A Benthic chamber with electric stirrer mixing

Benthic chambers incorporating electric stirrer mixing have been designed and tested and have proven reliable during seven 18-31 day, 4300m ocean deployments. The chambers are 21 cm diameter by 31 cm long acrylic tubes sealed with pvc lids. A stepper motor and pressure tolerant electronics contained within the lids are magnetically coupled to stirring paddles to provide mixing within the chambers. The stirrers exhibit stable mixing rates and uniform speeds between chambers, require less than 1/3 watt of power, and are maintenance free. Laboratory calibration of stirring and mixing characteristics demonstrate that areal averaged equivalent seawater-sediment boundary layer thickness can be set to agree with in situ measured values.Funding was provided by the National Science Foundation through Grant No. OCE87-11962

An autonomous instrument for time series analysis of TCO2 from oceanographic moorings

Author Posting. © Elsevier B.V., 2009. This is the author's version of the work. It is posted here by permission of Elsevier B.V. for personal use, not for redistribution. The definitive version was published in Deep Sea Research Part I: Oceanographic Research Papers 56 (2009): 1590-1603, doi:10.1016/j.dsr.2009.04.006.The design and testing of a robotic analyzer for autonomous TCO2 measurement from oceanographic moorings is described. The analyzer employs a conductimetric method of TCO2 measurement wherein CO2 from an acidified sample diffuses across a semi-permeable membrane into a NaOH solution decreasing the conductivity of the base. The instrument is capable of ~850 analyses over a period of at least six months. It is designed to operate to depths of at least 1000m. TCO2 calibration is based on in situ standardization throughout a deployment. We report both laboratory and in situ tests of the analyzer. In the laboratory automated analyses over a period of 38 days at temperatures ranging from 8° to 25° C yielded a TCO2 accuracy and precision of ±2.7 μmol/kg. In situ tests were conducted at the WHOI dock with a deployment of 8 weeks at in situ temperatures of 5°-13°C. The accuracy and precision of TCO2 analyses over the deployment period, based on in situ calibration, was ±3.6 μmol/kg. Laboratory tests of reagent and standard solution stability are also reported. Standards, based on Certified Reference Material were followed for periods of up to 2 years. In all cases TCO2 increased. Drift of the standards was the equivalent of ~1 to μmol/kg per 6 months. The conductivity indicator solution was found to be stable for at least 2 months.The Oceanographic Technology Program (OCE-9633022) and the Ocean Technology and Interdisciplinary Coordination Program (OCE-0104949) of the National Science Foundation, and by the Woods Hole Oceanographic Institution have provided financial support for this project

Chemical composition of interstitial solutions from sediments of DSDP Legs 6-8, 11, 12, 14, 15, and 22

Through the Deep Sea Drilling Project samples of interstitial solutions of deeply buried marine sediments throughout the World Ocean have been obtained and analyzed. The studies have shown that in all but the most slowly deposited sediments pore fluids exhibit changes in composition upon burial. These changes can be grouped into a few consistent patterns that facilitate identification of the diagenetic reactions occurring in the sediments. Pelagic clays and slowly deposited (<1 cm/1000 yr) biogenic sediments are the only types that exhibit little evidence of reaction in the pore waters. In most biogenic sediments sea water undergoes considerable alteration. In sediments deposited at rates up to a few cm/1000 yr the changes chiefly involve gains of Ca(2+) and Sr(2+) and losses of Mg(2+) which balance the Ca(2+) enrichment. The Ca-Mg substitution may often reach 30 mM/kg while Sr(2+) may be enriched 15-fold over sea water. These changes reflect recrystallization of biogenic calcite and the substitution of Mg(2+) for Ca(2+) during this reaction. The Ca-Mg-carbonate formed is most likely a dolomitic phase. A related but more complex pattern is found in carbonate sediments deposited at somewhat greater rates. Ca(2+) and Sr(2+) enrichment is again characteristic, but Mg(2+) losses exceed Ca(2+) gains with the excess being balanced by SO4(post staggered 2-) losses. The data indicate that the reactions are similar to those noted above, except that the Ca(2+) released is not kept in solution but is precipitated by the HCO3(post staggered -) produced in SO4(post staggered 2-) reduction. In both these types of pore waters Na(+) is usually conservative, but K(+) depletions are frequent. In several partly consolidated sediment sections approaching igneous basement contact, very marked interstitial calcium enrichment has been found (to 5.5 g/kg). These phenomena are marked by pronounced depletion in Na(+), Si and CO2, and slight enhancement in Cl(-). The changes are attributed to exchange of Na(+) for Ca(2+) in silicate minerals forming from submarine weathering of igneous rocks such as basalts. Water is also consumed in these reactions, accounting for minor increases in total interstitial salinity. Terrigenous, organic-rich sediments deposited rapidly along continental margins also exhibit significant evidences of alteration. Microbial reactions involving organic matter lead to complete removal of SO4(post staggered 2-), strong HCO3(post staggered -) enrichment, formation of NH4(post staggered +), and methane synthesis from H2 and CO2 once SO4(post staggered 2-) is eliminated. K+ and often Na+ (slightly) are depleted in the interstitial waters. Ca(2+) depletion may occur owing to precipitation of CaCO3. In most cases interstitial Cl- remains relatively constant, but increases are noted over evaporitic strata, and decreases in interstitial Cl- are observed in some sediments adjacent to continents

The release and migration of activation products from corrosion-resistant metal specimens in marine sediments

An investigation of the release of Ni-63, Co-60, and Fe-55 from Inconel 600 and 347SS stainless steel specimens implanted in marine sediment for one year is described. Radiochemical analysis of the sediment from overcores of the metal specimens permits estimation of integrated activities, release rates, and diffusion coefficients of the three radionuclides. Disturbance of the sediment upon recovery limits the values to order of magnitude estimates. The redox chemistry of the sediments is characterized by measurement of several naturally occurring oxidizing agents and is correlated with the behavior of the radionuclides. Details of the deployment, sampling and analytical procedures are also given