Water stable oxygen isotope records from six Antarctic ice core sites for the present and last interglacial periods

We compare the present and last interglacial periods as recorded in Antarctic water stable isotope records now available at various temporal resolutions from six East Antarctic ice cores: Vostok, Taylor Dome, EPICA Dome C (EDC), EPICA Dronning Maud Land (EDML), Dome Fuji and the recent TALDICE ice core from Talos Dome. We first review the different modern site characteristics in terms of ice flow, meteorological conditions, precipitation intermittency and moisture origin, as depicted by meteorological data, atmospheric reanalyses and Lagrangian moisture source diagnostics. These different factors can indeed alter the relationships between temperature and water stable isotopes. Using five records with sufficient resolution on the EDC3 age scale, common features are quantified through principal component analyses. Consistent with instrumental records and atmospheric model results, the ice core data depict rather coherent and homogenous patterns in East Antarctica during the last two interglacials. Across the East Antarctic plateau, regional differences, with respect to the common East Antarctic signal, appear to have similar patterns during the current and last interglacials. We identify two abrupt shifts in isotopic records during the glacial inception at TALDICE and EDML, likely caused by regional sea ice expansion. These regional differences are discussed in terms of moisture origin and in terms of past changes in local elevation histories, which are compared to ice sheet model results. Our results suggest that elevation changes may contribute significantly to inter-site differences. These elevation changes may be underestimated by current ice sheet models

Benthic and planktonic foraminifera of sediment core GIK17957-2

A detailed age model for core 17957-2 of the southern South China Sea was developed based on delta18O, coarse fraction, magnetostratigraphy, and biostratigraphy for the last 1500 kyr. The delta18O record has clear ~100-kyr cycles after the Mid-Pleistocene Revolution (MPR) at the entrance of marine isotopic stage (MIS) 22. Planktonic foraminifera responded to the MPR immediately, showing the increased sea surface temperature (SST) and dissolution after the MPR. Benthic foraminifera did not respond to it until the Brunhes/Matuyama boundary. Since the MPR, the depth of thermocline gradually became shallower until MISs 6-5. This major change within MISs 6-5 was also reflected in the decreased SSTs and increased productivity and Deep Water Mass. Thus two major Pleistocene paleoceanographic changes were found: One was around the MPR; the other occurred within MISs 6-5, which speculatively might be ascribed to the reorganization of surface and deep circulation, possibly induced by tectonic forces.

Seismic investigations of the Greenland ice sheet at EGIG points

The compressional and the shear wave velocities in the Greenland ice sheet are derived from seismic records of the EGIG 1959. Further the variation of velocities in the firn and the dependance of Poisson's ratio from depth are determined. At Station Centrale, two P-waves are recorded from underground layers. Their velocities show that the ice basement consists of crystalline rocks. The P-wave velocities derived from reflections agree well with those obtained by refraction shooting. From this agreement results that the ice is ± homogenous and ± isotropic for Pwaves. The elastic constants for isotropic ice are calculated. Finally the temperature dependence of the velocities is discussed.

