system, implying an anthropogenic source. Mercury and Pb anthropogenic inventories also present highest values in the canyon heads, which is consistent with its proximity to the Tagus and Sado river mouths. To a lesser extent, the Estremadura and Sines slopes and the deeper sections of the canyons also have slightly increasing Hg and Pb enrichment factor trends towards the present-day. For these areas, with a major influence of pelagic sedimentation, we infer atmospheric transport as a complementary source of contaminants. Therefore, our data suggest that although canyons are preferential conduits to transport sediments to the deep sea when compared to the slopes, Hg and Pb derived from human activities have reached both domains with different intensities down to a depth of 2000 mwd.

Late Little Ice Age palaeoenvironmental records from the Anzali and Amirkola Lagoons (south Caspian Sea): Vegetation and sea level changes

Two internationally important Ramsar lagoons on the south coast of the Caspian Sea (CS) have been studied by palynology on short sediment cores for palaeoenvironmental and palaeoclimatic investigations. The sites lie within a small area of very high precipitation in a region that is otherwise dry. Vegetation surveys and geomorphological investigations have been used to provide a background to a multidisciplinary interpretation of the two sequences covering the last four centuries. In the small lagoon of Amirkola, the dense alder forested wetland has been briefly disturbed by fire, followed by the expansion of rice paddies from AD1720 to 1800. On the contrary, the terrestrial vegetation reflecting the diversity of the Hyrcanian vegetation around the lagoon of Anzali remained fairly complacent over time. The dinocyst and non-pollen palynomorph assemblages, revealing changes that have occurred in water salinity and water levels, indicate a high stand during the late Little Ice Age (LIA), from AD < 1620 to 1800–1830. In Amirkola, the lagoon spit remained intact over time, whereas in Anzali it broke into barrier islands during the late LIA, which merged into a spit during the subsequent sea level drop. A high population density and infrastructure prevented renewed breaking up of the spit when sea level reached its maximum (AD1995). Similar to other sites in the region around the southern CS, these two lagoonal investigations indicate that the LIA had a higher sea level as a result of more rainfall in the drainage basin of the CS.

Temporal clustering of metals in a short sediment core of the Cascais Canyon (Portuguese Margin)

The Cascais Canyon delivers contaminated sediments from the shelf to the deep marine environment. Multi-core PE252-32, located at 2100 m water depth in the canyon, records the latest 300 years of sedimentation. It was dated by 210 Pb and analyzed texturally and geochemically for major elements and selected trace metals (Cu, Cr, Hg, Li, Ni, Pb and Zn). Cluster analysis performed on the down-core geochemical data identified four groups of variables related by grain-size, geochemical source and composition. Mercury, Pb and Zn were grouped in a cluster representing the anthropogenic component. Cluster analysis was applied again particularly to the latter cluster relatively to depth, in order to constrain the onset and temporal evolution of anthropogenic contamination. A second clustering, made on the basis of Hg, Pb and Zn, grouped samples by age and degree of anthropogenic contamination. One cluster contained relatively uncontaminated samples older than 1900 AD, and another cluster samples younger than 1900 AD with distinct metal enrichment. Maximum enrichments occurred during the early 1980s, followed by a slight recovery from the mid-1980s to the present. Mercury was the element with the highest enrichment factor (EFHg=5). Despite relatively low accumulation rates at this core location, our results show the importance of the Cascais Canyon as a transport route for contaminated sediments from the Tagus prodelta into the deep regions of the Portuguese Margin.

Quantifying large‐scale historical formation of accommodation in the Mississippi Delta

AbstractLarge volumes of new accommodation have formed within the Mississippi Delta plain since the mid‐1950s in association with rapid conversion of coastal wetlands to open water. The three‐dimensional aspects and processes responsible for accommodation formation were quantified by comparing surface elevations, water depths, and vertical displacements of stratigraphic contacts that were correlated between short sediment cores. Integration of data from remotely sensed images, sediment cores, and water‐depth surveys at 10 geologically diverse areas in the delta plain provided a basis for estimating the total volume of accommodation formed by interior‐wetland subsidence and subsequent erosion. Results indicate that at most of the study areas subsidence was a greater contributor than erosion to the formation of accommodation associated with wetland loss. Tens of millions of cubic meters of accommodation formed rapidly at each of the large open‐water bodies that were formerly continuous interior delta‐plain marsh. Together the individual study areas account for more than 440 × 106 × m3 of new accommodation that formed as holes in the Mississippi River delta‐plain fabric between 1956 and 2004. This large volume provides an estimate of the new sediment that would be needed just at the study areas to restore the delta‐plain wetlands to their pre‐1956 areal extent and elevations. Published 2010. This article is a US Government work and is in the public domain in the USA.

