Investigation of Pliocene foraminifera on sediment core CRP-1 from the Ross Sea, Antarctica

Mixed assemblages of Pliocene and Quaternary foraminifera occur within the Quaternary succession of the CRP-1 drillhole. Pliocene foraminifera are not present in the lowermost Unit 4.1. are rare in Unit 3.1 and 2.3, are relatively common in Units 2.2 and 2.1, and are absent in Unit 1.1. Fifteen and twelve species were documented in two of the samples from Units 2.2 and 2.1 respectively. A census count of foraminifera in a sample at 26.89 mbsf (Unit 2.2) indicated that 39% of the tests were from a Pliocene source, with the remaining 61% tests assigned to the in situ Quaternary assemblage. There appears to be a close correlation between the stratigraphic distribution of ice-rafted sediments and the test number and diversity of Pliocene taxa. It is concluded that Pliocene assemblages were not derived from submarine outcrops on Roberts Ridge, but are more likely to have been rafted to the site via major trunk valley drainage systems such as operated within the Mackay and Ferrar glacial valleys. The co-occurrence of marine biota (including foraminifera), fossil wood, pollen, and igneous clasts in the Quaternary succession of CRP-l, points to the marine and terrestrial facies of the Pliocene Sirius Group as a likely source. A major episode of erosion and transport of sediment into the offshore marine basins at about ~1 Ma may have been triggered by dynamism in the ice sheet-glacier system, an episode of regional uplift in the Transantarctic Mountains, sea level oscillations and associated changes in the land-to-sea drainage baselines, or some combination of these factors.

(Table 1) Cation exchange capacity and other characteristics of soils common in Lower Saxony, Germany

The chemical and biochemical processes associated with the filtration of rainwater through soils, a step in groundwater recharge, were investigated. Under simulated climatic conditions in the laboratory, undisturbed soil columns of partly loamy sands, sandy soils and loess were run as lysimeters. A series of extraction procedures was carried out to determine solid matter in unaltered rock materials and in soil horizons. Drainage water and moisture movement in the columns were analysed and traced respectively. The behaviour of soluble humic substance was investigated by percolation and suspension experiments. The development of seepage-water in the unsaturated zone is closely associated with the soil genetic processes. Determining autonomous chemical and physical parameters are mineral composition and grain size distribution in the original unconsolidated host rock and prevailing climatic conditions. They influence biological activity and transport of solids, dissolved matter and gases in the unsaturated zone. Humic substances, either as amorphous solid matter or as soluble humic acids play a part in diverse sorption, solution and precipitation processes.

Stable carbon and oxygen isotope record of foraminifera of IODP Site 303-1307

A major tipping point of Earth's history occurred during the mid-Pliocene: the onset of major Northern-Hemisphere Glaciation (NHG) and of pronounced, Quaternary-style cycles of glacial-to-interglacial climates, that contrast with more uniform climates over most of the preceding Cenozoic and continue until today (Zachos et al., 2001, doi:10.1126/science.1059412). The severe deterioration of climate occurred in three steps between 3.2 Ma (warm MIS K3) and 2.7 Ma (glacial MIS G6/4) (Lisiecki and Raymo, 2005, doi:10.1029/2004PA001071). Various models (sensu Driscoll and Haug, 1998, doi:10.1126/science.282.5388.436) and paleoceanographic records (intercalibrated using orbital age control) suggest clear linkages between the onset of NHG and the three steps in the final closure of the Central American Seaways (CAS), deduced from rising salinity differences between Caribbean and the East Pacific. Each closing event led to an enhanced North Atlantic meridional overturning circulation and this strengthened the poleward transport of salt and heat (warmings of +2-3°C) (Bartoli et al., 2005, doi:10.1016/j.epsl.2005.06.020). Also, the closing resulted in a slight rise in the poleward atmospheric moisture transport to northwestern Eurasia (Lunt et al., 2007, doi:10.1007/s00382-007-0265-6), which probably led to an enhanced precipitation and fluvial run-off, lower sea surface salinity (SSS), and an increased sea-ice cover in the Arctic Ocean, hence promoting albedo and the build-up of continental ice sheets. Most important, new evidence shows that the closing of the CAS led to greater steric height of the North Pacific and thus doubled the low-saline Arctic Throughflow from the Bering Strait to the East Greenland Current (EGC). Accordingly, Labrador Sea IODP Site 1307 displays an abrupt but irreversible EGC cooling of 6°C and freshening by ~2 psu from 3.25/3.16-3.00 Ma, right after the first but still reversible attempt of closing the CAS.

