Seawater Mg/Ca and Sr/Ca ratios worldwide from 2009 to 2017 collected in 79 cruises, including coupled measured data for temperature, salinity, total alkalinity, DIC, DO, and calculated pH and CO2 (NCEI Accession 0171017)

The long debate about the conservative behaviour of seawater Mg/Ca and Sr/Ca ratios becomes more complex by studying the ocean as a whole and not only open ocean settings or the deep sea. In this project we measured in 79 cruises around the world seawater Mg/Ca and Sr/Ca ratios to discover that the modern ocean ranges are well beyond the pre-assumed values used by modellers, paleoceanographers and experimentalists as the basis for their work (Mg/Ca = 4.5 to 6.5 mol:mol and Sr/CA = 7 to 9.8 mmol:mol).

We find out that modern seawater ranges are similar to the last 20 million years (Neogene) increase in these ratios, challenging the pre-assumed knowledge and a good number of methods used that assume a constant seawater Mg/Ca or Sr/Ca ratio. We agree that open ocean, the deep sea and reconstructions of past seawater based on samples derived from these settings give a good representation, but by no means they represent the ocean as a whole, especially coastal areas, upwelling zones, polar waters, and even the euphotic zone.