Quantifying the concentration of ferrimagnetic particles in sediments using rock magnetic methods

We have developed a quantification method that uses mainly room temperature rock magnetic measurements to calculate concentrations of ferrimagnetic particles in sediments. Our method uses saturation magnetization (Ms) as a total ferrimagnetic concentration proxy, the saturation remanence ratio (Mrs/Ms) as a magnetic grain‐size proxy, the anhysteretic remanence ratio (χa/Mrs) to estimate inter‐particle magnetostatic interactions, and the normalized susceptibility of the ferrimagnetic fraction (χf/Ms) to calculate the proportion of ultrafine, superparamagnetic particles. This approach eliminates the effect of dilution of the magnetic properties by weakly magnetic matter, and allows the calculation of direct concentrations (or fluxes for dated sedimentary profiles) of constituent ferrimagnetic components. We test our method on a short sediment core from an urban Minnesota lake, for which we calculate ferrimagnetic fluxes of four magnetic components, and compare their pre‐ and post‐European settlement values. Our quantification technique can be applied for reconstructing past environmental changes in a range of sedimentary environments, and is particularly useful for large sets of samples, where detailed magnetic unmixing methods are unfeasible due to time or instrument constraints.

Regional Pattern of Heavy Metal Content in Lake Sediments in Northeastern Poland

We investigated sediments from 23 lakes situated in northeastern Poland and analyzed them for major constituents and selected heavy metals. Short sediment cores were collected from the deepest parts of the lakes, and subsequently, a surface layer (0–2 cm) and reference layer (50–52 cm) were sampled from each. In the collected samples, the content of the major constituents (organic matter, carbonates, and minerogenic material) and chosen heavy metals (Cd, Cu, Ni, Pb, and Zn) was analyzed. In the reference layer, representing natural metal content, we identified quite a substantial diversity among lakes, making it difficult to pinpoint one geochemical background value for the whole region. A multivariate analysis of the interrelationships among elements and a comparison of the median values revealed no statistically significant differences between surface and reference levels. The ratio of the mean content in the surface and reference sediments ranged from 0.9 to 1.6, indicating the lack of or only slight anthropogenic pollution in surface sediments. From a spatial perspective, higher metal contents were observed in the eastern part of the study area, but this trend manifested in both surface and reference sediments. Thus, the inference is that the recently accumulated sediments are characterized by a content that is representative of the natural geochemical background for the selected metals.

Quaternary Arctic Ocean sea ice variations and radiocarbon reservoir age corrections

A short sediment core from a local depression forming an intra basin on the Lomonosov Ridge, was retrieved during the Healy-Oden Trans-Arctic Expedition 2005 (HOTRAX). It contains a record of the Marine Isotope Stages (MIS) 1–3 showing exceptionally high abundances of calcareous microfossils during parts of MIS 3. Based on radiocarbon dating, linear sedimentation rates of 7–9 cm/ka persist during the last deglaciation. The Last Glacial Maximum (LGM) is partly characterized by a hiatus. Planktic foraminiferal abundance variations of Neogloboquadrina pachyderma sinistral and calcareous nannofossils reflect changes in Arctic Ocean summer sea ice coverage and probably inflow of subpolar North Atlantic water. Calibration of the radiocarbon ages, using modeled reservoir corrections from previous studies and the microfossil abundance record of the studied core, results in marine reservoir ages of 1400 years or more, at least during the last deglaciation. Paired benthic–planktic radiocarbon dated foraminiferal samples indicate a slow decrease in age difference between surface and bottom waters from the Lateglacial to the Holocene, suggesting circulation and ventilation changes.

