Table 1: Densities of nitrate-dissimilating and nitrite-dissimilating bacteria in surface sediments in the German Bight, North Sea

At 24 stations in the Weser Estuary and the German Bight the Most Probable Numbers (MPN/g dry wt. sediment) of nitrate-dissimilating (= denitrifying) and of nitrate plus nitrite-dissimilating bacteria were recorded. The numbers of nitrite-dissimilating bacteria, i. e. denitrifiers not capable of reducing nitrate to nitrite, were calculated by subtraction of the MPN for nitrate-dissimilating from the MPN of nitrate plus nitrite-dissimilating bacteria. By determining the percentages of these bacteria in relation to the number of the heterotrophs, the ecological importance of denitrification, especially the nitrite dissimilation, was estimated. The results showed the MPN of nitrate-dissimilating bacteria to be in the range of 0-156 (up to 0.8 % of heterotrophic bacteria). An exception was the sediment of one station with a MPN of 1849, or 5.2 % of the heterotrophs. The amounts of nitrite-dissimilating bacteria were between 0 and 2352 (up to 13 % of heterotrophic bacteria). In the estuary the numbers of nitrate-dissimilating and of nitrite-dissimilating bacteria showed a decreasing tendency with distance from Bremerhaven. The highest numbers were found in the Weser off Bremerhaven and also at 3 stations in the German Bight, south of the Isle of Helgoland.

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).

Stable oxygen isotope data of Thoracosphaera heimii in surface sediment samples of the equatorial Atlantic and South Atlantic

To investigate the potential use of the stable isotope composition of the vegetative cysts of the photosynthetic dinoflagellate Thoracosphaera heimii for quantitative palaeotemperature reconstructions a method has been developed to purify T. heimii cysts from sediment samples. Stable oxygen and carbon isotopes have been measured on T. heimii cysts from 21 surface sediment samples from the equatorial Atlantic and South Atlantic Oceans. Calculated temperatures based on the palaeotemperature equation for inorganic calcite precipitation generally reflect mean annual temperatures of the upper water column, notably of thermocline depths. Although the present results suggest that the isotopic composition of T. heimii shells might be formed in equilibrium with the seawater in which the shells are being formed, future investigations are required to determine possible effects of metabolic and kinetic processes on the fractionation process. This pilot study therefore forms the basis for future investigations on the development of this tool and the determination of a species-specific palaeotemperature equation. The wide geographic and stratigraphic distribution of T. heimii cysts in sediments, the stable position of T. heimii within the water column and the high resistance of its cysts against calcite dissolution underline its potential for a wide usability in palaeotemperature reconstructions.