SO225

MANIHIKI II

Wochenbericht Nr. 1

(19.11. – 25.11.2012

Werner, Reinhard

English

SO225

MANIHIKI II

Wochenbericht Nr. 5

(17.12. – 23.12.2012

OceanRep

  SO225 MANIHIKI II Weekly Report No. 5 (17.12. – 23.12.2012)  R/V SONNE  11°03,1´S / 161°31,9´W  Sampling the flanks of the Danger Island Troughs by dredging was the focus of our work during the 5th week of R/V SONNE expedition SO225 to the Manihiki Plateau. The Danger Islands Troughs are elongated, deep basins, which represent large fault systems bifurcating the plateau into the Western Plateaus, to the west, and the High Plateau, to the east. Their flanks as well as the northern margin of the High Plateau expose the interior of the Manihiki Plateau which is not accessible elsewhere. First, however, we finished sampling along the northern margin of the High Plateau. Two dredge hauls at a ridge-like feature at the foot of the northern flank and at its base recovered partly olivine bearing sheet and pillow lavas as well as a large fragment of a pillow breccia. Afterwards R/V Sonne sailed to the northern end of the Danger Island Troughs. On Tuesday, December 18th, the deepest dredge haul of this cruise has been carried out at a small ridge located in the center of the northernmost basin in more than 5.800 m water depth. The dredge returned altered lava fragments and lithified sediments. Two dredges conducted in an adjacent trough yielded similar results, confirming our earlier impression from cruise SO193 in 2007, that lithified sediments dominate the upper rock layers in the entire northern part of the Danger Island Troughs. Therefore we decided to continue further south, where a SO193 dredge haul yielded particularly interesting, c. 120 m.y. old rocks of the plateau basement and where a seismic profile conducted on the previous cruise SO224 showed exposed plateau basement.   The geological lab full of rocks....   Cut sample of an only slightly altered lava.  Here, we conducted 11 dredge hauls in 4.800 to 3.000 m water depth between the early morning of Wednesday an Friday evening. Here, a structure of most likely tectonic origin, characterized by several terraces along its southwestern slope, has been studied particularly intense, through systematic sampling of the cliffs below each terrace. The dredges returned various lavas, a broad variety of volcaniclastic rocks and also some intrusives. Some lava fragments appeared oxidizied, which may indicate eruptions under subaerial conditions. A special highlight, however, was the recovery of considerable amounts of fresh volcanic glass from the base of this feature. Volcanic glass forms by rapid cooling of lava for example when hot lava comes in contact with water. Such unaltered glasses is of particular interest to study the original composition of melts. Volcanic glass, however, is not stable and alters over the course of time; initially to palagonite and finally to clay. This process can significantly accelerate when glass is exposed to sea water. The recovery of fresh glass from a presumably c. 120 million years old flood basalt province is therefore something special and a great achievement which will enable detailed petrological and geochemical studies of the plateau forming melts. Some 15 nm further north, two dredge tracks not only recovered lava and sediments, but also metamorphically overprinted rocks (greenshists). Most notably is the spinifex-texture of the lava, named after a sharp Australian grass species that describes the needle-like growth of pyroxene and olvine crystals. The very beautiful spinifex-texture forms by rapid crystallization of very hot, mostly ultramafic melts, pointing to unusual high magma temperatures during the formation of Manihiki Plateau. Finally, we dredged samples from the western and eastern flanks of Danger Island Troughs, at the intersection with detailed seismic profiles of SO224. On the western slope, sheet and pillow lava dominate, partly also with spinifex-texture. The eastern slope mainly exhibited lithified sediments and manganese crusts. Complementing mapping of the ocean floor and sediment echo sounding, a total of 17 dredges have been carried out during the first five days of this week. Of these, 12 dredges recovered magmatic rocks, 7 volcaniclastic rocks, and 6 lithified sediments. At the very end of the week, the paleoceanography group started again, carrying out 2 coring stations on the High Plateau. Site selection was based on seismic profiles from SO224, which showed sediment deposits characterized by hundreds of meters in thickness. Unfortunately, sediment recovery was not as easy as thought, with many coring failures and loss of equipment probably due to the hard and lithified sediment even at very shallow core depths. After many attempts at extremely hot conditions on the working deck, the paleoceanographers were finally paid off with a high quality sediment record.    Merry Christmas from the SO225 scientists. The picture was taken in the geology laboratory of R/V SONNE, as it started raining just prior to the shooting. On December 21, we celebrated that earth did not tumble down as predicted by the Mayan calendar, together with the birthday of a colleague in the seismic laboratory. On Christmas Eve, the scientific program of SO225 will be continued with dredging and mapping at Suvorov Trough in the southern part of Manihiki Plateau. In the evening, we will celebrate Christmas jointly in the mess, and with a ceremonial lunch on the first Christmas day. All SO225 participants send cordial greeting from the SW Pacific: Merry Christmas to all of you.  Reinhard Werner 

