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The Vaigat strait (Sullorsuaq) in central West Greenland is well known for its susceptibility to landslides and historical landslide-generated tsunamis. Recent mapping of the seabed in the Vaigat Strait has revealed several prehistoric giga-scale tsunamigenic landslides; however, their ages are unknown. Here, we report sedimentological evidence from six coastal lakes at 19 to 134 m above sea level (a.s.l.) on the Saqqaq foreland located at the eastern end of Vaigat. Using optical, X-ray fluorescence (XRF), and magnetic susceptibility core scanning in our sedimentological analysis along with a screening for marine diatoms and radiocarbon dating, we find evidence of at least two tsunami events occurring at 7.6 and 7.3 cal. ka BP. Using a previously published, recalibrated relative sea level curve from Arveprinsen Ejland (Alluttoq), located 40 km southeast of Saqqaq, we infer wave run-up heights of 41–66 and 45–70 m respectively for the two tsunamis. These run-up heights from prehistoric tsunamis are several orders of magnitude larger than the historic landslide-tsunami run-up heights at Saqqaq which only reached an elevation of c. 3 m in November 2000. While two giant tsunamis can be found in the lake sediment records, landforms from at least nine giga-scale landslides are present on the seafloor of Vaigat, we infer that the older giant tsunamis must have happened between the last deglaciation and the oldest sediment in the lakes (c. 10 to 8.5 cal. ka BP).

The Fram Strait is one of the largest gateways through which meltwater and sea ice are exported to thesubarctic North Atlantic, transiting the North-East Greenland shelf via the southward flowing EastGreenland Current. Observations indicate a recent freshening of the East Greenland Current that mayhave implications for wider oceanic circulation regimes. The North-East Greenland shelf is an opportuneregion to assess these changes back through time. Paleoceanographic reconstructions from the North-East Greenland shelf are sparse and their temporal coverage is limited to the Holocene, limiting ourability to assess the impact of rapid climatic variations on marine conditions, such as during the YoungerDryas/Holocene transition. Here, we present data from a well-dated marine sediment core retrieved fromthe North-East Greenland shelf (74N; east of Young Sound-Tyrolerfjord system) that captures the lateYounger Dryas Stadial through to the Mid-Holocene at sub-centennial resolution. We apply a multi-proxyapproach to reconstruct changes in productivity, surface and bottom ocean conditions. We show that at74 N the presence of warm Atlantic waters on the inner North-East Greenland shelf was limited to thelate Younger Dryas, as the Greenland Ice Sheet retreated landward and isostatic rebound caused the areato uplift. A unique dimension to this record is its location within one of the few biological hotspots on theEast Greenland shelf today; the Sirius Water polynya. Archaeological studies indicate the polynya wasforming as early as 4500 years ago, but nothing is known about its evolution from a marine perspective.Cooling of bottom waters, increasing sea-surface productivity and more frequent open water conditionsindicate an Early Holocene onset of the Sirius Water (ca. 10e8.7 ka BP).

Climate warming and the resulting acceleration of freshwater discharge from the Greenland Ice Sheet are impacting Arctic marine coastal ecosystems, with implications for their biological productivity. To accurately project the future of coastal ecosystems and place recent trends into perspective, palaeo-records are essential. Here, we show runoff estimates from the late 19th century to the present day for a large sub-Arctic fjord system (Nuup Kangerlua, southwest Greenland) influenced by both marine- and land-terminating glaciers. We followed a multiproxy approach to reconstruct spatial and temporal trends in primary production from four sediment core records, including diatom fluxes and assemblage composition changes and biogeochemical and sedimentological proxies (total organic carbon, nitrogen, C/N ratio, biogenic silica, δ13C, δ15N, and grain-size distribution). We show that an abrupt increase in freshwater runoff in the mid-1990s was reflected by a 3-fold increase in biogenic silica fluxes in the glacier-proximal area of the fjord. In addition to increased productivity, freshwater runoff modulates the diatom assemblages and drives the dynamics and magnitude of the diatom spring bloom. Our records indicate that marine productivity is higher today than it has been at any point since the late 19th century and suggest that increased mass loss of the Greenland Ice Sheet may continue promoting high productivity levels at sites proximal to marine-terminating glaciers. We highlight the importance of palaeo-records in offering a unique temporal perspective on ice–ocean–ecosystem responses to climate forcing beyond existing remote sensing or monitoring time series.

