Geochemistry on sediment core Co1014 from Rauer Group, Antarctica

The history of glacial advances and retreats of the East Antarctic ice sheet during the Holocene is not well-known, due to limited field evidence in both the marine and terrestrial realm. A 257-cm-long sediment core was recovered from a marine inlet in the Rauer Group, East Antarctica, 1.8 km in front of the present ice-sheet margin. Radiocarbon dating and lithological characteristics reveal that the core comprises a complete marine record since 4500 yr. A significant ice-sheet expansion beyond present ice margins therefore did not occur during this period.

Stable carbon isotope compositions and concentrations of biphytanes from IODP Hole 311-U1327C and 311-U1328B

We have investigated the distributions and carbon isotopic compositions of archaeal membrane lipids in gas-hydrate-bearing sediments collected from the northern Cascadia Margin offshore from Vancouver Island (Sites U1327 and U1328) by the R/V JOIDES Resolution during IODP Expedition 311. Archaeal lipid biomarkers, including glycerol dialkyl glycerol tetraethers (GDGTs), tend to become abundant below 100 mbsf (meters below sea floor). Tricyclic biphytane (BP[3]; which is a robust biomarker derived from GDGT), crenarchaeol, and other BPs exhibit d13C values of ca. -20 per mil, and become abundant between 130 and 230 mbsf at Site U1328. In this depth range, concentrations of ammonium and phosphate in interstitial waters also increase, suggesting that a larger population and higher activity of heterotrophic community consisting of crenarchaeota and other archaea decompose the sedimentary organic matter, thereby liberating ammonium and phosphate. Such crenarchaeotic activity can produce other metabolic products such as molecular hydrogen by fermentation of organic matter during diagenesis. Furthermore, near the organic matter decomposition zone (130 to 230 mbsf), a probable methanogen biomarker (13C-depleted BP[1] with d13C values as low as -48.8 per mil) becomes abundant, indicating that methanogens utilize these diagenetic products. The molecular and isotopic distributions of archaeal lipid biomarkers indicate that the archaeal community plays an important role in the biogeochemical cycles of deep-sea sediments, including both methanogenesis and nutrient recycling.

Lithology, age determination and pollen records of five profiles for nothern Bavaria, Germany

Palynological investigations in northeastern Bavaria (Bavarian Vogtland, Fichtelgebirge, Steinwald) reveal the Late Glacial and Postglacial history of the regional vegetation. Radiocarbon data in comparison with those from the neighbouring regions (Rhön, Oberpfälzer Wald, Bavarian Forests) show a time lag in the development of the arboreal vegetation due to migration processes. The Fichtelgebirge is the southernmost part ofnortheastern Bavaria where the early Alleröd period (pollen zone IIa) is characterised by a dominance of birch forests. Hazel reached maximal values around 8000 BP in the area from the Fichtelgebirge to the Bavarian Forests, e.g. about 600 years earlier than in the more northern Rhön mountains. For spruce there is a considerable time lag between the Bavarian Forests and the Fichtelgebirge. Spruce spreading started in the Fichtelgebirge during the older part of the Atlantic period (pollen zone VI). At the same time, spruce already was the dominant tree in the Bavarian Forests. During the younger part of the Atlantic period (pollen zone VII) spruce and mixed oak forest tree species frequently occurred in the Fichtelgebirge. At the end of pollen zone VI, spruce came to dominance. At the same time, the immigration of beech started. During the Subboreal period (pollen zone VIII), spruce remained being a dominant member in the forests and at the end of pollen zone VIII, fir began to spread rapidly. During the first part of the Subatlantic period (pollen zone IX) spruce, beech, fir and pine formed the mountainous forests in the Fichtelgebirge. In the area of the Bavarian Vogtland, however, fir was a dominant forest tree during pollen zone IX, while spruce and beech played a less important role. During the 12th century, human colonisation started in the area of the Fichtelgebirge. This is 400 years later as in the area of the Rhön mountains. Indicators for earlier forest clearances are rare or absent.

