Paleomagnetic of ODP Hole 133-823A

Hole 823A covers the upper 120 m (Subunits IA and IB) of Site 823 at the bottom of the Queensland Trough. This hole contains an abundance of gravity-flow deposits, but is thought to have a monotonic age sequence. Above 32 mbsf, a strong, stable (normal) magnetic remanence having a relatively small viscous remanent magnetization (VRM) is seen. Below 32 mbsf, the sediments are subject to widespread VRM, which appears to obliterate the primary magnetization and precludes identification of the Brunhes/Matuyama boundary. Progressive alternating field (AF) demagnetization is limited to low fields (typically <400 Oe) by the weak magnetization in these sediments. As a consequence, the possibility of a high-coercivity component of primary magnetization cannot be ruled out. Lowrie-Fuller tests indicate that this VRM overprinting does not have a multidomain origin. An approximately linear relationship exists between median destructive field (MDF) and the logarithm of the natural remanent magnetization (NRM). Carbonate dilution does not appear to be a dominant factor in controlling variations in concentration-dependent magnetic parameters, such as magnetic susceptibility. The sedimentological distinction between Subunits IA and IB does not show up in the magnetic record. However, a sharp change in magnetic properties does occur at 32 mbsf, with low background magnetizations below this level and high background magnetizations above it. The boundary coincides with a change from thick (>10 cm thick) to thin (<10 cm thick) turbidite deposition, and is also near the boundary separating the sulfate-reduction zone in the upper part of the sequence from the sulfate-free zone beneath. The abrupt nature of the magnetic boundary is evidence that nannofossil subzone CN14b is not condensed, but is missing in a hiatus at 32 mbsf. Nine peaks have been identified in the susceptibility (K) record that are superimposed on ôbackgroundö signals. ARM/K ratios are uniformly low for the background sediments below 32 mbsf, intermediate for strong susceptibility peaks, and high for background sediments above 32 mbsf and weak susceptibility peaks. Comparisons with results from Site 820 suggest that (1) the background sediments above 32 mbsf and the weak susceptibility peaks carry a stable single-domain magnetization, and (2) the high susceptibility peaks are caused by the addition of a superparamagnetic contribution. Expectations are that the distinctive features of the Hole 823A magnetic record are linked to major environmental changes.

Neogen carbonate and stable isotope record of ODP Hole 120-751A

Lower Miocene through upper Pleistocene benthic foraminifer assemblage records from Ocean Drilling Program Site 751 on the Southern Kerguelen Plateau (57°44'S, water depth 1634 m) were combined with benthic and planktonic foraminifer oxygen and carbon isotope records and high-resolution CaCO3 data from the same site. Implications for the Neogene productivity and paleoceanography of the southern Indian Ocean are discussed. We used distinctive features of the Miocene d18O and d13C curves for stratigraphic correlation. Coinciding with a lower middle Miocene hiatus from 14.2 to 13.4 Ma, there was a rapid increase in benthic d18O values by 1.2 per mil. This distinct increase occurs in middle Miocene benthic foraminifer oxygen isotope curves from all oceans. No major change, however, in benthic foraminifer faunal composition occurred in this period of growth of the Antarctic ice cap and cooling of deep ocean waters (14.9-14.2 Ma). A drastic change in benthic foraminifer faunas coincided with a hiatus from 8.4 to 5.9 Ma. Shortly after this hiatus, in the latest Miocene, the CaCO3 content of the sediments dropped from 75% to 0%. From that time ( 5.8 Ma) through the early Pliocene, Site 751 has been situated beneath a high biogenic siliceous productivity zone. Carbonate contents of upper Pliocene and Pleistocene sediments vary between 20% and 70%. The benthic foraminifer faunas in the uppermost Pliocene and lower Pleistocene reflect strong bottom current conditions, in contrast to those in the upper Pleistocene, which indicate calm sedimentation and high food supply. High d13C values of planktonic foraminifers compared with low values of benthic foraminifers suggest high primary productivity in the late Pleistocene. The changes in productivity were probably a result of latitudinal migration and meandering of the Polar Frontal Zone.

(Table 1) Geochemical composition of surface waters obtained aboard the R/V Rift along the Volga-Caspian canal

The Volga River discharge consists of the waters transferred by fast currents through channels and the waters which are passing through the shallow areas of the delta overgrown by cane. Using the hydrochemical data, it is possible to track distribution of the waters modified by 'biofilters' of macrophytes in the delta shallows starting from the external edge of the delta. The main distinctive features of these waters are the high content of dissolved oxygen, the abnormally high values of the pH, and the low content of dissolved inorganic carbon (both total and as CO2). These waters extend in the shape of 1 to 3-km-wide strips at a distance of 20-40 km from the outer border of the delta. The analysis of the data obtained during the expeditions run by the Institute of Oceanology of the Russian Academy of Sciences in 2003-2009, along with archived and published data, show that such 'modified' waters occur almost constantly along the outer edge of the Volga River delta.