In January 2021 we filled approximately 350 bottles with 500 mL and 100 bottles with 250 mL of seawater. The seawater was taken some years ago from an oligotrophic region in the North Atlantic. The samples were poisoned with HgCl2 and a detailed description of the preparation procedure can be found on OTC’s website.

The sub-standards are not meant to be a replacement of the Dickson CRMs. It should help the European community to operate in a quasi-reference mode until the Dickson lab can provide CRMs again. Due to the limited amount of sub-standard we are not able to provide bottles outside Europe.

In February some bottles were analyzed for DIC and Total Alkalinity using a SOMMA system and a VINDTA system, respectively. DIC and alkalinity were referenced against CRM’S from the Dickson lab and the reported uncertainty is a sum of the DICKSON CRM measurements and the sub-standards. We will keep a subset of the sub-standards to send it to the Dickson lab for reference.

Salinity was measured using a Seabird thermosalinograph SBE21.


The sub-standards are free of charge for ICOS labs. For non-ICOS labs have to add small amount per bottle but they are welcome to participate. More information can be found in the order form.

If you are interested in receiving bottles, please download the order form and fill in the requested information: Order Form.
Please be aware that we only have a very limited amount of bottles.