| 1. |
|
|
| 2. |
- Andersson, Eva, 1967-
(författare)
-
Hydrothermal alteration of organic matter at spreading centers
- 1998
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Alteration of organic matter, mainly amino acids, at sub-seafloor hydrothermal conditions has been investigated by performing laboratory experiments and by studying deep-sea sediments from hydrothermally active areas on the northern Juan de Fuca Ridge, northeast Pacific Ocean.Quaternary sediments from Middle Valley and the eastern flank of the Juan de Fuca Ridge recovered during the Ocean Drilling Program Legs 139 and 168 have been analyzed for total hydrolyzable amino acid concentrations, individual amino acid abundances and stereochemistry in order to evaluate the effects of hydrothermal stress on the decomposition of sedimentary amino acids. In near surface sediments, amino acids account for up to 3.3% of the total organic carbon content and up to 12% of the total nitrogen content. The non-protein amino acid b-alanine and g-aminobutyric acid become increasingly abundant with depth in low temperature holes (Leg 168) as a result of enzymatic decarboxylation of aspartic acid and glutamic acid, respectively. The decomposition of amino acid in high temperature holes (Leg 139) is enhanced with depth and the amino acid patterns indicates that most amino acids are incorporated into geopolymers and that condensation results in increased stability of some amino acids.The effects of low temperature hydrothermal activity on microbially mediated organic matter diagenesis were studied by comparing depth concentration profiles of interstitial sulfate and methane of Holes 1023A, 1024B, 1025B and 1028A, ODP Leg 168. Diffusional exchange between sulfate-rich basement fluids and pore-waters increases the interstitial sulfate concentrations with depth below local sulfate minima caused by bacterial sulfate reduction. The effects of diffusional processes on pore-water chemistry in the sediment column is reflected by the inhibition of methane production and is largely dependent on sediment thickness.The decomposition of alanine, leucine, aspartic acid and serine in aqueous solutions was studied at 200oC and 50 bar with the purpose of evaluating the effect dissolved oxygen on decomposition rates. The redox buffering mineral assemblage pyrite-pyrrhotite-magnetite was used to constrain the oxygen fugacity to geologically realistic values. Comparisons between results obtained from buffered and nonbuffered runs show that the decomposition is faster for most amino acids but serine in nonbuffered experiments.
|
|
| 3. |
- Andrén, Elinor, 1966-
(författare)
-
Holocene environmental changes recorded by diatom stratigraphy in the southern Baltic Sea
- 1999
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Sediment cores from the southern Baltic Sea and the Oder River estuary are analysed for their siliceous microfossil assemblages and organic carbon content. Long piston cores from the Bornholm and Gotland Basins provide data on the long-term Holocene history of the Baltic proper and serve as a natural background when evaluating the most recent environmental changes recorded in the short gravity cores. Corrected and calibrated 14C dates for the Holocene part, together with 210Pb and 137Cs dates for the sediments deposited during the last century, are used as a basis for constructing chronologies and age models. The main results are:The brackish phase of the Yoldia Sea stage in the Bornholm Basin is recorded by a diatom assemblage of periphytic taxa indicating a shallower water depth than today and more marine conditions than are recorded by the planktonic assemblage found in the Gotland Basin.The transition between the Yoldia Sea and the Ancylus Lake stages is distinguished in the offshore facies and recorded in the sediments in the form of a small increase in organic carbon coinciding with a peak in the diatom abundance and increased diatom diversity.The onset of the Initial Litorina Sea stage, recorded about 10,100 calendar years BP (c. 8900 14C years BP) in the Bornholm Basin, indicates a complex transition with different phases of brackish-water inflow.Six periods with major marine water inflow into the Baltic basin are recorded during the Holocene. Once an open connection was established with the North Sea, climatic influence seems to have been the most important factor controlling such inflow events.Comparison between the organic carbon content, the absolute abundance of siliceous microfossils and a regional climate proxy, the Greenland (GRIP) ice core (18O record, shows a tentative link between primary production in the Baltic proper and climate. A high temperature on Greenland corresponds to high organic carbon content and increased diatom abundance in the Baltic proper.Climate change is recorded in both the siliceous microfossil assemblages and the organic carbon content. A sediment sequence indicating high productivity c. 950-800 calendar years BP (AD 1000-1150) correlates with the Medieval warm period. An alteration in the diatom assemblage interpreted as being due to a deterioration in the climate correlates with the start of the Little Ice Age about 850-700 calendar years BP (AD 1100-1250).The effects of eutrophication are recorded AD 1850-1860 in the southwestern Baltic proper, AD 1900 in the Oder estuary and AD 1950-1960 in the Gotland Basin. These effects were probably caused by increased discharge of nutrients deriving from fertilisers, as the responding diatom species partly indicate a cold climate rather than a warm one, as would have been expected if this had been only a response to the warmer climate documented during the last 100 years or so.
