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).

Water, bottom deposits, and macrobenthos in the south part of the East Siberian Sea in September 2003

Macrobenthos biomass and bottom biocoenoses were studied in the sublittoral zone of the southern East Siberian Sea. The macrobenthos is characterized by relatively high abundance (from 30 to 2680 #/m**2), biomass (from 0.25 to 578.8 g/m**2), and diversity (83 species in total). Lateral distribution of macrobenthos biomass correlates with a substrate type and salinity and is substantially higher in areas washed by the Arctic water mass than in estuaries with mixed fresh and Arctic waters and shows a tendency to decreasing in the convergence zone of different water masses. The highest macrobenthos biomass is observed in cores of water masses in the Long Strait area and in the eastern part of the sea.

Morphology and size of Neogloboquadrina pachyderma in the North Atlantic

The variability in size and shape of shells of the polar planktonic foraminifer Neogloboquadrina pachyderma have been quantified in 33 recent surface sediment samples throughout the northern Atlantic Ocean and correlated with the properties of the ambient surface waters. The aim of the study was to determine whether any of the morphological features could be used to reconstruct sea surface properties in the polar realm of the North Atlantic, where most paleotemperature proxies appear to fail. The analyses revealed that shell morphology is only weakly controlled by habitat properties, whereas shell size showed a strong correlation with sea surface temperature. The regression of mean shell size on sea surface temperature revealed the presence of two trends among the sinistrally coiled shells: a continuous increase in shell size with decreasing SST in sediments deposited under polar water masses and a continuous increase in shell size with increasing SST in samples from transitional waters. The second trend mirrors the trend observed for dextrally coiled shells, which are frequent in the same samples and signal the presence of N. incompta. The identical mean shell size trends among the sinistral and dextral specimens in the temperate samples confirms the results of earlier genetic studies which indicated the existence of a small but distinct proportion of opposite coiling in N. incompta, to which the sinistral shells in the temperate samples could be attributed. The linear correlation between mean shell size and sea surface temperature in the polar domain (summer SST < 9 °C) has been used to develop an empirical formula for the reconstruction of past sea surface temperatures from shell sizes in fossil samples. The standard error of the residuals of the linear regression is 2.36 °C (1 sigma), which implies a much larger error than for most paleothermometers, but enough precision to allow resolution between results by individual paleothermometers in the polar domain. The resulting regression model has been applied on two sediment cores spanning the interval from the Last Glacial Maximum (LGM) to the present day. The results from core PS1906-1 are consistent with ice-free conditions during the LGM in the Norwegian Sea. The SST estimates for the LGM inferred from N. pachyderma shell size are similar or slightly higher than those for the latest Holocene. The results do not indicate anomalously high SST during the glacial and the LGM reconstructions thus appear more consistent with the results from foraminiferal transfer functions and geochemical proxies. Both sediment cores show the highest reconstructed SST during the early Holocene insolation optimum.

Radiocarbon dating of mollusk shells from southern Kara Sea sediments

Riverine water and sediment discharge to the Arctic Ocean is among the most important parameters influencing Arctic climate. It is clear that the evaluation of Arctic paleoclimate requires information on the paleodischarge of major rivers entering the sedimentation basin. Presently, the water discharge of the Ob River accounts for about 12% of the total input of river water into the Arctic Ocean. During the investigation of the Kara Sea in the framework of the Russian-German SIRRO Project, the history of Yenisei discharge received much attention in a number of publications. This paper presents the results of lithological and geochemical investigations with application to the Holocene discharge of the Ob River. Qualitative (SiO2, Al2O3, K2O, and some modules) and quantitative (sedimentation rates and absolute masses of sedimentary material) parameters were used to characterize the history of the Ob sediment discharge. It was shown that the investigated paleochannels of the Ob were initiated at the Pleistocene-Holocene boundary, and during the first half of the Holocene, the river discharge decreased irregularly with decreasing age of sediments. The observed maxima are in fairly good agreement with the data for the Yenisei. We proposed a hypothesis on the influence of glacioisostatic movements in the marginal region of the former Kara ice sheet of late Valdai age on the cessation of marine-fluvial glaciation in the paleochannels of Ob and Yenisei in the periphery of the Ob-Yenisei shoal.

