Abstract. We introduce the OSI-450, the SICCI-25km and the SICCI-50km climate data records of gridded global sea-ice concentration. These three records are derived from passive microwave satellite data and offer three distinct advantages compared to existing records: first, all three records provide quantitative information on uncertainty and possibly applied filtering at every grid point and every time step. Second, they are based on dynamic tie points, which capture the time evolution of surface characteristics of the ice cover and accommodate potential calibration differences between satellite missions. Third, they are produced in the context of sustained services offering committed extension, documentation, traceability, and user support. The three records differ in the underlying satellite data (SMMR & SSM/I & SSMIS or AMSR-E & AMSR2), in the imaging frequency channels (37 GHz and either 6 or 19 GHz), in their horizontal resolution (25 or 50 km), and in the time period they cover. We introduce the underlying algorithms and provide an evaluation. We find that all three records compare well with independent estimates of sea-ice concentration both in regions with very high sea-ice concentration and in regions with very low sea-ice concentration. We hence trust that these records will prove helpful for a better understanding of the evolution of the Earth's sea-ice cover.

Laboratory calibration of a beam transmissometer by using natural sedimentary particles fractionated into seven size classes demonstrates that slopes of light attenuation vs. particle mass concentration regressions systematically vary with the size distributions of the particles. Suspensions with a mean particle size of 8.5 μm attenuate 660‐nm light 15 times more efficiently than suspensions of similar particles with a mean diameter of 48 μm. Theoretical calculations of attenuation, based on scattering by spherical particles with the measured size distributions, underestimate observed attenuation by factors of 2–4, apparently because the nonspherical shape and roughness typical of natural particles create an effective optical diameter larger than that for a sphere of equal volume. These laboratory results agree with the trend established from a survey of published field data showing that calibration slopes experience a steady increase from inshore high‐energy waters, where large particles are common, to offshore low‐energy waters, where large particles are rare.

During two Atlantis II/Alvin cruises to the Juan de Fuca Ridge in 1984 active high temperature (140ø-284øC) vents were sampled for black smoker particulates using the Grassle Pump. Individual mineral phases were identified using standard X ray diffraction and petrographic procedures. In addition, elemental compositions and particle morphologies were determined by X ray energy spectrometry and scanning electron microscope/X ray energy spectrometry techniques. The vent particulates from the southern Juan de Fuca Ridge vent sites were highly enriched in S, Si, Fe, Zn, and Cu and were primarily composed of sphalerite, wurtzite, pyrite, pyrrhotite, barite, chalcopyrite, cubanite, hydrous iron oxides, and elemental sulfur. Two additional unidentified phases which were prevalent in the samples included an Fe-Si phase and a Ca-Si phase. The grain sizes of the individual particle phases ranged from < 2 #m for the sphalerite and Fe oxide particles to > 100 ttm for the Fe-Si particles. Grain size and current meter data were used in a deposition model of individual phase dispersal. For many of the larger sulfide and sulfate particles, the model predicts dispersal to occur over length scales of only several hundreds of meters. The high-temperature black smokers from the more northerly Endeavour Segment vents were highly enriched in Fe, S, Ca, Cu, and Zn and were primarily composed of anhydrite, chalcopyrite, sphalerite, barite, sulfur, pyrite, and other less abundant metal sulfide minerals. The grain sizes of the individual particles ranged from < 10 ttm to slightly larger than 500 ttm. The composition and size distributions of the mineral phases are highly suggestive of high-temperature mixing between vent fluids and seawater. A series of field and laboratory studies were conducted to determine the rates of dissolution of several sulfate and sulfide minerals. The dissolution rates ranged over more than 3 orders of magnitude, from 3.2 x 10 -8 cm s -• for anhydrite to 1.2 x 10 -12 cm s -• for chalcopyrite. The results indicate that for some minerals, particularly anhydrite and marcasite, total dissolution occurs within a few hours to a few weeks of their formation. For other more stable minerals, including pyrite, sphalerite and chalcopyrite, the time required for total dissolution is much longer, and consequently, individual crystals may be expected to persist in the sediments for considerable periods of time after deposition. conditions, should significantly enhance our understanding of hydrothermal sediment formation.In this paper, we report the initial results of our studies of the composition of black smoker particulates collected from active vents on the Juan de Fuca Ridge system. Also presented are the results of our field and laboratory experiments of sulfide oxidation and sulfate dissolution under in situ conditions and a model for the deposition of black smoker particulates in the near-field regions surrounding the vents. BACKGROUND Early studies of hydrothermal particulates indicated the existence of two major types...

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Evidence of large‐scale episodic venting of hydrothermal fluids was initially discovered in August 1986 in the form of a 130‐km3 radially symmetric “megaplume” over the southern Juan de Fuca Ridge. We report here on the discovery in September 1987 of a second, smaller megaplume about 45 km north of the location of the first megaplume. The 3He/heat, 3He/dissolved Mn, and 3He/dissolved silica ratios in both megaplumes were typical of high‐temperature vent fluids. Evidence from long‐term records of current flow over the southern Juan de Fuca Ridge, and from the mineralogy and Mn chemistry of megaplume particles, makes it unlikely that the second megaplume was a reencounter of the first. A plume model that relates the heat flux to the observed plume rise height of ∼1000 m finds that the total heat content of the fluids that formed the megaplumes was 1016–1017 J, or equivalently a fluid volume of 3–8 × 107 m3 at 350°C. The geometry and suspended particle population of the first megaplume imply that such features are formed within a few days time. The extraordinary heat and volume fluxes associated with megaplumes (102–103 greater than ordinary vent fields), as well as their typical hydrothermal chemistry, suggest that they resulted from tectonic or hydraulic fracturing that suddenly increased the permeability of the hydrothermal fluid reservoir in the axial crust. The flux of hydrothermal heat from continuous venting and episodic megaplumes on the southern Juan de Fuca Ridge is presently 4 − 10 × 109 W, a factor of 5–10 greater than various geophysical model calculations for this ridge segment. This imbalance may be symptomatic of a recent surge in the local cycle of magmatic activity.