ALBERT

Description: Most seals (pinnipeds) disperse from centralised terrestrial haul out sites to forage at sea which results in great intraspecific competition for prey. This competition may be reduced by gender-specific differences in depth use, something which should be enhanced by sexual dimorphism because diving ability is a function of body size. This thesis discusses the sex-specific behaviour of harbour seals (Phoca vitulina) in the North Sea. The aim was to determine the extent to which this species might have gender-dependent foraging strategies and, where apparent, to identify possible causes. The diving behaviour of six males and six females was analysed using animal-attatched data loggers (dead reckoners). With a weight of 73 kg (SD = 10) the equipped males were approx. 30 % heavier than females at 55 kg (SD = 8). All seals spent most of their time at sea (males 75.8 %, females 88.1 %) and perfmmed mainly U-shaped dives (ea. 80 %). The maximum recorded dive depth was 43 m for the males and 28 m for the females. Maximum dive duration lasted to 10 minuntes for females and 16 minutes for males. Mean trip duration was 44.1 h (SD = 65.5) for males and 46.8 h for females (SD = 35). Both genders showed significant correlations between dive duration and dive depth, as well as the durations of the descent, bottom and ascent phase and dive depth. However, there were no significant differences either in diving capabilities or in the foraging efficiency of the two sexes. An effect of body size on the diving capabilities of the seals could not been demonstrated. This indicates that the seals' diving capabilities in the North Sea are mainly determined by the bathymetry. Possible sex-specific differences might not be revealed because the seals do not reach their physiological limits in the shallow North Sea. Also, the large variance in the data as well as the small sample size mad it difficult to identify gender-specific differences. Tests of statistical power reveal that data from a total of 262 seals would be needed as an adequate sample size to determine with any certainty whether inter-sex differences occur.

Description: We explore a parameterization for mesoscale turbulence, closely related to that of Gent and McWilliams, in which forcing terms proportional to the isopycnal flux of potential vorticity appear in the averaged momentum equations. We show that in the presence of variable bottom topography, the parameterization predicts alongslope mean flow and a corresponding upslope bolus (eddy) flux of tracer that is associated with an alongslope-directed bottom eddy stress. The upslope bolus flux is in qualitative agreement with observations of a cold dome over seamounts. The predicted alongslope flow corresponds to flow fields found in geostrophic turbulence experiments and has some similarity (although conceptually very different, as discussed in the text) to Holloway's prediction based on statistical mechanics. By considering continuous stratification as a limiting case of a multilayer model, we show how to treat the surface and bottom boundaries. Practical application of the parameterization is illustrated using a three-dimensional -coordinate ocean circulation model that is very similar to the Bryan–Cox–Semtner model. The model-computed flow is consistent with observations of anticyclonic flow around a seamount. We show that the bottom eddy stress associated with the parameterization can be large, even compared to the annual mean surface wind stress, and hence could have important implications for the biology and water mass distribution of the coastal ocean as well as for the large-scale ocean circulation. From the climate modelling perspective, the approach adopted here provides a single formalism that combines the advantages of the Gent and McWilliams parameterization with alongslope mean flow similar to that suggested by Holloway.

Description: Herbivory can modify seaweed community structure by affecting variation in the abundance and distribution over spatial and temporal scales. To deter herbivores, seaweeds have developed several mechanisms, including the induction of chemical and morphological defenses, which may be influenced by environmental factors such as nutrient availability. In two sets of experiments 5 red, 4 brown, and 1 green seaweeds were tested for inducible defenses following exposure to direct consumption by an amphipod community. In addition, the effects of consumer presence and neighborhood grazing (indirect consumption) on the induction of defenses were examined in the red seaweed Gracilaria cearensis and the green seaweed Codium decorticatum under natural and additionally 100% elevated nutrient levels for C. decorticatum. In preliminary studies, suitable organisms for the induction experiments were determined in testing survival of potential tropical algae from the Brazilian littoral under laboratory conditions and performing multiple-choice feeding assays for four important Brazilian herbivore species in order to determine their preference rankings of these algae. The amphipod community dominated by Elasmopus brasiliensis was identified as the most suitable grazers. Induction of defense was evaluated after consumer exposure in choice-feeding experiments by offering live algae (LA, total defense) and reconstituted food (RF, chemical defense) of previously consumed (treated) and unconsumed algae (control). Nutrient enrichment did not affect induction of defense in C. decorticatum, yet unfertilized seaweeds were more palatable relatively to fertilized conspecifics. Different consumer activities did not affect palatability in G. cearensis, yet C. decorticatum seemed to induce resistance (LA) after reception of waterbome cues from consumed conspecifics. Unexpectedly C. decorticatum RF exhibited higher susceptibility to amphipods after consumer exposure in both experiments performed. While no significant decrease in palatability was observed in previously consumed algae compared to unconsumed controls after one week, two red seaweeds, Chondrophycus flagellifera (RF) and Pterocladiella capillacea (LA), exhibited significantly reduced palatability after consumer exposure. The brown seaweed Lobophora variegata showed significantly retarded chemical resistance after three weeks. This is the first report of inducible chemical defense in a red seaweed.

