Sources of dissolved silica to the fjords of northern Patagonia (44–48°S): the importance of volcanic ash soil distribution and weathering

Abstract

Dissolved silica (DSi) plays an important biogeochemical role in the fjords of northern Chilean Patagonia (44-48°S), where it drives high biogenic productivity and promotes carbon burial. It is generally believed that the DSi riverine input to lakes and coastal environments is controlled by a combination of factors including lithology, climate, topography, vegetation, and meltwater input. In northern Chilean Patagonia several authors have proposed that the postglacial volcanic ash soils (andosols) may play a significant role in the high supply of DSi to the regional fjords. To assess the influence of andosols on DSi concentrations in north Patagonian rivers, we mapped andosol thickness and compared our results with river chemistry. The mineralogical and geochemical composition of three representative andosol profiles was also examined to evaluate the efficiency of weathering processes. The andosol thickness map clearly demonstrates that volcanic ash was predominantly deposited on the eastern side of the regional volcanoes, reflecting the influence of the prevailing westerly winds on the distribution of pyroclastic material. Mineralogical and geochemical results show that the andosol parent material has the typical andesitic basaltic signature of the regional volcanoes, i.e. high amounts of amorphous material, plagioclase, K-feldspar, and pyroxene. Down-profile variations in soil mineralogy and geochemistry indicate increased leaching of silica with depth, resulting from weathering of the volcanic parent material. For the five studied watersheds, a highly positive correlation (R 2 =0.98) was found between average andosol thickness and DSi concentrations, suggesting that andosol thickness is the main parameter affecting DSi concentrations in north Patagonian river systems. On seasonal timescales, increased precipitation (winter) and glacial meltwater (summer) input can significantly reduce DSi concentrations. We argue that the weathering of andosols constitutes the most important source of DSi to the lakes and fjords of northern Chilean Patagonia, explaining the particularly high regional rates of biogenic silica production.

The Last Glacial Maximum and deglaciation in central Patagonia, 44°S–49°S

“…The regional geology of the southern Andes is characterized by intrusions of the Patagonian batholith within the Andean Cordillera, Mesozoic and Cenozoic volcanics, Mesozoic marine sediments, and a Paleozoic metamorphic complex (Vandekerkhove et al, 2016;Lagabrielle et al, 2004). The Taitao Peninsula and Chonos Archipelago are formed of Triassic metamorphic rocks and mid-Cenozoic volcanic and sedimentary deposits, with the Patagonian batholith constraining the eastern edges.…”

“…The Taitao Peninsula and Chonos Archipelago are formed of Triassic metamorphic rocks and mid-Cenozoic volcanic and sedimentary deposits, with the Patagonian batholith constraining the eastern edges. Basins to the east of the Andes are filled with Pliocene-Quaternary glacial and glaciofluvial sediments (Vandekerkhove et al, 2016;Lagabrielle et al, 2004). A gap in the active volcanic arc between the Southern Andean Volcanic Zone and Austral Andean Volcanic Zone exists in central Patagonia (46.5° S-49° S), near the Chile Triple Junction, where the Nazca, South American and Antarctic tectonic plates meet (Gutiérrez et al, 2005;Stern, 2004).…”

Dissolved Methane Distribution in the Reloncaví Fjord and Adjacent Marine System During Austral Winter (41°–43° S)

“…14,16,20,21,32,33,36,38) Also, a positive correlation was observed between Si(OH) 4 and salinity in the estuarine area ( Table 2), suggesting that water from continental runoff contributes high levels of Si(OH) 4 into the Reloncaví fjord. Indeed, northern Chilean Patagonia is characterized by andosol-type soil, which affects dissolved Si(OH) 4 concentrations in the river system and potentially explains the exceptionally high regional rates of biogenic Si(OH) 4 production (Vandekerkhove et al 2016). In addition, Si(OH) 4 is well correlated with both particle concentration and dissolved CH 4 ( Table 2), indicating that the majority of the particles suspended in the water column originate from continental runoff.…”

First Observations of Boeckella michaelseni Mrázek 1901 in and Optical Properties of a Central Patagonian Lake

“…General Carrera is a binational lake that is shared with Argentina, where it is called as Buenos Aires lake [6]. It has glacial and volcanic influence on its northern shore, whereas the southern part has no glacial influences [2,3] and is markedly oligotrophic [6]. The aim of the present study is do a study of zooplankton assemblage in terms of zooplankton abundances in General Carrera Lake and its potential association with optical properties using remote sensing techniques.…”

“…The Patagonian lakes located in southern Argentina and Chile (38-51°S) are of glacial origin [1][2][3][4], and some of these lakes are associated with ice fields in their surrounding basins that generate specific characteristics in landscapes such as those observed in Grey Lake in Torres del Paine National Park [5], or water colorations specifics for each lake, for example greenish bays in General Carrera or Todos los Santos lakes [1,6]. Also, the Patagonian lakes are characterized by their marked oligotrophy (2.1-0.4 µg/L Chlorophyll a) [1,5] generated as a consequence of low crustacean zooplankton species richness and the predominance of calanoids copepods of Boeckella and Tumeodiaptomus genera [1].…”