The numerous steps of geochemical analyses

By the team of the Bremen Core Repository (U. Prange, U. Röhl and L. Schnieders)

The clocks in geochemistry tick a bit differently from those of the various other expertise groups in the expedition’s Science Party. This is because its analytical focus ranges from samples removed directly after a core is retrieved to samples taken after the cores have been split.

The former includes pore water and gases, for example. The latter mostly consist of solid samples such as sediment. Most of these sample types for IODP standard geochemical analyses have been shipped from Japan to Bremen. As for all other science party members and most of the operator teams, the onshore phase of this unique, first hybrid onshore phase of an IODP expedition is still ongoing. Important for certain ephemeral parameters like salinity, ammonium and alkalinity is that these samples are analyzed within 24 to 48 hours after they have been retrieved – so these first samples were already taken aboard the RV Kaimei, during the offshore phase of the expedition (see blog posts from the offshore phase of the Expedition 386).

Two parameters in the pore water are measured in Bremen: anions and sulfides. For this purpose the ion chromatograph (IC) is utilized for the first and the photometer for the latter. For the IC, sets of samples are processed, then measured for these parameters. Naturally, the instrument is carefully set up and calibrated before any sample analysis. 100 samples are analyzed in one run, which takes about 2 days. 

Afterwards the data are processed, quality-checked, and evaluated by the geochemistry lab and interpreted by the geochemists among the science party.

The groups exchange a lot of information online during this hybrid Onshore Science Party (OSP) – at Zoom meetings, via Slack and by emails. The Bremen lab team and the geochemistry science team stay in frequent and close contact. A challenge for everyone, but it is working fine and very efficient. Because where normally the researchers actively work with the samples, can hold them in their hands while preparing for the analytical lanes, they now have just to wait until all the analyses, which often take several days, are completed and the data made available. Only then they also take a look at both the processed and raw data.

Once the samples have been analyzed, any residues will be temporarily archived at the IODP Bremen Core Repository from which they will be shipped to the Kochi Core Center after the end of the expedition´s moratorium for final archiving.

The majority of sediment samples are only taken during the OSP, where the cores were split and therefore accessible for sampling. All happened aboard the DV Chikyu. As always, the Bremen team processed the geochemistry samples in a very elaborate, but efficient way. After the samples were taken, directly after the cores have been split, they are dried over several hours and sent to Bremen. Here they will be homogenized by grinding the material with a pestle in a mortar. These IODP standard samples taken every 2 meters – for IODP Expedition 386 – result into about 460 samples being processed and afterwards analyzed for elemental composition.

Do you want to know more about the specific analyses in the geochemistry lab?

Coreflow in geochemistry: https://www.marum.de/en/Research/Geochemistry.html

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