Age determination and radiometric dates of cores from Okarito Pakihi in Australia

In agreement with the Milankovitch orbital forcing hypothesis (Imbrie et al., 1993) it is often assumed that glacial-interglacial climate transitions occurred synchronously in the Northern and Southern hemispheres of the Earth. It is difficult to test this assumption, because of the paucity of long, continuous climate records from the Southern Hemisphere that have not been dated by tuning them to the presumed Northern Hemisphere signals (Lynch-Stieglitz, 2004). Here we present an independently dated terrestrial pollen record from a peat bog on South Island, New Zealand, to investigate global and local factors in Southern Hemisphere climate changes during the last two glacial-interglacial cycles. Our record largely corroborates the Milankovitch model of orbital forcing but also exhibits some differences: in particular, an earlier onset and longer duration of the Last Glacial Maximum. Our results suggest that Southern Hemisphere insolation may have been responsible for these differences in timing. Our findings question the validity of applying orbital tuning to Southern Hemisphere records and suggest an alternative mechanism to the bipolar seesaw for generating interhemispheric asynchrony in climate change.

Pollen record and age determination of a sediment core from the Kara Sea

AMS-14C dated sediment cores from the Ob and Yenisei estuaries and the adjacent inner Kara Sea were investigated to determine the siliclastic and organic carbon fluxes and their relationship to paleoenvironmental changes. The variability of sediment fluxes during Holocene times is related to the post-glacial sea-level rise and changes in river discharge and coastal erosion input. Whereas during the late/middle Holocene most of the terrigenous sediments were deposited in the estuaries and the areas directly off the estuaries, huge amounts of sediments accumulated on the Kara Sea shelf farther north during the early Holocene before about 9 Cal. kyrs. BP. The maximum accumulation at that time is related to the lowered sea level, increased coastal erosion, and increased river discharge due to the final stage of mountain deglaciation of the Putoran Massif. Increased supply of Yenisei-derived material indicated by peak magnetic susceptibility values probably occurred in climate-related pulses culminating near 11, 10, and 9 Cal. kyrs. BP. As sea level rose, the main Holocene depocenter migrated southward. Based on hydrogen index values and n-alkanes, the organic matter is predominantly of terrigenous origin. Maximum accumulation rates of 1.5 to more than 6 g/cm2/y occurred in the early Holocene sediments, suggesting more humid climatic conditions with an increased vegetation cover in the source area at that time. In general, high organic carbon accumulation rates characterize the estuaries and the inner Kara Sea as important sink for terrigenous organic carbon. A high-resolution record of Holocene variability of magnetic susceptibility (MS) in an AMS14C-dated sediment core from the northern Yenisei estuary may indicate natural variability of Arctic climate change and river discharge on a centennial to millenial time scale. Short-term maxima in MS probably related to warmer climate, enhanced precipitation, intensified weathering/erosion and increased river discharge, display a frequency of about 300 to 700 years.

Late Miocene carbon isotope and paleoproductivity record

We examine whether or not a relationship exists between the late Miocene carbon isotope shift (~7.6-6.6 Ma) and marine productivity at four sites from the Indian and Pacific Oceans (Ocean Drilling Program Sites 721, 1146, 1172, and 846). We use a multiproxy approach based on benthic foraminiferal accumulation rates, elemental ratios, and dissolution indices, and we compare these data to benthic foraminiferal d13C values measured on the same samples. Although some of these sites have been targeted previously in studies of either the late Miocene/early Pliocene "biogenic bloom" (Sites 721 and 846) or the late Miocene carbon isotope shift (Site 1172), our records are the first to establish paired proxy records of carbon isotopes and paleoproductivity allowing a direct assessment of a potential link. Our results indicate that at all sites, productivity increased sometime during the d13C shift; at three sites (721, 1146, and 846), productivity increased at the beginning of the shift. The correlation coefficients derived from linear regression between micropaleontologically derived productivity and foraminiferal d13C values are relatively high during the time interval containing the late Miocene d13C shift (and statistically significant at three of the sites). Carbon flux and isotope mass balance considerations illustrate that transfer of organic matter between the terrestrial and marine reservoirs together with enhanced oceanic upwelling best approximates observed changes in carbon isotope records and paleoproductivity. We note that long-term trend in the Site 846 paleoproductivity record can be correlated to the long-term trend in the Site 848 eolian flux reconstructions of Hovan (1995, doi:10.2973/odp.proc.sr.138.132.1995) hinting at a link between strengthened wind regime and productivity during the late Miocene.

