Seasonal changes in carbonate saturation state and air‐sea CO2 fluxes during an annual cycle in a stratified‐temperate fjord (Reloncaví Fjord, Chilean Patagonia)

Changes may be occurring in the carbonate chemistry of fjords due to natural and anthropogenic disturbance of major freshwater sources. We present a high-frequency time series study of seasonal pH and CO2 partial pressure (pCO(2)) in a north Patagonian fjord with a focus on changes in freshwater inflows and biological processes. To do this, we monitored pH and pCO(2) in situ, along with river streamflow, salinity, temperature, and dissolved oxygen (DO) in the Reloncavi Fjord (41.5 degrees S) for a full year (January to December 2015). Strong seasonal variability was observed in the pCO(2), pH, and DO of the fjord's surface waters. During the summer, pCO(2) reached its annual minimum (range: 187-571 mu atm) and pH its maximum (range: 7.98-8.24), coinciding with lower freshwater inflows (204-307 m(3)/s) and high DO (280-378 mu mol/kg), as well as aragonite saturation states (omega(Arag)) higher than 1. In contrast, in winter, pCO(2) ranged from 461-1,008 mu atm and pH from 7.57-8.03, coinciding with high freshwater inflows (1,049-1,402 m(3)/s), lower oxygen (216-348 mu mol/kg), and constant undersaturation of omega(Arag). Reloncavi Fjord had an annual air-water CO2 flux of 0.716 +/- 2.54 mol center dot m(-2)center dot year(-1) during 2015 and thus acted as a low emission system. The annual cycle was mainly governed by seasonal changes in biological processes that enhanced the shift from a CO2 sink in late spring and summer, caused by high primary production rates, to a CO2 source during the rest of the year caused by high community respiration due to allochthonous organic carbon inputs.