Modelling and forecasting long-term dynamics of Western Baltic macrobenthic fauna in relation to climate signals and environmental change

Long-term macrobenthos data from Kiel Bight in the Western Baltic collected between 1968 and 2000 have been correlated with the winter NAO index (North Atlantic Oscillation Index) and other environmental data such as temperature, salinity and oxygen content in the bottom water in order to detect systematic patterns related to so far unexplained abiotic signals in the dynamics of zoobenthic species assemblages. The benthos data come from a cluster of five stations (Süderfahrt/ Millionenviertel) in Kiel Bay. Our investigations concentrated on the macrobenthic dynamics with a focus on the number of species m^− 2 (species richness). Using logarithms and the time series analysis approach of Box/Jenkins (ARIMA modelling, transfer function modelling) it was shown that species richness was strongly influenced by the winter NAO (adjusted for a linear time trend within the 1968-2000 period) and salinity (with a shift/lag of four years). Bootstrapping experiments (i.e. sampling from the error process) and analysis of prediction power (by means of the one- or more-years leaving-out method) showed that the parameter estimates behaved in a stable way, leading to a relatively robust model.     

Constraining the origin and evolution of confined turbidite systems: southern Cretan margin,Eastern Mediterranean Sea (34°30–36°N)

Bathymetric, 9.5-kHz long-range sidescan sonar (OKEAN), seismic reflection and sediment-core data are used in the analysis of two tectonic troughs south of Crete, Eastern Mediterranean Sea. Here, up to 1.2 s two-way travel time (TWTT) of strata have accumulated since the Middle Miocene in association with extension in the South Aegean region. The study area comprises >100-km- long by >25-km-wide basins filled by sediments subdivided into two seismic units: (1) an upper Unit 1 deposited in sub-basins which follow the present-day configuration of the southern Cretan margin; (2) a basal Unit 2, more than 500 ms (TWTT) thick, accumulated in deeper half-graben/grabens distinct from the present-day depocentres. Both units overlap a locally stratified Unit 3 comprising the pre-Neogene core complex of Crete and Gavdos. In this work, the interpreted seismic units are correlated with the onshore stratigraphy, demonstrating that denudation processes occurring on Crete and Gavdos in response to major tectonic events have been responsible for high sedimentation rates along the proximal southern Cretan margin. Consequently, topographically confined sedimentary units have been deposited south of Crete in the last 12 Ma, including turbidites and other mass-flow deposits fed by evolving transverse and axial channel systems. Surface processes controlling facies distribution include the direct inflow of sediment from alluvial-fan systems and incising mountain rivers onto the Cretan slope, where significant sediment instability processes occur at present. In this setting, seismic profiles reveal eight different types of stratigraphic contacts on basin-margin highs, and basinal areas show evidence of halokinesis and/or fluid escape. The acquired data also show that significant changes to the margin’s configuration occurred in association with the post-Alpine tectonic and eustatic episodes affecting the Eastern Mediterranean.     

First results from the North Iceland experiment

Between June 2004 and September 2004 a temporary seismic network was installed on the northern insular shelf of Iceland and onshore in north Iceland. The seismic setup aimed at resolving the subsurface structure and, thus, the geodynamical transition from Icelandic crust to typical oceanic crust along Kolbeinsey Ridge. The experiment recorded about 1,000 earthquakes. The region encloses the Tjörnes Fracture Zone containing the Husavik–Flatey strike-slip fault and the extensional seismic Grimsey Lineament. Most of the seismicity occurs in swarms offshore. Preliminary results reveal typical mid-ocean crust north of Grimsey and a heterogeneous structure with major velocity anomalies along the seismic lineaments and north–south trending subsurface features. Complementary bathymetric mapping highlight numerous extrusion features along the Grimsey Lineament and Kolbeinsey Ridge. The seismic dataset promises to deliver new insights into the tectonic framework for earthquakes in an extensional transform zone along the global mid-ocean ridge system.     

Geochemical characterization of the potential trace metal mobility in cohesive sediments

The Acid-Producing Potential (APP) and the Acid-Consuming Capacity (ACC) are introduced as basic parameters for long-term pollution assessment of mud disposal. They can be obtained by a four-step sequential leaching technique. The concentration of Ca extracted by the first Na-acetate step permits calculating the ACC. Both the Fe- and S-fractions deliberated by subsequent leaching steps are used to calculate the APP. When the APP of a sample is substacted from its ACC, a negative value indicates a potential increase of the bioavailability of the toxic metal load upon disposal of this mud in oxic environments.     

