ALBERT

Description: Between October 2008 and May 2009, the International Continental Scientific Drilling Program (ICDP) co-sponsored a campaign at Lake El´gygytgyn, located in a 3.6-Ma-old meteorite impact crater in northeastern Siberia. Drilling targets included three holes in the center of the 170-m-deep lake, utilizing the lake ice cover as a drilling platform, plus one hole close to the shore in the western lake catchment. At the lake’s center. the entire 315-m-thick lake sediment succession was penetrated. The sediments lack any hiatuses (i.e., no evidence of basin glaciation or desiccation), and their composition reflects the regional climatic and environmental history with great sensitivity. Hence, the record provides the first comprehensive and widely timecontinuous insights into the evolution of the terrestrial Arctic since mid-Pliocene times. This is particularly true for the lowermost 40 meters and uppermost 150 meters of the sequence, which were drilled with almost 100% recovery and likely reflect the initial lake stage during the Pliocene and the last ~2.9 Ma, respectively. Nearly 200 meters of underlying rock were also recovered; these cores consist of an almost complete section of the various types of impact breccias including broken and fractured volcanic basement rocks and associated melt clasts. The investigation of this core sequence promises new information concerning the El´gygytgyn impact event, including the composition and nature of the meteorite, the energy released, and the shock behavior of the volcanic basement rocks. Complementary information on the regional environmental history, including the permafrost history and lake-level fluctuations, is being developed from a 142-m-long drill core recovered from the permafrost deposits in the lake catchment. This core consists of gravelly and sandy alluvial fan deposits in ice-rich permafrost, presumably comprising a discontinuous record of both Quaternary and Pliocene deposits. doi:10.2204/iodp.sd.11.03.2011

Description: In order to assess the importance of different pollution sources for the increase in element concentration and accumulation, historical changes in selected elements were studied in the annually laminated sediment of Lake Korttajärvi in Central Finland (62°20′N; 25°41′E). The sediment chronology based on varve counting (256 BC to AD 2005) provided a unique opportunity to explore and date signals of metal emissions, including the ancient metallurgical activities of the Roman Empire at the beginning of the Current Era. Records of this kind are mostly lacking in Finland and northernmost Europe. The stratigraphic sequence of element concentrations did not reflect any major changes in the lake, but changes in element accumulation rates provided distinct pollution signals caused by airborne fallout, catchment erosion, and to some extent municipal wastewater loading. The maximum bulk sedimentation recorded in the twentieth century was 11-fold and organic sedimentation 4-fold higher than the mean background sedimentation rate (256 BC to AD 1019). The increase in the accumulation rates of the majority of the elements, such as Cd, Sn, Pb, Si, Ni, B, Cu, Zn, Sr, Na, K, Sb, Ca, Cr, U and Mg, in descending order, was at least equal to that of bulk sedimentation or much greater, especially for Cd, Sn, and Pb. Changes in the accumulation of Co, Fe, Mn, Mo and As were small and mainly followed those of organic sedimentation. The earliest pollution signals were those of Pb recorded in AD 1055–1141. A weak signal of Pb pollution from the Roman Era was detected in metal concentrations, but this could not be confirmed by the accumulation rate data for Pb.

Description: Holocene palaeomagnetic secular variation (PSV) in inclination and declination recorded in the sediment remanent magnetization of two small lakes, Lake Lehmilampi (63°37'N, 29°06'E) and Lake Kortejärvi (63°37'N, 28°56'E) in eastern Finland is presented. As an outcome of systematic coring, eight cores, 300–753 cm in length, were investigated. All samples (Lehmilampi n= 1320, Kortejärvi n= 943) were subjected to palaeo- and mineral magnetic analyses. The directions of the characteristic remanent magnetization (ChRM) were obtained from progressive alternating field demagnetization of the natural remanent magnetization (NRM) followed by principle component analysis. The younger sections of the sediment columns in the studied lakes are annually laminated, providing detailed chronologies for dating PSV features back to 5100 cal. BP. The underlying older sections of the cores were dated by palaeomagnetic pattern matching in respect to varve-dated Lake Nautajärvi PSV data (Ojala & Saarinen 2002), thus yielding a composite age model covering nearly the whole Holocene epoch. Average sedimentation rates ranging from ∼0.68 to 0.74 mm yr−1 enabled recording of changes in the geomagnetic field at decadal resolution. The carriers of remanence are dominantly magnetite of stable single-domain to pseudo-single-domain grain size, accompanied by magnetic minerals of harder coercivity. The sediments from both lakes exhibit strong and stable single-component magnetizations nearly throughout the whole cores. The sediment magnetization lock-in delay is estimated to range between 80 and 100 yr. PSV data were transformed into time-series and subsequently stacked to comprise North Karelian stack, and Fisher statistics were used to calculate mean directions together with the 95 per cent confidence level (α95). A comparison of declination and inclination features of the North Karelian stack with previously published data expresses remarkable similarity, therefore confirming the similar source behind the changes in the NRM directional records. The high quality of the PSV data extracted from Lehmilampi and Kortejärvi, in terms of dating as well as amplitude reconstruction, have a high potential to improve existing and future geomagnetic field models.

