NOAA/WDS Paleoclimatology - Morley and Heusser 1997 Orbital Forcing in East Asian Monsoon Climates Data

Proxy records of northeast Asian precipitation (marine pollen) and northwest Pacific sea surface temperatures (marine fauna) contain concentrations of variance (frequency peaks) coincident with those of orbital variations (eccentricity, obliquity, and precession). Time series of these monitors of various components of the east Asian monsoon system are coherent with changing solar insolation and climate boundary conditions (ice volume, snow cover, albedo) at 41- and 23-kyr frequencies. Winter sea surface temperature (WSST) maxima are in phase with global ice volume minima at all three Milankovitch frequencies (100-, 41-, and 23-kyr periods). WSST maxima are also linearly related to summer insolation at 30°N, lagging radiation maxima by ∼55° (∼3.5 kyr) across the precessional frequency band (23-kyr period). Our east Asian monsoon rainfall indicator (% Cryptomeria) reaches highest values immediately following summer insolation maxima during periods of low ice volume (interglacials). Across the eccentricity frequency band (100-kyr period), % Cryptomeria maxima are in phase with ice volume minima. At the higher frequency of orbital precession, monsoon rainfall lags both summer radiation maxima (∼125°; ∼8 kyr) and ice volume minima (∼60°; ∼3.8 kyr). Whereas much of the variation in northwest Pacific WSST can be attributed to summer radiation forcing and changes in global climate, mechanisms driving east Asian monsoon precipitation are more complex, involving other (possibly internal) factors.