[insu-01093152] Anchovy population and ocean-climatic fluctuations in the Humboldt Current System during the last 700 years and their implications

A marine sedimentary record collected from 87 m water depth in a coastal environment of the Humboldt Current System (Mejillones Bay, 23° S, northern Chile) was used to reconstruct the past 700 years of ocean-climatic con-ditions and to study the influence of any changes on anchovy population dynamics. We analyzed quartz, organic carbon, total nitrogen, alkenones and fish scales. Four stratigraphic units in the sediment column correspond with fluctuations in these and other proxies. Low Scale Deposition Rate (SDR) values from 1330 to 1420 suggest a low abundance of anchovy in this coastal environment. Three subsequent cycles of ca. 170 years each showed an increase and decrease of anchovy populations, which is in agreement with changes in the wind regime, sea surface temperature and primary productivity. Since ca. 1840, marked fluctuations of SDR have been observed, probably as a consequence of the onset of a different oceanographic regime characterized by intensified southern winds and upwelling, colder surface waters, higher primary productivity, and enhanced "La Niña like" interdecadal variability. An increase of the anchovy population was observed until halfway through the 20th century, followed by a decrease, even though water temperature decreased and primary productivity increased. This situation is likely the consequence of the increased fishery activity that developed in this zone during the last 60 years. After analyzing the results obtained for anchovy SDR, we can determine that there is a relation between the abundance of this species and phases of the Pacific Decadal Oscillation (PDO), in which an increase in the SDR coincides with a PDO cold phase, while a decline coincides with a warm phase. Fast Fourier transformation analysis applied to the time series obtained from the Mejillones sediment core and to the North Atlantic Oscillation (NAO), the PDO, and the solar irradiance index time series shows three different decadal cycles (80–100 years, 61–75 years and 45–48 years approximately). Furthermore, the results of this study suggest that both the PDO and the NAO and the biogeochemical markers of Mejillones exhibit periodicities that fall within the 80 to 100 year Gleissberg solar cycle, indicating that global solar radiation plays a key role in the local ocean-climatic processes and confirming teleconnection linkages between widely separated regions.



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