The central and northern Chilean coasts are part of the Humboldt Current System, which sustains one of the largest fisheries in the world due to upwelling. There are several upwelling focal points along the Chilean coast; however, from a physical standpoint, the region between 39 • and 41 • S has not been studied in detail despite being one of the most productive zones for pelagic extraction in Chile. Here, we evaluated the seasonal variability of coastal upwelling off central-southern Chile using principally daily sea surface temperature (SST) and sea surface wind (SSW), and 8-day composite chlorophyll-a concentration between 2003 and 2017. Through the seasonal evaluation of the net surface heat flux and its relationship with the SST as well as daily SST variability, we determined the "maximum upwelling" on our area. The direction of surface winds is controlled throughout the year by the Southeast Pacific Subtropical Anticyclone, which produces a cold tongue and an upwelling shadow north of Punta Galera (40 • S) in austral spring and summer. A cross-correlation analysis showed a decrease of SST follow the alongshore SSW with a lag of 2 days in the months favorable to the upwelling. However, the correlations were not as high as what would be expected, indicating that there is a large advection of waters from the south that could be related to the greater volume of subantarctic water present in the zone.

The Valdivia River estuary (VRE) located in south-central Chile is known as one of the largest estuarine ecosystems on the Pacific coast. This research aims to determine the intra-tidal and sub-tidal variability of saline intrusions into the VRE between November 2017 and March 2019 derived from salinity sensors located along the VRE. Complementary hydrographic measurements were conducted during flood and ebb conditions of the spring and neap tides for each of the four seasons of the year along the central axis of the VRE. The results of the salinity time series showed that saline intrusions (values greater than 0.5 Practical Salinity Units) occurred ~20 km from the estuary mouth, when the total flow of the Cruces and Calle-Calle rivers (main tributaries of the estuary) was low, around 280–300 m3 s−1. During the same period, the best co-variability was observed between the saline intrusions and the mixed-semidiurnal tide and the fortnightly and monthly periods of the tide. Regression analyses indicated that salinity intrusion length (L) is best correlated to discharge (D) with a fractional power model L α D−1/2.64 (R2 = 0.88). The decreasing discharge trend, found between 2008–2019, implies that saline water intrusions would negatively impact the Valdivia’s main drinking water intake during the low rainfall season under future climate conditions.

No abstract