Chemical composition of bottom sediments and interstitial waters from DSDP Sites 252, 285, 315, 317, 336, and 386

Six Deep Sea Drilling Project (DSDP) Sites (252, 285, 315, 317, 336, 386) were examined for the chemical composition of the dissolved salts in interstitial waters, the oxygen isotopic composition of the interstitial waters, and the major ion composition of the bulk solid sediments. An examination of the concentration-depth profiles of dissolved calcium, magnesium, potassium, and H218O in conjunction with oxygen isotope mass balance calculations confirms the hypothesis that in DSDP pelagic drill sites concentration gradients in Ca. Mg. K, and H218O are largely due to alteration reactions occurring in the basalts of Layer 2 and to alteration reactions involving volcanic matter dispersed in the sediment column. Oxygen isotope mass balance calculations require substantial alteration of Layer 2 (up to 25% of the upper 1000 m). but only minor exchange of Ca, Mg, and K occurs with the overlying ocean. This implies that alteration reactions in Layer 2 are almost isochemical.

Chemistry of interstitial water of samples from DSDP Leg 38

Interstitial waters recovered during Leg 38 show large changes in major ion composition and also in oxygen isotope composition. Increases in Ca[++] and Sr[++] and decreases in K[+], Mg[++], and O18/O16 are interpreted in terms of extensive diagenesis of terrigenous, volcanic, or basaltic igneous materials in the sediments and underlying basalts. Slight, but well-established increases in chlorinity with depth indicate that these postulated weathering reactions involve uptake of water to a measurable extent. Interstitial waters from sites drilled on the Inner Voring Plateau suggest the infusion of fresh waters by aquifers from the mainland of Norway.

Magnetic properties of Cenozoic MORB and Cretaceous MORB from DSDP and ODP holes

The fact that the natural remanent magnetization (NRM) intensity of mid-oceanic-ridge basalt (MORB) samples shows systematic variations as a function of age has long been recognized: maximum as well as average intensities are generally high for very young samples, falling off rather rapidly to less than half the recent values in samples between 10 and 30 Ma, whereupon they slowly rise in the early Tertiary and Cretaceous to values that approach those of the very young samples. NRM intensities measured in this study follow the same trends as those observed in previous publications. In this study, we take a statistical approach and examine whether this pattern can be explained by variations in one or more of all previously proposed mechanisms: chemical composition of the magnetic minerals, abundance of these magnetization carriers, vectorial superposition of parallel or antiparallel components of magnetization, magnetic grain or domain size patterns, low-temperature oxidation to titanomaghemite, or geomagnetic field behavior. We find that the samples do not show any compositional, petrological, rock-magnetic, or paleomagnetic patterns that can explain the trends. Geomagnetic field intensity is the only effect that cannot be directly tested on the same samples, but it shows a similar pattern as our measured NRM intensities. We therefore conclude that the geomagnetic field strength was, on-average, significantly greater during the Cretaceous than during the Oligocene and Miocene.

Chemical composition and isotopic ratios of basic lavas from Iceland and the surrounding ocean floor

Major and trace dement data are used to establish the nature and extent of spatial and temporal chemical variations in basalts erupted in the Iceland region of the North Atlantic Ocean. The ocean floor samples are those recovered by legs 38 and 49 of the Deep Sea Drilling Project. Within each of the active zones on Iceland there are small scale variations in the light rare earth elements and ratios such as K/Y: several central complexes and their associated fissure swarms erupt basalts with values of K/Y distinct from those erupted at adjacent centres; also basalts showing a wide range of immobile trace element ratios occur together within single vertical sections and ocean floor drill holes. Although such variations can be explained in terms of the magmatic processes operating on Iceland they make extrapolations from single basalt samples to mantle sources underlying the outcrop of the sample highly tenuous. 87Sr/86Sr ratios measured for 25 of the samples indicate a total range from 0.7028 in a tholeiite from the Reykjanes Ridge to 0.7034 in an alkali basalt from Iceland and are consistent with other published ratios from the region. A positive correlation between 87Sr/86Sr and Ce/Yb ratios indicates the existence of systematic isotopic and elemental variations in the mantle source region. An approximately fivefold variation in Ce/Yb ratio observed in basalts with the same 87Sr/86Sr ratio implies that different degrees and types of partial melting have been involved in magma genesis from a single mantle composition. 87Sr/86Sr ratios above 0.7028, Th/U ratios close to 4 and La/Ta ratios close to 10 distinguish most basalts erupted in this part of the North Atlantic Ocean from normal mid-ocean ridge basalt (N-type MORB) - although N-type MORB has been erupted at extinct spreading axes just to the north and northeast of Iceland as well as the presently active Iceland-Jan Mayen Ridge. Comparisons with the hygromagmatophile element and radiogenic isotope ratios of MORB and the estimated primordial mantle indicate that the mantle sources producing Iceland basalts have undergone previous depletion followed by more recent enrichment events. A veined mantle source region is proposed in preference to the mantle plume model to explain the chemical variations.

