Generating synthetic fjord bathymetry for coastal Greenland

Abstract

Abstract. Bed topography is a critical boundary for the numerical modelling of ice sheets and ice-ocean interactions. A persistent issue with existing topography products for the bed of the Greenland Ice Sheet and surrounding sea floor is the poor representation of coastal bathymetry, especially in regions of floating ice and near the grounding line. Sparse data coverage, and the resultant coarse resolution at the iceocean boundary, poses issues in our ability to model ice flow advance and retreat from the present position. In addition, as fjord bathymetry is known to exert strong control on ocean circulation and ice-ocean forcing, the lack of bed data leads to an inability to model these processes adequately. Since the release of the last complete Greenland bed topography-bathymetry product, new observational bathymetry data have become available. These data can be used to constrain bathymetry, but many fjords remain completely unsampled and therefore poorly resolved. Here, as part of the development of the next generation of Greenland bed topography products, we present a new method for constraining the bathymetry of fjord systems in regions where data coverage is sparse. For these cases, we generate synthetic fjord geometries using a method conditioned by surveys of terrestrial glacial valleys as well as existing sinuous feature interpolation schemes. Our approach enables the capture of the general bathymetry profile of a fjord in north-west Greenland close to Cape York, when compared to observational data. We validate our synthetic approach by demonstrating reduced overestimation of depths compared to past attempts to constrain fjord bathymetry. We also present an analysis of the spectral characteristics of fjord centrelines using recently acquired bathymetric observations, demonstrating how a stochastic model of fjord bathymetry could be parameterised and used to create different realisations.

BedMachine v3: Complete Bed Topography and Ocean Bathymetry Mapping of Greenland From Multibeam Echo Sounding Combined With Mass Conservation

“…We also relied on gravity inversions downstream of Upernavik and Alison's ice fronts. In fjords where coverage is sporadic or nonexistent, we employed the approach proposed by Williams et al (2017) to construct synthetic yet plausible bathymetry.…”

“…This bed topography is then combined with all bathymetry data in the fjords and a natural neighbor interpolation along the fjords (Figure 1b). In uncharted or poorly charted fjords, we use a synthetic fjord method (Williams et al, 2017) that enforces a parabolic across-flow profile consistent with the bed depth at glacier termini and guided by available bathymetry measurements. We merge this map with RTopo-2 (Schaffer et al, 2016) 50 km away from the coast.…”

“…Here we employ new ocean bathymetry data from 30 different sources, in combination with the mass conservation method to produce a detailed, seamless, and comprehensive map of the bed topography and fjord bathymetry around the entire periphery of Greenland (within 50 km of the coast) at a horizontal spatial resolution of up to 150 m. In poorly charted fjords, we rely on synthetic fjord bathymetries (Williams et al, 2017). We merge the final map with RTopo-2/IBCAO (Schaffer et al, 2016) at a distance of 50 km away from the coast.…”

Multibeam bathymetry and CTD measurements in two fjord systems in southeastern Greenland

“…However, with the single major objective of IBCAO being to provide a portrayal of the Arctic Ocean seafloor (Jakobsson et al, 2012), it is understandable that not all fjord complexes are as well resolved as offshore bathymetry based on extensive multibeam mapping. However, large-scale efforts, such as the NASA OMG mission measuring bathymetry and the synthetic bathymetry datasets (Williams et al, 2017), are beginning to shed new light on the configurations of fjords around Greenland.…”

“…The publication of different datasets is continuously improving the bathymetry around Greenland (e.g., Arndt et al, 2015;Fenty et al, 2016;Rignot et al, 2015Rignot et al, , 2016Schumann et al, 2012;Williams et al, 2017), even if it is only based on a suite of single-point observations (Andresen et al, 2014) or inversion of gravity data to obtain bathymetry (Porter et al, 2014). Whereas the topography of the onshore area is more easily determined from air and satellite imagery and altimetry (e.g., Korsgaard et al, 2016;Willis et al, 2015), the relief of the submarine parts is hidden by the water column and can only be determined with hydroacoustic methods or aerial gravimetry.…”