Late Pliocene variations of the Mediterranean outflow

Late Pliocene changes in the advection of Mediterranean Outflow Water (MOW) derivates were reconstructed at northeast Atlantic DSDP/ODP sites 548 and 982 and compared to records of WMDW at West Mediterranean Site 978. Neodymium isotope (epsilon-Nd) values more positive than ~10.5/~ 11 reflect diluted MOW derivates that spread almost continuously into the northeast Atlantic from 3.7 to 2.55 Ma, reaching Rockall Plateau Site 982 from 3.63 to 2.75 Ma. From 3.4 to 3.3 Ma average MOW temperature and salinity increased by 2°-4 °C and ~1 psu both at proximal Site 548 and distal Site 982. The rise implies a rise in flow strength, coeval with a long-term rise in both west Mediterranean Sea surface salinity by almost 2 psu and average bottom water salinity (BWS) by ~1 psu, despite inherent uncertainties in BWS estimates. The changes were linked with major Mediterranean aridification and a drop in African monsoon humidity. In contrast to model expectations, the rise in MOW salt discharge after 3.4 Ma did not translate into improved ventilation of North Atlantic Deep Water, since it possibly was too small to significantly influence Atlantic Meridional Overturning Circulation. Right after ~2.95 Ma, with the onset of major Northern Hemisphere Glaciation, long-term average bottom water temperature (BWT) and BWS at Site 548 dropped abruptly by ~5 °C and ~1-2 psu, in contrast to more distal Site 982, where BWT and BWS continued to oscillate at estimates of ~2 °C and 1.5-2.5 psu higher than today until ~2.6 Ma. We relate the small-scale changes both to a reduced MOW flow and to enhanced dilution by warm waters of a strengthened North Atlantic Current temporarily replacing MOW derivates at Rockall Plateau.

Synthesis and Properties of a Series of 1,1,n,n-Tetramethyl[n](2,11)teropyrenophanes