Mechanisms controlling the temporal variation of the sea ice edge in the Southern Ocean

This paper examines the mechanism controlling the short time-scale variation of sea ice cover over the Southern Ocean. Sea ice concentration and ice velocity datasets derived from images of the Defense Meteorological Satellite Program (DMSP) Special Sensor Microwave Imager (SSM/I) are employed to reveal this mechanism. The contribution of both dynamic and thermodynamic processes to the change in ice edge location is examined by comparing the meridional velocity of ice edge displacement and sea ice drift. In the winter expansion phase, the thermodynamic process of new ice production off the ice edge plays an important role in daily advances of ice cover, whereas daily retreats are mostly due to southward ice drift. On the other hand, both advance and retreat of ice edges in the spring contraction phase are mostly caused by the dynamic process of the ice drift. Based on the above mechanism and the linear relation between the degree of ice production at the ice edge and northward wind speed, the seasonal advance of ice cover can be roughly reproduced using the meridional velocity of ice drift at the ice edge.     

The Levant Slumps and the Phoenician Structures: collapse features along the continental margin of the southeastern Mediterranean Sea

Two distinct series of slumps deform the upper part of the sedimentary sequence along the continental margin of the Levant. One series is found along the base of the continental slope, where it overlies the disrupted eastern edge of the Messinian evaporites. The second series of slumps transects the continental margin from the shelf break to the Levant Basin. It seemed that the two series were triggered by two unrelated, though contemporaneous, processes. The shore-parallel slumps were initiated by basinwards flow of the Messinian salt, that carried along the overlying Plio-Quaternary sediments. Seawater that percolated along the detachment faults dissolved the underlying salt to form distinctly disrupted structures. The slope-normal slumps are located on top of large canyons that cut into the pre-Messinian sedimentary rocks. A layer of salt is found in the canyons, and the Plio-Quaternary sediments were deposited on that layer. The slumps are bounded by large, NW-trending faults where post-Messinian faulted offset was measured. We presume that the flow of the salt in the canyons also drives the slope-normal slumps. Thus thin-skinned halokynetic processes generated the composite post-Tortonian structural patterns of the Levant margin. The Phoenician Structures are a prime example of the collapse of a distal continental margin due to the dissolution of a massive salt layer.     

Sub-lethal effects of metal exposure: physiological and behavioural responses of the estuarine bivalve Macoma balthica

Variation in glycogen concentration, condition index (CI) and filtration activity were measured in the bivalve Macoma balthica buried in sediment and experimentally exposed to cadmium (Cd). The stress due to elevated but sub-lethal concentrations (300 ppb Cd) affected the overall fitness of the organism as all parameters monitored responded significantly. Lower concentrations tested (10, 30 and 100 ppb) only induced a significant decrease in filtration activity, which may play a protective role, enabling the organism to slow down its metabolic activity and preserving the integrity of its reserves (reflected by stable CI and glycogen levels). Hence, the various endpoints selected show different thresholds. Our results also demonstrate that under high exposure, small individuals loose proportionally more glycogen per unit of weight than larger ones, thus confirming the higher sensitivity of small individuals to metal contamination. Furthermore, exposure to intermediate concentration (30 ppb) seems to be beneficial to the small individuals as indicated by their high CI values compared to the control. These results showed thus that non-sigmoidal concentration-response relationship and sizes of individuals should be considered in monitoring programmes and risk assessment.     

Mixed layer variability in Northern Arabian Sea as detected by an Argo float

Seasonal evolution of surface mixed layer in the Northern Arabian Sea (NAS) between 17° N–20.5° N and 59° E-69° E was observed by using Argo float daily data for about 9 months, from April 2002 through December 2002. Results showed that during April - May mixed layer shoaled due to light winds, clear sky and intense solar insolation. Sea surface temperature (SST) rose by 2.3 °C and ocean gained an average of 99.8 Wm⁻². Mixed layer reached maximum depth of about 71 m during June - September owing to strong winds and cloudy skies. Ocean gained abnormally low ∼18 Wm⁻² and SST dropped by 3.4 °C. During the inter monsoon period, October, mixed layer shoaled and maintained a depth of 20 to 30 m. November - December was accompanied by moderate winds, dropping of SST by 1.5 °C and ocean lost an average of 52.5 Wm⁻². Mixed layer deepened gradually reaching a maximum of 62 m in December. Analysis of surface fluxes and winds suggested that winds and fluxes are the dominating factors causing deepening of mixed layer during summer and winter monsoon periods respectively. Relatively high correlation between MLD, net heat flux and wind speed revealed that short term variability of MLD coincided well with short term variability of surface forcing.     

Spatial and Temporal Variations of Sound Speed at the PN Section

Gridded sound speed data were calculated using Del Grosso's formulation from the temperature and salinity data at the PN section in the East China Sea covering 92 cruises between February 1978 and October 2000. The vertical gradients of sound speed are mainly related to the seasonal variations, and the strong horizontal gradients are mainly related to the Kuroshio and the upwelling. The standard deviations show that great variations of sound speed exist in the upper layer and in the slope zone. Empirical orthogonal function analysis shows that contributions of surface heating and the Kuroshio to sound speed variance are almost equivalent. This revised version was published online in July 2006 with corrections to the Cover Date.