Lithium and rubidium concentrations in waters of seas and oceans

Data on lithium, rubidium and cesium concentrations in waters of open seas and oceans are summarized. Average amounts of these elements in the World Ocean inferred from published data and those obtained by the author are as follows: Li - 0.18 mg/l, Rb - 0.12 mg/l and Cs - 0.004 mg/l. Rare alkaline elements in the oceans and open seas are distributed (like sodium and potassium) in accordance with salinity. The ability of lithium to become a constituent of clay minerals accounts for its relatively low concentration in sea water as compared with that of sodium and potassium. Compared to rubidium and cesium that have high absorption energy and low hydration energy, lithium relatively enriches sea water. Residence times of these elements in the ocean are: Na - 120 My, Li - 2.7 My, Rb - 2.3 My and Cs - 0.3 My.

Chemistry of Late Quaternary sediments and their interstitial waters of sediment cores from the Nort-West African continental margin

In the sediments of the NW African continental margin the mainly biogenic carbonate constituents become increasingly diluted with terrigenous material as one approaches the coast, as indicated by the carbonate-CO2 content, the Al2O3/SiO2-ratios, and the presence of ammonia fixed to alumino-silicates, predominantly to illites. In the norther area of the investigation - off Cape Blanc and Cape Bojador . the terrigenous constituents are mainly quartz from the Sahara Desert, whereas in the south - off Senegal - more alumino-silicates as clay minerals are admixed with the carbonate constituents. The organic carbon content of the continental slope sediments off Senegal is higher than in samples of the continental rise or of the preservation of organic matter as a result of high production and relatively rapid sedimentation. The zone of manganese-oxide enrichment follows the redox potential of + 330 mV from the surface (0-5 cm) into the sediments (20-30 cm deep) at 2000--3000 m and 3700 m of water depths, respectively. At shallower water depths, low redox potentials preclude deposition of manganese oxides and cause their mobilization from the sediments. About 1/3 of the total sedimentary Zn and 1/4 of the Cu is associated with the carbonate mineral fraction, probably in calcium phosphate overgrowths as a result of the mineralization of phosphorus-containing organic matter. Besides the precipitation of calcium phosphate, the mineralization of organic matter mediated by bacterial sulfate reduction also results in calcium carbonate precipitation and the exchange of ammonia for potassium on illites. Because of these simultaneous reactions, the depth distribution of all mineralization constituents in the interstitial water can be determined using the actual molar carbon-to-nitrogen-to phosphorus ratios of the sedimentary organic matter. The amount of sulfide sulfur in this process indicates the predominance of bacterial sulfate reduction in the sediments off NW Africa. This process also preferentially decomposes nitrogen- and phosphorus-containing organic compounds so organic matter deficient in these elements is characteristic for the rapidly accumulating sediments than today, indicating there was increased production of organic carbon compounds and more favorable conditions of their preservations. During the last interglacial times conditions were similar to those to today. This differentiation with time has also been observed in sediments from the Argentine Basin and from slope off South India indicating perhaps world-wide environmental changes throughout Late Quaternary times.

Organic carbon and carbohydrates in waters of the Amazon River, Atlantic Ocean, and Tropical Indian Ocean

A method is presented to study carbohydrate composition of marine objects involved into sedimento- and diagenesis (plankton, particulate matter, benthos, and bottom sediments). Analysis of the carbohydrates is based on consecutive separation of their fractions with different solvents (water, alkali, and acid). Ratios of carbohydrate fractions allows to evaluate lability of carbohydrate complexes. They are also usable as an indicators of biogeochemical processes in the ocean, as well of genesis and degree of transformation of organic matter in bottom sediments and nodules. Similarity in monosaccharide composition is shown for dissolved organic matter and aqueous and alkaline fractions of seston and particulate matter.

