Mike J. Church

Abandoned Farms, Volcanic Impacts, and Woodland Management: Revisiting Þjórsárdalur, the “Pompeii of Iceland”

Geomorphological maps and nine soil profiles containing 92 tephra layers have been examined to explore the nature of medieval environmental change in Þjórsárdalur, Iceland, where farms are thought to have been abandoned after the massive tephra fall from the eruption of Hekla in 1104 A.D. This paper presents evidence for continued human activity in the area in the two centuries following the 1104 A.D. eruption, indicating that continued utilization of the region changed after another major episode of volcanic fallout in 1300 A.D. The paper proposes that measures were taken in the fourteenth century to conserve woodland in Þjórsárdalur resulting in localized landscape stabilization that continued throughout the following Little Ice Age episodes of climate deterioration.

Temporal and Spatial Variations in Freshwater 14C Reservoir Effects: Lake Mývatn, Northern Iceland

Lake Mývatn is an interior highland lake in northern Iceland that forms a unique ecosystem of international scientific importance and is surrounded by a landscape rich in archaeological and paleoenvironmental sites. A significant freshwater reservoir effect (FRE) has been identified in carbon from the lake at some Viking (about AD 870?1000) archaeological sites in the wider region (Mývatnssveit). Previous accelerator mass spectrometry (AMS) measurements indicated this FRE was about 1500-1900 14C yr. Here, we present the results of a study using stable isotope and 14C measurements to quantify the Mývatn FRE for both the Viking and modern periods. This work has identified a temporally variable FRE that is greatly in excess of previous assessments. New, paired samples of contemporaneous bone from terrestrial herbivores and omnivores (including humans) from Viking sites demonstrate at least some omnivore diets incorporated sufficient freshwater resources to result in a herbivore-omnivore age offset of up to 400 14C yr. Modern samples of benthic detritus, aquatic plants, zooplankton, invertebrates, and freshwater fish indicate an FRE in excess of 5000 14C yr in some species. Likely geothermal mechanisms for this large FRE are discussed, along with implications for both chronological reconstruction and integrated investigation of stable and radioactive isotopes.

Charcoal Production During the Norse and Early Medieval Periods in Eyjafjallahreppur, Southern Iceland

Timber procurement and the use of woodlands are key issues in understanding the open landscapes of the Norse and Medieval periods in the North Atlantic islands. This paper outlines evidence for the timing and mechanisms of woodland use and deforestation in an area of southern Iceland, which is tracked through the mapping and analysis of charcoal production pits. Precise dating of the use of these charcoal production pits within a Bayesian framework is demonstrated through the combination of tephrochronology, sediment accumulation rates, and multiple radiocarbon dates on the archaeological charcoal. Two phases of charcoal production and woodland exploitation have been demonstrated, the first within the first 2 centuries of settlement (cal AD 8701050) and the second phase over 100 yr later (cal AD 11851295). The implications for using charcoal as a medium for 14C dating in Iceland and the wider North Atlantic are then explored. Archaeobotanical analysis of the charcoal sampled from the pits has indicated that birch roundwood was the dominant wood used, that the roundwood was stripped from larger shrubs/trees in late spring/early summer, and that certain sizes and ages of roundwood were harvested. Finally, the timing of the charcoal production is placed into the wider debate on deforestation across Iceland during the Norse and early Medieval periods.

