(Table 1) Oxygen and carbon isotopes and calcium carbonte of bulk carbonate at DSDP Hole 72-516F

A detailed oxygen and carbon isotope study of the upper Maestrichtian-lower Paleocene section of Hole 516F from the Rio Grande Rise reveals that large isotopic anomalies are clearly associated with the Cretaceous/Tertiary boundary. Across the Cretaceous/Tertiary boundary, the total carbonate content reaches a maximum exceeding 80% before rapidly decreasing in covariance with the carbon isotope record. This strong covariance between d13C and percent CaCO3 suggests either a significant reduction in primary productivity or a rapid shoaling of the calcium carbonate compensation depth. Importantly, the d13C record 2 Ma after the Cretaceous/Tertiary boundary remained depleted in 13C by at least 0.5 per mil compared to the late Maestrichtian.

Geochemical data from the USGS #1 Portland core, Canon City, Colorado

During the Cretaceous, widespread black shale deposition occurred during a series of Oceanic Anoxic Events (OAEs). Multiple processes are known to control the deposition of marine black shales, including changes in primary productivity, organic matter preservation, and dilution. OAEs offer an opportunity to evaluate the relative roles of these forcing factors. The youngest of these events-the Coniacian to Santonian OAE 3-resulted in a prolonged organic carbon burial event in shallow and restricted marine environments including the Western Interior Seaway. New high-resolution isotope, organic, and trace metal records from the latest Turonian to early Santonian Niobrara Formation are used to characterize the amount and composition of organic matter preserved, as well as the geochemical conditions under which it accumulated. Redox sensitive metals (Mo, Mn, and Re) indicate a gradual drawdown of oxygen leading into the abrupt onset of organic carbon-rich (up to 8%) deposition. High Hydrogen Indices (HI) and organic carbon to total nitrogen ratios (C:N) demonstrate that the elemental composition of preserved marine organic matter is distinct under different redox conditions. Local changes in d13C indicate that redox-controlled early diagenesis can also significantly alter d13Corg records. These results demonstrate that the development of anoxia is of primary importance in triggering the prolonged carbon burial in the Niobrara Formation. Sea level reconstructions, d18O results, and Mo/total organic carbon ratios suggest that stratification and enhanced bottom water restriction caused the drawdown of bottom water oxygen. Increased nutrients from benthic regeneration and/or continental runoff may have sustained primary productivity.

Planktonic foraminifera of ODP Hole 107-654A

The late Miocene sediments of the Tyrrhenian ODP Site 654 encompass a deepening sequence which begins with glauconite shallow water sands followed by a rapid transition to deep water sediments and culminates with dolomitic mudstones associated with Messinian evaporites. The sequence compares well with the so-called 'Sahelian cycle' and with post-orogenic cycles recognized in peninsular Italy and Sicily. The studied interval, consisting of 55 m thick nannofossil oozes, belongs to the Globorotalia suterae subzone and lower part of the Globorotalia conomiozea Zone, indicating late Tortonian and early Messinian age, respectively. Biomagnetostratigraphic correlation assigns the Tortonian/ Messinian boundary an age of 6.44-6.45 Ma. In addition, six main events have been recognized, based on the range of keeled globorotaliids and coiling direction changes of keeled and unkeeled globorotaliids, which have been correlated to the geomagnetic time-scale. Comparison with North Atlantic sites and land sections of the Guadalquivir basin and northern Morocco provides good correlations with the events documented in these areas. In particular, Event IV, which predates the FO of Globorotalia conomiozea, may be used to recognize the Tortonian/Messinian boundary in extra-Mediterranean areas where G. conomiozea is missing. Variations in the distribution of different species of Globigerinoides are related to changes in the surficial marine environment. Although no clear trends can be recognized on the oxygen and carbon isotope records of Globigerinoides obliquus, the parallelism between the occurrence of low salinity species (G. sacculifer) and peaks of low 5180 values, as well as that of normal salinity species (G. obliquus) and peaks of high d18O values, suggests strong local changes of environmental conditions. The high amplitude of the fluctuations of d18O values suggests important variations in the salinity of the Tyrrhenian Sea, related to a rapidly changing water budget. The major feature of the carbon isotope record is a large decrease between 7.0 and 6.95 Ma, which therefore predates the 6.2 Ma global 'carbon shift'.

