Abstract
Manganese (Mn) and cerium (Ce) are known as reactive metals sensitive to marine redox conditions, and can therefore serve as useful proxies for paleoceanographic environments. Quaternary sedimentary records in the Arctic Ocean show a consistent cyclicity of Mn enrichments, but Mn sources, transportation and deposition patterns, and relationship to paleoclimatic conditions are not well understood. Sediment core ARC3-B85D from the Alpha Ridge with the estimated stratigraphy covering ~350 kyr is used to investigate a coupled distribution of Mn and Ce in Quaternary Arctic Ocean sediments. By analyzing Mn and Ce distribution patterns in the core and surface sediments from the western Arctic Ocean and adjacent shelves, we investigate the conditions and dynamics of concurrent metal enrichments. Stratigraphic Ce and Mn patterns follow inferred glacial-interglacial cycles, with enrichments generally occurring during interglacial-type conditions with high sea levels. However, the relationships involved are not straightforward as highest Mn and Ce enrichments seem to occur closer to the end of interglacial/major interstadial periods, when sea levels were lowering from their highest positions. We conclude that the enrichment patterns are primarily defined by sediment dynamics controlling resuspension and transportation of reactive metals and their deposition in the central Arctic Ocean after diagenetic preconditioning on the shelves. We further infer that major transportation agents are sea-level affected cross-shelf and mid-depth ocean currents rather than sea ice as has been proposed earlier. Comprehending this coupled geochemical and sedimentary system is important for improving the chronostratigraphic framework for Quaternary deposits in the Arctic Ocean.
Highlights
The fundamental challenge in Arctic paleoceanography is a lack of reliable chronostratigraphic age constraints, and the ability to compare Arctic Ocean sedimentary records to those from other oceans
The aim of this study was to gain a better understanding on the paleoceanographic significance of Mn in Quaternary Arctic Ocean sediments, where this labile metal forms consistent enrichment cycles as demonstrated by numerous studies (e.g., Jakobsson et al., 2000; Polyak et al., 2004; Stein et al., 2010; Wang et al., 2018)
Despite a compressed nature of this 130 cm-long record, its major lithostratigraphic features on glacial-interglacial time scales are consistent with other sedimentary records throughout the western Arctic Ocean
Summary
The fundamental challenge in Arctic paleoceanography is a lack of reliable chronostratigraphic age constraints, and the ability to compare Arctic Ocean sedimentary records to those from other oceans. Metal Enrichments in Arctic Sediments depositional environments reflected in sediment stratigraphy (e.g., Jakobsson et al, 2000; Polyak et al, 2004; Spielhagen et al, 2004; O’Regan et al, 2008; Stein et al, 2010) In this approach, brown, manganese (Mn) enriched layers in Arctic sediment cores were suggested to represent interglacials and major interstadials, important as potential paleo-analogs for comprehending the modern climate change. A number of transition metals recorded in Arctic Ocean sediment cores, such as Cu, Ni, Co, and Mo, share the same trends as Mn over glacial-interglacial cycles, since they are scavenged by the Fe–Mn (oxyhydr)oxides that precipitate from the water column and pore waters, and become enriched at the seafloor during interglacial-type conditions (März et al, 2011a; Meinhardt et al, 2014). Only few records of positive Ce anomalies have been reported from marine sedimentary pore waters within strongly reducing environments (Haley et al, 2004; Bau et al, 2014; Abbott et al, 2015), implying a simultaneous diffusion of dissolved Ce out of sediments, and/or its fast re-absorption/re-precipitation once pore water conditions are oxic again
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