Local-scale Arctic tundra heterogeneity affects regional-scale carbon dynamics

M J Lara,M J Lara,M J Lara,R Rutter,E S Euskirchen,V Sloan,A D Mcguire,C Iversen,S D Wullschleger,H Genet,S Yi

doi:10.1038/s41467-020-18768-z

Abstract

In northern Alaska nearly 65% of the terrestrial surface is composed of polygonal ground, where geomorphic tundra landforms disproportionately influence carbon and nutrient cycling over fine spatial scales. Process-based biogeochemical models used for local to Pan-Arctic projections of ecological responses to climate change typically operate at coarse-scales (1km2–0.5°) at which fine-scale (<1km2) tundra heterogeneity is often aggregated to the dominant land cover unit. Here, we evaluate the importance of tundra heterogeneity for representing soil carbon dynamics at fine to coarse spatial scales. We leveraged the legacy of data collected near Utqiaġvik, Alaska between 1973 and 2016 for model initiation, parameterization, and validation. Simulation uncertainty increased with a reduced representation of tundra heterogeneity and coarsening of spatial scale. Hierarchical cluster analysis of an ensemble of 21st-century simulations reveals that a minimum of two tundra landforms (dry and wet) and a maximum of 4km2 spatial scale is necessary for minimizing uncertainties (<10%) in regional to Pan-Arctic modeling applications.

Highlights

In northern Alaska nearly 65% of the terrestrial surface is composed of polygonal ground, where geomorphic tundra landforms disproportionately influence carbon and nutrient cycling over fine spatial scales
We evaluate the error of prediction in twenty-first century Arctic soil carbon stocks associated with tundra heterogeneity and spatial scale by running parallel DOS-TEM simulations with a range of resolved tundra landforms (6–1) and spatial scales (30 m–25 km2)
The mean annual temperature, precipitation, and snowfall are −11.2 °C, 115 mm, and 958 mm, respectively (1981–2010)[35] and the maximum thaw depth ranges from 30 to 90 cm[36,37]. This continuous permafrost region is characterized by meso-scale drained thaw lake basins (DTLBs)

Summary

Introduction

In northern Alaska nearly 65% of the terrestrial surface is composed of polygonal ground, where geomorphic tundra landforms disproportionately influence carbon and nutrient cycling over fine spatial scales. Uncertainties may be amplified in coarse-scale Pan-Arctic projections by the limited representation of local-scale processes, intrinsically linked with the mosaic of tundra landforms that profoundly influence ecosystem structure and function[9,10,11]. Due to the strong control of polygonal landforms on ecosystem structure and function, we hypothesize that the local-scale representation of tundra heterogeneity (defined here as the total number of landforms represented in the model) will markedly influence regionalscale soil carbon projections. We evaluate the error of prediction in twenty-first century Arctic soil carbon stocks associated with tundra heterogeneity and spatial scale by running parallel DOS-TEM simulations with a range of resolved tundra landforms (6–1) and spatial scales (30 m–25 km[2]). All efforts to advance the representation of local-scale heterogeneity in terrestrial and earth system models will significantly improve global climate change projections in response to thawing and degrading permafrost carbon

Methods

Results

Conclusion