Carbon pools and fluxes measured during a field campaign conducted in 2010 on the Tibetan Plateau at Kema

The Tibetan highlands host the largest alpine grassland ecosystems worldwide, bearing soils that store substantial stocks of carbon (C) that are very sensitive to land use changes. This study focuses on the cycling of photoassimilated C within a Kobresia pygmaea pasture, the dominating ecosystems on the Tibetan highlands. We investigated short-term effects of grazing cessation and the role of the characteristic Kobresia root turf on C fluxes and belowground C turnover. By combining eddy-covariance measurements with 13CO2 pulse labeling we applied a powerful new approach to measure absolute fluxes of assimilates within and between various pools of the plant-soil-atmosphere system. The roots and soil each store roughly 50% of the overall C in the system (76 Mg C/ha), with only a minor contribution from shoots, which is also expressed in the root:shoot ratio of 90. During June and July the pasture acted as a weak C sink with a strong uptake of approximately 2 g C/m**2/ in the first half of July. The root turf was the main compartment for the turnover of photoassimilates, with a subset of highly dynamic roots (mean residence time 20 days), and plays a key role for the C cycling and C storage in this ecosystem. The short-term grazing cessation only affected aboveground biomass but not ecosystem scale C exchange or assimilate allocation into roots and soil.

The magnesium isotope composition of diagenetic dolomites from ODP Hole 112-685A and 201-1230A of the Peru Margin

The magnesium isotope composition of diagenetic dolomites and their adjacent pore fluids were studied in a 250 m thick sedimentary section drilled into the Peru Margin during Ocean Drilling Program (ODP) Leg 201 (Site 1230) and Leg 112 (Site 685). Previous studies revealed the presence of two types of dolomite: type I dolomite forms at ~ 6 m below seafloor (mbsf) due to an increase in alkalinity associated with anaerobic methane oxidation, and type II dolomite forms at focused sites below ~ 230 mbsf due to episodic inflow of deep-sourced fluids into an intense methanogenesis zone. The pore fluid delta 26Mg composition becomes progressively enriched in 26Mg with depth from values similar to seawater (i.e. -0.8 per mil, relative to DSM3 Mg reference material) in the top few meters below seafloor (mbsf) to 0.8 ± 0.2 per mil within the sediments located below 100 mbsf. Type I dolomites have a delta 26Mg of -3.5 per mil, and exhibit apparent dolomite-pore fluid fractionation factors of about -2.6 per mil consistent with previous studies of dolomite precipitation from seawater. In contrast, type II dolomites have delta 26Mg values ranging from -2.5 to -3.0 per mil and are up to -3.6 per mil lighter than the modern pore fluid Mg isotope composition. The enrichment of pore fluids in 26Mg and depletion in total Mg concentration below ~ 200 mbsf is likely the result of Mg isotope fractionation during dolomite formation, The 26Mg enrichment of pore fluids in the upper ~ 200 mbsf of the sediment sequence can be attributed to desorption of Mg from clay mineral surfaces. The obtained results indicate that Mg isotopes recorded in the diagenetic carbonate record can distinguish near surface versus deep formed dolomite demonstrating their usefulness as a paleo-diagenetic proxy.

Pollen profile and age determination of sediment core Schwanengrabenrinne, Brandenburg, Germany

In der Döberitzer Heide nördlich von Potsdam wurden vegetationsgeschichtliche Untersuchungen durchgeführt. Das Untersuchungsgebiet befindet sich im östlichen Teil der Nauener Platte, die bisher vegetationsgeschichtlich weitgehend unerforscht war. In sechs verschiedenen Mooren wurden acht Bohrungen niedergebracht. Die Bohrkerne wurden stratigraphisch und pollenanalytisch untersucht und für die Radiocarbondatierung beprobt. Die Pollendiagramme ermöglichen die Rekonstruktion der Vegetationsentwicklung der terrestrischen Standorte und der Moore in der Döberitzer Heide in den letzten 14.000 Jahren. Neben einer Revision der Gliederungsprinzipien der spätglazialen Vegetationsentwicklung Brandenburgs und einer vergleichenden Betrachtung der Moorentwicklung in der Döberitzer Heide wurde besonderes Augenmerk auf die Geschichte des Döberitzer Lindenwaldes gerichtet, der einen Sonderfall in der brandenburgischen Vegetation darstellt. Die Untersuchungen boten die Möglichkeit, die Ursachen seiner Entstehung zu klären, Aussagen zu den Perspektiven seiner Entwicklung zu treffen und mögliche Entwicklungspotentiale von Lindenwäldern im Land Brandenburg aufzuzeigen.

