Guidelines and Terms of Use (Water Samples)

This document complies with the requirements for the "Nutzungsordnung" according to DFG form 55.04, 06.2016 – "Hinweise zu Gerätenutzungskosten und zu Gerätezentren".

The guidelines and terms of use in this document are generally binding for all users.

The MARUM Stable Isotope Laboratory operates as a service facility, where users submit their samples, but laboratory staff carries out the analyses of stable carbon (δ¹³C) isotope ratios of dissolved inroganic carbon in water. However, users from the University of Bremen will be asked to prepare their samples (flush vials, acidify samples, and cleanup), depending on the sample number (>~40). The staff will guide users through the preparation process and laboratory safety procedures.

Persons entitled to use the laboratory

The MARUM Stable Isotope Laboratory accepts samples from MARUM scientists. Other persons are accepted as users at the discretion of the head of the laboratory and the MARUM director.

Acknowledgement in publications

When publishing data, the laboratory must be acknowledged as "Measurements of δ¹³C of DIC were carried out at the MARUM Stable Isotope Laboratory, University of Bremen" or equivalent statements, typically in the "Materials and Methods" section of a journal article. Additional rules might apply within cooperation agreements.

For describing the methods, a template is provided in the appendix. Please, check the measurement data report to make sure you provide the correct instrument type and standard deviation. Copying the text from previous publications will more often than not result in incorrect statements.

Contact

For technical and scientific questions, please contact the head of the laboratory:

MARUM and University of Bremen

The in-house price of €5 per sample is charged to cover the consumables. After receipt of the analyses results the user will be asked to provide the account details ("Fondsnummer"). Usually, no further action is required on part of the user.

External collaborators

The price for measurements within collaborative research projects with external institutions, where the latter cover the costs, is €6.25 per sample (including 20% administrative overhead). Before sample submission, the collaboration partner(s) at MARUM and the external institution must sign a cooperation agreement that must also be accepted and signed by the legal department of the University of Bremen. Partners share the intellectual ownership of the isotope data (as detailed in the agreement). A template for the cooperation agreement is available upon request (in German). This paperwork is required; otherwise, the measurements are considered commercial by law, and salaries, overhead costs and taxes will be accounted for (see commissioned work below).

Commissioned work

The price for commercial measurements is about €16 per sample (plus VAT). For legal reasons, this is a non-binding estimate that does not represent a quotation. The latter is available upon request. Commercial customers have the intellectual ownership of the measurement data.

The mass spectrometer is shared with another working group that uses it for analysing organic material. Before switching to water samples, we need to agree on a time window with said working group. Organic matter that has settled on the ion source of the mass spectrometer needs to be removed, and a series of standards is measured to ascertain proper working conditions. This results in labour-extensive servicing of the instrument for at least one week before proper samples can be measured.

The minimum number of samples is therefore 20. There is no fixed upper limit, but above ~200 samples finding a time window might incur additional waiting time.

Once measurements have commenced the turnaround time is typically less than two weeks. But for the reasons outlined above the time between requesting the measurements and actually starting them is often more then one month.

The samples are processed on a first come, first served basis. Exception: Samples from University of Bremen bachelor and master projects will be given priority, but the number of samples is limited to about 100 per project.

In the event of a severe backlog, the laboratory might change the order of measurements so that users can meet urgent project deadlines (end of bachelor and master projects; end of funding period; report for funding agency; …). Internal samples take precedence over external samples in this case.

The laboratory is experienced in analyzing seawater and sediment porewater samples with natural isotopic compositions. For other sample types, contact us. We do not accept isotopically spiked samples, or samples with volatile organic compounds.

Typically, 2 mL seawater or 1 mL porewater are required. There is no upper limit to the sample volume upon submission, the laboratory staff takes care of using the right amount.

When taking, storing and sending their samples, users should aim to preserve the original isotopic signature of the dissolved inorganic carbon. Gas exchange between sample and air must be kept to a minimum. Biological activity and degradation of organic matter should be prevented.

• Required: Use glassware for sample storage. In contrast to plastic, glass is safe against diffusion of gases.
• Required: When taking the sample, avoid generation of air bubbles. For example, when filling the sample bottle with a tube, the end of the tube should be placed at the bottom of the bottle, and the water flow should be moderate without causing much turbulence. Do not direct a water jet onto the sample surface.
• Required: Keep the headspace as small as possible, i.e., the sample bottle must be filled up to the top.
• Recommended: Poison the sample to prevent biological activity. Use concentrated solutions of HgCl₂ or ZnCl₂. Always report the use of poison to the laboratory.
• Required: Never add any other chemicals, especially organic compounds and chemicals that alter the pH. Acid forces DIC to degas as CO₂.
• Required: Properly close the bottle immediately after sampling to minimize gas exchange with the atmosphere.
• Recommended for long-term storage: Additionally seal the cap with parafilm or inundate the closed cap in liquid wax (paraffin).
• Required: Store the sample cool (but not frozen) and dark. Keeping the samples at room temperature for a few days (e.g., during transport) is not an issue.
• During measurement, only the gas phase originating from the sample is used. Filtering the sample is therefore not necessary, as long as the sample is water rather than mud.

