Diversity and spatial distribution of amoA-encoding archaea in the deep-sea sediments of the tropical West Pacific Continental Margin

The ecological characteristics of the deep-sea amoA-encoding archaea (AEA) are largely unsolved. Our aim was to study the diversity, structure and distribution of the AEA community in the sediments of the tropical West Pacific Continental Margin, to develop a general view of the AEA biogeography in the deep-sea extreme environment. Archaeal amoA clone libraries were constructed. Diverse and novel amoA sequences were identified, with the Bohol Sea, Bashi Strait and Sibuyan Sea harbouring the highest and the Bicol Shelf the lowest AEA diversity. Phylogenetic and statistical analyses illustrate a heterogeneous distribution of the AEA community, probably caused by the differential distribution of the terrestrial or estuarine AEA in the various sampling sites. The deep-sea sedimentary environments potentially harbour diverse and novel AEA in the tropical West Pacific Continental Margin. The stations in the Philippine inland seas (including station 3043) may represent AEA assemblages with various terrestrial influences and the stations connected directly to the open Philippine Sea may represent marine environment-dominant AEA assemblages. Our study indicates the potential importance of geological and climatic events in the transport of terrestrial micro-organisms to the deep-sea sedimentary environments, almost totally neglected previously.

Geochemical analysis of sediments and interstitial water in sediment cores from the North-West African continental margin and from the Central Pacific