The work described in this thesis revolves around the 1,1,n,ntetramethyl[n](2,11)teropyrenophanes, which are a series of [n]cyclophanes with a severely bent, board-shaped polynuclear aromatic hydrocarbons (PAH). The thesis is divided into seven Chapters. The first Chapter conatins an overview of the seminal work on [n]cyclophanes of the first two members of the “capped rylene” series of PAHs: benzene and pyrene. Three different general strategies for the synthesis of [n]cyclophanes are discussed and this leads in to a discussion of some slected syntheses of [n]paracyclopahnes and [n](2,7)pyrenophanes. The chemical, structural, spectroscopic and photophysical properties of these benzene and pyrene-derived cyclophanes are discussed with emphasis on the changes that occur with changes in the structure of the aromatic system. Chapter 1 concludes with a brief introduction to [n]cyclophanes of the fourth member of the capped rylene series of PAHs: teropyrene. The focus of the work described in Chapter 2 is the synthesis of of 1,1,n,ntetramethyl[n](2,11)teropyrenophane (n = 6 and 7) using a double-McMurry strategy. While the synthesis 1,1,7,7-tetramethyl[7](2,11)teropyrenophane was successful, the synthesis of the lower homologue 1,1,6,6-tetramethyl[6](2,11)teropyrenophane was not. The conformational behaviour of [n.2]pyrenophanes was also studied by 1H NMR spectroscopy and this provided a conformation-based rationale for the failure of the synthesis of 1,1,6,6-tetramethyl[6](2,11)teropyrenophane. Chapter 3 contains details of the synthesis of 1,1,n,n-tetramethyl[n](2,11)teropyrenophanes (n = 7-9) using a Wurtz / McMurry strategy, which proved to be more general than the double McMurry strategy. The three teropyrenophanes were obtained in ca. 10 milligram quantities. Trends in the spectroscopic properties that accompany changes in the structure of the teropyrene system are discussed. A violation of Kasha’s rule was observed when the teropyrenophanes were irradiated at 260 nm. The work described in the fourth Chapter concentrates on the development of gram-scale syntheses of 1,1,n,n-tetramethyl[n](2,11)teropyrenophanes (n = 7–10) using the Wurtz / McMurry strategy. Several major modifications to the orginal synthetic pathway had to be made to enable the first several steps to be performed comfortably on tens of grams of material. Solubility problems severely limited the amount of material that could be produced at a late stage of the synthetic pathways leading to the evennumbered members of the series (n = 8, 10). Ultimately, only 1,1,9,9- tetramethyl[9](2,11)teropyrenophane was synthesized on a multi-gram scale. In the final step in the synthesis, a valence isomerization / dehydrogenation (VID) reaction, the teropyrenophane was observed to become unstable under the conditions of its formation at n = 8. The synthesis of 1,1,10,10-tetramethyl[10](2,11)teropyrenophane was achieved for the first time, but only on a few hundred milligram scale. In Chapter 5, the results of an investigation of the electrophilic aromatic bromination of the 1,1,n,n-tetramethyl[n](2,11)teropyrenophanes (n = 7–10) are presented. Being the most abundant cyclophane, most of the work was performed on 1,1,9,9-tetramethyl[9](2,11)teropyrenophane. Reaction of this compound with varying amounts of of bromine revealed that bromination occurs most rapidly at the symmetryrelated 4, 9, 13 and 18 positions (teropyrene numbering) and that the 4,9,13,18- tetrabromide could be formed exclusively. Subsequent bromination occurs selectively on the symmetry-related 6, 7, 15 and 16 positions (teropyrene numbering), but considerably more slowly. Only mixtures of penta-, hexa-, hepta and octabromides could be formed. Bromination reactions of the higher and lower homologues (n = 7, 8 and 10) revealed that the reactivity of the teropyrene system increased with the degree of bend. Crystal structures of some tetra-, hexa-, hepta- and octa-brominated products were obtained. The goal of the work described in Chapter 6 is to use 1,1,9,9- tetramethyl[9](2,11)teropyrenophane as a starting material for the synthesis of warped nanographenophanes. A bromination, Suzuki-Miyaura, cyclodehydrogenation sequence was unsuccessful, as was a C–H arylation / cyclodehydrogenation approach. Itami’s recently-developed K-region-selective annulative -extension (APEX) reaction proved to be successful, affording a giant [n]cyclophane with a C84 PAH. Attempted bay-region Diels-Alder reactions and some cursory host-guest chemistry of teropyrenophanes are also discussed. In Chapter 7 a synthetic approach toward a planar model compound, 2,11-di-tbutylteropyrene, is described. The synthesis could not be completed owing to solubility problems at the end of the synthetic pathway.

High resolution study of narrow tailed radio galaxies in clusters

Clusters of galaxies are the most massive and large gravitationally bounded systems in the whole Universe. Their study is of fundamental importance to constrain cosmological parameters and to obtain informations regarding various kind of emission in different wavebands. In particular, in the radio domain, beside the diffuse emission, the study is focused on the radio galaxies emission. Radio galaxies in clusters can have peculiar morphology, since they interact with the intracluster medium (ICM) in which they are embedded. Particularly, in this thesis we focused our attention on the so-called Narrow-Angle Tailed radio galaxies (NAT), which present radio jets that are bent at extreme angle, up to 90 degrees, from their original orientation. Some NAT show a narrow extended structure and the two radio tails are not resolved even with high resolution radio observations. An example is provided by the source IC310, in the Perseus Cluster, whose structure has been recently interpreted as due to Doppler boosting effects of a relativistic jet oriented at a small angle with respect to the line of sight. If the structure is due to relativistic effects, this implies that the jets are relativistic at about 400 kpc from the core, but this is in contrast with unified models, which predict that for low-power radio source (NAT are classified as FRI radio galaxies) the jets decelerate to sub-relativistic speed within a few kpc from the core. To investigate this scientific topic, in this thesis we have analyzed the innermost structure of a sample of eleven radio galaxies showing a very narrow NAT structure. We can conclude that the structure of these radio galaxies is different from that of IC310. These radio galaxies are indeed strongly influenced by environmental effects and are similar to classical NAT sources.

