Abstract
Abstract Centennial- to millennial-scale climate variations are often attributed to solar forcing or internal climate system variability, but recognition of such variations in the deep-time paleoclimate record is extremely rare. We present an exceptionally well-preserved, millimeter-scale laminated marlstone from a succession of precession-driven limestone-marlstone couplets deposited in the Western Interior Seaway (North America) immediately preceding and during the Cretaceous mid-Cenomanian event (ca. 96.5 Ma). Sedimentological, geochemical, and micropaleontological data indicate that individual pairs of light-dark laminae record alternations in the extent of water-column mixing and oxygenation. Principal component analysis of X-ray fluorescence element counts and a grayscale scan of a continuous thin section through the marlstone reveal variations with 80–100 yr, 200–230 yr, 350–500 yr, ∼1650 yr, and 4843 yr periodicities. A substantial fraction of the data indicates an anoxic bottom water variation with a pronounced 10,784 yr cycle. The centennial to millennial variations are reminiscent of those found in Holocene total solar irradiance variability, and the 10,784 yr anoxia cycle may be a manifestation of semi-precession-influenced Tethyan oxygen minimum zone waters entering the seaway.
Highlights
Climate change models with elevated atmospheric CO2 indicate that natural forcing contributions from total solar irradiance (TSI) variations are likely to be small (Myhre et al, 2013)
TSI variations occur across centennial to millennial (C-M) time scales, knowledge is limited by the availability of data
We investigated C-M paleoclimate variability immediately preceding and during the lower part of the mid-Cenomanian event (MCE; ca. 96.6–96.2 Ma; Eldrett et al, 2015a), a “greenhouse” period characterized by high atmospheric CO2 concentrations (500–1500 ppmv) and warm global sea-surface temperatures (>35 °C; Wang et al, 2014; O’Brien et al, 2017)
Summary
Climate change models with elevated atmospheric CO2 indicate that natural forcing contributions from total solar irradiance (TSI) variations are likely to be small (Myhre et al, 2013). TSI variations occur across centennial to millennial (C-M) time scales, knowledge is limited by the availability of data. Holocene solar activity proxies reveal variations that include the Schwabe (11 yr), Gleissberg (80–100 yr), de Vries-Suess (200–250 yr), Eddy (∼1000 yr), and Halstatt (or Bray) (∼2400 yr) cycles (Usoskin, 2017). Many of these records exhibit cycles with periodicities reminiscent of those of the solar activity proxies indicated above. Pre-Holocene C-M paleoclimate records from sediment are exceedingly rare, due to low sediment accumulation rates, postdepositional mixing, incomplete preservation, and the lack of precise chronologies
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