A. Continental slope sediments off Spanish-Sahara and Senegal contain up to 4% organic carbon and up to 0.4% total nitrogen. The highest concentrations were found in sediments from water depths between 1000 and 2000 m. The regional and vertical distribution of organic matter differs significantly. Off Spanish-Sahara the organic matter content of sediment deposited during glacial times (Wuerm, Late Riss) is high whereas sediments deposited during interglacial times (Recent, Eem) are low in organic matter. Opposite distribution was found in sediments off Senegal. The sediments contain 30 to 130 ppm of fixed nitrogen. In most sediments this corresponds to 2-8 % of the total nitrogen. Only in sediments deposited during interglacial times off Spanish-Sahara up to 20 % of the total nitrogen is contained as inorganically bound nitrogen. Positive correlations of the fixed nitrogen concentrations to the amounts of clay, alumina, and potassium suggest that it is primarily fixed to illites. The amino acid nitrogen and hexosamine nitrogen account for 17 to 26 % and 1.3 to 2.4 %, respectively of the total nitrogen content of the sediments. The concentrations vary between 200 and 850 ppm amino acid nitrogen and 20 to 70 ppm hexosamine nitrogen, both parallel the fluctiations of organic matter in the sediment. Fulvic acids, humic acids, and the total organic matter of the sediments may be clearly differentiated from one another and their amino acid and hexosamine contents and their amino acid composition: a) Fulvic acids contain only half as much amino acids as humic acids b) The molar amino acid/hexosamine ratios of the fulvic acids are half those of the humic acids and the total organic matter of the sediment c) The amino acid spectra of fulvic acids are characterized by an enrichment of aspartic acid, alanine, and methionine sulfoxide and a depletion of glycine, valine, isoleucine, leucine, tyrosine, phenylalanine, lysine, and arginine compared to the spectra of the humic acids and those of the total organic matter fraction of the sediment. d) The amino acid spectra of the humic acids and those of the total organic matter fraction of the sediments are about the same with the exception that arginine is clearly enriched in the total organic matter. In general, as indicated by the amino compounds humic acids resemble closer the total organic matter composition than the low molecular fulvic acids do. This supports the general idea that during the course of diagenesis in reducing sediments organic matter stabilizes from a fulvic-like structure to humic-like structure and finally to kerogen. The decomposition rates of single aminio acids differ significantly from one another. Generally amino acids which are preferentially contained in humic acids and the total organic matter fraction show a smaller loss with time than those preferably well documented in case of the basic amino acids lysine and arginine which- although thermally unstable- are the most stable amino acids in the sediments. A favoured incorporation of these compounds into high molecular substances as well as into clay minerals may explain their relatively high "stability" in the sediment. The nitrogen loss from the sediments due to the activity of sulphate-reducing bacteria amounts to 20-40 % of the total organic nitrogen now present. At least 40 % of the organic nitrogen which is liberated by sulphate-reducing bacteria can be explained ny decomposition of amino acids alone. B. Deep-sea sediments from the Central Pacific The deep-seas sediments contain 1 to 2 orders of magnitude less organic matter than the continental slope sediments off NW Africa, i.e. 0.04 to 0.3 % organic carbon. The fixed nitrogen content of the deep-sea sediments ranges from 60 to 270 ppm or from 20 to 45 % of the total nitrogen content. While ammonia is the prevailing inorganic nitrogen compound in anoxic pore waters, nitrate predominates in the oxic environment of the deep-sea sediments. Near the sediment/water interface interstital nitrate concentrations of around 30 µg-at. N/l were recorded. These generally increase with sediment depth by 10 to 15 µg-at. NO3- N/l. This suggests the presence of free oxygen and the activity of nitrifying bacteria in the interstitial waters. The ammonia content of the interstitial water of the oxic deep-sea sediments ranges from 2 to 60 µg-at. N/l and thus is several orders of magnitude less than in anoxic sediments. In contrast to recorded nitrate gradients towards the sediments/water interface, there are no ammonia concentration gradients. However, ammonia concentrations appear to be characteristic for certain regional areas. It is suggested that this regional differentiation is caused by ion exchange reactions involving potassium and ammonium ions rather than by different decomposition rates of organic matter. C. C/N ratios All estimated C/N ratios of surface sediments vary between 3 and 9 in the deep-sea and the continental margin, respectively. Whereas the C/N ratios generally increase with depth in the sediment cores off NW Africa they decrease in the deep-sea cores. The lowest values of around 1.3 were found in the deeper sections of the deep-sea cores, the highest of around 10 in the sediments off NW Africa. The wide range of the C/N ratios as well as their opposite behaviour with increasing sediment depth in both the deep-sea and continental margin sediment cores, can be attributed mainly to the combination of the following three factors: 1. Inorganic and organic substances bound within the latticed of clay minerals tend to decrease the C/N ratios. 2. Organic matter not protected by absorption on the clay minerals tends to increase C/N ratios 3. Diagenetic alteration of organic matter by micro-organisms tends to increase C/N ratios through preferential loss of nitrogen The diagenetic changes of the microbially decomposable organic matter results in both oxic and anoxic environments in a preferential loss of nitrogen and hence in higher C/N ratios of the organic fraction. This holds true for most of the continental margin sediments off NW Africa which contain relatively high amounts of organic matter so that factors 2 and 3 predominate there. The relative low C/N ratios of the sediments deposited during interglacial times off Spanish-Sahara, which are low in organic carbon, show the increasing influence of factor 1 - the nitrogen-rich organic substances bound to clay minerals. In the deep-sea sediments from the Central Pacific this factor completely predominates so that the C/N rations of the sediments approach that of the substance absorbed to clay minerals with decreasing organic matter content. In the deeper core sections the unprotected organic matter has been completely destroyed so that the C/N ratios of the total sediments eventually fall into the same range as those of the pure clay mineral fraction.

Particle export during a bloom of Emiliania huxleyi in the North-West European continental margin

Coccolithophores, the dominant pelagic calcifiers in the oceans, play a key role in the marine carbon cycle through calcification, primary production and carbon export, the main drivers of the biological CO2 pump. In May 2002 a cruise was conducted on the outer shelf of the North-West European continental margin, from the north Bay of Biscay to the Celtic Sea (47.0 degrees-50.5 degrees N, 5.0 degrees-11.0 degrees W), an area where massive blooms of Emiliania huxleyi are observed annually. Biogeochemical variables including primary production, calcification, partial pressure of CO2 (pCO(2)), chlorophyll-a (Chl-a), particle load, particulate organic and inorganic carbon (POC, PIC) and Th-234, were measured in surface waters to assess particle dynamic and carbon export in relation to the development of a coccolithophore bloom. We observed a marked northward decrease in Chl-a concentration and calcification rates: the bloom exhibited lower values and may be less well developed in the Goban Spur area. The export fluxes of POC and PIC from the top 80 m, determined using the ratios of POC and PIC to Th-234 of particles, ranged from 81 to 323 mg C m(-2) d(-1) and from 30 to 84 mg C m(-2) d(-1), respectively. The highest fluxes were observed in waters presenting a well-developed coccolithophore bloom, as shown by high reflectance of surface waters. This experiment confirms that the occurrence of coccolithophores promotes efficient export of organic and inorganic carbon on the North-West European margin.