Investigations of artificial sediments from two deep-sea in situ recolonization experiments deployed for one year at the central HAUSGARTEN station IV during ARK-XIX/3c

Commercial exploitation and abrupt changes of the natural conditions may have severe impacts on the Arctic deep-sea ecosystem. The present recolonisation experiment mimicked a situation after a catastrophic disturbance (e.g. by turbidites caused by destabilized continental slopes after methane hydrate decomposition) and investigated if the recolonisation of a deep-sea habitat by meiobenthic organisms is fostered by variations innutrition and/or sediment structure. Two "Sediment Tray Free Vehicles" were deployed for one year in summer 2003 at 2500 m water depth in the Arctic deep-sea in the eastern Fram Strait. The recolonisation trays were filled with different artificial and natural sediment types (glass beads, sand, sediment mixture, pure deep-sea sediment) and were enriched with various types of food (algae, yeast, fish). After one year, meiobenthos abundances and various sediment related environmental parameters were investigated. Foraminifera were generally the most successful group: they dominated all treatments and accounted for about 87% of the total meiobenthos. Colonizing meiobenthos specimens were generally smaller compared to those in the surrounding deep-sea sediment, suggesting an active recolonisation by juveniles. Although experimental treatments with fine-grained, algae-enriched sediment showed abundances closest to natural conditions, the results suggest that food availability was the main determining factor for a successful recolonisation by meiobenthos and the structure of recolonised sediments was shown to have a subordinate influence.

Documentation and sedimentology of core PS1021-1 from the Antarctic continental margin off Kap Norvegia

Sedimentological analyses concerning ice rafted debris, grain size distribution, biogenous components, and clay mineral composition of four sediment cores from the Antarctic continental margin off Kapp Norvegia reveal a cyclical pattern of three different sediment facies. These are classified into warm and cold types representing warm and cold climatic periods and a short transition period from cold to warm events. The sedimentological parameters reflect the variations within the cryosphere and the hydrosphere, which are directly influenced by the climatic fluctuations. The unusually high content of carbonaceous planktonic and benthonic foraminifera in these polar sediments, as well as the interfingering of terrigeneous and biogeneous-rich sediments with increasing distance from the continent, might reflect the influence of the Weddell Sea Polynya and the oscillations of polynya, pack-ice and ice shelf extent during the late Pleistocene.

Planktonic foraminiferal d18O and d13C values, derived sea-surface temperatures from d18O and selected planktonic foraminiferal species for core P69 of Hawke Bay off eastern North Island

Recent evidence suggests that the Subtropical Convergence (STC) zone east of New Zealand shifted little from its modern position along Chatham Rise during the last glaciation, and that offshore surface waters north of the STC zone cooled only slightly. However, at nearshore core site P69 (2195 m depth), 115 km off the east coast of North Island and ca 300 km north of the modern STC zone, planktonic foraminiferal species, transfer function data and stable oxygen and carbon isotope records suggest that surface waters were colder by up to 6°C during the late last glacial period compared to the Holocene, and included a strong upwelling signature. Presently site P69 is bathed by south-flowing subtropical waters in the East Cape Current. The nearshore western end of Chatham Rise supports a major bathymetric depression, the Mernoo Saddle, through which some exchange between northern subtropical and southern subantarctic water presently occurs. It is proposed that as a result of much intensified current flows south of the Rise during the last glaciation, a consequence of more compressed subantarctic water masses, lowered sea level, and an expanded and stronger Westerly Wind system, there was accelerated leakage northwards of both Australasian Subantarctic Water and upwelled Antarctic Intermediate Water over Mernoo Saddle in a modified and intensified Southland Current. The expanded cold water masses displaced the south-flowing warm East Cape Current off southeastern North Island, and offshore divergence was accompanied by wind-assisted upwelling of nutrient-rich waters in the vicinity of P69. A comparable kind of inshore cold water jetting possibly characterised most glacial periods since the latest Miocene, and may account for the occasional occurrence of subantarctic marine fossils in onland late Cenozoic deposits north of the STC zone, rather than invoking wholesale major oscillations of the oceanic STC itself.

