[M-IS22] Biogeochemistry

[MIS22-02] Distribution of trace elements near the interface of the ocean and a tidewater glacier in the Southern Patagonia Icefield

*Naoya Kanna¹, Shin Sugiyama³, Daiki Nomura², Marius Schaefer⁴, Hajime Obata¹ (1.Atmosphere and Ocean Research Institute, The University of Tokyo, 2.The Field Science Center for Northern Biosphere, Hokkaido University, 3.Institute of Low Temperature Science, Hokkaido University, 4.Universidad Austral de Chile)

The Southern Patagonia Icefield (SPI) is the largest temperate ice mass in the Southern Hemisphere, of which the glaciers have been retreating since the last glacial maximum. Amalia Glacier, characterized as a tidewater glacier in SPI, has experienced a dramatic retreat of over 8 km since 1945 (Giacaman, 2023). Increasing glacial melt can affect hydrographic properties, sedimentation processes, and biogeochemical cycles in proglacial fjords. Despite increased interest in the processes occurring in the proglacial fjords of Greenland and Antarctica, Patagonia fjords are still one of the least studied areas of the world. This study reports data on trace elements in the fjord fed by Amalia Glacier and discusses the factors controlling the concentrations and distributions of trace elements on the fjord.
Oceanographic observation was conducted near the front of Amalia Glacier in the austral summer of 2024. Seawater was collected from a depth of approximately 5 m using a peristaltic pump (Geotech Environmental Equipment). Samples of the dissolved fractions of trace elements including iron (dFe), manganese (dMn), aluminum (dAl), nickel (dNi), zinc (dZn), copper (dCu), cobalt (dCo), and lead (Pb) were collected in polyethylene bottles after filtration through a 0.2 μm pore size AcroPak filter (Pall). The trace elements in the samples were pre-concentrated using an InertSep ME-2 resin (GL Science). The trace elements preconcentrated onto the resin were eluted with nitric acid and analyzed by a high-resolution ICP-MS (ELEMENT XR, Thermo Fisher Scientific). The hydrographic properties were measured using a portable CTD sensor equipped with a turbidity sensor (JFE Advantech).
Temperature and salinity on the fjord's surface ranged from 3℃ to 11℃ and from 3 to 25. The water near the glacier front was relatively fresh (salinity < 10) and cold (temperature < 5℃) consistent with meltwater originating from Amalia Glacier. The fjord received sediments from proglacial streams, as observed by the high turbidity near the glacier front. All analyzed trace element concentrations increased significantly at stations closer to Amalia Glacier, except for dFe, dNi, and dPb. The fjord likely received dMn, dAl, dZn, dCu, and dCo from proglacial streams as well as sediments. The dFe concentration rapidly decreased within 5 km from the glacier front, likely because Fe was more rapidly co-precipitated with suspended particles and/or flocculated in the water column than the other elements. Interestingly, there were no dNi and dPb inputs from proglacial streams. The dissolved trace element distributions in the fjord are likely influenced by several factors including the amount of meltwater discharge, local geology, scavenging, and drawdown by primary production. In this presentation, we show more details of results obtained by the field observation in the Patagonia fjord.