Climatic and anthropogenic impacts on the Ría de Vigo (NW Iberia) over the last two centuries: A high-resolution dinoflagellate cyst sedimentary record

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.