RV SONNE Fahrtbericht/Cruise Report SO225, Manihiki II Leg 2, The Manihiki Plateau - Origin, structure and effects of oceanic plateaus and Pleistocene dynamic of the West Pacific warm water pool ; 19.11.2012 - 06.01.2013, Suva/Fiji - Auckland/New Zealand

Abstract

R/V SONNE cruises SO-224 and SO-225 are part of the cooperative project MANIHIKI II between GEOMAR Helmholtz Centre for Ocean Research Kiel and the Alfred Wegener Institute Helmholtz Centre 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. SO-225 focused on stratigraphically controlled sampling of the igneous successions of the Manihiki Plateau. This has been accomplished by using the remotely operated vehicle ROV Kiel 6000 and chain bag dredges. Coring of deep sea sediments and sampling of the overlying water column has been added to the program. SO-225 and subsequent shore-based research in the home institutes mainly address (1) the temporal, spatial, and compositional evolution of the igneous basement of Manihiki Plateau, (2) the environmental impact of the large volcanic eruptions, which formed the Manihiki Plateau, (3) the Plio-Pleistocene dynamics and evolution of the West Pacific Warm Pool during the last ~3 million years, and (4) the potential oceanographic interaction between the equatorial Pacific and the Southern Ocean (“ocean tunnel hypothesis”) and its climatic responses. The integration of scientific results from SO-224 and SO-225 with existing data from the West Pacific large igneous provinces Manihiki, Hikurangi, and Ontong Java 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. R/V SONNE cruise SO-225 started in Suva/Fiji on November 21st, 2012, and ended in Auckland/New Zealand on Januar 5th, 2013. Complementing 2,940 nm multi-beam mapping and 2,250 nm sediment echo-sounding, a total of 62 deployments of various devices have been carried out during SO-225. Ten of 11 multi corers yielded sediment samples, 16 piston corer and 3 gravity corer deployments recovered altogether 131.6 m sediment cores. The sampling of the water column by CTD and multi net was successful. Foraminiferal sand and ooze dominate among the sediment samples, some cores also contained sandy clayey silt rich in foraminifers and nanno ooze. The sediment cores cover a more than 1,100 km core transect extending from the ocean floor to the north of the Manihiki Plateau to the southern foothills of the High Plateau. Preliminary studies on board showed that the SO-225 sediment sampling yielded excellent paleoceanographic archives which can be correlated along the entire core transect and dated back to Pliocene. Further preliminary results include that past climate changes significantly affected the West Pacific Warm Pool. The sediment samples also will allow to reconstruct the Plio/Pleistocene variability of equatorial currents and the Antarctic intermediate water. Four ROV dives yielded 32 rock samples from two profiles across the slopes in the northern and central part of the Manihiki Plateau (North Plateau and Danger Island Troughs). Stratigraphically controlled sampling along c. 3 km long profile reaching from 4,600 m up to 3,260 m water depth across the flank of the south-eastern foothills of the North Plateau was particularly successful. Due to a series of unfortunate circumstances beyond our control, further ROV sampling on SO-225 had to be cancelled. Instead we decided to run dredges to considerably broaden the range of samples from the Manihiki Plateau basement by dredging. Twenty-three dredge hauls have been conducted in an average water depth of 4,380 m. Of these, 20 delivered magmatic rocks, 12 volcaniclastics, 8 sedimentary rocks, and 13 Mn-Fe-Oxide crusts. Notably, some of the dredged rocks show spinifex textures indicating unusual high eruption temperatures and several dredges contained fresh volcanic glass. The recovery of fresh glass from a presumably c. 120 million years old flood basalt province is a great achievement which will enable detailed petrological and geochemical studies of the plateau forming melts. Finally, mapping of submarine volcano Monowai en route on the transit to Auckland SO-225 should contribute to a time series of maps which continuously document the evolution of the volcano. During profiling, however, a sudden and significant increase in volcanic activity hindered us in mapping the top area of Monowai.