Age determination and stable isotope record of planktonic foraminifera from sediments of the Baffin Shelf

Stable isotopic values on planktonic foraminifera in a suite of cores from basins across the SE Baffin Shelf are used to extract a record of meltwater events during Termination I deglaciation. Resolution and Hatton basins lie on the SE Baffin Shelf at water depths > 500 m, seaward of major conduits for ice drainage from the eastern sector of the Laurentide Ice Sheet (LIS). Accelerator mass spectrometry 14C dates are used to constrain our chronology of events in ten cores. In Resolution Basin, three cores have 14C AMS dates on foraminifera of > 20 ka at their bases; whereas Hatton Basin cores terminate in sediments < 13 kyr. Sedimentation rates varied between 0.1 to 4.5 m/ka. Stable oxygen and carbon isotopic ratios were obtained on 146 samples of the planktonic foraminifera Neogloboquadrina pachyderma (Ehrenberg) sinistral, from seven of the ten cores. No evidence was found to indicate that test morphology or size affected delta18O. Between 7 and 13.5 ka the surface water on the shelf was on average 1 per mil lower than the open ocean signal. Significant temporal variations were found in both delta18O and delta13C. Evidence for significant low delta18O events occurred between 13 and 8 ka. The delta13C record from the planktonic foraminifera suggests a threefold division of events between 13 and 7 ka, with positive values between 10.8 and 13.0 ka, negative values between 9 and 10.8 ka, and positive values from 7 to 9 ka. The delta18O data suggest the presence of meltwater on the shelf some 3,000 years prior to the first late glacial dates on terrestrial deglaciation (at circa 10.4 ka). "Hudson Strait must be the real key to the importance of the calving process during deglaciation, because it is potentially the largest marine outlet for the Laurentide Ice Sheet and because it leads into the very center of the ice sheet.....the rates of calving through Hudson Strait during the period of initial ?18O rise unfortunately are unknown." W. F. Ruddiman (1987, p. 151)

Analyses of ferromanganese micronodules from the central Arctic Ocean

In order to determine geochemical compositions of Late Cenozoic Arctic seawater, oxide fractions were chemically separated from 15 samples of hand-picked ferromanganese micronodules (50-300 mu m). The success of the chemical separation is indicated by the fact that >97% of the Sr in the oxide fraction is seawater-derived. Rare-earth element (REE) abundances of the Arctic micronodule oxide fractions are much lower than those of bulk Fe-Mn nodules from other ocean basins of the world (e.g., 33 vs. 145 ppm Nd), but the Arctic oxides are enriched in Ce relative to Nd (Ce-N/Nd-N=2.2+/-0.5) and have convex-upward, shale-normalized REE patterns (Nd-N/Gd-N=0.61+/-0.06, Gd-N/Yb-N = 1.5+/-0.2, Nd-N/Yb-N = 0.9+/-0.2), typical of other hydrogenous and diagenetic marine Fe-Mn-oxides. Bulk sediment samples from the central Arctic Ocean have REE abundances and patterns that are characteristic of those of post-Archean shale. Non-detrital fractions (calcite + oxide coatings) of Recent Arctic foraminifera have REE abundances and patterns similar to those of Recent foraminifera from the Atlantic Ocean. Electron microprobe analyses (n=178) of transition elements in 29 Arctic Fe-Mn micronodules from five different stratigraphic intervals of Late Cenozoic sediment indicate that oxide accretion occurred as a result of hydrogenetic and diagenetic processes close to the sediment-seawater interface. Transition element ratios suggest that no oxide accretion occurred during transitions from oxic to suboxic diagenetic conditions. Only K is correlated with Si and Al, and ratios of these elements suggest that they are associated with illite or phillipsite. Ca and Mg are correlated with Mn, which indicates variable substitution of these elements from seawater into the manganate phase. The geochemical characteristics of Arctic Fe-Mn micronodules indicate that the REEs of the oxide fractions were ultimately derived from seawater. However, because of minute contributions of Sr from siliciclastic detritus during diagenesis or during the chemical leaching procedure, Sr isotope compositions of the oxide fractions cannot be used to trace temporal changes in the Sr-87/Sr-86 ratio of Arctic seawater or to improve the chronostratigraphy.

