Arctic in Rapid Transition (ART) : science plan

The Arctic is undergoing rapid transformations that have brought the Arctic Ocean to the top of international political agendas. Predicting future conditions of the Arctic Ocean system requires scientific knowledge of its present status as well as a process-based understanding of the mechanisms of change. The Arctic in Rapid Transition (ART) initiative is an integrative, international, interdisciplinary pan-Arctic program to study changes and feedbacks among the physical and biogeochemical components of the Arctic Ocean and their ultimate impacts on biological productivity. The goal of ART is to develop priorities for Arctic marine science over the next decade. Three overarching questions form the basis of the ART science plan: (1) How were past transitions in sea ice connected to energy flows, elemental cycling, biological diversity and productivity, and how do these compare to present and projected shifts? (2) How will biogeochemical cycling respond to transitions in terrestrial, gateway and shelf-to-basin fluxes? (3) How do Arctic Ocean organisms and ecosystems respond to environmental transitions including temperature, stratification, ice conditions, and pH? The integrated approach developed to answer the ART key scientific questions comprises: (a) process studies and observations to reveal mechanisms, (b) the establishment of links to existing monitoring programs, (c) the evaluation of geological records to extend time-series, and (d) the improvement of our modeling capabilities of climate-induced transitions. In order to develop an implementation plan for the ART initiative, an international and interdisciplinary workshop is currently planned to take place in Winnipeg, Canada in October 2010

Millennial-scale oscillations and an environmental regime shift around the Middle to Late Holocene transition in the North Atlantic region based on a multiproxy record from Isfjorden, West Spitsbergen

Palynological and sedimentological analyses were performed on the sediment core HH16-1205-GC retrieved from the central Isfjorden, West Spitsbergen. The sequence, which spans the last 7000 years, revealed an overall cooling trend with an important climate shift between 4.4 and 3.8 cal. ka BP, in addition to millennial-scale oscillations. Sea-surface reconstruction from dinocyst assemblages indicates a decrease in summer sea-surface temperature, from 2.5 to 1.5 °C, and primary productivity, from 750 to 650 gC m−2 a−1 over the last 7000 years. From around 6.8 to 5.8 cal. ka BP, the sedimentological and palynological data suggest a predominant sediment supply from the inner part of the fjord, ice rafting, dense sea ice cover, strongly stratified water masses and high primary productivity. The interval from 4.4 to 3.8 cal. ka BP is marked by a layer of coarser material and a significant decrease in the grain-size mode. Our geochemical data show large-amplitude fluctuations after 2.0 cal. ka BP, while an increase in the dinocysts Impagidinium pallidum and Spiniferites elongatus from 2.0 to 1.2 cal. ka BP suggests enhanced Atlantic Water inflow. The dinocyst-based reconstructions also reveal large-amplitude millennial fluctuations in sea ice cover, summer sea-surface temperature and salinity. Wavelet analysis and cross-wavelet analysis on K/Ti ratio coupled with sea-ice estimates confirm a strong signal with a periodicity of 1200–1500 years

Submarine geomorphology at the front of the retreating Hansbreen tidewater glacier, Hornsund fjord, southwest Spitsbergen

A 1:10,000 scale bathymetric map as well as 1:20,000 scale backscattering and geomorphological maps of two bays Isbjørnhamna and Hansbukta in the Hornsund fjord (Spitsbergen) present the submarine relief that was primarily formed during and after the retreat of the Hansbreen tidewater glacier. Geomorphological mapping was performed using multibeam bathymetric data and seismoacoustic profiling. The identified landforms include two types of transverse ridges interpreted as terminal and annual moraines, flat areas that are depressions filled with glaciomarine sediments, iceberg-generated pits and ploughmarks, pockmarks and fields of megaripples. Most of the identified landforms are genetically related to the retreat of Hansbreen since the termination of the Little Ice Age at the beginning of the twentieth century. Although Hansbreen has been speculated to be a surge-type glacier, no evidence of surging was identified in the submarine landform assemblage, which is in accordance with the absence of historically documented surges for that period.The work has been partially supported by National Science Centre (Poland) [grant number 2013/09/B/ST10/04141], [grant number 2013/10/E/ST10/00166], Arctic Field Grant funded by the Research Council of Norway [grant number 256879/E10] (Svalbard Science Forum), the Leading National Research Centre (KNOW) received by the Centre for Polar Studies for the period 2014–2018, and statutory activities no. 3841/E-41/S/2017 of the Ministry of Sciences and Higher Education of Poland

