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As an example for the potential use of multi-block chemometric methods to provide improved unsupervised characterization of compositionally complex materials through the integration of multi-modal spectrometric data sets, we analysed spectral data derived from five field instruments (one XRF, two NIR, and two FT-Raman), collected on 76 bedrock samples of diverse composition. These data were analysed by single- and multi- block latent variable models, based on principal component analysis (PCA) and partial least squares (PLS). For the single-block approach, PCA and PLS models were generated; whilst hierarchical partial least squares (HPLS) regression was applied for the multi-block modelling. We also tested whether dimensionality reduction resulted in a more computationally efficient muti-block HPLS model with enhanced model interpretability and geological characterization power using the variable influence on projection (VIP) feature selection method.

The results showed differences in the characterization power of the five spectrometer data sets for the bedrock samples based on their mineral composition and geological properties; moreover, some spectroscopic techniques under-performed for distinguishing samples by composition. The multi-block HPLS and its VIP-strengthened model yielded a more complete unsupervised geological aggrupation of the samples in a single parsimonious model. We conclude that multi-block HPLS models are effective at combining multi-modal spectrometric data to provide a more comprehensive characterization of compositionally complex samples, and VIP can reduce HPLS model complexity, while increasing its data interpretability. These approaches have been applied here to a geological data set, but are amenable to a broad range of applications across chemical and biomedical disciplines.

The middle of the first millennium AD in Sweden witnessed significant changes in the archaeological record, prompting various discussions about the underlying causes. This paper reviews the research developments surrounding the global climate cooling, which was caused by severe volcanic eruptions in AD 536/540 and is referred to as the Late Antique Little Ice Age or Fimbulwinter, and its potential impacts, with a specific focus on Swedish Iron Age societies, drawing upon published climatic and archaeological data. Furthermore, it discusses the research gaps that impede a comprehensive understanding of the potential relationship between the AD 536/540 event and socioeconomic changes in Iron Age Sweden. Additionally, it suggests that isotopic analysis will offer additional insights and help bridge the research gap.

The geoarchaeological investigation of the large settlement at Dilling involved 1171 bulk geochemical analyses (fractionated P, LOI, MS, and MS550) and 92 thin section studies (including SEM/EDS microchemistry). Geology played a crucial role in site location and development, and Pre-Roman Iron Age–Roman Iron Age Areas 1-6 span the beach sands and finest sediments, with Area 6 at the lowest elevation. The very large number of 14C dates available allowed the suggestion that settlement in Areas 2-6, which had been established and consolidated from ca. 600 BC, had ceased by ca. AD 250. This date coincides with the onset of climatic change when conditions became wetter and cooler. We conclude that the settlement was first established on low ground on fine marine sediments, but as the climate deteriorated free drainage from the end-moraine led to increased soil wetness and wetland development downslope. PCA analysis of dated posthole and post imprints also highlighted this settlement shift upslope. Chemistry clearly suggested a dominance of organic phosphate (LOI v PQuota) at Dilling, reinforcing the long-held view that the Pre-Roman Iron Age–Roman Iron Age settlements were mixed farming communities that concentrated on organic manured arable fields (Hristova et al., this volume). Livestock were housed in long house byres and possible postals – sunken byres, like those found across Roman Belgium, for example. Trackways recorded animal movements and possible transport of composted dung to the fields through time, rather than always employing raw byre waste (see Ødegaard, this volume). Settlement morphology and function were also scrutinised.

Environmental conditions for trees that established in central Fennoscandia shortly after the final retreat of the Weichselian ice sheet remain poorly understood. In this study we examine tree rings of five well-preserved Pinus sylvestris (Scots pines) that grew in the area in front of the retreating ice sheet in northern Sweden. They became buried in flood sediments deposited by a glacial outburst flood (jökulhlaup) about 9.5–9.9 kyr cal bp and the aim of our study was to search for information regarding damage from fires and bioclimatic conditions in their ancient tree ring records. Our analysis, providing a glimpse into the local early Holocene environment in north-central Sweden, suggests that: 1, there were repeated fires (four fire events detected) during the early Holocene; and 2, bioclimatic conditions when the ancient pines were growing resembled those of modern sub-alpine pine woods. The latter is indicated by their patterns of tree ring growth (growth rate and variation), which were statistically similar to those of pines growing in sub-alpine woods with an open canopy, but different from pines in protected and managed boreal forests. Lower δ¹³C for the ancient latewood in comparison to pine wood from trees growing near the Scandinavian mountains before the 1850s were probably caused both by stomata fractionation due to lower atmospheric CO₂ during the early Holocene and by the moist local environment created by the nearby ancient Ancylus lake, which preceded the Baltic Sea. Periods with cloudy and cold summers were also indicated by the occurrence of ‘false rings’. Finds of charred fragments of Calluna vulgaris (heather, ling), an understory shrub that can burn even with a relatively high moisture content, suggest that heath vegetation was crucial to make fire a reoccurring ecological factor in the area during the early Holocene.