Late-Holocene land surface change in a coupled social-ecological system, southern Iceland: a cross-scale tephrochronology approach

The chronological challenge of cross-scale analysis within coupled socio-ecological systems can be met with tephrochronology based on numerous well-dated tephra layers. We illustrate this with an enhanced chronology
from Skaftártunga, south Iceland that is based on 200 stratigraphic profiles and 2635 individual tephra deposits from 23 different eruptions within the last 1140 years.We present newsediment-accumulation rate based dating of tephra layers from Grímsvötn in AD 1432+/-5 and AD 1457 +/- 5. These and other tephras underpin an analysis of land surface stability across multiple scales. The aggregate regional sediment accumulation records suggest a relatively slow rate of land surface change which can be explained by climate and
land use change over the period of human occupation of the island (afterADw870), but the spatial patterning of change shows that it is more complex, with landscape scale hysteresis and path dependency making the
relationship between climate and land surface instability contingent. An alternative steady state of much higher rates of sediment accumulation is seen in areas below300masl afterADw870 despite large variations in climate, with two phases of increased erosion, one related to vegetation change (AD 870e1206) and another related to climate (AD 1597e1918). In areas above 300masl there is a short lived increase in erosion and related deposition after settlement (AD w870e935) and then relatively little additional change to present. Spatial correlation between rates of sediment accumulation at different profiles decreases rapidly after ADw935 fromw4kmto less than 250mas the landscape becomes more heterogeneous. These new insights
are only possible using high-resolution tephrochronology applied spatially across a landscape, an approach that can be applied to the large areas of the Earth’s surface affected by the repeated fallout of cm-scale tephra
layers.