A Driftwood-Based Record of Arctic Sea Ice During the Last 500 Years From Northern Svalbard Reveals Sea Ice Dynamics in the Arctic Ocean and Arctic Peripheral Seas

We present a 500-year history of naturally felled driftwood incursion to northern Svalbard, directly reflecting regional sea ice conditions and Arctic Ocean circulation. Provenance and age determinations by dendrochronology and wood anatomy provide insights into Arctic Ocean currents and climatic conditions at a fine spatial resolution, as crossdating with reference chronologies from the circum-Arctic boreal forests enables determination of the watershed the driftwood originated from. Sample crossdating may result in a wide range of matches across the pan-boreal region, which may be biased toward regions covered by the reference chronologies. Our study considers alternate approaches to selecting probable origin sites, by weighting scores via reference chronology span and visualizing results through spatiotemporal density plots, as opposed to more basic ranking systems. As our samples come from naturally felled trees (not logged or both), the relative proportions of different provenances are used to infer past ocean current dominance. Our record indicates centennial-to decadal-scale shifts in source regions for driftwood incursion to Svalbard, aligning with Late Holocene high variability and high frequency shifts in the Transpolar Drift and Beaufort Gyre strengths and associated fluctuating climate conditions. Driftwood occurrence and provenance also track the northward ice formation shift in peripheral Arctic seas in the past century. A distinct decrease in driftwood incursion during the last 30 years matches the observed decline in pan-Arctic sea ice extent in recent decades. Our new approach successfully employs driftwood as a proxy for Arctic Ocean surface circulation and sea ice dynamics

Holocene glacier history of Svalbard: Retracing the style of (de-)glaciation

Through the Holocene, Svalbard glaciers have exhibited at least two phases of re-advance, one during the Early Holocene and another throughout the entire Late Holocene. No geomorphological features have been identified corresponding to glacier re-advances between 9.0 – 4.5 ka BP. The Early Holocene glacier re-advances identified across Svalbard and they correspond to a diverse range of glacier sizes. With our current level of age constraint, these ice marginal fluctuations do not appear synchronous. Furthermore, the Early Holocene climate is believed to warm, unfavorable for glacier growth, and characterized by deglaciation. Early Holocene glacier re-advances appear to relate to the time-transgressive nature of deglaciation, correspond to dynamics (not mass balance) and reflect the complex style of ice-mass-loss during a changing climate. Landforms and deposits from glaciers re-advancing during the Late Holocene have been the primary focus of Holocene glacial studies. Glacier re-advances and corresponding deposits have been attributed to episodic Neoglacial cooling and the Little Ice Age (LIA). The majority of Late Holocene glacier re-advances have been dated to between 4.0 - 0.5 ka BP with the highest frequency of re-advances constrained to 1.0 – 0.5 ka BP, during the first half of the LIA. It has been suggested that glacial landforms and deposits from LIA re-advances indicate rapid and dynamic glacier behavior, and in some cases surge-type events. During the 20th century (i.e. post-LIA), Svalbard glaciers have exhibited widespread negative mass balance, ice marginal retreat, and glacier thinning. This phase of retreat has had a direct influence on glacier thermal regime, hydrologic system and surface profile. Through the 20th century, some Svalbard glaciers have continued to exhibit surge-type re-advances. Several glaciers have exhibited this behavior numerous times. These glacio-dynamic re-advances have been un-sustained and each subsequent surge has been less extensive then prior surges. Consequently, and despite re-advance, glaciers reflect a continual phase of ice-mass-loss in a periodic fashion

Persistence of Holocene ice cap in northeast Svalbard aided by glacio-isostatic rebound

The deglaciation of the Svalbard-Barents Sea Ice Sheet was driven by relative sea-level rise, the incursion of North Atlantic waters around Spitsbergen, and increasing summer insolation. However, ice retreat was inter rupted by asynchronous re-advances that occurred into high relative seas, during a period associated with warm regional waters and elevated summer temperatures. Better understanding of this complex style of deglaciation and the dynamic response to a warming climate can serve as an important analogue for modern warming and today’s ice sheets. We present evidence from northern Svalbard of glacier re-advances during the Late Glacial Early Holocene in hand with relative sea-level history and the occurrence of thermophilous molluscs. We argue that glacio-isostatic adjustment during the transition into the Holocene influenced ice marginal dynamics and as a result, the southern region of the Åsgardfonna ice cap persisted through the Holocene Thermal Maximum