Glacigenic landforms and sediments in Store Koldewey Trough, NE Greenland – preliminary results

The glaciation history of NE Greenland remains poorly constrained, resulting in conceptual and uncertain reconstructions of the configuration of the Greenland Ice Sheet during the Last Glacial Maximum (c. 24-19 ka BP), as well as the timing and the dynamics of the deglaciation. New studies suggests that the ice sheet in NE Greenland probably was more dynamic than previously thought, extending all the way to the shelf edge during the last glacial (Laberg et al., 2013, 2017). Swath bathymetry, high-resolution seismic data and sediment cores from Store Koldewey Trough, off NE Greenland, reveal glacigenic landforms and deposits, providing evidence of the presence and subsequent retreat of the Greenland Ice Sheet in the middle part of the continental shelf. Mega-scale glacial lineations oriented parallel to the trough axis are identified along with a complex pattern of transverse ridges. These lineations are interpreted to be products of a fast-flowing ice stream draining eastward towards the shelf break, whilst the transverse ridges are inferred to be formed subglacially as crevasse fills or at the grounded ice front. Sediment cores contain a characteristic sequence of compact clast-rich diamicton with muddy matrix, absent of shells and bioturbation. This is overlain by laminated mud and massive mud. IRD is generally observed in the upper part of the cores. The diamicton is suggested to be basal till, whereas the overlying deposits are interpreted to be of glaciomarine origin, going from an ice-proximal to a more ice-distal environment. The laminated mud supports deposition from turbid meltwater plumes with variable discharge in an ice-proximal setting, whereas the massive mud indicates deposition from more ice-distal conditions. Within the massive mud the abundance of IRD in the cores increased relative to the surrounding material, probably reflecting increasing distal conditions where deposition from icebergs dominates compared to deposition from suspension settling

Late Weichselian and Holocene palaeoceanography of Storfjordrenna, southern Svalbard

Multiproxy analyses (including benthic and planktonic foraminifera, δ18O and δ13C records, grain-size distribution, ice-rafted debris, XRF geochemistry and magnetic susceptibility) were performed on a 14C-dated marine sediment core from Storfjordrenna, located off of southern Svalbard. The sediments in the core cover the termination of Bølling–Allerød, the Younger Dryas and the Holocene and reflect general changes in the oceanography/climate of the European Arctic after the last glaciation. Grounded ice of the last Svalbard–Barents Sea Ice Sheet retreated from the coring site ca. 13 950 cal yr BP. During the transition from the subglacial to glaciomarine setting, Arctic Waters dominated the hydrography in Storfjordrenna. However, the waters were not uniformly cold and experienced several warmer spells. A progressive warming and marked change in the nature of the hydrology occurred during the early Holocene. Relatively warm and saline Atlantic Water began to dominate the hydrography starting from approximately 9600 cal yr BP. Although the climate in eastern Svalbard was milder at that time than at present (smaller glaciers), two periods of slight cooling were observed in 9000–8000 and 6000–5500 cal yr BP. A change in the Storfjordrenna oceanography occurred at the beginning of the late Holocene (i.e. 3600 cal yr BP) synchronously with glacier growth on land and enhanced bottom current velocities. Although cooling was observed in the Surface Water, Atlantic Water remained present in the deeper portion of the water column of Storfjordrenna.Polish Ministry of Science and Higher Education grant no. NN 306 469938; Polish Ministry of Science and Higher Education grant no. IP2010 040970113587603Climate of the Pas

Multiproxy paleoceanographic study from the western Barents Sea reveals dramatic Younger Dryas onset followed by oscillatory warming trend