In recent decades the surface water temperature and salinity in the Labrador Sea have been influenced by atmospheric circulation patterns, such as the North Atlantic Oscillation (NAO), as well as a trend to increasingly warm atmospheric temperatures in recent years. These changes are concerning, given the important role that temperature and salinity have on deep convection in the Labrador Sea. Yet, due to the shortness of available records, the long-term patterns of climate variability in the region are not clear. Here, a diatom-based reconstruction of summer sea-surface temperature (SST) developed from Trinity Bay, Newfoundland, provides insight into variations of SST since 7.2 cal ka BP in the southwestern Labrador Sea. The results show that the Holocene Thermal Maximum (HTM) lasted until c. 5.2 cal ka BP, which was followed by a gradual cooling trend overprinted by centennial temperature fluctuations of 1–2°C. Long-term cooling was likely the result of declining Northern Hemisphere orbital summer insolation, potentially amplified by long-term changes in surface and bottom water salinity, which led to a gradual reduction in the stratification of the water column. Centennial fluctuations in temperature vary in-phase with reconstructed variations in the NAO, supporting a consistent relationship between atmospheric circulation and SST over centennial-millennial timescales. Other factors influencing the SST variability may have been solar forcing during the mid-Holocene and variations in the strength of the subpolar gyre during the late-Holocene. The most prolonged cool period at 5.2–4.1 cal ka BP coincides with sharply reduced salinity in the Labrador Sea and a weakening of deep ventilation in the northeast Atlantic, highlighting a period with altered ocean surface conditions and circulation across the northern North Atlantic.

The Greenland Ice Sheet has been losing mass at an increasing rate over the past decades due to atmospheric and oceanic warming. As a result, freshwater discharge from the Greenland Ice sheet has doubled in the last two decades and is expected to strongly increase in the future, with a large impact on the functioning of coastal marine ecosystems. While glacier runoff delivers nutrients and labile carbon into the fjords, an increase in sediment inputs is expected to have a negative impact in primary productivity, due to increased turbidity and subsequent reduction in available light for photosynthesis. Bridging modern satellite, historical and paleo-records is a key approach, as our capacity to project future scenarios requires an understanding of long-term dynamics, and insight into past warm(er) climate periods that may serve as analogues for the future. We will present results from a master’s project developed within the framework of project GreenShift: Greenland fjord productivity under climate change. Two high-resolution sediment core records from two contrasting fjord systems in NE and SW Greenland were analysed to assess the impact of Greenland Ice Sheet melt on sediment fluxes and primary productivity, focusing on the time period from the Little Ice Age until present. The overall goal of this work is to gain a better understanding of the possible linkages between GIS melt and productivity in Greenland fjord systems, with a view to improve future projections. We followed a multiproxy approach including grain-size distribution, organic carbon and biogenic silica fluxes; and dinoflagellate cyst analyses. Our preliminary results show an overall trend towards sea-surface freshening in recent decades for both fjords influenced by land-terminating (NE) and marine-terminating (SW) glaciers, alongside with important differences both in terms of sedimentary organic composition and dinoflagellate cyst assemblages.

Knowledge of the impact of past climate warming on Greenland Ice Sheet stability is an important issue for assessing thresholds that are critical for a potential ice sheet collapse. For the late Holocene, evidence has recently been found of a so-called 4.2 ka BP event(1) including a prominent warming spike in several ice core records from Greenland and Canada (Agassiz). Also lake records from both Northwest(2) and South Greenland(3) support pronounced summer warming during that time. After c. 4.0 ka BP NW Greenland July air temperature dropped by about 3o C. Coeval with this exceptional atmospheric warming anomaly over northern Canada and parts of Greenland, abrupt cooling and freshening affected the N-Atlantic subpolar gyre where Labrador Sea deep convection ceased(4). Northern N-Atlantic climate generally deteriorated. With our contribution we present Holocene sub-bottom profiling and sedimentary shelf and fjord records from Southwest Greenland and Disko Bay that indicate exceptional Greenland Ice Sheet melting 4.4-4.0 ka BP at a rate and magnitude not recorded since early Holocene deglaciation. Extremely strong melt water discharge resulted in erosion of fjord sediments(5) and local deposition of up to several meters thick meltwater sediment on the shelf(6-8). Timing of this melting event corresponds to a significant anomaly in hydrographic parameters of the Labrador Current off Newfoundland(9,10), which is concluded to have resulted in thermohaline perturbation of the N-Atlantic Subpolar gyre. (1) Weiss, H. 2019. Clim Past doi:10.5194/cp-2018-162-RC2 (2) McFarlin, J.M. et al. 2018. PNAS doi:10.1073/pnas.1720420115 (3) Andresen, C.S. et al. 2004. J Quat Sci 19(8) doi:10.1002/jqs.886 (4) Klus, A. et al. 2018. Clim Past doi:10.5194/cp-14-1165-2018 (5) Ren, J. et al. 2009. Mar Micropal doi:10.1016/j.marmicro.2008.12.003 (6) Hygom Jacobsen, S. 2019. Master Thesis Aarhus Univ, Dept. of Geoscience, pp105 (7) Schneider, R. 2015. Cruise Rep epic.awi.de/id/eprint/37062/131/msm-44-46-expeditionsheft.pdf (8) Kuijpers, A. et al. 2001. Geol. Greenland Surv Bull 189, 41-47 (9) Solignac, S. et al. 2011. The Holocene, doi: 10.1177/0959683610385720 (10) Orme, L. et al 2019. The Holocene (submitted)

