Morphodynamic evolution of paraglacial spit complexes on a tide-influenced Arctic fjord delta (Dicksonfjorden, Svalbard)

Abstract

Recent global warming triggered pronounced geomorphic changes such as coastal retreat and delta progradation along the coastlines of the Arctic regions. Coastal morphodynamics and associated sediment transport at the Arctic fjord head remain relatively unexplored due to the logistically limited accessibility to the field area, especially at short-term temporal scales. A repeat survey using an unmanned aerial vehicle (UAV)-assisted photogrammetry was conducted to quantify the annual morphodynamics of gravel spit complexes developed on the tidal delta plain of the deglaciated Dicksonfjorden, Svalbard of Arctic. Results show that the spit morphodynamics varies in time and space with an overall downfjord increase in the growth and migration rate of the spits. The youngest spits elongated 22 m yr(-1) and migrated landward 4.3 m yr(-1) between 2015 and 2019, marking the most pronounced spit morphodynamics documented to date in the Svalbard fjord systems. The spit morphodynamics is driven primarily by longshore drift and to a lesser degree by overwash processes. Gravels constituting the spits originate from the unconsolidated debris-flow deposits of old alluvial fans, which locally retreat 0.5 m yr? 1. The growth of the spit complexes is also fed by snow meltwater discharge on the alluvial fans, accounting for a downfjord imbrication of angular gravel layers that are intercalated with interlaminated sands and muds on the landward sides of the spits. The breached spits at the most upfjord location have remained stationary during the study period and presumably since the 1930s. Rapid delta progradation combined with an isostatic rebound after the Little Ice Age (LIA) has decreased spit morphodynamics on the tidal delta plain upfjord in Dicksonfjorden with infrequent and insignificant wave influence. Sparse distribution of the isolated spits signifies the intermittent spit development, which is constrained by the proximity to the protruded alluvial fans. The spit complexes in Dicksonfjorden highlight that climate change accelerates coastal geomorphic changes at the fjord head by enhancing wave intensity and regulating episodic sediment delivery that led to the downfjord shift in the locus of wave shoaling.