Global cooling during the Eocene Oligocene Transition

About 34 million years ago, Earth's climate shifted from a relatively ice-free world to one with glacial conditions on Antarctica characterized by substantial ice sheets. How Earth's temperature changed during this climate transition remains poorly understood, and evidence for Northern Hemisphere polar ice is controversial. Here, we report proxy records of sea surface temperatures from multiple ocean localities and show that the high-latitude temperature decrease was substantial and heterogeneous. High-latitude (45 degrees to 70 degrees in both hemispheres) temperatures before the climate transition were ~20°C and cooled an average of ~5°C. Our results, combined with ocean and ice-sheet model simulations and benthic oxygen isotope records, indicate that Northern Hemisphere glaciation was not required to accommodate the magnitude of continental ice growth during this time.

(Table 5) Quaternary paleoproductivity of organic carbon in oceans based on DSDP cores

By analogy with the present-day ocean, primary productivity of paleoceans can be reconstructed using calculations based on content of organic carbon in sediments and their accumulation rates. Results of calculations based on published data show that primary productivity of organic carbon, mass of phosphorus involved in the process, and content of phosphorus in ocean waters were relatively stable during Cenozoic and Late Mesozoic. Prior to precipitation on the seafloor together with biogenic detritus, dissolved phosphorus could repeatedly be involved in the biogeochemical cycle. Therefore, only less than 0.1% of phosphorus is retained in bottom sediments. Bulk phosphorus accumulation rate in ocean sediments is partly consistent with calculated primary productivity. Some epochs of phosphate accumulation also coincide with maxima of primary productivity and minima of the fossilization coefficient of organic carbon. The latter fact can testify to episodes of acceleration of organic matter mineralization and release of phosphorus from sediments leading to increase in the phosphorus reserve in paleoceans and phosphate accumulation in some places.

Occurrence of hiatuses PH and NH 1 through NH 7 in DSDP holes

Miocene paleoceanographic evolution exhibits major changes resulting from the opening and closing of passages, the subsequent changes in oceanic circulation, and development of major Antarctic glaciation. The consequences and timing of these events can be observed in variations in the distribution of deep-sea hiatuses, sedimentation patterns, and biogeographic distribution of planktic organisms. The opening of the Drake Passage in the latest Oligocene to early Miocene (25-20 Ma) resulted in the establishment of the deep circumpolar current, which led to thermal isolation of Antarctica and increased global cooling. This development was associated with a major turnover in planktic organisms, resulting in the evolution of Neogene assemblages and the eventual extinction of Paleogene assemblages. The erosive patterns of two widespread hiatuses (PH, 23.0-22.5 Ma; and NH 1, 20-18 Ma) indicate that a deep circumequatorial circulation existed at this time, characterized by a broad band of carbonate-ooze deposition. Siliceous sedimentation was restricted to the North Atlantic and a narrow band around Antarctica. A major reorganization in deep-sea sedimentation and hiatus distribution patterns occurred near the early/middle Miocene boundary, apparently resulting from changes in oceanic circulation. Beginning at this time, deep-sea erosion occurred throughout the Caribbean (hiatus NH 2, 16-15 Ma), suggesting disruption of the deep circumequatorial circulation and northward deflection of deep currents, and/or intensification of the Gulf Stream. Sediment distribution patterns changed dramatically with the sudden appearance of siliceous-ooze deposition in the marginal and east equatorial North Pacific by 16.0 to 15.5 Ma, coincident with the decline of siliceous sedimentation in the North Atlantic. This silica switch may have been caused by the introduction of Norwegian Overflow Water into the North Atlantic acting as a barrier to outcropping of silica-rich Antarctic Bottom Water. The main aspects of the present oceanic circulation system and sediment distribution pattern were established by 13.5 to 12.5 Ma (hiatus NH 3), coincident with the establishment of a major East Antarctic ice cap. Antarctic glaciation resulted in a broadening belt of siliceous-ooze deposition around Antarctica, increased siliceous sedimentation in the marginal and east equatorial North Pacific and Indian Oceans, and further northward restriction of siliceous sediments in the North Atlantic. Periodic cool climatic events were accompanied by lower eustatic sea levels and widespread deep-sea erosion at 12 to 11 Ma (NH 4), 10 to 9 Ma (NH 5), 7.5 to 6.2 Ma (NH 6), and 5.2 to 4.7 Ma (NH 7).

