Egon T. Degens

The amino acid and sugar composition of diatom cell-walls

The cell walls of diatoms consist of a silica frustule encased in an organic coating. Biochemical characterization of this coating should allow insight into: (1) the mechanism of silicification; (2) taxonomy and evolution of diatoms; (3) preservation of fossil frustules. The amino acid and sugar composition of cell walls from 6 diatom species have been elucidated. When compared to cellular protein, cell-wall protein is enriched in serine plus threonine and glycine, and depleted in acidic, sulfur-containing and aromatic amino acids. The sugars of the cell-wall carbohydrates are quite variable and fucose tends to replace glucose in estuarine species. Condensation of silicic acid, in epitaxial order, on a protein template enriched in serine and threonine, is suggested as the Si-depositing mechanism in diatoms. The nature of this template and the polysaccharides in the cell wall may determine the solubility of diatom frustules in various environments. There is sufficient variability in cell-wall amino acids to warrant further investigation of their taxonomic utility. The sugars appear to be related to environmental factors, but they may also serve in biosystematic studies.

Molecular structure and composition of fish otoliths

Recent and fossil otoliths from 25 different fishes have been studied for their amino acid content and for their C13/C12 and O18/O16 distribution in the carbonate fraction. The selection includes specimens from a wide phylogenetic range as well as from various freshwater and marine habitats. All otoliths are composed of aragonite, and their total organic matter ranges from 0.2 to 10%. The organic matter is a protein (MW>150,000), which is characterized by a high abundance of acidic amino acids. In comparison to molluscs that exhibit a wide variety of different mineralized tissues which are species specific, the proteinaceous matter of all otoliths is chemically rather uniform. The high abundance of oxygen-rich amino acids accounts for the ease of mineralization of the organic template. Namely, oxygen supplied by carboxyl grops is used for the coordination of Ca++ ions, resulting in the formation of metal ion coordination polyhedra. Carbonate groups linked via hydrogen bridges to the template will exchange their oxygen with that of the metal polyhedra to stabilize the structure; Ca++O9 polyhedra are the consequence. Subsequent nucleation and crystal growth will lead to aragonite. Oxygen and carbon isotope data indicate that the aragonite is formed close to isotopic equilibrium with the sea. This is surprising, because seawater has no direct access to the inner ear where the otolith orginates. Isotope data may serve a threefold purpose: (1) to determine the mean water temperature where the fish lived, (2) to distinguish between fresh water and marine fish in ancient deposits, and (3) to reveal information on migrtory tendencies of fish.

