Planktonic foraminifera Mg/Ca-based temperatures and planktonic foraminiferal cenus counts of core GeoB10065-7 (Lombok Basin, Indonesia)

Modern variability in upwelling off southern Indonesia is strongly controlled by the Australian-Indonesian monsoon and the El Niño-Southern Oscillation, but multi-decadal to centennial-scale variations are less clear. We present high-resolution records of upper water column temperature, thermal gradient and relative abundances of mixed layer- and thermocline-dwelling planktonic foraminiferal species off southern Indonesia for the past two millennia that we use as proxies for upwelling variability. We find that upwelling was generally strong during the Little Ice Age (LIA) and weak during the Medieval Warm Period (MWP) and the Roman Warm Period (RWP). Upwelling is significantly anti-correlated to East Asian summer monsoonal rainfall and the zonal equatorial Pacific temperature gradient. We suggest that changes in the background state of the tropical Pacific may have substantially contributed to the centennial-scale upwelling trends observed in our records. Our results implicate the prevalence of an El Niño-like mean state during the LIA and a La Niña-like mean state during the MWP and the RWP.

Eocene through Pleistocene planktonic foraminifera off Peru

Planktonic foraminifers were studied from 213 samples collected during Leg 112 at 10 sites located on the continental shelf and slope off Peru. Because planktonic foraminifers occur discontinuously downcore, detailed biostratigraphic zonation was not defined. However, it was possible to distinguish early and middle Eocene, early and late Miocene, Pliocene, and Pleistocene sediments on the basis of the planktonic foraminifers. The oldest sediments of Zone P6 of early Eocene age were obtained from the basal part of Hole 688E, which was penetrated to 779.0 m below seafloor (bsf). A biosiliceous facies of the area predominates above the N6-N7 zonal interval of early Miocene age. All sites are within the present coastal upwelling area off Peru, and many of the late Pliocene and Pleistocene assemblages are similar to those that are characteristic of modern upwelling areas. The core samples differ, however, by having a predominance of cold-water elements, such as Neogloboquadrina incompta and N. pachyderma. Warm-water species are prevalent at some horizons in the cores, suggesting shifts of the coastal upwelling centers or warmer climatic events.