Chemical composition of bottom sediments and rocks from DSDP Holes 3-14 through 64-477

Data on analyses of chemical composition of DSDP samples of bottom sediments and rocks carried out in P.P. Shirshov Institute of Oceanology are reported. Basal sediments and sedimentary rocks prevail in the sample set.

Chemical composition of glauconite and montmorillonite group minerals from sediments and rocks of the Norwegian Sea

Two quadrupole splitting doublets with delta E_q = 0.74 and 1.62 mm/s were found in the montmorillonite spectra. The more intense doublet corresponds to iron in a somewhat distorted tetrahedral coordination, while the less intense corresponds to quadri-coordinated iron. The EPR spectrum also exhibits two lines with a q-factor of 3 and 4.3, which corresponds to transformed minerals.

Morphology of Cycladophora davisiana davisiana from the Atlantic Ocean

In recent years, temporal fluctuations in the abundance of C. d. davisiana have been used frequently as a highresolution stratigraphic and paleoenvironmental tool. The modern ecology and morphologic variation (temporal and geographic) of this radiolarian species is evaluated to ascertain its potential stratigraphic and paleoenvironmental significance. Statistics were obtained on the width and height of all C. d. davisiana segments from Pleistocene populations of differing ages from the Northern Hemisphere (Labrador Sea and Iceland-Faeroe Ridge) and Southern Hemisphere (Namibian shelf and Meteor Rise). Results reveal that segment height variations between and within populations are more conservative than segment width. The mean sizes of the thorax and first abdominal segment have distinguishable differences between C. d. davisiana found in the North and South Atlantic. All populations have no significant difference in first abdominal segment width, however, mean heights of this segment differ greatly between populations of the North and South Atlantic. Second abdominal segment sizes show no clear population grouping. Size differences in post-cephalic segment size of these populations would appear to be related to some isolation of gene pools and possibly unknown paleoenvironmental factors. Temporal changes in the postcephalic size of C. d. davisiana may be used to: (1) identify temporally equivalent peaks in abundance of the species in a given region, (2) possibly evaluate the degree of mixing of water'masses between regions, and (3) trace the initial spread of the species from its area of origin. Cleve's 1887 plankton samples, between Greenland and Spitzsbergen, were studied and used in conjunction with other data to make the following conclusions on the modern ecology of C. d. davisiana in the Arctic and Greenland-Norwegian Seas. (1) It is presently absent in surface water plankton samples, (2) it currently lives at depths below 500 m, where it is rare, (3) it does not live in the upper 200 m under Arctic ice but is rare at greater depths, (4) it is absent in the upper 200 m near permanent Greenland Sea ice where normal oceanic salinity prevails, and (5) it is most common in deep marginal fjord environments which may serve as a refuge for the species during interglacial periods. In the Atlantic Ocean, the abundance of C. d. davisiana does not exceed 1% of the assemblage between the Subtropical Convergence of each hemisphere. In the Norwegian and Labrador Seas the species may occasionally be in the range of 1-5% of the modern radiolarian assemblage and never more than 5% in the southern high latitudes. Apparently only in the modern Sea of Okhotsk, does the species presently occur in high abundance. We concur with Morley and Hays (1983) that increased abundances are likely caused by the development of a strong low-salinity surface layer associated with seasonal sea ice melting and a strong temperature minimum above warmer and higher salinity intermediate waters. Similar conditions were frequent during the Pleistocene in the high latitudes and its modern scarcity outside the Sea of Okhotsk must be related to the absence of the presently unique conditions in the latter region.

Magnetic properties of the oceanic igneous rocks (Table 1)

Hysteresis measurements have been carried out on a suite of ocean-floor basalts with ages ranging from Quaternary to Cretaceous. Approximately linear, yet separate, relationships between coercivity (Bc) and the ratio of saturation remanence/saturation magnetization (Mrs/Ms) are observed for massive doleritic basalts with low-Ti magnetite and for pillow basalts with multi-domain titanomagnetites (with x= 0.6). Even when the MORB has undergone lowtemperature oxidation resulting in titanomaghemite, the parameters are still distinguishable, although offset from the trend for unoxidized multidomain titanomagnetite. The parameters for these iron oxides with different titanium content reveal contrasting trends that can be explained by the different saturation magnetizations of the mineral types. This plot provides a previously underutilized and non-destructive method to detect the presence of low-titanium magnetite in igneous rocks, notably MORB.