Cosmic ray flux variations, modulated by the solar and earth’s magnetic fields, and climate changes. 1. Time interval from the present to 10–12 ka ago (the Holocene Epoch)

Direct and indirect data on variations in cosmic rays, solar activity, geomagnetic dipole moment, and climate from the present to 10–12ka ago (the Holocene Epoch), registered in different natural archives (tree rings, ice layers, etc.), have been analyzed. The concentration of cosmogenic isotopes, generated in the Earth’s atmosphere under the action of cosmic ray fluxes and coming into the Earth archives, makes it possible to obtain valuable information about variations in a number of natural processes. The cosmogenic isotopes ¹⁴C in tree rings and ¹⁰Be in ice layers, as well as cosmic rays, are modulated by solar activity and geomagnetic field variations, and time variations in these concentrations gives information about past solar and geomagnetic activities. Since the characteristics of natural reservoirs with cosmogenic ¹⁴C and ¹⁰Be vary with climate changes, the concentrations of these isotopes also inform about climate changes in the past. A performed analysis indicates that cosmic ray flux variations are apparently the most effective natural factor of climate changes on a large time scale.     

Volcanogenic massive sulfide deposits of ophiolite associations

Volcanogenic massive sulfide deposits in ophiolite complexes are usually attributed to the Cyprus type. They associate with basaltic volcanics that are formed in mid-ocean or back-arc spreading centers and much less frequently in intra-plate settings. The deposits are characterized by copper or copper-zinc ores that are enriched in Ni, Co, and in places Mn and As, but are very poor in Pb and demonstrate a low to moderate content of Ag and Au. Typically, the deposits are low to very low in ore and metal reserves. Cyprus-type deposits were irregularly distributed during geological history. The most ancient of them were formed in the Neoproterozoic, while the bulk of the deposits are Ordovician or Cretaceous in age. Their possible Paleoproterozoic analogues can be found in the Svecofennian belt (Outokumpu ore district), while modern ones are confined to the Explorer and Endeavour Ridges and southern segment of the Juan de Fuca Ridge.     

Reconstruction of the Wolf Numbers Based on Radiocarbon Data from the Early 11th Century until the Middle of the 19th Century with Respect to Climate Changes

Geomagnetism and Aeronomy - The results of the reconstruction of Wolf numbers from the 11th century until the middle of the 19th century A.D. based on radiocarbon data are presented. This time span...     

Reconstruction of the Production Rate of Cosmogenic 14C in the Earth’s Atmosphere for 17 000–5000 BC

Geomagnetism and Aeronomy - Carbon isotope 14С is produced in the Earth’s atmosphere by energetic cosmic-ray (CR) particles. The data on its atmospheric abundance are used to...     

Cyclical Changes in the Pleistocene Climate from an Analysis of Biogenic Silica in a Bottom Sediment Core Sample of Lake Baikal

An inhomogeneous time series of measurements of the percentage content of biogenic silica in the samples of joint cores BDP-96-1 and BDP-96-2 from the bottom of Lake Baikal drilled at a depth of 321 m under water has been analyzed. The composite depth of cores is 77 m, which covers the Pleistocene Epoch to 1.8 Ma. The time series was reduced to a regular form with a time step of 1 kyr, which allowed 16 distinct quasi-periodic components with periods from 19 to 251 kyr to be revealed in this series at a significance level of their amplitudes exceeding 4σ. For this, the combined spectral periodogram (a modification of the spectral analysis method) was used. Some of the revealed quasi-harmonics are related to the characteristic cyclical oscillations of the Earth’s orbital parameters. Special focus was payed to the temporal change in the parameters of the revealed quasi-harmonic components over the Pleistocene Epoch, which was studied by constructing the spectral density of the analyzed data in the running window of 201 and 701 kyr.     

Analysis of Past Temperature Changes in Ice Layers and the Ocean Based on the Ratios of Argon,Krypton, and Xenon with Nitrogen

Geomagnetism and Aeronomy - New research methods are being developed to get a broad picture of the temperature changes throughout the World Ocean. A permanent global network of oceanographic...     

Manifestation of Solar-Activity Cycles in the Rhythms of the Lacustrine Banded Clay of the Late Pleistocene and the Modern Era

Geomagnetism and Aeronomy - The paper considers the ratio between the spectral and time structures of solar activity, which consists of five main cycles (Schwabe, Hale, Brueckner, Gleissberg, and...     

Reconstructions of the heliospheric modulation potential and Wolf numbers based on the content of the <Superscript>14</Superscript>C isotope in tree rings during the Maunder and Spörer minimums

Data on variations in the content of the 14C cosmogenic isotope in tree rings and the Earth’s atmosphere (Δ¹⁴C) make it possible to study the behavior of solar activity (SA) in previous centuries and millenniums. The latter is related to the fact that SA temporal variations result in a change in the IMF (Interplanetary Magnetic Field) parameters and, as a consequence, in the galactic cosmic ray (GCR) flux, under the action of which the ¹⁴C isotope is produced in the Earth’s atmosphere. This makes it possible to study SA history based on data on the ¹⁴C isotope content in tree rings. However, in this case we have several difficulties related to climate change. Climate changes result in carbon redistribution between natural reservoirs, which is reflected in radiocarbon data and results in solar signal distortion. The effect of variations in the global temperature and carbon dioxide concentration on the reconstruction of the heliospheric modulation potential and Wolf numbers from the late 14th century to the early 19th century is considered. It has been shown that the radiocarbon data do not make it possible to conclude that SA during the Maunder minimum was extremely low as compared to SA during the Dalton minimum.     

Cycles revealed in Jurassic paleoclimatic data (ca. 200–145 Ma B.P.)

Limestone varves from the Todilto Basin, New Mexico (United States), are studied. These deposits cover a time interval of 1592 years and belong to the Jurassic (ca. 200–145 Ma B.P.). Via the construction of a combined spectral periodogram, quasiharmonic components are revealed in the initial data. The periods of these components are close to the basic contemporary solar activity cycles: the periods of 13 and 20 years agree with the Schwabe and Hale cycles; that of 78 years is in accord with the Gleissberg cycle (with both branches of 69 and 105 years represented); and the components of 179 and 235 years can be probably related to the Suess or de Vries cycles. The results indicate the influence of solar activity on the terrestrial climate in the geological past.