Glassy objects from DSDP Hole 5-32 in the northeastern Pacific Ocean

Small glassy spheres, ellipsoids, teardrops, cylinders and dumbbells occur in large numbers in Tertiary deep sea clays cored in the northeastern Pacific by the Deep Sea Drilling Project. These objects morphologically resemble microtektites, but have the composition of an oceanic tholeiite. On the basis of their composition and stratigraphic relationship it is considered that they are of volcanic origin and most likely have been formed in deep water by submarine volcanic processes.

Pleistocene sedimentology of ODP Hole 133-820A from the northeastern Australian margin

A principal objective at Site 820, situated on the outer shelf, upper slope of the northeastern Australian continental margin, was to test the relationships between changes in Pleistocene sea level and sedimentary packages produced on a mixed carbonate-siliciclastic continental margin. To this end, we have examined the downcore distribution of grain size, magnetic susceptibility, and calcium-carbonate content throughout Hole 820A and, in particular, the top 35 meters below the seafloor (mbsf). These data are compared with variations in the oxygen-isotope signal defined for the same hole and are interpreted as indicating sea-level oscillations. The distribution of sand, mud, calcium carbonate of the mud fraction and total sample, and magnetic susceptibility during the last 20,000 yr defines the position of a sea-level regression (41,000-18,000 yr B.P.), a lowstand, early (18,000-9,400 yr B.P.) and late transgressions (9400-900 yr B.P.), and a highstand (4900 yr to the present). The regression is seen first in a high-carbonate content peak. Calcium carbonate constituents mainly comprise skeletal carbonate grains, with abundant planktonic and benthic foraminifers, and lime muds. The lowstand is characterized by a maximum abundance of the sand fraction, which contains dominantly skeletal carbonate grains and a minor abundance of lithoclasts. Sand-sized terrigenous sediments are proposed to have bypassed the continental shelf during a lowstand of sea level. Sedimentation rates throughout the regression and lowstand are low (3.0 cm/k.y.). The early transgression, marked by highest values in magnetic susceptibility, displays a rapid increase in sedimentation rate that coincided with an increase in terrigenous mud. Highest sedimentation rates of 82.3 cm/k.y. occurred during the late transgression, with increasing percentages of lime-mud. A decrease in noncarbonate constituents in the mud fraction during the late transgression and highstand of sea level is thought to be the result of restricted inner-shelf sedimentation of terrigenous sediments. The same relationship is also seen in the major sea-level oscillation, which is interpreted as isotope stage 6.

Sediment total reflectance measurements from the Cariaco Basin (MD03-2621) and northeastern Arabian Sea (SO130-289KL)

During the last glacial period, the North Atlantic region experienced pronounced, millennial-scale alternations between cold, stadial conditions and milder interstadial conditions-commonly referred to as Dansgaard-Oeschger oscillations-as well as periods of massive iceberg discharge known as Heinrich events. Changes in Northern Hemisphere temperature, as recorded in Greenland, are thought to have affected the location of the Atlantic intertropical convergence zone and the strength of the Indian summer monsoon. Here we use high-resolution records of sediment colour-a measure of terrigenous versus biogenic content-from the Cariaco Basin off the coast of Venezuela and the Arabian Sea to assess teleconnections with the North Atlantic climate system during the last glacial period. The Cariaco record indicates that the intertropical convergence zone migrated seasonally over the site during mild stadial conditions, but was permanently displaced south of the basin during peak stadials and Heinrich events. In the Arabian Sea, we find evidence of a weak Indian summer monsoon during the stadial events. The tropical records show a more variable response to North Atlantic cooling than the Greenland temperature records. We therefore suggest that Greenland climate is especially sensitive to variations in the North Atlantic system-in particular sea-ice extent-whereas the intertropical convergence zone and Indian monsoon system respond primarily to variations in mean Northern Hemisphere temperature.