Reservoirs and radiocarbon: C-14 dating problems in Myvatnssveit, northern Iceland

This paper examines 2 potential sources of the radiocarbon offset between human and terrestrial mammal (horse) bones recovered from Norse (~AD 8701000) pagan graves in Mvatnssveit, north Iceland. These are the marine and freshwater 14C reservoir effects that may be incorporated into human bones from dietary sources. The size of the marine 14C reservoir effect (MRE) during the Norse period was investigated by measurement of multiple paired samples (terrestrial mammal and marine mollusk shell) at 2 archaeological sites in Mvatnssveit and 1 site on the north Icelandic coast. These produced 3 new Δ R values for the north coast of Iceland, indicating a Δ R of 106 10 14C yr at AD 868985, and of 144 28 14C yr at AD 12801400. These values are statistically comparable and give an overall weighted mean Δ R of 111 10 14C yr. The freshwater reservoir effect was similarly quantified using freshwater fish bones from a site in Mvatnssveit. These show an offset of between 1285 and 1830 14C yr, where the fish are depleted in 14C relative to the terrestrial mammals. This is attributed to the input of geothermally derived CO2 into the groundwater and subsequently into Lake Mvatn. We conclude the following: i) some of the Norse inhabitants of Mvatnssveit incorporated non-terrestrial resources into their diet that may be identified from the stable isotope composition of their bone collagen; ii) the MRE off the north Icelandic coast during the Norse period fits a spatial gradient of wider North Atlantic MRE values with increasing values to the northwest; and iii) it is important to consider the effect that geothermal activity could have on the 14C activity of samples influenced by groundwater at Icelandic archaeological sites.

Puffins, Pigs, Cod and Barley: Palaeoeconomy at Undir Junkarinsfløtti, Sandoy, Faroe Islands

Abstract This paper reports on the zooarchaeological and archaeobotanical remains from the initial season of excavations at the Norse period site at Undir Junkarinsfløtti in the Faroe islands. These remains represent the first zooarchaeological analysis undertaken for the Faroes and only the third archaeobotanical assemblage published from the islands. The excavated deposits are described and the key findings from the palaeoenvironmental remains highlighted within the context of the wider North Atlantic environmental archaeology of the Norse period.

1000 years of environmental change and human impact at Stóra-Mörk, southern Iceland: A multiproxy study of a dynamic and vulnerable landscape

Multiproxy pollen, sediment, plant macrofossil and subfossil insect analyses are used to explore environmental change at Stóra-Mörk in southern Iceland between ad 500 and 1500. Previous palaeoecological studies in Iceland have indicated that vegetation and landscape change rapidly succeeded the initial settlement of the island around ad 871, with strong environmental consequences. However, recent high-resolution studies in western and northern Iceland suggest that the timing and amplitude of these changes may be less uniform than previously assumed. The palaeoecological evidence from Stóra-Mörk shows an initially muted anthropogenic signal. Before the early tenth century, the area was characterized by damp birch and willow woodland. Large-scale human impact did not begin until after ad 920 when a change in land use to grazing and crop production is observed in the pollen, insect and plant macrofossil records. Shifts in vegetation and insect taxa and in aeolian deposition indicate that this activity resulted in woodland reduction, increased soil instability, eutrophication and land surface drying. The relatively late appearance of large-scale human impact at Stóra-Mörk is consistent with the tenth-century farm establishment suggested by the historical record, and the delay in settlement at the location may relate to an initial avoidance of labour-intensive woodland clearance and/or management of woodland resources. This paper adds to the emerging body of evidence that suggests that the scale and timing of the initial effect of the human presence on Icelandic environments was influenced by complex and varied climatic, landscape, vegetational and cultural factors.

An Icelandic freshwater radiocarbon reservoir effect: Implications for lacustrine 14C chronologies

