GEOSCAN, résultats de la recherche


TitreHolocene climate change influences on trace metal and organic matter geochemistry in the sediments of an Arctic lake over 7,000 years
AuteurOutridge, P M; Sanei, H; Courtney-Mustaphi, C J; Gajewski, K
SourceApplied Geochemistry vol. 78, 2016 p. 35-48,
Séries alt.Secteur des sciences de la Terre, Contribution externe 20160366
Documentpublication en série
Mediapapier; en ligne; numérique
Lat/Long OENS -90.0000 -89.0000 75.7500 75.5000
Sujetsgéochimie des sediments lacustres; sediments lacustres; géochimie organique; dépôts organiques; débit de sedimentation; carottes de sediments lacustres; carbonates; dolomites; calcaires; schistes; réflectance; réflectance de la vitrinite; kérogène; algues; macéraux; effets climatiques; Changement climatique; géochimie; sédimentologie; Nature et environnement
Illustrationsequations; graphs; tables; geochemical plots
ProgrammeGestion du programme, Géosciences environnementales
Résumé(disponible en anglais seulement)
This 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.
Résumé(Résumé en langage clair et simple, non publié et disponible en anglais seulement)
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