Christian Katlein

The thickness and consolidation state of pressure ridges are variables relevant for sea ice mass balance, melt processes and ecosystem habitat. We show how both variables can be detected by the multi-frequency electromagnetic induction (EMI) sounding, based on data collected during Multidisciplinary drifting Observatory for the Study of Arctic Climate (MOSAiC) in the central Arctic Ocean between November 2019 and July 2020. We validate the EMI results by collocating them to sea ice topography from the airborne laser scanner, underwater topography from multi-beam sonar, and sea ice thickness and structure from drill holes. Selected channels of low frequency give good estimates of total thickness, while selected channels of high frequency give good estimates of consolidated layer thickness. The MOSAiC EMI dataset was collected over a large number of ridge systems formed between freeze-up and break-up. Nine individual ridge transects can be used to track the seasonal development. The footprint size and sensitivity of the method make the EMI sounding appropriate for the detection of ridges with up to 10 m total thickness. Where available, the ridge structure data from other methods are consistent with our results. The superior temporal and spatial coverage of the MOSAiC EMI data permits further analysis that indicates a slow reduction of the total thickness towards the consolidated layer thickness. Interestingly, the consolidated layer thickness exceeds the level ice thickness by a factor of 1.6 to 2 and also shows, at least for individual ridges, a seasonal decrease. This may be a feature of the thin snow cover at MOSAiC. Multi-frequency EMI is a promising method for non-intrusive pressure ridge surveying with a large potential for pressure ridge dataset extension.

There is no light for photosynthesis by phytoplankton and sea-ice algae during the polar night, but microbial grazers remain active through the dark winter months in the Arctic Ocean. Where the energy to sustain these organisms comes from is unknown. Here we observed active tintinnid ciliates during the polar night, heterotrophic protists known to feed on phytoplankton and smaller heterotrophic protists. Our calculations indicate that the pelagic microbial loop transferring energy from bacterial production through microbial grazers was not sufficient to sustain the observed tintinnid biomass. However, the sea ice contained frozen-in particulate organic carbon produced during the previous growth seasons. We show that enough food particles can be released by mechanical break-up during sea-ice ridging, which together with bacterial production, sustained the observed tintinnid biomass in the water column. This is an important but overlooked mechanism for winter survival of plankton in the Arctic Ocean.

The thickness and consolidation state of pressure ridges are variables relevant for sea ice mass balance, melt processes and ecosystem habitat. We show how both variables can be detected by the multi-frequency electromagnetic induction (EMI) sounding, based on data collected during Multidisciplinary drifting Observatory for the Study of Arctic Climate (MOSAiC) in the central Arctic Ocean between November 2019 and July 2020. We validate the EMI results by collocating them to sea ice topography from the airborne laser scanner, underwater topography from multi-beam sonar, and sea ice thickness and structure from drill holes. Selected channels of low frequency give good estimates of total thickness, while selected channels of high frequency give good estimates of consolidated layer thickness. The MOSAiC EMI dataset was collected over a large number of ridge systems formed between freeze-up and break-up. Nine individual ridge transects can be used to track the seasonal development. The footprint size and sensitivity of the method make the EMI sounding appropriate for the detection of ridges with up to 10 m total thickness. Where available, the ridge structure data from other methods are consistent with our results. The superior temporal and spatial coverage of the MOSAiC EMI data permits further analysis that indicates a slow reduction of the total thickness towards the consolidated layer thickness. Interestingly, the consolidated layer thickness exceeds the level ice thickness by a factor of 1.6 to 2 and also shows, at least for individual ridges, a seasonal decrease. This may be a feature of the thin snow cover at MOSAiC. Multi-frequency EMI is a promising method for non-intrusive pressure ridge surveying with a large potential for pressure ridge dataset extension.

