Degrees of success : evaluating the environmental impacts of long term settlement in South Iceland.

This paper focuses on the occupation and landscape history of Dalur and Mörk, two areas of long-term settlement in the Eyjafjallahreppur district of southern Iceland. The aim is to illustrate the importance of evaluating not only farm occupation and abandonment, but also to assess the complexities of the environmental interactions of long-term settlements. Environmental records are assessed using data from 50 sediment profiles, constrained by tephrochronology, located in the farm infields (tún) and outfields (hagi). This record indicates that despite similar outward appearances today, the environs of Dalur and Mörk have experienced different histories of environmental change over the last 1000 years. At least 14 subsidiary settlements were at one time or another established within Dalur, or were dependent on the Church farm there. Ten of these settlements were subsequently abandoned and sediment accumulation rates, a proxy indicator of erosion, remained low, indicating restricted local human impact. We conclude that this illustrates the importance of access and rights to additional resources out with the principal farm. In addition, much of the immediate environs of the main farm site was probably un-wooded at the time of settlement, so the total degree of vegetative change was limited. In contrast, palaeoenvironmental data indicates that the environs of Mörk were extensively wooded at the time of Landnám, but this woodland was rapidly cleared and this was followed by several centuries of landscape instability. In a cultural contrast, the landholdings of Mörk experienced less subdivision with a total of only five dependent farms established across the land belonging to three main farms (all of which had chapels). From the early 10th to 14th centuries there was significantly enhanced erosion within the Mörk landholdings, but this stabilised and the principal farms endured and to form sites of long-term settlement. The ownership of additional resource rights, including woodland further up-valley, may have made the crucial contribution to long term endurance

Settlement history, land holdings and landscape change, Eyjafjallahreppur, Iceland

In this paper we focus on a region in south Iceland and assess the confidence with which it is possible to determine the changing patterns of settlement history for a region and relate it to contemporaneous land boundaries. For a geographically coherent group of up to 38 possible farm sites in the northern and western part of Eyjafjallahreppur, south Iceland, the timing of occupation and abandonment is assessed. In addition, boundaries of landholdings, probable status and inter-site relationships are identified. Currently only 10 sites are occupied. There is some uncertainty over the location of the earliest settlements, but after the 11th century, successful principle farm sites such as Dalur, Seljaland and Mörk remain in the same locations. As a result, recent data on landholdings combined with a knowledge of the form of landholding sub-division, offers insights into pre-modern times, with some data relevant to medieval times. An ‘abandoned frontier’ exists in the inland area of Þórsmörk, but abandonment is not restricted to the uplands; it has occurred throughout the region. Most desertion occurred before the cold phases of the Little Ice Age in the 18th century. Overall, much farm desertion can be attributed to landscape destruction as a result of river migration, but it is also biased towards small dependent farms often established for social reasons (such as the property requirement for marriage) and evidently insufficiently resourced for long term success in a changing physical environment

An over-optimistic pioneer fringe ? environmental perspectives on medieval settlement abandonment in Þórsmörk, South Iceland.

We assess environmental factors that may have contributed to farm abandonment in Þórsmörk, south Iceland. Here farms were established during the initial Norse colonisation of Iceland and abandoned by the 13th century AD. Soil erosion has been identified as a possible factor in this settlement change. This hypothesis is assessed using sediment profiles constrained by tephrochronology in Þórsmörk and the nearby area of Stakkholt. In Þórsmörk, there is evidence for episodes of landscape instability between the 10th and 13th centuries and localised episodes of soil erosion to bedrock that ended before 1300 AD and the onset of the Little Ice Age (LIA) climate changes. This early instability is absent from Stakkholt. Later LIA stability in Þórsmörk contrasts with episodes of instability in Stakkholt. The implication is that Þórsmörk was sensitive to early settlement impacts that lead to extensive erosion. After farm abandonment in Þórsmörk, the surviving woodland was successfully conserved as a valuable source of wood and charcoal for lowland farms where woodland resources had been depleted. Mounting pressure on woodland resources in the 11th -12th centuries could have been an important factor in determining the precise timing of abandonment

Gas Accretion and Galactic Chemical Evolution: Theory and Observations

This chapter reviews how galactic inflows influence galaxy metallicity. The goal is to discuss predictions from theoretical models, but particular emphasis is placed on the insights that result from using models to interpret observations. Even as the classical G-dwarf problem endures in the latest round of observational confirmation, a rich and tantalizing new phenomenology of relationships between $M_*$, $Z$, SFR, and gas fraction is emerging both in observations and in theoretical models. A consensus interpretation is emerging in which star-forming galaxies do most of their growing in a quiescent way that balances gas inflows and gas processing, and metal dilution with enrichment. Models that explicitly invoke this idea via equilibrium conditions can be used to infer inflow rates from observations, while models that do not assume equilibrium growth tend to recover it self-consistently. Mergers are an overall subdominant mechanism for delivering fresh gas to galaxies, but they trigger radial flows of previously-accreted gas that flatten radial gas-phase metallicity gradients and temporarily suppress central metallicities. Radial gradients are generically expected to be steep at early times and then flattened by mergers and enriched inflows of recycled gas at late times. However, further theoretical work is required in order to understand how to interpret observations. Likewise, more observational work is needed in order to understand how metallicity gradients evolve to high redshifts.Comment: Invited review to appear in Gas Accretion onto Galaxies, Astrophysics and Space Science Library, eds. A. J. Fox & R. Dav\'e, to be published by Springer. 29 pages, 2 figure

