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TitleHolocene climate change influences on trace metal and organic matter geochemistry in the sediments of an Arctic lake over 7,000 years
AuthorOutridge, P M; Sanei, H; Courtney-Mustaphi, C J; Gajewski, K
SourceApplied Geochemistry vol. 78, 2016 p. 35-48,
Alt SeriesEarth Sciences Sector, Contribution Series 20160366
Mediapaper; on-line; digital
File formatpdf
AreaDevon Island
Lat/Long WENS -90.0000 -89.0000 75.7500 75.5000
Subjectsgeochemistry; sedimentology; lake sediment geochemistry; lake sediments; organic geochemistry; organic deposits; sedimentation rates; lake sediment cores; carbonates; dolomites; limestones; shales; reflectance; vitrinite reflectance; kerogen; algae; macerals; climate effects; Holo
Illustrationsequations; graphs; tables; geochemical plots
ProgramManagement, Environmental Geoscience
AbstractThis study employed a 6.48 m long dated sediment core to characterize the amount of variation in background trace metal concentrations, and develop an understanding of the role of climatic influences on sediment inorganic and organic geochemistry in a High Arctic lake over ~7000 years of the Holocene. Element geochemistry reflected varying detrital contributions from two geological sources within the catchment: carbonates (dolomites and limestones) which provided the dominant major element by weight (i.e., Ca), and carbonaceous mudrocks (primarily shales) which may have contributed most of the other trace and minor elements. The presence of eroded shale-hosted organic matter (OM) in sediments was confirmed by reflectance measurements on reworked vitrinitic macerals which had similar values to Palaeozoic carbonaceous rocks in the watershed. Bimodal distribution of the reflectance data suggested that two sources of vitrinitic macerals were present, from different formations. Variable dilution of shalesourced elements by carbonates, related to climate (temperature)-influenced rates of dissolution and erosion, was the dominant process controlling inorganic geochemical composition. RockEval pyrolysis of bulk sediment OM revealed the unusual finding of two distinct sources of sediment kerogen which alternated in importance during the Holocene: a “baseline” state of eroded shale-hosted OM which was probably always present but which dominated sediment OM when autochthonous (algal) production was minimal, and an “enhanced algal state” which dominated when limnological conditions favored higher autochthonous productivity. Periods with more frequent examples of the enhanced algal state occurred during the mid- and late-Holocene, coincident with periods of relatively high summer air temperatures in the region. This study provides evidence that climate, particularly air temperature, influenced sediment inorganic and organic geochemical compositions in this lake through its effect on catchment geology erosion rates and aquatic primary productivity. It shows the value of studying very long periods of sediment accumulation as a background context for recent sediment metal concentrations.
Summary(Plain Language Summary, not published)
In a northern Canadian lake, two geological sources in the catchment provided all of the trace metals in the sediment: Ordovician limestone and dolomite, and Paleozoic shales, with the shales providing the bulk of most metals. Throughout the last 7,000 years of the Holocene, varying inputs of carbonates, influenced by climate-driven rates of dissolution and erosion, diluted the inputs of shale-hosted trace elements, resulting in an inverse relationship between most element concentrations and summer air temperatures. The shales also contributed ancient organic matter (OM) to the sediments which probably was the carrier of most of the metals from that source. During warm periods, algal productivity was increased so that the relative importance of ancient and modern OM in the sediments alternated in a climate-related pattern