Samples must be accompanied by a tabular sample list in both printed and digital form. The samples must appear on the list in the same order as on the sample tray. Where appropriate, use the following table format:

Header: Name, email, and affiliation of submitter; type of samples (e.g., pore water), region or name of site.

Columns: Site, sample depth or running number.

Please, do not use the cryptic IODP and MeBo sample identifiers. Identifiers are typed in manually in the spectrometer software, and these excessively complicated formats are prone to errors and longer than the software can handle.

Each line in the list must correspond to a separate sample container and vice versa.

Sample labels

All samples must be properly labeled. Abbreviated identifiers are fine as long as they remain unambiguous and clearly correspond to the accompanying documentation (see above). When using adhesive labels make sure that they do not detach from the sample bottle, especially when moisture condenses on the cool surface. Suggestion: Inscribe sticky tape with a permanent pen and wrap it around the whole perimeter of the bottle.

When your samples are properly stored, labeled, and documented...

MARUM and University of Bremen: Contact Henning Kuhnert (Room Marum I, 1150; [Bitte aktivieren Sie Javascript]; phone: 65520).

External samples shipped by mail should be addressed to:

Henning Kuhnert

Universität Bremen

MARUM I, 1150

Leobener Straße 8

28359 Bremen

Germany

For shipments, make sure to comply with the laws for hazardous material in case the samples are poisoned.

Customs declaration

Shipments from inside the EU do not require customs documents. Otherwise, check details with your shipping company. A common pitfall is declaring scientific samples as "samples". In customs terms this refers to ware samples (such as trial packages) which makes the shipment subject to taxes. Provide a value between 10 and 20€ for the total content. A value of 0 is not accepted by the customs (why would you pay the shipment for something worthless?). A value exceeding 20€ makes the shipment subject to import taxes. Should these additional costs arise, the laboratory will charge them to the sample submitter.

A small volume (6 drops) of concentrated phosphoric acid is dropped into an autosampler vial. The vial is closed with a septum and repeatedly evacuated and flushed with helium. 1-2 mL of the water sample are added using a syringe with cannula. A similar procedure is carried out for the laboratory standard (ground limestone). In the latter case, the standard is given into the vial, the vial is evacuated and flushed, and the acid is added with the syringe. The vials of both samples and standards are placed in a temperature-controlled autosampler and left there overnight. The DIC of the samples is converted to CO₂ and degases. The carbonate of the standards is quantitatively dissolved, and CO₂ is generated.

The sample probe guides the CO₂ to the Gasbench II. The latter operates in continuous flow mode and toggles between samples / standards, reference CO₂ of known isotopic composition, and helium for flushing the lines. The gases end up in the mass spectrometer, a Finnigan MAT 252 that measures the isotopologues of CO₂: ¹²C¹⁶O¹⁶O (mass 44) and ¹³C¹⁶O¹⁶O (mass 45). δ¹³C is derived from the intensity ratio of both masses.

Each sequence may consist of up to 48 samples and 12 standards. The throughput is about 3 measurements per hour.

The laboratory standard is ground and sieved Solnhofen limestone (calcite) with known δ¹³C that itself is calibrated against NBS 19. When dissolved in H₃PO₄, the carbon from the calcite quantitatively ends up in CO₂. δ¹³C of the carbonate and the CO₂ are identical. Similarly, the entire inorganic carbon of the water sample ends up in CO₂. Therefore, the DIC from the water sample can be calibrated against solid carbonate, although it may sound counter-intuitive.

This method does not work for δ¹⁸O due to the isotopic fractionation of oxygen between CO₂ and H₂O.

The repeatability is the standard deviation for the measurements of the laboratory standard (see above). The typical value is between 0.05‰ and 0.10‰ for δ¹³C. The exact number is provided with each set of measurements.

Public information

Upon publishing their data, typically in the form of peer-reviewed journal articles, non-commercial users are obliged to make their data publicly available through the PANGAEA data base.

User information

The sample submitter receives an Excel workbook with two spreadsheets via email. Each line of the first spreadsheet contains the sample name, the raw data (δ¹³C as reported by the instrument software), the calibrated data (offline-corrected for the measurements of the laboratory standard), and the internal standard deviation. Each measurement is associated with a unique identifier. Process information for each measurement includes the signal intensities.

A separate column of the spreadsheet reports series-specific information, including the unique identifier of the sample series (a running number), the type of instrument, and the external reproducibility based on repeat measurements of the laboratory standard.

The second spreadsheet contains the measurement information of the laboratory standards that were used for calibration.

Data storage

Digital copies of each daily run and each sample series and a printout of the first are kept by the laboratory. Data are not passed to third parties.