Plattform Platform	Reise-Nr. Cruise-No.	Zeitraum Period	Projekt Project	Arbeitsgebiet Working area
Poseidon	POS436	06.07.2012 - 31.07.2012		Kolbeinsey Ridge North Atlantic Ocean

Fahrtleiter Chief Scientist	Institut Institute	Auslaufhafen Port of departure	Einlaufhafen Port of return	Stationskarte Station map	Schiffsroute Trackchart
Devey Collin W.	Helmholtz Centre for Ocean Research Kiel (GEOMAR)	Kiel	Akureyri

Ziel der Reise / Objectives of Cruise:

Although the magmas erupting at the global mid-ocean ridges are almost always tholeiitic, implying a globally common source mineralogy and melting regime, they show large variations in their trace element and isotopic compositions, presumably reflecting a fundamental heterogeneity of the Earth??s convecting upper mantle. Whilst some of this heterogeneity may be related to the interaction with nearby hotspots, large areas of the spreading axis are enriched in trace elements but show no nearby seamount chains. The enrichment on such ridges has been proposed to be the result of the presence of either localised blobs of enriched mantle or sublithospheric feeding of material over long distances from more distant hotspots - determining which of these is the correct cause can provide us with important knowledge about the heterogeneity of the Earth and global chemical cycles. Determining the mineralogy and chemical nature of a mantle source is notoriously difficult, however, because of the trace element fractionation which occurs during melting. Only isotopic disequilibrium studies present the chance to determine true source characteristics, but these studies depend wholly on the availability of young (and, if possible, known age) samples. For very young submarine volcanic samples, the best time information is usually given by additional geological information from the sampling locations, allowing a relative stratigraphy and age scale to be determined. One such shallow, enriched ridge segment whose geological and geochemical surroundings are particularly well characterized is Eggvin Bank on the northern Kolbeinsey Ridge. As part of a project involving researchers from GEOMAR, WHOI and Bryn Mawr College we used ships multibeam surveyed followed up by deep-diving AUV mapping to attempt to determine the location of the youngest volcanism on this ridge. A combination of holocene glaciation and high present-day sedimentation rates means that this ridge segment is highly suitable for distinguishing young volcanics, especially using the AUV side-scan sonar to identify sedimented and un-sedimented areas. The cruise provided a clear proof-of-principle for this type of stratigraphic work using an AUV and yielded some of the best-characterized mid-ocean ridge samples available anywhere on Earth. In the course of surveying and sampling work, the ridge axis was also thoroughly prospected for hydrothermal activity both by the AUV and by the use of MAPR attached to the sampling cable.

Messungen / Measurements