Northwards and eastwards velocities extracted from a historical run (for the year 2000) of the UVic Earth System Climate Model of Weaver et al. (2001)

This study provides a theoretical assessment of the potential bias due to differential lateral transport on multi-proxy studies based on a range of marine microfossils. Microfossils preserved in marine sediments are at the centre of numerous proxies for paleoenvironmental reconstructions. The precision of proxies is based on the assumption that they accurately represent the overlying watercolumn properties and faunas. Here we assess the possibility of a syn-depositional bias in sediment assemblages caused by horizontal drift in the water column, due to differential settling velocities of sedimenting particles based on their shape, size and density, and due to differences in current velocities. Specifically we calculate the post-mortem lateral transport undergone by planktic foraminifera and a range of other biological proxy carriers (diatoms, radiolaria and fecal pellets transporting coccolithophores) in several regions with high current velocities. We find that lateral transport of different planktic foraminiferal species is minimal due to high settling velocities. No significant shape- or size-dependent sorting occurs before reaching the sediment, making planktic foraminiferal ideal proxy carriers. In contrast, diatoms, radiolaria and fecal pellets can be transported up to 500km in some areas. For example in the Agulhas current, transport can lead to differences of up to 2°C in temperature reconstructions between different proxies in response to settling velocities. Therefore, sediment samples are likely to contain different proportions of local and imported particles, decreasing the precision of proxies based on these groups and the accuracy of the temperature reconstruction.

Late Pliocene stratigraphic distribution of Globoconella taxa in the North Atlantic

Quantitative records of Globorotalia puncticulata and Globorotalia inflata, the last two members of the Globorotalia (Globoconella) lineage, obtained from North Atlantic sediments collected at DSDP Site 552, ODP Site 659 and ODP Site 665, are used to examine fluctuations in the biogeographic distribution of these species in the Late Pliocene between 3 and 2 Ma. Abundance data indicate that prior to the expansion of Northern Hemisphere glaciation at about 2.5 Ma, Gr. puncticulata was an important component of the planktonic foraminiferal fauna and had a geographic distribution ranging from 2°N to at least 56°N in the North Atlantic. A previously undescribed 6 chambered variant of Gr. puncticulata is found at both Sites 659 and 665. The stratigraphic distribution of this morphotype is restricted, first occurring at 2.9 Ma and then disappearing when glacial intensity increased at 2.75 Ma (isotope stage 110). Similar declines in Gr. puncticulata abundances occurred during glacial isotope stages 102, 100, and 98 immediately prior to the extinction of Gr. puncticulata during glacial isotope stage 96. It appears that this extinction event was latitudinally diachronous within the North Atlantic, occurring earliest in the north at Site 552 (2.453 Ma), then at Site 659 (2.443 Ma) and later still in the Site 665 equatorial record (2.438 Ma). At Site 665 the first record of Gr. inflata occurs during glacial isotope stage 94 (2.416 Ma), shortly after the extinction of Gr. puncticulata. In the mid latitude North Atlantic there was a 340,000 year period following the disappearance of Gr. puncticulata when the Globoconella lineage was absent (the Gr. inflata gap). The Gr. inflata population found in the equatorial Atlantic must therefore have been introduced from the South Atlantic, probably by the South Equatorial Current. Faunal records from Sites 552 and 659 show that it was not until glacial isotope stage 78 (2.10 Ma) that Gr. inflata became widely established in the North Atlantic. Prior to this large-scale migration event, there were two limited colonisation events during glacial isotope stages 86 and 82 when Gr. inflata populations reached as far as Site 659 in the eastern North Atlantic. These incursions are believed to be reflect the entrainment of Gr. inflata within South Atlantic Central Water and the northward subsurface transport of individuals to the coastal upwelling zone off northwest Africa. It seems likely that the same mechanism was responsible for the re-establishment of the Globoconella lineage in the North Atlantic at 2.10 Ma, but in this instance additional factors, such as enhanced glacial circulation patterns and ecological changes within planktonic foraminiferal faunas, resulted in the successful expansion of Gr. inflata across the North Atlantic and the Mediterranean.

Age models of ODP sites from the Barents Sea-Svalbard region

Based on a revised chronostratigraphy, and compilation of borehole data from the Barents Sea continental margin, a coherent glaciation model is proposed for the Barents Sea ice sheet over the past 3.5 million years (Ma). Three phases of ice growth are suggested: (1) The initial build-up phase, covering mountainous regions and reaching the coastline/shelf edge in the northern Barents Sea during short-term glacial intensification, is concomitant with the onset of the Northern Hemisphere Glaciation (3.6-2.4 Ma). (2) A transitional growth phase (2.4-1.0 Ma), during which the ice sheet expanded towards the southern Barents Sea and reached the northwestern Kara Sea. This is inferred from step-wise decrease of Siberian river-supplied smectite-rich sediments, likely caused by ice sheet blockade and possibly reduced sea ice formation in the Kara Sea as well as glacigenic wedge growth along the northwestern Barents Sea margin hampering entrainment and transport of sea ice sediments to the Arctic-Atlantic gateway. (3) Finally, large-scale glaciation in the Barents Sea occurred after 1 Ma with repeated advances to the shelf edge. The timing is inferred from ice grounding on the Yermak Plateau at about 0.95 Ma, and higher frequencies of gravity-driven mass movements along the western Barents Sea margin associated with expansive glacial growth.

