Early Holocene sea level in the Canadian Beaufort Sea constrained by radiocarbon dates from a deep borehole in the Mackenzie Trough, Arctic Canada

Abstract

Deglacial and Holocene relative sea level (RSL) in the Canadian Beaufort Seawas influenced by the timing and extent of glacial ice in the Mackenzie River corridor and adjacent coastal plains. Considerable evidence indicates extensive ice cover in this region of northwestern Canada during the Late Wisconsinan. However, no absolute ages exist to constrain maximum RSL lowering before the late Holocene (4.2-0 ka). In 1984, the Geological Surveyof Canada drilled an 81.5m-deep borehole in the western Mackenzie Trough at 45 m water depth (MTW01). The lower 52.5 m of the borehole was interpreted as a deltaic progradational sequence deposited during a period of rising sea level. The upper 29 m was described as foraminifer-bearing marine sediments deposited after transgression of the site, when RSL rose abovẽ À74 m. Here, we present radiocarbon measurements from MTW01, acquired from benthic foraminifera, mollusc fragments and particulate organic carbon in the >63 lm fraction (POC >63 lm ) in an attempt to constrain the chronology of sediments within this borehole and date the timing of transgression. The deepest carbonate macrofossil was acquired from 8 m above the transgressive surface (equivalent to 21 m b.s.l.), where mollusc fragments returned a date of 9400 +180-260 cal. a BP (2r). This provides the oldest constraint on Holocene sea-level lowering in the region, and implies that transgression at this site occurred prior to the early Holocene. Ages obtained from the lower 52.5 m of the borehole are limited to POC >63 lm samples. These indicate that progradational sediments were deposited rapidly after 24 820 +390-380 cal. a BP (2r). Due to the incorporation of older reworked organic matter, the actual age of progradation is likely to be younger, occurring after Late Wisconsinan glacial ice retreated from the coast. Matt O'Regan

Vegetal Undercurrents—Obscured Riverine Dynamics of Plant Debris

“…While these shelf sediments are enriched in N due to the contribution of marine primary productivity, their OC signature is generally more degraded and depleted in 14 C, suggesting protracted storage on the continental margin. In comparison to fluvial suspended sediments, shelf sediments contain higher proportions of clay (Goñi et al., 2005 ; Vonk et al., 2015 ) and are devoid of discrete terrestrial organic matter, as noted in sediment cores retrieved in front of the Mackenzie Delta (Hilton et al., 2015 ; O’Regan et al., 2018 ; Richerol et al., 2008 ). The lack of litter and wood debris on the Mackenzie Shelf raises questions regarding the depositional regime and fate of coarse OC.…”

“…These lenses correspond to typical river scour and bar facies. The warm climatic interval enabled the northward migration of boreal forests, enhancing the supply and accumulation of detrital wood in floodplains (Davies et al., 2014 ; O’Regan et al., 2018 ). The increased burial of undegraded plant debris under warm Pliocene conditions implies that alluvial settings can preserve substantial amounts of OC.…”

Constraints on the source of reactive phases in sediment from a major Arctic river using neodymium isotopes

“…Two silicate residue samples were analysed from two of the shallowest core sites. The sedimentation rate at shallow sites in the Canadian Beaufort sea is high (on the order of 2-3 m/ka, O Regan et al, 2018), indicating that the range and depth sampled within the cores (~10 cm) represents sediment that is likely several decades old, and homogenises inter-annual and seasonal variability.…”

A new 30,000 year chronology for rapidly deposited sediments on the Lomonosov Ridge using bulk radiocarbon dating and probabilistic stratigraphic alignment

“…(Jakobsson et al, 2010). High-resolution marine sediment cores from Arctic margins are used to constrain deglacial transgression of the shelves (Bauch et al, 2001;Cronin et al, 2017;Jakobsson et al, 2017;O'Regan et al, 2018), reconstruct variability in sea-ice (Stein and Fahl, 2000;De Vernal et al, 2005;Xiao et al, 2015), and fluxes of organic matter from rivers and coastal erosion (Hilton et al, 2015;Martens et al, 2019;Tesi et al, 2016).…”