The natural holocene vegetation development and the introduction of agriculture in northern Norrland, Sweden : studies of soil, peat and especially varved lake sediments

The Holocene vegetation history of northern Norrland was studied by pollen analysis of sediement, peat and soil samples, with the aim to improve our knowledge about vegetation development in northern Norrland, and also about the history of man and the introduction of agriculture in the area. Earlier made pollen analyses from the four northernmost provinces were summarized and a series of new analyses from northern Norrland added. Pollen anlyses were conducted on sediment and peat profiles from four sites in the Luleälv valley, in Norrbotten, and from Kassjön in coastal Västerbotten. Furthermore, the hypothesis was tested that pollen analysis of thin mor humus soils could be used to trace and identify ancient cultivated fields. When the interior parts of the Luleälv valley were deglaciated about 9500 BP, an open ecosystem formed dominated by shrubs and dwarf-shrubs. A few hundred years later Betula and Pinus invaded and rapidly formed forests, and by 9000 BP Alnus had immigrated and become common in most of Norrland. With climatic improvement Betula and Alnus increased in abundance, and nemoral broad-leaved trees colonized from south to north: between 6000-3500 BP Ulmus and Corvlus had become common as far north as Västerbotten. In Norrbotten, however, Betula and Alnus were the dominant deciduous trees. Around 3400 BP Picea abies reached the coast of Norrland from Finland, established itself and within 300 years became the major forest tree along a coastal zone. It occupied the moist, fine sediment substrates in those areas which earlier had been mainly dominated by Alnus and Betula. Climatic deterioration resulted in a steady retreat of the more southerly forest elements, and by 2000 BP only small, remnant stands at isolated sites were left. Over the last 2000 years little natural change has occurred in the forest vegetation. Man invaded the area soon after the deglaciation. These first occupants were hunters and fishermen, however, and their impact on the vegetation development was minor and restricted to small camp clearings. Not until an agricultural economy became established, did the influence of man become pronounced. In coastal Västernorrland and Västerbotten, traces of agriculture and animal husbandry occurred between 4700-2500 BP, but these first cereal cultivations were temporary, short-lived and occurred primarily at coastal sites. In those areas, permanent cultivation developed due to changed settlement structure during the first centuries AD. In the Luleälv valley in Norrbotten, cereal cultivation and animal husbandry was introduced between 500-1000 AD, although the hunter/gatherer economy continued to dominate, as it did in most of interior Norrland. Concomitant with the general agricultural expansion in Västernorrland and Västerbotten between 1000-1200 AD, permanent field cultivation developed in the coastal parts of the Luleälv valley. In the interior of northern Norrland, however, agriculture did not become important until the 17th-19th centuries.Diss. (sammanfattning) Umeå : Umeå universitet, 1990, härtill 4 uppsatser.digitalisering@um

Holocene climatic change reconstructed from diatoms, chironomids, pollen and near-infrared spectroscopy at an alpine lake (Sjuodjijaure) in northern Sweden

The results of a multiproxy study reconstructing the climate history of the last 9300 years in northern Sweden are presented. It is based on diatom, chironomid and pollen analyses, as well as near-infrared spec troscopy (NIRS), of a radiocarbon dated sediment core from Sjuodjijaure (67°22N, 18°04E), situated 100 m above tree-line in the Scandes mountains. Mean July air temperature was reconstructed using transfer functions established for the region. The biological proxies show significant changes in composition during the Holocene and the inferred temperatures all follow the same general trend. For the period between about 9300 to 7300 cal. BP the reconstructions should be interpreted with caution due to the lack of convincing modern analogues in the training set. However the reconstruction suggest that July temperature was on average about the same as today, with several rapid short-term cold and warm periods. Cold periods were dated to about 8500, 8200 and 7600 cal. years BP and a warm period to about 7700 cal. BP. About 7300 cal. BP, a major shift to a warmer climate occurred. Pine migrated into the area, which was previously covered with birch forest. From the mid-Holocene until today the sediment record suggests a descending tree-limit and a gradual lowering of July temperature

Tracing modern environmental conditions to their roots in early mining, metallurgy, and settlement in Gladhammar, southeast Sweden: Vegetation and pollution history outside the traditional Bergslagen mining region

We present results from a multidisciplinary project using lake sediment as a natural archive in combination with archaeology to investigate the earliest history of the Gladhammar mining area, southeastern Sweden. The aim was to identify and trace human impacts on the landscape, specifically in connection with settlement and metal production. Sediment records from two lakes linked to different processes in metal production were analyzed; Tjursbosjön down-slope of the mining area and Hyttegöl situated downstream of an excavated blast furnace, 1.8 km from the mines. The sediment analyses included multi-element geochemistry (WD-XRF), stable lead isotopes, pollen, and charcoal. Although historical documents record activities beginning in AD 1526, the archaeological study found indications that mining and metal production likely predated this period. The known historical period is well reflected in the sediment records, such as a 500-fold increase in copper, stream erosion, loss of forest cover and an expansion in agriculture. More importantly, already in the 12th–13th centuries, there was a 2- to 10-fold increase in lead, copper, and charcoal particles and evidence of erosion linked to the establishment of a blast furnace. Lead isotopes reveal a change from natural conditions to an input of lead from regional ores as early as the 9th–10th centuries. Settlement in the form of agriculture can be seen from 2000 BP. This sediment evidence of early mining or metallurgy during the 9th–15th centuries is supported by a few radiocarbon dates from the excavated mining fields, which on their own were considered as vague or improbable outliers by archaeologists.SCOPUS: ar.jinfo:eu-repo/semantics/publishe

Lake Ecosystem Responses to Holocene Climate Change at the Subarctic Tree-Line in Northern Sweden

A Holocene sediment sequence from Lake Seukokjaure, a subarctic lake at tree-line in northern Sweden, was analyzed to assess major changes in the structure and functioning of the aquatic ecosystem in response to climate change and tree-line dynamics. The compiled multi-proxy data, including sedimentary pigments, diatoms, chironomids, pollen, biogenic silica (BSi), carbon (C), nitrogen (N) elemental and stable-isotope records, and total lake-water organic carbon (TOC) concentration inferred from near-infrared spectroscopy (NIRS), suggest that the Holocene development of Lake Seukokjaure was closely coupled to changes in terrestrial vegetation with associated soil development of the catchment, input of allochthonous organic carbon, and changes in the light regime of the lake. A relatively productive state just after deglaciation around 9700 to 7800 cal years BP was followed by a slight long-term decrease in primary production. The onset of the local tree-line retreat around 3200 cal years BP was accompanied by more diverse and altered chironomid and diatom assemblages and indications of destabilized soils in the catchment by an increase in variability and absolute values of delta C-13. An abrupt drop in the C/N ratio around 1750 cal years BP was coupled to changes in the internal lake structure, in combination with changes in light and nutrient conditions, resulting in a shift in the phototrophic community from diatom dominance to increased influence of chlorophytes, likely dominated by an aquatic moss community. Thus, this study emphasizes the importance of indirect effects of climate change on tree-line lake ecosystems and complex interactions of in-lake processes during the Holocene