ALBERT

Beschreibung: Surface water distributions of dissolved Al (dAl) and dissolved Ti (dTi) were investigated along a meridional Atlantic transect and related to dust deposition estimates. In the zone of Saharan dust deposition, highest dAl concentrations occurred in the tropical salinity minimum and suggest increasing Al dissolution from Saharan aerosols with wet deposition. By contrast, the dTi distribution is not related to precipitation but agrees with the pattern of annual dust deposition. In the zone of Patagonian dust deposition, elevated dTi concentrations contrasted with decreased dAl concentrations, indicating excess dAl scavenging onto biogenic particles in surface waters. Estimated residence times range from months to years for dAl and are ∼10 times higher for dTi. This suggests that dAl reflects seasonal changes in dust deposition, while dTi is related to longer temporal scales. However, spatial variations in input and removal processes complicate the quantification of dust deposition from surface water concentrations.

Beschreibung: Seventeen inorganic germanium and silicon concentration profiles collected from the Atlantic, southwest Pacific, and Southern oceans are presented. A plot of germanium concentration versus silicon concentration produced a near-linear line with a slope of 0.760 × 10−6 (±0.004) and an intercept of 1.27 (±0.24) pmol L−1 (r2 = 0.993, p 〈 0.001). When the germanium-to-silicon ratios (Ge/Si) were plotted versus depth and/or silicon concentrations, higher values are observed in surface waters (low in silicon) and decreased with depth (high in silicon). Germanium-to-silicon ratios in diatoms (0.608–1.03 × 10−6) and coupled seawater samples (0.471–7.46 × 10−6) collected from the Southern Ocean are also presented and show clear evidence for Ge/Si fractionation between the water and opal phases. Using a 10 box model (based on PANDORA), Ge/Si fractionation was modeled using three assumptions: (1) no fractionation, (2) fractionation using a constant distribution coefficient (KD) between the water and solid phase, and (3) fractionation simulated using Michaelis-Menten uptake kinetics for germanium and silicon via the silicon uptake system. Model runs indicated that only Ge/Si fractionation based on differences in the Michaelis-Menten uptake kinetics for germanium and silicon can adequately describe the data. The model output using this fractionation process produced a near linear line with a slope of 0.76 × 10−6 and an intercept of 0.92 (±0.28) pmol L−1, thus reflecting the oceanic data set. This result indicates that Ge/Si fractionation in the global ocean occurs as a result of subtle differences in the uptake of germanium and silicon via diatoms in surface waters.

Beschreibung: Iron solubility measurements in the Mauritanian upwelling and the adjacent Open Ocean of the Tropical Atlantic show for all stations lower values in the surface mixed layer than at depth below the pycnocline. We attribute this distribution to a combination of loss terms, chiefly photo-oxidation of organic ligands in the surface, and supply terms, predominantly from the release of ligands from the decomposition of organic matter. Significant correlations with pH, oxygen and phosphate for all samples below the surface mixed layer indicate that biogenic remineralisation of organic matter results in the release of iron binding ligands into the dissolved phase. The comparison of the cFe(S)/PO(4)(3-) ratio with other published data from intermediate and deep waters in the Pacific suggests an enhanced release of iron chelators in the more productive Mauritanian upwelling zone. Citation: Schlosser, C., and P.L. Croot (2009), Controls on seawater Fe(III) solubility in the Mauritanian upwelling zone

Beschreibung: Nitrogen fixation supports new production in the oligotrophic oceans and removes dinitrogen and carbon dioxide from mixed layer waters. N‐fixation rates have been estimated in various ways but measurements are still too rare and factors limiting N‐fixation are not yet fully understood. Here we present data from a transect along 10°N through the tropical Atlantic on the Meteor Cruise 55 where N‐fixation rates between 3.7 and 255 μmol N*m−2*d−1 were recorded. The highest rates occurred off Africa in the eastern tropical North Atlantic (ETNA), and in the Amazon River plume in the West and contributed to 1–12.2% of the N‐demand of primary production. N‐fixation rates correlated with dissolved Fe concentrations, which were 20–280 times greater than the estimated demand. High atmospheric Fe inputs combined with the shallow nutricline make the ETNA a favourable environment for N‐fixers.

