Radiolarians from the Southwest Pacific

Radiolarians are very rare in all Leg 90 sites. They are relatively more frequent only in Neogene sediments from Sites 586 and 594, and in Eocene sediments at Site 592. In this chapter radiolarian abundances are recorded as comparative percentages for 92 Neogene morphotypes at Site 586B. Relative abundances only are estimated at Sites 592 and 594, where preservation is poor to moderate. A tentative correlation of radiolarian events at Hole 586B and Site 594 shows that only a few species can be found in both tropical and subantarctic areas. New evolutionary lineages are proposed. 1. Middle Miocene eucyrtids like Eucyrtidium teuscheri group evolved into a widespread species (E. teuscheri teuscheri) ranging from middle Miocene to Holocene and a temperate species (E. teuscheri orthoporus) ranging from middle Miocene to early Pleistocene. 2. Phormostichoartus pitomorphus appears to be a temperate descendant of the cosmopolitan P. fistula and disappears in early Pleistocene time. 3. The discovery of Lamprocyrtis daniellae n.sp. calls into question the lineage L. heteroporos -> L. nigriniae. 4. The evolution of Lamprocyclas maritalis from an ancestor group (L. aff. maritalis) is located in the early part of the Pterocanium prismatium Zone.

Radiocarbon dates of Mytilus shells and peat and wood samples collected on Drayton Island

A multidisciplinary study was undertaken at the Qijurittuq Site (IbGk-3) on Drayton Island in Low-Arctic Quebec (Canada) to document the relationships between climatic, environmental, and cultural changes and the choice of Thule/Inuit dwelling style in the eastern Arctic. Several marine terraces were 14C-dated with shells in order to reconstruct the area's uplift (glacioisostatic rebound) curve. Plant macrofossil analysis of peat was conducted to reconstruct past vegetation and, indirectly, past climate. Archaeological surveys and excavations characterized the structure of subterranean sod houses at the Qijurittuq Site and were supplemented with open interviews with Inuit elders for a better understanding of site location and the use of household space. The sites selected for habitation were well-drained sandy marine terraces in a valley sheltered from prevailing winds. Sod houses were in turn made possible by the abundance of driftwood on the island and the presence of nearby peatland. Thule/Inuit people used semi-subterranean houses rather than igloos at the Qijurittuq Site during the dry, cold conditions toward the end of the Little Ice Age. Stable environmental conditions and food supply during winter possibly explain the use of those semipermanent houses on Drayton Island. However, it does not exclude the use of igloos during short expeditions on ice.

Biogenic sedimentation of DSDP Site 85-574

The equatorial Pacific is an important part of the global carbon cycle and has been affected by climate change through the Cenozoic (65 Ma to present). We present a Miocene (12-24 Ma) biogenic sediment record from Deep Sea Drilling Project (DSDP) Site 574 and show that a CaCO3 minimum at 17 Ma was caused by elevated CaCO3 dissolution. When Pacific Plate motion carried Site 574 under the equator at about 16.2 Ma, there is a minor increase in biogenic deposition associated with passing under the equatorial upwelling zone. The burial rates of the primary productivity proxies biogenic silica (bio-SiO2) and biogenic barium (bio-Ba) increase, but biogenic CaCO3 decreases. The carbonate minimum is at ~17 Ma coincident with the beginning of the Miocene climate optimum; the transient lasts from 18 to 15 Ma. Bio-SiO2 and bio-Ba are positively correlated and increase as the equator was approached. Corg is poorly preserved, and is strongly affected by changing carbonate burial. Terrestrial 232Th deposition, a proxy for aeolian dust, increases only after the Site 574 equator crossing. Since surface production of bio-SiO2, bio-Ba, and CaCO3 correlate in the modern equatorial Pacific, the decreased CaCO3 burial rate during the Site 574 equator crossing is driven by elevated CaCO3 dissolution, representing elevated ocean carbon storage and elevated atmospheric CO2. The length of the 17 Ma CaCO3 dissolution transient requires interaction with a 'slow' part of the carbon cycle, perhaps elevated mantle degassing associated with the early stages of Columbia River Basalt emplacement.