Oceanographic investiations from the Sea of Ochotsk

The Sea of Okhotsk is a marginal sea of the Pacific Ocean, which is characterized by strong variations in the productivity and sediment supply due to sea ice transport and river input. Furthermore the variations in the hydrological cycle determine the formation of the SOIW (Sea of Okhotsk Intermediate Water) which plays an important role in the ventilation processes in the intermediate water of the N-Pacific. Isotope data measured on planktonic and benthic foraminifera, sedimentological and geochemical studies of sediment cores and surface samples from the Sea of Okhotsk are used to reconstruct the paleoceanography during the past 350.000 years. The dating and correlation of the sediments are based on oxygen isotope stratigraphy, absolute ages, magnetic susceptibility as well as a detailled tephrachronology of the entire basin. The sedimentation rates are characterized by temporal and spatial variations. The maximum sedimentation rate takes place at the continental slope off Sakhalin due to the input of the Amur River, the sea ice drift and the high productivity. The sedimentation rate in the eastern part of the Sea of Okhotsk is generelly high because of the influence of the nutrient-rich Kamchatka Current. In the central and northern parts of the Sea of Okhotsk, areas with low productivity and reduced terrestrial supply, the sedimentation rate is the lowest. The analyses of the surface sediment samples make it possible to characterize the (sub)- recent sediment supply and transportation processes. The bulk sediment measurements, isotope data and the accumulation rate of ice-rafted debris (IRD) show a dominant sea ice cover and a region with a high productivity as well as a high Amur River input in the western part of the sea. The eastern part of the Sea of Okhotsk, however, is marked by the predominance of warm and nutrient-rich water masses coming from the Kamchatka Current which restricts the sea ice cover. This is reflected in low content of ice-rafted debris and high productivity proxies as well as in isotope data. The deposits of the Sea of Okhotsk are characterized by terrestrial, biogenic and volcanogenic sediment input which varies temporally and spatially. Here, the sedimentation pattern is dominated by the terrestrial input. Bulk sediment measurements and sample analyses of the > 63 micron particle input make it possible to distinguish glacial and interglacial fluctuations. The sedimentation processes during glacial times are determined by a high content of ice-rafted debris, whereas the primary production is higher during interglacial periods. During the last glacial/interglacial cycle the IRD-distribution pattern indicates a strong sea ice transport in the western part and in large areas of the open sea in the eastern part of the Sea of Okhotsk with a relatively constant ice-drift system. The IRD flux in sediments of the oxygen isotope Stage 6 reflects a new sedimentation pattern in the eastern part of the sea. This high IRD accumulation rate indicates ice advances beyond the shelf margin and an iceberg transport from NE-E direction into the Sea of Okhotsk. The several large, brief, negative anomalies in d13C values of Neogloboquadrina pachyderma (s) show releases of methane from basin sediments which correspond to periods of relative sea level falls. The high sedimentation rates on the Sakhalin slope allow insights into the climatic history in Holocene and indicate shorter-scale variations oscillation in Stage 3, which correlate with the global climatic changes. These variations are described as Dansgaard-Oeschger cycles in Greenland ice cores and as Heinrich-Events in several marine sediment cores from the N-Atlantic.