Distribution of benthos in late Quaternary turbidite layers of sediment cores from the North-West African continental margin

The CaCO3-contents and the fractions > 40 µm have been analysed from 5 kastenloten, one piston core and two kastengreifer taken between Senegal and Cape Verde Islands. Numerous benthonic and planktonic organisms and different terrigenous components have been distinguished. The four cores off Senegal reach middle Wuerm sediments; cores GIK12329-6 and TAG72-1 reach the V-zone and core GIK12331-4 the X-zone (Eem); the two kastengreifer contain sediments of Holocene age. Correlation of the cores has been made. Holocene sedimentation rates decrease from the shallow cores (6-11 cm/1000 years) to the deep-sea (1-2 cm/1000 years). The following climatic variations could be deduced from the sediments off the Senegal: during Holocene climate was in general as today, the Senegal river transporting fine grained material to the sea. The upper Wuerm was arid with no river influence but with red dune sand transported to the continental slope. During middle Wuerm the climate was humid again. The deep-sea cores have been influenced by eolian material from arid regions during glacial and interglacial periods, indicated by relatively high "Wuestenquarz-numbers". However, during Wuerm "Wuestenquarz-numbers" are higher than during Holocene and Eem, indicating that more intensely red coloured sediment was exposed to wind activity on the continent during this period. Varying amounts of terrigenous material and CaCO3-contents indicate varying wind strengths (lower in Holocene and Eem than during Wuerm). The boundary between humid and arid Wuerm climate was at approximately 20 °N. Influence of upwelling is difficult to establish in the sediments off Senegal, because river influence, while increasing fertility also dilutes the diatoms which are typical for upwelling. High amounts of organic carbon, low plankton/benthos ratios of foraminifers and low plankton foraminifer/radiolarian ratios in Holocene sections might be interpreted as influenced by upwelling. Turbidites occur in cores 72 and 31 and at the Holocene/Pleistocene boundary of core GIK12329-6. Their composition indicates provenance from the continental shelf of the Cape Verde Islands for core 31 and the continental shelf and slope off Senegal for core TAG72-1. Volcanic material, rare in the normal pelagic sediment of core GIK12331-4 is more frequent in the turbidites.

Sediment accumulation rates of sediment cores from the North-West African continental margin

Six soft sediment cores, up to and over 9 m in length, and additional surface samples were selected for study of their planktonic foraminifera to provide information on the Holocene and Pleistocene stratigraphy of the West African continental margin south of the present boundary of the Sahara. The material was collected by the German research vessel "Meteor" during Cruise 25 in 1971. The residues larger than 160 microns determined, counted and statistically evaluated. Stratigraphical correlations with trans- Antlantic regions are given by occurrence of Truncorotalidoides hexagonus and Globorotalia tumidula flexuosa which mark the last interglacial stage. According to the climatic record the two deep-sea cores extend down to the V-zone, considered here as equivalent to the Mindel-Riss-interglacial time, as there are three distinctly warm and two cold periods indicated in the cores by planktonic foraminiferal faunas. Z-zone = Holocene is present in all cores, Y-zone = Wuermian glacial can be divided into five section, three cold and two warm stages; the X-zone can be divided into three warm stages, separated into two cool periods. The earliest warm stage is indicated to be the warmest one. There are excellent correlations to the Camp century ice core from Greenland, to the Mediterranean, to the Carribean and to the tropical Atlantic as well as to the Barnados stage. The W-zone was correlated to the Riss-glacial. V-zone is a warm period, the upper limit of which being not sufficiently defined, which contains also some cool sections. Increasing sedimentation rates from the deep-sea to the upper slope reveal climatic and regional details in Holocene and Late Pleistocene history of the continental margin. These were based mainly on different parameters of planktonic foraminiferal thanatocoenoses which are the main components of the size fraction >160 microns of the pelagic core. They become incerasingly diluted by other faunal and terrigenous components with decreasing slope depths. Estimates of absolute abundances, ranging from 25000 specimens/gm of sediment in the deep sea to less than 100, indicate various sedimentary processes at the continental margin. An ecological correlation by dominant species is possible. Readily computed temperature indices of different scales are presented which indicate, for instance, three distinctly cold sections within the last glacial and seven warm sections within the last interglacial lime. These are used for estimates of sedimentation rates. During cold periods sedimentation rates are higher than during warmer periods. Stratigraphic correlation and faunal record, combined with absolute abundances and sedimentation rates, indicated that in the deep sea turbidity currents not only cause high sedimentation rates for short periods of time, but also that material is occasionally eroded. Effects of upwelling may be detected in the surfacc sediment samples as well as in late Pleistocene and early Holocene samples of the slope by planktonic foraminiferal data which are not influenced by sedimentary processes.