A freshwater radiocarbon (14C) reservoir effect (FRE) is a 14C age offset between the atmospheric and freshwater carbon reservoirs. FREs can be on the order of 10 000 14C yr in extreme examples and are a crucial consideration for 14C dating of palaeoenvironmental and archaeological samples. Correction for a FRE may be possible, provided the FRE and the proportion of FRE-affected carbon within a sample can be accurately quantified. However, although such correction is desirable for affected samples, it is essential that such correction is accurate in order to produce useful chronological information. Accuracy of FRE correction can be limited by spatial variation in FRE within a freshwater system, but despite this there is currently a paucity of information to identify and quantify such variability within affected systems. Here we present results of a study that investigates the effects of spatial FRE variation upon dating accuracy within the freshwater system of Lake Mývatn, northern Iceland. A substantial FRE (>10 000 14C yr) has previously been identified in archaeological and modern samples from the region, which shows the potential for considerable spatial variability. The study also assesses the use of δ13C and δ15N in age correction of affected samples. The results show that benthic detritus and organisms at primary trophic levels from locations within the lake are affected by a FRE of at least 3500 14C yr, with clear spatial variation resulting in 14C age differences of up to 7670 14C yr between samples. There is a broad correlation between stable isotope values and FRE within the data set. However, large associated uncertainties currently preclude highly accurate and precise stable isotope-based quantification of the proportion of FRE-affected carbon within archaeological and palaeoenvironmental samples from Mývatn and the surrounding region.

Archaeological evidence for the first Mesolithic occupation of the Western Isles of Scotland

The examination of eroding coastal dunes at the prehistoric site of Northton, Harris, has produced the first archaeological evidence of Mesolithic activity in the Western Isles in the form of two midden-related deposits. The first phase of Mesolithic activity is dated to 7060-6650 cal. BC based on AMS dating of charred hazelnut shells. This discovery appears to validate the frequent pollen-based inferences of Mesolithic impact for the area and, as predicted, allows the Atlantic fringe of Scotland to become part of the European Mesolithic mainstream. A detailed pedological analysis also suggests that these early midden layers may have been amended during the Neolithic period as part of a possible phase of cultivation.

Mineral magnetism and archaeology at Galson on the Isle of Lewis, Scotland

Abstract Coastal erosion is cutting a section through a complex later prehistoric archaeological site at Galson. 168 samples from individual features e.g. middens and hearts, and also from several continuously-sampled vertical profiles were collected from the site. A range of mineral magnetic measurements, including susceptibilities, and laboratory induced remanent magnetisations have been carried out on the samples. The strong magnetic signal of the hearth material can be traced in selected floors and middens giving an indication of the anthropogenic use within the dwellings. The magnetic data also highlight differences between visually similar soils. The variation of susceptibility with temperature, measured at 2cm intervals in a vertical profile through a hearth in one of the dwellings, has revealed two distinct magnetic mineralogies, with varying domain states, possibly reflecting different fuel sources.

Re-deposited cryptotephra layers in Holocene peats linked to anthropogenic activity

Tephra layers can form useful age-equivalent stratigraphic markers for correlating palaeoenvironmental sequences and they provide information about the spatio-temporal nature of past volcanic ash fall events. The use of microscopic ‘cryptotephra’ layers has both increased the stratigraphic resolution of tephra sequences in proximal areas and extended the distal application of tephrochronology to regions of the world situated far from volcanoes. Effective tephrochronology requires the discrimination between in situ tephra deposited directly from volcanic plumes and tephras that have been remobilised since their initial deposition. We present tephrostratigraphic and glass chemistry data from two proximal peat profiles (one lowland, one upland) from the Shetland Islands, UK. Both profiles contain the Hekla-Selsund tephra (deposited c. 1800–1750 cal. bc), whilst the Hekla 4 ash (c. 2395–2279 cal. bc) is present in the upland record. Overlying the Hekla-Selsund tephra are a number of distinct peaks in tephra shard abundance. The geochemistry of these layers shows that they represent re-working of the Hekla 4 and Hekla-Selsund layers rather than primary air-fall deposits. Pollen analysis of the peat sequences illustrates that these re-deposited tephra layers are coincident with a rise in heather-dominated vegetation communities (heath and/or moorland) and a subsequent intensification of burning in the landscape. We suggest that burning caused increased erosion of peats resulting in the remobilisation of tephra shards. The study demonstrates both the need for caution and the opportunities created when applying tephrochronologies in regions heavily affected by past human activity that contain both reworked tephra layers and in situ fallout.