Tropical Atlantic SST during the mid-Pleistocene transition (MPT) of ODP Hole 175-1077B

We compare a new mid-Pleistocene sea surface temperature (SST) record from the eastern tropical Atlantic to changes in continental ice volume, orbital insolation, Atlantic deepwater ventilation, and Southern Ocean front positions to resolve forcing mechanisms of tropical Atlantic SST during the mid-Pleistocene transition (MPT). At the onset of the MPT, a strong tropical cooling occurred. The change from a obliquity- to a eccentricity-dominated cyclicity in the tropical SST took place at about 650 kyr BP. In orbital cycles, tropical SST changes significantly preceded continental ice-volume changes but were in phase with movements of Southern Ocean fronts. After the onset of large-amplitude 100-kyr variations, additional late glacial warming in the eastern tropical Atlantic was caused by enhanced return flow of warm waters from the western Atlantic driven by strong trade winds. Pronounced 80-kyr variations in tropical SST occurred during the MPT, in phase with and likely directly forced by transitional continental ice-volume variations. During the MPT, a prominent anomalous long-term tropical warming occurred, likely generated by extremely northward displaced Southern Ocean fronts. While the overall pattern of global climate variability during the MPT was determined by changes in mean state and frequency of continental ice volume variations, tropical Atlantic SST variations were primarily driven by early changes in Subantarctic sea-ice extent and coupled Southern Ocean frontal positions.

Quantitative study of evolution in the Sphaeroidinella lineage in mid-Pleistocene sediment of ODP Hole 154-926A (Appendix A)

Morphological evolution in the late Neogene planktonic foraminifer Sphaeroidinella lineage involves a sudden increase of the percentage of specimens equipped with supplementary apertures (from <30% to >70%) in the mid-Pliocene (about 3.5 Ma). This evolutionary transition, marked by the first occurrence of specimens with large supplementary apertures in the lineage, is denoted the Sphaeroidinella event. Changes in the proportions of the supplementary apertures in the lineage were studied in 24 samples from ODP Hole 926A drilled in the equatorial Atlantic Ocean. In addition, detailed chronological models have been compiled for this section as well as for Pliocene sections from DSDP Holes 214, 502A, and 503B, where evolution in the lineage have been analyzed previously. Stratigraphic correlation of the studied sequences suggests that the Sphaeroidinella event took place at about 3.6 Ma in the eastern equatorial Pacific (Hole 503B) and at 3.5-3.6 Ma in the Caribbean (Hole 502A), while in the Atlantic Ocean (Hole 926A) and in the Indian Ocean (Hole 214) the event occurred after 3.5 Ma. The inferred diachrony of the mid-Pliocene Sphaeroidinella transition, which is considered to represent a prime example of punctuated anagenesis, suggests that this evolutionary modality may have an allopatric component. Its short duration (on average less than 50 kyr) and the detailed biochronology that could be established for this event qualifies it as a useful biostratigraphic tool in the low-latitude Pliocene oceans.

(Table 1) Dinoflagellate cysts and acritarchs in upper Pliocene and Pleistocene sediments from ODP Hole 151-911A

Pliocene and Pleistocene sediments from Ocean Drilling Program Leg 151, Hole 911 A, drilled on the innermost Yermak Plateau (Eastern Arctic Ocean), were studied for their dinoflagellate cyst content. Three assemblage zones were tentatively defined, characterized by the predominance of few species. The composition of the assemblages changed markedly, even within single assemblage zones, during the last 2.6 to 2.8 m.y., reflecting the variable influence of warmer water from the Norwegian Sea, fluctuations in the influence of cold polar water masses, and the extent of sea-ice cover. Polar to subpolar surface water masses prevailed on the Yermak Plateau during the late Pliocene, when the eastern Arctic Ocean was probably isolated from the Norwegian-Greenland Sea. Intrusions of warmer water are recorded since the latest Pliocene, alternating with colder periods and a prolonged seasonal sea-ice cover. The composition of the dinoflagellate cyst assemblages has also changed considerably since the middle Pleistocene, reflecting the establishment of stronger fluctuations in surface water mass conditions than before at Yermak Plateau.

