Late Holocene sedimentary response to solar and cosmic ray activity influenced climate variability in the NE Pacific

Abstract

Marine-laminated sediments along the NE Pacific coast (Effingham inlet, Vancouver Island) provide an archive of climate variability at annual to millennial scales. A 7.75-m portion of piston core TUL99B-03 was deposited during a ∼3045-year interval [∼1440–4485 years before present (yBP)] under primarily anoxic conditions. Darker clay laminae were deposited under higher precipitation conditions in winter, and diatom-dominated laminae were laid down when marine productivity was higher in the spring through autumn. Wavelet transform and other time-series analysis methods were applied to sediment color (i.e. gray-scale values) line-scans obtained from X-ray images and compared with global records of cosmogenic nuclides 14C and 10Be, as well as the Ice Drift Index (hematite-stained grains) record to detect cycles, trends, and nonstationarities in the climate and sedimentary pattern. Our results show that the marine sedimentary record in the NE Pacific responded to abrupt changes and long-term variability in climate that can be linked to external forcing (e.g., solar and cosmic irradiance). Specifically, a strong cooling in the NE Pacific at ∼3550±160 yBP can be correlated to a weakening of high-frequency (50–150 years) pulses in sun activity at the Gleissberg cycle band, similar to what occurred at the onset of the ‘Little Ice Age’ at ∼1630 AD. Three intervals of unusually low sun activity at ∼2350, 2750, and ∼3350 yBP are characterized by thick, clay-rich annual sedimentation that we interpret as representative of unusually wet conditions. These intervals of higher precipitation conditions may have been related to a regional intensification of the Aleutian Low (AL) caused by an eastward migration of the Center of Action (COA) of the AL, which occurs during intervals of solar minima. Dryer conditions in the region occur when the COA of AL migrates westward and the COA of the North Pacific High (NPH) migrates northward during intervals of solar maxima. A cyclicity of 50–85, 33–36, and 22–29 years in the sediment color record, lamination thickness, and 14C cosmogenic nuclide, characterized the relatively warm interval from 3550 to 4485 yBP. This record is similar to that of present-day low- and high-frequency variants of the Pacific Decadal Oscillation and Aleutian Low.