|
|
| 4. |
|
|
| 5. |
- Estmark Kalinowski, Birgitta
(författare)
-
Dissolution Kinetics and Alteration Products of Micas and Epidote in Acidic Solutions at Room Temperature
- 1997
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The reaction kinetics of the weathering of several phyllosilicates and one sorosilicate were stud ied experimentally. The alteration products were characterised by various methods in clud ing XRD, HRTEM, SEM, FTIR, NMR and Mössbauer spectroscopy. Weathering of silicates is of particular concern to our knowledge of several areas in low temperature geochemistry, such as el e ment cy cling, ground water chemistry and soil formation. The importance of these processes ex tends to the long-term nutrient supply to forest ecosystems and control of soil and water acidity, es pe cial ly in Scandinavia.Several soil models designed to predict the impact of acid rain on the soil chemistry rely on kinetic data of mineral weathering. The reaction kinetics for minerals are used in such models to predict chang es in soil chem is try. This enables calculation of the effect of acid rain (i. e. critical load) in a 100-year per spec tive. For some minerals relatively little knowledge is available for the reaction kinetics. There fore the dissolution kinetics of muscovite, biotite, phlogopite, vermiculite and epi dote were studied over the pH range 1 to 6.5 at room temperature using flow-through reactors.Silica release rates based on specific surface area are about the same for as divers silicates as epidote (sorosilicate), K-feldspar (tectosilicate) and phlogopite (phyllosilicate). At pH 3 log R = -15.41, -15.5 and -15.46 respectively for these min er als. However, the framework of Si and Al is likely to determine with what ease cations positioned in between the conformation of Si and Al tetrahedra are re leased. For example, K in micas have transportation channels due to the layer struc ture and ought there fore to be released easier than in K-feldspar. In most cases Si is the most slowly released element in silicates, but in epidote, Si and Ca are the fastest released elements from the structure, while Al and Fe are retained. Leaching of inter framework cations creates strain and charge im bal ance in the silicate structure, causing Si to be more readily released in base cation containing silicates than in quartz. Released Si may repolymerise directly at the surface of silicates or interlayers. Amor phous silica gel has been detected, as a weathering product between packages of 2:1 layers in bi otite, using AEM. Iron(hydr)oxides have been found as the end-product of biotite weathering. Re sid u al layer calculations based on the solution composition show that Al and Fe form an enriched layer with a thickness of 1-2 nm at the surface of epidote.Biotite and phlogopite probably alter to trioctahedral vermiculite from the edges and inwards. Mössbauer spectroscopy shows that weathering of biotite as well as ver micu lite is accompanied by oxidation. Al-hydroxy polymers are introduced in the in ter lay er during weathering of phlogopite and vermiculite, which is supported by both XRD and 27Al MAS-NMR analyses. Additions of KCl and AlCl3 to the reactant solutions show that release rates, exfoliation and oxidation processes decrease with increased concentrations for both biotite and phlogopite. Leaching of interlayer cat i ons seems thus to initiate oxidation of ferrous iron.
|
|
| 6. |
|
|
| 7. |
- Machiwa, John
(författare)
-
Fate of organic carbon in a tropical mangrove ecosystem
- 1999
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The aim of this thesis was to study the budget and fluxes of organic carbon in a tropical mangrove forest. Maruhubi forest is located in the Island of Zanzibar, East Africa. Aspects of structure and functions of the ecosystem are investigated. Litterfall, litter standing stock and the effect of macrofauna and the tidal regime on litter turn-over, are key factors in the present study.The inventory of the forest in terms macrofauna and flora was taken. Avicennia marina forms an almost pure stand at the terrestrial edge of the forest, nevertheless, the species is ubiquitous in the area. Sonerratia alba grows exclusively at the marine fringe and the shoreline areas that are frequently inundated. Grapsid crabs, mainly Neosarmatium meinerti occupy the terrestrial edge mangrove area which has a hard mud substrate. Ocypodid crabs, mainly Uca spp occur seaward in the marine fringe and shoreline zones with a sand/muddy bottom. The mollusc Cerithidea decollata is entirely abundant in the terrestrial mangrove fringe sub-area. The marine fringe and shoreline sub-areas are colonised by several species of snails.Lateral fluxes of macrodetritus, suspended particulate matter and dissolved organic carbon showed a significant export of mangrove litter to the adjacent marine area during spring tides. However, in the terrestrial fringe litter was not effectively transported by the tide. Net organic carbon export for the entire forest was 79 x 106 g C y-1, dissolved organic carbon accounted for 78% of the total export.Distribution of sedimentary organic carbon in this mangrove forest which is partly contaminated with raw sewage, shows that a high proportion of carbon in the landward extending zone is organic. Relative content of inorganic carbon increases seaward with carbonate shells of gastropods, oysters and coral sand dominating. Vertical profiles of organic carbon showed a general surface enrichment and subsurface depletion. Interstitial water in the terrestrial mangrove fringe with sewage was acidic (pH 4 - 5) and strongly reducing (Eh approx. -300 mV). pH in the terrestrial fringe sub-area without sewage was close to neutral values (pH > 6). There was no significant difference between the rates of organic matter mineralization in the forest zones. Relative values, however, indicate mineralization was slowest in sewage contaminated areas followed by areas with high litter loading on the sediment floor. The rate was high in the frequently inundated mangrove areas.An empirical model of the fate of organic carbon in Maruhubi forest was constructed. Results from the model supports the field observation that outwelling of dissolved organic carbon was the dominant component of the mangrove forest which influences litter dynamics. Grapsid crabs are important for litter turn-over in the intermittently flooded zones of the forest. Further, stable isotope data confirmed that crabs in the terrestrial fringe zone fed almost exclusively on mangrove litter (d13C = 27.97±0.25). In addition to that, the sedimentary organic matter (d13C = 22.50±3.54) was also to a large extent, of mangrove origin.
|
|
| 8. |
|
|
| 9. |
|
|
| 10. |
|
|
