Evidence of early deglaciation (18 000 cal a bp) and a postglacial relative sea‐level curve from southern Karmøy, south‐west Norway

Abstract

Based on six consistent radiocarbon dates from the isolation basins Grødheimsvatnet and Kringlemyr, we estimate a minimum deglaciation age for southern Karmøy, an island in outer Boknafjorden (south‐west Norway), of around 18 000 calibrated years before present (18k cal a bp). We use microscopic phytoplankton, macrofossils, lithostratigraphic evidence and X‐ray fluorescence data to identify the isolation contacts in the basins, and date them to 17.52–17.18k cal a bp in Grødheimsvatnet [15.57 m above present mean sea level (MSL)] and 16.19–15.80k cal a bp in Kringlemyr (11.99 m above MSL). Combining these data with previous studies, we construct a relative sea‐level (RSL) curve from 18k cal a bp until the present, which is ~3 ka longer than any previous RSL reconstruction from southern Norway. Following deglaciation, southern Karmøy has experienced a net emergence of around 16–19 m, although with significant RSL fluctuations. This includes two RSL minima well below present MSL around ~13.8 and ~10k cal a bp, and two maxima that culminated around 5–7 m above MSL during the Younger Dryas and early to mid‐Holocene, respectively. Considering eustatic sea level and modelled gravitational deformation of the geoid, we estimate a net postglacial isostatic uplift of ~120 m. © 2019 John Wiley & Sons, Ltd

Northward Shifts in the Polar Front Preceded Bølling and Holocene Warming in Southwestern Scandinavia

“…Horizontal error bars in (a) and (e) show 2 σ age uncertainty for each sample. (f) Loss on ignition as % of dry sediment mass (Vasskog et al, 2019). (g) July temperature reconstructed from pollen assemblages at Vassnestjern (Karlsen, 2009).…”

“…There is evidence for warm surface water entering the Norwegian sea by at least 14.8 ka (Mangerud, 1977; Mangerud et al, 2017; Mangerud & Svendsen, 2018) and retreat of the seasonal sea ice front northward along the Norwegian coast around 15 ka (Rochon et al, 1998; Wiig, 2019), at the same time or slightly after the inferred moisture transport changes at Kringlemyr. In this part of western Norway, a significant deglaciation of the Boknafjord region occurred at least 1,000 years before the onset of the Bølling (Vasskog et al, 2019). Additional marine evidence from near Svalbard confirms a reduction in sea ice extent after 16.3 ka and shows progressively increasing primary productivity from 16.3 ka to the onset of the Bølling (Köseoğlu et al, 2019).…”

“…Karmøy is adjacent to the Norwegian Channel, which became ice free after 18.5 ka, indicated by 14 C ages on marine foraminifera (Brendryen et al, 2020; Sejrup et al, 2016). Basal radiocarbon ages from Kringlemyr suggest that the site became ice free shortly before 18 ka (Vasskog et al, 2019), providing a uniquely long‐duration sediment record for Scandinavia. Kringlemyr is well positioned to record changes in precipitation sources as a result of repositioning of the polar front and variable Atlantic Meridional Overturning Circulation intensity, as it lies near sea level in the path of prevailing westerly winds on the Norwegian Sea coast.…”

“…The lowest part of the core consists of marine sediments that transitioned to lacustrine sediments (646 cm) after the outlet sill of the basin was raised above sea level around 16 ka, indicated by a shift from marine to freshwater phytoplankton at that depth (Vasskog et al, 2019). Lithostratigraphic transitions in the lacustrine portion of Core KGM 507-02, discussed more fully in Vasskog et al (2019), show a similar pattern to other late-glacial lake sediments in the region (Krüger et al, 2011;Lohne et al, 2004Lohne et al, , 2007. Our age-depth model (supporting information Figures S1 and S2 and Text S1) is based on the age-depth model presented by Vasskog et al (2019), restricted to the lacustrine portion of the record (646-480 cm) and incorporates two additional radiocarbon ages at 622.3 and 581.3 cm (Table S1).…”

UncertainData.jl: a Julia package for working with measurements and datasets with uncertainties.

“…UncertainData.jl was originally designed to form the backbone of the uncertainty handling in the CausalityTools.jl package, with the aim of quantifying the sensitivity of statistical time series causality detection algorithms. Recently, the package has also been used in paleoclimate research (Vasskog et al, 2019).…”