ALBERT

Description: The SO-84 cruise from Las Palmas to Cape Town studied the underwater volcanism associated with the St Helena hotspot. Wide-spaced grid mapping of a region south and west of St Helena island identified three previously unknown hotspot volcanoes (which we named Josephine 16°27'S-9°W, Jade 16°13'S-7°46'W and Benjamin 16°12'S-8°31'W) and several older, probably near-ridge-generated seamounts. The newly discovered hotspot seamounts, and the previously-known seamounts of Bagration, Bonaparte and Kutuzov were mapped and sampled. Onboard geochemical studies confirm that they all show trace-element (Rb, Nb, Y, Zr, Sr) enriched, hotspot magma-type compositions. Morphological studies and the state of the samples collected from the seamounts (all have at least 1 mm-thick Mn crusts) suggest that none of the volcanoes is presently active, and that the St Helena hotspot is probably extinct at the present time. Josephine appears to be the youngest volcano, and one dredge here yielded fossil hydrothermal material (Fe-hydroxides). To test the hypothesis that the extinction of the hotspot is due to its magmas being channelled to the Mid-Atlantic Ridge, several dredges were taken on the ridge opposite St Helena. Furthermore, in the proposed influence zone of the St Helena plume head, Grattan seamount (9°44'S-12°48'W) was also sampled to examine whether its composition has been affected by the St Helena plume. During the transit from Las Palmas to St Helena, several sediment cores were taken in 3000 m water depth close to the ridge axis for palaeoclimatological work.

Description: Die an Bord von FS METEOR durchgeführten sedimentphysikalischen Analysen des M 16/1 Kernmaterials aus verschiedenen Arealen des Guinea-, Angola-und Brasil-Beckens umfassen im einzelnen folgende Arbeiten: -Messungen der Kompressionswellengeschwindigkeit, -Messungen der elektrischen Leitfahigkeit, -Messungen der magnetischen Suszeptibilitat, -Beprobungen für palao-und gesteinsmagnetische Untersuchungen. Erstmalig wurde auf diesem Fahrtabschnitt eine Methode zur Messung der elektrischen Leitfahigkeit getestet, mit der Zielsetzung ein schnelles und effizientes Verfahren zur Bestimmung von Porositats-und Dichteprofilen der Sedimentkerne zu entwickeln. Abbildung 30 zeigt das Blockschaltbild des MeBaufbaus. Zur Messung an den Halbschalen der geöffneten Kerne in Abstanden von in der Regel 5 cm wurde eine Wenner-Anordnung verwendet. AIs Elektroden dienen vier Platindrähte (ø 0,6 mm), die im Abstand von 4 mm in einen Kunststoffstab (16 x 4 x 100 mm) eingegossen sind; er ist zur besseren Ankopplung im unteren, ins Sediment eingefiihrten Teil auf einen etwa dreieckigen Querschnitt abgeschrägt. Der Strom wird über die beiden äußeren Elektroden eingespeist. AIs Stromquelle dienen ein Funktionsgenerator und ein Stromkonstanter, die einen Rechteck-Wechselstrom von 330 Hz und 400 µA erzeugen. Über die beiden inneren Elektroden wird der Spannungsabfall im Sediment bestimmt. Die wesentlichen Gerätekomponenten sind dabei ein Differentialverstärker, ein phasenempfindlicher Detektor und ein Voltmeter.

Description: Während des Fahrtabschnittes M 16/2 wurden an Bord von FS METEOR folgende sedimentphysikalische Arbeiten am Kernmaterial durchgeführt: - Messungen der Kompressionswellengeschwindigkeit, - Messungen der elektrischen Leitfähigkeit, - Messungen der magnetischen Suszeptibilität, - Beprobungen für paläo- und gesteinsmagnetische Untersuchungen

Description: Multibeam bathymetry raw data using the ship's own Atlas Hydrographic Hydrosweep DS multibeam echo sounder was not continuously recorded during RV METEOR cruise M16/1. Data was recorded on 25 days between 1991-03-30 and 1991-04-24. This dataset contains a survey in the South Atlantic Ocean, also covering data around St. Helena. The approximate average depth of the entire dataset is around 4500m. The data are archived at the Federal Maritime and Hydrographic Agency of Germany (Bundesamt für Seeschifffahrt und Hydrographie, BSH) and provided to PANGAEA database for data curation and publication. No ancillary sound velocity profiles (SVP) files from the cruise are archived at the BSH, thus no SVP files are added to this dataset. Data analysis of the multibeam raw data could not reveal whether the SVP has been changed during the survey. This publication is conducted within the efforts of the German Marine Research Alliance in the core area 'Data management and Digitalization' (Deutsche Allianz Meeresforschung, DAM). Data are unprocessed and therefore contains incorrect depth measurements (artifacts) without further processing. Note that refraction errors can be expected due to the lack of proper SVP. Overall, it appears that the data quality is rather moderate since the gridded hillshade data showed areas where the data coverage is occasionally interrupted. Note that the end date is wrong for file a031.dux (also indicated in the parameter "comment"). All files have been renamed from the suffix *.0 (stored at BSH) to *.dux. Data can be processed e.g. with the open source software package MB-System (Caress, D. W., and D. N. Chayes, MB-System: Mapping the Seafloor, http://www.mbari.org/products/research-software/mb-system/, 2022).