Description: Given the variability of seasonal, annual, and in particular langer time-scales, the dispersal and fate of the river discharge and its influence on the hydrographical and sedimentological settings are the central tasks in understanding the Holocene history of the Laptev Sea shelf. The main goal of this study was to investigate short- and long-term environmental changes in the strongly coupled land-shelf system of the Laptev Sea using isotopic evidence in sediments and biogenic carbonates. In order to trace the modern spatial distribution of terrestrial organic matter, which is strongly affected by the riverine input and the thermal erosion of the ice-rich permafrost coast, stable carbon isotope ratios of total organic carbon in surface sediments were analyzed. The stable carbon isotope composition of surface sediments reveal a dominant impact of terrestrial organic matter on the modern depositional environment of the Laptev Sea shelf with distinct south to north and east to west gradients. Based on downcore 8 13Carg records in radiocarbon-dated sediment cores the spatial and temporal deposition of terrestrial organic matter during the past 12.7 ka is specified and can be related to depositional changes which occurred after the last glacial maximum when this region became flooded due to a global rising sea level. The major changes in the deposition of terrestrial organic matter occurred between 11 and 7 ka BP and comprise the main phase of the southward retreat of the coastline and river depocenters due to the postglacial sea level rise. Stable oxygen and carbon isotope profiles from recent and fossil bivalve shells were investigated in order to trace modern and past hydrographical conditions and their changes during the postglacial history of the Laptev Sea. The serial dissection of bivalve shell valves along their growth axis from the umbo towards the ventral margin provides an isotopic record of hydrographical and physiological changes during the life of the individual specimen. The oxygen isotopic profiles of modern bivalve species of Astarte borealis exhibit amplitude cycles interpreted as recording annual hydrographical cycles. Regarding the well-known relationship between the carbonate 8 180, temperature, and the isotopic composition of water (8180w), it is possible to relate isotopic phases to seasonal hydrographical phases like summer and winter. The within shell isotopic variations are mainly attributed to variations in the isotopic composition and in the salinity of bottom waters in the Laptev Sea. Seasonal temperature changes can be regarded of minor importance. Using a modern linear relationship between 8 180w and salinity of 0.50 %0/salinity, salinity records are reconstructed from the oxygen isotope records of the bivalve shells and can be directly compared with hydrographical parameters at the investigated sites. Carbon isotope profiles from modern specimens reveal a correspondence to the river breakup and to seasonal phytoplankton productivity. Trends towards lighter 8 13 C values through ontogeny suggest the effects of metabolic changes from a juvenile into a mature adult. Differences in the 8 13C of shell carbonate between the sites appear to reflect the regional distribution of the ö 13C of sedimentary organic matter. Given a good conformance between isotope profiles from modern bivalve shells and oceanographic observations, oxygen isotope profiles of radiocarbon bivalve shells from a sediment core from northeast off the Lena Delta are usecl to obtain in formation about passt hydrological conditions. Although isotope profiles from fossil bivalves of the Laptev Sea shelf reflect only a brief interval of time, they may offer new important insights into the paleohydrography during snapshots of the last 8.4 ka and their relation to the Holocene transgression. A reconstructed bottom water salinity of 29.5 at 8.4 ka BP indicates that the particular site was much more affectecl by riverine water than nowaclays causecl by the proximity to the coastline and to the paleo-1iver mouth. Due to the continuing southward retreat of the coastline ancl the Lena River mouth relative to the study site an increase in the bottom water salinity at 7.3 ka BP is reconstructecl. The oxygen isotope shell profile at 7.3 ka BP gives an evidence of a bottom water hydrography which is characterized by a high variability of summer and winter conditions on the level of modern bottom water conditions. The following time slices at 3.6 ka and 1.6 ka BP reveal that modern hydrological conditions are fully established. The presented salinity reconstruction enables us to make further presurnptions on the relative proximity of the study site to the coast and to the river rnouth during snapshot views of the Holocene history and thus can be related to the postglacial transgression of the Laptev Sea shelf.