In the past few decades, warming of the Arctic region has resulted in an abrupt increase of freshwater discharge from the Greenland Ice Sheet into its surrounding ocean. Greenland fjords are modulated by ice-ocean interactions and are very productive ecosystems that sustain important fisheries and other societal ecosystem services. While many studies are ongoing to understand seasonal and inter-annual changes, very little is known about the long-term impacts of freshwater discharge on primary producers and overall Arctic marine ecosystem functioning and structure. This long-term perspective is particularly important because freshwater runoff is expected to increase in the future along with rising atmospheric temperatures. Here, we present records from three marine sediment cores from the Godthåbsfjord that were used to reconstruct past marine productivity and freshwater discharge. The results based on diatom assemblages, BSi and TOC indicate marked fluctuations in past fjord productivity since the end of the Medieval Climate Anomaly, and periodical bursts of freshwater into the fjord resulting in a lowered productivity.

Existing paleoclimate data are exceedingly sparse from southern Spitsbergen, a High Arctic region predicted to experience significant environmental changes because of amplified warming. We analyzed biotic and isotopic paleolimnological proxies to reconstruct past climate from a lacustrine sediment core, with a basal age of ∼5500 a BP, in southern Spitsbergen (77°N). We used fossil Chironomidae assemblages to quantitatively reconstruct past mean July air temperatures and stable oxygen isotope values (δ18O) of these fossils to estimate changes in mean annual air temperature. These proxy records are strikingly similar and show that the coldest anomaly since the mid-Holocene occurred between 350 and 50 cal a BP, during the ‘Little Ice Age’, whereas the warmest period in the summer temperature record occurred between 5500–5000 and ∼2000 cal a BP. Our findings indicate that the natural long-term air temperature dynamics in our study area are most likely connected to solar minima and positive feedback mechanisms from sea-surface temperature maxima. The results also highlight that the recent temperature increase is unprecedented in its rate with a ∼2 °C increase in the summer temperatures during the past ∼50 years.

Sound knowledge of present-day diatom species and their environments is crucial when attempting to reconstruct past climate and environmental changes based on fossil assemblages. For the North Atlantic region, the biogeography and ecology of many diatom taxa that are used as indicator-species in paleoceanographic studies are still not well known. Using information contained in large diatom-environment calibration datasets can greatly increase our knowledge on diatom taxa and improve the accuracy of paleoenvironmental reconstructions. A diatom calibration dataset including 183 surface sediment samples from the northern North Atlantic was used to explore the distribution and ecology of 21 common Northern Hemisphere diatom taxa. We define the ecological responses of these species to April sea ice concentrations and August sea surface temperatures (aSSTs) using Huisman-Olff-Fresco (HOF)-response curves, provide distribution maps, temperature optima and ranges, and high-quality light microscope images. Based on the results, we find species clearly associated with cold, warm and temperate waters. All species have a statistically significant relationship with aSST, and 15 species with sea ice. Of these, Actinocyclus curvatulus, Fragilariopsis oceanica and Porosira glacialis are most abundant at high sea ice concentrations, whereas Coscinodiscus radiants, Shionodiscus oestrupii, Thalassionema nitzschioides, Thalassiosira angulata, Thalassiosira nordenskioeldii and Thalassiosira pacifica are associated with low sea ice concentrations/ice-free conditions. Interestingly, some species frequently used as sea ice indicators, such as Fragilariopsis cylindrus, show similar abundances at high and low sea ice concentrations with no statistically significant relationship to sea ice.