Geochemistry of labile organic matter in sediments and interstitial waters of ODP Sites 107-651 and 107-653

Sediment and interstitial water from Sites 651 and 653 (ODP Leg 107) were investigated by organic geochemical methods to characterize labile organic compound classes (amino compounds and carbohydrates) and to evaluate their progressive diagenetic and thermal degradation in deep-sea sediments. Downhole distribution of dissolved organic carbon (DOC) appears related to redox zones associated with bacterial activity and of diagenetic recrystallization of biogenic tests and not so much to organic matter concentrations in ambient sediments. DOC ranges from 250 to 8300 µmol/L (3-100.1 ppm). Amino acids contribute 10%-0.3% of DOC; carbohydrates range from 78 to 5 µmol/L. Rate of degradation of amino acids by thermal effects and/or bacterial activity at both sites (significantly different in sedimentation rates: average 41 cm/1000 yr in the top 300 m at Site 651, average 3.9 cm/1000 yr in the Pliocene/Quaternary sequence at Site 653 to 220 mbsf) is more dependent on exposure time rather than on the depth within the sediment column. Variability in neutral, acidic, and basic amino acid fractions of total amino acids (with a range of 1.1-0.02 µmol/g sediment; up to 2.5% of organic carbon) varies with carbonate content and by differences in thermal stability of amino acids. Distribution patterns of monosaccharides are interpreted to result from differences in organic matter sources, sedimentation rates, and the degree of organic matter decomposition prior to and subsequent to burial. Total particulate carbohydrates range from 1.82 to 0.21 µmol/g sediment and contribute about 8% to the sedimentary organic matter. Investigation of trace metals in the interstitial waters did not show any correlation of either DOC, amino compounds, or carbohydrates.

Phosphorus dynamics in waters of the Pacific Ocean

Tagged phosphorus was used to measure principal indices of mineral phosphorus variations in the euphotic zone of the East Pacific, i.e. total rate of uptake of phosphate phosphorus by microplankton (A_t), fraction consumed by phytoplankton (A_p/A_t), and turnover time (T). A_t reached its greatest values (150-280 ng/l/hour) in the upwelling zone of the Peru traverse, where development of phytoplankton was induced by upwelling. In other areas of this traverse values were 40-80 ng/l/hour in surface layers. In less productive waters on two other profiles (off Central America and California), values were lower, between 20 and 40 ng/l. On the vertical profile maxima of A_t were found at the upper boundary of the thermocline. Turnover time of PO4 phosphorus (T) in zones of phytoplankton abundance was very short, between 1.5 and 4 days. At most other stations it was 10-40 days, increasing to 100-200 days or longer at the lower boundary of the euphotic zone. In areas of phytoplankton abundance it accounted for 60-80% of total uptake of PO4 phosphorus. But in zones of elevated bacterial abundance, A_p/A_t fell to 20-40%. Data indicating lack of correlation between PO4 phosphorus and productivity are presented. It is emphasized that the above measures of PO4 phosphorus dynamics can be used for obtaining measures of functional condition and successional phase of marine plankton communities.

Geochemistry of sediments and interstitial waters of ODP Sites 128-798 and128-799

Interstitial waters in sediments below 400 (Site 798) and 435 meters below seafloor (Site 799) have chloride concentrations of 516-527 and 501-515 mM, respectively, lower than the 540 mM of the modern-day Japan Sea. The chemical composition of interstitial waters, bulk sediments, clay-size sediment fraction, and carbonate nodules from Oki Ridge (Site 798) and Kita-Yamato Trough (Site 799), Japan Sea, reflect in-situ diagenetic processes superimposed on geochemical signals that may indicate freshening of Miocene local marginal basin waters. Interstitial waters at both sites exhibit changes in chemical composition which coincide with the occurrence of low-porosity and high-bulk density layers composed of dolomite and opal-CT, which impede diffusive communication with the overlying interstitial waters. Based on interstitial water stable isotope evidence and mass-balance calculations of chloride dilution, diagenetic reactions that involve the release of structural bound water from opal-A and/or clay minerals contribute to the observed geochemical signals, but cannot account for all the measured chloride dilution.

