Holocene environmental change in subarctic aeolian dune fields: The chronology of sand dune re-activation events in relation to forest fires, palaeosol development and climatic variations in Finnish Lapland

Abstract

Sand dune stratigraphy, radiocarbon-dated charcoal layers, palaeosol development and luminescence dating are used to reconstruct the Holocene environmental history of the dune fields in Finnish Lapland since deglaciation in the early Holocene (~10,900–10,200 cal. BP). After rapid formation and stabilisation of parabolic dunes and the immigration of Scots pine ( Pinus sylvestris), forest fires are inferred to have played a key role in triggering episodes of aeolian erosion of the dunes (deflation) leading to 16 sand dune re-activation events. These events were widespread in the dune fields from ~8300 cal. BP and occurred with increasing frequency towards the late Holocene. Each event is interpreted as relating to local fires that occurred up to 100–400 years after the date of each charcoal layer; the radiocarbon age of the charcoal being affected by the age of the wood when burned, and the accumulation and/or recycling of charcoal from earlier fires. Well-developed buried iron podzols, which can develop within 500–1000 years, indicate prolonged phases of dune stability, four of which are dated to between 4500 and 1050 cal. BP. Indirect associations are evident between the sand dune re-activation events and climatic phases that were relatively cold and/or wet. These associations are explained by a conceptual geo-ecological model in which the effects of century- to millennial-scale climatic variability are modulated by the interactions between fire and vegetation. Thus, the subarctic dune field is viewed as a heterogeneous landscape of stable and unstable areas in space and through time. The unstable elements of this spatial mosaic become more extensive at times when the climatic environment promotes fire and deflation.

Holocene colluvial chronology in a sub‐arctic esker landscape atKuttanen,FinnishLapland: kettleholes as geo‐ecological archives of interactions amongst fire, vegetation, soil, climate and geomorphological instability

“…It is possible that some of the older buried podzols took longer, as suggested by three of the four individual estimates from sites 1 and 2 (Table 4). The youngest three phases and one outlier correspond quite well with the four podzolization phases recognized by Matthews & Seppälä (2014) within the dune fields of Finnish Lapland (Fig. Estimates of the date of cessation of podzol formation from overlying radiocarbon dates, combined with the assumed ∼750 years required for podzols to form, suggest five phases of podzol formation when colluvial activity on the slopes of the kettleholes was likely to have been at a low level.…”

“…Occhietti & Hillaire-Marcel 1977;Matthews et al 2005;Matthews & Seppälä 2014). Recognition of individual fires and the associated colluvial response was based on stratigraphical/ geomorphological evidence as well as the statistical confidence intervals associated with the radiocarbon dates.…”

“…Most of the charcoal found in soils and palaeosols in Finnish Lapland seems to have originated from Scots pine (Rudner & Seppälä 2005). Notwithstanding the possibility of the survival of much older wood in standing dead or forest floor wood, this led Matthews & Seppälä (2014) to conclude that the inbuilt age factor is unlikely to exceed ∼100-150 years in the sub-alpine forests of Finnish Lapland near the tree line. Notwithstanding the possibility of the survival of much older wood in standing dead or forest floor wood, this led Matthews & Seppälä (2014) to conclude that the inbuilt age factor is unlikely to exceed ∼100-150 years in the sub-alpine forests of Finnish Lapland near the tree line.…”

“…In Finnish Lapland, for example, Matthews & Seppälä (2014) identified 16 sand dune re-activation events triggered by forest fires, the earliest occurring about 8300 years ago, which were only weakly related to secular climatic change on century-to millennial time scales but had profound effects on the sub-arctic dune-field landscape. In Finnish Lapland, for example, Matthews & Seppälä (2014) identified 16 sand dune re-activation events triggered by forest fires, the earliest occurring about 8300 years ago, which were only weakly related to secular climatic change on century-to millennial time scales but had profound effects on the sub-arctic dune-field landscape.…”

“…The specific objectives were to (i) describe the colluvial stratigraphy of several representative kettleholes in the sub-arctic esker landscape; (ii) establish, in as much detail as possible, the Holocene chronology of forest fires and colluvial activity based primarily on radiocarbon dating of charcoal layers; (iii) confirm the age of the kettleholes and test the radiocarbon chronology using luminescence dating of sand; (iv) analyse the chronostratigraphical variation within and amongst the kettleholes and test whether consistent century-to millennial-scale patterns exist in the data; (v) explore possible inter-relationships amongst Holocene colluvial activity, the vegetation cover, the frequency of forest fires, podzolic soil development and climatic variations; and (vi) compare the temporal pattern of colluvial activity with parallel research on other aspects of Holocene landscape instability in Finnish Lapland, including sand-dune deflation (aeolian erosion) and solifluction lobe initiation (Matthews et al 2005;Matthews & Seppälä 2014). The specific objectives were to (i) describe the colluvial stratigraphy of several representative kettleholes in the sub-arctic esker landscape; (ii) establish, in as much detail as possible, the Holocene chronology of forest fires and colluvial activity based primarily on radiocarbon dating of charcoal layers; (iii) confirm the age of the kettleholes and test the radiocarbon chronology using luminescence dating of sand; (iv) analyse the chronostratigraphical variation within and amongst the kettleholes and test whether consistent century-to millennial-scale patterns exist in the data; (v) explore possible inter-relationships amongst Holocene colluvial activity, the vegetation cover, the frequency of forest fires, podzolic soil development and climatic variations; and (vi) compare the temporal pattern of colluvial activity with parallel research on other aspects of Holocene landscape instability in Finnish Lapland, including sand-dune deflation (aeolian erosion) and solifluction lobe initiation (Matthews et al 2005;Matthews & Seppälä 2014).…”