Lake Kivu: structure, chemistry and biology of an East African rift lake

ZusammenfassungGeophysikalische, geochemische und biologische Daten werden vorgelegt und miteinander in Beziehung gebracht, um einen besseren Einblick in Entstehung und Evolution eines ungewöhnlichen Sees zu gewinnen. Das nördliche Becken des Kivu-Sees enthält Sedimente von etwa 0,5 km Mächtigkeit, die dem präkambrischen kristallinen Grundgebirge überlagert sind. Die im Norden des Sees vorliegenden vulkanischen Gesteine erklären die hohen magnetischen Anomalien, die bis zu 300 γ betragen. Der Wärmefluß schwankt zwischen 0,4 und 4 cal/cm2/sec. Diese Schwankungsbreite erklärt sich zum Teil aus den Sedimentationsverhältnissen oder den lokalen Temperaturveränderungen im Tiefenwasser. Scharfe Grenzflächen in der vertikalen Temperatur- und Salinitätsstruktur des Wassers über den Gesamtsee sind das Ergebnis von Konvektion, die zu übereinanderliegenden Konvektionszellen führt, in denen jeweils Temperatur und Salinität konstant sind. Die Bildung, Anzahl und Stabilität solcher Zellen hängt von dem Verhältnis der durch Temperatur und Salzgehalt hervorgerufenen Dichteveränderungen ab.Die Konzentrationen der im Tiefenwasser gelösten Gase, d. h. von Kohlendioxyd und Methan, liegen für alle Tiefen unterhalb der Löslichkeit. Die vorliegenden Salze entstammen weitgehend hydrothermalen Lösungen, die dem Seeboden entweichen und deren Salinität etwa 4‰ beträgt; der Vergleichswert für das Tiefenwasser beträgt 2,5‰ Diese hydrothermalen Ausschüttungen haben eine Größe von etwa 0,5 km3 pro Jahr, was etwa ein Tausendstel des Gesamtseevolumens ausmacht. Zinkanomalien im Wasser sind ebenfalls hydrothermal bedingt.Physikalische, geochemische und paläontologische Indikatoren erlauben eine stratigraphische Korrelation aller Sedimentkerne. Die Sedimentationsraten liegen bei 30 cm/ 1000 Jahren, und ein pliozänes Alter errechnet sich daraus für das tiefe nördliche Becken. Perioden hydrothermaler Aktivitäten und verstärkter vulkanischer Tätigkeit, die sich in den Sedimenten nachweisen lassen, scheinen mit Pluvialzeiten zu koinzidieren.Die Anreicherung der Oberflächenwässer vom Kivusee durch Mineralstoffe führte zu einer explosionsartigen Spezisierung in der GattungNitzschia. Verschiedene neue Arten von Methan-oxidierenden und -produzierenden Bakterien wurden isoliert. Das Auftreten von Methan ist zum Teil bakteriell und zum Teil diagenetisch bedingt.AbstractGeophysical, geochemical and biological data are integrated to unravel the origin and evolution of an unusual rift lake. The northern basin of Lake Kivu contains about 0.5 km of sediments which overlie a basement believed to be crystalline rocks of Precambrian age. Volcanic rocks at the northern end of the lake have created large magnetic anomalies of up to 300γ. Heat flow varies from 0.4 to 4 hfu. The extreme variability may be due in part to sedimentation or recent changes in the temperature of the bottom water. Sharp boundaries in the vertical temperature and salinity structure of the water across the lake can best be explained as separate convecting layers. Such convecting cells are the result of the increase in both temperature and salinity with depth.Concentrations of the major dissolved gases in the deep water, CO2 and CH4, approach saturation but do not exceed it at any depth. The salts are supplied mainly by hydrothermal discharges at the bottom of the lake which we calculate to have a salinity of 4‰ which is about 60% higher than the salinity of the bottom water. The annual discharge at the present time is about 0.5 km3. Zinc anomalies in the water are explained by the accumulation of sphalerite-containing globules at certain depths.Stratigraphic correlation of sediments is possible across the entire lake, based on physical, geochemical and paleontological criteria. Sedimentation rates are of the order of 30 cm/1000 years implying a Pliocene age for the deepest part of the lake. Periods of hydrothermal activities and heightened volcanism, as recorded in the sediments, appear to have coincided with pluvial times.Enrichment of the surface waters of Lake Kivu by nutrients has led to explosive speciation in the diatom genusNitzschia. Several new types of methane oxidizing and-producing bacteria were isolated. Bacterial degradation of recent plankton appears insufficient to explain the amount of methane in the lake, and some of it is derived