Solar activity expressed in a modern varve thickness sequence

• Published in: Canadian journal of earth sciences Vol. 56; no. 1; pp. 32 - 46
• Main Authors: Hughes, Gary B, Adams, Jordan, Cockburn, Jaclyn M. H
• Format: Journal Article
• Language: English
• Published: Ottawa National Research Council of Canada 01.01.2019; NRC Research Press; Canadian Science Publishing NRC Research Press
• Subjects: Alaska; Albedo; Albedo (solar); Amplification; Catchment area; Cenozoic; Climate; Computer simulation; concentration; deposition; depositional environment; Earth; Earth science; Epistemology; Fluctuations; glacial environment; glacial geology; Glacier ice; Glaciers; Glaciohydrology; Holocene; Ice caps; Icebergs; Lakes; laminations; mathematical models; Meltwater; Natural history; numerical models; Ozone; Ozone concentration; paleoclimatology; Periodicities; planar bedding structures; Polar caps; Quaternary; Quaternary geology; Runoff; Runoff volume; sed rocks, sediments; Sedimentary petrology; sedimentary structures; Sediments; Sequencing; Silt; simulation; Solar activity; solar cycles; solar radiation; Solar variability; spectra; Sun; Sunspots; Thickness; Ultraviolet radiation; ultraviolet spectra; United States; Variation; Varves; United States > US; Alaska
• ISSN: 0008-4077; 1480-3313
• DOI: 10.1139/cjes-2018-0111

Annually laminated sediments (varves) form in particular depositional settings, e.g., where seasonal climate produces fluctuations in runoff volume; variations in runoff affect the amount and type of sediment delivered to a catchment. Prior studies confirm that variations in selected varve traits correlate with inter-annual climate signals. In some locations, solar activity also appears to be expressed in varve characteristics, either through a direct effect or indirectly via influence of solar activity on climate. Evidence from proglacial Iceberg Lake, Alaska, indicates that solar activity may have directly contributed to varve deposition. A varve thickness sequence is compared to sunspot observations from 1610-1995 CE. Maunder and Dalton minima are clearly expressed in a varve power spectrogram; varve signal amplification beginning ca. 1950s CE coincides with increasing activity evident in a sunspot spectrogram, features that are only vaguely discernible in the raw time-series plots. Spectral relationships at sunspot periodicities are consistent with direct solar forcing of varve thickness, independent of any effect solar activity might otherwise have on climate. Simulations based on a meltwater model indicate that direct forcing could result from amplified ultraviolet (UV) emission during solar maxima, combined with lower UV albedo of glacial ice. The plausible forcing mechanism bolsters epistemology for concluding a cause-effect relationship: solar variability likely contributed directly to inter-decadal patterns in Iceberg Lake varve thicknesses. The putative effect could be enhanced at higher latitudes, where Earth's atmosphere absorbs less of the UV energy emitted by the Sun; periods of lowered ozone concentration near the poles would exacerbate the natural abetting UV phenomena, potentially linking human activity to recent and accelerated polar ice cap melting.