Benthic foraminifera in eastern equatorial Indian Ocean surface sediments

Study of Recent abyssal benthic foraminifera from core-top samples in the eastern equatorial Indian Ocean has identified distinctive faunas whose distribution patterns reflect the major hydrographic features of the region. Above 3800 m, Indian Deep Water (IDW) is characterized by a diverse and evenly-distributed biofacies to which Globocassidulina subglobosa, Pyrgo spp., Uvigerina peregrina, and Eggerella bradyi are the major contributors. Nuttalides umbonifera and Epistominella exigua are associated with Indian Bottom Water (IBW) below 3800 m. Within the IBW fauna, N. umbonifera and E. exigua are characteristic of two biofacies with independent distribution patterns. Nuttalides umbonifera systematically increases in abundance with increasing water depth. The E. exigua biofacies reaches its greatest abundance in sediments on the eastern flank of the Ninetyeast Ridge and in the Wharton-Cocos Basin. The hydrographic transition between IDW and IBW coincides with the level of transition from waters supersaturated to waters undersaturated with respect to calcite and with the depth of the lysocline. Carbonate saturation levels, possibly combined with the effects of selective dissolution on the benthic foraminiferal populations, best explain the change in faunas across the IDW/IBW boundary and the bathymetric distribution pattern of N. umbonifera. The distribution of the E. exigua fauna cannot be explained with this model. Epistominella exigua is associated with the colder, more oxygenated IBW of the Wharton-Cocos Basin. The distribution of this biofacies on the eastern flank of the Ninetyeast Ridge agrees well with the calculated bathymetric position of the northward flowing deep boundary current which aerates the eastern basins of the Indian Ocean.

Stable oxygen isotope record and age determination of benthic foraminiferal faunas of the Norwegian-Greenland Sea

Fluctuations in benthic foraminiferal faunas over the last 130,000 yr in four piston cores from the Norwegian Sea are correlated with the standard worldwide oxygen-isotope stratigraphy. One species, Cibicides wuellerstorfi, dominates in the Holocene section of each core, but alternates downcore with Oridorsalis tener, a species dominant today only in the deepest part of the basin. O. tener is the most abundant species throughout the entire basin during periods of particularly cold climate when the Norwegian Sea presumably was ice covered year round and surface productivity lowered. Portions of isotope Stages 6, 3, and 2 are barren of benthic foraminifera; this is probably due to lowered benthic productivity, perhaps combined with dilution by ice-rafted sediment; there is no evidence that the Norwegian Sea became azoic. The Holocene and Substage 5e (the last interglacial) are similar faunally. This similarity, combined with other evidence, supports the presumption that the Norwegian Sea was a source of dense overflows into the North Atlantic during Substage 5e as it is today. Oxygen-isotope analyses of benthic foraminifera indicate that Norwegian Sea bottom waters warmer than they are today from Substage 5d to Stage 2, with the possible exception of Substage 5a. These data show that the glacial Norwegian Sea was not a sink for dense surface water, as it is now, and thus it was not a source of deep-water overflows. The benthic foraminiferal populations of the deep Norwegian Sea seem at least as responsive to near-surface conditions, such as sea-ice cover, as they are to fluctuations in the hydrography of the deep water. Benthic foraminiferal evidence from the Norwegian Sea is insufficient in itself to establish whether or not the basin was a source of overflows into the North Atlantic at any time between the Substage 5e/5d boundary at 115,000 yr B.P. and the Holocene.

Relative contents of foraminifera species in bottom sediments of northern and southern seas

Correlation of paleoceanographic events in several key regions of the World Ocean: North Atlantic, Antarctic, West Arctic Seas, North Pacific and tropical Indo-Pacific has been carried out for the last 135 ka based on micropaleontological, stable isotope, geochronological (AMS-14C) and other data. It has been shown that the global thermohaline circulation controls remote climatic teleconnections on millennial-scale and partly on centennial-scale, while short-term climate changes are mainly transferred by the atmosphere. The basic information is given about the recent thermohaline circulation and stages of its development during Neogene.

