Report on cruises and data stations 2021

The report gives an overview of cruises in 2021, by the Institute of Marine Research, University of Bergen and Tromsø and Norwegian Polar Institute, on board our research vessels and many of the hired commercial vessels. Each cruise has a short description and a track chart showing CTD and trawl stations. A table displaying the coverage of the oceanographic sections in addition to a table showing the number of observations per month for the fixed stations are included at the end of the report. Meta data about the cruises are reported to the International Council for the Exploration of the Sea (ICES) using the form “Cruise Summary Report”: https://www.seadatanet.org/Metadata/CSR-Cruises . Research data (and chart) are available from the Norwegian Marine Data Centre at Institute of Marine Research (https://www.nmdc.no). Charts are generated by Silje Smith-Johnsen using ggOceanMaps by Mikko Vihtakari (IMR). There are no overview or maps for the cruises with our vessels "Fangst" and "Hans Brattstrøm".Report on cruises and data stations 2021publishedVersio

The role of subglacial hydrology in ice streams with elevated geothermal heat flux

The spatial distribution of geothermal heat flux (GHF) under ice sheets is largely unknown. Nonetheless, it is an important boundary condition in ice-sheet models, and suggested to control part of the complex surface velocity patterns observed in some regions. Here we investigate the effect of including subglacial hydrology when modelling ice streams with elevated GHF. We use an idealised ice stream geometry and a thermomechanical ice flow model coupled to subglacial hydrology in the Ice Sheet System Model (ISSM). Our results show that the dynamic response of the ice stream to elevated GHF is greatly enhanced when including the interactive subglacial hydrology. On the other hand, the impact of GHF on ice temperature is reduced when subglacial hydrology is included. In conclusion, the sensitivity of ice stream dynamics to GHF is likely to be underestimated in studies neglecting subglacial hydrology.publishedVersio

Exceptionally high heat flux needed to sustain the Northeast Greenland Ice Stream

The Northeast Greenland Ice Stream (NEGIS) currently drains more than 10 % of the Greenland Ice Sheet area and has recently undergone significant dynamic changes. It is therefore critical to accurately represent this feature when assessing the future contribution of Greenland to sea level rise. At present, NEGIS is reproduced in ice sheet models by inferring basal conditions using observed surface velocities. This approach helps estimate conditions at the base of the ice sheet but cannot be used to estimate the evolution of basal drag in time, so it is not a good representation of the evolution of the ice sheet in future climate warming scenarios. NEGIS is suggested to be initiated by a geothermal heat flux anomaly close to the ice divide, left behind by the movement of Greenland over the Icelandic plume. However, the heat flux underneath the ice sheet is largely unknown, except for a few direct measurements from deep ice core drill sites. Using the Ice Sheet System Model (ISSM), with ice dynamics coupled to a subglacial hydrology model, we investigate the possibility of initiating NEGIS by inserting heat flux anomalies with various locations and intensities. In our model experiment, a minimum heat flux value of 970 mW m−2 located close to the East Greenland Ice-core Project (EGRIP) is required locally to reproduce the observed NEGIS velocities, giving basal melt rates consistent with previous estimates. The value cannot be attributed to geothermal heat flux alone and we suggest hydrothermal circulation as a potential explanation for the high local heat flux. By including high heat flux and the effect of water on sliding, we successfully reproduce the main characteristics of NEGIS in an ice sheet model without using data assimilation.publishedVersio

Time-lapse techniques for surface velocity, front position and calving rate measurement of a fast-flowing tidewater glacier in Svalbard

Calving is the mechanical loss of icebergs from tidewater glaciers, responsible for 70% of the annual transfer of mass from the cryosphere to the ocean (van der Veen 1998a, 2002). To be able to correctly predict future global sea level changes it is important to understand calving processes and incorporate them into the models. The aim of this thesis is to investigate surface velocities, front positions and calving rates of a fast flowing tidewater glacier in Svalbard using an automatic oblique terrestrial time-lapse camera. The camera took pictures every 30 min from May 1st to September 16th 2014 resulting in 6600 images. The project forms part of the ConocoPhillips-Lundin Northern Area Program project CRIOS (Calving Rates and Impact on Sea Level) program whose overall aim is to develop better calving-process models. Mean velocities of Kronebreen increased from 3 m/day in May and reached a peak in mid-July of 5.3 m/day, with a velocity pattern showing increasing velocities towards the front and the centreline. Velocity results were filtered, sensitivity tested, averaged both spatially and temporally and fit well with previous results. Results suggest that velocity has a forcing from air temperature and rain events due to water inputs in the glacier system. Mean front positions showed a total retreat of 320 m, and calving rates reached a peak in early August of 11 m/day. Different parts of the front showed different styles of retreat, and therefore calving styles. Inter-meltwater-plume areas were dominated by infrequent large calving events, and plume areas were dominated by continuous calving. Mean calving rates may be atmospherically controlled, but internal dynamics, melt-water plumes and fjord temperatures may also play a role. The high resolution both spatially and temporally gained using this method makes it possible to investigate the nature of calving and the evolution of surface velocity patterns in more detail than satellite derived results. These data are required for improving the understanding of calving dynamics to develop sea level rise models