Chronology and nutrients change in recent sediment of Taihu Lake, lower Changjiang River Basin, east China

Two short sediment cores named ZS and THS dated by the 210 Pb or 137 Cs method were collected from the northwest and southwest of Taihu Lake respectivly, and total organic carbon (TOC) and nutrients including total nitrogen (TN) and total phosphorus (TP) were determined to analyze the chronology and nutrients change in recent sediment. The results show that 137 Cs activities are low (less than 15 Bq/kg) in the two cores, attributed to the 137 Cs migration. Based on 210 Pb constant rate of supply (CRS) model, the sedimentation accumulation rates range from 0.13 g/(cm 2 •yr) to 0.76 g/(cm 2 •yr) in the ZS core, and from 0.10 g/(cm 2 •yr) to 0.56 g/(cm 2 •yr) in the THS core. A remarkable increase in organic matter and nutrients has occurred in the two dated cores since the mid-1980s. The historical changes of organic matter and nutrients in the two cores are consisitent with the monitoring data for surface sediment after the 1960s. The TP accumulation rates after the early 1980s are 0.97 and 0.92 times higher than those from the 1950s to the 1980s in ZS and THS cores, respectively. Higher TP concentrations in the past two-decade deposits of Taihu Lake are due to both diagenetic factors and human activities.

Geochemical sources, deposition and enrichment of heavy metals in short sediment cores from the Pearl River Estuary, Southern China

The Pearl River Estuary (PRE) is the largest estuary in the Southern China. Four short sediment cores (45–60 cm long) recovered within the PECAI project from the estuary have been analyzed for grain size and geochemistry to reveal geochemical source and deposition environment and to assess enrichment and pollution of heavy metals in the sediments. Four geochemical sources were identified as lithogenic, marine biogenic, anthropogenic and reductive deposit by the correlation analysis and principal component analysis. The representative elements and related elemental ratio reflected different depositional environments in the four cores, which are controlled by the hydrodynamic conditions in the PRE. Core IOW300 190 at the mid West Shoal maintained a constant sub-oxic environment with abundant fluvial deposits; core IOW300 480 at the mouth of the estuary formed an oxic environment influenced by the strong two-layer currents, while two cores (IOW300 020 and IOW300 630) at the East Shoal experienced an evident change from marine anoxic condition to a weak anoxic or a sub-oxic condition caused by increasing riverine discharges. According to the enrichment factors (EFs) of heavy metals (Co, Cr, Cu, Hg, Ni, Pb and Zn), there was no significant metal enrichment and contamination in the core sediments in spite of that some metals increased and was partly enriched in the uppermost or surface sediments. Hg was enriched in all four cores due to its non-point sources; enrichment of Cu and Pb in the core IOW300 020 was attributed to the proximity with the point sources of the pollutants. Core IOW300 630, with a constant sedimentation rate of 0.45 cm/a by Cs 137 and Pb 210 dating, exhibits that heavy metals began to increase in the 1960s and increased progressively in the 1980s and 1990s, responding to the rapid economic development in the Pearl River delta region in the last three decades.

Nutrients and heavy metals in multi-cores from Zhushan Bay at Taihu Lake, the largest shallow lake in the Yangtze Delta, China

Taihu Lake is the third largest freshwater lake of China. The Taihu Lake drainage basin is an economically developed area, with one of the highest population densities in China. Zhushan Bay was one of the most polluted water bodies in northern Taihu Lake. Ten short sediment cores were collected from Zhusan Bay in 2003 and 2004. Heavy metals and nutrients were analyzed in order to understand their temporal and spatial change in recent sediments. The profiles of heavy metals (Cu, Pb, Zn, Cr and Ni) and nutrients (TOC, TN and TP) were similar showing upcore increasing tendencies in the top 5–10 cm sediments for most cores while the depth of increase for OP was deeper than for other nutrients. TOC, TN, TP and OP averages are, respectively, 8.17, 0.92, 0.37 and 0.015 g/kg and 11.65, 1.16, 0.67, 0.093 g/kg for 10–30 cm and 0–10 cm sediment. The average value of Cu, Pb, Cr, Zn and Ni is 18.4, 24.6, 52.8, 55.6 and 27.8 mg/kg for 10–30 cm sediment, and 30.2, 39.5, 73.9, 100.2 and 41.0 mg/kg for 0–10 cm sediment, respectively. Except for lead, high positive correlations (>0.86, P < 0.001) were found for Cr–Cu, Cr–Zn, Cr–Ni, Cu–Zn, Cu–Ni, Ni–Zn elements indicating the different source of lead pollution. According to Sediment Quality Guidelines, most layers of 0–5 cm sediment were moderately or heavily polluted by Pb, Cu, Zn, Cr and Ni in cores from Zhushan Bay. Most 5–30 cm sediments were unpolluted by Pb, Cu and Zn. However, all sediments from Zhushan cores were polluted by Ni and Cr. Compared with the background level of Ni and Cr elements, high local levels of Ni and Cr for Jiangsu paddy field leads to high concentration of Ni in Zhushan core sediment.