diagenetically.RésuméDes données géophysiques, géochimiques et biologiques sont présentées et collationnées pour donner une vue meilleure sur lorigine et lévolution dun lac particulier de la «Rift valley». La baie septentrionale du lac Kivu contient environ 500 mètres de sédiments qui recouvrent le socle cristallin dâge précambrien. Des épanchements volcaniques au Nord du lac expliquent les fortes anomalies magnétiques qui atteignent 300γ. Les valeurs du flux thermique varient entre 0.4 et 4 cal/cm2/sec. Cette importante variation sexplique en partie par la sédimentation ou par des changements locaux de la température de leau de fond. Des surfaces-limites brusques dans la structure verticale de la répartition de la température et de la salinité de leau dans létendue du lac sont dûs à la convection; celle-ci conduit à la superposition de cellules de convection dans lesquelles la température et la salinité sont constantes. La formation, le nombre et la stabilité de telles cellules dépendent du rapport des variations de densité dues à la température et à la teneur en sels.Les concentrations des gaz dissouts dans leau profonde, en loccurrence CO2 et CH4, sont, à toute profondeur, inférieures à la saturation. Les sels minéraux proviennent surtout de solutions hydrothermales qui émanent du fond du lac, et dont la salinité est voisine de 4‰; la valeur comparative pour leau profonde est de 2,5‰. Lapport annuel de ces sources est de lordre de 0,5 km3, soit 1/1000 du volume total du lac. Les teneurs anormales en Zn sont dues également à ce caractère hydrothermal.Des données physiques, géochemiques et paléontologiques permettent la corrélation stratigraphique des sédiments. Les vitesses de sédimentation sont de lordre de 30 cm/1000 ans, donnant ainsi un âge pliocène pour la partie profonde de la baie septentrionale. Les périodes dactivité hydrothermale et de renforcement de la vulcanicité qui se manifestent dans les sédiments, semblent coïncider avec les périodes pluviales.Lenrichissement des eaux de surface du lac Kivu en substances minérales a entraîné un développement explosif des diatomées, en particulier du genreNitzchia. Différentes espèces nouvelles de bactéries oxydant et produisant CH4 ont été isolées. La présence de méthane est due en partie à la destruction du plancton par les bactéries et en partie à une transformation diagénétique.Краткое содержаниеСравнили и сопостави ли данные геофизичес кого, геохимического и био логического исследований, чтобы п олучить представлен ие об образовании и эвоюци и одного из необычных о зер. В северной части б ассейна озера Kivu осадочные породы достигают мош ности в 0,5 км, перекрыва я докембрийские крист аллические основные породы. Прис утствие в северной ча сти озера вулканических пород объясняет высо кую магнитную аномал ию, доходящую до 300 у. Перен ос тепла колеблется от 0,4 д о 4 кал (см2) сек. Такие ко лебания объясняются частично условиями о садконакопления, или местными изменениями темпера туры на глубине. В результа те конвенкции образу ются отдельные резко очер ченные горизонты с постоянн ой температурой и сол еностью. Образование таких го ризонтов, как число и стабильно сть их, зависят от изме нений плотности, вызванной температурой и содер жанием солей.Концентрация раство ренных в глубине вод г азов, т. е. СО2 и СН4 во всех горизонтах ниже раст воримости. Найденные соли происходят преимуще ственно иа гидротермальных р астворов, бьющих из дн а озера и соелность которых до стигает 4%. Соленость глубинных вод равна 2,5%. Объем этих гидротермальных выбросов равен приме рно 0,5 км3, в год, что сост авляет 1/1000 общего объема. Аномалия цинка в воде также обусловлена гидротермальными ра створами.Физические, геохимич еские и палеонтологи ческие индикаторы разрешаю т провести стратиграф ическую корреляцию в сех кернов осадочных пород. Для северной части бассе йна скорость осадкон акопления равняется 30 см/1000 лет, т. е. она плиоценового в озраста. Кажется, что п ериоды гидротермальной акт ивности и усиленной вулканич еской деятельности, о тмеченные по осадоным породам, совпадает с п лювиальным периодом.Накопление поверхно стных слоев воды озер а Kivu минеральными вещест вами ведет в взрыву специа лизации Nitzschia. Выделены ра зличные новые штамы бактерий, окисляющих и образующих метан. По явление метана обусловленно частично бактериаль ным разложением план ктона, а частично — процессам и диагенеза.