Gas Accretion and Star Formation Rates

Cosmological numerical simulations of galaxy evolution show that accretion of metal-poor gas from the cosmic web drives the star formation in galaxy disks. Unfortunately, the observational support for this theoretical prediction is still indirect, and modeling and analysis are required to identify hints as actual signs of star-formation feeding from metal-poor gas accretion. Thus, a meticulous interpretation of the observations is crucial, and this observational review begins with a simple theoretical description of the physical process and the key ingredients it involves, including the properties of the accreted gas and of the star-formation that it induces. A number of observations pointing out the connection between metal-poor gas accretion and star-formation are analyzed, specifically, the short gas consumption time-scale compared to the age of the stellar populations, the fundamental metallicity relationship, the relationship between disk morphology and gas metallicity, the existence of metallicity drops in starbursts of star-forming galaxies, the so-called G dwarf problem, the existence of a minimum metallicity for the star-forming gas in the local universe, the origin of the alpha-enhanced gas forming stars in the local universe, the metallicity of the quiescent BCDs, and the direct measurements of gas accretion onto galaxies. A final section discusses intrinsic difficulties to obtain direct observational evidence, and points out alternative observational pathways to further consolidate the current ideas.Comment: Invited review to appear in Gas Accretion onto Galaxies, Astrophysics and Space Science Library, eds. A. J. Fox & R. Dav\'e, to be published by Springe

Degrees of success: evaluating the environmental impacts of long term settlement in south Iceland

This paper focuses on the occupation and landscape history of Dalur and Mörk, two areas of long-term settlement in the Eyjafjallahreppur district of southern Iceland. The aim is to illustrate the importance of evaluating not only farm occupation and abandonment, but also to assess the complexities of the environmental interactions of long-term settlements. Environmental records are assessed using data from 50 sediment profiles, constrained by tephrochronology, located in the farm infields (tún) and outfields (hagi). This record indicates that despite similar outward appearances today, the environs of Dalur and Mörk have experienced different histories of environmental change over the last 1000 years. At least 14 subsidiary settlements were at one time or another established within Dalur, or were dependent on the Church farm there. Ten of these settlements were subsequently abandoned and sediment accumulation rates, a proxy indicator of erosion, remained low, indicating restricted local human impact. We conclude that this illustrates the importance of access and rights to additional resources out with the principal farm. In addition, much of the immediate environs of the main farm site was probably un-wooded at the time of settlement, so the total degree of vegetative change was limited. In contrast, palaeoenvironmental data indicates that the environs of Mörk were extensively wooded at the time of Landnám, but this woodland was rapidly cleared and this was followed by several centuries of landscape instability. In a cultural contrast, the landholdings of Mörk experienced less subdivision with a total of only five dependent farms established across the land belonging to three main farms (all of which had chapels). From the early 10th to 14th centuries there was significantly enhanced erosion within the Mörk landholdings, but this stabilised and the principal farms endured and to form sites of long-term settlement. The ownership of additional resource rights, including woodland further up-valley, may have made the crucial contribution to long term endurance

Settlement history, land holdings and landscape change, Eyjafjallahreppur, Iceland

In this paper we focus on a region in south Iceland and assess the confidence with which it is possible to determine the changing patterns of settlement history for a region and relate it to contemporaneous land boundaries. For a geographically coherent group of up to 38 possible farm sites in the northern and western part of Eyjafjallahreppur, south Iceland, the timing of occupation and abandonment is assessed. In addition, boundaries of landholdings, probable status and inter-site relationships are identified. Currently only 10 sites are occupied. There is some uncertainty over the location of the earliest settlements, but after the 11th century, successful principle farm sites such as Dalur, Seljaland and Mörk remain in the same locations. As a result, recent data on landholdings combined with a knowledge of the form of landholding sub-division, offers insights into pre-modern times, with some data relevant to medieval times. An ‘abandoned frontier’ exists in the inland area of Þórsmörk, but abandonment is not restricted to the uplands; it has occurred throughout the region. Most desertion occurred before the cold phases of the Little Ice Age in the 18th century. Overall, much farm desertion can be attributed to landscape destruction as a result of river migration, but it is also biased towards small dependent farms often established for social reasons (such as the property requirement for marriage) and evidently insufficiently resourced for long term success in a changing physical environment