Beschreibung: Measuring temperature and salinity profiles in the world's oceans is crucial to understanding ocean dynamics and its influence on the heat budget, the water cycle, the marine environment and on our climate. Since 1983 the German research vessel and icebreaker Polarstern has been the platform of numerous CTD (conductivity, temperature, depth instrument) deployments in the Arctic and the Antarctic. We report on a unique data collection spanning 33 years of polar CTD data. In total 131 data sets (1 data set per cruise leg) containing data from 10 063 CTD casts are now freely available. During this long period five CTD types with different characteristics and accuracies have been used. Therefore the instruments and processing procedures (sensor calibration, data validation, etc.) are described in detail. This compilation is special not only with regard to the quantity but also the quality of the data - the latter indicated for each data set using defined quality codes. The complete data collection includes a number of repeated sections for which the quality code can be used to investigate and evaluate long-term changes. Beginning with 2010, the salinity measurements presented here are of the highest quality possible in this field owing to the introduction of the OPTIMARE Precision Salinometer.

Beschreibung: In the years 2000 and 2001 we measured methane concentrations exceeding up to two orders of magnitude the equilibrium with the atmosphere in the water column on the SW-Spitsbergen continental shelf. This methane anomaly extended from its centre on the shelf westwards over the upper slope and eastwards well into the inner basins of the two southernmost Spitsbergen fjords, the Hornsundfjord and the van Mijenfjord. Methane concentrations and stable carbon isotopic ratios varied between 2 and 240 nM, and between -53 per mill and -20 per mill VPDB, respectively. Methane in high concentrations was depleted in 13C whereas in low concentrations d13CCH4 values were highly variable. On the continental shelf we found that methane discharged from seeps on top of sandy and gravelly banks is isotopically heavier than methane escaping from troughs filled with silty and clayey sediments. These distinct isotopic signatures suggest that methane is gently released from several inter-granular seepages or micro-seepages widely spread over the shelf. A potential migration path for thermogenic or hydrate methane may be the Hornsund Fracture Zone, a south–north running reactivated fault system created by stretching of the continental crust. After discharge into the water column, local water currents fed by Atlantic water, coastal water, and freshwater outflows from the fjords further determine pathways and fate of the methane. We used d18Owater and 222Rn data to trace origin and advection of the local water masses and water mixing processes. Methane spreads predominantly along pycnoclines and by vertical mixing. During transport methane is influenced simultaneously by oxidation and dilution, as well as loss into the atmosphere. Together these processes cause the spatial variability of the anomaly and heterogeneity in d13CCH4 in this polar shelf environment.