At unprecedented resolution we investigate the nature of Dansgaard-Oeschger events in the Fram Strait, the gateway between the Nordic Seas and the Arctic Ocean. The new reconstructions of biomarkers and sea ice variability, stable isotopes and IRD will be seen in context of sea ice conditions, ocean hydrography and climate of the Nordic Seas as seen in multi-model output from three transient glacial GCM simulations (NorESM, CESM, MPI-ESM) and high-resolution reconstructions from an eastern Nordic Seas transect (from the Faeroe-Shetland Channel, via the Norwegian Sea to the Fram Strait). The combined results show that ocean-atmosphere-sea ice processes and dynamics during the transition from H4 to GI8 are strongly coupled. 

Both model results and reconstructions suggest subsurface ocean warming and polynya events in the southern- and northernmost Nordic Seas during the cold stadial. For a short time during the stadial to interstadial transition, a corridor of open water and hence sea ice-free conditions existed from the southern Nordic Seas all the way to the Fram Strait. The breakup of the sea ice cover is likely caused by the overshoot of AMOC during the transition and the associated enhanced ocean heat transport into the Nordic Seas. After the transition, winter sea ice grows back in the Fram Strait during the interstadial state, but the Southern Nordic Seas remain ice-free.

How to cite: Risebrobakken, B., Wang, Y., Guo, C., Blindheim, D. I., Dokken, T., Fahl, K., Jansen, E., Klockmann, M., Tessier, J., Tisserand, A., Stein, R., Vetteretti, G., and Witkowski, A.: ABRUPT Arctic Climate Change, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-9642, https://doi.org/10.5194/egusphere-egu23-9642, 2023.

The Arctic has warmed about four times faster than the global average during the last four decades. One of the consequences of this intensive warming is increasing Arctic land ice loss. In particular, mass loss from the Greenland Ice Sheet has been estimated to have increased sixfold between 1980 and 2020. Glaciers and ice caps outside of Greenland, though receiving less attention, have also been reported to be losing mass at an increasing rate. This is caused by a combination of negative surface mass balance – due to decreasing snowfall and/or increasing melting and runoff – and increasing ice discharge. However, negative surface mass balance due to increasing melting and runoff has become the dominant cause of mass loss in Greenland and the Canadian Arctic during the last 10-15 years. This indicates the increasing role of meltwater discharge into fjords and coastal seas, influencing a wide-range of physical, chemical and biological processes and also the large-scale oceanic circulation. Despite recent advancements, no meltwater discharge data products are available that cover the entire Arctic at a high spatial (< 1 km) and temporal (sub-monthly) resolution. To fill this data gap, we use daily ~6km runoff data from a regional climate model, Modéle Atmosphérique Régional (MAR), for the period of 1950-2021 – covering Greenland, Arctic Canada, Iceland, Svalbard, and Arctic Russia. We employ a statistical downscaling algorithm that utilises a high resolution (250 m) DEM, land mask (Copernicus GLO-90), and ice mask (GIMP, RGI). A hydrological routing scheme is also applied to the downscaled runoff to provide meltwater runoff data at coastal outflow points. Meltwater components coming from non glacierized land, bare glacier ice, and glacierized area above the snowline are separated to aid further analyses. The software pipeline is designed to be fully operational so that it can be used to update the time series as soon as the input data are available, so providing a continuous time series for the entire Arctic within the framework of a project aimed to develop a holistic, integrated observing system for the Arctic (www.arctipassion.eu).

How to cite: Igneczi, A. and Bamber, J.: A high-resolution, operational pan-Arctic meltwater discharge database from 1950 to 2021, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-8351, https://doi.org/10.5194/egusphere-egu23-8351, 2023.

The Northeast Greenland shelf is a broad Arctic shelf located between Greenland and Fram Strait. It is the principal gateway for sea ice export and sea ice-associated freshwater from the Arctic Ocean. Sea ice thickness has decreased by 15% per decade since the early 1990s and meteoric freshwater discharge has increased. The consequence of changing sea-ice and freshwater conditions in the region on ocean dynamics and the biological system remains unknown. Determining the source(s) of freshwater is important to be able to understand how the area will react to future upstream change. Here we present a synoptic survey of the Northeast Greenland shelf and slope with observations of hydrography, the nutrients nitrate, phosphate and silicate, and conservative tracers δ18O, δ2H and total alkalinity during late summer 2017. We compare these to previously published values, including those which identify Pacific and Atlantic water, the Siberian shelf seas, and the 6 largest Arctic rivers. We show that a major source of freshwater on the Northeast Greenland shelf during late summer 2017 is the Laptev Sea and find no conclusive evidence of Pacific Water. Our observations provide a direct link between Northeast Greenland hydrology and processes occurring on Eurasian shelves.