Bubble sizes in waters of the Atlantic Ocean

Typical size of bubbles obtained from cavitation inception pressure measured in the surface layer of the Atlantic Ocean in situ aboard R/V Professor Vize in 1971 and Nerey in 1973 are reported. These results do not contradict ones of bubble size measurements using optical or acoustical techniques. Variability of bubble size is discovered and described. This variability is related to passing from one geographical region to another (from 68°55'S to 61°52'N), to changes in depth (from 5 to 100 m) and in day time, as well as to spatial fluctuations within an aquatic area. It is suggested that, in addition to wave breaking, there is another source of bubbles at depth 10-20 m that associates with hydrobiological processes.

(Table T1) Amino acid ratios and concentrations in interstitial waters of seven ODP Leg 201 sites

Proteins and their amino acid building blocks form a major group of biomolecules in all organisms. In the sedimentary environment, proteins and amino acids have two sources: (1) soft tissues and detritus and (2) biotic skeletal structures, dominantly from calcium carbonate-secreting organisms. The focus of this report is on D/L ratios and concentrations of selected amino acids in interstitial waters collected during ODP Leg 201. The Peru margin sites are generally low in carbonates, whereas the open-ocean sites are more carbonate rich. Seifert et al. (1990, doi:10.2973/odp.proc.sr.112.152.1990) reported amino acid concentrations in interstitial waters from Site 681 (ODP Leg 112) comparable to Leg 201 Site 1229.

Hafnium and neodymium in surface waters of the Atlantic sector of the Southern Ocean

Radiogenic isotopes of hafnium (Hf) and neodymium (Nd) are powerful tracers for water mass transport and trace metal cycling in the present and past oceans. However, due to the scarcity of available data the processes governing their distribution are not well understood. Here we present the first combined dissolved Hf and Nd isotope and concentration data from surface waters of the Atlantic sector of the Southern Ocean. The samples were collected along the Zero Meridian, in the Weddell Sea and in the Drake Passage during RV Polarstern expeditions ANT-XXIV/3 and ANT-XXIII/3 in the frame of the International Polar Year (IPY) and the GEOTRACES program. The general distribution of Hf and Nd concentrations in the region is similar. However, at the northernmost station located 200 km southwest of Cape Town a pronounced increase of the Nd concentration is observed, whereas the Hf concentration is minimal, suggesting much less Hf than Nd is released by the weathering of the South African Archean cratonic rocks. From the southern part of the Subtropical Front (STF) to the Polar Front (PF) Hf and Nd show the lowest concentrations (<0.12 pmol/kg and 10 pmol/kg, respectively), most probably due to the low terrigenous flux in this area and efficient scavenging of Hf and Nd by biogenic opal. In the vicinity of landmasses the dissolved Hf and Nd isotope compositions are clearly labelled by terrigenous inputs. Near South Africa Nd isotope values as low as epsilon-Nd = -18.9 indicate unradiogenic inputs supplied via the Agulhas Current. Further south the isotopic data show significant increases to epsilon-Hf = 6.1 and epsilon-Nd = -4.0 documenting exchange of seawater Nd and Hf with the Antarctic Peninsula. In the open Southern Ocean the Nd isotope compositions are relatively homogeneous (epsilon-Nd ~ -8 to -8.5) towards the STF, within the Antarctic Circumpolar Current, in the Weddell Gyre, and the Drake Pasage. The Hf isotope compositions in the entire study area only show a small range between epsilon-Hf = +6.1 and +2.8 support Hf to be more readily released from young mafic rocks compared to old continental ones. The Nd isotope composition ranges from epsilon-Nd = -18.9 to -4.0 showing Nd isotopes to be a sensitive tracer for the provenance of weathering inputs into surface waters of the Southern Ocean.

(Table 1) Mineral phosphorus contents in bottom sediments and interstitial waters of the Southeast Atlantic

Concentrations of mineral phosphorus in interstitial waters from sediments of the Southeast Atlantic generally increases from the ocean bed to the continental slope and shelf. In diatomaceous oozes of the Southwest Africa shelf, phosphorus concentration in fresh interstitial waters reaches 2.5 mg/l in absence of phosphorite concretions and 0.1-0.7 mg/l in their presence. After prolonged storage of samples concentration of dissolved mineral phosphorus sometimes increases up to 7-8 mg/l. The key factor regulating phosphorus content of solid and liquid phases of unaltered sediments are content and composition of organic matter.

