Sulfur isotopic variations in nodular and disseminated pyrite at DSDP Hole 93-603B

Analyses of modern marine sediments have suggested that availability and type of organic matter, sedimentation rate, and openness of the sulfate system influence the degree of isotopic fractionation between seawater sulfate and sedimentary iron sulfides. Isotopic studies of ancient sulfides should, therefore, provide insights into conditions of deposition and early diagenesis. Analysis of d34S of disseminated pyrite from Cretaceous sediments of Hole 603B yielded fractionations relative to coeval seawater sulfate ranging from 40 to 55 per mil, which are within the range for modern oxic marine sediments reported by others. Sulfur/carbon ratios are similar to those found from modern marine sediments and suggest that disseminated pyrite formation was dependent upon available organic carbon. These results imply that depositional and early diagenetic conditions during the Cretaceous in Hole 603B were similar to those occurring in initially oxic marine environments today. Macroscopic (nodular) pyrite from Hole 603B is isotopically variable (d34S values = - 48 to + 33 per mil), but generally more positive than disseminated pyrite. The isotopic evidence suggests that macroscopic pyrite formed during late stages of sulfate reduction in a system closed with respect to sulfate. However, detailed analyses of large pyrite nodules did not yield a consistent pattern of isotopic variation from center to rim.

Short-term variations in radiolarian faunal dsitribution in the eastern equatorial Pacific

Two short time intervals centered at 2.3 and 4.7 Ma were studied to investigate short-term variations in surface-ocean processes as indicated by changes in the radiolarian microfossil population. These time intervals represent two different settings of late Neogene climate. The older interval represents a time when tropical circulation between the Pacific and Atlantic oceans was not blocked by the Isthmus of Panama, whereas the younger interval represents a time when Northern Hemisphere glaciation was present but did not display the dominance of the 100,000-yr cycle that characterizes the late Pleistocene. The younger time slice at 2.3 Ma was sampled at all Leg 138 sites except Site 844, where significant reworking was evident. All sites except 844, 853, and 854 were sampled for the older time slice. Samples were taken at 10- to 20-cm intervals at each site and spanned a GRAPE density maximum and minimum. Thus, it was possible to investigate whether the changes in carbonate content (as indicated by GRAPE density) were associated with changes in surface-ocean conditions (indicated by radiolarian assemblage variations). For both time slices, the radiolarian data indicate that intervals of decreased carbonate content are periods of cooler water conditions and possibly enhanced biogenic production. Times of increased carbonate content are associated with inferred warmer oceanographic conditions, as indicated by the dominance of tropical assemblages at 2.3 Ma and tropical and western Pacific assemblages during the time slice centered at 4.8 Ma. However, the spatial patterns of change during each time slice show a distinct difference in the mapped patterns of radiolarian assemblage dominance. The older time slice, representing a period before the closing of the Isthmus of Panama, shows more zonal patterns presumably associated with a more zonal character of equatorial circulation. After the closing of the isthmus, the shifts in faunal patterns between times of high and low carbonates are characterized by shifts in the dominance of the tropical and transitional assemblages, respectively, throughout the region.

Theoretical model simulations for variations in thermal reaction norms

Thermal reaction norms for growth rates of six Emiliania huxleyi isolates originating from the central Atlantic (Azores, Portugal) and five isolates from the coastal North Atlantic (Bergen, Norway) were assessed. We used the template mode of variation model to decompose variations in growth rates into modes of biological interest: vertical shift, horizontal shift, and generalist-specialist variation. In line with the actual habitat conditions, isolates from Bergen (Bergen population) grew well at lower temperatures, and isolates from the Azores (Azores population) performed better at higher temperatures. The optimum growth temperature of the Azores population was significantly higher than that of the Bergen population. Neutral genetic differentiation was found between populations by microsatellite analysis. These findings indicate that E. huxleyi populations are adapted to local temperature regimes. Next to between-population variation, we also found variation within populations. Genotype-by-environment interactions resulted in the most pronounced phenotypic differences when isolates were exposed to temperatures outside the range they naturally encounter. Variation in thermal reaction norms between and within populations emphasizes the importance of using more than one isolate when studying the consequences of global change on marine phytoplankton. Phenotypic plasticity and standing genetic variation will be important in determining the potential of natural E. huxleyi populations to cope with global climate change.

Short-term temporal and spatial variations in physical, optical and biogeochemical parameters in June of 2013 in Alfacs Bay (NW Mediterranean)

With the aim of analyzing the complex physical and biogeochemical interactions at high temporal and spatial resolution in the complex estuarine waters of Alfacs Bay, a beam attenuation-based approach was used as optical proxy of different biogeochemical variables. Thus, the dataset contains the attenuation proxies as well as laboratory results from the analysis of water samples, which were used to validate our approach. In addition, the major physical forcing in the Bay was also measured.

Seasonal variations in surface metabolite composition of Fucus vesiculosus and Fucus serratus sampled at outer Kiel Fjord (August 2012 - July 2013)

The chemical composition of surface associated metabolites of two Fucus species (Fucus vesiculosus and Fucus serratus) was analysed by means of gas chromatography-mass spectrometry (GC-MS) to describe temporal patterns in chemical surface composition. Method: The two perennial brown macroalgae F. vesiculosus and F. serratus were sampled monthly at Bülk, outer Kiel Fjord, Germany (54°27'21 N / 10°11'57 E) over an entire year (August 2012 - July 2013). Per month and species six non-fertile Fucus individuals were collected from mixed stands at a depth of 0.5 m under mid water level. For surface extraction approx. 50 g of the upper 5-10 cm apical thalli tips were cut off per species. The surface extraction of Fucus was performed according to the protocol of de Nys and co-workers (1998) with minor modifications (see Rickert et al. 2015). GC/EI-MS measurements were performed with a Waters GCT premier (Waters, Manchester, UK) coupled to an Agilent 6890N GC equipped with a DB-5 ms 30 m column (0.25 mm internal diameter, 0.25 mM film thickness, Agilent, USA). The inlet temperature was maintained at 250°C and samples were injected in split 10 mode. He carrier gas flow was adjusted to 1 ml min-1. Alkanes were used for referencing of retention times. For further details (GC-MS sample preparation and analysis) see the related publication (Rickert et al. submitted to PLOS ONE).