Benthic foraminifera in Hornsund, Svalbard: Implications for paleoenvironmental reconstructions

Benthic foraminifera in Hornsund, Svalbard: Implications for paleoenvironmental reconstructions Modern hydrology of a typical Arctic fjord (Hornsund, SW Spitsbergen, Svalbard) was investigated and compared with commonly used in paleoceanography proxies: benthic foraminiferal assemblages and their stable isotope (Δ18O and Δ13C) composition. The benthic foraminifera from Hornsund comprised 45 species and 28 genera. Their spatial variations follow the zonation pattern, resulting from the influence of Atlantic water at the fjord mouth and glacial meltwaters at the fjord head. At the mouth of the fjord, the total number of species and the contribution of agglutinating species were the highest. In the inner part of fjord, the foraminiferal faunas were poor in species and individuals, and agglutinating species were absent. "Living" (stained) foraminifera were found to be common throughout the short sediment cores (~10 cm long) studied. The stable isotope values of Δ18O and Δ13C were measured on tests of four species: Elphidium excavatum forma clavata, Cassidulina reniforme, Nonionellina labradorica and Cibicides lobatulus. The results confirmed the importance of species-specific vital effects, particularly in the case of C. lobatulus. The variability in the isotopic composition measured on different individuals within a single sample are comparable to isotopic composition of the same species test between sampling stations. The temperatures and bottom water salinities calculated from Δ18O values in different foraminifera tests mirrored those recorded for bottom waters in the central and outer fjords relatively well. However, in the case of the inner fjord, where winter-cooled bottom waters were present, the calculated values from Δ18O were systematically higher by about 2°C. The obtained results imply that particular caution must be taken in interpretation of fjord benthic foraminifera assemblages in high resolution studies and in selection of material for isotope analyses and their interpretation in cores from inner fjords or silled fjords, where winter-cooled waters may be present.

Climatic significance of hydrogen isotope ratios of terrigenous n-alkanes in Kongmo Co on the southern Tibetan Plateau

We sampled a short sediment core in Lake Kongmo Co on the southern Tibetan Plateau,and extracted terrigenous alkanes (n-C_(25) to n-C_(31)) from the core spanning the past near-50 years at 7-year resolution,and compared the hydrogen isotope ratios of these biomarkers with meteorological records of the nearby Langkazi and Lhasa weather stations.Hydrogen isotope ratios of these n-alkanes significantly correlated with mean growing season air temperature,whereasδD values of these biomarkers showed poor correlations with both precipitation amount and relative humidity during the growth seasons,indicating that these n-alkanes recorded the air temperature signal and can be used as a proxy for paleotemperature reconstruction.

Assessment of recent eutrophication and climate influence in the Archipelago Sea based on the subfossil diatom record

Two short sediment cores from the Archipelago Sea in the northern Baltic Sea were examined for their siliceous microfossils in order to study recent eutrophication in the area. The diatom record was divided into diatom assemblage zones. Locally weighted weighted averaging regression and calibration was applied for the quantitative reconstruction of past TN concentrations. The cores were dated using radiometric (210Pb, 226Ra and 137Cs) methods. The diatom assemblages in the topmost zones in both cores indicate eutrophication during the last decade. TN reconstructions partially fail to trace the actual measured TN concentrations. Especially from the late 1980s to the mid 1990s, the dominating diatom species are more influenced by other factors, such as the length of the ice season, than by nutrient concentrations. It seems that in the Archipelago Sea, diatom assemblages are principally governed by climatic fluctuations with a moderate influence of eutrophication in recent years. The peak in sedimentation in the early 1990s coincides with the short ice seasons indicating that sedimentation may increase with decreasing ice-cover extent due to warming climate.

