The Impact of the Major Baltic Inflow of December 2014 on the Mercury Species Distribution in the Baltic Sea.

The Baltic Sea is a marginal sea characterized by stagnation periods of several years. Oxygen consumption in its deep waters leads to the buildup of sulfide from sulfate reduction. Some of the microorganisms responsible for these processes also transform reactive ionic mercury to neurotoxic methylmercury. Episodic inflows of oxygenated saline water from the North Sea temporally re-establish oxic life in deep waters of the Baltic Sea. Thus, this sea is an especially important region to better understand mercury species distributions in connection with variable redox conditions. Mercury species were measured on three Baltic Sea campaigns, during the preinflow, ongoing inflow, and subsiding inflow of water, respectively, to the central basin. The inflowing water caused the removal of total mercury by 600 nmol m-2 and of methylmercury by 214 nmol m-2 in the Gotland Deep, probably via attachment of the mercury compounds to sinking particles. It appears likely that the consequences of the oxygenation of Baltic Sea deep waters, which are the coprecipitation of mercury species and the resettlement of the oxic deep waters, could lead to the enhanced transfer of accumulated mercury and methylmercury to the planktonic food chain and finally to fish.

A Multi-Pumping Flow System for In Situ Measurements of Dissolved Manganese in Aquatic Systems.

A METals In Situ analyzer (METIS) has been used to determine dissolved manganese (II) concentrations in the subhalocline waters of the Gotland Deep (central Baltic Sea). High-resolution in situ measurements of total dissolved Mn were obtained in near real-time by spectrophotometry using 1-(2-pyridylazo)-2-naphthol (PAN). PAN is a complexing agent of dissolved Mn and forms a wine-red complex with a maximum absorbance at a wavelength of 562 nm. Results are presented together with ancillary temperature, salinity, and dissolved O 2 data. Lab calibration of the analyzer was performed in a pressure testing tank. A detection limit of 77 nM was obtained. For validation purposes, discrete water samples were taken by using a pump-CTD system. Dissolved Mn in these samples was determined by an independent laboratory based method (inductively coupled plasma-optical emission spectrometry, ICP-OES). Mn measurements from both METIS and ICP-OES analysis were in good agreement. The results showed that the in situ analysis of dissolved Mn is a powerful technique reducing dependencies on heavy and expensive equipment (pump-CTD system, ICP-OES) and is also cost and time effective.

Effect of large magnetotactic bacteria with polyphosphate inclusions on the phosphate profile of the suboxic zone in the Black Sea.

The Black Sea is the world's largest anoxic basin and a model system for studying processes across redox gradients. In between the oxic surface and the deeper sulfidic waters there is an unusually broad layer of 10-40 m, where neither oxygen nor sulfide are detectable. In this suboxic zone, dissolved phosphate profiles display a pronounced minimum at the upper and a maximum at the lower boundary, with a peak of particulate phosphorus in between, which was suggested to be caused by the sorption of phosphate on sinking particles of metal oxides. Here we show that bacterial polyphosphate inclusions within large magnetotactic bacteria related to the genus Magnetococcus contribute substantially to the observed phosphorus peak, as they contain 26-34% phosphorus compared to only 1-5% in metal-rich particles. Furthermore, we found increased gene expression for polyphosphate kinases by several groups of bacteria including Magnetococcaceae at the phosphate maximum, indicating active bacterial polyphosphate degradation. We propose that large magnetotactic bacteria shuttle up and down within the suboxic zone, scavenging phosphate at the upper and releasing it at the lower boundary. In contrast to a passive transport via metal oxides, this bacterial transport can quantitatively explain the observed phosphate profiles.

PUMP-CTD-System for trace metal sampling with a high vertical resolution. A test in the Gotland Basin, Baltic Sea.

It is a great challenge to sample seawater across interfaces, for example the halocline or the redoxcline, to investigate trace metal distribution. With the use of 10l sampling bottles mounted to a wire or a CTD-Rosette it is possible to obtain a maximum vertical resolution of 5m. For the detection of small vertical structures in the vertical distribution of trace metals across the redoxcline, the CTD-Bottle-Rosette is not sufficient. Therefore, a PUMP-CTD-System was developed, which enables water sampling with high resolution (1m maximum) along a vertical profile. To investigate the suitability and possible contamination sources of this device two experiments were carried out in the Gotland Basin. The first experiment consisted of two separate profiles. The first profile was obtained with the CTD-Bottle-Rosette and the second with the PUMP-CTD-System. Both were taken from the bottom to the surface water layer. The second experiment was a combined profile obtained from the surface to the bottom with the PUMP-CTD-System attached to the CTD-Bottle-Rosette. Concentrations of dissolved Pb, Cd, Cu, Zn, Fe, Mn, Co and Ni from the "Niskin Bottles" and from the PUMP were measured and compared for each investigation. We demonstrate that it is useful to perform vertical sampling from lower to higher concentrations, e.g. surface to bottom in this environment, and that a longer flushing is required for sampling seawater in the anoxic bottom water. A comparison of the two systems for oxygen and hydrogen sulphide measurements showed an improvement of the precision and the quality of the sampling when using the PUMP. Thus, metal speciation at the oxic-anoxic gradient zone and on a high vertical resolution will be accessible. As concentrations of dissolved Pb, Cd, Cu, Zn, Co, Ni, Fe and Mn in seawater sampled with both devices were in the same range, we conclude that the PUMP-CTD-System is well suited to sample seawater for trace metal analyses.

Measuring unbiased metatranscriptomics in suboxic waters of the central Baltic Sea using a new in situ fixation system.

An analysis of the microbial metabolism is fundamental to understanding globally important element transformations. One culture-independent approach to deduce those prokaryotic metabolic functions is to analyze metatranscriptomes. Unfortunately, since mRNA is extremely labile, it is unclear whether the abundance patterns detected in nature are vulnerable to considerable modification in situ simply due to sampling procedures. Exemplified on comparisons of metatranscriptomes retrieved from pelagic suboxic zones of the central Baltic Sea (70-120 m depth), earlier identified as areas of high aerobic ammonium oxidation activity, and quantification of specific transcripts in them, we show that different sampling techniques significantly influence the relative abundance of transcripts presumably diagnostic of the habitat. In situ fixation using our newly developed automatic flow injection sampler resulted in an abundance of thaumarchaeal ammonia monooxygenase transcripts that was up to 30-fold higher than that detected in samples obtained using standard oceanographic sampling systems. By contrast, the abundance of transcripts indicative of cellular stress was significantly greater in non-fixed samples. Thus, the importance of in situ fixation in the reliable evaluation of distinct microbial activities in the ecosystem based on metatranscriptomics is obvious. In consequence, our data indicate that the significance of thaumarchaeota to aerobic ammonium oxidation could yet have been considerably underestimated. Taken these results, this could in general also be the case in attempts aimed at an unbiased gene expression analysis of areas below the epipelagic zone, which cover 90% of the world's oceans.