The thickness and consolidation state of pressure ridges are variables relevant for sea ice mass balance, melt processes and ecosystem habitat. We show how both variables can be detected by the multi-frequency electromagnetic induction (EMI) sounding, based on data collected during Multidisciplinary drifting Observatory for the Study of Arctic Climate (MOSAiC) in the central Arctic Ocean between November 2019 and July 2020. We validate the EMI results by collocating them to sea ice topography from the airborne laser scanner, underwater topography from multi-beam sonar, and sea ice thickness and structure from drill holes. Selected channels of low frequency give good estimates of total thickness, while selected channels of high frequency give good estimates of consolidated layer thickness. The MOSAiC EMI dataset was collected over a large number of ridge systems formed between freeze-up and break-up. Nine individual ridge transects can be used to track the seasonal development. The footprint size and sensitivity of the method make the EMI sounding appropriate for the detection of ridges with up to 10 m total thickness. Where available, the ridge structure data from other methods are consistent with our results. The superior temporal and spatial coverage of the MOSAiC EMI data permits further analysis that indicates a slow reduction of the total thickness towards the consolidated layer thickness. Interestingly, the consolidated layer thickness exceeds the level ice thickness by a factor of 1.6 to 2 and also shows, at least for individual ridges, a seasonal decrease. This may be a feature of the thin snow cover at MOSAiC. Multi-frequency EMI is a promising method for non-intrusive pressure ridge surveying with a large potential for pressure ridge dataset extension.

Ice coring has developed into one of the most frequently used sampling methods across cryospheric sciences. Sea ice, firn and glacial ice are sampled using a range of different coring systems. These systems can retrieve core samples with lengths ranging from several cm to tens of meters when operated by hand or drilling machines, while specialized coring systems have retrieved cores from Antarctica's ice caps with a length of over 3 km. In the last decade more robotic subsea vehicles like remotely operated vehicles (ROV) and autonomous underwater vehicles (AUV) have ventured into polar waters beneath sea ice and ice shelves, but retrieval of ice samples from the sub-ice environment has not been achieved on a regular basis. Other geophysical investigation methods such as push core sediment coring and rock drilling have been successfully adapted for subsea robotic vehicles. Hence the purpose of this work is to investigate the feasibility of adapting the techniques of retrieving short ice cores from sea ice and glacial research to the subsea environment. We successfully demonstrate the retrieval of an ice sample in a laboratory setting using traditional ice coring systems in conjunction with a subsea manipulator arm. We discuss challenges and further improvements to our experiments towards enabling reliable ice sampling in the subsea environment using generic tooling readily available on subsea vehicles. In conclusion, ice core sampling in the subsea environment seems feasible using industrial work class manipulators particularly when cartesian inverse-kinematic control is available.

In this work, we demonstrate the utilization of a compact, consumer-grade 360° camera for measuring the in-ice spectral angular radiance distribution. This novel technique allows for the instantaneous acquisition of all radiometric quantities at a given depth with a non-intrusive probe. This gives the opportunity to monitor the light field structure (mean cosines) from the atmosphere to the underlying ocean beneath ice. In this study, we report vertical profiles of the light field geometric distribution measured at two sites representative of distinct ice types: High Arctic multi-year ice and Chaleur Bay (Quebec, Canada) landfast first-year ice. We also propose a technique to empirically retrieve the depth-resolved inherent optical properties by matching simulated profiles of spectral irradiances calculated with the HydroLight radiative transfer model to the observed ones. As reported in other studies, the derived reduced scattering coefficients were high (641.57 m⁻¹; 72.85 m⁻¹) at the top (2 cm; 5 cm) for both sites (High Arctic; Chaleur Bay) and lower in the interior part of the ice (0.48–4.10 m⁻¹; 0.021–7.79 m⁻¹). Due to the inherent underdetermined nature of the inversion problem, we emphasize the importance of using a similarity parameter that considers both the absorption and the reduced scattering coefficients. Finally, we believe that this radiometric device, combined with the proposed inversion technique, will allow the research community to scale up the measurements of the inherent optical properties of different kinds of sea ice, making it possible to take better account of terrain variability in radiative transfer models.

Ice coring has developed into one of the most frequently used sampling methods across cryospheric sciences. Sea ice, firn and glacial ice are sampled using a range of different coring systems. These systems can retrieve core samples with lengths ranging from several cm to tens of meters when operated by hand or drilling machines, while specialized coring systems have retrieved cores from Antarctica’s ice caps with a length of over 3 km. In the last decade more robotic subsea vehicles like remotely operated vehicles (ROV) and autonomous underwater vehicles (AUV) have ventured into polar waters beneath sea ice and ice shelves, but retrieval of ice samples from the sub-ice environment has not been achieved on a regular basis. Other geophysical investigation methods such as push core sediment coring and rock drilling have been successfully adapted for subsea robotic vehicles. Hence the purpose of this work is to investigate the feasibility of adapting the techniques of retrieving short ice cores from sea ice and glacial research to the subsea environment. We successfully demonstrate the retrieval of an ice sample in a laboratory setting using traditional ice coring systems in conjunction with a subsea manipulator arm. We discuss challenges and further improvements to our experiments towards enabling reliable ice sampling in the subsea environment using generic tooling readily available on subsea vehicles. In conclusion, ice core sampling in the subsea environment seems feasible using industrial work class manipulators particularly when cartesian inverse-kinematic control is available.