Stable isotope record and trace element ratios of Eocene and Oligocene foraminifers from ODP Site 120-748

Stable carbon and oxygen isotope analyses were conducted on well-preserved planktonic and benthic foraminifers from a continuous middle Eocene to Oligocene sequence at Ocean Drilling Program (ODP) Site 748 on the Kerguelen Plateau. Benthic foraminifer d18O values show a 1.0 per mil increase through the middle and upper Eocene, followed by a rapid 1.2 per mil increase in the lowermost Oligocene (35.5 Ma). Surface-dwelling planktonic foraminifer d18O values increase in the lowermost Oligocene, but only by 0.6 per mil whereas intermediate-depth planktonic foraminifers show an increase of about l.0 per mil. Benthic foraminifer d13C values increase by 0.9 per mil in the lowermost Oligocene at precisely the same time as the large d18O increase, whereas planktonic foraminifer d13C values show little or no change. Site 748 oxygen isotope and paleontological records suggest that southern Indian Ocean surface and intermediate waters underwent significant cooling from the early to late Eocene. The rapid 1.2 per mil oxygen isotope increase recorded by benthic foraminifers just above the Eocene/Oligocene boundary represents the ubiquitous early Oligocene d18O event. The shift here is unique, however, as it coincided with the sudden appearance of ice-rafted debris (IRD), providing the first direct link between Antarctic glacial activity and the earliest Oligocene d18O increase. The d18O increase caused by the ice-volume change in the early Oligocene is constrained by (1) related changes in the planktonic to benthic foraminifer d18O gradient at Site 748 and (2) comparisons of late Eocene and early Oligocene planktonic foraminifer d18Ovalues from various latitudes. Both of these records indicate that 0.3 per mil to 0.4 per mil of the early Oligocene d18O increase was ice-volume related.

Seawater carbonate chemistry, nutrients and growth rate during experiments with coral Astrangia poculata and field observations, 2010

Zooxanthellate colonies of the scleractinian coral Astrangia poculata were grown under combinations of ambient and elevated nutrients (5 µM NO, 0.3 µM PO4, and 2nM Fe) and CO2 (780 ppmv) treatments for a period of 6 months. Coral calcification rates, estimated from buoyant weights, were not significantly affected by moderately elevated nutrients at ambient CO2 and were negatively affected by elevated CO2 at ambient nutrient levels. However, calcification by corals reared under elevated nutrients combined with elevated CO2 was not significantly different from that of corals reared under ambient conditions, suggesting that CO2 enrichment can lead to nutrient limitation in zooxanthellate corals. A conceptual model is proposed to explain how nutrients and CO2 interact to control zooxanthellate coral calcification. Nutrient limited corals are unable to utilize an increase in dissolved inorganic carbon (DIC) as nutrients are already limiting growth, thus the effect of elevated CO2 on saturation state drives the calcification response. Under nutrient replete conditions, corals may have the ability to utilize more DIC, thus the calcification response to CO2 becomes the product of a negative effect on saturation state and a positive effect on gross carbon fixation, depending upon which dominates, the calcification response can be either positive or negative. This may help explain how the range of coral responses found in different studies of ocean acidification can be obtained.

Uranium and radioactive isotopes in bottom sediments and Fe-Mn nodules and crusts of seas and oceans

The main stages of the sedimentary cycle of uranium in modern marine basins are under consideration in the book. Annually about 18 thousand tons of dissolved and suspended uranium enters the ocean with river runoff. Depending on a type of a marine basin uranium accumulated either in sediments of deep-sea basins, or in sediments of continental shelves and slopes. In the surface layer of marine sediments hydrogenic uranium is predominantly bound with organic matter, and in ocean sediments also with iron, manganese and phosphorus. In diagenetic processes there occurs partial redistribution of uranium in sediments, as well as its concentration in iron-manganese, phosphate and carbonate nodules and biogenic phosphate detritus. Concentration of uranium in marine sediments of various types depending on their composition, as well as on forms of its entering, degree of differentiation and of sedimentation rates, on hydrochemical regime and water circulation, and on intensity of diagenetic processes.