Chemistry of interstitial waters of ODP Leg 117 samples (Table 1)

Interstitial water analyses made at 12 sites during Leg 117 are used to define the nature of diagenetic reactions in organic-rich sediments on the Owen Ridge and Oman Margin. Minor variations in chloride concentration profiles are ascribed to past changes in bottom water salinity at two mid-depth margin sites and to upward migration of low salinity water at another. There is no evidence for subsurface brine movement, unlike the case on the Peru Margin. Dolomitization is widespread and accounts for the depletions of magnesium observed in pore waters at variable depths at nearly all sites. The mineral occurs both as disseminated euhedral limpid crystals and, in at least one location, in massive stringers. Formation of the latter is suggested to reflect precipitation during sea level transgressions when the sedimentation rate was low, but when productivity was high. Authigenic carbonate fluorapatite is also widespread, the phosphorus being derived from the breakdown of organic matter. Sulfate is quantitatively depleted at depth at most locations but the rate of depletion is markedly less than that observed on the Peru Margin where sedimentation is also similarly influenced by high rates of upwelling. The reason for this contrast is not clear and merits further investigation.

(Table 1) Mn, Fe, TOC and CaCO3 concentrations in bottom sediments and silt waters of Kandalaksha Bay, White Sea

The redox stratification of bottom sediments in Kandalaksha Bay, White Sea, is characterized by elevated concentrations of Mn (3-5%) and Fe (7.5%) in the uppermost layer, which is two orders of magnitude and one and a half times, respectively, higher than the average concentrations of these elements in the Earth's crust. The high concentrations of organic matter (Corg = 1-2%) in these sediments cannot maintain (because of its low reaction activity) the sulfate-reducing process (the concentration of sulfide Fe is no higher than 0.6%). The clearest manifestation of diagenesis is the extremely high Mn2+ concentration in the silt water (>500 µM), which causes its flux into the bottom water, oxidation in contact with oxygen, and the synthesis of MnO2 oxy-hydroxide enriching the surface layer of the sediments. Such migrations are much less typical of Fe. Upon oxygen exhaustion in the uppermost layer of the sediments, the synthesized oxyhydroxides (MnO2 and FeOOH) serve as oxidizers of organic matter during anaerobic diagenesis. The calculated diffusion-driven Mn flux from the sediments (280 µM/m**2 day) and corresponding amount of forming Mn oxyhydrate as compared to opposite oxygen flux to sediments (1-10 mM/m**2 day) indicates that >10% organic matter in the surface layer of the sediments can be oxidized with the participation of MnO2. The roles of other oxidizers of organic matter (FeOOH and SO4**2-) becomes discernible at deeper levels of the sediments. The detailed calculation of the balance of reducing processes testifies to the higher consumption of organic matter during the diagenesis of surface sediments than it follows from the direct determination of Corg. The most active diagenetic redox processes terminate at depths of 25-50 cm. Layers enriched in Mn at deeper levels are metastable relicts of its surface accumulation and are prone to gradual dissemination.

Abundance of tintinnids in waters of the Argentine Shelf and the Drake Passage 2002-2003

The relationship between the abundance and diversity of tintinnids and the concentration of chlorophyll a (Chl a) was contrasted between neritic and oceanic waters of the SW Atlantic during autumn and summer. Chl a and tintinnid abundance and biomass reached maximum values (17.53 µg/L, 2.76 x 10**3 ind./L and 6.29 µg C/L, respectively) in shelf waters during summer, and their mean values generally differed by one order of magnitude between environments. Peaks in species richness (13) and Shannon diversity index (2.12) were found in the shelf-ocean boundary, but both variables showed nonsignificant differences between areas. Species richness correlated significantly with both Chl a and abundance. Such relationships, which followed a negative linear or quadratic function in the shelf and a positive linear function in oceanic waters, are thought to reflect either the competitive dominance of one species or a relatively wide spectrum of tintinnid size-classes, respectively.