Sr, C and O isotope ratios of Neogene sediments from DSDP Hole 38-341, Voring Plateau

The Neogene sediments from DSDP site 341 on the Voring Plateau, Norwegian Sea, contain a thin glauconitic pellet-bearing subunit, which separates underlying pelagic clays from overlying glacial-marine sediments. Oxygen isotope measurements of benthic foraminifera show a delta18O shift of + 1? during deposition of this subunit, probably a combined effect of a drop in bottom water temperature and a rise in seawater delta18O. The chronology of this sedimentological and O isotope transition is, however, poorly constrained by fossil evidence. Rb-Sr dating of glauconitic pellets indicates that the lower part of the glauconitic subunit was deposited 11.6 +/- 0.2 Ma ago. Further geochronological evidence, derived from the Sr and C isotopic compositions of foraminifera compared with known seawater-time variations, indicates that the lower pelagic clays are early to middle Miocene, deposited at a mean rate of ~15 m/Ma. The glauconitic subunit contains part of the middle Miocene and probably all of the late Miocene in a condensed sequence with a very low mean depositional rate (~0.2 m/Ma). The overlying glacial marine sediments are probably Pliocene, with a high mean rate of deposition, ~45 m/Ma. This is the first application of C, O and Sr isotopic stratigraphy combined with Rb-Sr dating of glauconitic minerals, and it illustrates the applications of this integrated approach in geochronology.

Sediment, isotopic and geochemical record during Marine Isotope Stages 29 to 34 of IODP Site 339-U1387

Centennial-to-millennial scale records from IODP Site U1387, drilled during IODP Expedition 339 into the Faro Drift at 558 m water depth, now allow evaluating the climatic history of the upper core of the Mediterranean Outflow (MOW) and of the surface waters in the northern Gulf of Cadiz during the early Pleistocene. This study focuses on the period from Marine Isotope Stage (MIS) 29 to 34, i.e. the interval surrounding extreme interglacial MIS 31. Conditions in the upper MOW reflect obliquity, precession and millennial-scale variations. The benthic d18O signal follows obliquity with the exception of an additional, smaller d18O peak that marks the MIS 32/31 transition. Insolation maxima (precession minima) led to poor ventilation and a sluggish upper MOW core, whereas insolation minima were associated with enhanced ventilation and often also increased bottom current velocity. Millennial-scale periods of colder sea-surface temperatures (SST) were associated with short-term maxima in flow velocity and better ventilation, reminiscent of conditions known from MIS 3. A prominent contourite layer, coinciding with insolation cycle 100, was formed during MIS 31 and represents one of the few contourites developing within an interglacial period. MIS 31 surface water conditions were characterized by an extended period (1065-1091 ka) of warm SST, but SST were not much warmer than during MIS 33. Interglacial to glacial transitions experienced 2 to 3 stadial/interstadial cycles, just like their mid-to-late Pleistocene counterparts. Glacial MIS 30 and 32 recorded periods of extremely cold (< 12°C) SST that in their climatic impact were comparable to the Heinrich events of the mid and late Pleistocene. Glacial MIS 34, on the other hand, was a relative warm glacial period off southern Portugal. Overall, surface water and MOW conditions at Site U1387 show strong congruence with Mediterranean climate, whereas millennial-scale variations are closely linked to North Atlantic circulation changes.

(Table 2) Sedimentation and accumulation rates of DSDP Holes 38-337 and 38-338

The modern depositional environment of the deep Norwegian-Greenland Sea is highly asymmetric in an E-W direction because of the hydrography of the surface water masses and because of the more or less permanent pack ice cover of the East Greenland Current regime along the Greenland continental margin. By means of sedimentation rates we have tried to investigate whether this hydrographic asymmetry influenced the sediment input to the Norwegian-Greenland Sea over the past 60 m.y. Sediment input can be quantified if thicknesses of sediment sections accumulated over known time intervals can be measured and if some of their physical properties have been determined. Sedimentation rates have been estimated for Tertiary and Quaternary times, and their temporal as well as their spatial changes are discussed. Basin structure and morphology exerted an important influence on sediment distribution. During the Early Tertiary major sediment source regions in the southern Barents Sea and to the north and west of Iceland could be identified; these source regions supplied the bulk of the sediment fill of the Norwegian-Greenland Sea. Since inception of a "glacial" type sedimentation major elements of the sea surface circulation seem to have controlled the sediment input into this polar and subpolar deep-sea basin.