Sedimentology of the northwestern Weddel Sea continental shelf and slope

Geologie cores on two profiles oriented normaly to the continental shelf and slope, have been investigated to reconstruct the Quaternary sedimentary history of the southeast continental border of South Orkney (NW Weddell Sea). The sediments were described macroscopically and their fabric investigated by use of X-radiographs. Laboratory work comprised detailed grain-size analysis, determination of the watercontent, carbonate, organic carbon and sand fraction.composition. Stable oxygen and carbon isotopes have been measured On planktonic foraminifera. Palaeomagnetism, analysis of 230Th-content and detailed comparison of the lithlogic Parameters with the oxygen isotope stages (Martinson curve) were used for stratigraphic classification of the sediments. The sediment cores from the continental slope comprise a maximum age of 300,000 years B. P.. Bottom currents, ice rafting and biogenic input are the main sources of sediment. Based on lithologic parameters a distinction between glacial and interglacial facies is possible. Silty clays without microfossils and few bioturbation characterise the sediments of the glacial facies. Only small amounts of icerafted debris can be recognized. This type of sediment was accumulated during times of lower sea-level and drastically reduced rate of bottom water production. Based on grain-size distribution, bottom current velocities of 0.01 cmls were calculated. Thick sea-ice coverage reduced biogenic production in the surface water, and as consequence benthic communities were depleted. Because of the reduced benthic life, sediments are only slithly bioturbated. At the beginning of the interglacial Stage, the sea-level rised rapidly, and calving rate of icebergs, combined with input of ice-rafted material, increased considerably. Sediments of this transition facies are silty cliiys with a high proportion of coarse ice-rafted debris, but without microfossils. With the onset of bottom water production in connection with shelf ice water, sediments of interglacial facies were formed. They consist of silty clays to clayey silts with considerable content of sand and gravel. Sediments are strongly bioturbated. Based On the sediment caracteristics, current velocities of the bottom water were calculated to be of 0.96 cmls for interglacials. At the southern slope of a NW/SE-striking ridge, bottom water current is channelized, resulting in a drastic increase of current velocities. Current velocities up to 7.5 cm/s lead to formation of residual sediments. While the continental slope has predominantly fine sediments, the South Orkney shelf are mainly sandy silts and silty sands with a high proportion of gravel. These sediments were formed dominantly by ice-rafting during Brunhes- and Matuyama-Epoch. Currents removed the fine fraction of the sediments. Based on microfossil contents it was not possible to differentiate sediments from glacial to interglacial. In the upper Parts of the cores graded sequences truncated by erosion were observed. These sequences were formed during Brunhes-Epoch by strong currents with velocities decreasing periodically from about 7.5 cm/s to about 1 cm/s. Sediments with a high proportion of siliceous microfossils but barren of foraminifera compose the lower part of the shelf cores. These sediments have formed during the warmer Matuyama-Epoch.

Sedimentology on two cores from Scoresby Sund, Greenland

Reconstruction of the postglacial palaeoenvironmental evolution was the main objective of marine geological investigations in the Scorcsby Sund fjord system. For this purpose, samples of marine sediments, taken on RV Polarstern cruises ARK-V/3b and ARK-VII/3b in 1988 and 1990, have been analysed. All investigated fjord sediments are paratills. However, remarkable changes in sediment fabric and composition occur with depth in cores. They are attributable to different modes of sediment deposition. Therefore, a subdivision of the postglacial palaeoenvironmental history into periods of considerably different sedimentary conditions is feasible. The change of sedimentary fades with time is interpreted by deposition under changing climatic conditions during the postglacial. Displacements of cyclonic and anticyclonic centers in the atmosphere change amount of precipitation at the east coast of Greenland. Precipitation strongly influences extension of local ice caps of coastal areas and duration of coverage of the fjords by sea ice. These factors again control the sedimentary regime in the fjord system.

Investigations on sediment coring site PS1823 in the Riiser-Larsen Sea, Southern Ocean