Late Cretaceous and Cainozoic bathyal Ostracoda of DSDP Site 62-463 in the Central Pacific (Fig. 3)

Cainozoic deep-sea ostracod assemblages from the summits of Mid-Pacific guyots point to high levels of endemism possibly as a result of their bathymetric separation from the surrounding sea floor. However, the interpretation of these fossil assemblages is hampered by the paucity of comparative material from surrounding non-guyot sites. Fifteen ostracod assemblages from DSDP Site 463 (Late Cretaceous-Pleistocene) were studied to compare with those from nearby guyots. Three distinct faunal assemblages are recognised at Site 463: Assemblage A (Maastrichtian-Eocene), Assemblage B (Oligocene-Upper Miocene) and Assemblage C (Upper Miocene-Pleistocene) although the palaeoenvironmental significance of these units is unclear. Sixty-two ostracod species are identified, the thirteen most abundant are discussed in the taxonomic section, five of which are described as new. Between 30 and 100% of the species encountered in each sample are considered as endemic to Site 463, while some of the remaining species were previously thought to be endemic to individual guyots. Similarly high levels of endemism on nearby guyots probably reflect an incomplete knowledge of deep-sea ostracod faunas rather than the establishment of geographically or bathymetrically restricted populations. The presence of globally pandemic and geographically widespread taxa on sites such as the Mid-Pacific Mountains, surrounded by abyssal depths which lie below the CCD, indicates that some faunal exchange or migration of ostracods does take place. This must be achieved within the intermediate waters and probably occurs passively.

(Table 1) Age and sedimentation rates of Pleistocene/Holocene sequences at DSDP Sites 86-580 and 94-611

The recovery from the North Atlantic (Site 611) of a continuous Pleistocene sedimentary record with a siliceous microfaunal component made it possible to compare the high-latitude abundance pattern of the radiolarian species Cycladophora davisiana in the Atlantic with that produced from analyses of a high-latitude record (Site 580) from the northwest Pacific. Previous studies had shown that the late Pleistocene (0-0.45 Ma) abundance variations of this species in these high-latitude regions were similar. Cycladophora davisiana maxima in the North Atlantic record reach abundance levels three to four times higher than C. davisiana maxima registered in sediments from the northwest Pacific site. This difference in magnitude of abundance peaks is most likely an effect of the more northerly location of Site 611 (53°N) compared with that of Site 580 (42°N), since high-latitude time-slice studies have shown a direct relationship between increasing latitude and C. davisiana abundance. Discontinuous preservation of radiolarians in sediments from North Atlantic Site 611 allows only tentative correlation of the North Atlantic and northwest Pacific C. davisiana abundance curves. These correlations are confined to those portions of the cores where ages are tightly constrained by magnetic boundaries, and to intervals with comparable sedimentation rates.

Description of the fossil manganese nodules found in the Oligocene clay deposits of Moravia, Brno area, Czech Republic

In the green Oligocene clay of Krizanovice (former Krzyzanowicz) the author found numerous black nodules. In the 3-4 centimeter thick black crust of a particular specimen the concentration in MnO2 is evaluated at 46.6% MnO2. The determination was done using the Volhard's method (precipitation of Fe by ZnO and titration with KMnO4). Only the dissoleved part in HCL was analysed. The non soluble residue was essentially a silica precipitate in the form of many gray flakes. The specific gravity of the crust was evaluated at 3.8. In the internal yellow core the amount of manganese is about 2.39% MnO2. Due to the light color it is judged to probably be in the form of Mn2O3.

