Magnetic detection of bacterial magnetite in the high-latitude lake Fiskvatnet, northern Norway

Details Magnetic detection of bacterial magnetite in the high-latitude lake Fiskvatnet, northern Norway Magnetic detection of bacterial magnetite in the high-latitude lake Fiskvatnet, northern Norway

Apr 2003

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2003eaeja....10250l&link_type=abstract

EGS - AGU - EUG Joint Assembly, Abstracts from the meeting held in Nice, France, 6 - 11 April 2003, abstract #10250

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The lacustrine sediments in the small lake Fiskvatnet (69.5^oN) covering the last ≈14.500 calibrated years B.P. exhibit a uniform and almost constant sedimentation rate (25cm/1000 yrs). The lower, Late Glacial part of the core (≈10 cm) consists of glacigenic derived meltwater sediments with a relatively strong magnetic signal (MS, SIRM). S-ratios (=IRM-03.T/SIRM) indicate a mixture of magnetite and high-coercivity minerals, probably reflecting the adjacent Lower Paleozoic metamorphic gabbros and quartzite bedrock. The gyttja in the upper Holocene part of the core carries a low MS-signal reflecting the high organic/water content and negligible amount of detrital material. This is also supported by the positive correlation between LOI (loss-on-ignition) and concentration dependent imposed magnetisations (ARM, SIRM). The low-gradient topography surrounding the lake precludes any significant run-off, and consequently the organic content is primarily produced within the lake. S-ratios show two temporal trends (1) in the upper ca 180 cm S-ratio is close to -1.0 and (2) the preceding Holocene part where S-ratios gradually decrease to approximately -0.6. This latter trend is tentatively explained by either dissolution of magnetite through reductive processes (Snowball 1994), or increasing production of magnetite within the lake. Magnetic hysteresis curves of these magnetic weak sediments show characteristic features of SD magnetite (wide and early closed curves) while in the Day-plot, data points are distributed towards the PSD-MD region. However, in the Moskowitz-plot (ARM/SIRM versus cross-over point (Raf)) (Moskowitz et al. 1993) the data plots close to the bacterial magnetite range supporting the SD interpretation. This is yet another case that questions the discriminating power of the Day-plot. We assume that the Holocene magnetic signal in the lake Fiskvatnet is carried by magnetosomes. This observation suggests that lake-produced bacterial magnetite may be a common feature in biological lakes - even at such high latitudes. Moskowitz B.M., Frankel R.B. and Bazylinski D.A., 1993. Rock magnetic criteria for the detection of biogneic magnetite. Earth and Planetary Science Letters, 120, 283-300. Snoball I., 1994. Bacterial magnetite and the magnetic proerties of sediments in a Swedish lake. Earth and Planetary Science Letters, 126, 129-142.

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