Physical and sedimentological investigations were carried out on a 14 m long gravity core and a 0.5 m long box core from 4440 m water depth off Queen Maud Land, East-Antarctica. Strongly bioturbated hemipelagic muds of predominantly terrigenous origin and a very small biogenic part build up the 'Normal-Facies'. Several sandy to silty layers are inserted in the 'Normal-Facies'. These layers are seperated by lithology, structure and the investigated parameters of this study and are interpreted as turbidites. The source area for the turbidity currents is supposed to be at the uppermost continental margin, close to the shelf break and there is evidenee for this gravity transport within the erosive Ritscher-Canyon, which extends close to the core position. The distribution of biogenic components indicates an age of 1.3 million years or more, with an average sedimentation rate of about 1 cm/1000 years. Early diagenetic proeesses caused water loss by compaction, errosion and dissolution of biogenic components and precipitation and recrystallization of manganese micronodules. Cyclic fluctuations of the sediment-parameters within the 'Normal-Facies' enable the distinction of a 'Glazial'- and an 'Interglazial'-Facies. The 'Glazial'-Facies reflects glacial sedimentary conditions and shows a dark olive gray colour, high susceptibility, low silt/clay-ratios, only a few biogenic components and the regular occurence of interrelated turbidite layers. In contrast, the 'Interglazial'-Facies is dominated by a light olive or olive-brown colour, low susceptibility, high silt/clay-ratios and an increased number of biogenic components. This facies corresponds to interglacial conditions. Three main processes are supposed to have been responsible for the observed facies changes: (1) the bottom water mass circulation, (2) the gravity transport by turbidity currents and (3) the biogenic surface production. These processes are related to the quaternary climatic changes. The extension of the ice shelves directed the gravity transport to the deep sea and the formation of Antarctic Bottom Water, which in turn influenced the silt/clay-ratios in the sediment record. Fluctuations in sea ice coverage controlled the biogenic surface production.

Sedimentology and faunal compositions of surface sediments from the southern Florida Strait

The water masses in the Florida Straits and Bahamas region are important sources for the Northern Atlantic surface ocean circulation. In this study, we analyse carbonate preservation in surface sediments located above the chemical lysocline in the Florida Straits and Bahamas region and discuss possible reasons for supralysoclinal dissolution. Calcite dissolution proxies such as the variation of the foraminiferal assemblage, Fragmentation Index, Benthic Foraminifera Index, and Resistance Index displayed a good preservation in both areas. The pteropod species Limacina inflata showed very good preservation in sediments of inter-platform channels from the Great Bahama Bank (Providence Channel, Exuma Sound) above the aragonite lysocline. Supralysoclinal aragonite dissolution, however, was observed at two water depth levels (800-1000 m and below 1500 m) in the Florida Straits. Our observations suggest that the supralysoclinal dissolution in the Florida Straits is due to the degradation of organic material. The presence of Antarctic Intermediate Water (AAIW) may be a contributing factor for the significant aragonite dissolution in 800-1000 m. The comparison of modern preservation patterns of the surface sediments with hydrographical measurements shows that the L. inflata Dissolution Index (LDX) might be an adequate proxy to reconstruct paleo-water mass conditions in an area which is highly saturated with respect to calcium carbonate.

Benthic foraminiferal record and age dating of sediment cores from the Gullmar Fjord at the west coast of Sweden

A high-resolution study of benthic foraminiferal assemblages was performed on a ca. eight metre long sediment core from Gullmar Fjord on the west coast of Sweden. The results of 210Pb- and AMS 14C-datings show that the record includes the two warmest climatic episodes of the last 1500 years: the Medieval Warm Period (MWP) and the recent warming of the 20th century. Both periods are known to be anomalously warm and associated with positive NAO winter indices. Benthic foraminiferal successions of both periods are compared in order to find faunal similarities and common denominators corresponding to past climate changes. During the MWP, Adercotryma glomerata, Cassidulina laevigata and Nonionella iridea dominated the assemblages. Judging from dominance of species sensitive to hypoxia and the highest faunal diversity for the last ca. 2400 years, the foraminiferal record of the MWP suggests an absence of severe low oxygen events. At the same time, faunas and d13C values both point to high primary productivity and/or increased input of terrestrial organic carbon into the fjord system during the Medieval Warm Period. Comparison of the MWP and recent warming revealed different trends in the faunal record. The thin-shelled foraminifer N. iridea was characteristic of the MWP, but became absent during the second half of the 20th century. The recent Skagerrak-Kattegat fauna was rare or absent during the MWP but established in Gullmar Fjord at the end of the Little Ice Age or in the early 1900s. Also, there are striking differences in the faunal diversity and absolute abundances of foraminifera between both periods. Changes in primary productivity, higher precipitation resulting in intensified land runoff, different oxygen regimes or even changes in the fjord's trophic status are discussed as possible causes of these faunal differences.