Stable isotope record of northeastern Australian Margin

Stable isotopic data obtained from planktonic and benthic foraminifers were used to study paleoceanographic changes along the northeastern Australian margin from late Miocene (10 Ma) to Holocene time, and to evaluate the influence of these changes on reef growth. The data indicate that variations in surface-water temperatures may have had an important effect on the reef complexes on the Queensland Plateau and possibly off the northeastern Australian margin. Three sites were studied: Leg 21, Site 209 on the eastern edge of the Queensland Plateau, and Leg 133, Site 811 on the western margin, and Site 817 on the lower southern slope of the plateau. Shallow-water bioclasts recovered from Holes 811A and 817A indicate extensive reef growth on the Queensland Plateau during the middle Miocene (before 12 Ma), signifying surface-water temperatures of 20°C or greater. The amount of reefal detritus produced during the late Miocene (10.0-5.2 Ma) decreased progressively, resulting in a reduction in area of the reef complexes. The isotopic data from planktonic foraminifers in these late Miocene age sediments indicate the presence of relatively cool surface waters (16°-19°C), which may have been a major factor contributing to the demise of the reefs on the Queensland Plateau. Surface waters remained cool until the middle Pleistocene (1.2-0.5 Ma), when the surface-water temperature apparently increased to approximately 25°C, recorded both in the isotopic data and by renewed reef growth. This increase occurred simultaneously (within the error of the age model) with the initiation of the Great Barrier Reef. We propose that cooling of surface waters during the early late Miocene contributed to reef decline on the Queensland Plateau, and that subsequent warming of surface waters during the middle Pleistocene promoted the initiation of reef growth on the northeastern Australian margin. Reef development on the Queensland Plateau never recovered to the middle Miocene extent because of a combination of tectonic (accelerated subsidence of the plateau) and paleoceanographic (the cooler surface waters present from the late Miocene throughout the Pliocene) factors. Variations in seafloor d18O appear to be controlled by regional factors, as indicated by the similarity of data from Sites 811 and 817 to those from Site 590 on Lord Howe Rise.

Temperature reconstruction of sediment cores from the northeastern Arabian Sea

In order to reconstruct the monsoonal variability during the late Holocene we investigated a complete, annually laminated sediment record from the oxygen minimum zone (OMZ) off Pakistan for oxygen isotopes of planktic foraminifera and alkenone-derived sea surface temperatures (SST). Significant SST changes of up to 3°C which cannot be explained by changes in the alkenone-producing coccolithophorid species (inferred from the Gephyrocapsa oceanica / Emiliania huxleyi ratio) suggest that SST changes are driven by changes in the monsoon strength. Our high-(decadal)-resolution data indicate that the late Holocene in the northeastern Arabian Sea was not characterized by a stable uniform climate, as inferred from the Greenland ice cores, but by variations in the dominance of the SW monsoon conditions with significant effects on temperatures. Highest SST fluctuations of up to 3.0°C and 2.5°C were observed for the time interval from 4600 to 3300 years B.P. and during the past 500 years. The significant, short-term SST changes during the past 500 years might be related to climatic instabilities known from the northern latitudes ("Little Ice Age") and confirm global effects. Surface salinity values, reconstructed from delta18O records after correction for temperature-related oxygen isotope fractionation, suggest that in general, the past 5000 years were characterized by higher-than-recent evaporation and more intense SW monsoon conditions. However, between 4600 and 3700 years B.P., evaporation dropped, SW monsoon weakened, and NE monsoon conditions were comparatively enhanced. For the past 1500 years we infer strongly fluctuating monsoon conditions. Comparisons of reconstructed salinity records with ice accumulation data from published Tibetan ice core and Tibetan tree ring width data reveal that during the past 2000 years, enhanced evaporation in the northeastern Arabian Sea correlates with periods of increased ice accumulation in Tibet, and vice versa. This suggests a strong climatic relationship between both monsoon-controlled areas.

Stable isotope ratios of foraminifera from sediment cores off northeastern Brazil

The western South Atlantic boundary currents represent a sensitive system within the global thermohaline circulation (THC). We investigated the impact of deglacial THC changes on the western tropical Atlantic studied in six high resolution sediment cores from the upper continental slope of Brazil. The stratigraphy of the cores is mainly based on 14C AMS dating of monospecific foraminiferal samples. Changes in the upper layer tropical ocean during the deglaciation are inferred from stable oxygen isotope measurements on planktic and benthic foraminifera. Variations in the delta18O residuals are assumed to be mainly temperature related. During the Oldest and Younger Dryas cooling periods, two major deglacial THC disturbances are reported from North Atlantic sediment cores. Concomitant to the repeated THC slowdown, we observe an upper layer warming in the tropical ocean. A reduced northward heat export from the tropical areas during these periods (weak North Brazil Current) is additionally reflected by low meridional gradients in the stable oxygen records. This generally agrees with results from coupled ocean atmosphere models.

