Environmental control on the occurrence of high-coercivity magnetic minerals and formation of iron sulfides in a 640 ka sediment sequence from Lake Ohrid (Balkans)

Abstract

Abstract. The bulk magnetic mineral record from Lake Ohrid, spanning the past 637 kyr, reflects large-scale shifts in hydrological conditions, and, superimposed, a strong signal of environmental conditions on glacial-interglacial and millennial timescales. A shift in the formation of early diagenetic ferrimagnetic iron sulfides to siderites is observed around 320 ka. This change is probably associated with variable availability of sulfide in the pore water. We propose that sulfate concentrations were significantly higher before ∼ 320 ka, due to either a higher sulfate flux or lower dilution of lake sulfate due to a smaller water volume. Diagenetic iron minerals appear more abundant during glacials, which are generally characterized by higher Fe / Ca ratios in the sediments.While in the lower part of the core the ferrimagnetic sulfide signal overprints the primary detrital magnetic signal, the upper part of the core is dominated by variable proportions of high-to low-coercivity iron oxides. Glacial sediments are characterized by high concentration of high-coercivity magnetic minerals (hematite, goethite), which relate to enhanced erosion of soils that had formed during preceding interglacials. Superimposed on the glacial-interglacial behavior are millennial-scale oscillations in the magnetic mineral composition that parallel variations in summer insolation. Like the processes on glacial-interglacial timescales, low summer insolation and a retreat in vegetation resulted in enhanced erosion of soil material. Our study highlights that rock-magnetic studies, in concert with geochemical and sedimentological investigations, provide a multi-level contribution to environmental reconstructions, since the magnetic properties can mirror both environmental conditions on land and intra-lake processes.

Aligning and synchronization of MIS5 proxy records from Lake Ohrid (FYROM) with independently dated Mediterranean archives: implications for DEEP core chronology

“…Figure 2 shows the correlation of selected proxy series from the DEEP site. The general structure of the different proxies shows a relatively good agreement, as already discussed in other contributions of this themed issue Lacey et al, 2016;Just et al, 2016). Interglacial sediments are typically characterized by calcareous and slightly calcareous silty clay, while clastic, silty clayey material dominates in the glacial periods .…”

Recordings of Fast Paleomagnetic Reversals in a 1.2 Ma Greigite‐Rich Sediment Archive From Lake Ohrid, Balkans

“…The DEEP drill site ICDP 5045-1 is shown by the red dot, and an area with hydrothermal activity is indicated by a hatched pattern. Modified afterJust et al (2016) andVogel et al (2010).…”

Physical interpretation of isothermal remanent magnetization end‐members: New insights into the environmental history of Lake Hovsgul, Mongolia

“…While in marine environments, the differentiation between bacterial greigite and greigite of abiotic origin is known to be difficult [ Rowan et al ., ; Roberts et al ., ; Chang et al ., ], also in lacustrine environments examples for high‐coercive abiotic greigite phases have recently been reported by Just et al . [].…”

“…Therefore admixture of an uncertain amount of abiotic greigite, common in suboxic/anoxic sediments, has to be assumed to explain the wide range of high IRM coercivities in this component. While in marine environments, the differentiation between bacterial greigite and greigite of abiotic origin is known to be difficult [Rowan et al, 2009;Roberts et al, 2011;Chang et al, 2014], also in lacustrine environments examples for high-coercive abiotic greigite phases have recently been reported by Just et al [2016].…”