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Variações oceanográficas ao largo da margem Ocidental Portuguesa durante o final do Holocénico
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Resumo(s)
During the Holocene, over the last 11,700 years, significant climatic variations have occurred, despite numerous studies, the mechanisms and chronology are not fully understood yet. In this period, the Little Ice Age (LIA) stands out, being the coldest period of the last 4000 years, characterized by colder conditions, with its transition marking the last major natural variation in the climate system, before anthropogenic influence became the primary driver of climate change. This study aimed to reconstruct oceanographic conditions over the last millennium by analysing three cores (64-PE332 3/7; 64-PE332 4/1; PO287-6G), collected off the coast of Porto, at depths ranging from 2000 m to 80 m. Planktonic foraminifera assemblages were analysed to estimate temperature and productivity variations during this period, with a focus on the LIA. The species Globigerina bulloides dominates in the coastal core, reflecting the influence of coastal upwelling, while Neogloboquadrina incompta prevails in the offshore core, associated with the Portugal Current and colder waters. In the coastal core, increased abundances of Turborotalita quinqueloba, Neogloboquadrina pachyderma, and estimated productivity, suggest an increase in river discharges (coinciding with a negative NAO phase and higher n-alkane concentrations). The temperature, estimated from foraminifera, decreased by 2°C from the coast to offshore, while exported productivity remained similar across the three cores. The offshore and intermediate cores reflect typical open-ocean conditions, while the coastal core represents an environment under coastal influence. The results suggest that the LIA had two phases: an earlier phase, warmer, and more productive phase, followed by a colder and less productive phase. A new temporal range for the LIA – 1400-1820 AD – is proposed, which should be verified with additional analyses to improve the temporal resolution of this study and refine the age model.
Descrição
Tese de Mestrado, Ecologia Marinha, 2025, Universidade de Lisboa, Faculdade de Ciências
Palavras-chave
Holocene Little Ice Age Foraminifera Temperature Productivity