Susceptibility, density, iron and calcium concentrations of ODP holes 165-999B and 165-1001A

Pelagic sediments recording an extreme and short-lived global warming event, the Late Paleocene Thermal Maximum (LPTM), were recovered from Hole 999B (Colombian Basin) and Holes 1001A and 1001B (lower Nicaraguan Rise) in the Caribbean Sea during Ocean Drilling Program Leg 165. The LPTM consists of a 0.3-0.97 m calcareous claystone to claystone horizon. High-resolution downhole logging (Formation MicroScanner [FMS]), standard downhole logs (resistivity, velocity, density, natural gamma ray, and geochemical log), and non-destructive chemical and physical property (multisensor core logger [MSCL] and X-ray fluorescence [XRF] core scanner) data were used to identify composite sections from parallel holes and to record sedimentological and environmental changes associated with the LPTM. Downhole logging data indicate an abrupt and distinct difference in physical and chemical properties that extend for tens of meters above and below the LPTM. These observations indicate a rapid environmental change at the LPTM, which persists beyond the LPTM anomaly. Comparisons of gamma-ray attenuation porosity evaluator (GRAPE) densities from MSCL logging on split cores with FMS resistivity values allows core-to-log correlation with a high degree of accuracy. High-resolution magnetic susceptibility measurements of the cores are compared with elemental concentrations (e.g., Fe, Ca) analyzed by high-resolution XRF scanning. The high-resolution data obtained from several detailed core and downhole logging methods are the key to the construction of composite sections, the correlation of both adjacent holes and distant sites, and core-log integration. These continuous-depth series reveal the LPTM as a multiphase event with a nearly instantaneous onset, followed by a much different set of physical and chemical conditions of short duration, succeeded by a longer transition to a new, more permanent set of environmental circumstances. The estimated duration of these 'phases' are consistent with paleontological and isotopic studies of the LPTM

Paleomagnetic analysed of two sediment cores off Cape Ghir

Holocene records documenting variations in direction and intensity of the geomagnetic field during the last about seven and a half millennia are presented for Northwest Africa. High resolution paleomagnetic analyses of two marine sediment sequences recovered from around 900 meter water depth on the upper continental slope off Cape Ghir (30°51'N, 10°16'W) were supplemented by magnetic measurements characterizing composition, concentration, grain size and coercivity of the magnetic mineral assemblage. Age control for the high sedimentation rate deposits (~60 cm/kyr) was established by AMS radiocarbon dates. The natural remanent magnetization (NRM) is very predominantly carried by a fine grained, mostly single domain (titano-)magnetite fraction allowing the reliable definition of stable NRM inclinations and declinations from alternating field demagnetization and principal component analysis. Predictions of the Korte and Constable (2005) geomagnetic field model CALS7K.2 for the study area are in fair agreement with the Holocene directional records for the most parts, yet noticeable differences exist in some intervals. The magnetic mineral inventory of the sediments reveals various climate controlled variations, specifically in concentration and grain size. A very strong impact had the mid-Holocene environmental change from humid to arid conditions on the African continent which also clearly affects relative paleointensity (RPI) estimates based on different remanence normalizers. To overcome this problem the pseudo-Thellier RPI technique has been applied. The results represent the first Holocene record of Earth's magnetic field intensity variations in the NW Africa region. It displays long term trends similar to those of model predictions, but also conspicuous millennium scale differences.

Ocean acidification affects growth but not nutritional quality of the seaweed Fucus vesiculosus (Phaeophyceae, Fucales)

Understanding the ecological implications of global climate change requires investigations of not only the direct effects of environmental change on species performance but also indirect effects that arise from altered species interactions. We performed CO2 perturbation experiments to investigate the effects of ocean acidification on the trophic interaction between the brown seaweed Fucus vesiculosus and the herbivorous isopod Idotea baltica. We predicted faster growth of F. vesiculosus at elevated CO2-concentrations and higher carbon content of the algal tissue. We expected that I. baltica has different consumption rates on algae that have been grown at different CO2 levels and that the isopods remove surplus carbon metabolically by enhanced respiration. Surprisingly, growth of F. vesiculosus as well as the C:N-ratio of the algal tissue were reduced at high CO2-levels. The changes in the elemental composition had no effect on the consumption rates and the respiration of the herbivores. An additional experiment showed that consumption of F. vesiculosus by the isopod Idotea emarginata was independent of ocean acidification and temperature. Our results could not reveal any effects of ocean acidification on the per capita strength of the trophic interaction between F. vesiculosus and its consumers. However, reduced growth of the algae at high CO2-concentrations might reduce the capability of the seaweed to compensate losses due to intense herbivory.

Consumers mediate the effects of experimental ocean acidification and warming on primary producers

It is well known that ocean acidification can have profound impacts on marine organisms. However, we know little about the direct and indirect effects of ocean acidification and also how these effects interact with other features of environmental change such as warming and declining consumer pressure. In this study, we tested whether the presence of consumers (invertebrate mesograzers) influenced the interactive effects of ocean acidification and warming on benthic microalgae in a seagrass community mesocosm experiment. Net effects of acidification and warming on benthic microalgal biomass and production, as assessed by analysis of variance, were relatively weak regardless of grazer presence. However, partitioning these net effects into direct and indirect effects using structural equation modeling revealed several strong relationships. In the absence of grazers, benthic microalgae were negatively and indirectly affected by sediment-associated microalgal grazers and macroalgal shading, but directly and positively affected by acidification and warming. Combining indirect and direct effects yielded no or weak net effects. In the presence of grazers, almost all direct and indirect climate effects were nonsignificant. Our analyses highlight that (i) indirect effects of climate change may be at least as strong as direct effects, (ii) grazers are crucial in mediating these effects, and (iii) effects of ocean acidification may be apparent only through indirect effects and in combination with other variables (e.g., warming). These findings highlight the importance of experimental designs and statistical analyses that allow us to separate and quantify the direct and indirect effects of multiple climate variables on natural communities.

Early Cenozoic Atlantic and Pacific benthic foraminiferal isotopes from 12 sites

Oxygen and carbon isotope records are important tools used to reconstruct past ocean and climate conditions, with those of benthic foraminifera providing information on the deep oceans. Reconstructions are complicated by interspecies isotopic offsets that result from microhabitat preferences (carbonate precipitation in isotopically distinct environments) and vital effects (species-specific metabolic variation in isotopic fractionation). We provide correction factors for early Cenozoic benthic foraminifera commonly used for isotopic measurements (Cibicidoides spp., Nuttallides truempyi, Oridorsalis spp., Stensioina beccariiformis, Hanzawaia ammophila, and Bulimina spp.), showing that most yield reliable isotopic proxies of environmental change. The statistical methods and larger data sets used in this study provide more robust correction factors than do previous studies. Interspecies isotopic offsets appear to have changed through the Cenozoic, either (1) as a result of evolutionary changes or (2) as an artifact of different statistical methods and data set sizes used to determine the offsets in different studies. Regardless of the reason, the assumption that isotopic offsets have remained constant through the Cenozoic has introduced an 1-2°C uncertainty into deep sea paleotemperature calculations. In addition, we compare multiple species isotopic data from a western North Atlantic section that includes the Paleocene-Eocene thermal maximum to determine the most reliable isotopic indicator for this event. We propose that Oridorsalis spp. was the most reliable deepwater isotopic recorder at this location because it was best able to withstand the harsh water conditions that existed at this time; it may be the best recorder at other locations and for other extreme events also.