5. Wochenbericht SO225

  SO225 MANIHIKI II Weekly Report No. 1 (19.11. – 25.11.2012)  R/V SONNE  10°13,6´S / 165°52,0´W  The starting point of R/V SONNE expedition SO-225 was the port of Suva on Viti Levu island (Fiji). After 48 hours of travel the first group of scientists, engineers, and technicians from Germany arrived safe but somewhat tiered in Suva in the late evening of Saturday the 19th of November. There, the unloading of nine containers with scientific equipment for SO-225 and the mobilization of the remotely operated vehicle ROV Kiel 6000 kept us busy during the following days. In the evening of November 19th, the remaining scientists arrived in Suva, finally completing the scientific party of the SO-225 expedition. In tropical heat and occasionally heavy rain showers we managed to finish all port related cruise preparations on time thanks to the excellent support from the SONNE crew. Approximately one hour after a test program of the ROV Kiel 6000 was successfully completed, RV SONNE left Suva and headed towards the Manihiki Plateau, located ~1.000 nm to the northeast of Fiji in the area of the northern Cook Islands.   Views of Suva/Fiji upon departure of R/V Sonne. RV Sonne cruises SO-224 and SO-225 are part of the cooperative project MANIHIKI II between GEOMAR and the Alfred Wegener Institute for Polar and Marine Research (AWI), funded by the German Ministry of Education and Research (BMBF). This multidisciplinary project continues previous research at the Manihiki Plateau conducted since 2007 (SO-193) on morphological, volcanological, geochemical, and geochronological studies and is now broadened by geophysical and paleoceanographic research foci. But why do we study the Manihiki Plateau located far away in the Pacific Ocean? The Manihiki Plateau is a approximately 120 Mill. years old submarine lava plateau, approximately equal in size to France. Besides the significantly larger Ontong Java Plateau and the somewhat smaller Hikurangi Plateau it is one of the three "Large Igneous Provinces" (LIPs) in the Southwest-Pacific. LIPs represent the largest volcanic events on Earth. Some scientists assume that these three LIPs formed synchronously at the same time. If this were the case almost one percent of the Earth´s surface would have been covered by lava within a few million years only. To date, however, very little is actually known about these huge magmatic events. It is, for example, still unclear, if the plateaus are the result of a single or multiple magmatic events, how long the volcanic activity lasted, what their causes and effects on the environment are, and how the Plateaus are internally structured. The Manihiki Plateau is predestinated to shed some light into these questions because SO-193 revealed up to 2,000 m thick lava sequences exposed along fault zones, allowing unique insights into the plateau´s interior. Its location at the southeastern margin of the West Pacific Warm Pool also defines the Manihiki Plateau as a key area for a better understanding of the Pacific Ocean paleoceanography and its effects on the global climate. On the preceding RV SONNE SO-224 expedition, scientists from the AWI conducted an extensive geophysical program. We are very grateful to our colleagues who have laid lots of data and information to our disposal which are a perfect base for the investigations scheduled on the SO-225 cruise. SO-225 focuses on the stratigraphically controlled sampling of the igneous successions of the Manihiki Plateau. This challenge will be accomplished by using the ROV Kiel 6000 that can operate down to 6,000 m water depth. Coring of deep sea sediments and sampling of the overlying water column will add to the program. The integration of scientific results from SO-224 and SO-225 with existing data from the Manihiki, Hikurangi, and Ontong Java Plateaus will contribute towards a better understanding of the origin and effects of volcanic mega events, the formation of large igneous provinces, and the paleoceanography and paleoclimate of the equatorial West Pacific. The four days of transit to the Manihiki Plateau were used by the scientists to accommodate on board, to unpack the equipment, and to setup the labs and the ROV Kiel 6000. In the evening of November 25th, we finally reached the southwestern margin of the Manihiki Plateau, which rises here about 1,000 m above the surrounding 5,000 m deep seafloor. Now we are close to our first sampling station, where we will core sediments and take water samples from tomorrow morning on. On the following day we will deploy the ROV Kiel 6000 for the first time on this cruise. We really look forward to start the sampling soon after the long-lasting and complex preparations. All cruise participants are doing well, enjoy the excellent food and the pleasant atmosphere on board, and send greetings to everyone at home. For all cruise participants Reinhard Werner   Links: SO-193: http://www.geomar.de/forschen/fb4/fb4-muhs/projekte/so193-manihiki-projekt/ SO-224: (http://www.awi.de/en/research/research_divisions/geosciences/geophysics/projects/ marine_geophysics_margin_basin_plateaux/manihiki_ii/) SO-225: http://www.geomar.de/forschen/expeditionen/detailansicht/exp/current/315731/  

