Average process length variation of the marine dinoflagellate cyst Operculodinium centrocarpum in the tropical and Southern Hemisphere Oceans: Assessing its potential as a palaeosalinity proxy

The study investigates the morphological variability of the dinoflagellate cyst Operculodinium centrocarpum (resting cyst of Protoceratium reticulatum) in core-top samples distributed over the Southern Hemisphere and the tropics in relation to sea-surface temperature (SST) and sea-surface salinity (SSS) at the corresponding sites. The process lengths show a moderate inverse relationship to summer SST (sSST) (R² = 0.44) and sSSS/sSST (R² = 0.4), however, lateral transport of cysts probably produced noise in the plots. After excluding tropical and Southern Hemisphere sites considered to have been affected by long distance lateral transport, the relationship between process length and density follows the equation sD = 0.8422x + 1016.9 (R² = 0.55) with a Root Mean Square Error = 0.63 kg m− 3, while the negative correlation with sSST increases up to R² = 0.79. Next to salinity, this study thus highlights the importance of a second factor, temperature, affecting process length in the topics and the Southern Hemisphere oceans.

► O. centrocarpum process length correlates with sea surface water density.
► Lateral transport of cysts may affect the correlation with sea surface density.
► Different relationships in remote geographical areas, molecular analyses needed.