How to cite: Willcox, E., Bendtsen, J., Mortensen, J., Mohn, C., Lemes, M., Juul-Pedersen, T., Seidenkrantz, M.-S., Holding, J., Møller, E., Sejr, M., and Rysgaard, S.: An updated view on water masses on the Northeast Greenland shelf and their link to the Laptev Sea and Lena River, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-8460, https://doi.org/10.5194/egusphere-egu23-8460, 2023.

In the crucial region of the Yermak Plateau where warm Atlantic water enters the Arctic ocean, we examined high frequency variations in the Yermak Pass Branch over a 34 months-long mooring data set. The mooring was ice covered only half of the time with ice-free periods both in summer and winter. We investigated the contribution of residual tidal currents to the low frequency flow of Atlantic Water (AW) and high frequency variations in velocity shears possibly associated with internal waves. High resolution model
simulations including tides show that diurnal tide forced an anticyclonic circulation around the Yermak Plateau. This residual circulation helps the northward penetration of the AW into the Arctic. Tides should be taken into account when examining low frequency AW inflow. High frequency variations in velocity shears are mainly concentrated in a broad band around 12 hr in the Yermak Pass. Anticyclonic eddies, observed during ice-free conditions, modulate the shear signal. Semi-diurnal internal stationary waves dominate high frequency variations in velocity shears. The stationary waves could result from the interaction of freely propagating semi-diurnal internal waves generated by diurnal barotropic tides on critical slopes around the plateau. The breaking of the stationary waves with short length scales possibly contribute to mixing of AW at the entrance to the Arctic.

How to cite: Provost, C., Artana, C., Ferrari, R., Bricaud, C., Poli, L., and Park, Y.-H.: Tides, Internal and Near-Inertial Waves in the Yermak Pass at the Entrance of the Atlantic Water to the Arctic Ocean., EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-3330, https://doi.org/10.5194/egusphere-egu23-3330, 2023.

Mixing in the Arctic Ocean drives water mass transformations critical to the heat and freshwater budgets of the Arctic Ocean, impacting sea ice extent and volume, stratification, circulation, and heat and freshwater release to the subpolar N. Atlantic. Observations indicate that mixing rates in the Arctic Ocean are highly variable, however this variability is typically not well-represented in models.

This study uses a regional Arctic Ocean model to addresses the question “How does imposing a spatially-varying map of background vertical diffusivity with rates and spatial structure informed by observations impact the modelled Arctic Ocean state?” It seeks to understand impacts based on model experiments that systematically vary the diffusivity uniformly in space.

It is shown that prescribing the observationally-informed mixing map results in increased heat loss, a redistribution of freshwater storage, and increased heat and freshwater export to the N. Atlantic relative to a control case with an equal-on-average-but-spatially-uniform distribution of mixing. These effects can be understood as the result of enhancing (reducing) mixing on the shelves (basins) relative to the control case. They highlight sensitivities of the Arctic Ocean heat and freshwater budgets to shelf and basin mixing respectively.

These findings are relevant to the impacts of the changing Arctic Ocean mixing environment on Arctic Ocean functioning and subpolar ocean variability. They further suggest ways in which the prescription of Arctic Ocean mixing may be important to improving model representations of Arctic Ocean dynamics.

How to cite: O'Connor, B., Waterman, S., Scott, J., Dosser, H., and Chanona, M.: How does imposing a spatially-varying map of background vertical diffusivity with rates and spatial structure informed by observations impact the modelled Arctic Ocean state?, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-13560, https://doi.org/10.5194/egusphere-egu23-13560, 2023.

Global warming has raised mean surface temperatures by 0.99 ± 0.15 °C from 1850-1900 to 2011-2020. The temperature rise has been greatest in the high latitudes. Alaska has one of the largest temperate and subarctic glaciated areas in the world, which is highly sensitive to climate change. Currently, the mass loss from these glaciers contributes to about a third of the global sea-level rise. For example, the tidewater glacier Columbia Glacier located within Prince William Sound is the largest single contributor to sea level rise through its rapid retreat, which started in the early 1980s. Although internal controls strongly influence the tidewater glacier cycle, the ubiquitous retreat of Alaskan tidewater glaciers indicates climatic forcing is involved. However, it is unlikely climate controls the rate of retreat. There are insufficient meteorological observations from this region to assess the role of climate across a whole tidewater cycle. This project reconstructs the regional climate of southern Alaska from 1836–2015 using dynamical downscaling of the NOAA-CIRES-DOE 20th Century Reanalysis (20CRv3). To do this, the Weather Research and Forecasting model (WRF) has been used to spatially downscale the reanalysis data to produce high-resolution 4 km (convection permitting) output for southcentral/southeastern Alaska. Five different physics parametrisations have been tested for the year 2010. The model output of these five configurations were evaluated using observational records from the Global Surface Summary of the Day (GSOD). The physics scheme that performed most realistically was identified using root mean square error, R squared and normalized mean error for temperature and precipitation. The study shows that 20CRv3 can successfully be downscaled for the study region. As a result, the leading parametrisation was used for a long-term simulation (179 years) to reconstruct local climate and weather over southern Alaska over a significant part of a tidewater glacier cycle. The results will be used to evaluate the influence of climate on these glaciers for the downscaling period from 1836 to 2015.