1. Wochenbericht SO225

SO225

MANIHIKI II

Wochenbericht Nr. 7

(24.12.2012 – 30.12.2012

  SO225 MANIHIKI II Wochenbericht Nr. 6 (24.12. – 30.12.2012)  F.S. SONNE  21°33,9´S / 171°47,4´W  In dieser Woche wurden die Stationsarbeiten am Manihiki-Plateau mit mehreren Dredgezügen am Suvorov Trough, einer von NW nach SE durch das High Plateau verlaufenenden Störungszone, und einer letzten Kernstation im Süden des Manihiki-Plateaus abgeschlossen. Der Suvorov Trough ist eine ca. 8 - 12 km breite grabenartige Struktur mit einer Sohle in bis zu 4.500 m Wassertiefe und meist steilen, bis zu 1.000 m hohen Flanken. Der für diese Gegend ungewöhnliche russische Name dieser Störungszone kommt von einem nahe gelegenen gleichnamigen Atoll, dass im Jahre 1814 von der Mannschaft des russischen Schiffes „Suvorov“ entdeckt wurde. Von der vorherigen Reise SO193 wussten wir, dass an den Flanken des Suvorov Trough überwiegend verfestigte (lithifizierte) Sedimente anstehen. An der Westflanke einer quer zum Suvorov Trough verlaufenden, vermutlich tektonisch entstandenen Rückenstruktur fanden wir 2007 jedoch olivin-reiche mafische Gesteine, die für uns von besonders großem Interesse sind, da sie ursprüngliche Mantelschmelzen repräsentieren und somit Auskunft über die Tiefe und Art der Magmenquelle der Manihiki-Laven geben können. Daher war es das vorrangige Ziel der Dredgearbeiten am Suvorov Trough, ein möglichst weites Spektrum an Gesteinen von dieser Rückenstruktur zu erhalten.    Eine randvolle Dredge bildete den krönenden Abschluss der Hartgesteins-beprobung von SO225.  Typischer Foraminiferensand des Manihiki-Plateaus. Die meisten Foraminiferen hier sind planktonische Protozoa mit Kalkgehäusen, deren geochemische Analyse die genaue Rekonstruktion der Eigenschaften der Ozeane in der Vergan-genheit erlaubt (Größe der Gehäuse max. 0,5 mm).  Insgesamt haben wir während der Weihnachtstage dort 5 Dredgezüge durchgeführt. Diese erbrachten neben den unvermeidlichen lithifizierten Sedimenten eine große Vielfalt an Laven und Vulkaniklastika sowie - ebenso erstaunlicher- wie erfreulicherweise - wieder frisches vulkanisches Glas. Bemerkenswert ist, dass in jeder erfolgreichen Dredge andere Gesteine waren, obwohl alle Dredgezüge relativ nahe beieinander an der gleichen Struktur durchgeführt wurden. Dies stützt unsere Hypothese, dass dort starke tektonische Prozesse wirksam waren. Neben den Dredgezügen haben wir noch Kartierungslücken am Suvorov Trough geschlossen in der Hoffnung, weitere Strukturen zu finden, an denen eine Beprobung vielversprechend wäre. Fündig wurden wir aber leider nicht.     