Ecological implications of heavy metal concentrations in the sediments of Burullus Lagoon of Nile Delta, Egypt

This paper examines the spatial and temporal distribution of heavy metals (Fe, Al, Cu, Zn, Mn, Cd, Pb and Ni) from three short sediment cores collected from Burullus lagoon of the Nile delta, Egypt. 210Pb and 137Cs measurement is applied to understand sedimentation rate and related chronology. Remarkably low isotopic activities and intensive bioturbation in the lagoonal sediments rendered age determination difficult. Samples with detectable 137Cs in the upper core sediments together with sediment lithology could help infer a sedimentation rate of about 2.0 mm yr −1, thereby indicating post-dam (after 1964) sedimentation of the upper 10-cm core sediments. Our results demonstrate that most heavy metals in the surficial sediments after normalization to Al decrease seaward, showing a function of distance to the sewerage outlet on the inland lake coast. Also, there is an upwardly increasing trend of normalized heavy metals, especially in the upper 10-cm core sediments. Relevancy analysis has identified Mn, Pb and Cd as the diagnostic heavy metals in Burullus lagoon, most likely derived from Tanta and Kafrelsheihk, the major downtowns in the central Nile delta plain, from where wastewaters are directly discharging into the lake via canal networks. Although Burullus lagoon is presently least affected by pollution as compared to other major lagoons of the Nile delta, the increasing quantities of diagnostic metals, especially Mn, are extremely toxic, as they are potentially linked to the risks of digestive issues and pancreatic cancer reportedly. The situation calls for a rational planning for sewerage treatment in the protected Burullus coast.

A quantitative high-resolution summer temperature reconstruction based on sedimentary pigments from Laguna Aculeo, central Chile, back to AD 850

We present a pigment-based quantitative high-resolution (five years) austral summer DJF (December to February) temperature reconstruction for Central Chile back to AD 850. We used non-destructive in situ multichannel reflection spectrometry data from a short sediment core of Laguna Aculeo (33°50′S/70°54′W, 355 m a.s.l., central Chile). Calibration-in-time (period AD 1901—2000, cross-validated with split periods) revealed robust correlations between local DJF temperatures and total sedimentary chlorin (relative absorption band depth (RABD) centred in 660—670 nm RABD660;670: r=0.79, P&lt;0.01; five-years triangular filtered) and the degree of pigment diagenesis ( R660nm/670 nm: r=0.82, P&lt;0.01; five-years triangular filter). Root Mean Squared Error values are small (between 0.24 and 0.34°C) suggesting that most of the reconstructed decadal-scale climate variability is significant. Our data provide quantitative evidence for the presence of a Medieval Climate Anomaly (in this case, warm summers between AD 1150 and 1350; Δ T = +0.27 to +0.37°C with respect to (wrt) twentieth century) and a very cool period synchronous to the ‘Little Ice Age’ starting with a sharp drop between AD 1350 and AD 1400 (−0.3°C/10 yr, decadal trend) followed by constantly cool (Δ T = −0.70 to −0.90°C wrt twentieth century) summers until AD 1750. The structure of variability is consistent in great detail with annually resolved tree-ring based warm-season temperature and river discharge reconstructions from northern Patagonia (42°S) for the past 400 years, with qualitative climate reconstructions from Andean glacier fluctuations, and with hydrological changes in Patagonian lake sediment records.