Lake sediments from Store Koldewey, Northeast Greenland

A 2.9 m long sedimentary record was studied from a small lake, here referred to as Duck Lake, located at 76°25'N, 18°45'W on Store Koldewey, an elongated island off the coast of Northeast Greenland. The sediments were investigated for their geophysical and biogeochemical characteristics, and for their fossil chironomid assemblages. Organic matter began to accumulate in the lake at 9.1 cal. kyr BP, which provides a minimum age for the deglaciation of the basin. Although the early to mid-Holocene is known as a thermal maximum in East Greenland, organic matter accumulation in the lake remained low during the early Holocene, likely due to late plant immigration and lack of nutrient availability. Organic matter accumulation increased during the middle and late Holocene, when temperatures in East Greenland gradually decreased. Enhanced soil formation probably led to higher nutrient availability and increased production in the lake. Chironomids are abundant throughout the record after 9.1 cal. kyr BP and seem to react sensitively to changes in temperature and nutrient availability. It is concluded that relative temperature reconstructions based on biogeochemical data have to be regarded critically, particularly in the period shortly after deglaciation when nutrient availability was low. Chironomids may be a suitable tool for climatic reconstructions even in those high arctic environments. However, a better understanding of the ecology of chironomids under these extreme conditions is needed.

(Table 2) Oxygen isotopic of composition of Pliocene to late Pleistocene planktonic foraminifera of the Mediterranean Sea

Stable isotopic and micropaleontological studies were made of selected sapropels (organic-rich sediments) deposited in the Mediterranean Sea during the last 5.0 m.y. to determine the processes responsible for their formation. Distinct isotopic and faunal changes occur across sapropels of late Pleistocene, early Pleistocene and latest Pliocene age, while smaller isotopic changes and more stable faunal assemblages are associated with the early and mid-late Pliocene sapropels. The large d18O depletions and euryhaline fauna associated with latest Pliocene-Pleistocene sapropels supports a density stratification model with a low salinity surface layer. In contrast, early Pliocene and mid-late Pliocene sapropels appear to have been formed as the result of sluggish circulation and low oxygen contents in bottom waters of the eastern Mediterranean due to the stable, warm climatic conditions of that time period.

Pleistocene rhyolithic tephra of ODP Leg 181 sites

Taupo Volcanic Zone (TVZ), in the North Island, New Zealand, is arguably the most active Quaternary rhyolitic system in the world. Numerous and widespread rhyolitic tephra layers, sourced from the TVZ, form valuable chronostratigraphic markers in onshore and offshore sedimentary sequences. In deep-sea cores from Ocean Drilling Program (ODP) Leg 181 Sites 1125, 1124, 1123 and 1122, located east of New Zealand, ca 100 tephra beds are recognised post-dating the Plio-Pleistocene boundary at 1.81 Ma. These tephras have been dated by a combination of magnetostratigraphy, orbitally tuned stable-isotope data and isothermal plateau fission track ages. The widespread occurrence of ash offshore to the east of New Zealand is favoured by the small size of New Zealand, the explosivity of the mainly plinian and ignimbritic eruptions and the prevailing westerly wind field. Although some tephras can be directly attributed to known TVZ eruptions, there are many more tephras represented within ODP-cores that have yet to be recognised in near-source on-land sequences. This is due to proximal source area erosion and/or deep burial as well as the adverse effect of vapour phase alteration and devitrification within near-source welded ignimbrites. Despite these difficulties, a number of key deep-sea tephras can be reliably correlated to equivalent-aged tephra exposed in uplifted marine back-arc successions of Wanganui Basin where an excellent chronology has been developed based on magnetostratigraphy, orbitally calibrated sedimentary cycles and isothermal plateau fission track ages on tephra. Significant Pleistocene tephra markers include: the Kawakawa, Omataroa, Rangitawa/Onepuhi, Kaukatea, Kidnappers-B, Potaka, Unit D/Ahuroa, Ongatiti, Rewa, Sub-Rewa, Pakihikura, Ototoka and Table Flat Tephras. Six other tephra layers are correlated between ODP-core sites but have yet to be recognised within onshore records. The identification of Pleistocene TVZ-sourced tephras within the ODP record, and their correlation to Wanganui Basin and other onshore sites is a significant advance as it provides: (1) an even more detailed history of the TVZ than can be currently achieved from the near-source record, (2) a high-resolution tephrochronologic framework for future onshore-offshore paleoenvironmental reconstructions, and (3) well-dated tephra beds correlated from the offshore ODP sites with astronomically tuned timescales provide an opportunity to critically evaluate the chronostratigraphic framework for onshore Plio-Pleistocene sedimentary sequences (e.g. Wanganui Basin, cf. Naish et al. (1998, doi:10.1016/S0277-3791(97)00075-9).