Miocene planktonic foraminifera of ODP Hole 130-806B

We document the waxing and waning of a "proto-warm pool" in the western equatorial Pacific (WEP) based on a study of multi-species planktic foraminiferal isotope ratios and census data spanning the 13.2-5.8 Ma interval at ODP Site 806. We hypothesize that the presence or absence of a proto-warm pool in the WEP, caused by the progressive tectonic constriction of the Indonesian Seaway and modulated by sea level fluctuations, created El Niño/La Niña-like alternations of hydrographic conditions across the equatorial Pacific during the late Miocene. This hypothesis is supported by the general antithetical relationship observed between carbonate productivity and preservation in the western and eastern equatorial Pacific, which we propose is caused by these alternating ocean-climate states. Warming of thermocline and surface waters, as well as a major change in planktic foraminferal assemblages record a two-step phase of proto-warm pool development ~11.6-10 Ma, which coincides with Miocene isotope events Mi5 and Mi6, and sea-level low stands. We suggest that these changes in the biota and structure of the upper water column in the WEP mark the initiation of a more modern equatorial current system, including the development of the Equatorial Undercurrent (EUC), as La Niña-like conditions became established across the tropical Pacific. This situation sustained carbonate and silica productivity in the eastern equatorial Pacific (EEP) at a time when carbonate preservation sharply declined in the Caribbean. Proto-warm pool weakening after ~10 Ma may have contributed to the nadir of a similar "carbonate crash" in the EEP. Cooling of the thermocline and increased abundances of thermocline taxa herald the decay of the proto-warm pool and higher productivity in the WEP, particularly ~ 9.0-8.8 Ma coincident with a major perturbation in tropical nannofossil assemblages. We suggest that this interval of increased productivity records El Niño-like conditions across the tropical Pacific and the initial phase of the widespread "biogenic bloom". Resurgence of a later proto-warm pool in the WEP ~6.5-6.1 Ma may have spurred renewed La Niña-like conditions, which contributed to a strong late phase of the "biogenic bloom" in the EEP.

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.

Planktonic foraminiferal d18O values and apparent calcification depths of core-top samples along an east-west transect across the tropical Atlantic/Caribbean

D18O values of nine tropical-subtropical planktonic foraminiferal species with different preferential habitat depths collected from 62 core-top samples along an east-west transect across the tropical Atlantic/Caribbean were used to test the applicability of interspecific d18O gradients for reconstructions of tropical upper ocean stratification. In general, the d18O difference (Delta d18O) between intermediate- and shallow-dwelling species decreases, and Delta d18O between deep and intermediate dwellers increases with increasing thermocline depth towards the west. The statistical significance of regional differences in Delta d18O highlights Delta d18O between the intermediate dwellers (in particular Globorotalia scitula and Globorotalia tumida) and the shallow dweller Globigerinoides ruber pink, as well as Delta d18O between the deep dwellers Globorotalia crassaformis or Globorotalia truncatulinoides dextral and intermediate dwellers as most sensitive to changes in tropical Atlantic thermocline depth. Based on the observed regional variations in interspecific Delta d18O, we propose a multispecies stratification index "STRAtrop" = (d18Ointermediate - d18Oshallow) / (d18Odeep - d18Oshallow) for the tropical ocean. Statistically significant differences in STRAtrop values between the E-Atlantic and the Caribbean suggest that this index may be a useful tool to monitor variations in tropical upper ocean stratification in the geological record.

Table 2. Lead and Ba concentrations and Pb isotopic compositions measured in Law Dome ice cores

Lead isotopic compositions and Pb and Ba concentrations have been measured in ice cores from Law Dome, East Antarctica, covering the past 6500 years. 'Natural' background concentrations of Pb (ab. 0.4 pg/g) and Ba (ab. 1.3 pg/g) are observed until 1884 AD, after which increased Pb concentrations and lowered 206Pb/207Pb ratios indicate the influence of anthropogenic Pb. The isotopic composition of 'natural' Pb varies within the range 206Pb/207Pb=1.20-1.25 and 208Pb/207Pb=2.46-2.50, with an average rock and soil dust Pb contribution of 8-12%. A major pollution event is observed at Law Dome between 1884 and 1908 AD, elevating the Pb concentration four-fold and changing 206Pb/207Pb ratios in the ice to ab. 1.12. Based on Pb isotopic systematics and Pb emission statistics, this is attributed to Pb mined at Broken Hill and smelted at Broken Hill and Port Pirie, Australia. Anthropogenic Pb inputs are at their greatest from 1900 to 1910 and from ab. 1960 to ab. 1980. During the 20th century, Ba concentrations are consistently higher than 'natural' levels and are attributed to increased dust production, suggesting the influence of climate change and/or changes in land coverage with vegetation.