A high-resolution dinoflagellate cyst record spanning the period of ~1830–2012 CE from Ría de Vigo (Atlantic margin of NW Iberia) is presented. Changes in concentrations and percentages of dinoflagellate cysts and freshwater algal spores reflect climatic and anthropogenic influences on the ria, i.e. coastal inlet formed by the partial submergence of a river valley. Statistical analyses (PCA and clustering) were used to identify the main patterns of change in the cyst assemblages. The cyst record was compared with reconstructed and measured instrumental environmental data (NAO, temperatures, mean sea level, etc.) to support (palaeo)reconstructions. Four main phases were identified: the first phase (~1830–1855 CE) of lower relative sea level (RSL), temperatures and precipitations represents the last stages of the LIA (Little Ice Age); the second phase (~1855–1910 CE) is interpreted as a transition between the colder LIA and the wetter and warmer conditions that prevailed through the 20th century; the third phase (~1910–1975 CE) is characterized by strong river inputs and water stratification in the ria; and the fourth phase (~1975–2012 CE) reflects impacts of anthropogenic warming and pollution. The anthropogenic signal consists of increases in heterotrophic cyst proportions and cysts diversity, as well as of a marked decline of potentially toxic Lingulodinium machaerophorum. Increasing organic matter content, nutrients and industrial wastes have likely caused detrimental impacts on the autotrophic dinoflagellates, by increasing turbidity and toxicity. The B5-cyst record and its comparison with previously published data suggest that increased concentrations of L. machaerophorum in the 20th century were mainly related to river flow variations, that in turn were primarily driven by NAO changes, rather than cultural eutrophication. We also report high abundances of Peridinium ponticum in our record, determining that this species is not exclusive to the Black and Marmara Seas and has much wider natural distribution.
Bibliographical noteFunding Information:
This work was funded by the Spanish Ministry of Education and Science CGL2012-33584 (co-financed with EFRD funds) and the Xunta de Galicia GRC2015/020 projects. Iria García-Moreiras was supported by a research fellowship from Xunta de Galicia (PRE/2013/404). The authors thank Natalia Martínez Carreño for her contribution with grain size and elemental data. Partial funding for this research was provided by the Natural Science and Engineering Research Council of Canada (NSERC) to Vera Pospelova (Discovery Grant program). The collaboration between the XM-3 group from the University of Vigo and the SEOS department from the University of Victoria was possible thanks to the International Postgraduate Scholarship Programme of the Fundación Barrié conceded to Iria García Moreiras in 2015. Finally, we would like to thank the editor and three anonymous reviewers for their valuable comments that improved the manuscript.
- Coastal palaeoenvironments
- Lingulodinium polyedrum
- North Atlantic Oscillation (NAO), Atlantic Iberian margin
- Sea level