Mercury accumulation and attenuation at a rapidly forming delta with a point source of mining waste

The Walker Creek intertidal delta of Tomales Bay, California is impacted by a former mercury mine within the watershed. Eleven short sediment cores (10 cm length) collected from the delta found monomethylmercury (MMHg) concentrations ranging from 0.3 to 11.4 ng/g (dry wt.), with lower concentrations occurring at the vegetated marsh and upstream channel locations. Algal mats common to the delta's sediment surface had MMHg concentrations ranging from 7.5 to 31.5 ng/g, and the top 1 cm of sediment directly under the mats had two times greater MMHg concentrations compared to adjacent locations without algal covering. Spatial trends in resident biota reflect enhanced MMHg uptake at the delta compared to other bay locations. Eighteen sediment cores, 1 to 2 m deep, collected from the 1.2 km 2 delta provide an estimate of a total mercury (Hg) inventory of 2500 ± 500 kg. Sediment Hg concentrations ranged from pre-mining background conditions of approximately 0.1 μg/g to a post-mining maximum of 5 μg/g. Sediment accumulation rates were determined from three sediment cores using measured differences of 137Cs activity. We estimate a pre-mining Hg accumulation of less than 20 kg/yr, and a period of maximum Hg accumulation in the 1970s and 1980s with loading rates greater than 50 kg/yr, corresponding to the failure of a tailings dam at the mine site. At the time of sampling (2003) over 40 kg/yr of Hg was still accumulating at the delta, indicating limited recovery. We attribute observed spatial evolution of elevated Hg levels to ongoing inputs and sediment re-working, and estimate the inventory of the anthropogenic fraction of total Hg to be at least 1500 ± 300 kg. We suggest ongoing sediment inputs and methylation at the deltaic surface support enhanced mercury levels for resident biota and transfer to higher trophic levels throughout the Bay.

Past atmospheric Pb deposition in Lake Qinghai, northeastern Tibetan Plateau

Two short sediment cores were recovered from sub-basins of Lake Qinghai, China and were analyzed for concentrations of Pb and 16 other elements to determine historic, regional atmospheric Pb deposition on the Tibetan Plateau. Core chronologies, dating back to the eighteenth century, were established using activities of 210Pb and 137Cs. The 17 elements were divided into three principal components. Variations in concentrations of PC1 elements (Al, Cr, Cu, Fe, K, Mn, Ni, and Ti) demonstrate different patterns between the two cores, and are attributed to different sediment sources in the two sub-basins. PC2 elements (Ba, Ca, Na, and Sr) may be associated with the degree of catchment weathering and/or water chemistry. Four elements (Pb, Zn, P, and Co) are related to both PC1 and PC2, and reflect a mixture of natural and anthropogenic sources. The PC3 element is Mg in the north sub-basin, and is perhaps related to aragonite precipitation and/or increased farming. Elevated Pb concentrations in uppermost sediments of both cores signify a recent regional/global increase in anthropogenic Pb release into the environment. After subtracting lithogenic Pb, derived from rock weathering and/or dust and normalized to the background immobile element Ti, results suggest that excess, anthropogenic Pb is transferred to the lake and its sediments predominantly via the atmosphere. This anthropogenic atmospheric Pb is comparable in magnitude and displays similar variation patterns in the two cores, reflecting regional atmospheric deposition and local erosion. The average anthropogenic Pb deposition rate in Lake Qinghai since the 1960s has been ~12.2 ± 3.5 mg/m2/a, comparable with atmospheric Pb fluxes reported for sites elsewhere in the northern hemisphere.

A 1000‐year record of dry conditions in the eastern Canadian prairies reconstructed from oxygen and carbon isotope measurements on Lake Winnipeg sediment organics

