Pollen and macroremains from profiles from site Osterholz and Elm

The biostratigraphic classification of the Pleistocene in north-western and central Europe is still insufficiently known, in spite of numerous geological and vegetation-history investigations. The question is not even clear, for example, how often a warm-period vegetation with thermophilous trees such as Quercus, Ulmus, Tilia, Carpinus etc could develop here. In past years, on the basis of several geological and vegetation-history findings, suspicion has often been expressed that some of the classical stages of the Pleistocene could include more warm periods than heretofore assumed, and as a result of recent investigations the period between the Waal and Holstein interglacials seems to include at least two warm periods, of which the Cromer is one. This paper contributes to this problem. The interglacial sediments coming from the Elm-Mountains near Brunswick and from the Osterholz near Elze - both within the limits of the German Mittelgebirge - were investigated by pollen analysis. In both cases a Pinus-Betula zone and a QM zone were found. The vegetation development of the Pinus-Betula zone is characterized in both sequences by the early appearance of Picea. Because of strong local influence at the Osterholz a detailed correlation is difficult. However, vegetation development at the time of the QM zone at both sites was similar; it is especially characterized by the facts that Ulmus clearly migrated to the site earlier than Quercus and was very abundant throughout this time. Furthermore, both diagrams show very low amounts of Corylus. The interglacial of the Osterholz shows in addition to the above; a Carpinus-QM-Picea-zone in which Eucommia reaches a relative high value and in the upper of which Azolla filiculoides was also found. The similarity of vegetation development justifies acceptance of the same age for the occurrences. A comparison of the vegetation development at the Elm and the Osterholz with those of the Eem, Holstein, Waal, and Tegelen warm periods as well as with all the Cromer sites so far investigated shows that only a correlation with the Cromer Complex is possible. This correlation is supported by the geologic relations in the Osterholz (the deposit is overlain by Elster till). Therefore the till-like material with Scandinavian rock fragments underlying the deposit at Elm is of particular interest. The 'Rhume' interglacial beds at Bilshausen, only 60 km south of Osterholz, is also assigned to the Cromer complex, but the two deposits cannot be of the same age because the vegetation development differs. Therefore the Cromer complex must include at least two warm periods. Further conclusions about the relative stratigraphic position of these two occurrences and correlations of other Cromer sites are at this time not possible, however.

Geochemistry of the sheeted dike complex at Pito Deep

Alteration of sheeted dikes exposed along submarine escarpments at the Pito Deep Rift (NE edge of the Easter microplate) provides constraints on the crustal component of axial hydrothermal systems at fast spreading mid-ocean ridges. Samples from vertical transects through the upper crust constrain the temporal and spatial scales of hydrothermal fluid flow and fluid-rock reaction. The dikes are relatively fresh (average extent of alteration is 27%), with the extent of alteration ranging from 0 to >80%. Alteration is heterogeneous on scales of tens to hundreds of meters and displays few systematic spatial trends. Background alteration is amphibole-dominated, with chlorite-rich dikes sporadically distributed throughout the dike complex, indicating that peak temperatures ranged from <300°C to >450°C and did not vary systematically with depth. Dikes locally show substantial metal mobility, with Zn and Cu depletion and Mn enrichment. Amphibole and chlorite fill fractures throughout the dike complex, whereas quartz-filled fractures and faults are only locally present. Regional variability in alteration characteristics is found on a scale of <1-2 km, illustrating the diversity of fluid-rock interaction that can be expected in fast spreading crust. We propose that much of the alteration in sheeted dike complexes develops within broad, hot upwelling zones, as the inferred conditions of alteration cannot be achieved in downwelling zones, particularly in the shallow dikes. Migration of circulating cells along rides axes and local evolution of fluid compositions produce sections of the upper crust with a distinctive character of alteration, on a scale of <1-2 km and <5-20 ka.