K-Ar age and chemical composition of volcanites from the Sea of Okhotsk

Volcanogenic rocks from the Sea of Okhotsk are divided into seven age complexes: Late Jurassic, Early Cretaceous, Late Cretaceous, Eocene, Late Oligocene, Late Miocene, and Pliocene-Pleistocene. All these complexes are united into two groups - Late Mesozoic and Cenozoic. Each group reflects a certain stage of development of the Sea of Okhotsk region. Late Mesozoic volcanites build the geological basement of the Sea of Okhotsk, and their petrochemical features are similar to those of the volcanic rocks from the Okhotsk-Chukotka Volcanogen. Pliocene-Pleistocene volcanites reflect stages of tectono-magmatic activity; the latter destroyed the continental margin and produced riftogenic troughs. Geochemical features of volcanites from the Sea of Okhotsk indicate influence of the sialic crust on magma formation and testify formation of the Okhotsk Sea Basin on the destructive margin of the Asian continent.

Age of samples from the sedimentary cover of the Primorye continental slope and from the submarine Bogorov Rise

Results of a complex study of the sedimentary cover (continuous seismic profiling and diatom analysis) in the northeastern Sea of Japan including the Bogorov Rise an adjacent part of the Japan Basin and the continental slope, are presented. Two varied-age complexes were distinguished in the sedimentary cover of the continental slope of Primorye: Middle Miocene and Late Miocene - Pleistocene. These complexes formed in a stable tectonic setting with no significant vertical movements. A depression in the acoustic basement is located along the continental slope and it is divided from the Japan Basin by a group of volcanic structures, the most uplifted part of which forms the Bogorov Rise. The depression probably formed before Middle Miocene. In Middle Miocene the Bogorov Rise was already at depths close to modern ones. In the sedimentary cover near the Bogorov Rise buried zones were found. Probably they were channels for gas transportation in pre-Pleistocene. Deformations of sediments that occurred in the beginning of Pleistocene are established in the basin.

Tab. 1: Radiocarbon ages of the late Pleistocene and early Holocene of Mecklenburg-Vorpommern and surrounding areas

Several geoscientific projects in the last decade led to a marked increase of radiocarbon dates in Mecklenburg-Vorpommern and in neighbouring areas. The studies were mostly focussed on the genesis of the Baltic Basin and the last termination. In this Paper, a regional collection of 271 radiocarbon dates of the late Pleistocene and early Holocene (ca. 50,000-8,000 14C yr BP) is presented. The dates were calibrated, correlate, and assessed with regard to their credibility. The evaluation of the data is focussed on problems of regional palaeogeography. The age of the last Weichselian deglaciation (deglaciation after the Mecklenburg Advance) is assumed to be around 14,000 14C yr BP through radiocarbon dates from the Pomeranian Bay. This data is ca. 1,000 years older compared to former views. On the other hand, the database allows the dating of late Pleistocene basin sequences from the Baltic coast, This indicates three stratigraphic units for basin areas 0-15 m above sea level - glaciolacustrine sedimentation in the late Pleniglacial, lacustrine and telmatic sedimentation as well as soil formation in the early Lateglacial and Alleroed and aeolian sedimentation in the Younger Dryas. The Younger Dryas in the huge Mecklenburg Bay-Darss Basin NE of Rostock is characterised by lacustrine sedimentation ca. 20 m below sea level ("Baltic Ice Lake"), and by aeolian sedimentation above sea level.

Abundance of benthic foraminifera in late Paleocene to eraly Pliocene sediments of DSDP Hole 74-525A on the Walvis Ridge, South Atlantic (Table 1)