Description: The objective of this study is to reconstruct past environmental settings locked in the sediments of a carbonate mound in the northern Porcupine Seabight, west off Ireland. Benthic foraminiferal assemblages were investigated on two sediment cores, one located on top of the mound and a second one from an off-mound position further north as control site. The off-mound samples reveal two different assemblages: (1) an Interglacial group dominated by infaunal species, and (2) a Glacial group, dominated by cassidulinid species. Due to an incomplete stratigraphic record in the on-mound core, same species of the off-mound assemblages were grouped in on-mound samples. The Interglacial group dominates and the Glacial group is less abundant throughout the entire core indicating the lack of glacial time intervals in the on-mound core, which is coherent with stable oxygen isotope data and U/Th dates on coral fragments. A third assemblage is abundant in samples of the on-mound core showing elevated epibenthic species. This Mound group shows a great affinity to strong currents, high nutrient availability and is supposed to indicate Mediterranean Outflow Water in the northern Porcupine Seabight, as well as a higher coral cover on Propeller Mound in an earlier interglacial period. A Late Pleistocene decline in mound growth for Propeller Mound is suggested by the decrease of the Mound group towards the Holocene. Finally, the reconstructed environmental setting portrays the boundary conditions of the habitable range for the cold-water corals. Their growth occurred during interglacial and interstadial periods, whereas a glacial retreat of corals is documented in the absence of glacial sediments in the on-mound core. These conclusions are summarised in a model which efficiently accounts for the mound development covering the period of the Northern Hemisphere Glaciation.

Description: Die im Arbeitsgebiet kartierten geologischen Einheiten reichen vom Unter-Kambrium (Lancara Formation) bis in das Westfal des mittleren Karbons (San Emiliano Formation). Dabei dokumentieren die Wechsel zwischen klastischen und karbonatischen Sedimente Schwankungen des Ablagerungsmilieus, die durch Veränderungen des Reliefs aufgrund tektonischer Ereignisse und eustatischer Meeresspiegelschwankungen verursacht wurden. Während der tektonischen Hauptphase der variszischen Orogenese im mittleren und oberen Karbon kam es in der Kantabrischen Zone zu großräumigen Deckenüberschiebungen zum Kern des Asturischen Bogens. Die basalen Schiefer der Lancara Formation dienten dabei überwiegend als Gleithorizont. Als Folge des weiteren Transports der Decken nach N erfolgte eine zunehmende Verfaltung der paläozoischen Abfolge, die in einem komplexen Schuppenbau resultierte. Im Kartiergebiet lassen sich drei Decken voneinander unterscheiden: die Bodón Einheit im N, die Gayo Einheit im Zentrum und die Correcilla Einheit im S. Innerhalb der Bodón und Correcilla Einheit sind großräumige Sattel- und Muldenstrukturen anzutreffen. Die Gayo Einheit beschreibt dagegen eine kontinuierliche Abfolge aus dem unteren Kambrium bis zum mittleren Karbon mit einem Hiatus im Ordoviz und einem zweiten im Oberdevon. Die einzelnen Kalkrippen in der San Emiliano Formation wurden auf ihre lithologischen Unterschiede genauer untersucht, an denen die Muldenstruktur der im W fortgesetzten Carmenes-Synkline erkannt werden konnte. Zwei unterschiedliche Kalke dominieren die Kalkrippen. Die gut gebankten und dunkelgrauen Mudstones nehmen im Bereich des Kartiergebietes von E nach W zu und deuten auf ein hoher energetisches Ablagerungsmilieu im W hin. Im E keilen sie dagegen aus und ein massiger, knolliger und dunkelgrauer Mudstone dominiert die einzelnen Kalkrippen, in denen sich auch geringmächtige Mudflows und Riffbreccien einschalten. Diese Ablagerungen deuten auf einen ruhigeren Sedimentationsraum hin, das nur durch kurze, aber heftigere Sturmereignisse auszeichnet. Die Riffbreccien dienten als Substrat für ein erneutes Riffwachstum. Da die einzelnen Riffe aber gegen die Subsidenz des Beckens und dem erhöhten terrigenen Eintrag vom Festland ankämpfen muBten, sind die Kalkrippen im Kartiergebiet nur wenige Meter, maximal wenige 10er Meter mächtig. Zum Top der San Emiliano Formation nehmen die Kalkeinschaltungen ab, und es treten zunehmend kohleführende Schichten auf, die in einem sehr landnahen Milieu ablagerten.

