The <Emphasis Type="Italic">M</Emphasis><Subscript>w</Subscript> 3.1–4.7 earthquakes in the southern Baltic Sea and adjacent areas in 2000, 2001 and 2004

The area south and east of the Baltic Sea has very minor seismic activity. However, occasional events occur as illustrated by four events in recent years, which are analysed in this study: near Wittenburg, Germany, on May 19, 2000, M _w = 3.1, near Rostock, Germany, on July 21, 2001, M _w = 3.4 and in the Kaliningrad area, Russia, two events on September 21, 2004 with M _w = 4.6 and 4.7. Locations, magnitudes (M _L and M _w) and focal mechanisms were determined for the two events in Germany. Synthetic modeling resulted in a well-confined focal depth for the Kaliningrad events. The inversion of macroseismic observations provided simultaneous solutions of the location, focal depth and epicentral intensity. The maximum horizontal compressive stress orientations obtained from focal mechanism solutions, approximately N–S for the two German events and NNW–SSE for the Kaliningrad events, show a good agreement with the regionally oriented crustal stress field.     

Lofar

H01 A first glance at LOFAR: Experience with the Initial Test Station H02 The Square Kilometer Array (SKA) – Status and Prospects H03 LOFAR calibration: confrontation with real WSRT data H04 Simulations of magnetic fields in the cosmos H05 RM structure in the polarized synchrotron emission from our Galaxy and the Perseus cluster of Galaxies H06 Mapping the Reionization Era through the 21 cm Emission Line H07 Spiral galaxies seen with LOFAR H08 Software Infrastructure for Distributed Data Processing H09 The Low Frequency Array (LOFAR) – Status and Prospects H10 Coincident cosmic ray measurements with LOPES and KASCADE‐Grande H11 Radio relics in a cosmological cluster merger simulation H12 Detection of radio pulses from cosmic ray air showers with LOPES H13 Geosynchrotron radio emission from extensive air showers H14 Imaging capabilities of future radio telescopes H15 Digital signal processing system of Multi‐Beam Meter Wavelengths Array. H16 The Multi‐Beam Meter Wavelengths Array H17 Monitoring of the Solar Activity by LOFAR H18 Calibration of LOPES30 H19 An Outreach Project for LOFAR and Cosmic Ray Detection H20 Galactic tomography based on observations with LOFAR and Effelsberg H21 150 MHz observations with the Westerbork and GMRT radio telescopes of Abell 2256 and the Bootes field: Ultra‐steep spectrum radio sources as probes of cluster and galaxy evolution H22 Experience of simultaneous observations with two independent multi‐beams of the Large Phased Array H23 GRID Computing at Forschungszentrum Karlsruhe suitable for LOFAR     

Growth,dynamics and deglaciation of the last British–Irish ice sheet: the deep-sea ice-rafted detritus record

The evolution and dynamics of the last British–Irish Ice Sheet (BIIS) have hitherto largely been reconstructed from onshore and shallow marine glacial geological and geomorphological data. This reconstruction has been problematic because these sequences and data are spatially and temporally incomplete and fragmentary. In order to enhance BIIS reconstruction, we present a compilation of new and previously published ice-rafted detritus (IRD) flux and concentration data from high-resolution sediment cores recovered from the NE Atlantic deep-sea continental slope adjacent to the last BIIS. These cores are situated adjacent to the full latitudinal extent of the last BIIS and cover Marine Isotope Stages (MIS) 2 and 3. Age models are based on radiocarbon dating and graphical tuning of abundances of the polar planktonic foraminifera Neogloboquadrina pachyderma sinistral (% Nps) to the Greenland GISP2 ice core record. Multiple IRD fingerprinting techniques indicate that, at the selected locations, most IRD are sourced from adjacent BIIS ice streams except in the centre of Heinrich (H) layers in which IRD shows a prominent Laurentide Ice Sheet provenance. IRD flux data are interpreted with reference to a conceptual model explaining the relations between flux, North Atlantic hydrography and ice dynamics. Both positive and rapid negative mass balance can cause increases, and prominent peaks, in IRD flux. First-order interpretation of the IRD record indicates the timing of the presence of the BIIS with an actively calving marine margin. The records show a coherent latitudinal, but partly phased, signal during MIS 3 and 2. Published data indicate that the last BIIS initiated during the MIS 5/4 cooling transition; renewed growth just before H5 (46 ka) was succeeded by very strong millennial-scale variability apparently corresponding with Dansgaard–Oeschger (DO) cycles closely coupled to millennial-scale climate variability in the North Atlantic region involving latitudinal migration of the North Atlantic Polar Front. This indicates that the previously defined “precursor events” are not uniquely associated with H events but are part of the millennial-scale variability. Major growth of the ice sheet occurred after 29 ka with the Barra Ice Stream attaining a shelf-edge position and generating turbiditic flows on the Barra–Donegal Fan at ～27 ka. The ice sheet reached its maximum extent at H2 (24 ka), earlier than interpreted in previous studies. Rapid retreat, initially characterised by peak IRD flux, during Greenland Interstadial 2 (23 ka) was followed by readvance between 22 and 16 ka. Readvance during H1 was only characterised by BIIS ice streams draining central dome(s) of the ice sheet, and was followed by rapid deglaciation and ice exhaustion. The evidence for a calving margin and IRD supply from the BIIS during Greenland Stadial 1 (Younger Dryas event) is equivocal. The timing of the initiation, maximum extent, deglacial and readvance phases of the BIIS interpreted from the IRD flux record is strongly supported by recent independent data from both the Irish Sea and North Sea sectors of the ice sheet.     