Benthic forammifers in the size-fraction greater than 0.073 mm were studied in 88 Paleocene to Pleistocene samples from Deep Sea Drilling Project Site 525 (Hole 525A, Walvis Ridge, eastern south Atlantic). Clustering of the samples on the basis of the 86 most abundant foramimfers (in total, 331 taxa were identified) allowed separating two major assemblage zones: the Paleocene to Eocene interval, and the Oligocene to Pleistocene interval. Each of these, in turn, were subdivided into three minor subzones as follows: lower upper Paleocene (approx. 62.4 to 57 8 Ma); upper upper Paleocene (56.6 to 56 2 Ma), lower and middle Eocene (55.3 to 46 8 Ma); upper Oligocene to middle Miocene (25.3 to 16 Ma), middle Miocene to Pliocene (15.7 to 4.2 Ma), and lower Pleistocene (0.4 to 0.02 Ma), with only minor differences with the previous zone. Some very abundant taxa span most of the column studies (Bolivina huneri, Cassidulina subglobosa, Eponides bradyi, E. weddellensis, Gavelinella micra, Oridorsalis umbonatus, etc.). Several of the faunal breaks recorded coincide with conspicuous minima in the specific diversity curve, thus suggesting that the corresponding turnovers signal the final stages of periods of faunal impoverishment. At least one major bottomwater temperature drop (as derived from delta18O data) is synchronous with a decrease in the forammiferal specific diversity. On the other hand, a specific diversity maximum in the middle Miocene might be associated with a delta13C increase at approx 16 to 12 Ma. Highest foraminiferal abundances (up to 600-800 individuals per gram of dry sediment) occurred in the late Paleocene and in the early Pleistocene, in coincidence with the lowest diversity figures calculated. The magnitude of the most important faunal turnover recorded, between the middle Eocene and the late Oligocene, is magnified in our data set by the large hiatus which separates the middle Eocene from the upper Oligocene sediments. Considerably smaller overturns occurred within the late Paleocene (in coincidence with changes in the specific diversity, absolute abundance of forammiferal tests, and delta13C), and in the middle Miocene (in coincidence with a specific diversity maximum and a delta13C excursion). New reformation on the morphology and the stratigraphic ranges of several species is furnished. For all the taxa recorded the number of occurrences, total number of individuals identified and first and last appearances are listed.

Variability of the Brazil Current during the late Holocene analysed on two marine sediment cores

Our understanding of the centennial-scale variability of the Brazil Current (BC) during the late Holocene is elusive because of the lack of appropriate records. Here we used the Mg/Ca and oxygen isotopic composition of planktonic foraminifera from two marine sediment cores collected at 27° S and 33° S off southeastern South America to assess the late Holocene variability in the upper water column of the BC. Our results show in phase fluctuations of up to 3 °C in sea surface temperatures (SST), and 0.8 per mil in oxygen isotopic composition of surface sea water, a proxy for relative sea surface salinity (SSS). Time-series analyses of our records indicate a cyclicity with a period of ca. 730 yr. We suggest that the observed cyclicity reflects variability in the strength of the BC associated to changes in the Atlantic meridional overturning circulation (AMOC). Positive (negative) SST and SSS anomalies are related to a strong (weak) BC and a weak (strong) AMOC. Moreover, periods of peak strength in the BC occur synchronously to a weak North Brazil Current, negative SST anomalies in the high latitudes of the North Atlantic, and positive (negative) precipitation anomalies over southeastern South America (equatorial Africa), further corroborating our hypothesis. This study shows a tight coupling between the variability of the BC and the high latitudes of the North Atlantic mediated by the AMOC even under late Holocene boundary conditions.

Age determinations of sediment cores from the Baffin Shelf

Cores HU82-034-057 and HU84-035-008, Resolution Basin, SE Baffin Shelf, contain 200 and 450 cm, respectively, of sediment that spans the Younger Dryas chron. In both cores the interval is bracketed by 14C dates on foraminifera or molluscs. These sites were close to the margin of the late Wisconsin (Foxe) ice sheet as it flowed toward the Labrador Sea. Prior to 11 ka, both cores record moderate to high accumulations of foraminifera, relatively high del 18O values in planktonic foraminifera, and low values of detrital carbonate. The diatom and percent opal records imply occasional seasonally open water conditions. During part of the Younger Dryas chron both the diatom and opal analyses imply a shutoff of biogenic silica production, suggesting surface water conditions affected by increased sea ice and/or reduced nutrients. In addition, the Younger Dryas interval is marked by an increase in coarse sand and detrital carbonate, a decrease in total organic carbon and foraminifera, and high rates of sediment accumulation. The inferred environment during the Younger Dryas is ice-proximal. In HU82-034-057, the foraminifera and other data suggest a change in conditions during the middle part of the Younger Dryas chron.