Distribution of planktonic foraminifera and other biogenic components in ODP Hole 113-693A (Figure 2)

A planktonic foraminiferal fauna of probable late Aptian age is recorded in Cores 113-693A-47R and -48R, located on the Antarctic continental margin. Moderate to highly productive surface waters and upper bathyal paleodepths are inferred from benthic and planktonic foraminifers, and other biotic and mineral components in the >63 µm size fraction.

Planktonic foraminiferal (Globigerinoides ruber) Mg/Ca ratios and SSTs of sediment cores GeoB9501-4 and GeoB9501-5

Multidecadal variations in Atlantic sea surface temperatures (SST) influence the climate of the Northern Hemisphere. However, prior to the instrumental time period, information on multidecadal climate variability becomes limited, and there is a particular scarcity of sufficiently resolved SST reconstructions. Here, we present an eastern tropical North Atlantic reconstruction of SSTs based on foraminiferal (Globigerinoides ruber pink) Mg/Ca ratios that resolves multidecadal variability over the past 1700 years. Spectral power in the multidecadal band (50 to 70 years period) is significant over several time intervals suggesting that the Atlantic Multidecadal Oscillation (AMO) has been influencing local SST. Since our data exhibit high scatter the absence of multidecadal variability in the remaining record does not exclude the possibility that SST variations on this time scale might have been present without being detected in our data. Cooling by ~0.5 °C takes place between about AD 1250 and AD 1500; while this corresponds to the inception of the Little Ice Age (LIA), the end of the LIA is not reflected in our record and SST remains relatively low. This transition to cooler SSTs parallels the previously reconstructed shift in the North Atlantic Oscillation towards a low pre-20th century mean state and possibly reflects common solar forcing.

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.

Magnesium/calcium and stable isotope ratios of planktonic foraminifera from the Timor Sea

We present sea surface and upper thermocline temperature records (60-100 yr temporal resolution) spanning Marine Isotope Stage 3 (~24-62 kyr BP) from IMAGES Core MD01-2378 (121°47.27'E and 13°04.95'S; 1783 m water depth) located in the outflow area of the Indonesian Throughflow within the Timor Sea. Stable isotopes and Mg/Ca of the near surface dwelling planktonic foraminifer Globigerinoides ruber (white) and the upper thermocline dwelling Pulleniatina obliquiloculata reveal rapid changes in the thermal structure of the upper ocean during Heinrich Events. Thermocline warming and increased delta18Oseawater (P. obliquiloculata record) during Heinrich Events 3, 4, and 5 reflect weakening of the relatively cool and fresh thermocline flow and reduced export of less saline water from the North Pacific and Indonesian Seas to the tropical Indian Ocean. Three main factors influenced Indonesian Throughflow variability during Marine Isotope Stage 3: (1) global slow-down in thermohaline circulation during Heinrich Events triggered by northern hemisphere cooling; (2) increased freshwater export from the Java Sea into the Indonesian Throughflow controlled by rising sea level from ~60 to 47 ka and (3) insolation related changes in Australasian monsoon with associated migration of hydrological fronts between Indian Ocean and Indonesian Throughflow derived water masses at ~46-40 ka.

Oxygen and carbon isotopic composition in Eocene and Oligocene planktonic and benthic foraminifera from DSDP sediments

Oxygen and carbon isotope ratios in Eocene and Oligocene planktonic and benthic foraminifera have been investigated from Atlantic, Indian, and Pacific Ocean locations. The major changes in Eocene-Oligocene benthic foraminiferal oxygen isotopes were enrichment of up to 1 per mil in 18O associated with the middle/late Eocene boundary and the Eocene/Oligocene boundary at locations which range from 1- to 4-km paleodepth. Although the synchronous Eocene-Oligocene 18O enrichment began in the latest Eocene, most of the change occurred in the earliest Oligocene. The earliest Oligocene enrichment in 18O is always larger in benthic foraminifera than in surface-dwelling planktonic foraminifera, a condition that indicates a combination of deep-water cooling and increased ice volume. Planktonic foraminiferal d18O does not increase across the middle/late Eocene boundary at our one site with the most complete record (Deep Sea Drilling Project Site 363, Walvis Ridge). This pattern suggests that benthic foraminiferal d18O increased 40 m.y. ago because of increased density of deep waters, probably as a result of cooling, although glaciation cannot be ruled out without more data. Stable isotope data are averaged for late Eocene and earliest Oligocene time intervals to evaluate paleoceanographic change. Average d18O of benthic foraminifera increased by 0.64 per mil from the late Eocene to the early Oligocene d18O maximum, whereas the average increase for planktonic foraminifera was 0.52 per mil. This similarity suggests that the Eocene/Oligocene boundary d18O increase was caused primarily by increased continental glaciation, coupled with deep sea cooling by as much as 2°C at some sites. Average d18O of surface-dwelling planktonic foraminifera from 14 upper Eocene and 17 lower Oligocene locations, when plotted versus paleo-latitude, reveals no change in the latitudinal d18O gradient. The Oligocene data are offset by ~0.45 per mil, also believed to reflect increased continental glaciation. At present, there are too few deep sea sequences from high latitude locations to resolve an increase in the oceanic temperature gradient from Eocene to Oligocene time using oxygen isotopes.

Stable carbon and oxygen isotope record of planktonic and benthic foraminifera at ODP Site 111-677 in the Panama Basin

Oxygen and carbon isotope ratio measurements are presented for Globigerinoides ruber and for benthic species (mainly Uvigerina spp.) in the Pleistocene and uppermost Pliocene section of ODP Hole 677A in the Panama Basin. This provides the best available continuous Pleistocene stable isotope records from any location, fully justifying the recoring of DSDP Site 504. Oxygen isotope stage 22 (age about 0.85 Ma) was of similar magnitude to the most extensive glacials of the Brunhes and constitutes a logical base for the middle Pleistocene. Oxygen isotope stages as defined by Ruddiman et al. (1986, doi:10.1016/0012-821X(86)90024-5) and by Raymo et al. (1989, doi:10.1029/PA004i004p00413) back to stage 104 are recognized. Although the internationally agreed base of the Quaternary at or near stage 62 (about 1.6 Ma) is not marked by a major isotopic event, it does approximate the base of a regime characterized by highly regular 41,000-yr climate cycles. The records at Site 677 are ideal for time-series analyses and will permit a new attempt to develop a chronology for the early Pleistocene based on tuning to the orbital frequencies. The carbon isotope records also appear to contain considerable variance at orbital frequencies throughout the sequence analyzed.