Evgeny L. Goldberg

Abrupt increase in precipitation and weathering of soils in East Siberia coincident with the end of the last glaciation (15 cal kyr BP)

Abstract An abrupt increase in the temperature in Greenland in the wake of the initiation of the Bolling–Allerod warm phase at ca. 15 cal kyr BP was followed after a few decades by a dramatic increase in the concentration of methane in the atmosphere of the Earth resulting from an increase in humidity in the tropics [J.P. Severinghaus, E.J. Brook, Science 286 (1999) 930–934]. Analysis of a sediment core from Lake Baikal (East Siberia), spanning the end of the last glacial period and the Holocene, revealed an abrupt, stepwise, 1.3–3.4-fold decrease in the concentration of several ‘soluble’ elements such as Na, K, Mg, Ca and Si in hot nitric acid extracts of small intervals (3 cm). This chemical change appears to have occurred over the same time span, based on similarities in the profiles of silica and diatoms found in other 14 C-dated cores. This suggests that the calcium-rich ‘mammoth steppe’ landscape [R.D. Guthrie, Quat. Sci. Rev. 20 (2001) 549–573] of Siberia created during the last glaciation underwent a dramatic transformation at the end of this period (at the beginning of the Bolling–Allerod warm phase) due to an increase in precipitation within a time interval of less than 300 yr.

A 1‐Myr record of paleoclimates from Lake Khubsugul, Mongolia

The ancient Lake Khubsugul in North Mongolia is situated at the far reach of moisture from the North Atlantic into continental Asia [Kuznetsova, 1978]. It is remote from the Pacific Ocean and shielded from the China Sea and the Indian Ocean by high mountains. Information on the paleoclimates in this territory is scarce and sometimes controversial. In winter of 2003, due to a joint project (Khubsugul Drilling Project or KDP) of the Siberian Branch of the Russian Academy of Sciences and the Academy of Sciences of Mongolia, a 53-m drilling core (KDP-1) of sediments of Lake Khubsugul was obtained. This article describes the first results of paleomagnetic and geochemical studies of this core, which was found to span the time interval of the last 1.05 Myr. The data suggest that global climate oscillations manifested themselves in repeated desiccation and filling of the lake due to changes in humidity.

Model for anomalous transport of oxygen in nonstoichiometric perovskites: 1. General formulation of the problem

An attempt to explain the phenomenon of anomalous fast oxygen anion transport previously observed in the course of low temperatures topotactic oxidation of perovskite-related nonstoichiometric compounds has been made. According to the model developed the fast oxygen uptake relates to the high concentration of extended defects which exist in these compounds or can arise during oxidation. Experimentally observed specific kinetics has been described as being a result of fast oxygen transport taking place along the extended defects and followed by slow diffusion into undisturbed areas of the lattice.

Model for anomalous transport of oxygen in nonstoichiometric perovskites: Analytical and numerical solutions

The present work is a development of the model for anomalous transport of oxygen in nonstoichiometric perovskites which includes precise analytical solutions of the mathematical model formulated earlier, their comparison with approximate solutions and numerical modeling of the process.

Geochemical multielement signatures of glacial and interglacial facies of the Okhotsk Sea deepwater sediments during the past 350 kyr: A response to global climate changes at the orbital and millennial scales

The previously dated deepwater sediment core MR06-04 PC-7R (length 1723 cm; 350 kyr) recovered from the central Okhotsk Sea (OS) was analyzed for biogenic compounds and for 63 chemical elements (using the inductively coupled plasma–mass spectrometry method) with a high resolution (1 cm; ~200 years). A one box model with two main members” and mathematical methods (based on multielemental composition of sediments) for the calculation of weight fractions (at each time slice) of two main types of geochemical facies that dominate during considerably diverse climatic periods (glacial maxima and interglacial optima) were proposed and tested. This model can be applied to other analogous natural systems whose sedimentation is driven by two main types of geochemical facies. The application of the developed model to the studied core revealed that variations of weight fractions of the typical interglacial and glacial geochemical facies in the sediments along the core depth (named as warm and cold “covariators,” respectively) change synchronously with global and regional climate variability. Profiles of warm and inversed cold covariators coincide tightly, and their values increase during warm marine isotope stages and substages and decrease during cold ones over the last 350 kyr. Millennial scale changes in covariators had occurred simultaneously with abrupt variability in the OS productivity and sediment lithology and with millennial global climate variability. Some discrepancies in the warm and inversed cold covariators calculated using specific mathematical treatments revealed the episodic influence of volcanogenic matter presented in the core by visible tephra layers and cryptotephras.