Mineralogy of ODP Site 105-645

Cores from the upper 70 meters below seafloor (mbsf) (upper Pleistocene) at Ocean Drilling Program (ODP) Site 645 in Baffin Bay show dramatic meter-scale changes in color and mineralogy. Below this interval, mineralogical changes are more gradual to the top of the Miocene at about 550 mbsf. The Pliocene-Pleistocene section can be divided into five facies: Facies 1 - massive, poorly sorted, gravel-bearing muds; Facies 2 - gray silty clays and silty muds; Facies 3 - laminated detricarbonate silty muds; Facies 4 - silty sand and sandy silt; and Facies 5 - poorly sorted muddy sands and silty muds. Facies 4 and 5 are restricted to the Pliocene section below depths of about 275 mbsf. The mineralogical/color cycles in the upper 70 mbsf are the result of alternations between Facies 2 and three lithotypes of Facies 1: lithotype A - tan-colored, carbonate-rich, gravel-bearing mud; lithotype B - weak, red-colored, gravel-bearing mud rich in sedimentary rock fragments; and lithotype C - gray, gravel-bearing mud. A fourth lithotype, D, is restricted to depths of 168-275 mbsf and is dark gray, carbonate-poor, gravel-bearing mud. We believe that all lithotypes of Facies 1 and the sand and gravel fractions of Facies 2 and 3 were deposited by ice rafting. Depositional processes for Facies 4 and 5 probably include ice rafting and bottom- and turbidity-current transport. Data from petrographic analyses of light and heavy sand-sized grains and X-ray analyses of silt- and clay-size fractions suggest that tan-colored sediments (lithotype A of Facies 1; Facies 3) were derived mainly from Paleozoic carbonates of Ellesmere, Devon, and northern Baffin islands. Weak red sediments (lithotype B) contain significant red sedimentary clasts, reworked quartzarenite grains and clasts, and rounded colorless garnets, all derived from Proterozoic sequences of the Borden and Thule basins, and from minor Mesozoic red beds. Other sediments in the upper 335 mbsf at Site 645 contain detritus from a heterogeneous mixture of sources, including Precambrian shield terranes around Baffin Bay. Sediments from 335 to 550 mbsf (Facies 5) are rich in friable sedimentary clasts and detrital micas and contain glauconite and, in a few samples, reworked diatoms. These components suggest derivation from poorly consolidated Mesozoic-Tertiary sediments in coastal outcrops and beneath the modern shelves of northeastern Baffin Island and western Greenland. For the upper Pleistocene section (about 0-100 mbsf), marked mineralogical cyclicity is attributed to fluctuating glacial margins, calving rates, and iceberg melting rates, particularly around the northern end of Baffin Bay. Tan-colored, carbonate-rich units were derived at times of maximum advance of glaciers on Ellesmere and Devon islands, during relatively warm intervals induced by incursion of warm Atlantic surface water into the bay. At the beginning of these warmer episodes, most icebergs were contributed by glaciers near sea level around the Arctic channels, which resulted in deposition of weak red, ice-rafted units rich in Proterozoic sedimentary clasts.

Epibenthic macrofauna abundance during RSS James Clark Ross cruise JR144, South Sandwich arc

The remote South Sandwich arc is an archipelago of small volcanic islands and seamounts entirely surrounded by deep water and about 600 km away from the closest island, South Georgia. As some of the youngest islands (< 5 m.y.) in the Southern Ocean they are ideal for studying colonization processes of the seabed by benthic fauna, but are rarely investigated because of remoteness and extreme weather. The current study attempted to quantify the richness and abundance of the epibenthic macrofauna around the Southern Thule group by taking five epibenthic sledge samples along a depth transect including three shelf (one at 300 m and two at 500 m) and two slope stations (1000 and 1500 m). Our aim was to investigate higher taxon richness and community composition in an isolated Antarctic locality, since recent volcanic eruptions between 1964 and 1997. We examined patterns across all epibenthic macrofauna at phylum and class levels, and investigated trends in some model groups of crustaceans to order and family level. We found that abundance was highest in the shallowest sample and decreased with depth. Shelf samples (300 and 500 m) were dominated by molluscs and malacostracans while at the deeper stations (1000 and 1500 m) nematodes were the most abundant taxon. Surprisingly, the shallow shelf was dominated by animals with restricted dispersal abilities, such as direct developing brooders (malacostracans) or those with lecithotrophic larvae (bivalves of the genus Yoldiella, most bryozoan species). Despite Southern Thule's geological youth, recent eruptions, and its remoteness the shallow shelf was rich in higher taxa (phyla/classes) as well as orders and families of our model groups. Future work at higher taxonomic resolution (species level) should greatly increase understanding of how life has reached and established on these young and highly disturbed seabeds.

Paleomagnetic and age determinations on rocks from Nares Strait

The Nares Strait controversy concerns the debate about whether or not a major sinistral transcurrent fault (the Wegener Fault) separates northern Greenland and Canada. To date no firm evidence has been found for the proposed 200 km sinistral offset, and to the contrary, geological correlations, mainly involving Paleozoic rocks across the Nares Strait, suggest that total left-lateral motion is no more than 70 km. The E-W trending Thule (Greenland) and Devon Island (Canada) dyke swarms lie on opposite sides of Baffin Bay and are offset sinistrally about 200 km, suggesting that if their correlation is established a convincing case for the Wegener Fault can be made. Paleomagnetic, geochemical and petrographic data allow, but do not yet establish, the correlation. Paleomagnetic results for Canadian sites (VGP = 6.9°N, 181.8 °E, A95 = 12.7°, N = 5) and Greenland sites (VGP = 11.5 °N, 178.3 °E, A95 = 13.8°, N = 4) are not significantly different at the 95 % confidence level. These levels are too large to resolve whether or not the Thule and Devon Island swarms have been offset. Geochemical data reveal a distinct and identical pattern in incompatible elements, while petrographically, the dykes are indistinguishable. U-Pb geochronological results for a Canadian dyke (720.2 ±2.0 Ma) and a Thule dyke (720.4 ±2.7 Ma) are identical within error and clearly identify the two sets of dykes as being parts of the same magmatic episode.