Part of the global DOC versus AOU (dissolved organic carbon/apparent oxygen utilization) data compilation, Arabian Sea

Concentrations of total organic carbon (TOC) were determined on samples collected during six cruises in the northern Arabian Sea during the 1995 US JGOFS Arabian Sea Process Study. Total organic carbon concentrations and integrated stocks in the upper ocean varied both spatially and seasonally. Highest mixed-layer TOC concentrations (80-100 µM C) were observed near the coast when upwelling was not active, while upwelling tended to reduce local concentrations. In the open ocean, highest mixed-layer TOC concentrations (80-95 µM C) developed in winter (period of the NE Monsoon) and remained through mid summer (early to mid-SW Monsoon). Lowest open ocean mixed-layer concentrations (65-75 µM C) occurred late in the summer (late SW Monsoon) and during the Fall Intermonsoon period. The changes in TOC concentrations resulted in seasonal variations in mean TOC stocks (upper 150 m) of 1.5-2 mole C/m**2, with the lowest stocks found late in the summer during the SW Monsoon-Fall Intermonsoon transition. The seasonal accumulation of TOC north of 15°N was 31-41 x 10**12 g C, mostly taking place over the period of the NE Monsoon, and equivalent to 6-8% of annual primary production estimated for that region in the mid-1970s. A net TOC production rate of 12 mmole C/m**2/d over the period of the NE Monsoon represented ~80% of net community production. Net TOC production was nil during the SW Monsoon, so vertical export would have dominated the export terms over that period. Total organic carbon concentrations varied in vertical profiles with the vertical layering of the water masses, with the Persian Gulf Water TOC concentrations showing a clear signal. Deep water (>2000 m) TOC concentrations were uniform across the basin and over the period of the cruises, averaging 42.3±1.4 µM C.

Oil slicks and hydrocarbons in sea water

Surface and upper-layer pollution of seas and oceans by crude oil and refinery products is under study by investigators in many countries. The Intergovernmental Oceanographic Commission (IOC) and World Meteorological Organization (WMO) have prepared an international experimental project that is to be carried out within the framework of the Integrated Global Oceanic Station System (IGOSS). The purpose of the project is to prepare a picture of distribution and dynamics of oil pollution. Parameters to be observed include: oil patches (slicks), floating lumps of tar on the surface, and hydrocarbons emulsified and dissolved in water. Cruise 22 of R/V Akademik Kurchatov took the ship through regions being the most suitable for pollution studies. They were conducted from March through June 1976. On the cruise, oil slicks were observed visually by a procedure recommended by the international program. Areas of the slicks were determined from speed of the ship and time required to cross them. Surface samples were taken along the path of the ship for determination of concentrations of dissolved and emulsified hydrocarbons in water. In addition, samples were taken from deep water by a 7-liter vinyl water bottle at 17 stations. Hydrocarbons present in the samples were extracted immediately with carbon tetrachloride. Final determination of hydrocarbons was made by infrared spectrophotometry. This method is currently accepted in the Soviet Union in an arbitration capacity for determination of petroleum products dissolved and emulsified in sea water. Infrared spectrophotometry is used to determine hydrocarbons containing methyl and methylene groups, but they are not identified as to origin.

