Modelling subglacial fluvial sediment transport with a graph-based model, Graphical Subglacial Sediment Transport (GraphSSeT)

A quantitative understanding of how sediment discharge from subglacial fluvial systems varies in response to glaciohydrological conditions is essential for understanding marine systems around Greenland and Antarctica and for interpreting sedimentary records of cryosphere evolution. Here we develop a graph-based approach, Graphical Subglacial Sediment Transport (GraphSSeT), to model subglacial fluvial sedimentary transport using subglacial hydrology model outputs as forcing. GraphSSeT includes glacial erosion of bedrock and a dynamic sediment model with exchange between the active transport system and a basal sediment layer. Sediment transport considers transport-limited and supply-limited regimes and includes stochastically evolving grain size, network-scale flow management, and tracking of detrital provenance. GraphSSeT satisfies volume balance and sediment velocity and transport capacity constraints on flow. GraphSSeT is demonstrated for synthetic scenarios that probe the impact of variations in hydrological, geological, and glaciological characteristics on sediment transport over multi-diurnal to seasonal time frames. For steady-state hydrology scenarios on seasonal timescales, we find a primary control from the scale and organisation of the channelised hydrological flow network. The development of grain-size-dependent selective transport is identified as the major secondary control. Non-steady-state hydrology is tested on multi-diurnal timescales for which sediment discharge scales with peak water input, leading to increased sediment discharge compared to the steady state. Subglacial hydrology models are being applied more broadly, and GraphSSeT extends this capacity to quantitatively define the volume, grain-size distribution, and detrital characteristics of sediment discharge that through comparison with the sediment record may enable improved knowledge of the glaciohydrological system and its impact on marine systems.