How to cite: Koenigseder, S., Barrows, T., Fisher, J., Evans, J., and MacColl, C.: Performance evaluation of 20CRv3 downscaling using WRF over southern Alaska with focus on temperature and precipitation in glaciated areas, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-10585, https://doi.org/10.5194/egusphere-egu23-10585, 2023.

Radiogenic Sr, Nd, and Pb isotope compositions in marine sediments are widely used as provenance tracers delivering valuable information about past environmental conditions. Over the last ten years, several studies performing radiogenic isotope analysis on marine sediment records from Baffin Bay and Labrador Sea highlighted the strength of this method in shedding light upon past glacier dynamics and related environmental changes in Greenland and the Canadian Arctic. The main outcomes of our studies include precise information on the opening of Arctic gateways and the setting of oceanic connection from the Arctic Ocean to the Atlantic through Baffin Bay. At a more regional scale, these tracers document the late glacial to Holocene dynamics of Baffin Island glaciers, helping to understand how climate and oceanic conditions impacted glacier margin fluctuations. As importantly, our study also highlighted limitations in the sensitivity of radiogenic isotopes from Baffin Bay marine sediments as tracers. Most important for interpreting radiogenic isotope compositions is the availability of a sufficiently dense cover of their properties in bedrock and reference isotope signatures from such remote areas to better resolve potential sediment sources. Another challenge for sediment records obtained from core sites at near-proximity to ice margins is the effect of glacier dynamics on the sediment composition. Intense meltwater discharge can lead to grain size and mineral sorting, which could bias the radiogenic isotope composition of the sediment. Nonetheless, radiogenic isotopes present a significant advantage over lesser availability tracers, such as biological proxies, which can be restricted due to the harsh climate conditions. In several cases, radiogenic isotope analysis also reveals more information about sediment provenance than mineralogical assemblages. All in all, in combination with sedimentological and mineralogical features, the radiogenic Sr, Nd, and Pb isotope compositions of Arctic marine sequences can be used as reliable tracers for changes in sediment provenance.

How to cite: Hingst, J., Lucassen, F., Hillaire-Marcel, C., and Kasemann, S.: Strengths and limitations of using radiogenic isotope signatures of marine sediments from Baffin Bay for the reconstruction of ice dynamics and paleoenvironments in the Canadian Arctic and Greenland, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-12601, https://doi.org/10.5194/egusphere-egu23-12601, 2023.

Around Baffin Bay, the large continental Laurentide, Innuitian, and Greenland ice sheets retreated from their maximum extent reaching the shelf break during the Last Glacial Maximum (LGM) to their present-day close-to-minimum extent being largely confined to onshore settings. The associated changes in ice extent, erosion patterns, and material transport modes probably greatly affected spatial and temporal patterns of sediment deposition in Baffin Bay. While for many sites in Baffin Bay, local information about temporal changes in sedimentation rates exist, a spatial analysis allowing to compare sedimentation patterns is still lacking. To fill this gap, radiocarbon ages from over 50 sediment cores (with two or more dates) across Baffin Bay were compiled to assess the spatiotemporal variability in sediment input to Baffin Bay since the LGM. Preliminary results evaluating sedimentation rates (calculated from un-calibrated ¹⁴C ages) binned to 1 ka time slices reveal that during the LGM and the early deglacial, the slope beyond the shelf break and the deep basin were the only active depocenters, however, marked by very low sedimentation rates (mainly <20 cm ka^-1), suggesting a largely ice-covered bay. At ~15 ka, sediment supply to these settings increased, likely reflecting the onset of ice retreat during the deglaciation. With the beginning of deposition on the mid and outer shelves after ~10 ka, deposition on the slopes and in the basin ceased almost completely. Ongoing ice retreat progressively uncovered new depocenters in the over-deepened shelf troughs off Baffin Island and Greenland, where from ~9 ka onwards, especially the inner shelf off Greenland, experienced elevated sedimentation rates (~100-500 cm ka^-1), while Baffin Island fjords received less material (mainly <100 cm ka^-1). Most shelf records show a continuous decrease in sedimentation rates since the early Holocene but a few records from the Greenland shelf point to rates picking up over the last two millennia, probably reflecting the Neoglaciation. Sedimentation rates peak after ~6 ka in the wider northern Baffin Bay. These data generally reflect the transition from low glacial to enhanced deglacial sedimentation beyond the shelves, followed by a progressive landward displacement of the main depocenters towards the over-deepened inner shelf troughs. There, sediment input decreased when the ice sheets attained their minimum extent in the mid-Holocene. Only in northernmost Baffin Bay is this trend turned around, with the highest sediment input in the Late Holocene.

