What Controls Global Glacial Erosion Rates?

The text you have provided is a detailed methodological description about the synthesis of glacial erosion rates from multiple published studies prior to January 2021. Here’s a concise summary and key points from the described methodology and data processing:

Summary of Synthesis of Glacial Erosion Rates and Related Data:

1. Data Collection and Scope:

• Glacial erosion rates were synthesized from published data primarily measuring the removal of material from glacier beds (164 contemporary rates + 17 Holocene rates).
• Only data from topographically constrained extant glaciers and ice caps with dominantly warm basal thermal regimes were included.
• Measurements come from four methods:
  • Sediment discharge from meltwater streams.
  • Bulk sediment in proglacial areas.
  • Bedrock erosion via terrestrial cosmogenic nuclide dating.
  • Instrumental measurements from extant glaciers.
• Multiple measurements from the same glacier were included to reflect the range of observed erosion rates.

2. Glaciological Variables:

• Variables like ice mass length, area, median elevation, surface slope, glacier termination type, form, surge behaviour were sourced primarily from the Randolph Glacier Inventory (RGI25).
• Missing variables were supplemented by digital elevation models (SRTM and ASTER GDEM).
• Surface and sliding velocities and ice thicknesses were included where available, preferring multi-year averages temporally matching erosion measurements.
• Where velocity/ice thickness not available from original sources, they were estimated from published velocity datasets or ice thickness models.
• Sliding velocity (U_sliding) was estimated from surface speed (U_surface) and local surface slope (β) using a constrained ratio and linear interpolation.

3. Geological Variables:

• Glacier bed lithology was extracted from the Global Lithological Map (GLiM) using glacier centroids.
• Lithologies categorized into:
  • Crystalline (igneous and metamorphic)
  • Sedimentary (carbonates, sandstones, shales)
  • Volcanics (volcanics, basalts)
• Seismicity approximated using PGA (Peak Ground Acceleration) from the Global Seismic Hazard Assessment dataset, filling gaps for polar regions where needed.

4. Climatic Variables:

• Mean Annual Air Temperature (MAAT) and Mean Annual Precipitation (MAP) were extracted from the CHELSA climate dataset for modern erosion rates and from PaleoClim for Holocene rates, using glacier centroids.

5. Dataset and Analysis Limitations:

• Methods differ in the processes they capture, potentially biasing erosion rates (e.g., instrumental measurements focus on abrasion only).
• Bulk sediment and sediment discharge methods might underestimate or misattribute erosion due to sediment storage effects or partial sediment load measurement.
• Timescale dependence is mitigated by focusing on short-term (~350 years or less) erosion rates; no significant correlation between rate and timespan was observed.
• Temporal mismatches between velocity and erosion rate measurements remain a limitation, though methods to mitigate this were employed.
• Velocity data were selected preferentially to match erosion measurement periods, with sensitivity analyses confirming this approach improved model performance.
• Surge-type glaciers were underrepresented (<15% of data), which may limit extrapolation for those glacier types.

Additional Notes:

• Velocity estimation: sliding velocity is a proportion of surface speed scaled by slope β constrained between 0.001 and 0.1, interpolated linearly.
• Velocity variability and surge behaviour introduce further complexities.
• Data synthesis incorporated multiple data quality and spatial resolution sources to achieve as comprehensive and consistent a dataset as possible.

Application of This Dataset:

• Enables near-global estimation of glacial erosion rates.
• Can be used to investigate relationships between glacial erosion and glaciological, geological, climatic, and seismic variables.
• Provides a basis for “velocity–erosion” rules and erosion scaling models relevant to Earth surface processes, landscape evolution, and glaciology.

If you have any specific questions regarding this synthesis, such as the methods for velocity estimation, geological categorizations, or limitations on data interpretation, please let me know!