Geochemistry of recent marine sediments, interstitial water, and sea water from the West African continental margin

Carbon dioxide, ammonia, and reactive phosphate in the interstitial water of three sediment cores of the West African continental margin result from oxidation of sedimentary organic matter by bacterial sulfate reduction. The proposed model is a modification of one initially suggested by Richards (1965) for processes in anoxic waters: (CH2O)106 (NH3)8 (H3PO4) (0.7-0.2) + 53 SO4**2- =106 CO2 + 106 H20 + 8 NH3 + (0.7 - 0.2) H3PO4 + 53 S**2- The amount of reduced interstitial sulfate, the carbon-to-nitrogen-to-phosphorus atomic ratio of the sedimentary organic matter, as well as small amounts of carbon dioxide, which precipitated as interstitial calcium carbonate, are included in the general oxidation-reduction reaction. Preferential loss of nitrogen and phosphorus from organic matter close to the surface was recorded in both the interstitial water and sediment composition. It appeared that in deeper sections of the core organic carbon compounds were oxidized which were probably in an even lower oxidation state than that indicated by the proposed model. An estimated 2 % of the amount of organic matter still present was oxidized after it became incorporated into the sediment; whereas sulfide sulfur contents indicate that a much larger percentage (15-20%) seemed to have been subject to bacterial oxidation during the Pleistocene period, when a very thin oxidizing layer on the sediment allowed the above decomposition process to start relatively early favoured by almost fresh organic matter, and by almost unrestricted exchange of sulfate with the overlying water.

Radium in Arctic surface water

The transpolar drift is strongly enriched in 228Ra accumulated on the wide Arctic shelves with subsequent rapid offshore transport. We present new data of Polarstern expeditions to the central Arctic and to the Kara and Laptev seas. Because 226Ra activities in Pacific waters are 30% higher than in Atlantic waters, we correct 226Ra for the Pacific admixture when normalizing 228Ra with 226Ra. The use of 228Ra decay as age marker critically depends on the constancy in space and time of the source activity, a condition that has not yet adequately been tested. While 228Ra decays during transit over the central basin, ingrowth of 228Th could provide an alternative age marker. The high 228Th/228Ra activity ratio (AR = 0.8-1.0) in the central basins is incompatible with a mixing model based on horizontal eddy diffusion. An advective model predicts that 228Th grows to an equilibrium AR, the value of which depends on the scavenging regime. The low AR over the Lomonosov Ridge (AR = 0.5) can be due to either rapid transport (minimum age without scavenging 1.1 year) or enhanced scavenging. Suspended particulate matter load (derived from beam transmission and particulate 234Th) and total 234Th depletion data show that scavenging, although extremely low in the central Arctic, is enhanced over the Lomonosov Ridge, making an age of 3 years more likely. The combined data of 228Ra decay and 228Th ingrowth confirm the existence of a recirculating gyre in the surface water of the eastern Eurasian Basin with a river water residence time of at least 3 years.

(Table 3) Boron and chlorine in atmospheric moisture and rain water collected on the shore of the Golubaya Bay in 1970

Boron and chlorine were determined in rain water and in atmospheric moisture condensed in a "Saratov" refrigerator. Ocean is the main source of boron on the earth surface. Boron evaporates from the ocean and enriches atmospheric precipitation: B/Cl ratio of ocean water (0.00024) increases by factor of 10-15. Assuming that the average Cl content in global river runoff is 7.8 mg/l and boron content 0.013 mgl, B/Cl ratio in this runoff is 0.0017. The average B/Cl ratio in rain water of the Golubaya (Blue) Bay (Gelendzhik, Black Sea region) is 0.0026 and in condensates of atmospheric moisture during onshore and offshore winds in the same region it averages from 0.0029 to 0.0033. The maximum boron content in the condensates of this region during onshore winds was 0.032 mg/l and the minimum during offshore winds, 0.004 mg/l. /Cl ratio in sea water over the Atlantic Ocean and in the Gelendzhik area of the Black Sea varied within narrow range, mostly from 0.0025 to 0.0035. Similar B/Cl ratio (0.0024) was found for atmospheric precipitation on the slope of the Terskei Ala-Tau near the Issyk-Kul Lake in 1969. Thus, although chemistries of boron and chlorine (in chlorides) are very different, the B/Cl ratio in the atmosphere is fairly constant. This can be taken as a confirmation of an assumption that salt composition of sea water passes into the atmosphere in molecularly dispersed state. Supposing that the ocean-atmosphere system is in equilibrium as regards to the boron budget, it can be assumed that the same amount of boron passes from the ocean into bottom sediments and from lithosphere rocks and soils into the hydrosphere.