Description: A high-resolution geochemical profile from a 5,500-year-old sediment core of Lake Lehmilampi in eastern Finland was analyzed to study long-term trends and variability in element concentrations and accumulation rates. The accumulation rates of all studied elements followed the same trend, responding to changes in the total sedimentation rate. Concentration profiles differed among elements and showed considerable variation over time. Principal components analysis (PCA) was used on the concentration data to identify groups of elements that have similar geochemical controls. The first principal component was influenced by changes in mineral matter accumulation, and it incorporated elements that are associated with stable allochthonous minerals (such as Mg, K, Cs, Rb, Li, Ti and Ga), as well as elements in forms that become diluted when mineral matter increases (e.g., S, Fe and Mn). The second and third principal components showed that a large proportion of the variance was accounted for by elements with continuously increasing or decreasing concentrations related to pedogenetical development of the catchment soil. In the case of Hg, Pb and Cd, however, accumulation rates increased faster at the surface than is simply accounted for by changes in total sedimentation rates. For Cu, Cr, Ni and Zn, concentrations increased over the past 150 years, but there were no indications of a significant addition due to atmospheric deposition. These elements had more variable concentrations before the mid nineteenth century than after, as did elements that are often used for normalization. These findings suggest that lake sediments may not properly reflect the history of atmospheric metal deposition in remote areas.

Description: Standard mineral magnetic measurements, including magnetic susceptibility, ARM and IRM, were carried out on two Holocene sediment cores from Lake Lehmilampi (Finland), which span the last ~9,700 years. Paleoenvironmental changes were inferred from stratigraphic variations in the sediment mineral magnetic properties. Total organic carbon (TOC) measurements supplement the bulk mineral magnetic data. Development of Lake Lehmilampi is closely connected with Lake Pielinen, from which Lake Lehmilampi was gradually isolated ~5,066 Cal. years BP. Since the isolation of Lake Lehmilampi, its sediment has been annually laminated, with clastic-organic varves in the deep basin. Magnetic mineralogy is dominated by ferrimagnetic minerals, interpreted as magnetite throughout the sediment column, with a variable, but minor contribution of antiferromagnetic minerals. Sediment magnetic properties indicate a series of changes in sediment composition during the Holocene, which correlate well with sediment lithology and TOC. Magnetic properties differ in pre- and post-isolation sediments with respect to concentration of fine-grained magnetite, as expressed by χARM and χARM/SIRM, showing variation in response to organic matter content in post-isolation varved sediments. This may reflect authigenic bacterial production of magnetite in the weakly anoxic environment. Preliminary data suggest that magnetosome production in Lake Lehmilampi is controlled by lake productivity, and ultimately by climate.

Description: As part of understanding and reconstructing our climate history it is important to investigate the link between climate and solar activity. Ice cores and ocean sediments have provided information on a range of timescales on atmospheric 10Be production, which is a proxy for past solar activity due to its cosmogenic nature of production. We here present results from the first, to our knowledge, multi-centennial and annual resolution study of 10Be in varved lake sediments. Varves were sampled over an interval covering the period 1468–2006 CE in sediment cored from Lake Lehmilampi in eastern Finland. The measured concentrations were converted into annual 10Be deposition rates by using the weights of dried samples as an estimation of sedimentation rates and scaling the result from sampling to catchment area size. We compare the lake catchment 10Be deposition rates to those derived from the Greenlandic ice cores NGRIP and Dye-3 along with past solar activity. Sediment 10Be concentrations range 2.1–17.6 × 108 atoms g−1. The high end of this range is represented by a limited number of samples, and the average is near the lower end at 4.1 × 108 atoms g−1. The deposition rates range 0.5–3.9 × 106 atoms cm−2 year−1, with an average of 1.8 × 106 atoms cm−2 year−1 (0.057 atoms cm−2 s−1). We note higher 10Be deposition during the Spörer (∼1415–1535 CE) and Maunder (∼1645–1715 CE) solar minima, and also at the onset of the Dalton (∼1790–1830 CE) minimum. Equally high 10Be values in the 1840s and lower deposition during the Dalton minimum are not consistent with contemporaneous solar activity. Although this may in part be a result of incomplete measurements in the 19th century, it also shows the complexity of deposition and the intricacy of reconstructing past solar activity from sediment 10Be data. A comparison with ice core data reveals particularly good agreement between sediment and Dye-3 10Be flux around 1500–1750 CE.