Holocene Landscape Disturbances in the Central Highlands of Iceland as Recorded in Soil Sediment Archives

Ongoing and widespread soil erosion in the Icelandic Highlands threatens the sustainability of terrestrial environments in this ecologically sensitive region. This study uses tephrochronology and sedimentology of remnant soil accumulations to characterize recent terrestrial changes (i.e. land denudation and desertification) in the Kjölur region of central Iceland, placing them in a Holocene context. We have excavated a suite of >20 soil sedimentary profiles, varying in length from 0.85m—4.3m, situated along a ~100 km latitudinal transect between Langjökull and Hofsjökull ice caps. All soil sections contain a series of distinct tephra layers from Holocene volcanic eruptions of known ages. Spatial and temporal patterns of soil accumulation rates are correlated and quantified through precise chronologies developed from robust tephrostratigraphies unique to each site. Sedimentological parameters including: bulk density, organic content, grain size, and accumulation rates were analyzed to characterize Holocene environmental conditions and determine periods of landscape changes, including intervals of accelerated soil erosion. Soil age models indicate that, where present, relict soils have persisted for at least the past ~8 ka and that accelerated erosion rates in the last millennium are unprecedented within the length of the records. Our results suggest temporal variability in the onset of widespread erosion during the late Holocene, generally occurring between ~1300 AD and ~1720 AD. This event is recorded in soil stratigraphy by diagnostic changes in sediment parameters, often expressed as a sharp transition to coarser grained, minerogenic sediment, low in organic content, from finer-grained relict soils that had accumulated gradually through the Holocene. By integrating our collection of soil sediment sequences with new and existing sedimentary records from central Iceland, we aim to identify the relative roles of climate change and human activity in driving vegetation loss and soil erosion in this region during the Holocene.