AbstractA short sediment core (162 cm), covering the period AD 920–1999, was sampled from the south basin of Lake Winnipeg for a suite of multi‐proxy analyses leading towards a detailed characterisation of the recent millennial lake environment and hydroclimate of southern Manitoba, Canada. Information on the frequency and duration of major dry periods in southern Manitoba, in light of the changes that are likely to occur as a result of an increasingly warming atmosphere, is of specific interest in this study. Intervals of relatively enriched lake sediment cellulose oxygen isotope values (δ18Ocellulose) were found to occur from AD 1180 to 1230 (error range: AD 1104–1231 to 1160–1280), 1610–1640 (error range: AD 1571–1634 to 1603–1662), 1670–1720 (error range: AD 1643–1697 to 1692–1738) and 1750–1780 (error range: AD 1724–1766 to 1756–1794). Regional water balance, inferred from calculated Lake Winnipeg water oxygen isotope values (δ18Oinf‐lw), suggest that the ratio of lake evaporation to catchment input may have been 25–40% higher during these isotopically distinct periods. Associated with the enriched δ18Ocellulose intervals are some depleted carbon isotope values associated with more abundantly preserved sediment organic matter (δ13COM). These suggest reduced microbial oxidation of terrestrially derived organic matter and/or subdued lake productivity during periods of minimised input of nutrients from the catchment area. With reference to other corroborating evidence, it is suggested that the AD 1180–1230, 1610–1640, 1670–1720 and 1750–1780 intervals represent four distinctly drier periods (droughts) in southern Manitoba, Canada. Additionally, lower‐magnitude and duration dry periods may have also occurred from 1320 to 1340 (error range: AD 1257–1363), 1530–1540 (error range: AD 1490–1565 to 1498–1572) and 1570–1580 (error range: AD 1531–1599 to 1539–1606). Copyright © 2009 John Wiley &amp; Sons, Ltd.

Climate changes and human activities recorded in the sediments of Lake Estanya (NE Spain) during the Medieval Warm Period and Little Ice Age

A multi-proxy study of short sediment cores recovered in small, karstic Lake Estanya (42°02′ N, 0°32′ E, 670 m.a.s.l.) in the Pre-Pyrenean Ranges (NE Spain) provides a detailed record of the complex environmental, hydrological and anthropogenic interactions occurring in the area since medieval times. The integration of sedimentary facies, elemental and isotopic geochemistry, and biological proxies (diatoms, chironomids and pollen), together with a robust chronological control, provided by AMS radiocarbon dating and 210Pb and 137Cs radiometric techniques, enabled precise reconstruction of the main phases of environmental change, associated with the Medieval Warm Period (MWP), the Little Ice Age (LIA) and the industrial era. Shallow lake levels and saline conditions with poor development of littoral environments prevailed during medieval times (1150–1300 AD). Generally higher water levels and more dilute waters occurred during the LIA (1300–1850 AD), although this period shows a complex internal paleohydrological structure and is contemporaneous with a gradual increase of farming activity. Maximum lake levels and flooding of the current littoral shelf occurred during the nineteenth century, coinciding with the maximum expansion of agriculture in the area and prior to the last cold phase of the LIA. Finally, declining lake levels during the twentieth century, coinciding with a decrease in human pressure, are associated with warmer climate conditions. A strong link with solar irradiance is suggested by the coherence between periods of more positive water balance and phases of reduced solar activity. Changes in winter precipitation and dominance of NAO negative phases would be responsible for wet LIA conditions in western Mediterranean regions. The main environmental stages recorded in Lake Estanya are consistent with Western Mediterranean continental records, and show similarities with both Central and NE Iberian reconstructions, reflecting a strong climatic control of the hydrological and anthropogenic changes during the last 800 years.

Reconstruction of human influence during the last two centuries on two small oxbow lakes near Warsaw (Poland)

Short sediment cores from two small oxbow lakes located in the Vistula valley near Warsaw (Poland) were analysed for chemical composition and zooplankton (Cladocera) remains. The results of these analyses were evaluated using ordination techniques and the results were used to reconstruct the history of human impact of the lakes. The cores were dated using the 210Pb method. These analyses show that the collected sediments (60 cm- and 67 cm-long-cores) were deposited during the last 150–200 years. Cladocera assemblages were different in the two lakes; however, Bosmina longirostris was dominant among subfossil Cladocera species in both lakes. The presence of this species indicates the high trophic state of the lakes. Changes in Cladocera species composition suggest that a significant increase in the lakes’ trophic levels has occurred since the 1920s. The change could be related to the construction of flood dikes along the river Vistula, the isolation of the studied lakes from the river, changes in land use, or some combination of these factors. The chemical composition of sediments, particularly the increase in phosphorus and sulphur concentrations, confirms that the construction of dikes against flood was the major factor inducing eutrophication of the oxbow lakes. This study shows that the Warsaw small water bodies are especially sensitive to local disturbances caused by human activity, mainly water management, land use changes and agriculture.