(Table 2) Concentrations of dissolved aluminum in interstitial water from sediments of the Indian Ocean

Results are presented of application of laser stepwise photoionization of atoms in combination with thermal atomization of matter in vacuum for direct determination of aluminum dissolved in sea and interstitial waters. Dry residue from evaporation of 40 ?l sea water was atomized in a crucible at 1800°C, and aluminum atoms in the beam thus formed were energized into Rydberg state in two steps by two tunable dye laser beams; the atoms were then ionized by an electric pulse and resulting ions were recorded by secondary emission electron multiplier (ion detector). Ionic signal dependence on sample vaporization time was studied. The procedure is suggested for separating out a selective signal in a single measurement. Dissolved aluminum concentrations in interstitial waters of the Indian Ocean and in waters of the river-sea zone were determined using preliminarily plotted calibration characteristics for aluminum solutions in deionized and sea waters. The minimum detectable Al concentration in seawater was 1 ?g/l that corresponds to 40 pg of Al in a sample.

Radionuclides measured on water bottle samples

Actinium is one of the rarest naturally occurring elements on earth. We measured its longest-lived isotope 227Ac (half-life 21.77 yr) for the first time in the water column of the Southeast Pacific, the Central Arctic, the Antarctic Circumpolar Current (ACC) and the Weddell Gyre (WG). Besides the profile in the Southeast Pacific, which confirms earlier findings about the role of diapycnal mixing for 227Ac distribution, we found three other different types of vertical profiles. These profiles point to a prominent role of advection for 227Ac distribution, especially in the Southern Ocean. Depending on the type of profile found, 227Ac is proposed as a tracer for different oceanographic questions. In the Southern Ocean, up to 4.93±0.32 dpm/m**3 227Ac is found close to the sea floor, which is the highest concentration ever observed in the ocean. Close to the sea surface in the WG, 0.46±0.05 dpm/m**3 227Acex (227Ac in excess of its progenitor 231Pa) is detected. We use 227Acex there to determine the upwelling velocity in the Eastern WG to be about 55 m/yr. In the ACC, Upper and Lower Circumpolar Deep Water (UCDW and LCDW) are found to differ clearly in their 227Acex activity. High 227Acex activities are therefore a promising tracer for recent inputs of LCDW to the sea surface, which may help to understand the role of deep upwelling for iron inputs into Antarctic surface waters. The expected release of 227Ac is compared with 228Ra to make sure that the large near-surface excess in the water column of the Southern Ocean is not due to lateral inputs by isopycnal mixing. Data from the Central Arctic and from a transect across the ACC confirm that 228Ra and 227Acex differ strongly in their sources. The first measurements of 227Ac on suspended matter (less than 1.7% of total 227Ac close to the sea floor) indicate that the particle reactivity of 227Ac is negligible in the open ocean, in agreement with earlier findings [Y. Nozaki, Nature 310 (1984) 486-488]. Despite the extremely low concentrations of 227Ac, new measurement techniques [W.S. Moore, R. Arnold, J. Geophys. Res. 101 (1996) 1321-1329] point to a comfortable and comparably simple determination of 227Ac in the future. Finally, 227Acex may become a widely used deep-sea specific tracer.

In situ pore water oxygen microprofiles from the Polar Front, Southern South Atlantic Ocean

Without doubt, global climate change is directly linked to the anthropogenic release of greenhouse gases such as carbon dioxide (CO2) and methane (UN IPCC-Report 2007). Therefore, research efforts to comprehend the global carbon cycle have increased during the last years. In the context of the observed changes, it is of particular interest to decipher the role of the hydro-, bio- and atmospheres and how the different compartments of the earth system are affected by the increase of atmospheric CO2. Due to its huge carbon inventory, the marine carbon cycle represents the most important component in this respect. Numerous findings suggest that the Southern Ocean plays a key role in terms of oceanic CO2 uptake. However, an exact quantification of such fluxes of material is hard to achieve for large areas, not least on account of the inaccessibility of this remote region. In particular, there exist so far only few accurate data for benthic carbon fluxes. The latter can be derived from high resolution pore water oxygen profiles, as one possible method. However the ex situ flux determinations carried out on sediment cores, tend to suffer from temperature and pressure artefacts. Alternatively, oxygen microprofiles can be measured in situ, i.e. at the seafloor. Until now, no such data have been published for the Southern Ocean. During the Antarctic Expedition ANT-XXI/4, within the framework of this thesis, in situ and ex situ oxygen profiles were measured and used to derive benthic organic carbon fluxes. Having both types of measurements from the same locations, it was possible to establish a depth-related correction function which was applied subsequently to revise published and additional unpublished carbon fluxes to the seafloor. This resulted in a consistent data base of benthic carbon inputs covering many important sub-regions of the Southern Ocean including the Amundsen and Bellingshausen Seas (southern Pacific), Scotia and Weddell Seas (southern South Atlantic) as well as the Crozet Basin (southern Indian Ocean). Including additional locations on the Antarctic Shelf, there are now 134 new and revised measurement locations, covering almost 180° of the Southern Ocean, for which benthic organic carbon fluxes and sedimentary oxygen penetration depth values are available. Further, benthic carbon fluxes were empirically related to dominant diatom distributions in surface sediments as well as to long-term remotely sensed chlorophyll-a estimates. The comparison of these results with benthic carbon fluxes of the entire Atlantic Ocean reveals significantly higher export efficiencies for the Southern Ocean than have previously been assumed, especially for the area of the opal belt.