Core alignment and composite depth scale of DSDP Site 86-577

Deep Sea Drilling Project Site 577 on Shatsky Rise (North Pacific Ocean) recovered a series of cores at three holes that contain calcareous nannofossil ooze of latest Cretaceous (late Maastrichtian) through early Eocene age. Several important records have been generated using samples from these cores, but the stratigraphy has remained outdated and confusing. Here we revise the stratigraphy at Site 577. This includes refining several age datums, realigning cores in the depth domain, and placing all stratigraphic markers on a current time scale. The work provides a template for appropriately bringing latest Cretaceous and Paleogene data sets at old drill sites into current paleoceanographic literature for this time interval. While the Paleocene Eocene Thermal Maximum (PETM) lies within core gaps at Holes 577* and 577A, the sedimentary record at the site holds other important events and remains crucially relevant to understanding changes in oceanographic conditions from the latest Cretaceous through early Paleogene.

Diagenetic dolomite formation in Quaternary anoxic diatomaceous muds at DSDP Leg 64 Holes

During drilling in the Gulf of California, diagenetic carbonate rocks were recovered at 7 out of 8 sites. These are primarily dolomites which record 13C isotopic evidence of the incorporation of carbon derived from the decomposition of organic matter. In Hole 479, drilled to a sub-bottom depth of 440 meters on the Guaymas Slope, under a fertile upwelling belt, we recognized an excellent example of deep sea dolomitization in progress. This Quaternary section of organic-carbon- rich, low-carbonate, hemipelagic diatomaceous oozes contains numerous fine-grained, decimeter-thin, episodic beds of dolomite, which show sedimentologic, geochemical, and isotopic evidence of accretion by precipitation below 40 meters sub-bottom in zones of high alkalinity and low sulfate. The beds preserve original sedimentary structures. Carbon-13 varies from +3 to +14 per mil, indicating biogenic CO2 reservoirs related to active methanogenesis. In single beds, 18O values range outwardly from +5 to -7 per mil, reflecting increasing temperature with progressive accretion of dolomite with depth; the values parallel progressive trends in lithification, texture, mineralogy, and fossil preservation. We estimate slow accretion rates on the order of 0.1-0.7 mm/10**3 yr. with burial. Dolomitization does not proceed merely at the expense of nearby nannofossils. Ca and Mg ions must be derived from interstitial waters. The episodic appearance of beds in the sequence seems partly a reflection of latent climate signals. This process of deep sea dolomitization carries implications for hydrocarbon migration, as well as an interpretation of the presence of dolomite in other modern and ancient pelagic to hemipelagic sediment sequences.

Early Maastrichtian stable isotopes: changing deep water sources in the North Atlantic?

We propose that the observed short-term stable isotope fluctuations reflect changes in high- and low-latitude intermediate to deep water sources, based on a high-resolution stable isotope record of planktic and benthic foraminifera from the Early Maastrichtian (~71.3 to ~ 69.6 Ma) of Blake Nose (DSDP Site 390A, North Atlantic). Sources of these waters may have been the low-latitude eastern Tethys and high-latitude North Atlantic. Changes in intermediate to deep water sources were probably steered by eccentricity-controlled insolation fluctuations. Lower insolation favored the formation of high-latitude deep waters due to positive feedback mechanisms resulting in high-latitude cooling. This led to a displacement of low-latitude deep waters at Blake Nose. Higher insolation reduced intermediate to deep-water formation in high latitudes, yielding a more northern flow of low-latitude deep waters.