Description: In dieser Arbeit wurde die Auswirkung von Gashydraten auf die Abundanz, Biomasse und taxonomische Zusammensetzung der Meiobenthosgesellschaft auf dem südlichen Gipfel des Hydratrückens vor Oregon untersucht. In Wassertiefen zwischen 785 und 852 m wurden drei unterschiedliche Habitate beprobt. Bakterienmatten (Beggiatoa) mit den höchsten Sulfidflüssen und -konzentrationen im Porenwasser, in denen die Gashydrate an oder unmittelbar unter der Sedimentoberfläche gefunden wurden; Muschelfelder (Calyptogena) mit etwas geringeren Sulfidflüssen und -konzentrationen sowie tiefer im Sediment liegenden Gashydraten und Kontrollstationen, in denen weder Gashydrat gefunden noch Sulfid im Porenwasser festgestellt wurde. Zusätzlich wurden zwei tiefere und vom eigentlichen Untersuchungsgebiet entfernte Referenzstationen beprobt (westliches und östliches Becken). Die medianen Gesamtabundanzen der Meiofauna waren in den Kontrollsedimenten mit 1350 Ind./10cm2 am höchsten und nahmen über die Muschelfelder (1188 Ind./10cm2) zu den stark sulfidischen Sedimenten der Bakterienmatten (860 Ind./1Ocm2) ab. Unterschiede der meiobenthischen Gesamtbiomasse der Kontrollen (211,50 μgC/10cm2) und Muschelfelder (203,09 μgC/10cm2) waren gering, die kleinste Biomasse hatte die Meiofauna in den Bakterienmatten (59,35 μgC/10cm2). Sulfid, das Produkt der Kombination von anaerober Methanoxidation und Sulfatreduktion, welches sich im Porenwasser anreichert, hat durch seine Toxizität für aerobe Metazoen offenbar generell einen eher negativen Einfluss auf die Abundanzen und Biomassen der Meiofauna. Dieses steht im Gegensatz zu den Ergebnissen anderer Autoren, die an "cold seeps" im Flachwasser und der Tiefsee zum Teil sehr hohe Abundanzen der Meiofauna feststellten und diese auf die erhöhte bakterielle Produktion im Sediment und die Vergrößerung des Nahrungsangebotes zurückführten. Häufig in den Proben gefundene Taxa waren Nematoden, Rotatorien, Copepoden und teilweise auch Polychaeten. Sowohl in den Kontrollen als auch in den Referenzstationen dominierten die Nematoden das Meiobenthos. Mit zunehmender Beeinflussung der Sedimente durch Gashydrate in den Muschelfeldern und Bakterienmatten wurde ein vollständiger Wechsel der Dominanz von den Nematoden zu den Rotatorien der Gattungen Lecane und Monostyla festgestellt. Die Vertikalverteilung der Nematoden zeigte deutliche Oberflächenmaxima in allen Habitaten, wahrend die Rotatorien in tieferen Sedimenthorizonten ihre größten Abundanzen hatten. Auf taxonomischer Ebene konnte keine spezielle Meiobenthosgesellschaft in den gashydratbeeinflussten Sedimenten festgestellt werden.