Clay mineralogy of South Atlantic surface sediments

Surface samples, mostly from abyssal sediments of the South Atlantic, from parts of the equatorial Atlantic, and of the Antarctic Ocean, were investigated for clay content and clay mineral composition. Maps of relative clay mineral content were compiled, which improve previous maps by showing more details, especially at high latitudes. Large-scale relations regarding the origin and transport paths of detrital clay are revealed. High smectite concentrations are observed in abyssal regions, primarily derived from southernmost South America and from minor sources in Southwest Africa. Near submarine volcanoes of the Antarctic Ocean (South Sandwich, Bouvet Island) smectite contents exhibit distinct maxima, which is ascribed to the weathering of altered basalts and volcanic glasses. The illite distribution can be subdivided into five major zones including two maxima revealing both South African and Antarctic sources. A particularly high amount of Mg- and Fe-rich illites are observed close to East Antarctica. They are derived from biotite-bearing crystalline rocks and transported to the west by the East Antarctic Coastal Current. Chiorite and well-crystallized dioctaedral illite are typical minerals enriched within the Subantarctic and Polarfrontal-Zone but of minor importance off East Antarctica. Kaolinite dominates the clay mineral assemblage at low latitudes, where the continental source rocks (West Africa, Brazil) are mainly affected by intensive chemical weathering. Surprisingly, a slight increase of kaolinite is observed in the Enderby Basin and near the Filchner-Ronne Ice shelf. The investigated area can be subdivided into ten, large-scale clay facies zones with characteristic possible source regions and transport paths. Clay mineral assemblages of the largest part of the South Atlantic, especially of the western basins are dominated by chlorite and illite derived from the Antarctic Peninsula and southernmost South America and supported by advection within the Circumantarctic Deep Water flow. In contrast, the East Antarctic provinces are relatively small. Assemblages of the eastern basins north of 30°S are strongly influenced by African sources, controlled by weathering regimes on land and by a complex interaction of wind, river and deep ocean transport. The strong gradient in clay mineral composition at the Brazilian slope indicate a relatively low contribution of tropically derived assemblages to the western basins.

Data from PhD thesis

The ocean quahog, Arctica islandica is the longest-lived non-colonial animal known to science. A maximum individual age of this bivalve of 405 years has been found in a population off the north western coast of Iceland. Conspicuously shorter maximum lifespan potentials (MLSPs) were recorded from other populations of A. islandica in European waters (e.g. Kiel Bay: 30 years, German Bight: 150 years) which experience wider temperature and salinity fluctuations than the clams from Iceland. The aim of my thesis was to identify possible life-prolonging physiological strategies in A. islandica and to examine the modulating effects of extrinsic factors (e.g. seawater temperature, food availability) and intrinsic factors (e.g. species-specific behavior) on these strategies. Burrowing behavior and metabolic rate depression (MRD), tissue-specific antioxidant and anaerobic capacities as well as cell-turnover (= apoptosis and proliferation) rates were investigated in A. islandica from Iceland and the German Bight. An inter-species comparison of the quahog with the epibenthic scallop Aequipecten opercularis (MLSP = 8-10 years) was carried out in order to determine whether bivalves with short lifespans and different lifestyles also feature a different pattern in cellular maintenance and repair. The combined effects of a low-metabolic lifestyle, low oxidative damage accumulation, and constant investment into cellular protection and tissue maintenance, appear to slow-down the process of physiological aging in A. islandica and to afford the extraordinarily long MLSP in this species. Standard metabolic rates were lower in A. islandica when compared to the shorter-lived A. opercularis. Furthermore, A. islandica regulate mantle cavity water PO2 to mean values < 5 kPa, a PO2 at which the formation of reactive oxygen species (ROS) in isolated gill tissues of the clams was found to be 10 times lower than at normoxic conditions (21 kPa). Burrowing and metabolic rate depression (MRD) in Icelandic specimens were more pronounced in winter, possibly supported by low seawater temperature and food availability, and seem to be key energy-saving and life-prolonging parameters in A. islandica. The signaling molecule nitric oxide (NO) may play an important role during the onset of MRD in the ocean quahog by directly inhibiting cytochome-c-oxidase at low internal oxygenation upon shell closure. In laboratory experiments, respiration of isolated A. islandica gills was completely inhibited by chemically produced NO at low experimental PO2 <= 10 kPa. During shell closure, mantle cavity water PO2 decreased to 0 kPa for longer than 24 h, a state in which ROS production is supposed to subside. Compared to other mollusk species, onset of anaerobic metabolism is late in A. islandica in the metabolically reduced state. Increased accumulation of the anaerobic metabolite succinate was initially detected in the adductor muscle of the clams after 3.5 days under anoxic incubation or in burrowed specimens. A ROS-burst was absent in isolated gill tissue of the clams following hypoxia (5 kPa)-reoxygenation (21 kPa). Accordingly, neither the activity of antioxidant enzymes superoxide dismutase (SOD) and catalase (CAT), nor the specific content of the ROS-scavenger glutathione (GSH) was enhanced in different tissues of the ocean quahog after 3.5 days of self-induced or forced hypoxia/anoxia to prepare for an oxidative burst. While reduced ROS formation compared to routine levels lowers oxidative stress during MRD and also during surfacing, the general preservation of high cellular defense and the efficient removal and replacement of damaged cells over lifetime seem to be of crucial importance in decelerating the senescent decline in tissues of A. islandica. Along with stable antioxidant protection over 200 years of age, proliferation rates and apoptosis intensities in most investigated tissues of the ocean quahog were low, but constant over 140 years of age. Accordingly, age-dependent accumulations of protein and lipid oxidation products are lower in A. islandica tissues when compared to the shorter-lived bivalve A. opercularis. The short-lived swimming scallop is a model bivalve species representing the opposite life and aging strategy to A. islandica. In this species permanently high energy throughput, reduced investment into antioxidant defense with age, and higher accumulation of oxidation products are met by higher cell turnover rates than in the ocean quahog. The only symptoms of physiological change over age ever found in A. islandica were decreasing cell turnover rates in the heart muscle over a lifetime of 140 years. This may either indicate higher damage levels and possibly ongoing loss of functioning in the heart of aging clams, or, the opposite, lower rates of cell damage and a reduced need for cell renewal in the heart tissue of A. islandica over lifetime. Basic physiological capacities of different A. islandica populations, measured at controlled laboratory conditions, could not explain considerable discrepancies in population specific MLSPs. For example, levels of tissue-specific antioxidant capacities and cell turnover rates were similarly high in individuals from the German Bight and from Iceland. Rather than genetic differences, the local impacts of environmental conditions on behavioral and physiological traits in the ocean quahog seem to be responsible for differences in population-specific MLSPs.