How environmental conditions influence current distributions of organisms at the local scale in sensitive high Arctic freshwaters is essential to understand in order to better comprehend the cascading consequences of the ongoing climate change. This knowledge is also important background data for paleolimnological assessments of long-term limnoecological changes and in describing the range of environmental variability. We sampled five limnologically different freshwater sites from the Fuglebergsletta marine terrace in Hornsund, southern Svalbard, for aquatic invertebrates. The invertebrate communities were tested against non-climatic environmental drivers (limnological and catchment variables). A clear separation in the communities between the sites was observed. The largest and deepest lake was characterized by a diverse Chironomidae community but Cladocera were absent. In a pond with marine influence, crustaceans, such as Ostracoda, Amphipoda, and calanoid Copepoda were the most abundant invertebrates. Two nutrient-rich ponds were dominated by a chironomid, Orthocladius consobrinus, whereas the most eutrophic pond was dominated by the cladoceran Daphnia pulex suggesting decreasing diversity along with the trophic status. Overall, nutrient related variables appeared to have an important influence on the invertebrate community composition and diversity, the trophic state of the sites being linked with their exposure to geese guano. Other segregating variables included water color, presence/absence of fish, abundance of aquatic vegetation and lake depth. These results suggest that since most of these variables are climate-driven at a larger scale, the impacts of the ongoing climate change will have cumulative effects on aquatic ecosystems. How environmental conditions influence current distributions of organisms at the local scale in sensitive High Arctic freshwaters is essential to understand in order to better comprehend the cascading consequences of the ongoing climate change. This knowledge is also important background data for paleolimnological assessments of long-term limnoecological changes and in describing the range of environmental variability. We sampled five limnologically different freshwater sites from the Fuglebergsletta marine terrace in Hornsund, southern Svalbard, for aquatic invertebrates. Invertebrate communities were tested against non-climatic environmental drivers as limnological and catchment variables. A clear separation in the communities between the sites was observed. The largest and deepest lake was characterized by a diverse Chironomidae community but Cladocera were absent. In a pond with marine influence, crustaceans, such as Ostracoda, Amphipoda, and calanoid Copepoda were the most abundant invertebrates. Two nutrient-rich ponds were dominated by a chironomid, Orthocladius consobrinus, whereas the most eutrophic pond was dominated by the cladoceran Daphnia pulex, suggesting decreasing diversity along with the trophic status. Overall, nutrient related variables appeared to have an important influence on the invertebrate community composition and diversity, the trophic state of the sites being linked with their exposure to geese guano. Other segregating variables included water color, presence/absence of fish, abundance of aquatic vegetation and lake depth. These results suggest that since most of these variables are climate-driven at a larger scale, the impacts of the ongoing climate change will have cumulative effects on aquatic ecosystems.

We conducted a paleolimnological study to examine how changes in human activity interacted with climate to influence productivity and biodiversity over the past millennium in oligotrophic Lake Atnsjøen, SE Norway. The study included analyses of sediment geochemistry, subfossil diatoms and cladocerans, and macrofossils. Results were compared with the historical record of human activities in the catchment, pollen analysis and paleoclimate inferences from the lake. During the first 750 years of the record (1000–1750 CE), a time of relatively low human activity, lake productivity and biodiversity were strongly related to climate. During the Little Ice Age (1550–1800 CE), lake productivity and diatom diversity were constrained by cold climate. A century of climate warming (1780–1880 CE) initiated an increase in productivity. Accelerated human settlement after 1850 CE, however, had an even stronger impact on productivity, mediated by increased agriculture and/or forestry, which led to greater nutrient loading of the lake. Similarly, diatoms in the lake responded to the rise in temperature, but increasing human activity also had a moderate impact on the diatom community, which displayed weak signs of nutrient enrichment. From 1980 to 1990 CE onwards, lake productivity declined as a consequence of a recent decrease in human activity and changing land use. The human-induced increase in lake productivity starting ca. 1850 CE propagated through the food web and increased consumer productivity, as reflected by greater accumulation rates of cladocerans, trichopterans and turbellarians. The cladoceran community was likely under top-down control of fish, as indicated by changes in size structure and diversity. Our study showed that increasing human activity during the settlement period had a stronger impact on lake productivity than did climate. Furthermore, the slight human-mediated increase in nutrient loading had different impacts on productivity and biodiversity in the study lake. This study demonstrates that even relatively small changes in human activities in watersheds can have measurable impacts on nutrient-poor lakes.