Seawater chemistry, nutrients, chlorophyll a, and growth rate of Phaeocystis globosa during experiments

Phaeocystis globosa (Prymnesiophyceae) is an ecologically dominating phytoplankton species in many areas around the world. It plays an important role in both the global sulfur and carbon cycles, by the production of dimethylsulfide (DMS) and the drawdown of inorganic carbon. Phaeocystis globosa has a polymorphic life cycle and is considered to be a harmful algal bloom (HAB) forming species. All these aspects make this an interesting species to study the effects of increasing carbon dioxide (CO2) concentrations, due to anthropogenic carbon emissions. Here, the combined effects of three different dissolved carbon dioxide concentrations (CO2(aq)) (low: 4 µmol/kg, intermediate: 6-10 µmol/kg and high CO2(aq): 21-24 µmol/kg) and two different light intensities (low light, suboptimal: 80 µmol photons/m**2/s and high light, light saturated: 240 µmol photons/m**2/s) are reported. The experiments demonstrated that the specific growth rate of P. globosa in the high light cultures decreased with increasing CO2(aq) from 1.4 to 1.1 /d in the low and high CO2 cultures, respectively. Concurrently, the photosynthetic efficiency (Fv/Fm) increased with increasing CO2(aq) from 0.56 to 0.66. The different light conditions affected photosynthetic efficiency and cellular chlorophyll a concentrations, both of which were lower in the high light cultures as compared to the low light cultures. These results suggest that in future inorganic carbon enriched oceans, P. globosa will become less competitive and feedback mechanisms to global change may decrease in strength.

Response of the calcifying coccolithophore Emiliania huxleyi to low pH/high pCO2: from physiology to molecular level, 2011

The emergence of ocean acidification as a significant threat to calcifying organisms in marine ecosystems creates a pressing need to understand the physiological and molecular mechanisms by which calcification is affected by environmental parameters. We report here, for the first time, changes in gene expression induced by variations in pH/pCO2 in the widespread and abundant coccolithophore Emiliania huxleyi. Batch cultures were subjected to increased partial pressure of CO2 (pCO2; i.e. decreased pH), and the changes in expression of four functional gene classes directly or indirectly related to calcification were investigated. Increased pCO2 did not affect the calcification rate and only carbonic anhydrase transcripts exhibited a significant down-regulation. Our observation that elevated pCO2 induces only limited changes in the transcription of several transporters of calcium and bicarbonate gives new significant elements to understand cellular mechanisms underlying the early response of E. huxleyi to CO2-driven ocean acidification.

Late Pleistocene oxygen isotope record of biognic silica

We determined the isotopic composition of oxygen in marine diatoms in eight deep-sea cores recovered from the Atlantic sector of the Southern Ocean. The analytical reproducibility and core-to-core consistency of the isotopic signal suggests that diatom delta18O can be used as a new paleocenographic tool to reconstruct past variations in surface water characteristics and to generate 18O -isotope-based stratigraphy for the Southern Ocean. The data indicate that diatom delta18O reflects sea surface temperature and seawater isotopic composition and that diatoms retain their isotopic signal on timescales of a least 430 ka. The delta18O analyses of different diatom assemblages reveal that the isotopic signal is free of species effects and that the common Antarctic species have the same water-opal fractionation. The transition from the last glacial maximum (LGM) to the Holocene is fully recorded in high sedimentation rate cores. An 18O enrichment during the LGM, a post-LGM meltwater spike and an input of meltwater during the late Holocene are the main isotopic features observed in down core records. The origin of this meltwater was very likely melting icebergs and/or continental ice or by melting sea ice that had accumulated snow. The most pronounced meltwater effects are recorded in cores that are associated with the Weddel gyre. Our results provide the basis for extending isotope studies to oceanic regions devoid of carbonate; further, isotopic stratigraphies may be constructed for records and regions where they were previously not possible.