Dynamics of the Northeast Greenland Ice Stream: the role of geothermal heat and subglacial hydrology

Ice streams are rivers of fast flowing ice, crucial for the mass balance of ice sheets. The Greenland Ice Sheet shows a complex flow pattern, where a few major ice streams drain most of the ice sheet, contributing to sea level rise. It is therefore crucial to capture ice streams in ice flow models when predicting the future response of the Greenland Ice Sheet to a warmer climate. The Northeast Greenland Ice Stream (NEGIS) drains 12% of the ice sheet, and holds 1.1 m of sea level equivalent. It displays a unique velocity pattern with fast flow initiated close to the ice divide. This is further inland than any other ice stream in Greenland. Geothermal heat flux, the natural heat from the Earth, is thought to be the trigger of the ice stream. A local high geothermal heat flux at the head of the Northeast Greenland Ice Stream generates basal water which lubricates the ice-bed interface and induces fast flow. Models of geothermal heat flux display a large range for Greenland, and their coarse resolution is unable to capture local anomalies, as the one suggested at the onset of the Northeast Greenland Ice Stream. Previous studies investigated how geothermal heat flux influences ice dynamics, and did not find a significant impact. However, these studies focused on the direct thermal effect on ice softness, and did not include the indirect effect of water pressure. I hypothesize that, excluding the combined effect of geothermal heat flux and subglacial hydrology, accounts for the fact that the observed velocity of the Northeast Greenland Ice Stream is poorly represented in ice sheet models. This thesis investigates how geothermal heat flux influences the subglacial hydrol- ogy and the dynamics of ice streams. The goal is to understand the processes at the bed of the Northeast Greenland Ice Stream, and to improve its representation in an ice sheet model. The model used is the Ice Sheet System Model (ISSM), a state of the art fully coupled thermomechanical ice flow model. Here, for the first time, a sophisticated subglacial hydrology model is coupled to ice dynamics in ISSM. The simulations show that the choice of geothermal heat flux largely controls whether the bed of the Northeast Greenland is frozen or thawed. This sets the basal melt rates and controls the subglacial hydrology. As a consequence, the effect of geother- mal heat flux on ice flow is increased tenfold when including the coupling between subglacial hydrology and ice dynamics. In summary, local geothermal heat flux anomalies can induce fast flow. For the Northeast Greenland Ice Stream, subglacial hydrology accounts for a substantial part of the observed velocity pattern. By introducing an exceptionally high and locally contained geothermal heat flux anomaly, the ice flow model successfully reproduces the velocity pattern of the Northeast Greenland Ice Stream

Report on cruises and data stations 2021

The report gives an overview of cruises in 2021, by the Institute of Marine Research, University of Bergen and Tromsø and Norwegian Polar Institute, on board our research vessels and many of the hired commercial vessels. Each cruise has a short description and a track chart showing CTD and trawl stations. A table displaying the coverage of the oceanographic sections in addition to a table showing the number of observations per month for the fixed stations are included at the end of the report. Meta data about the cruises are reported to the International Council for the Exploration of the Sea (ICES) using the form “Cruise Summary Report”: https://www.seadatanet.org/Metadata/CSR-Cruises . Research data (and chart) are available from the Norwegian Marine Data Centre at Institute of Marine Research (https://www.nmdc.no). Charts are generated by Silje Smith-Johnsen using ggOceanMaps by Mikko Vihtakari (IMR). There are no overview or maps for the cruises with our vessels "Fangst" and "Hans Brattstrøm"