Paleoclimate records are crucial for understanding current changes taking place in the Arctic, e.g., the amplified warming and associated changes in sea-ice cover. However, paleoclimate and -oceanographic reconstructions, especially from the high Arctic, are scarce. Here, we present a reconstruction of sea surface and paleoenvironmental conditions from a Holocene marine sediment core collected from a high-Arctic fjord, Isvika Bay, Nordauslandet, Svalbard (79°N). Our proxies include qualitative diatom assemblage data [focusing on the Marginal Ice Zone (MIZ) taxa], a quantitative diatom-based August sea surface temperature (aSST) reconstruction, sediment grain-size distribution, and ice-rafted debris (IRD) spanning the period from 4200 cal. yr BP to the Little Ice Age (LIA) at ca. 200 cal. yr BP. The results reveal cold and stable, glacier-proximal conditions for the beginning of the late Holocene (from 4200 to 2500 cal. yr BP). Then, at 2500 cal. yr BP, the environment shifted into distinctly more fluctuating conditions, where colder and warmer aSSTs alternated in a glacier-distal environment. During the latter part of the late Holocene, sea-ice cover was extensive, yet variable, negatively co-varying with aSST. Based on our diatom data, we observe a clear increase in the influence of Atlantic water in Isvika Bay during the last ca. 600 years.

The transition from the last ice age to the present-day interglacial was interrupted by the Younger Dryas (YD) cold period. While many studies exist on this climate event, only few include high-resolution marine records that span the YD. In order to better understand the interactions between ocean, atmosphere and ice sheet stability during the YD, more high-resolution proxy records from the Arctic, located proximal to ice sheet outlet glaciers, are required. Here we present the first diatom-based high-resolution quantitative reconstruction of sea surface conditions from central-eastern Baffin Bay, covering the period 14.0–10.2 kyr BP. Our record reveals warmer sea surface conditions and strong interactions between the ocean and the West Greenland ice margin during the YD. These warmer conditions were caused by increased Atlantic-sourced water inflow combined with amplified seasonality. Our results emphasize the importance of the ocean for ice sheet stability under the current changing climate., We would like thank the captain and all members of the cruise MSM09/2. We also thank O. Hyttinen, University of Helsinki, for her help with grain size distribution analysis. Funding from the Finnish Graduate School in Geology is kindly acknowledged as is the funding from the Academy of Finland (A.E.K. Ojala, QUAL-project 259343). We are grateful to F.M. Nick, H. Machguth, T. Luoto, and K. Pauli for insightful discussions.

The sedimentary environment, sediment characteristics and age-depth models of sediment sequences from Arctic lakes Revvatnet and Svartvatnet, located near the Polish Polar Station in Hornsund, southern Svalbard (77°N), were studied with a view to establishing a basis for paleolimnological climate and environmental reconstructions. The results indicate that catchment-to-lake hydroclimatic processes probably affect the transportation, distribution and accumulation of sediments in different parts of lakes Revvatnet and Svartvatnet. Locations with continuous and essentially stable sedimentary environments were found in both lakes between water depths of 9 and 26 m. We used several different dating techniques, including 137Cs, 210Pb, AMS 14C, and paleomagnetic dating, to provide accurate and secured sediment chronologies. Arecovered sequence from the northern basin of Revvatnet spans more than one thousand years long with laminated stratigraphy in the upper part of the sediment. Based on AMS 14C dates, it is possible to suppose that Revvatnet basin was not occupied by a valley glacier during the Little Ice Age. The dates were supported by 137Cs chronologies, but not confirmed with other independent dating methods that extent beyond the last 50 years. A sedimentary sequence from the northern basin of Svartvatnet provides a potential archive for the study of climate and environmental change for the last ca. 5000 years. Based on the stratigraphy and a Bayesian age-depth model of AMS14C and paleosecular variation (PSV) dates, the recovered sediment sections represent a continuous and stable sedimentation for the latter half of the Holocene.