Reconstruction of oceanographic and climatic changes over the past ∼ 600 years over Coquimbo Bay, Chile (30°S)
Cantarutti, Gabriel
- 1Universite de Caen Normandie
- 2Universidad Catolica del Norte
- 3Ctr Estudios Avanzados Zonas Aridas CEAZA
- 4Inst Antart Chileno INACH
- 5
- 6Soc Chilena Arqueol SCHA
Journal
Marine Geology
ISSN
0025-3227
1872-6151
Open Access
closed
Volume
490
The upwelling system off Coquimbo (30 degrees S) is strongly influenced by interannual variability driven by the El Nino-Southern Oscillation (ENSO), which decreases primary productivity and increases precipitation during the warm phase (El Nino events). This study examined the historical variations in the primary oceanographic and climatic characteristics of the region based on recent sedimentary records from Coquimbo Bay. In a sediment core (BC117; 83 cm), nine sedimentary units were identified and categorized into two groups: u1, u3, u5, and u9 represent marine sedimentation, as indicated by the major contribution of marine diatoms and higher delta C-13 and delta N-15 values reflecting marine conditions. In contrast, u4, u6 and u7 exhibited more depleted delta 13C values and an increase in freshwater diatom valves, suggesting a significant continental influence, likely from alluvial events. These units showed elevated concentrations of Fe, K, and Cu and an increase in fine sediment content, likely associated with El Nino-induced heavy rainfall around 1700-1730 CE. This period was followed by a decrease in continental input owing to reduced pluviosity. Spanning from 1403 CE to 1850 CE, the core reflects a period dominated by La Nina-like conditions, sustained by an intensified Southern Oscillation Index (SOI) and diminished Interdecadal Pacific Oscillation (IPO). During this period, the seafloor experienced an increase in reduced conditions, likely leading to anoxic environments, which were subsequently followed by less reduced conditions encompassing the Current Warm Period (CWP) due to enhanced ventilation processes. Nevertheless, increasing proxies for primary productivity have suggested an intensification of upwelling in recent times. Based on the characteristics of the units, three tsunami events were characterized by a significant reduction in total diatom counts contingent on the energy of the event and a sharp basal contact between the lower undisturbed unit and the very disturbed overlying layer (1420, 1471, and 1751 CE).