Composition of sediments from the north-west African continental margin

Entlang dreier Profile vom NW-afrikanischen Kontinentalrand wurden Oberflächensedimente aus Wassertiefen zwischen 39m und 1514m auf ihre Zusammensetzung der Sandfraktion, auf ihre Gehalte an Karbonat und organischer Substanzen sowie auf ihre mineralogische Zusammensetzung hin untersucht. 1) Die auf dem Schelf und dem oberen Hang abgelagerten Sedimente (<500m) zeichnen sich durch hohe Sandgehalte (>70%) und durch hohe Grob/Fein-Verhältnisse aus. Unterhalb dieses Bereiches nimmt der Einfluß von Strömungen, die die Ablagerung von wesentlichen Mengen an Feinmaterial oberhalb 500m verhindern, ab, wie die starke Abnahme des Sandgehaltes, des Quarz/Glimmer und des Grob/Fein-Verhältnisses zeigen. Die Sedimente aus diesen Wassertiefen werden zum großen Teil aus Partikeln der Siltfraktion aufgebaut. Mit zunehmender Tiefe ist auch eine Zunahme der Tonfraktion zu beobachten, wobei höhere Tonanteile (>10%) erst in Tiefen unterhalb von 1200m auftreten. 2) Die quantitative Komponentenanalyse der Sandfraktion zeigt, daß der karbonatische Anteil fast ausschließlich biogener Herkunft ist. Er besteht zum wesentlichen Teil aus planktonischen Komponenten, vorwiegend Foraminiferen und mengenmäßig nur sehr untergeordnet auftretenden Pteropoden. Das opalkieselige Plankton (Diatomeen, Radiolarien) ist nur in geringen Mengen in den untersuchten Proben vorhanden. Auch das Benthos stellt nur eine untergeordnete Komponente der Sandfraktion dar. Vor allem der Anteil von Foraminiferen und Mollusken nimmt mit zunehmender Wassertiefe relativ deutlich ab. Die übrigen benthonischen Komponenten sind im Sediment nur in geringen Anteilen vertreten. 3) Hauptsedimentbildner im Profil Nouakchott sind die nichtbiogenen, terrigen-detritischen Sandkomponenten. Sie bestehen vorwiegend aus Quarz und mit zunehmender Wassertiefe aus Kotpillen bzw. Kotpillenaggregaten. Je nach Tiefe treten vor allem Glimmer (>1000m) und Glaukonit (<800m) hinzu. Die restlichen Komponenten treten nur gelegentlich und in äußerst geringen Mengen im rezenten Oberflächensediment auf. 4) Quarz wird als Windstaub mit dem NE-Passat und vor allem durch den "Harmattan" aus der Sahara heraustransportiert und vorwiegend über dem Schelfbereich sedimentiert. Windstaubmaterial besteht primär weitgehend aus Siltkorngrößen, die vor Nouakchott über die Schelfkante hinaustransportiert werden und zu einer Grobsiltanreicherung am mittleren Hang führen. 5) Das Verhältnis zwischen den karbonatischen Biogenkomponenten und den nichtbiogenen Partikeln spiegelt sich deutlich in der Karbonatverteilung sowohl des Gesamtsedimentes als auch der Sandfraktion wider. Relativ hohe Karbonatgehalte vor Cap Leven im Norden stehen sehr geringen Anteilen von Nouakchott gegenüber. Mit zunehmender Wassertiefe ist eine deutliche Abnahme des Karbonatanteils zu verfolgen. 6) Die Tatsache, daß das Profil Cap Blanc im Bereich des ganzjährigen Auftriebs liegt, spiegelt sich nicht in der Zusammensetzung der Sandfraktion wider. Südlich der Zone des ganzjährigen Auftriebs weisen verschiedene Parameter (Radiolarien, Diatomeen, Verhältnis von Radiolarien zu planktonischen Foraminiferen, Benthos/Plankton-Verhältnis der Foraminiferen) trotz abnehmender Auftriebsintensität eher steigende Werte auf. Dies ist wesentlich auf eine infolge des Nährstoffeintrages durch Flußzufuhr bedingte Verschiebung der maximalen Primärproduktion weit in südliche Richtung zurückzuführen. 7) In den aufgeführten Parametern zeigen sich von Profil zu Profil sehr deutliche fazielle Unterschiede, obwohl der großklimatische Hintergrund im gesamten Untersuchungsgebiet etwa gleich ist. Vor Cap Leven bildet sich eine Fazies, die im wesentlichen aus planktonischen Foraminiferen besteht, während das Sediment vor Nouakchott zum überwiegenden Teil aus nichtbiogenen Komponenten aufgebaut wird. Im Übergangsbereich vor Cap Blanc bildet sich eine Mischfazies, die keinerlei Prägung durch das Auftriebsgeschehen erhält. Die Ursachen dieser faziellen Unterschiede werden auf fehlenden Terrigeneinfluß vor Cap Leven einerseits und hohe Terrigenanlieferung vor Nouakchott andererseits zurückgeführt. 8) Die Zusammensetzung und Verteilung der rezenten Grobfraktionssedimente am Kontinentalrand vor Nw-Afrika wird somit im wesentlichen als Ergebnis einer Überprägung der Biogenanlieferung durch nichtbiogene Komponenten angesehen. Wesentlicher steuernder Faktor ist demnach das hier vorherrschende Windsystem.

