Nd-Sr isotopes in fossil fish debris from IODP Exp302

Strontium and neodymium radiogenic isotope ratios in early to middle Eocene fossil fish debris (ichthyoliths) from Lomonosov Ridge (Integrated Ocean Drilling Program Expedition 302) help constrain water mass compositions in the Eocene Arctic Ocean between 55 and 45 Ma. The inferred paleodepositional setting was a shallow, offshore marine to marginal marine environment with limited connections to surrounding ocean basins. The new data demonstrate that sources of Nd and Sr in fish debris were distinct from each other, consistent with a salinity-stratified water column above Lomonosov Ridge in the Eocene. The 87Sr/86Sr values of ichthyoliths (0.7079 - 0.7087) are more radiogenic than Eocene seawater, requiring brackish to fresh water conditions in the environment where fish metabolized Sr. The 87Sr/86Sr variations probably record changes in the overall balance of river Sr flux to the Eocene Arctic Ocean between 55 and 45 Ma and are used here to reconstruct surface water salinity values. The eNd values of ichthyoliths vary between -5.7 and -7.8, compatible with periodic (or intermittent) supply of Nd to Eocene Arctic intermediate water (AIW) from adjacent seas. Although the Norwegian-Greenland Sea and North Atlantic Ocean were the most likely sources of Eocene AIW Nd, input from the Tethys Sea (via the Turgay Strait in early Eocene time) and the North Pacific Ocean (via a proto-Bering Strait) also contributed.

Abundance and biomass of benthic foraminifera in bottom sediments from the Sea of Okhotsk and the Pacific Ocean

A study of distribution of live individuals of benthic foraminifera in sediments of the Sea of Okhotsk and of the Northwestern Basin of the Pacific Ocean shows that they can be present in sediments up to depth of 30 cm and probably can live there for long periods, sometimes forming high concentrations. Living individuals in the subsurface layer often account for more than 50% of total biomass, which varies from 1 to 21 g/m**2 in different morphological structures. The largest biomass values are attained in underwater rises embedded in relatively warm, oxygen-saturated Pacific waters. Minimum total biomass concentrations occur in deep-water depressions where stagnation phenomena are observed. Foraminifera biomass everywhere decreases gradually with increasing depth from the surface of sediments regardless of relief, depth, and nature of sediments.

Benthic foraminifera in surface sediments of the Arabian Sea

Assemblages of living deep-sea benthic foraminifera, their densities, vertical distribution pattern, and diversity, were investigated in the intermonsoon period after the northeast monsoon in the Arabian Sea in spring 1997. Foraminiferal numbers show a distinct gradient from north to south, with a maximum of 623 foraminifera in 50 cm**3 at the northern site. High percentages of small foraminifera were found in the western and northern part of the Arabian Sea. Most stations show a typical vertical distribution with a maximum in the first centimeter and decreasing numbers with increasing sediment depths. But at the central station, high densities can be found even in deeper sediment layers. Diversity is very high at the northern and western sites, but reduced at the central and southern stations. Data and faunal assemblages were compared with studies carried out in 1995. A principal component analysis of intermonsoon assemblages shows that the living benthic foraminifera can be characterized by five principal component communities. Dominant communities influencing each site differ strongly between the two years. In spring 1997, stations in the north, west and central Arabian Sea were dominated by opportunistic species, indicating the influence of fresh sedimentation pulses or enhanced organic carbon fluxes after the northeast monsoon.

Benthic and planktonic foraminifera in the Japan Sea

Biostratigraphy and paleoenvironmental history of deep and surficial waters of the Japan Sea are addressed using sequences recovered from the floor of the backarc basin. The study is divided into two parts: (1) foraminifer biostratigraphy and paleoenvironmental assessment of sedimentary sequences recovered from above igneous basement at the four sites and (2) detailed planktonic foraminifer paleoenvironmental analysis of Quaternary and Pliocene sequences from Sites 794 and 797 in the Yamato Basin. A total of 253 samples were examined for the foraminifer biostratigraphy and 325 samples for the detailed paleoenvironmental study of Quaternary and Pliocene sequences. Low abundance and sporadic occurrence of foraminifers limited interpretation of results. Foraminifer-bearing intervals were correlated where possible to diatom and calcareous nannofossil zonations, and the sequences were successfully assigned to the foraminifer zonation of Matsunaga. Unfortunately, extensive barren intervals and sporadic occurrences of planktonic foraminifers prevented zonation of Quaternary and Pliocene intervals, although some interesting conclusions about paleoenvironment were possible and are listed below. A sequence of Neogene (sensu lato) paleoenvironmental events were identified: (1) deepening of the Yamato basins to middle bathyal depths by the early to middle Miocene, an event contemporaneous with the age of some deep basins known from uplifted sections adjacent to the Japan Basin; (2) cooling of the Japan Sea in the early middle Miocene; (3) oxygenation of deep waters in the late Miocene; (4) further cooling of surficial water masses between the Olduvai Subchron and the Brunhes/Matuyama Boundary; and (5) extermination of lower middle bathyal faunas and replacement by upper middle bathyal faunas near the base of the Quaternary.

Stable isotope ratios of foraminifera from sediment cores off northeastern Brazil

The western South Atlantic boundary currents represent a sensitive system within the global thermohaline circulation (THC). We investigated the impact of deglacial THC changes on the western tropical Atlantic studied in six high resolution sediment cores from the upper continental slope of Brazil. The stratigraphy of the cores is mainly based on 14C AMS dating of monospecific foraminiferal samples. Changes in the upper layer tropical ocean during the deglaciation are inferred from stable oxygen isotope measurements on planktic and benthic foraminifera. Variations in the delta18O residuals are assumed to be mainly temperature related. During the Oldest and Younger Dryas cooling periods, two major deglacial THC disturbances are reported from North Atlantic sediment cores. Concomitant to the repeated THC slowdown, we observe an upper layer warming in the tropical ocean. A reduced northward heat export from the tropical areas during these periods (weak North Brazil Current) is additionally reflected by low meridional gradients in the stable oxygen records. This generally agrees with results from coupled ocean atmosphere models.

Occurence of ostracoda and foraminifera in Mainz Basin

Central European marine to brackish ostracod and benthic foraminiferal phenetic similarities between seven areas have been calculated (Jaccard index) for the early Chattian, late Chattian (Late Oligocene) and Aquitanian (Early Miocene) time slices. The results demonstrate the existence of three (micro-) faunal palaeobiogeographic units: a northern unit, the Upper Rhine Subprovince (URSP for Ostracoda; or Upper Rhine Area, URA for Foraminifera; encompassing the Mainz Basin, northern Upper Rhine Graben and Hanau Basin/Wetterau) and the Western Paratethys. Progressive isolation of the URSP is indicated by reduced indices that bottomed in the basal Miocene, when connections appear to be completely interrupted (Ostracoda) or reduced to a few cosmopolitan species (Foraminifera). The interpretations are, to a large extent, in agreement with other palaeontological data (e.g. molluscs, fish). The general isolation trend is not always continuous for ostracod or foraminiferal assemblages.