How to cite: Okuma, E., Titschack, J., Kienast, M., and Hebbeln, D.: Sedimentation rates across Baffin Bay since the last glacial period (based on radiocarbon age control), EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-5088, https://doi.org/10.5194/egusphere-egu23-5088, 2023.

After the last glaciation numerous temperature sensitive climate proxies from around the Arctic – ice cores, terrestrial and marine archives alike – show a tight connection to northern insolation with highest temperatures noted in the early Holocene. However, until the mid-Holocene (5-6ka; start of neoglaciation) all environmental change and reorganization occurred under circumstances still caused by deglaciation and global sea-level rise. Thus, the situation observed since then is interpreted to be mainly driven by a kind of ocean-atmospheric system that has little in common with the time before. In the Arctic the flooding of the vast shelves ended thereby massively expanding the area of winter sea-ice. And in the Nordic Seas water fronts were established which caused intensification of the gyre systems leading to the modern-like circulation pattern during the past 4kyrs. In several records these past 4 millennia were relatively cool. In the largest Arctic delta (Lena) peat-based island accumulation started at 4ka and another major change in growth occurred after 2.5ka in both, accumulation and species composition.

Neoglacial cooling in the colder Nordic Seas is witnessed by a persistent sedimentation of ice-rafted debris (IRD) after 6 ka, a trend which continued until recent time. Although within the eastern, Atlantic-influenced sector warm conditions persisted until about 1 ka, as seen in both planktic and benthic O-isotopes, variability among foraminiferal species would indicate major surface changes, as the abundance of the polar species increased to 70 % since then (in the Little Ice Age). That drastic increase was associated with highly variable O-isotope values throughout the entire water column. Thus, for the Little Ice Age the particular situation caused a rerouting of polar water masses and sea-ice far into the eastern Nordic seas. The major force behind such centennial-long climatic events must be sought in a complex atmosphere-surface ocean interaction rather than in the often-mentioned meridional ocean overturning circulation. Thus, spatial expansion of sea-ice impacts both the polar vortex and the temperature gradient between the high and low latitudes thereby exerting climate pressure on regions well beyond the Arctic realm.

How to cite: Bauch, H.: Effects of atmosphere-ocean interactions on late Holocene climate in the Arctic-Subarctic region, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-2775, https://doi.org/10.5194/egusphere-egu23-2775, 2023.

The present interglacial is a relatively warm and stable interval, especially compared to the preceding glacial period. However, several prominent cooling events have been identified within the Holocene epoch. Most of them occurred in its early or late part, while the middle Holocene was generally considered the warmest and most stable phase. Some of the cooling events (e.g., the well-known 8.2 ka BP event) have been proven to be of overregional importance. Here we focus on an event centred around 6.5 ka BP observed in marine records from the Norwegian Sea and the Fram Strait that has not been described previously. Planktic foraminiferal records from cores along the North Atlantic Drift reveal a subsurface water cooling that in the Fram Strait was more prominent than the well-known 8.2 ka BP event. The increase in the abundance of cold water foraminiferal species is preceded by a stepwise expansion of sea ice in the eastern Fram Strait and is accompanied by a decrease in the abundance of planktic foraminiferal species, an increase in shell fragmentation and IRD deposition. At the same time, alkenone-derived surface water temperatures in the north-eastern Norwegian Sea remain high, suggesting that the cooling was related to a drop in Atlantic Water advection rather than an external forcing. We discuss the possible causes of this event and its potential consequences, including the triggering of a global climatic deterioration that occurred shortly thereafter. Understanding the mechanisms behind such cold spells occurring within a generally warm interval is invaluable for future climate predictions. This study was supported by grant no. 2020/39/B/ST10/01698 funded by the National Science Centre, Poland.

How to cite: Telesiński, M. M. and Zajączkowski, M.: 6.5 ka BP cold spell in the Nordic Seas: a potential trigger for a global cooling event?, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-38, https://doi.org/10.5194/egusphere-egu23-38, 2023.