Beschreibung: Surface active substances (SAS) in the water column were measured by voltammetry using the electrochemical probe o-nitrophenol (ONP) during EIFEX, a mesoscale open ocean iron enrichment experiment in the Southern Ocean. SAS levels were low throughout the experiment (〈0.005 – 0.03 mg L−1 Triton X-100 equivalents). Initially SAS was extremely low in the photic zone, but as the phytoplankton bloom developed concentrations markedly increased throughout the upper 100 m (∼0.02 mg L−1 Triton X-100 equivalents). Highest concentrations of SAS (〉0.02 mg L−1 Triton X-100 equivalents) were found at the end of the bloom particularly at density discontinuities where organic material may accumulate. Exudates from diatoms appeared to be the major source of SAS during EIFEX, either from direct extracellular release or in the action of being grazed upon by zooplankton.

Beschreibung: Volcanoes confront Earth scientists with new fundamental questions: Can airborne volcanic ash release nutrients on contact with seawater, thereby excite the marine primary productivity (MPP); and, most notably, can volcanoes through oceanic fertilization affect the global climate in a way that is so far poorly understood? Here we present results from biogeochemical experiments showing that 1) volcanic ash from subduction zone volcanoes rapidly release an array of nutrients (co-)limiting algal growth in vast oceanic areas, 2) at a speed much faster (minute-scale) than hitherto known and that marine phytoplankton from low-iron oceanic areas can swiftly, within days, utilize iron from volcanic sources. We further present satellite data possibly indicating an increase of the MPP due to the seaward deposition of volcanic particulate matter. Our study supports the hypothesis that oceanic (iron) fertilization with volcanic ash may play a vital role for the development of the global climate.

Beschreibung: The effects of physical processes on the distribution, speciation, and sources/sinks for Fe in a high-nutrient low-chlorophyll (HNLC) region were assessed during FeCycle, a mesoscale SF6 tracer release during February 2003 (austral summer) to the SE of New Zealand. Physical mixing processes were prevalent during FeCycle with rapid patch growth (strain rate γ = 0.17–0.20 d−1) from a circular shape (50 km2) into a long filament of ∼400 km2 by day 10. Slippage between layers saw the patch-head overlying noninfused waters while the tail was capped by adjacent surface waters resulting in a SF6 maximum at depth. As the patch developed it entrained adjacent waters containing higher chlorophyll concentrations, but similar dissolved iron (DFe) levels, than the initial infused patch. DFe was low ∼60 pmol L−1 in surface waters during FeCycle and was dominated by organic complexation. Nighttime measurements of Fe(II) ∼20 pmol L−1 suggest the presence of Fe(II) organic complexes in the absence of an identifiable fast Fe(III) reduction process. Combining residence times and phytoplankton uptake fluxes for DFe it is cycled through the biota 140–280 times before leaving the winter mixed layer (WML). This strong Fe demand throughout the euphotic zone coupled with the low Fe:NO3 − (11.9 μmol:mol) below the ferricline suggests that vertical diffusion of Fe is insufficient to relieve chronic iron limitation, indicating the importance of atmospheric inputs of Fe to this region.

Beschreibung: The paper presents the current status of the Maritime Aerosol Network (MAN), which has been developed as a component of the Aerosol Robotic Network (AERONET). MAN deploys Microtops handheld Sun photometers and utilizes the calibration procedure and data processing (Version 2) traceable to AERONET. A web site dedicated to the MAN activity is described. A brief historical perspective is given to aerosol optical depth (AOD) measurements over the oceans. A short summary of the existing data, collected on board ships of opportunity during the NASA Sensor Intercomparison and Merger for Biological and Interdisciplinary Oceanic Studies (SIMBIOS) Project is presented. Globally averaged oceanic aerosol optical depth (derived from island-based AERONET measurements) at 500 nm is similar to 0.11 and Angstrom parameter (computed within spectral range 440-870 nm) is calculated to be similar to 0.6. First results from the cruises contributing to the Maritime Aerosol Network are shown. MAN ship-based aerosol optical depth compares well to simultaneous island and near-coastal AERONET site AOD.

Beschreibung: Measurements of dissolved (DFe) and total iron (TFe) in the upper water column are presented from the German SOLAS (Surface Ocean ‐ Lower Atmosphere Study) cruise (M55), along a west to east transect at 10°N, in the equatorial Atlantic in October/November 2002. Aerosol samples were collected simultaneously during this time and are used to estimate an iron flux to the surface waters. Resulting flux estimates combined with iron inventories in the near surface waters reveal extremely short fractional mean residence times (6–62 days) for total (dissolved and particulate) iron in waters directly under the path of Saharan dust plumes. These results suggest that individual dust storms can supply a significant amount of the present iron upper water column inventory which is subsequent rapidly removed by aggregation and sinking.