No abstract

The study presents the effect of soil erosion on vegetation, soil accumulation (SA), SA rate (SAR), soil quality, soil mass, and the soil organic carbon (SOC) pool in Brown Andosols and Histosols in a 24-km area in southwest Iceland. Undisturbed prehistoric soils were distinguished from disturbed historic soils using tephrochronology. Soil erosion has been severe during historic time (last 1135 yr), resulting in the increase of the soil mass deposited in soils covered by vegetation by a factor of 7.3–9.2 and net loss of soil in unvegetated areas. The SAR correlated positively with SOC sequestration. SOC is easily transported and given the extensive accumulation of soil, the net effect of burial and subsequent reduction in decomposition is to increase SOC storage. Nevertheless, the increased accumulation and soil depletion has decreased soil quality, including the SOC, and reduced soil resistance to erosion with the depleted SOC contributing to enrichment of atmospheric CO2. The initial terrestrial disturbance was triggered by anthropogenic land use during the Medieval Warm Period, followed by volcanic activity approximately three centuries later. The combination of harsh climate during the Little Ice Age and drastic anthropogenic perturbations has led to land degradation at a catastrophic scale.

Long-and short-term climate variations in the North Atlantic have been of sufficient magnitude to leave a discernible mark on the history of vegetation and landscape stability in Iceland during the Holocene. A reconstruction of early-and mid-Holocene vegetation around Lake Kagaðarhóll, Northwest Iceland, examines how climate fluctuations have affected the terrestrial ecosystem. A thorough reconstruction has been made using pollen and plant macrofossil analyses combined with proxies for organic and inorganic matter. The record shows the development from a period of pioneer vegetation towards a woodland ecosystem. The deposition of the Saksunarvatn tephra at c. 10,300 cal. yr BP caused a 100-year period of instability, followed by a gradual trend of stabilization over several centuries while material left behind by retreating glaciers and tephra was being contained by expanding and developing vegetation. Early-Holocene warmth is indicated by high pollen production of Juniperus communis around the lake by c. 10,100 cal. yr BP and birch woodland being established around the lake by c. 9200 cal. yr BP, much earlier than previously believed for this locale. Cooling climate between c. 8700 and 8200 cal. yr BP halted woodland development, with reduced plant reproduction likely caused by cold spring and summer temperatures. Woodlands became re-established from c. 7900 cal. yr BP before entering a decline from c. 6000 cal. yr BP, with harsher environmental conditions apparent after c. 4200 cal. yr BP. The Kagaðarhóll record compares favourably with other palaeoclimatic data from the North Atlantic, demonstrating the potential of pollen and macrofossil data for reconstructions of environmental change in Iceland and as an indicator of climate variability in the North Atlantic during the Holocene.

Pre--industrial human impacts on the past environment are apparent in different proxy records at different times in different places. Recognising environmentally--transformative human impacts in palaeoenvironmental archives, as opposed to natural variability, is a key challenge in understanding the nature of the transition to the Earth's current 'Anthropocene' condition. Here we consider the palaeoenvironmental record for Iceland over the past 2.5 ka, both before and after the late--9 th century human settlement (landnám). The Scandinavian colonization of the island was essentially abrupt, involving thousands of people over a short period. The colonization triggered extensive changes in Icelandic ecosystems and landscapes. A volcanic ash known as the Landnám 2 tephra was deposited over most of Iceland immediately before the settlement began.The Landnám tephra layer thus provides a uniquely precise litho--chrono--stratigraphic marker of colonization. We utilise this marker horizon as an independent definition of the effective onset of the local palaeoanthropocene (which is conceptually related to, but distinct from, the global Anthropocene). This allows us to evaluate proxy records for human impact on the Icelandic environment and to assess how and when they show transformative impact. Based on this analysis, we consider the implications for understanding and defining the Anthropocene in those areas of the Earth where such a clear independent marker of the onset of significant human impacts is lacking.

Tephra-dated, high-resolution pollen profiles from Ketilsstaðir, southern Iceland, indicate a largely unwooded pre-settlement environment, a probable consequence of the exposed coastal location. The degree of change associated with the Norse landnám is more limited than in many Icelandic pollen diagrams. There are three main periods of change in the post-settlement vegetational development of the area. Firstly, Norse settlement affected the hydrology of the bog, resulting in the near-disappearance of Sphagnum and agricultural activity led to a reduction of some species (e.g. Angelica spp. and Salix). Secondly, the establishment of probable permanent settlement in the mid-11th century AD initiated expansion of such apophytic taxa as Plantago spp. Lactuceae, Ranunculus spp. and Pteridophytes. Thirdly, the ≥ 10 cm thick Katla tephra, deposited in AD 1357, enhanced drainage of the bog surface, favouring dryland taxa (e.g. Poaceae, Galium and Lactuceae). The tephra deposit and the associated drainage probably caused or contributed to the local extinction of the wetland beetle Hydraena britteni. The study has enabled a series of natural and humanly-related issues to be addressed including tephra-vegetation relationships, the anthropogenic reduction in plant diversity, and comparisons between historical and environmental settlement records.