(Table 3) Sulfur and oxygen isotopic composition of cold water soluble sulfate, and strontium content and isotopic composition of upper Miocene evaporite samples recovered from DSDP Site 23-227

The origin of three Red Sea submarine brine pools was investigated by analysis of the S and O isotope ratios of dissolved sulfate and Sr isotope ratios of dissolved Sr in the brines. Sulfur and O isotope ratios of sulfate and Sr isotope ratios of evaporitic source rocks for the brines were measured for comparison. The S, O and Sr isotope ratios of evaporites recovered from DSDP site 227 are consistent with an upper Miocene evaporites age. The Valdivia Deep brine formed by karstic dissolution of Miocene evaporites by overlying seawater and shows no signs of hydrothermal input. The Suakin Deep brines are derived from, or have isotopically exchanged with Miocene or older evaporites. There has been only minor dilution of the brine by overlying seawater. Strontium isotope ratios of Suakin brine may indicate addition of a minor (15%) amount of volcanic Sr to the brine, but there is no evidence of high temperature brine-rock interaction. The sulfate in the Atlantis II brine was apparently derived from seawater. The O isotope ratio of sulfate in the present Atlantis II brine could reflect isotopic exchange between seawater sulfate and the brine at approximately 255°C. Approximately 30% of the Sr in the Atlantis II brine is derived from the underlying basalt, probably by hydrothermal leaching. Atlantis II brine is the only known example from the Red Sea which has a significant high-temperature hydrothermal history.

Water temperature, salinity, DOC content and THNS concentration in samples taken during POLARSTERN cruise to the Fram Strait and Greenland Sea

Dissolved organic matter (DOM) was isolated with XAD-2 and 4 resins from different water masses of the Greenland Sea and Fram Strait. The contribution of XAD-extractable dissolved organic carbon (DOC), operationally defined as 'recalcitrant' or humic substances, to total DOC was in the range of 45 ± 9% in surface waters and 60 ± 6% in deep waters. The carbohydrate concentration and composition were determined using the l-tryptophan/sulfuric acid method (for the bulk carbohydrate concentration, TCHO) and high performance anion-exchange chromatography after sulfuric acid hydrolysis (for the distribution of total hydrolysable neutral sugars, THNS). Carbohydrates contributed up to 6.8% to both total and recalcitrant DOC. TCHO contribution to total DOC decreased with depth from on average 4.1 ± 1.2% in surface waters to 2.2 ± 1.0% in deep waters, whereas the THNS contribution was similar in both layers, accounting for 2.5 ± 1.6% (surface) and 2.4 ± 0.2% (at depth). TCHO contribution to XAD-extractable DOC also decreased with depth from 4.5 ± 1.7% to 2.1 ± 1.0%, whereas THNS contribution was almost constant, with yields of 0.5 ± 0.3% for surface samples and 0.6 ± 0.1% at depth. The molecular size distribution of the recalcitrant DOM showed for all fractions a clear trend towards small molecules in the deep sea. More than half of the XAD-extractable carbohydrates of surface samples and more than 70% of deep sea samples were found in the nonpolar fraction from XAD, which was eluted with methanol. Glucose was the dominant carbohydrate in the surface water samples, whereas in the deep sea the composition was more uniform. In the XAD extracts, the compositions were less variable than in the original samples. The neutral sugar composition, in particular glucose and the deoxysugars, is indicative of the diagenetic state of the extracted DOM. The molar ratio (fucose + rhamnose)/(arabinose + xylose) was lowest for deep sea extractable DOM, indicating a high contribution of material modified by microorganisms. The THNS composition and distribution reveal that "recalcitrant" carbohydrates are heteropolysaccharides, carbohydrate units incorporated into a framework of a highly nonpolar structure with a lack of functional groups.