Age assignment of a diatomaceous ooze deposited in the western Amundsen Sea Embayment after the Last Glacial Maximum

Reliable dating of glaciomarine sediments deposited on the Antarctic shelf since the Last Glacial Maximum (LGM) is challenging because of the rarity of calcareous (micro‐) fossils and the recycling of fossil organic matter. Consequently, radiocarbon (¹⁴C) ages of the acid‐insoluble organic fraction (AIO) of the sediments bear uncertainties that are difficult to quantify. Here we present the results of three different methods to date a sedimentary unit consisting of diatomaceous ooze and diatomaceous mud that was deposited following the last deglaciation at five core sites on the inner shelf in the western Amundsen Sea (West Antarctica). In three cores conventional ¹⁴C dating of the AIO in bulk samples yielded age reversals down‐core, but at all sites the AIO ¹⁴C ages obtained from diatomaceous ooze within the diatom‐rich unit yielded similar uncorrected ¹⁴C ages between 13 517 ± 56 and 11 543 ± 47 years before present (a BP). Correction of these ages by subtracting the core‐top ages, which probably reflect present‐day deposition (as indicated by ²¹⁰Pb dating of the sediment surface at one core site), yielded ages between ca. 10 500 and 8400 cal. a BP. Correction of the AIO ages of the diatomaceous ooze by only subtracting the marine reservoir effect (MRE) of 1300 a indicated deposition of the diatom‐rich sediments between 14 100 and 11 900 cal. a BP. Most of these ages are consistent with age constraints between 13.0 and 8.0 ka for the diatom‐rich unit, which we obtained by correlating the relative palaeomagnetic intensity (RPI) records of three of the sediment cores with global and regional reference curves. As a third dating technique we applied conventional radiocarbon dating of the AIO included in acid‐cleaned diatom hard parts extracted from the diatomaceous ooze. This method yielded uncorrected ¹⁴C ages of only 5111 ± 38 and 5106 ± 38 a BP, respectively. We reject these young ages, because they are likely to be overprinted by the adsorption of modern atmospheric carbon dioxide onto the surfaces of the diatom hard parts prior to sample graphitisation and combustion for ¹⁴C dating. The deposition of the diatom‐rich unit in the western Amundsen Sea suggests deglaciation of the inner shelf before ca. 13 ka BP. The deposition of diatomaceous oozes elsewhere on the Antarctic shelf around the same time, however, seems to be coincidental rather than directly related. Copyright © 2009 John Wiley & Sons, Ltd.     

Controls of 234Th removal from the oligotrophic ocean by polyuronic acids and modification by microbial activity

To gain new insights into the variability of particulate organic carbon (POC) fluxes and to better understand the factors controlling the POC/²³⁴Th ratios in suspended and sinking particulate matter, we investigated the relationships between POC/²³⁴Th ratios and biochemical composition (uronic acids, URA; total carbohydrates, TCHO; acid polysaccharides, APS; and POC) of suspended and sinking matter from the Gulf of Mexico in 2005 and 2006. Our data show that URA/POC in sediment traps (STs), APS/POC in the suspended particles, and turnover times of particulate ²³⁴Th in the water column and those of bacteria in STs inside eddies usually increased with depth, whereas particulate POC/²³⁴Th (10–50 μm) and the sediment-trap parameters (POC flux, POC/²³⁴Th ratio, bacterial biomass, and bacterial production) decreased with depth. However, this trend was not the case for most biological parameters (e.g., phytoplankton and bacterial biomass) or for the other parameters at the edges of eddies or at coastal-upwelling sites.In general, the following relationships were observed: 1) ²³⁴Th/POC ratios in STs were correlated with APS flux, and these ratios in the 10–50 μm suspended particles also correlated with URA/POC ratios; 2) neither URA fluxes nor URA/POC ratios were significantly related to bacterial biomass; 3) the sum of two uronic acids (G2, glucuronic, and galacturonic acid, which composed most of the URA pool) was positively related to bacterial biomass; and 4) the POC/²³⁴Th ratios in intermediate-sized particles (10–50 μm) were close to those in sinking particles but much lower than those in > 50 μm particles. The results indicate that acid polysaccharides, though a minor fraction (~ 1%) of the organic carbon, act more likely as proxy compound classes that might contain the more refractory ²³⁴Th-binding biopolymer, rather than acting as the original ²³⁴Th “scavenger” compound. Moreover, these acid polysaccharides, which might first be produced by phytoplankton and then modified by bacteria, also influence the on-and-off “piggy-back” processes of organic matter and ²³⁴Th, thus causing additional variability of the POC/²³⁴Th in particles of different sizes.