AUTHOR=Vellojin Jurleys P. , Saldías Gonzalo S. , Allen Susan E. , Torres Rodrigo , Vergara-Jara Maximiliano , Sobarzo Marcus , DeGrandpre Michael D. , Iriarte José Luis 

TITLE=Understanding the Implications of Hydrographic Processes on the Dynamics of the Carbonate System in a Sub-Antarctic Marine-Terminating Glacier-Fjord (53°S)

JOURNAL=Frontiers in Marine Science

VOLUME=Volume 9 - 2022

YEAR=2022

URL=https://www.frontiersin.org/journals/marine-science/articles/10.3389/fmars.2022.643811

DOI=10.3389/fmars.2022.643811

ISSN=2296-7745

ABSTRACT=The biogeochemical dynamics of fjords along the southeastern Pacific Ocean are strongly influenced by hydrological and oceanographic processes occurring at a seasonal scale. In this study we describe the role of hydrographic forcing on the seasonal variability of the carbonate system of the Sub-Antarctic glacial fjord, Seno Ballena, in the Strait of Magellan (53°S). Biogeochemical variables were measured in 2018 during three seasonal hydrographic cruises (fall, winter, spring) and from a high-frequency pCO2-pH mooring for 10 months at 10 ± 1 m depth in the fjord. The hydrographic data showed that freshwater input from the glacier influenced the adjacent surface layer of the fjord and forced undersaturated CO2 values (< 400 μatm) and low aragonite saturation (ΩAr < 1). During spring the surface water had relatively low pCO2 (mean = 365, range: 167- 471 μatm), high pH (mean = 8.1, range: 8.0 - 8.3), and high ΩAR (mean = 1.6, range: 1.3 - 4.0). Concurrent measurements of phytoplankton biomass and nutrient conditions during spring indicated that the periods of lower pCO2 values corresponded to higher phytoplankton photosynthesis rates, resulting from autochthonous nutrient input and vertical mixing. In contrast, higher values of pCO2 (mean = 398, range: 365–433 μatm) and relatively lower values of pH (mean = 8.0, range: 8.0–8.1) and ΩAr (mean = 1.3, range: 0.9–2.0) were recorded in cold surface waters during winter and fall. Low ΩAr in fall is attributed to the input of low alkalinity freshwater that decreased the concentration of calcium carbonate species in the surface layer which could not be compensated by primary productivity, unlike in the spring. Assuming global climate change will bring further glacier retreat and ocean acidification, this study represents important advances in our understanding of glacier meltwater processes on CO2 dynamics in Sub-Antarctic glacier–fjord systems.