Seasonal Changes in Carbonate Saturation State and Air‐Sea CO₂ Fluxes During an Annual Cycle in a Stratified‐Temperate Fjord (Reloncaví Fjord, Chilean Patagonia)

Abstract

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 (pCO2) in a north Patagonian fjord with a focus on changes in freshwater inflows and biological processes. To do this, we monitored pH and pCO2 in situ, along with river streamflow, salinity, temperature, and dissolved oxygen (DO) in the Reloncaví Fjord (41.5°S) for a full year (January to December 2015). Strong seasonal variability was observed in the pCO2, pH, and DO of the fjord's surface waters. During the summer, pCO2 reached its annual minimum (range: 187–571 μatm) and pH its maximum (range: 7.98–8.24), coinciding with lower freshwater inflows (204–307 m3/s) and high DO (280–378 μmol/kg), as well as aragonite saturation states (ΩArag) higher than 1. In contrast, in winter, pCO2 ranged from 461–1,008 μatm and pH from 7.57–8.03, coinciding with high freshwater inflows (1,049–1,402 m3/s), lower oxygen (216–348 μmol/kg), and constant undersaturation of ΩArag. Reloncaví Fjord had an annual air‐water CO2 flux of 0.716 ± 2.54 mol·m−2·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.

General Hydrography of the Beagle Channel, a Subantarctic Interoceanic Passage at the Southern Tip of South America

“…Due to the pronounced seasonality of marine high latitude ecosystems, the productive period is limited to spring and summer (from October to mid-March, Almandoz et al, 2011) when the net uptake of CO 2 exceeds the community respiration, creating a net sink of CO 2 (Torres et al, 2011). During the remaining months, Chl-a concentration falls to < 1 µg Chl-a L −1 (Almandoz et al, 2011) and heterotrophic processes tend to dominate (e.g., Torres et al, 2011;Vergara-Jara et al, 2019). In a scenario of intensive aquaculture, we might expect higher loads of dissolved and particulate organic matter as well as an increase in nutrients (N and P mainly), which will primarily be remineralized by heterotrophic organisms, thus increasing pCO 2 levels and altering the carbonate chemistry of the seawater.…”

Plastic response of the oyster Ostrea chilensis to temperature and pCO2 within the present natural range of variability

“…Based on our data, the undersaturation levels of O cal and O arg were registered during autumn-winter season and relatively saturated conditions were registered during spring-summer season. Similarly, Vergara-Jara et al [43] shown strong seasonal variability of pH and pCO 2 in the Reloncaví fjord, Chilean Patagonia, with the undersaturation levels of O arg in winter and saturated conditions of aragonite in the summer. Our study shows the first time series of temperature and salinity associated with the parameters of the carbonate system within the Chilean oyster farm.…”

“…Our study shows the first time series of temperature and salinity associated with the parameters of the carbonate system within the Chilean oyster farm. The environmental conditions described for the Quempillén estuary share similarities with other estuaries in the region, such as a marked seasonal cycle characterized by minimum values of temperature and pH during the winter [43]. However, the intensity and timing of freshwater input to the estuary, as well as its concomitant effects on salinity and speciation of carbon chemistry, are expected to vary in association with local hydrographic characteristics (eg.…”

Climate and Land Cover Trends Affecting Freshwater Inputs to a Fjord in Northwestern Patagonia

“…The system's stratification varies along the fjord and between seasons, decreasing toward the mouth and being maximum in winter. The Reloncaví Fjord has been extensively studied by several research projects, mainly oceanographic, including paleoclimate (Rebolledo et al, 2015), fjord hydrodynamics (Valle-Levinson et al, 2014;Castillo et al, 2016), fjord biogeochemistry (Farías et al, 2017;González et al, 2019;Vergara-Jara et al, 2019;Yevenes et al, 2019) and plankton biology (González et al, 2013;Iriarte et al, 2017).…”