Sea surface temperature estimation for the last 70 ka from IODP Site 306-U1313

During the six Heinrich Events of the last 70 ka episodic calving from the circum-Atlantic ice sheets released large numbers of icebergs into the North Atlantic. These icebergs and associated melt-water flux are hypothesized to have led to a shutdown of Atlantic Meridional Overturning Circulation (AMOC) and severe cooling in large parts of the Northern Hemisphere. However, due to the limited availability of high-resolution records the magnitude sea surface temperature (SST) changes related to the impact of Heinrich Events on the mid-latitude North Atlantic is poorly constrained. Here we present a record of UK37'-based SSTs derived from sediments of Integrated Ocean Drilling Project (IODP) Site U1313, located at the southern end of the ice-rafted debris (IRD)-belt in the mid-latitude North Atlantic (41°N). We demonstrate that all six Heinrich Events are associated with a rapid warming of surface waters by 2 to 4°C in a few thousand years. The presence of IRD leaves no doubt about the simultaneous timing and correlation between rapid surface water warming and Heinrich Events. We argue that this warming in the mid-latitude North Atlantic is related to a northward expansion of the subtropical gyre during Heinrich Events. As a wide-range of studies demonstrated that in the central IRD-belt Heinrich Events are associated with low SSTs, these results thus identify an anti-phased (seesaw) pattern in SSTs during Heinrich Events between the mid-latitude (warm) and northern North Atlantic (cold). This highlights the complex response of surface water characteristics in the North Atlantic to Heinrich Events that is poorly reproduced by fresh water hosing experiments and challenges the widely accepted view that within the IRD-belt of the North Atlantic Heinrich Events coincide with periods of low SSTs.

Geochemistry of ODP Site 135-834 basalts

New major, trace element, and isotope data (Pb, Sr, and Nd) reveal an impressive compositional variation in the basalts recovered from Site 834. Major element compositions span almost the entire range observed in basalts from the modern axial systems of the Lau Basin, and variations are consistent with low-pressure fractionation of a mid-ocean-ridge-basalt (MORB)-like parent, in which plagioclase crystallization has been somewhat suppressed. Trace element compositions deviate from MORB in all but one unit (Unit 7) and show enrichments in large-ion-lithophile elements (LILEs) relative to high-field-strength elements (HFSEs) more typically associated with island-arc magmas. The Pb-isotope ratios define linear trends that extend from the field of Pacific MORB to highly radiogenic values similar to those observed in rocks from the northernmost islands of the Tofua Arc. The Sr-isotope compositions also show significant variation, and these too project from radiogenic values back into the field for Pacific MORB. The variations in key trace element and isotopic features are consistent with magma mixing between two relatively mafic melts: one represented by Pacific MORB, and the other by a magma similar to those erupted on 'Eua when it was part of the original Tongan arc, or perhaps members of the Lau Volcanic Group (LVG). Based on our model, the most radiogenic compositions (Units 2 and 8) represent approximately 50:50 mixtures of these MORB and arc end-members. Magma mixing requires that both components are simultaneously available, and implies that melts have not shown a compositional progression from arc-like to MORB-like with extension at this locality. Rather, it is apparent that essentially pristine MORB can erupt as one of the earliest products of backarc initiation. Indeed, repetition of isotopic and trace element signatures with depth suggests that eruptions have been triggered by periodic injections of fresh MORB melts into the source regions of these magmas. The slow and almost amagmatic extension of the original arc complex envisaged to explain the observed chemistry is also consistent with the horst-and-graben topography of the western side of the Lau Basin. Given the similarities between basalts erupted at the modern Lau Basin spreading centers and MORB from the Indian Ocean, the overwhelming evidence for involvement of mantle similar to Pacific MORB in the petrogenesis of basalts from Site 834 is a new and important observation. It indicates that the original arc was underlain by asthenospheric material derived from the Pacific mantle convection cell, and that this has somehow been replaced by Indian Ocean MORB during the last ~5.5 Ma.

Sedimentology and Cd/Ca ratios of benthic foraminifera from ODP Site 172-1060 in the western Nort Atlantic

