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Martin Klug

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The warehouse of the past

Fig. 1: Stacked sediment cores in Bremen Core repository. 1.5m long sediment cores are stored at 4°C in plastic tubes to protect against mechanical damage and dessication. Foto M. Klug
Do you know where marine sediment cores from the International Ocean Discovery Program (IODP) are stored? Partly, they are in Bremen, Germany in a huge reefer hall.

Here you will find cores from the Southern to the Northern Atlantic Ocean, from the Mediterranean, Black, and the Baltic Sea, and the Polar Ocean. It is the coring location which defines where cores from that program are stored and who takes care of them. In total, there are three partners who share the stewardship for the enormous outcome from all ship expeditions in that program: The Bremen Core repository in Germany, the Gulf Coast Repository i Texas, USA and Kochi Core Center in Japan.

The latter stores sediment cores from the western Pacific Ocean and the Indian Ocean, whereas cores from the eastern Pacific and the Antarctic Ocean, the Caribbean Sea and Gulf of Mexico are stored in the USA.

So it is about a third of all IODP cores which are available in Bremen. They are stored in an impressive cooling hall of about 1000m2 at 4° Celsius (Fig. 1).

90 different cruises

The cooling facility was opened in 1994 and house more than 150.000 m sediment cores from about 90 different scientific cruises. And there is room for more. About 200 scientists from all over the world visit the Bremen Core repository each year for core investigations, for sub-sampling or for core logging in dedicated laboratories. During the 23 years after opening of the repository more the 4.300 sample requests have been managed – this makes up to 950.000 single samples explains Dr. Holger Kuhlmann, who is superintendent of the core repository and researcher at MARUM in Bremen. He further tells that the oldest sediment core in Bremen is from 1968 – due to the policy: No core will be discarded. It is not only the tremendous value these core represent which makes them keeping it is also that with new analyses techniques more information can be obtained.

For example, the undersigned Martin Klug from NGU in Trondheim, works as guest scientist with cores from 1993 taken from the Yermak Plateau, NW Svalbard. “In 1993 it has been impossible to log these cores with today’s XRF core logging methods (Fig. 2). Now, we are able to scan these cores with high resolution to get an elemental composition of more than 25 elements in a reasonably short time.

Fig. 2: XRF core logging facilities at MARUM in Bremen, Germany. Foto M. Klug

Of course, the time, almost 24 years since coring, has left it’s imprint on the archive halves. The sediment is partly dried out, cracks and sediment imperfections occur (Fig. 3). But with some delicate sediment surface preparations, we are able to produce an unique dataset. In total we will end up with about 600.000 data points from total 120m sediment core – only from XRF logging. Combined with existing data like magnetic susceptibility, gamma-attenuated density, chemical measurements, microfossil studies and paleaomagnetic investigations we have a solid basis for a multidisciplinary study of paleoclimatic and palaeoenvironmental changes covering the last 2.000.000 years in that area. But this requires first a profound data management to merge all datasets.

Fig. 3: Core image of ODP borehole section 151-912A-7H-7-A (upper 30 cm) with cleaned sediment surface prior to XRF scanning. Multiple cracks are due to desiccation or release of methane gas after core recovery. Foto M. Klug

With this multidisciplinary approach we are trying to identify past episodes of methane leakage at the sea floor, says Jochen Knies, project leader of NFR Petromaks2 “NORCRUST – Norwegian Margin Fluid Systems and Methane-Derived Carbonate Crusts”. On Yermak Plateau, both gas hydrate occurrences and active methane seepage have previously been inferred from geophysical and geological data. The cores from borehole ODP Site 912 we have investigated over the past 2 years are crucial to find the exact age of these past methane emission events.

The data will help to improve the chronostratigraphic framework of the sediments and to find anomalies where high amounts of methane has ascended to the seafloor during the Quaternary epoch.