Glacial and interglacial sediment history on Bol’shoy Lyakhovsky, New Siberian Archipelago, from multiple permafrost cores

Bol’shoy Lyakhovsky, the southernmost island of the New Siberian Archipelago, holds the longest record of palaeoenvironmental history in the non-glaciated Siberian Arctic preserved in permafrost. It stretches back to ~200 kyr before present and includes prominent last interglacial thermokarst and Yedoma (Ice Complex) sections. Yet, it is unknown, whether or not the depositional history of the site is affected by the deglaciation of the northern part of the New Siberian Archipelago. Potentially, it could give insight into the break-up of the proposed MIS 6 ice sheet located on the East Siberian Sea shelf (Jakobsson et al., 2014). The lithostratigraphy of southern part of the island consists of palaeosols, floodplain and lake deposits, subaerial Yedoma and lacustrine to palustrine alas formations. Large ice wedges (partially up to several meters high and thick), segregation and pore ice record a syngenetic freezing of the Yedoma silts. Polymodal particle size distributions suggest that more than one transport mechanism drove sediment accumulation from more than one source. Recent papers conclude that the palaeoclimate record matches the general Late Quaternary climate history in northern Siberia (Andreev et al., 2011; Wetterich et al., 2011). From a multi proxy data set we focus on (i) the mineral composition (63-125 μm fraction) to determine the provenance of the deposits and to identify possible changes of transport pathways. Complementary, we use (ii) pore ice hydrochemistry as a means to track changes of the soil solution that principally reflects the site’s chemical weathering history preserved in permafrost. Presumably the two approaches complement each other, since the weathering solution should largely reflect the mineral matter composition. The heavy mineral association suggests that most of the minerals derive from the underlying bedrock (Upper Jurassic-Lower Cretaceous sandstones and Upper Cretacous granites and diorites); among others it has high amounts of ilmenite and leucoxene, epidote, pyroxenes and amphiboles, along with garnet, tourmaline, apatite, and sphene. Ratios of stable versus unstable mineral associations show that the Late Quaternary strata overlying bedrock are enriched in more stable minerals (i.e. zircon, tourmaline, ilmenite), whereas more unstable minerals (i.e. amphiboles and pyroxenes) dominate the chronostratigraphically younger Quaternary strata. A remarkably high portion of weathered mica appears in MIS4 to MIS3 deposits and raises the question upon particular hydrodynamic conditions during that time, e.g. a floodplain environment that persisted for several thousands to ten thousands of years. It may have produced various impulses of flooding with floating particles that settle out quickly on the banks of the channel and on the leeward side. Overall pore ice chemistry shows that high electrical conductivity corresponds to low ice content (60 wt.-%) the electrical conductivity is low. When compared with the average ion composition of tundra and taiga rivers, the whole core record is enriched in the sodium- potassium load, which partially even dominates over the combined calcium-magnesium load. We preliminary conclude that the observed trends of heavy mineral and pore ice chemical variations in the Bol’shoy Lyakhovsky cores reflect short-distance material transport from weathered bedrock in the depositional area. The enrichment of mica in ice-rich deposits suggests floodplain hydrodynamics in the area during MIS 4 to MIS3. The fairly constant ionic proportions of the light soluble load in the ground ice confirm a local origin of the weathering solutes. High amounts of potassium are linked to the weathering of the granitic bedrock. Distinct concentration gradients in the downcore electrical conductivity are caused by postdepositional ionic migration from the bedrock weathering crust into the overlying Late Quaternary strata, by intensified weathering during the Last Interglacial (MIS5e), and by stable surfaces that promoted effective (e.g. cryogenic) weathering during the last Glacial (MIS4 to MIS3). Andreev, A.A., Schirrmeister, L., Tarasov, P.E., Ganopolski, A., Brovkin, V., Siegert, C., ... & Hubberten, H.-W. (2011). Vegetation and climate history in the Laptev Sea region (Arctic Siberia) during Late Quaternary inferred from pollen records. Quaternary Science Reviews, 30, 2182-2199. Jakobsson, M., Andreassen, K., Bjarnadóttir, L.R., Dove, D., Dowdeswell, J.A., England, J.H., ... & Larsen, N.K. (2014). Arctic Ocean glacial history. Quaternary Science Reviews, 92, 40-67. Wetterich, S., Tumskoy, V., Rudaya, N., Andreev, A.A., Opel, T., Meyer, H., ... & Hüls, M. (2014). Ice Complex formation in arctic East Siberia during the MIS3 Interstadial. Quaternary Science Reviews, 84, 39- 55