Black Sea: Recent Sedimentary History

Three distinct sedimentary units, which can be correlated throughout the basin, occur in cores collected from the Black Sea. Carbon-14 ages help to define the recent sedimentary history of the Black Sea.

Lake tanganyika: Water chemistry, sediments, geological structure

The water chemistry of the lake is uniform throughout its entire length and depth except for the nutrient minerals ammonia, nitrate, phosphate, and silica. Sediment fill in the lake is very massive. Because the sediments are almost entirely composed of biological debris, changes in the fossil inventory can be linked to the chemical and in turn biological evolution of the lake. Rates of depositions are about 30 to 50 cm per 1 000 years in the deep basins and 5 cm per 1 000 years in the sill area separating the southern and northern basins. Seismic profiles indicate graben-type structures. Magnetic surveys reveal no magnetic lineation typical of rifting. Free air and simple Bouguer anomalies suggest that lake and land structures are grossly similar. Low heat flow and similarity with surrounding values in Africa is consistent with a lack of active volcanicity and sea-floor spreading in Lake Tanganyika. A new concept on the evolution of a rift is proposed.

Paleobiochemistry of molluscan shell proteins

Abstract The amino acid composition in calcified and uncalcified tissues of mollucs can be described by a limited number of independent factors which are related to both phylogeny and environment.

Concentration of Dissolved Amino Acids from Saline Waters by Ligand-Exchange Chromatography

Amino acids dissolved in salt solutions may be concentrated and removed from the solution by ligand exchange on copper-Chelex 100 resin. Competing inorganic ligands do not interfere, and ion exchange with cations does not occur; thus loss of metal ion from this column is avoided. To test the potentiality of ligand exchange for chromatography, the type and nature of the dissolved amino compounds in sea water were investigated. The data revealed that the bulk of the dissolved amino compounds is present in a combined rather than a free state.

Chronology of the Black Sea over the last 25,000 years☆

Abstract Deep-water sediments of the Black Sea deposited during Late Pleistocene and Holocene time are distinguished by three sedimentary units: (1) a microlaminated coccolith ooze mainly consisting of Emiliania huxleyi ; (2) a sapropel; and (3) a banded lutite. The base of the first unit lies at 3,000 years B.P., that of the second at 7,000 years B.P., and that of the third at least at about 25,000 years B.P. Fossils and geochemical criteria are used to decipher the environmental events of this time period. Beginning with the base of the section dated at about 25,000 years B.P. we witness the final stage of metamorphosis from anoxic marine to oxic freshwater conditions. By the time this stage ended, about 22,000 years B.P., the Black Sea had become a truly freshwater habitat. The lake phase lasted about 12,000 to 13,000 years. Sedimentation rates were in the order of 1 m/10 3 years, but began to decrease as sea level rose during the last 5,000 years of this phase (9,000–15,000 years B.P.). Starting at about 9,000 years B.P. and continuing to 7,000 years B.P., Mediterranean waters occasionally spilled over the Bosporus as a consequence of ice retreat and sea level rise. This marked the beginning of a gradual shift from freshwater to marine, and from well aerated to stagnant conditions. At about 7,000 years B.P. when deposition of unit 2 started, the H 2 S zone was well established. Sedimentation rates dropped to 10 cm/10 3 years. Environmental conditions similar to those of today finally became established around 3,000 years B.P., almost exactly the time when Jason and the Argonauts sailed through the Bosporus in search of the Golden Fleece.

Methane in Lake Kivu: New Data Bearing on Its Origin

Lake Kivu, an African rift lake, contains about 50 cubic kilometers of methane (at standard temperature and pressure) in its deep water. Data resulting from two recent expeditions to the lake and a reevaluation of earlier data suggest that most of the methane was formed by bacteria from abiogenetic carbon dioxide and hydrogen, rather than being of volcanic origin or having formed from decomposing organic matter.

A new chromatographic sugar autoanalyzer with a sensitivity of 10−10 moles

Abstract Construction of a new automatic sugar analyzer is described. The system is: ( 1 ) rapid—monosaccharide mixtures are fully resolved in 3 to 4 hr; ( 2 ) highly sensitive, 10 −10 to 10 −11 mole sugar is detected; ( 3 ) capable of excellent reproducibility; and ( 4 ) capable of yielding high resolution. Sugars are separated by pumping 89% ethanol under pressure (400 psi) through a long narrow column (110×.28 cm) packed with a finegrained strongly anionic resin in the sulfate form. The eluted sugars are stained during reaction with an alkaline solution of tetrazolium blue. This dye is considerably more sensitive and less corrosive than dyes used by other investigators. Until now it had not been employed in analytical systems for sugars because of the precipitation of diformazan, which clogs capillary tubing. However, extensive laboratory experimentation by the authors have succeeded in rendering tetrazolium blue applicable.