Auxiliary material and basic geochemical and benthic foraminiferal stable isotope data for the interval bracketing Eocene Thermal Maximum 2 (ETM2) at DSDP Sites 401 and 550 in the northeastern Atlantic Ocean

Ever since its discovery, Eocene Thermal Maximum 2 (ETM2; ~53.7 Ma) has been considered as one of the "little brothers" of the Paleocene-Eocene Thermal Maximum (PETM; ~56 Ma) as it displays similar characteristics including abrupt warming, ocean acidification, and biotic shifts. One of the remaining key questions is what effect these lesser climate perturbations had on ocean circulation and ventilation and, ultimately, biotic disruptions. Here we characterize ETM2 sections of the NE Atlantic (Deep Sea Drilling Project Sites 401 and 550) using multispecies benthic foraminiferal stable isotopes, grain size analysis, XRF core scanning, and carbonate content. The magnitude of the carbon isotope excursion (0.85-1.10 per mil) and bottom water warming (2-2.5°C) during ETM2 seems slightly smaller than in South Atlantic records. The comparison of the lateral d13C gradient between the North and South Atlantic reveals that a transient circulation switch took place during ETM2, a similar pattern as observed for the PETM. New grain size and published faunal data support this hypothesis by indicating a reduction in deepwater current velocity. Following ETM2, we record a distinct intensification of bottom water currents influencing Atlantic carbonate accumulation and biotic communities, while a dramatic and persistent clay reduction hints at a weakening of the regional hydrological cycle. Our findings highlight the similarities and differences between the PETM and ETM2. Moreover, the heterogeneity of hyperthermal expression emphasizes the need to specifically characterize each hyperthermal event and its background conditions to minimalize artifacts in global climate and carbonate burial models for the early Paleogene.

Physico-chemical parameters of sediment core PG1972-1 (09-Tik-03) from a Tundra Lake, Northeastern Siberia

Thermokarst lakes in the Siberian Arctic contain sediment archives that can be used for paleoenvironmental inference. Until now, however, there has been no study from the inner Lena River Delta with a focus on diatoms. The objective of this study was to investigate how the diatom community in a thermokarst lake responded to past limnogeological changes and what specific factors drove variations in the diatom assemblage. We analysed fossil diatom species, organic content, grain-size distribution and elemental composition in a sediment core retrieved in 2009 from a shallow thermokarst lake in the Arga Complex, western Lena River Delta. The core contains a 3,000-year record of sediment accumulation. Shifts in the predominantly benthic and epiphytic diatom species composition parallel changes in sediment characteristics. Paleoenvironmental and limnogeological development, inferred from multiple biological and sedimentological variables, are discussed in the context of four diatom zones, and indicate a strong relation between changes in the diatom assemblage and thermokarst processes. We conclude that limnogeological and thermokarst processes such as lake drainage, rather than direct climate forcing, were the main factors that altered the aquatic ecosystem by influencing, for example, habitat availability, hydrochemistry, and water level.

Stable isotope record of DSDP Hole 81-552A in the northeastern Atlantic Ocean

Oxygen and carbon isotope ratios in benthic foraminifers have been determined at 10 cm intervals through the top 59 m of DSDP Hole 552A. This provides a glacial record of remarkable resolution for the late Pliocene and Pleistocene. The major glacial event which marked the onset of Pleistocene-like glacial-interglacial alternations was at about 2.4 m.y. ago. These very high-resolution data do not support the notion of significant Northern Hemisphere glaciation between 3.2 and 2.4 m.y. ago.

Tab. 1: Ar40/Ar39 results from Kuyul terrane, northeastern Russia

The Kamchatka Peninsula of northeastern Russia is located along the northwestern margin of the Bering Sea and consists of zones of complexly deformed accreted terranes. Along the northern portion of the peninsula, progressing from then orthwestem Bering Sea inland the Olyutorskiy, Ukelayat, and Koryak superterranes area acreted to the Okhotsk-Chukotsk volcanic-plutonic bell in northern-most Kamchatka. A sedimentary sequence of Albian to Maastrichtian age overlap terranes and units of the Koryak superterrane and constrains their accretion time with this region of the North America plate. Ophiolite complexes, widespread within the Koryak superterrane, are associated with serpentinite melanges and some of the ophiolite terranes include large portions of weakly serpentinized hyperbasites, layered gabbro, sheeted dikes, and pillow basalts outcropping as internally coherent blocks within a sheared melange matrix. Interpretation of magnetic anomalies allow the correlation of the Ukelayat with the West Kamchatka and Sredinny Range superterranes. The Olyutorskiy composite terrane may be correlated with the central and southern Kamchatka Peninsula Litke, Eastern Ranges and Vetlov composite terranes. The most "out-board" of the central and southern Kamchatka Peninsula terranes is the Kronotsky composite terrane, weil exposed along the Kamchatka, Kronotsky and Shipunsky Capes. Using regional geological constraints, paleomagnetism, and plate kinematic models for the Pacific basin a regional model can be proposed in which accretion of the Koryak composite terrane to the North America plate occurs during the Campanian-Maastrichtian, followed by the accretion of the Olyutorskiy composite terrane in the Middle Eocene, and the Late Oligocene-Early Miocene collision of the Kronotsky composite terrane. A revised age estimate of a key overlapping sedirnentary sequence of the Koryak superterrane, calibrated with new Ar40/Ar39 data, supports its Late Cretaceous accretion age.

