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The cosmic ray increases at 35 and 60 kyr BP.

V Florinski, W I Axford, G P Zank

Abstract


Concentrations of (super 10) Be in ice cores and marine sediments exhibit 2 peaks with significant enhancements at 35,000 and 60,000 BP. This radioisotope is produced in the upper atmosphere by spallation of cosmic-ray protons and secondary neutrons on atmospheric nitrogen and oxygen. Previously suggested explanations for the increases include geomagnetic field reversals, a decrease in solar activity, and a supernova explosion. We propose an alternative explanation which involves a change in the galactic environment of the solar system. The structure of the heliosphere is investigated for a period when the Sun enters a cold, dense, unmagnetized interstellar cloud. Under these conditions, the heliosphere contracts to 25% its present size, significantly affecting galactic cosmic ray modulation and increasing anomalous cosmic ray fluxes. A tenfold increase in anomalous cosmic ray flux and a twofold increase in galactic cosmic ray intensity at Earth are possible in this high-density case if heliosheath modulation is reduced. We show that this increase in galactic cosmic ray intensity could be responsible for the peaks in (super 10) Be records.

Keywords


alkaline earth metals;Antarctica ;Arctic region;Be 10;beryllium ;California ;Cenozoic ;concentration ;cores ;correlation ;cosmic rays;global ;Greenland ;Holocene ;ice cores;isotopes ;marine sediments;Mediterranean Sea;metals ;models ;Mono County California;Mono Lake;paleoenvironment ;Quaternary ;radioactive isotopes;sediments ;solar activity;solar wind;Sun ;United States;variations

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