Composition of the sand fraction of sediment cores from the West-African continental margin

Seven cores from the West African continental margin in 12-18° N have been investigated by means of a coarse fraction analysis. Four of the seven cores contain allochthonous material: turbidites and debris flow deposits. The source of the allochthonous material is in about 300-600 m water depth. The age of the slide induced debris flow deposits is at the end of oxygen isotope stage 2. One debris flow deposit is covered by a turbidite (core GIK13211-1). The turbidites in the deep-sea core GIK13207-3 originate from river-influenced sediments from the West-African continental margin, whereas the autochthonous sequences are influenced by volcanic material from the Cape Verde Islands. Particle by particle supply from upper slope areas has been found in all four cores from the continental slope. Current sorting occurs on the submarine diapir (core GIK13289-3), whereas core GIK13291-1 on the NW-flanc, 200 m below core GIK13289-3, has no current sorting, except for stage 1 and parts of stage 5. The current sorting is reflected by parallel variations of median diameters of whole tests and of fragments of planktonic foraminifers, by higher median diameters of foraminifers on top of the diapir, by reduced accumulation rates and increased sand fraction percentages in core GIK13289-3 compared to core GIK13291-1. The Late Quarternary climatic history of the West-African near coastal area (12-18° N) has been redrawn: - in oxygen isotope stage 1 a humid climate is found in 12-18° N (This "humid impression" in 18° N, which is actually an arid area, is due to the poleward directed undercurrent, which transports Senegal river material to the north). - in oxygen isotope stage 2 an arid climate existed in 14-18° N, whereas in 12° N river discharfe persisted. But within stage 2 dune formation occured in 12° N on the (dry) shelf, additionally to fluviatile sediment input. - Older periods are preserved in autochthonous sediments of core GIK13289-3 and GIK13291-1, where oxygen stage 3,5 and 7 (the latter only in core GIK13289-3 present) show a humid climate (as well as in stage 5 of core GIK13255-3), interrupted by short arid intervals in core GIK12389-3, and stage 4 and 6 show an arid climate, interrupted by short humid periods The allochthonous stage 5 sediment in core GIK13211-1 also reflects a humid climate. The dissolution of planktonic foraminifers is strongest in th eLate Holocene and shows a minimum in the early Holocene, where also pteropods are preserved. The degree of carbonate dissolution is related mainly to the fine matter content (< 63 µm) whereas water depth is a less decisvive factor.

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.