(Table 2) Rates of nitrate and ammonium uptake, concentrations of particulate organic nitrogen and carbon, and dissolved nitrate and ammonium in waters of the Black Sea August-September 1990 and November 1991

To study inorganic nitrogen uptake rates by microplankton in the Black Sea the first 15N-experiments were carried out in August-September 1990 and in November 1991. In surface waters nitrate uptake rates varied from 5.7 to 28.5 nM/l/h in summer and from 1.9 to 7.8 nM/l/h in autumn. In both seasons maximal and minimal rates were observed in frontal zones of shelf/slope areas and in open waters, respectively. In summer average nitrate uptake rate per unit of particulate organic nitrogen was 0.0037 1/h for all stations. In autumn it varied from 0.0007 1/h in the central part of the sea to 0.0033 1/h in the slope near the southeastern Crimean coast. In autumn ammonium uptake rate varied from 7.1 to 22.2 nM/l/h and from 0.0025 to 0.00094 1/h. Ammonium uptake correlated linearly with nitrate uptake, with new production being 22-36% of total summary nitrate and ammonium uptake. There was a linear correlation between nitrogen uptake and chlorophyll a concentrations in the Black Sea. In the water column in autumn both nitrate and ammonium uptake decreased as chlorophyll a concentration diminishes with depth.

Carbon isotopic composition of dissolved CO2, CO2 gas and methane in sediments from ODP Leg 172 sites

Carbon isotopic data of interstitial dissolved CO2 (CO2), CO2 gas, and methane show that a variety of microbial diagenetic processes produce the observed isotopic trends. Anaerobic methane oxidation (AMO) is an important process near the sulfate-methane interface (SMI) that strongly influences the isotopic composition of CO2 in the sulfate reduction and upper methanogenic zones, which in turn impacts methane isotopic composition. Dissolved CO2 and methane are maximally depleted in 13C near the SMI, where 13C values are as light as -31.8 and -101 PDB for CO2 and methane, respectively. CO2 reduction links the CO2 and methane pools in the methanogenic zone so that the carbon isotopic composition of both pools evolves in concert, generally showing increasing enrichments of 13C with increasing depth. These isotopic trends mirror those within other methane-rich continental rise sediments worldwide.

Dissolved actinium in the ocean

The measurement of short-lived 223Ra often involves a second measurement for supported activities, which represents 227Ac in the sample. Here we exploit this fact, presenting a set of 284 values on the oceanic distribution of 227Ac, which was collected when analyzing water samples for short-lived radium isotopes by the radium delayed coincidence counting system. The present work compiles 227Ac data from coastal regions all over the northern hemisphere, including values from ground water, from estuaries and lagoons, and from marine end-members. Deep-sea samples from a continental slope off Puerto Rico and from an active vent site near Hawaii complete the overview of 227Ac near its potential sources. The average 227Ac activities of nearshore marine end-members range from 0.4 dpm/m**3 at the Gulf of Mexico to 3.0 dpm m? 3 in the coastal waters of the Korean Strait. In analogy to 228Ra, we find the extension of adjacent shelf regions to play a substantial role for 227Ac activities, although less pronounced than for radium, due to its weaker shelf source. Based on previously published values, we calculate an open ocean 227Ac inventory of 1.35 * 1018 dpm 227Acex in the ocean, which corresponds to 37 moles, or 8.4 kg. This implies a flux of 127 dpm/m**2/y from the deep-sea floor. For the shelf regions, we obtain a global inventory of 227Ac of 4.5 * 10**15 dpm, which cannot be converted directly into a flux value, as the regional loss term of 227Ac to the open ocean would have to be included. Ac has so far been considered to behave similarly to Ra in the marine environment, with the exception of a strong Ac source in the deep-sea due to 231Paex. Here, we present evidence of geochemical differences between Ac, which is retained in a warm vent system, and Ra, which is readily released [Moore, W.S., Ussler, W. and Paull, C.K., 2008-this issue. Short-lived radium isotopes in the Hawaiian margin: Evidence for large fluid fluxes through the Puna Ridge. Marine Chemistry]. Another potential mechanism of producing deviations in 227Ac/228Ra and daughter isotope ratios from the expected production value of lithogenic material is observed at reducing environments, where enrichment in uranium may occur. The presented data here may serve as a reference for including 227Ac in circulation models, and the overview provides values for some end-members that contribute to the global Ac distribution.

Dissolved organic carbon in soil solution of the Jena Experiment (Main Experiment, year 2003)

This data set contains measurements of dissolved organic carbon in samples of soil water collected from the main experiment plots of a large grassland biodiversity experiment (the Jena Experiment; see further details below). In the main experiment, 82 grassland plots of 20 x 20 m were established from a pool of 60 species belonging to four functional groups (grasses, legumes, tall and small herbs). In May 2002, varying numbers of plant species from this species pool were sown into the plots to create a gradient of plant species richness (1, 2, 4, 8, 16 and 60 species) and functional richness (1, 2, 3, 4 functional groups). Plots were maintained by bi-annual weeding and mowing. In April 2002 glass suction plates with a diameter of 12 cm, 1 cm thickness and a pore size of 1-1.6 mm (UMS GmbH, Munich, Germany) were installed in depths of 10, 20, 30 and 60 cm to collect soil solution. The sampling bottles were continuously evacuated to a negative pressure between 50 and 350 mbar, such that the suction pressure was about 50 mbar above the actual soil water tension. Thus, only the soil leachate was collected. Cumulative soil solution was sampled biweekly and analyzed for dissolved organic carbon concentration by a high TOC elemental analyzer (Elementar Analysensysteme GmbH, Hanau, Germany). Samples were analyzed as soon as possible and stored at 4°C if necessary. Often in summer, no free soil solution was available for collection, especially in the upper soil layers. Annual mean values of measured biweekly concentrations of dissolved organic carbon are provided.