Stable isotope ratios in shells of marine organisms

Oxygen and carbon isotope analyses have been carried out on calcareous skeletons of important recent groups of organisms. Annual temperature ranges and distinct developmental stages can be reconstructed from single shells with the aid of the micro-sampling technique made possible by modern mass-spectrometers. This is in contrast to the results of earlier studies which used bulk sampIes. The skeletons analysed are from Bermuda, the Philippines, the Persian Gulf and the continental margin off Peru. In these environments, seasonal salinity ranges and thus annual variations in the isotopic composition of the water are small. In addition, environmental parameters are weIl documented in these areas. The recognition of seasonal isotopic variations is dependant on the type of calcification. Shells built up by carbonate deposition at the margin, such as molluscs, are suitable for isotopic studies. Analysis is more difficult where chambers are added at the margin of the shell but where older chambers are simultaneously covered by a thin veneer of carbonate e. g. in rotaliid foraminifera. Organisms such as calcareous algae or echinoderms that thicken existing calcareous parts as weIl as growing in length and breadth are the most difficult to analyse. All organisms analysed show temperature related oxygen-isotope fractionation. The most recent groups fractionate oxygen isotopes in accordance with established d18O temperature relationships (Tab. 18, Fig. 42). These groups are deep-sea foraminifera, planktonic foraminifera, serpulids, brachiopods, bryozoa, almost all molluscs, sea urchins, and fish (otoliths). A second group of organisms including the calcareous algae Padina, Acetabularia, and Penicillus, as weIl as barnacles, cause enrichment of the heavy isotope 18O. Finally, the calcareous algae Amphiroa, Cymopolia and Halimeda, the larger foraminifera, corals, starfish, and holothurians cause enrichment of the lighter isotope 16O. Organisms causing non-equilibrium fractionation also record seasonal temperature variations within their skeletons which are reflected in stable-oxygen-isotope patterns. With the exception of the green algae Halimeda and Penicillus, all organisms analysed show lower d13C values than calculated equilibrium values (Tab. 18, Fig. 42). Especially enriched with the lighter isotope 12C are animals such as hermatypic corals and larger foraminifera which exist in symbiosis with other organisms, but also ahermatypic corals, starfish, and holothurians. With increasing age of the organisms, seven different d13C trends were observed within the skeletons. 1) No d13C variations are observed in deep-sea foraminifera presumably due to relatively stable environmental conditions. 2) Lower d13C values occur in miliolid larger foraminifera and are possibly related to increased growth with increasing age of the foraminifera. 3) Higher values are found in planktonic foraminifera and rotaliid larger foraminifera and can be explained by a slowing down of growth with increasing age. 4) A sudden change to lower d13C values at a distinct shell size occurs in molluscs and is possibly caused by the first reproductive event. 5) A low-high-Iow cycle in calcareous algae is possibly caused by variations in the stage of calcification or growth. 6) A positive correlation between d18O and d13C values is found in some hermatypic corals, all ahermatypic corals, in the septa of Nautilus and in the otoliths of fish. In hermatypic corals from tropical areas, this correlation is the result of the inverse relationship between temperature and light caused by summer cloud cover; in other groups it is inferred to be due to metabolic processes. 7) A negative correlation between d18O and d13C values found in hermatypic corals from the subtropics is explained by the sympathetic relationship between temperature and light in these latitudes. These trends show that the carbon isotope fractionation is controlled by the biology of the respective carbonate producing organisms. Thus, the carbon isotope distribution can provide information on the symbiont-host relationship, on metabolic processes and calcification and growth stages during ontogenesis of calcareous marine organisms.

Geochemical analysis of bulk sediment and interstitial water of sediment cores from the North-West African continental margin

Molybdenum and vanadium were analysed in 9 scediment cores recovered from the continental slope and rise off NW Africa. Additionall chemical and sedimentological parameters as well as isotope stage boundaries were available for the same core profiles from other investigations. Molybdenum, ranging between <1 and 10 ppm, occurs in two associateions, either with organic carbon and sulphides in sediments with reducing conditions or with Mn oxides in oxidized near-surface core sections. Highest values (between 4 and 10 ppm Mo) are found in sulphide-rich core sections deposited during glacial times in a core from 200 m water depth. The possibility of anoxic near-bottom water conditions prevailing at thhis site during certain glacial intervals is discussed. In oxidized near-surface core sections, the diagenetic mobility of Mo becomes evident from strong Mo enrichment together with Mn oxides (values up to 4 ppm Mo). This enrichment is probably due to coprecipitation and/or adsorption of Mo from interstitial water to the diagenetically forming Mn oxides. The close relation between Mo and Corg results in strongly covarying sedimentation rates in both components reaching up to 10 times the rates in glacial compared to interglacial core sections. Vanadium (values between 20 and 100 ppm) does not show clear relations to climate and near-bottom or sediment milieu. It occurs mainly bound to the fine grained terrigenous fraction, associated with aluminium silicates (clay minerals) and iron oxides. Additionally positive covariation of vanadium with phosphorus in most core profiles suggest that some V may be bound to phosphates.

(Table 1) Adenosine triphosphate, urea, dissolved organic carbon, nitrogen and methane concentrations in bottom water of the northwestern Indian Ocean

Concentrations of adenosine triphosphate (ATP), urea, and dissolved organic carbon in bottom water are shown to be considerable, sometimes several times higher than in the photic and surface layers of the ocean. Urea and ATP concentrations are inversely proportional. Identified biochemical characteristics of bottom water are of great importance in determining the status of the aquatic environment. The highest life activity (maximum ATP content) in bottom water appeared in the vicinity of faults in rift zones of the ocean, where high gas concentrations were also found. Population of chemoautotrophic microorganisms was clearly present under these conditions. Biochemical investigations provide additional criteria for identifying oil and gas prospects. They are also of definite interest in combination with gasometric determinations, which will undoubtedly give us deeper understanding of processes of formation of oil and gas and will help in finding them.