Sensitivity of the Northeast Greenland Ice Stream to Geothermal Heat

Recent observations of ice flow surface velocities have helped improve our understanding of basal processes on Greenland and Antarctica, though these processes still constitute some of the largest uncertainties driving ice flow change today. The Northeast Greenland Ice Stream is driven largely by basal sliding, believed to be related to subglacial hydrology and the availability of heat. Characterization of the uncertainties associated with Northeast Greenland Ice Stream is crucial for constraining Greenland's potential contribution to sea level rise in the upcoming centuries. Here, we expand upon past work using the Ice Sheet System Model to quantify the uncertainties in models of the ice flow in the Northeast Greenland Ice Stream by perturbing the geothermal heat flux. Utilizing a subglacial hydrology model simulating sliding beneath the Greenland Ice Sheet, we investigate the sensitivity of the Northeast Greenland Ice Stream ice flow to various estimates of geothermal heat flux, and implications of basal heat flux uncertainties on modeling the hydrological processes beneath Greenland's major ice stream. We find that the uncertainty due to sliding at the bed is 10 times greater than the uncertainty associated with internal ice viscosity. Geothermal heat flux dictates the size of the area of the subglacial drainage system and its efficiency. The uncertainty of ice discharge from the Northeast Greenland Ice Stream to the ocean due to uncertainties in the geothermal heat flux is estimated at 2.10 Gt/yr. This highlights the urgency in obtaining better constraints on the highly uncertain subglacial hydrology parameters

Exceptionally high heat flux needed to sustain the Northeast Greenland Ice Stream

The Northeast Greenland Ice Stream (NEGIS) currently drains more than 10 % of the Greenland Ice Sheet area and has recently undergone significant dynamic changes. It is therefore critical to accurately represent this feature when assessing the future contribution of Greenland to sea level rise. At present, NEGIS is reproduced in ice sheet models by inferring basal conditions using observed surface velocities. This approach helps estimate conditions at the base of the ice sheet but cannot be used to estimate the evolution of basal drag in time, so it is not a good representation of the evolution of the ice sheet in future climate warming scenarios. NEGIS is suggested to be initiated by a geothermal heat flux anomaly close to the ice divide, left behind by the movement of Greenland over the Icelandic plume. However, the heat flux underneath the ice sheet is largely unknown, except for a few direct measurements from deep ice core drill sites. Using the Ice Sheet System Model (ISSM), with ice dynamics coupled to a subglacial hydrology model, we investigate the possibility of initiating NEGIS by inserting heat flux anomalies with various locations and intensities. In our model experiment, a minimum heat flux value of 970 mW m−2 located close to the East Greenland Ice-core Project (EGRIP) is required locally to reproduce the observed NEGIS velocities, giving basal melt rates consistent with previous estimates. The value cannot be attributed to geothermal heat flux alone and we suggest hydrothermal circulation as a potential explanation for the high local heat flux. By including high heat flux and the effect of water on sliding, we successfully reproduce the main characteristics of NEGIS in an ice sheet model without using data assimilation

Shifts in Greenland interannual climate variability lead Dansgaard-Oeschger abrupt warming by hundreds of years

During the Last Glacial Period (LGP), Greenland experienced approximately thirty abrupt warming phases, known as Dansgaard-Oeschger (D-O) Events, followed by cooling back to baseline glacial conditions. Studies of mean climate change across warming transitions reveal indistinguishable phase-offsets between shifts in temperature, dust, sea salt, accumulation and moisture source, thus preventing a comprehensive understanding of the “anatomy” of D-O cycles (Capron et al,. 2021). One aspect of abrupt change that has not been systematically assessed is how high-frequency, interannual-scale climatic variability surrounding mean temperature changes across D-O transitions. Here, we utilize the EGRIP ice core high-resolution water isotope record, a proxy for temperature and atmospheric circulation, to quantify the amplitude of 7–15 year isotopic variability for D-O events 2–13, the Younger Dryas and the Bølling-Allerød. On average, cold stadial periods consistently exhibit greater variability than warm interstadial periods. Most notably, we often find that reductions in the amplitude of the 7–15 year band led abrupt D-O warmings by hundreds of years. Such a large phase offset between two climate parameters in a Greenland ice core has never been documented for D-O cycles. However, similar centennial lead times have been found in proxies of Norwegian Sea ice cover relative to abrupt Greenland warming (Sadatzki et al., 2020). Using HadCM3, a fully coupled general circulation model, we assess the effects of sea ice on 7–15 year temperature variability at EGRIP. For a range of stadial and interstadial conditions, we find a strong relationship in line with our observations between colder simulated mean temperature and enhanced temperature variability at the EGRIP location. We also find a robust correlation between year-to-year North Atlantic sea-ice fluctuations and the strength of interannual-scale temperature variability at EGRIP. Thus, both paleoclimate proxy evidence and model simulations suggest that sea ice plays a substantial role in high-frequency climate variability prior to D-O warming. This provides a clue about the anatomy of D-O Events and should be the target of future sea-ice model studies