Nach der letzten Dredge am Suvorov Trough, die auch die letzte dieser Reise war, machte sich die Sonne am 26. Dezember gegen Mittag auf den Weg nach Südosten, um noch eine Kernstation am High Plateau durchzuführen. Diese Station war sehr wichtig, da sie den südlichsten Punkt des großen N-S-Kerntransektes über das Manihiki-Plateau bildete, das auf SO225 beprobt werden sollte. Daher hofften wir sehr, dass wir diesmal mehr Glück haben als bei den letzten beiden Kernstationen auf dem High Plateau. Allerdings sah es zu Anfang nicht so aus. Der Multicorer und das Schwerelot erbrachten zwar Sediment, aber die Eindringung der Geräte war relativ gering, was auf ähnlich schwierig zu beprobende Sedimente wie an den vorherigen Stationen schließen ließ. Dennoch machten die Paläozeanographen noch einen Versuch mit einem 15 m langem Kolbenlot - und hatten Erfolg! Ein mehr als 12 m langer Sedimentkern aus diesem bisher unbeprobten Gebiet bildete den krönenden Abschluss der Sedimentbeprobung.   Die Probenahmestationen von SO225 am Manihiki-Plateau (POZ/gelb = Kernstation, ROV/rot = Tauchroboter-Profil,  DR/rot = Dredgezug). Nach einer letzten CTD machten wir uns am Abend des 27. Dezember auf den fast 2.000 nm langen Weg zu unserem Endhafen Auckland, den wir aber noch einmal für eine Kartierung des Vulkans Monowai unterbrechen werden. Die ersten Tage dieses Transits wurden dazu genutzt, Proben aufzuarbeiten und Berichte zu schreiben, Arbeiten, die sich neben Packen und Saubermachen auch noch über die nächste Woche hinziehen werden. Und dann war da natürlich noch Weihnachten. Da im Gegensatz zu den Danger Island Troughs Teile des Suvorov Trough noch kartiert werden mussten, hatten wir auch etwas Zeit Weihnachten zu feiern. Heiligabend gab es Würstchen mit Kartoffelsalat und Glühwein in der Messe und danach sogar eine kleine Bescherung. Anschließend haben wir den Abend in der lauen Tropennacht an Deck ausklingen lassen. Am ersten Feiertag folgte mittags ein Festessen, bei dem sich unser Koch mit einem vorzüglichen Gänsebraten wieder einmal selbst übertroffen hat. Aber nach einer kurzen Mittagspause ging dann auch schon wieder die Dredge zu Wasser.  Alle Fahrtteilnehmer grüßen aus dem Südwest-Pazifik und wünschen allen zu Hause einen guten "Rutsch" ins Neue Jahr!  Reinhard Werner 

1. Wochenbericht SO225

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