The Younger Dryas (YD) is recognized as a cool period that began and ended abruptly during a time of general warming at the end of the last glacial. New multi-proxy data from a sediment gravity core from Storfjordrenna (western Barents Sea, 253 m water depth) reveals that the onset of the YD occurred as a single short-lived dramatic environment deterioration, whereas the subsequent warming was oscillatory. The water masses in the western Barents Sea were likely strongly stratified at the onset of the YD, possibly due to runoff of meltwater combined with perennial sea-ice cover, the latter may last up to several decades without any brake-up. Consequently, anoxic conditions prevailed at the bottom of Storfjordrenna, leading to a sharp reduction of benthic biota and the appearance of vivianite microconcretions which formation is favoured by reducing conditions. While the anoxic conditions in Storfjordrenna were transient, the unfavorable conditions for benthic foraminifera lasted for c. 1300 years. We suggest that the Pre-Boreal Oscillation, just after the onset of the Holocene, may have been a continuation of the oscillatory warming trend during the YD.Narodowe Centrum Nauki granty: 2016/21/B/ST10/02308, 2019/33/B/ST10/00297, 2013/10/E/ST10/0016

Late Quaternary glacial/interglacial variability in Arctic sea ice and related organic carbon flux: A 180 ka record from Yermak Plateau

The recent dramatic decline of Arctic sea over the last decades and its controlling processes are still poorly understood. In order to distinguish between natural and anthropogenic processes controlling these changes in sea ice, we have to look back to the past beyond the times of direct measurements. For this purpose, we carried out a multi-proxy approach combining organic-geochemical data (bulk parameters: C/N, TOC, δ13Corg; biomarkers: IP25, sterols, GDGTs) with sedimentological data (core lithology, physical properties, IRD counting, XRF scanning) determined in sediments of Yermak Plateau Core PS92/039-2. This core is situated close to the modern summer ice edge and thus very sensitive for environmental changes. Based on magnetostratigraphy and correlations with dated sediment cores, this core represents the time span from MIS 6 to 1 (ca. 180,000 years) and allows the reconstruction of sea ice variability and related changes in oceanic circulation patterns and the Svalbard Barents Ice Sheet (SBIS) fluctuations during glacial/interglacial changes. As sea ice and phytoplankton biomarkers occur throughout the entire sedimentary section but show some strong variability, a more seasonal sea ice cover was probably predominant during the entire time interval, superimposed by a distinct short-term variability in extent. Significant fluctuations in most of our proxy records indicate highly variable sea ice conditions over the Yermak Plateau during MIS 6. Based on our biomarker data, the SBIS could not have reached the Yermak Plateau during MIS 6. During MIS 4 and 2, coevally elevated concentrations of the sea ice proxy IP25 and the biomarkers for phytoplankton productivity and terrigenous input point to a stationary ice margin above the core position at that time. Strengthened Atlantic Water inflow possibly coupled with katabatic winds from the protruding SBIS may have created this stable ice edge situation and the related sedimentary regime

Neogene dinoflagellate cysts and acritarchs from the high northern latitudes and their relation to sea surface temperature

Submitted manuscript version. Published version available at https://doi.org/10.1016/j.marmicro.2017.09.003. Submitted manuscript version, licensed CC BY-NC-ND 4.0.Organic-walled dinoflagellate cysts and acritarchs are a vital tool for reconstructing past environmental change, in particular in the Neogene of the high northern latitudes where marine deposits are virtually barren of traditionally used calcareous microfossils. Yet only little is known about the paleoenvironmental value of fossil assemblages that do not have modern analogues, so that reconstructions remain qualitative. Thus, extracting their paleoecological signals still poses a major challenge, in particular on pre-Quaternary timescales. Here we unravel the relationship between species relative abundance and sea surface temperature for extinct dinoflagellate cyst and acritarch taxa from the Neogene of the Iceland Sea using palynological assemblages and organic geochemical (alkenone) data generated from the same set of samples. The reconstructed temperatures for the Miocene to Pliocene sequence of Ocean Drilling Program Site 907 range from 3 to 26 °C and our database consists of 68 dinoflagellate cyst and acritarch samples calibrated to alkenone data. The temperature range of five extant species co-occurring in the fossil assemblage agrees well with their present-day distribution providing confidence to inferred temperature ranges for extinct taxa. The 14 extinct dinoflagellate cyst and acritarch species clearly exhibit a temperature dependency in their occurrence throughout the analysed section. The dinoflagellate cyst species Batiacasphaera hirsuta, Labyrinthodinium truncatum, Cerebrocysta irregulare, Cordosphaeridium minimum, Impagidinium elongatum and Operculodinium centrocarpum s.s., and the acritarch Lavradosphaera elongatum, which are confined to the Miocene, have highest relative abundances and restricted temperature ranges at the warm end of the reconstructed temperature spectrum. The latter five species disappear when Iceland Sea surface temperatures permanently drop below 20 °C, thus indicating a distinct threshold on their occurrence. In contrast, species occurring in both the Miocene and Pliocene interval (Batiacasphaera micropapillata, Habibacysta tectata, Reticulatosphaera actinocoronata, Cymatiosphaera? invaginata) show a broader temperature range and a tolerance towards cooler conditions. Operculodinium? eirikianum may have a lower limit on its occurrence at around 10 °C. The calibration of species relative abundance versus reconstructed sea surface temperature provides a quantitative assessment of temperature ranges for extinct Miocene to Pliocene species indicating that temperature is a decisive ecological factor for regional extinctions that may explain the frequently observed asynchronous highest occurrences across different ocean basins. It demonstrates that qualitative assessments of ecological preferences solely based on (paleo) biogeographic distribution should be treated with caution. In addition to enhancing knowledge on marine palynomorph paleoecology, this study ultimately improves the application of palynomorphs for paleoenvironmental reconstructions in the Neogene of the Arctic and subarctic seas, a region essential for understanding past global climate

