Abstract:
A distinctive period of global change occurred during the PUocene between the warm
Miocene and subsequent Quaternary cooling. Samples from Ocean Drilling Project Site 11 79
(-5586 mbsl, 41°4'N, 159°57'E), Site 881 (-5765 mbsl, 47°6.133'N, 161°29.490'E) and Site
882 (-3255 mbsl, 50°22'N, 167°36'E) were studied to determine the magnitude and
composition ofterrigenous flux to the western mid-latitude North Pacific and its relation to
climate change in East Asia since the mid-Pliocene.
Dust-sized particles (including pollen), sourced from the arid regions and loess
plateaus in East Asia are entrained by prevailing westerly winds and transported to the midlatitude
northwest North Pacific Ocean. This is recorded by peaks in the total concentration
of pollen and spores, as well as the mean grain size of allochthonous and autochthonous
silicate material in abyssal marine sediments.
Aridification of the Asian interior due to the phased uplift of the Himalayan-Tibetan
Plateau created the modem East Asian Monsoon system dominated by a strengthening of the
winter monsoon. The winter monsoon is further enhanced during glacials due to the
expansion of desert and steppe environments at the expense ofwoodlands and forests
recorded by the composition of palynological assemblages.
The late Pliocene-Pleistocene glacials at ODP Sites 1 179, 881, and 882 are
characterized by increases in grain size, magnetic susceptibility, pollen and spore
concentrations around 3.5-3.3, 2.6-2.4, 1.7-1.6, and 0.9-0.7 Ma (ages based on
magnetostratigraphic and biostratigraphic datums). The peaks during these times are
relatively rich in pollen taxa derived primarily from steppe and boreal vegetation zones,
recording cool, dry climates. The overall size increase of sediment and abundance of
terrestrial palynomorphs record enhanced wind strength. The increase in magnitude of pollen and spore concentrations as well as grain size record global cooling and Northern
Hemisphere glaciation.
The peaks in grain size as well as pollen and spore abundance in marine sediments
correlate with the mean grain size of loess in East Asia, consistent with the deflation of
unarmoured surfaces during glacials. The transport of limiting nutrients to marine
environments enhanced sea surface productivity and increased the rate of sediment
accumulation.
