ALBERT

Description: The surface water in the Transpolar Drift in the Arctic Ocean has a strong signature of 228Ra. In an earlier study of 228Ra in the open Arctic we showed that the major 228Ra source had to be in the Siberian shelf seas, but only a single shelf station was published so far. Here we investigate the sources of this signal on the Siberian shelves by measurements of 228Ra and 226Ra in surface waters of the Kara and Laptev Sea, including the Ob, Yenisey and Lena estuaries. In the Ob and Lena rivers we found an indication for a very strong and unexpected removal of both isotopes in the early stage of estuarine mixing, presumably related to flocculation of organic-rich material. Whereas 226Ra behaves conservatively on the shelf, the distribution of 228Ra is governed by large inputs on the shelves, although sources are highly variable. In the Kara Sea the maximum activity was found in the Baydaratskaya Bay, where tidal resonance and low freshwater supply favour 228Ra accumulation. The Laptev Sea is a stronger source for 228Ra than the Kara Sea. Since a large part of Kara Sea water flows through the Laptev Sea, the 228Ra signal in the Transpolar Drift can be described as originating on the Laptev shelf. The combined freshwater inputs from the Eurasian shelves thus produce a common radium signature with a 228Ra/226Ra activity ratio of 4.0 at 20% river water. The radium signals of the individual Siberian rivers and shelves cannot be separated, but their signal is significantly different from the signal produced on the Canadian shelf (Smith et al., in press). In this respect, the radium tracers add to the information given by Barium. Moreover, with the 5.8 year half-life of 228Ra, they have the potential to serve as a tracer for the age of a water mass since its contact with the shelves.

Description: Ocean acidification and warming effects on the macroalgal species Fucus vesiculosus forma mytili were simulated in the tidal benthic mesocosm facility at the AWI Wadden Sea Station on the island of Sylt, Germany (55°01'19.2''N, 8°26'17.7''E). The SY1 experiment in spring 2014 (11 weeks from early April to late June) was based on a "Temp X pCO2" full-factorial setup (ambient or delta 5°C temperature X ambient or 1000 ppm pCO2) resulting in 4 treatment levels à 3 replicates. The seawater parameters (temperature, pH, salinity, total alkalinity, pCO2) and seawater inorganic nutrient concentrations (silicate, nitrite, phosphate, ammonium, total nitrogen oxide, nitrate) were measured on a weekly basis. The biomass growth rates (RGR) of Fucus vesiculosus forma mytili were calculated over time, and its physiological parameters (carbon, nitrogen, CN ratio, mannitol) were measured at the beginning and end of the experiment.

Description: The upper water column in the Fram Strait and the outer Laptev Sea was sampled for water column isotopes and living planktic foraminifer species Neogloboquadrina pachyderma (sinistral coiling) (Ehrenberg), 1861 and Turborotalita quinqueloba (Natland),1938. Their shell delta18O and delta13C values are compared to water oxygen and dissolved inorganic carbon isotope data to determine the environmental influence on the foraminifers' isotopic ratio. Major controls on the oxygen isotope composition of both species are the shallow depth habitat under permanent ice coverage, the low salinity surface layer, and the rate of metabolic activity. None of the specimens precipitated its shell in isotopic equilibrium with the ambient sea water. They are all depleted in 13C and 18O, attributed to a species-specific vital effect. For nonencrusted N. pachyderma (sin.) in the 125-250 µm size class, this vital effect amounts to 1.3 per mil in delta18O and 2.0 per mil in delta13C. It increases to higher values in waters under permanent ice cover. T. quinqueloba reveals a mean vital effect of about 1.3 per mil in delta18O and 2.6 per mil in delta13C. The general isotopic trends are similar for N. pachyderma (sin.) and T. quinqueloba. Differences in the species' isotope ratio at the same sites are caused by different calcification depths and metabolic activity. The oxygen isotope composition of N. pachyderma (sin.) shows a relationship to salinity measurements and indicates that it is a good quantitative proxy for salinity reconstructions, while no relationship exists in this region between N. pachyderma (sin.) oxygen isotopes and water temperature.