The Western Boundary Undercurrent (WBUC), off eastern America, is an important component of the Atlantic Meridional Overturning circulation and is the principal route for southward transport of North Atlantic waters and southward return of Southern Source Water (SSW). Here a direct flow speed proxy (mean grain size of the sortable silt) is used to infer the vigour of flow of the palaeo-WBUC at Blake Outer Ridge, (ODP Site 1060, depth 3481 m) during Marine Isotope Stage (MIS) 3. The overall shape of the flow speed proxy record shows a complex pattern of variability, with generally more vigorous flow and larger-scale flow variations between 35 and 60 ka than in the younger part of MIS 3 and MIS 2 (b35 ka). Six events of reduced bottom flow vigour (Slow Events, SEs) occur. These appear uncorrelated with Heinrich events, but are instead synchronous with the warming phases of Antarctic Warm Events A-1 to A-4 (with one new one, A-1a and one poorly defined, 'A-0'). This indicates that Antarctic climate exerts a stronger control on deep flow vigour in the North Atlantic during MIS 3 than Northern Hemisphere climate. The correspondence of SEs with Antarctic warming suggests a weaker WBUC flow due to reduced volume flux at SSW source or reduced SSW density. Because the variability of the lower limb of the WBUC was not connected to sharp North Atlantic changes in temperature, it is unlikely that the Dansgaard/Oeschger cycles were associated with a mode of MOC variation involving wholeocean overturn, but more likely with perturbations of only the shallow Glacial Gulf Stream-Glacial Northern Source Intermediate Water cell. Nutrient proxies (benthic carbon isotopes and Cd/Ca of Uvigerina peregrina) at this site show similar trends to the GRIP delta18O record. This correlation has previously been attributed mainly to hydrographic and flow changes but is here shown to be better explained by variations in surface ocean productivity and subsequent decomposition of 12C rich organic material on the sea floor.

Dinoflagellate abundance and events of ODP Site 189-1172 sediments

Palynomorphs were studied in samples from Ocean Drilling Program (ODP) Leg 189, Holes 1172A and 1172D (East Tasman Plateau; 2620 m water depth). Besides organic walled dinoflagellate cysts (dinocysts), broad categories of other palynomorphs were quantified in terms of relative abundance. In this contribution, we provide an overview of the dinocyst distribution from the Maastrichtian to lowermost Oligocene and Quaternary intervals and illustrate main trends in palynomorph distribution. The uppermost Cretaceous-lowermost Oligocene succession of Site 1172 has a confident biomagnetostratigraphy, enabling us to tie early Paleogene Southern Hemisphere dinocyst events to the geomagnetic polarity timescale for the first time. Dinocyst species from the Maastrichtian to earliest Oligocene at Site 1172 are largely endemic ("Transantarctic Flora") or bipolar; cosmopolitan taxa are present in the background as well. The Maastrichtian-early late Eocene dinocyst assemblages are indicative of shallow-marine to restricted marine, pro-deltaic conditions, closely tied to a massive siliciclastic sequence. By middle late Eocene times (~35.5 Ma), the siliciclastic sequence gave way to a thin glauconitic unit, considered to reflect the deepening of the Tasmanian Gateway. This transition coincides with the most prominent change in dinocyst associations of the Paleogene. The turnover is inferred to reflect a change from marginal marine to more offshore conditions, with increased winnowing and oxidation. Overlying pelagic carbonate ooze of middle early Oligocene and younger age is virtually barren of organic microfossils, although Quaternary assemblages have been recovered. This aspect is taken to reflect average low sedimentation rates and well-oxygenated water masses during most of the Oligocene and Neogene. The few palynologically productive samples from the Oligocene-Quaternary interval have a stronger cosmopolitan to subtropical signature, with warm-water species being common to abundant.

Porewater concentrations, pH, single cell number, anaerobic oxidation of methane (AOM) rate, sulfate reduction (SR) rate of samples during METEOR cruise M76/3b at the REGAB cold seep site from the West African margin in 2008

The giant pockmark REGAB (West African margin, 3160 m water depth) is an active methane-emitting cold seep ecosystem, where the energy derived from microbially mediated oxidation of methane supports high biomass and diversity of chemosynthetic communities. Bare sediments interspersed with heterogeneous chemosynthetic assemblages of mytilid mussels, vesicomyid clams and siboglinid tubeworms form a complex seep ecosystem. To better understand if benthic bacterial communities reflect the patchy distribution of chemosynthetic fauna, all major chemosynthetic habitats at REGAB were investigated using an interdisciplinary approach combining porewater geochemistry, in situ quantification of fluxes and consumption of methane, as well bacterial community fingerprinting. This study revealed that sediments populated by different fauna assemblages show distinct biogeochemical activities and are associated with distinct sediment bacterial communities. The methane consumption and methane effluxes ranged over one to two orders of magnitude across habitats, and reached highest values at the mussel habitat, which hosted a different bacterial community compared to the other habitats. Clam assemblages had a profound impact on the sediment geochemistry, but less so on the bacterial community structure. Moreover, all clam assemblages at REGAB were restricted to sediments characterized by complete methane consumption in the seafloor, and intermediate biogeochemical activity. Overall, variations in the sediment geochemistry were reflected in the distribution of both fauna and microbial communities; and were mostly determined by methane flux.