A complete Holocene lake sediment ancient DNA record reveals long-standing high Arctic plant diversity hotspot in northern Svalbard

Publisher's version (útgefin grein)Arctic hotspots, local areas of high biodiversity, are potential key sites for conservation of Arctic biodiversity. However, there is a need for improved understanding of their long-term resilience. The Arctic hotspot of Ringhorndalen has the highest registered diversity of vascular plants in the Svalbard archipelago, including several remarkable and isolated plant populations located far north of their normal distribution range. Here we analyze a lake sediment core from Ringhorndalen for sedimentary ancient DNA (sedaDNA) and geochemical proxies to detect changes in local vegetation and climate. Half of the plant taxa appeared already before 10,600 cal. yr BP, indicating rapid colonization as the ice retreated. Thermophilous species had a reoccurring presence throughout the Holocene record, but stronger signal in the early than Late Holocene period. Thus, thermophilous Arctic plant species had broader distribution ranges during the Early Holocene thermal maximum c. 10,000 cal. yr BP than today. Most of these thermophilous species are currently not recorded in the catchment area of the studied lake, but occur locally in favourable areas further into the valley. For example, Empetrum nigrum was found in >40% of the sedaDNA samples, whereas its current distribution in Ringhorndalen is highly restricted and outside the catchment area of the lake. Our findings support the hypothesis of isolated relict populations in Ringhorndalen. The findings are also consistent with main Holocene climatic shifts in Svalbard identified by previous studies and indicate an early warm and species-rich postglacial period until c. 6500 cal. yr BP, followed by fluctuating cool and warm periods throughout the later Holocene.The core-samplingfield campaign, subsequent sub-sampling ofsediments and macrofossils, ITRAX-scans, and radiocarbon datingwere funded by the Svalbard Environmental Protection Fund(project 16/35 to WRF). Financial support for molecular analysisandfield work was provided by the Svalbard Environmental Pro-tection Fund (project 14/118 to PBE) and Jan Christensen’sendowment (to LHV). IGA and PDH acknowledge support from theResearch Council of Norway (Grant 250963:“ECOGEN”). We thankJohannes Sand Bolstad forfield assistance, Kari Klanderud forproject administration, the wider ECOGEN research group inTromsø, including Dilli Rijal for pooling and cleaning of the PCRproducts and Youri Lammers for helping with bioinformatic ana-lyses and reference libraries. Bioinformatic analyses were per-formed on the Abel Cluster, owned by the University of Oslo andUninett/Sigma2, and operated by the Department for ResearchComputing at USIT, the University of Oslo IT-department.http://www.hpc.uio.no/. We thank Marie-Louise Siggaard-Andersen forassistance with the ITRAX-scanning of the sediment core as well asDr. Skafti Brynj olfsson and Dr. Marc Macias-Fauria for collaborationin the field.Peer Reviewe

Vedde Ash constrains Younger Dryas glacier re-advance and rapid glacio-isostatic rebound on Svalbard

The distal deposition of tephra from explosive volcanism has the potential to geochronologically constrain sedimentary archives and landforms. With this technique, we constrain a Late Glacial glacier re-advance on Svalbard and suggest that glacioisostatic emergence rates during the Younger Dryas chronozone were at least three times greater than previous estimates. The identification of cryptotephra (i.e., non-visible) horizons, outside the extent of visible fallout, has greatly expanded the field of application of tephrochronology. While the cryptotephra revolution has triggered a burst of investigations using low-concentration tephra to constrain distal sedimentary sequences, as of yet, few investigations have used this tool to constrain the age of glacial landforms. Here we constrain a moraine formed during a glacier re-advance (12.8–12.2 cal ka BP) into a high relative sea level during the early Younger Dryas chronozone, with the first identified occurrence of the Icelandic Vedde Ash on Svalbard. Low concentrations (∼63 shards/g dried sediment) of the bimodal Vedde Ash (rhyolitic long axis c. 30–90 μm; basaltic c. 35–100 μm) were identified in a lake sediment sequence collected from the Heftyebreen glacier foreland, in a tributary valley to Grønfjorden, western Spitsbergen. Given that the cryptotephra was deposited within a lacustrine isolation basin, we further reconstruct a minimum rate of glacio-isostatic emergence during the end of the Late Glacial. Strong and longstanding evidence suggests Svalbard's west-coast cirque glaciers were less extensive during the Late Glacial than the Late Holocene. However, the Late Glacial Heftyebreen moraine suggests Svalbard glacier dynamics during this period may have been more complex