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Título

TRACING MONSOON-DRIVEN UPWELLING: FORAMINIFERAL AND PALYNOLOGICAL RECORDS FROM THE NW ARABIAN SEA

Texto do resumo

The Indian Ocean Monsoon is one of the most significant climatic systems on Earth, profoundly influencing regional and global climates and socio-economic conditions. The NW Arabian Sea, known for its high productivity due to intense upwelling driven by the Indian Summer Monsoon, offers a unique opportunity to study past oceanographic and climatic conditions through marine sediment records. Understanding variations in monsoonal intensity and their impact on oceanography is crucial for reconstructing past climates and predicting future climatic scenarios. This study focuses on the integrated analysis of planktic foraminiferal faunas and palynological data from an Ocean Drilling Program (ODP) core (117-721A-1H-1-W), located approximately 300 km offshore of the Omani coast. The selected interval spans from >43500 BP to 40390 +/- 550 BP cal, providing an overview of the interval prior the Heinrich Event 4. Our study comprises 11 samples over a 54 cm interval resampled every ~4 cm. The objectives of this study are: 1) to qualitatively analyze and identify the palynological record, 2) identify and quantify the foraminiferal species preserved in the sediments, 3) and correlate the results. This aims to identify and characterize the oscillations of the Indian Ocean Monsoon and their imprint on the marine sediment record. The planktic foraminiferal assemblages, including species such as Globigerina bulloides, Globigerinoides ruber, Pulleniatina obliquiloculata, Globorotalia menardii, Neogloboquadrina dutertrei, Orbulina universa, Globigerinoides sacculifer, and Globigerinita glutinata, were identified and quantified. These species have been divided into two different assemblages representing distinct oceanographic conditions: 1) tropical Assemblage: G.ruber, G.sacullifer, P.obliquiloculata, G.siphonifera, G.elongatus and O.universa 2) Upwelling Assemblage: G.bulloides, N.dutertrei, G.menardii. The oscillations between the predominance of these two assemblages indicates that the intensity of the upwelling has varied over the interval. G. bulloides correlates with periods of lower sea-surface temperatures and enhanced nutrient levels, indicative of increased upwelling and stronger monsoonal winds. In parallel, palynological analysis was conducted. Although pollen and spore concentrations were low (ranging from 3 to 27 specimens), NPP, particularly dinocysts, fungi, and microscopic algae, were relatively abundant. Our results indicate significant changes in the physical and chemical properties of the NW Arabian Sea driven by climatic shifts. The seasonal production variations of major planktonic foraminiferal species are well-preserved in the sediment record, serving as reliable paleoclimatic indicators. Additionally, this study provides palynological insights, highlighting the imprints left by Indian Ocean Monsoon oscillations in the past. These findings enhance our understanding of past oceanographic and climatic conditions and their impact on regional monsoon dynamics.

Palavras Chave

Indian Ocean Monsoon; Paleoceanography; NW Arabian Sea.