Palynology, source vegetation, environment and age of ODP Site 188-1166 sediments

Twenty-three core catcher samples from Site 1166 (Hole 1166A) in Prydz Bay were analyzed for their palynomorph content, with the aims of determining the ages of the sequence penetrated, providing information on the vegetation of the Antarctic continent at this time, and determining the environments under which deposition occurred. Dinocysts, pollen and spores, and foraminiferal test linings were recovered from most samples in the interval from 142.5 to 362.03 meters below seafloor (mbsf). The interval from 142.5 to 258.72 mbsf yielded palynomorphs indicative of a middle-late Eocene age, equivalent to the lower-middle Nothofagidites asperus Zone of the Gippsland Basin of southeastern Australia. The Prydz Bay sequence represents the first well-dated section of this age from East Antarctica. Dinocysts belonging to the widespread "Transantarctic Flora" give a more confident late Eocene age for the interval 142.5-220.5 mbsf. The uppermost two cores within this interval, namely, those from 142.5 and 148.36 mbsf, show significantly higher frequencies of dinocysts than the cores below and suggest that an open marine environment prevailed at the time of deposition. The spore and pollen component may reflect a vegetation akin to the modern rainforest scrubs of Tasmania and New Zealand. Below 267 mbsf, sparse microfloras, mainly of spores and pollen, are equated with the Phyllocladidites mawsonii Zone of southeastern Australia, which is of Turonian to possibly Santonian age. Fluvial to marginal marine environments of deposition are suggested. The parent vegetation from this interval is here described as "Austral Conifer Woodland." The same Late Cretaceous microflora occurs in two of the cores above the postulated unconformity at 267 mbsf. In the core at 249.42 mbsf, the Late Cretaceous spores and pollen are uncontaminated by any Tertiary forms, suggesting that a clast of this older material has been sampled; such a clast may reflect transport by ice during the Eocene. At 258.72 mbsf, Late Cretaceous spores and pollen appear to have been recycled into the Eocene sediments.

Biosiliceous sedimentation at ODP Site 128-798

Upper Pliocene through Holocene sediments recovered at Site 798 in the Japan Sea (Oki Ridge) exhibit rhythmic variation in weight percent biogenic opal at intervals of ~5 m and periods equivalent to the 41-k.y. obliquity cycle. Variance at 17 and 100 k.y. is observed prior to 1.3 Ma. These cycles are also clearly defined by log data and correspond to clusters of decimeter-scale dark-colored sediment units alternating with clusters of light-colored units. Opal content varies between 3% and 22% between 0 and 1.3 Ma and from 3% to 43% between 1.3 and 2.6 Ma. Long-term opal accumulation rates average 1.8 g/cm**2/k.y. in the late Pliocene/early Pleistocene and decrease by about 60% at ~1.3 Ma. Rough calculations suggest that opal accumulation rates increased and terrigenous flux decreased during the Holocene relative to the last glacial period. Our age control is not yet sufficient to allow a similar analysis of the 41-k.y. cyclicity in opal content throughout the Pleistocene. Stable isotope results from planktonic foraminifers confirm previous suggestions of a strong surface-water freshening event during isotope stage 2; however, this episode appears to be unique during the Pleistocene. Benthic foraminifers are depleted in 18O during parts of glacial stages 2 and 6 relative to adjacent interglacials, suggesting unusual warming and/or freshening of deep waters. Collectively, the stable isotope and %opal data are consistent with continuing isolation of the Japan Sea during the Quaternary with important transitions occurring at 1.3, 0.7 to 1.0, and 0.2 to 0.3 Ma. Complex relationships among the stable isotope results, %opal data, and sediment characteristics such as color and organic and inorganic carbon content preclude development of a simple model to explain cyclical sedimentation. Opal maxima occur within both light and dark intervals and the processes that control surface-water productivity are at times decoupled from the factors that regulate deep-water dysaerobia. We suggest that water column overturn is controlled largely by regional atmospheric circulation that must also have an as yet poorly understood effect on surface-water fertility.