Ice coring has developed into one of the most frequently used sampling methods across cryospheric sciences. Sea ice, firn and glacial ice are sampled using a range of different coring systems. These systems can retrieve core samples with lengths ranging from several cm to tens of meters when operated by hand or drilling machines, while specialized coring systems have retrieved cores from Antarctica’s ice caps with a length of over 3 km. In the last decade more robotic subsea vehicles like remotely operated vehicles (ROV) and autonomous underwater vehicles (AUV) have ventured into polar waters beneath sea ice and ice shelves, but retrieval of ice samples from the sub-ice environment has not been achieved on a regular basis. Other geophysical investigation methods such as push core sediment coring and rock drilling have been successfully adapted for subsea robotic vehicles. Hence the purpose of this work is to investigate the feasibility of adapting the techniques of retrieving short ice cores from sea ice and glacial research to the subsea environment. We successfully demonstrate the retrieval of an ice sample in a laboratory setting using traditional ice coring systems in conjunction with a subsea manipulator arm. We discuss challenges and further improvements to our experiments towards enabling reliable ice sampling in the subsea environment using generic tooling readily available on subsea vehicles. In conclusion, ice core sampling in the subsea environment seems feasible using industrial work class manipulators particularly when cartesian inverse-kinematic control is available.

In this work, we demonstrate the utilization of a compact, consumer-grade 360-degree camera for measuring the in-ice spectral angular radiance distribution. This novel technique allows for the instantaneous acquisition of all radiometric quantities at a given depth with a non-intrusive probe. This gives the opportunity to monitor the light field structure (mean cosines) from the atmosphere to the underlying ocean beneath ice. In this study, we report vertical profiles of the light field geometric distribution measured at two sites representative of distinct ice types: High Arctic multi-year ice and Chaleur Bay (Quebec, Canada) landfast first-year ice. We also propose a technique to empirically retrieve the depth-resolved inherent optical properties by matching simulated profiles of spectral irradiances calculated with the HydroLight radiative transfer model to the observed ones. As reported in other studies, the derived reduced scattering coefficients were high (641.57 m^-1, 72.85 m^-1) in the first (2 cm, 5 cm) for both sites (High Arctic, Chaleur Bay) and lower in the interior part of the ice (0.48 to 4.10 m^-1, 0.021 to 7.79 m^-1). Due to the inherent underdetermined nature of the inversion problem, we emphasize the importance of using the similarity parameter that considers both the absorption and the reduced scattering coefficients. Finally, we believe that this radiometric device, combined with the proposed inversion technique, will allow to scale up the measurements of the inherent optical properties of different kinds of sea ice enabling to take better account of terrain variability in radiative transfer models.

In this work, we demonstrate the utilization of a compact, consumer-grade 360-degree camera for measuring the in-ice spectral angular radiance distribution. This novel technique allows for the instantaneous acquisition of all radiometric quantities at a given depth with a non-intrusive probe. This gives the opportunity to monitor the light field structure (mean cosines) from the atmosphere to the underlying ocean beneath ice. In this study, we report vertical profiles of the light field geometric distribution measured at two sites representative of distinct ice types: High Arctic multi-year ice and Chaleur Bay (Quebec, Canada) landfast first-year ice. We also propose a technique to empirically retrieve the depth-resolved inherent optical properties by matching simulated profiles of spectral irradiances calculated with the HydroLight radiative transfer model to the observed ones. As reported in other studies, the derived reduced scattering coefficients were high (641.57 m^-1, 72.85 m^-1) in the first (2 cm, 5 cm) for both sites (High Arctic, Chaleur Bay) and lower in the interior part of the ice (0.48 to 4.10 m^-1, 0.021 to 7.79 m^-1). Due to the inherent underdetermined nature of the inversion problem, we emphasize the importance of using the similarity parameter that considers both the absorption and the reduced scattering coefficients. Finally, we believe that this radiometric device, combined with the proposed inversion technique, will allow to scale up the measurements of the inherent optical properties of different kinds of sea ice enabling to take better account of terrain variability in radiative transfer models.