Composition and fluxes of sinking particulate material and bottom sediments in the northeast Black Sea in 1998-1999

For the first time deep-sea mooring stations with sediment traps were deployed in the northeast Black Sea. One sediment trap for long-term studies was located at Station 1 (44°15'N, 37°43'E, deployment depth 1800 m, depth 1900 m). The trap collected sinking sedimentary material from January to May 1998. Material collectors were changed every 15 days. Other stations with sediment traps for short-term studies (September-October 1999) were located on the shelf: Station 2 (44°16'N, 38°37'E, deployment depth 45 m, depth 50 m) and on the bottom of the canyon: Station 3 (44°16'N, 38°22'E, deployment depth 1145 m, depth 1150 m), Station 4 (44°11'N, 38°21'E, deployment depths 200, 1550, 1650 m, depth 1670 m). Collected material indicates that vertical particle fluxes are controlled by seasonal changes of in situ production and by dynamics of terrigenous matter input. Higher vertical particle flux of carbonate and biogenic silica was in spring due to bloom of plankton organisms. Maximum of coccolith bloom is in April-May. Bloom of diatoms begins in March. In winter and autumn lithogenic material dominates in total flux. Its amount strongly depends on storms and river run-off. Suspended particle material differs from surface shelf sediments by finer particles (mainly clay fraction) and high content of clay minerals and biogenic silica. This material may form lateral fluxes with higher concentration of particles transported along the bottom of deep-sea canyons from the shelf to the deep basin within the nepheloid layer. In winter such transportation of sedimentary material is more intensive due to active vertical circulation of water masses.

Whole rock geochemistry and stable isotopes of rocks, fragments and foraminifers from two ODP Leg 166 holes

Total carbon and carbonate contents, quantitative carbonate mineralogy, trace metal concentrations, and stable isotope compositions were determined on a suite of samples from the Miocene sections at Sites 1006 and 1007. The Miocene section at Site 1007, located at the toe-of-slope, contains a relatively high proportion of bank-derived components and becomes fully lithified at a depth of ~300 meters below seafloor (mbsf). By contrast, Miocene sediments at Site 1006, situated in Neogene drift deposits in the Straits of Florida and composed primarily of pelagic carbonates, do not become fully lithified until a depth of ~675 mbsf. Diagenetic and compositional contrasts between Sites 1006 and 1007 are reflected in geochemical data derived from sediment samples from each site.

Low-molecular-weight hydrocarbon concentrations, organic carbon contents, and Rock-Eval pyrolysis hydrogen indices at DSDP Holes 75-530A and 75-532

A series of C2-C8 hydrocarbons (including saturated, aromatic, and olefinic compounds) from deep-frozen core samples taken during DSDP Leg 75 (Holes 530A and 532) were analyzed by a combined hydrogen-stripping/thermovaporization method. Concentrations representing both hydrocarbons dissolved in the pore water and adsorbed on the mineral surfaces vary in Hole 530A from about 10 to 15,000 ng/g of dry sediment weight depending on the lithology (organic-carbon-lean calcareous oozes versus "black shales"). Likewise, the organic-carbon-normalized C2-C8 hydrocarbon concentrations vary from 3,500 to 93,100 ng/g Corg, reflecting drastic differences in the hydrogen contents and hence the hydrocarbon potential of the kerogens. The highest concentrations measured of nearly 10**5 ng/g Corg are about two orders of magnitude below those usually encountered in Type-II kerogen-bearing source beds in the main phase of petroleum generation. Therefore, it was concluded that Hole 530A sediments, even at 1100 m depth, are in an early stage of evolution. The corresponding data from Hole 532 indicated lower amounts (3,000-9,000 ng/g Corg), which is in accordance with the shallow burial depth and immaturity of these Pliocene/late Miocene sediments. Significant changes in the light hydrocarbon composition with depth were attributed either to changes in kerogen type or to maturity related effects. Redistribution pheonomena, possibly the result of diffusion, were recognized only sporadically in Hole 530A, where several organic-carbon lean samples were enriched by migrated gaseous hydrocarbons. The core samples from Hole 530A were found to be severely contaminated by large quantities of acetone, which is routinely used as a solvent during sampling procedures on board Glomar Challenger.