Ralf D. Prien

Hydrothermal exploration of the Fonualei Rift and Spreading Center and the Northeast Lau Spreading Center

We report evidence for active hydrothermal venting along two back-arc spreading centers of the NE Lau Basin: the Fonualei Rift and Spreading Center (FRSC) and the Northeast Lau Spreading Center (NELSC). The ridge segments investigated here are of particular interest as the potential source of a mid-water hydrothermal plume (1500–2000 m depth) which extends more than 2000 km across the SW Pacific Ocean dispersing away from an apparent origin close to the most northeastern limits of the Lau Basin. Our results indicate the presence of at least four new hydrothermal plume sources, three along the FRSC and one on the NELSC, the latter situated within 150 km of the maximum for the previously identified SW Pacific regional-scale plume. However, TDFe and TDMn concentrations in the southernmost FRSC plume that we have identified only reach values of 19 and 13 nmol/L and dissolved 3He anomalies in the same plume are also small, both in relation to the SW Pacific plume and to local background, which shows evidence for extensive 3He enrichment throughout the entire Lau Basin water column. Our results reveal no evidence for a single major point hydrothermal source anywhere in the NE Lau Basin. Instead, we conclude that the regional-scale SW Pacific hydrothermal plume most probably results from the cumulative hydrothermal output of the entire topographically restricted Lau Basin, discharging via its NE-most corner.

Trajectories of sinking particles and the catchment areas above sediment traps in the northeast Atlantic

A Lagrangian analysis of particles sinking through a velocity field observed by Eulerian frame measurements was used to evaluate the effects of horizontal advection and particle sinking speed on particle fluxes as measured by moored sediment traps. Characteristics of the statistical funnel above moored deep-ocean sediment traps at the German JGOFS quasi-time series station at 47N, 20W (Biotrans site) were determined. The analysis suggests that the distance and direction between a given sediment trap and the region at the surface where the particles were produced depends on the mean sinking velocity of the particles, the horizontal velocity field above the trap and the deployment depth of the trap. Traps moored at different depths at a given mooring site can collect particles originating from different, separated regions at the surface ocean. Catchment areas for a given trap vary between different years. Typical distances between catchment areas of traps from different water depth but for a given time period (e.g., the spring season) are similar or even larger compared to typical length scales of mesoscale variability of phytoplankton biomass observed in the temperate northeast Atlantic. This implies that particles sampled at a certain time at different depth horizons may originate from completely independent epipelagic systems. Furthermore catchment areas move with time according to changes in the horizontal flow field which jeopardizes the common treatment of interpreting a series of particle flux measurements as a simple time series. The results presented in this work demonstrate that the knowledge of the temporal and spatial variability of the velocity field above deep-ocean sediment traps is of great importance to the interpretation of particle flux measurements. Therefore, the one-dimensional interpretation of particle flux observations should be taken with care.

Optical measurements of nitrate and H 2 S concentrations in Baltic waters

Nitrate and H2S concentrations were measured in 31 water samples from 4 CTD Stations in the North Atlantic and 234 water samples from all basins of the Baltic Sea, using standard wet chemical laboratory methods in parallel with a commercial in situ absorption spectrometer. The parameters for fitting the absorption spectra to sets of calibration spectra were optimized as a preparation to use the commercial instrument in situ.

Development and first results of a new mesoporous microelectrode DO-sensor

A new dissolved oxygen (DO) sensor for marine application was developed and first tests in the field were carried out. The sensor uses a mesoporous microelectrode as the sensing element that has an inherently fast response and an increased resistivity to bio-fouling due to the properties of the electrode material, mesoporous platinum. Introduction of a cleaning cycle, where the potential applied to the electrode is altered, allows the elimination of material build up at the electrode surface as well as the reconditioning of the electrode-surface, thus minimising drift and the effect of bio-fouling. Mesoporous microdisc electrodes ranging between 10 and 50 /spl mu/m diameter have been tested. The sensor has been adapted to operate on a CTD system. Results of two test cruises are presented, showing that although the general sensor performance is good further work has to be done to exploit the inherently fast response of the microelectrodes.

Development and first results of a new fast response microelectrode DO-sensor

A new dissolved oxygen sensor for marine application was developed and first tests in the field were carried out. The sensor uses a micro-electrode as the sensing element that has an inherently fast response and an increased resistance to bio-fouling due to the properties of the electrode material, platinum, and the employed operation regime. Introduction of a cleaning cycle, where the potential applied to the electrode is altered, allows the elimination of material building up at the electrode surface as well as the reconditioning of the electrode-surface, thus minimizing drift and the effect of bio-fouling. Microdisc electrodes ranging between 10 and 50 /spl mu/m diameter have been tested. The sensor has been adapted to operate on a CTD system or on towed instrument platforms. Results of test cruises will be presented.

Diffusive Convection under Rapidly Varying Conditions

AbstractIn most observations of diffusive convection in the ocean and in lakes, the characteristic diffusive staircases evolve over long time scales under quasi-stationary background conditions. In...

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 O2 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.