The mineral magnetic properties of an annually laminated Holocene lake-sediment sequence in northern Sweden

Abstract

Detailed mineral magnetic measurements were conducted on a 9000-year varved lake sediment sequence in northern Sweden (Lake Sarsjön). The results demonstrate that the paramagnetic susceptibility reflects the concentration of detrital minerogenic material in the lake sediments, which is controlled to a large extent by the intensity of the spring snow melt. In contrast, the concentration of ferrimagnetic magnetite (reflected by initial magnetic susceptibility and magnetic hysteresis parameters) is positively correlated to the concentration of organic carbon, which is most likely of an autochthonous origin. This magnetite has magnetic properties that are characteristic of stable single-domain magnetite grains produced by magnetotactic bacteria. The paramagnetic susceptibility record clearly points to a climatic excursion in the early Holocene between 6100± 174 bc and 5700± 167 bc, which can be correlated to an d18O excursion (a cold event) in the Greenland ice cores and lake sediments in southern Germany, and also to a short period of increased glacial activity in Scandinavia. The middle Holocene (4000–1760 bc) is characterized by sediment with a low concentration of detrital minerals and a high organic carbon content, whereas the late Holocene (1760 bc–ad 1918) is marked by more frequent and intense periods of detrital sedimentation.

Palaeolimnological and sedimentary responses to Holocene forest retreat in the Scandes Mountains, west-central Sweden

“…BP, during an episode of pronounced cooling and/or increased humidity as suggested by numerous proxy records from northwestern Europe (Anderson et al, 1998;Snowball et al, 1999;Seppa et al, 2002;Hammarlund et aL, 2003 (Hammarlund et al, 2002;Seppa and Birks, 2002). More detailed palaeoecological relationships, such as the changing species composition and density of the former high-altitude forests, cannot be assessed based on the available stratigraphic data.…”

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

“…A colder climate with some short-term fluctuations is indicated during the past c. 4000 years by a lowering of the pine tree-limit (Kullman, 1995;Barnekow, 1999;Eronen et al, 1999), glacier advances (Nesje and Kvamme, 1991;Snowball and Sandgren, 1996) and increased erosion (Snowball et al, 1999). Diatominferred temperatures from Tsuolbmajavri show only small changes with slightly higher temperatures between 2000 and 1000 cal.…”

“…Possible explanations for the low LOI values are high snow accumulation (Snowball et al, 1999) before 8000 cal. BP in combination with unstable soils after deglaciation or a low production of organic material.…”

“…BP in the North Atlantic region, which this study also supports. The diatom-inferred temperature from Tsuolbmajavri in Finland shows a drop at this time (Korhola et al, 2000) and there are indications for a decline in the pine-tree limit in the Scandes (Kullman, 1995;Karlén, 1976), a glacier advance in northern Sweden and southern Norway (Karlén, 1976;Dahl and Nesje, 1996), increased accumulation of minerogenic material in 560 The Holocene 11 (2001) northern Sweden (Snowball et al, 1999), and a notable ␦ 18 O minimum in Greenland ice cores at 8210 Ϯ 30 cal. BP (Johnsen et al, 1992;Alley et al, 1997).…”

Constant Flux of Spatial Niche Partitioning through High-Resolution Sampling of Magnetotactic Bacteria

“…Upon death, they become entrained in the sediment column, where eventually, through lithification, the magnetosomes become important recorders of the geomagnetic field (9,10). Magnetosome concentrations in sediments also serve as paleoclimate proxies (11)(12)(13)(14). As they contain 2 to 4% (dry weight) Fe (15,16), MTB could influence iron cycles in nature by acting to sequester Fe in sediments (17).…”