210Pb dates, radiocarbon ages and sedimentation and accumulation rates of sediment cores JM99-1198 and MD99-2297

The magnitude of Late Holocene climatic variations are less significant than those that took place during ice ages and deglaciations. However, detailed knowledge about this period is vital in order to understand and model future climate scenarios both as a result of natural climate variation and the effects of global warming. Oceanic heat flux is important for the sensitive climate regime of northern Europe. Our aim is to connect hydrographical changes, reflected by the dinoflagellates cyst (dinocysts) assemblages in the sediments in the Malangen fjord, to local and regional climatic phases. Previous studies have shown that dinocyst assemblages are influenced by temperature, salinity, and the availability of nutrients (e.g. de Vernal et al. 2005, doi:10.1016/j.quascirev.2004.06.014; de Vernal et al. 2001, doi:10.1002/jqs.659; Grosfjeld et al. this volume; Rochon et al. 2008, doi:10.1016/j.marmicro.2008.04.001; Solignac et al. this volume). Dinoflagellates are mostly unicellular organisms that make up one of the main groups of phytoplankton. They are able to regulate their depth within the photic zone and to concentrate along oceanic fronts, which provide nutrient-enriched waters. The dinoflagellate cysts are the hypnozygotes of dinoflagellates naturally produced during the life cycle. Their wall is composed of a highly resistant organic material, which has a high potential to fossilize. Because dinocysts species are linked to particular abiotic and biotic parameters, the dinocyst assemblages provide information about past surface water conditions. Since each fjord has its own hydrographic setting, it is necessary to establish a firm link between the dinocyst composition of the sediment surface samples and the surface water conditions. Indeed the modern dinocyst distribution in subarctic fjords is little known. Thus, in addition to detailing dinocyst results from two shallow cores, several sediment surface samples located along a transect running from the head to the mouth of the fjord, and extending onto the shelf, are also presented.

Dissolved organic carbon in waters of the Okhotsk and Bering Seas

A comparison was made of capability of two methods: photochemical oxidation and high-temperature catalytic combustion - to oxidize organic carbon in organic substances different in their element composition and in their degree of complexity. Results of measurements of dissolved organic carbon obtained by both of these methods in waters of the Black, Bering and Okhotsk Seas are presented. Varying oxidation degree of organic matter was shown to be dependent on the region and depth. A conclusion was made that the high-temperature catalytic combustion method was to be preferred for dissolved organic carbon determination due to its easier standardization, while values obtained by the wet-oxidation method may be influenced by a great number of factors that are difficult to be controlled.

Geochemistry of DSDP Hole 86-577B samples

THE chemical, mineralogical and isotopic characteristics of deposits at the Cretaceous/Tertiary (K/T) boundary are suggestive of a large impact event, the prime candidate (Sharpton et al., 1992, doi:10.1038/359819a0) being the Chicxulub crater in Yucatan, Mexico. Spinel-bearing spherules, which may be associated with such impacts, have been reported (Smit and Romein, 1985, doi:10.1016/0012-821X(85)90019-6) at several K/T boundary sites worldwide, but their origin is still uncertain. We have examined the spinel-bearing material recovered from K/T boundary deposits at site 577 in the Pacific Ocean (Heath et al., 1985, doi:10.2973/dsdp.proc.86.104.1985) and find two distinct populations of particles: spherules with dendritic spinel textures dispersed throughout the grains and irregularly shaped fragments with spinels essentially confined to the rim. The morphology and composition of the particles are characteristic of melted and partially melted meteoritic ablation debris, but their location is difficult to reconcile with an impact on the Yucatan peninsula, some 10,000 km away. We suggest instead that the spinel-bearing particles at site 577 are derived from the impact of a 2-km asteroid in the Pacific Ocean, and that several accretionary events of this type are required to explain the global distribution of spinel-bearing spherules at the K/T boundary.