Holocene glacial history of Svalbard: Status, perspectives and challenges

© 2020 The Author(s) We synthesize the current understanding of glacier activity on Svalbard from the end of the Late Pleistocene (12,000 yrs. before present) to the end of the Little Ice Age (c. 1920 AD). Our glacier history is derived from the SVALHOLA database, the first compilation of Holocene geochronology for Svalbard and the surrounding waters, including over 1,800 radiocarbon, terrestrial cosmogenic nuclide and optically stimulated luminescence ages. Data have been categorized by geological setting, uniformly (re-)calibrated, quality assessed and ultimately used to constrain glacier fluctuations (deglaciation, ice free conditions, glacier re-advances and ice marginal positions). We advance existing knowledge by mapping the extent and distribution of ice-cover during the Holocene glacial maximum and the glacial minimum, as well as present retreat rates (and percentages) within Early Holocene fjord-systems. Throughout the Holocene, Svalbard glaciers have responded to a varying combination of climatic, environmental and dynamic driving factors which influence both the extent and behavior of ice margins. We discuss the complexities of glacier systems and their dynamics in response to changes in climate. This review provides a holistic state of the art of Holocene glaciers on Svalbard, suitable for orienting future works which address gaps in our current knowledge

Past ice sheet-seabed interactions in the northeastern Weddell Sea Embayment, Antarctica

The Antarctic Ice Sheet extent in the Weddell Sea Embayment (WSE) during the Last Glacial Maximum (LGM; ca. 19–25 calibrated kiloyears before present, cal. ka BP) and its subsequent retreat from the shelf are poorly constrained, with two conflicting scenarios being discussed. Today, the modern Brunt Ice Shelf, the last remaining ice shelf in the northeastern WSE, is only pinned at a single location and recent crevasse development may lead to its rapid disintegration in the near future. We investigated the seafloor morphology on the northeastern WSE shelf and discuss its implications, in combination with marine geological records, for reconstructions of the past behaviour of this sector of the East Antarctic Ice Sheet (EAIS), including ice-seafloor interactions. Our data show that an ice stream flowed through Stancomb-Wills Trough and acted as the main conduit for EAIS drainage during the LGM. Post-LGM ice-stream retreat occurred stepwise, with at least three documented grounding line still stands, and the trough had become free of grounded ice by ~10.5 cal. ka BP. In contrast, slow-flowing ice once covered the shelf in Brunt Basin and extended westwards toward McDonald Bank. During a later time period, only floating ice was present within Brunt Basin, but large ‘ice slabs’ enclosed within the ice shelf occasionally ran aground at the eastern side of McDonald Bank, forming ten unusual ramp-shaped seabed features. These ramps are the result of temporary ice-shelf grounding events buttressing the ice further upstream. To the west of this area, Halley Trough very likely was free of grounded ice during the LGM, representing a potential refuge for benthic shelf fauna at this time