Holocene sedimentation in the Strait of Otranto, Mediterranean Sea

An extensive radiograph study of 24 undisturbed, up to 206-cm long box and gravity cores from the western part of the Strait of Otranto revealed a great variety of primary bedding structures and secondary burrowing features. The regional distribution of the sediments according to their structural, textural, and compositional properties reflects the major morphologic subdivisions of the strait into shelf, slope, and trough bottom (e.g., the bottom of the northern end of the Corfu-Kephallinia Trough, which extends from the northeastern Ionian Sea into the Strait of Otranto): (1) The Apulian shelf (0 to -170m) is only partly covered by very poorly sorted, muddy sands without layering. These relict(?) sands are rich in organic carbonate debris and contain glauconite and reworked (?Pleistocene) ooids. (2) The slope sediments (-170 to -1,000 m) are poorly sorted, sandy muds with a high degree of burrowing. One core (OT 5) is laminated and shows slump structures. An origin of these slumped sediment masses from older deposits higher on the slope was inferred from their abnormal compaction, color, texture, organic content, and mineral composition. (3) Cores from the northern end of the Corfu-Kephallinia Trough (-980 to -1,060 m) display a few graded sand layers, 2-5 cm (maximum 30 cm) thick with parallel and ripple-cross-laminations, deposited by oceanic bottom or small-scale turbidity currents. They are intercalated with homogeneous lutite. (4) Hemipelagic sediments prevail in the more southerly part of the Corfu-Kephallinia Trough and on the "Apulian-Ionian Ridge", the southern submarine extension of the Apulian Peninsula. Below a core depth of 160 cm, these cores have a laminated ("varved") zone, representing an Early Holocene (Boreal-Atlanticum) "stagnation layer" (14C age approximately 9,000 years). The terrigenous components of the surface sediments as well as those of the deeper sand layers can be derived from the Apulian shelf and the Italian mainland (Cretaceous Apulian Plateau and Gargano Mountains, southern Apennines, volcanic province of the Monte Vulture). Indicated by the heavy mineral glaucophane, a minor proportion of the sedimentary material is probably of Alpine origin. If this portion is considered to be first-cycle clastic material it reaches the Strait of Otranto after a longitudinal transport of 700 km via the Adriatic Sea. The lack of phyllosilicates in the coarse- to medium-grained shelf samples might be explained by the activity of the "Apulian Current" (surface velocities up to 4 knots) which in the past possibly has affected the bottom almost down to depths of the shelf edge. The percentage of planktonic organisms, and also the plankton: benthos ratio in the sediments is a useful indicator for bathymetry (depth zonation).

The hydrographic conditions at depth below 1000 m water depth in the region of the Romanche Fracture Zones

During the "Atlantic Expedition" in1965 (IQSY) a comprehensive bathymetric survey and a few hydrographic stations were made by R.V. "Meteor" in the equatorial region of the Mid-Atlantic Ridge. The survey results are shown in a bythymetric chart covering the western parts of the Romanche- and Chain Fracture Zones. West of the original Romanche Trench another deep trench with a medium depth of 6000 m was discovered. The maximum sounding obtained was 7028 m. Both trenches apparently belong to the same fracture zone, but are distinctly separated from each other. The estern boundary of the trench against the Brasil Basin is formed by a sill rising to a depth of about 4400 m. The serial hydrographic observations give some indications of the flow of the cold Westatlantic deep water in the fracture zone area and its influence on the hydrographic conditions in the East-Atlantic Basin. The upper limit of the nearly homogenious Westatlantic bottom water with an Antarctic components lies about 4400 m. The water mass entering the system of trenches of the Romanche Fracture Zone over the western sill originates from the lower part of the discontinuity layer lying above the bottom water. Potential temperatures of 0.6°C were the lowest observed by "Meteor" in the western trench. There seems to be a remarkable tongue of relatively high salinity and a minimum of oxygen in the deep water of this trench. At present we can only speculate upon the origin of this highly saline deep water tongue underneath the eastward moving relatively thin layer of less saline Westatlantic deep water. In the range of the sill separating both trenches a lee wave is indicated by the distribution of salinity and oxygen, which implies a vertical transport of water masses. Caused by this transport it is assumed that relatively cold water may be lifted temporarily to a depth, where it can pass the northbounding ridge, thus getting directly into the Sierra Leone Basin. In the original Romanche Trench the cold Westatlantic deep water seems to fill the whole trough, but its extension remains limited to the trench itself. The water masses found east of the sill separating the trench from the East-Atlantic Basin originate from the lower part of the discontinuity layer. With potential temperatures of about 1.3°C they are much warmer than those observed in the Romanche Trench bottom water.

Chemical composition, characteristics and age of glauconites at DSDP Leg 66 Holes

During the analysis of "glaucony" recovered during Leg 66, off Mexico, we reviewed the data on previously studied glaucony layers in active margin areas. We found the depth of Leg 66 glaucony sediments to be significantly greater than conventionally assumed appropriate to their genesis (100-500 m). Accordingly, we hypothesize their occurrence at unusual depth to be due to (1) transport of shallow sediments and redeposition at greater depths, (2) margin subsidence, or (3) genesis at greater depth than is generally assumed. For the area off Mexico, we reject (1). (2) has already been verified in Japan and is possible as an explanation for the present phenomenon without excluding (3), which we investigate in this chapter.