Geochemistry of carbon at DSDP Legs 56-57 Holes

Forty-three core sections from Sites 434, 435, 438, 439, and 440 on the landward side and six core sections from Site 436 on the seaward side of the Japan Trench were obtained through the JOIDES Organic Geochemistry Advisory Panel for study of the origin and state of genesis of the organic matter associated with these continental slope, accretionary wedge, and outer trench slope sediments of the Japan Trench. The lipid fraction of these sediments is derived primarily from terrigenous organic matter and thus is allochthonous to the area. The associated kerogen fraction is of mixed allochthonous and autochthonous origin. The total organic carbon content seaward of the trench is less than that on the landward side. The composition of this organic matter is similar but not identical to that found in the landward side sediments. The organic matter within these sediments is in a diagenetic state in which geopolymerization of biogenic organic matter is nearly complete, but microbial alteration is still occurring.

Age models for sediment cores in the eastern tropical Pacific

We present new high-resolution N isotope records from the Gulf of Tehuantepec and the Nicaragua Basin spanning the last 50-70 ka. The Tehuantepec site is situated within the core of the north subtropical denitrification zone while the Nicaragua site is at the southern boundary. The d15N record from Nicaragua shows an 'Antarctic' timing similar to denitrification changes observed off Peru-Chile but is radically different from the northern records. We attribute this to the leakage of isotopically heavy nitrate from the South Pacific oxygen minimum zone (OMZ) into the Nicaragua Basin. The Nicaragua record leads the other eastern tropical North Pacific (ETNP) records by about 1000 years because denitrification peaks in the eastern tropical South Pacific (ETSP) before denitrification starts to increase in the Northern Hemisphere OMZ, i.e., during warming episodes in Antarctica. We find that the influence of the heavy nitrate leakage from the ETSP is still noticeable, although attenuated, in the Gulf of Tehuantepec record, particularly at the end of the Heinrich events, and tends to alter the recording of millennial timescale denitrification changes in the ETNP. This implies (1) that sedimentary d15N records from the southern parts of the ETNP cannot be used straightforwardly as a proxy for local denitrification and (2) that denitrification history in the ETNP, like in the Arabian Sea, is synchronous with Greenland temperature changes. These observations reinforce the conclusion that on millennial timescales during the last ice age, denitrification in the ETNP is strongly influenced by climatic variations that originated in the high-latitude North Atlantic region, while commensurate changes in Southern Ocean hydrography more directly, and slightly earlier, affected oxygen concentrations in the ETSP. Furthermore, the d15N records imply ongoing physical communication across the equator in the shallow subsurface continuously over the last 50-70 ka.

Geochemistry on core 202-1240A

The modern Eastern Equatorial Pacific (EEP) Ocean is a large oceanic source of carbon to the atmosphere1. Primary productivity over large areas of the EEP is limited by silicic acid and iron availability, and because of this constraint the organic carbon export to the deep ocean is unable to compensate for the outgassing of carbon dioxide that occurs through upwelling of deep waters. It has been suggested that the delivery of dust-borne iron to the glacial ocean could have increased primary productivity and enhanced deep-sea carbon export in this region, lowering atmospheric carbon dioxide concentrations during glacial periods. Such a role for the EEP is supported by higher organic carbon burial rates documented in underlying glacial sediments but lower opal accumulation rates cast doubts on the importance of the EEP as an oceanic region for significant glacial carbon dioxide drawdown. Here we present a new silicon isotope record that suggests the paradoxical decline in opal accumulation rate in the glacial EEP results from a decrease in the silicon to carbon uptake ratio of diatoms under conditions of increased iron availability from enhanced dust input. Consequently, our study supports the idea of an invigorated biological pump in this region during the last glacial period that could have contributed to glacial carbon dioxide drawdown. Additionally, using evidence from silicon and nitrogen isotope changes, we infer that, in contrast to the modern situation, the biological productivity in this region is not constrained by the availability of iron, silicon and nitrogen during the glacial period. We hypothesize that an invigorated biological carbon dioxide pump constrained perhaps only by phosphorus limitation was a more common occurrence in low-latitude areas of the glacial ocean.