Constraining Weichselian high relative sea-level events in Basissletta, northeastern Spitsbergen

Abstract

The fluctuation of the Svalbard Barents Sea Ice Sheet is relatively well constrained during the Late Weichselian, yet its behaviour before the Last Glacial Maximum (LGM) remains elusive. Inter-fjord areas, largely covered by cold-based, non-erosive ice, have a higher preservation potential for older terrestrial records than fjord areas that were dominated by active ice streams during the Last Glacial Maximum. Basissletta, located on the northeast coast of Spitsbergen, represents one such inter-fjord setting and therefore offers the potential to recover stratigraphic records of the ice sheet fluctuation through the Weichselian.
The area is an undulating coastal area characterized by Quaternary deposits, which consist predominantly of raised marine sediments, glacial deposits, fluvial and glacifluvial deposits and periglacially altered surfaces. In order to reconstruct the paleoenvironment in Basissletta, and in particular identify high relative sea level stands, glacifluvial and littoral sedimentary sections above the proposed marine limit (ML) of 68 m a.s.l. were described and chronologically constrained using Optically stimulated Luminescence (OSL) dating and Radiocarbon (C14) dating. Geomorphological mapping was conducted through the identification of landforms using digital ortho-imagery and drone imagery obtained during a field excursion to Basissletta, complemented by field observations.
Chronology and stratigraphical analysis of a delta deposit reveal a composite landform comprising of two deltaic formations separated by an unconformity. The lower unit was deposited during early Marine Isotope Stage (MIS) 3 whereas the upper unit yielded post-LGM ages, indicating a renewed delta formation following deglaciation. The activation of an outwash plain in the foothills, constrains the ice margins retreat during deglaciation to 14 ± 2 ka. Prominent beach ridges are observed up until 78 m a.s.l, which have been constrained to the Late Weichselian deglaciation by OSL and radiocarbon chronologies, and is defined as the post glacial ML, making it about 10 m higher than previously thought. Two high relative sea level events were thus recorded in Basissletta, the former during MIS 3 following an extensive glaciation during MIS 4 and the latter during a post-LGM high stand in the Late glacial – early Holocene transition.

Popular Abstract

The Arctic archipelago of Svalbard has been shaped over thousands of years by the advance and retreat of vast ice sheets. While scientists have a relatively good understanding of the last major glaciation, known as the Last Glacial Maximum, around 20,000 years ago, what happened before remains much less clear.
This study investigates a coastal area called Basissletta, on the northeast coast of Spitsbergen, to piece together a more complete picture of how ice sheets and sea levels have changed over the last 70,000 years.

Basissletta is a gently undulating coastal plain covered by marine, glacial and sediments left behind by rivers. Because the area sits between major fjords rather than within them, it was sheltered from the most destructive phases of glacial erosion, meaning that older deposits are unusually well preserved here. This makes it a valuable natural archive for reconstructing past environments.
Using a combination of aerial and drone imagery, field observations, and sediment dating techniques, including Optically Stimulated Luminescence (OSL) and radiocarbon dating, both of which measure how long ago sediments were last exposed to light or when organisms were alive, the study reconstructed the history of glaciation and sea level change in the area.
One of the key findings concerns a river delta deposit that turns out to be a composite landform with two distinct phases of formation separated by a gap in the record. The lower, older phase was deposited around 50,000–66,000 years ago, during a period between major glaciations known as the Middle Weichselian Interstadial. The upper, younger phase formed after the last ice sheet retreated, approximately 14,000 years ago, when meltwater again began flowing across the landscape.
The study also identifies two separate periods when sea level was significantly higher than today in this area. The first occurred around 50,000 years ago, following an extensive glaciation that had pushed the Earth's crust downward under the weight of the ice. As the ice retreated, the crust slowly rebounded and the sea flooded low-lying areas, leaving behind beaches and marine sediments at elevations of up to 84 meters above present sea level. The second high sea level event followed the retreat of the last ice sheet around 14,000–12,000 years ago, with beach ridges preserved up to 78 meters above sea level and defining the post-glacial marine limit for the area.
These findings add important new detail to our understanding of how the Svalbard-Barents Sea Ice Sheet behaved during a critical and poorly understood period of Earth's recent glacial history, demonstrating that inter-fjord coastal settings like Basissletta hold invaluable records of past climate and landscape change that have yet to be fully explored.

• author: Ólafsdóttir Arnholtz, Edda Sól
• supervisor: Helena Alexanderson; Zoran Perić; Mark Furze
• organization: Department of Earth and Environmental Sciences (MGeo)
• course: GEOR11 20261
• year: 2026
• type: H2 - Master's Degree (Two Years)
• subject: Earth and Environmental Sciences
• keywords: Svalbard-Barents Sea Ice Sheet (SBSIS), Basissletta, Relative Sea-level, Marine Limit, Glacial morphology, Sedimentology, Optically Stimulated Luminescence (OSL) dating, Geomorphological mapping
• publication/series: 730
• language: English
• id: 9232359
• date added to LUP: 2026-06-12 09:35:30
• date last changed: 2026-06-12 09:35:30