Pollen and macrofossils profiles and age determination from three cores in Northeastern Kansas, U.S.A.

Two marshes near Muscotah and Arrington, Atchison County, northeastern Kansas, yielded a pollen sequence covering the last 25,000 yrs of vegetation development. The earliest pollen spectra are comparable with surface pollen spectra from southern Saskatchewan and southeastern Manitoba and might indicate a rather open vegetation but with some pine, spruce, and birch as the most important tree species, with local stands of alder and willow. This type of vegetation changed about 23,000 yrs ago to a spruce forest, which prevailed in the region until at least 15,000 yrs ago. Because of a hiatus, the vegetation changes resulting in the spread of a mixed deciduous forest and prairie, which was present in the region from 11,000 to 9,000 yrs ago, remain unknown. Prairie vegetation, with perhaps a few trees along the valleys, covered the region until about 5,000 yrs ago, when a re-expansion of deciduous trees began in the lowlands.

Neptunian dikes and their fillings in carbonates of the Warstein area (northeastern Rhenish massif)

Neptunian dikes and cavities as weil as their fillings are described from Middle to Upper Devonian carbonates of the Warstein area. The genesis of the pre-Upper Carboniferous dikes is due to pre-orogenic synsedimentary tensional movements. Lifting, subsidence and tilting caused joints and cracks, which are enlarged to dikes and cavities on submarine conditions. The post-Upper Carboniferous dikes are based on the orogenesis during Upper Carboniferous time, causing numerous tectonical divisional planes in the sediments. Along these planes a far-reaching karstification took place since mesozoic time. According to their size the cavities are subdivided into macro-, mega- and microdikes. With the exception of one macrodike all the others are limited to the massive limestone. Megadikes especially occur in Upper Devonian cephalopod limestone and in the Erdbach limestone, microdikes can be found in all carbonatic rocks. The dikes follow pre-orogenic, tectonical and sedimentary divisional planes and are orientated to ac-, bc- as well as bedding planes and diagonal directions. The fillings happened down from above either in a solitary event or repeatedly in long-lived dikes during a span of several ten millions of years. More seldom the fillings took place laterally or upside from beneath. The dikes contain - without regard to autochthonous conodont faunas - older and/or younger mixed faunas, too. Occasionally they were used as life district by a trilobite fauna adapted to the dikes. The dikes represent sedimentary pitfalls and conserve sediments eroded in other places. Therefore, by aid of the fillings, it can be demonstrated, that stratigraphic gaps are not absolutely due to primary interruptions of sedimentation, but were caused by reworking. Some dikes contain the distal offsets of slides and suspension streams. Relations between condensation and development of dikes could not be derived in the Warstein area. However, an increase of the frequency of dikes towards east to the eastern margin of the Warstein carbonate platform could be pointed out. This margin is a slope, persisting more than 10 millions of years, between a block and a basin. Evidently cracks and dikes, which were caused by settlements, slides and earth quakes, occured there frequently. The Warstein dikes and cavities, caused by karstification, are filled with terrestrial Lower Cretaceous, marine Upper Cretaceous and terrestrial Pleistocene to Holocene sediments. Tertiary sediments could not be detected.

(Table 1) Primary production and chlorophyll a concentration in the Northeastern Tropical Atlantic

Results of simultaneous determinations of chlorophyll "a" concentrations and primary production in the northeastern part of the Tropical Atlantic in spring 1977 are discussed. Primary production was low (250-350 mg C/m**2/day in the open parts of the ocean and high (600-1500 mg C/m**2/day) mainly in zones of current divergences and coastal region of the West Africa. Chlorophyll "a" concentration throughout the euphotic zone varied from 6 to 36 mg/m**3 and in the surface layer from 0.05 to 0.60 mg/m**3. Uneven distribution of primary production is due to physiological condition of phytoplankton.