Late Quaternary sedimentation and permafrost development in a Svalbard fjord‐valley, Norwegian high Arctic

Abstract

The infilling history of the Adventdalen fjord‐valley in central Spitsbergen is reconstructed, with a focus on permafrost development, based on sedimentological and cryostratigraphic evidence from drilling cores. The techniques of optically stimulated luminescence and radiocarbon accelerator mass‐spectrometry dating were used to establish sediment chronology. The fjord‐fill sedimentary succession includes the fjord‐bottom late Weichselian subglacial till of the Last Glacial Maximum, the early Holocene muddy glaciomarine deposits with ice‐rafted debris formed during the fjord deglaciation, and the younger Holocene deposits of a fjord‐head Gilbert‐type delta of which the fluvial distributary plain shows raised alluvial terraces hosting aeolian sedimentation. This sedimentary record of the last glaciation/deglaciation cycle is interpreted in terms of sequence stratigraphy. Zones of epigenetic and syngenetic permafrost are recognized from the vertical distribution of cryofacies, with a conclusion that the formation of permafrost commenced and extended down‐fjord as the fluvio‐deltaic fjord‐fill was gradually reaching subaerial exposure. The upwards‐grown syngenetic permafrost and the top part of downwards‐grown epigenetic permafrost below contain excess ice in a suite of cryofacies indicating ground‐ice segregation and segregative intrusion. The deeper epigenetic permafrost is ice‐poor and contains cryofacies formed solely by segregation processes. This case study may serve as an analogue for other similar Arctic fjord‐valleys where the fjord‐head shoreline was established during the post‐Weichselian deglaciation.

Ice‐wedge polygon dynamics in Svalbard: Lessons from a decade of automated multi‐sensor monitoring

“…The ice‐wedge research site is located on the outermost part of a large late Holocene alluvial fan in the Adventdalen valley, central Svalbard (Figure a). Adventdalen is a broad U‐shaped valley surrounded by flat‐top, 800–900 m high mountains composed of sedimentary rocks of Early Permian to Eocene age.…”

“…The ice-wedge research site is located on the outermost part of a large late Holocene alluvial fan 23,24 26 ). The polygons occur mainly as quadrangles, pentagons and hexagons with an average diameter of about 20 m and three-way junctions 27,28 (Figure 2).…”

Radium isotope fingerprinting of permafrost ‐ applications to thawing and intra‐permafrost processes

“…The first explanation assumes equilibrium (or steady state) between sediments and the ground ice (Figure a), while the latter should occur with limited contact between the two (e.g., large ground ice), where fast decay of the short‐lived isotope is hardly balanced by recoil. Given the eolian nature of the top few meters of the Adventdalen sediments and its attributed syngenetic permafrost (e.g., ), the first interpretation should be manifested by an increase in 226 Ra/ i Ra ratios with depth, which is not necessarily the case in some of our profiles (Figure a,b). This could reflect some polygenesis in the topmost part of the permafrost (i.e., mixed bottom‐up and top‐down freezing, e.g., ).…”

“…This could reflect some polygenesis in the topmost part of the permafrost (i.e., mixed bottomup and top-down freezing, e.g., 43 ). Alternatively, following the second explanation above, the occurrence of higher 226 Ra/ i Ra ratios near the permafrost table (Figure 2a) could be related to its higher ice content, 35 which results in a decline in the short-lived isotopes…”

“…Ra‐free tap water, up to twice the thawed water volume, was then added to the extracted water, to buffer the relatively low pH (5–6) permafrost water. Ice content, defined as gravimetric moisture content ( , where W and D refer to the wet and dry sample mass), was determined according to Gilbert as 25–160% (for the shallow part of the Adventdalen permafrost). The percentage of extracted thawed water in this study, calculated by weighing samples before microwaving and after centrifuging, was 10–50% (average of 20%).…”