Distribution patterns of recent organic-walled dinoflagellate cysts in relation to environmental parameters in the Mediterranean Sea

Abstract

To determine the relationship between the spatial dinoflagellate cyst distribution and oceanic environmental conditions, 34 surface sediments from the Eastern and Western Mediterranean Sea have been investigated for their dinoflagellate cyst content. Multivariate ordination analyses identified sea-surface temperature, chlorophyll-a , nitrate concentration, salinity, and bottom oxygen concentration as the main factors affecting dinoflagellate cyst distribution in the region. Based on the relative abundance data, two associations can be distinguished that can be linked with major oceanographic settings. (1) An offshore eastern Mediterranean regime where surface sediments are characterized by oligotrophic, warm, saline surface water, and high oxygen bottom water concentrations (Impagidinium species, Nematosphaeropsis labyrinthus, Pyxidinopsis reticulata and Operculodinium israelianum). Based on the absolute abundance, temperature is positively related to the cyst accumulation of Operculodinium israelianum. Temperature does not form a causal factor influencing the accumulation rate of the other species in this association. Impagidinium species and Nematosphaeropsis labyrinthus show a positive relationship between cyst accumulation and nitrate availability in the upper waters. (2) Species of association 2 have highest relative abundances in the Western Mediterranean Sea, Strait of Sicily/NW Ionian Sea, and/or the distal ends of the Po/Nile/Rhône River plumes. At these stations, surface waters are characterized by (relative to the other regime) higher productivity associated with lower sea-surface temperature, salinity, and lower bottom water oxygen concentrations (Selenopemphix nephroides, Echinidinium spp., Selenopemphix quanta, Quinquecuspis concreta, Brigantedinium spp. and Lingulodinium machaerophorum). Based on both the absolute and relative abundances, Selenopemphix nephroides is suggested to be a suitable indicator to trace changes in the trophic state of the upper waters. The distribution of Lingulodinium machaerophorum is related to the presence of river-influenced surface waters, notably the Nile River. We suggest that this species might form a suitable marker to trace past variations in river discharge, notably from the Nile.

Keywords:

• Mediterranean Sea
• dinoflagellate cysts
• temperature
• productivity
• preservation
• eutrophication

Acknowledgements

Thanks are given to Deutscher Akademischer Austausch Dienst (DAAD) for providing of the first author to study in Bremen University, Germany. Consumables and travel grants were funded by the international graduate college EUROPROX, DFG, and European society funded projects in the group of Karin Zonneveld. We gratefully acknowledge the Historical Geology and Palaeontology group in Bremen University for providing all laboratory facilities and equipment. We particularly thank the captain and crew of Meteor cruises M40/4, M44/3, and M51/3 for providing the investigated sediment samples. We thank Francesca Sangiorgi and Peta Mudie for the constructive reviews of an earlier version of this manuscript. Analyses and visualizations used in this study were produced with the Giovanni online data system, developed and mainted by NASA GES DISC.