Influences of riverine and upwelling waters on the coastal carbonate system off Central Chile and their ocean acidification implications

Abstract

A combined data set, combining data from field campaigns and oceanographic cruises, was used to ascertain the influence of both river discharges and upwelling processes, covering spatial and temporal variation in dissolved inorganic carbon (DIC) and aragonite saturation state. This work was conducted in one of the most productive river-influenced upwelling areas in the South Pacific coasts (36°S). Additionally, further work was also conducted to ascertain the contribution of different DIC sources, influencing the dynamics of DIC along the land-ocean range. Six sampling campaigns were conducted across seven stations at the Biobío River basin, covering approximately 200 km. Three research cruises were undertaken simultaneously, covering the adjacent continental shelf, including 12 sampling stations for hydrographic measurements. Additionally, six stations were also sampled for chemical analyses, covering summer, winter, and spring conditions over 2010 and 2011. Our results evidenced that seaward extent of the river plume was more evident during the winter field campaign, when highest riverine DIC fluxes were observed. The carbonate system along the river-ocean continuum was very heterogeneous varying over spatial and temporal scales. High DIC and pCO 2 were observed in river areas with larger anthropogenic effects. CO 2 supersaturation at the river plume was observed during all campaigns due to the influence of low pH river waters in winter/spring and high-pCO 2 upwelling waters in summer. δ 13 C DIC evidenced that main DIC sources along the river and river plume corresponded to the respiration of terrestrial organic matter. We have linked this natural process to the carbonate saturation on the adjacent river-influenced coastal area, suggesting that Ω aragonite undersaturation in surface/subsurface waters is largely modulated by the influence of both river discharge and coastal upwelling events in this productive coastal area. Conditions of low Ω aragonite might impact negatively physiological traits for marine organisms, such as bivalves, gastropods, and crustaceans. Therefore, local populations from river-influenced sites could be inherently more tolerant to ocean acidification than organisms living in regions with lower Ω aragonite variability. VARGAS ET AL.

Concomitant ocean acidification and increasing total alkalinity at a coastal site in the NW Mediterranean Sea (2007-2015)

“…Rivers as a potential driver of A T and C T trends at Point B could be achieved if the A T content discharged by rivers was changing, as was proposed for the Adriatic Sea (Luchetta et al, 2010). For example, terrestrial organic matter cycling influences riverine C T (Vargas et al, 2016), so changes in soil respiration could be expected to change A T of rivers. Increasing river A T has been documented in North America and occurs via a number of processes including: (1) the interplay of rainfall and land-use (Raymond and Cole, 2003), (2) anthropogenic limestone addition (a.k.a., liming) used to enhance agriculture soil pH (Oh and Raymond, 2006;Stets et al, 2014) and freshwater pH (Clair and Hindar, 2005), and (3) potentially indirect effects of anthropogenic CO 2 on groundwater CO 2 -acidification and weathering (Macpherson et al, 2008).…”

“…Compared to the open ocean, shallow coastal sites exhibit natural variability in carbonate chemistry over annual timeframes (Hofmann et al, 2011;Kapsenberg and Hofmann, 2016;Kapsenberg et al, 2015), complicating the detection and relevance of open ocean acidification in isolation of other processes (Duarte et al, 2013). Variability stems from both physical (e.g., upwelling, river discharge; Feely et al, 2008;Vargas et al, 2016) and biological processes (e.g., primary production, respiration, net calcification). Within watersheds, coastal carbonate chemistry is affected by eutrophication (Borges and Gypens, 2010;Cai et al, 2011), groundwater supply (Cai et al, 2003), and land use and rain influence on river alkalinity (Raymond and Cole, 2003;Stets et al, 2014).…”

Long‐Term Changes of Carbonate Chemistry Variables Along the North American East Coast

“…Anthropogenic carbon dioxide (CO 2 ) emitted to the atmosphere from human activities, primarily fossil fuel burning, increases the amount of CO 2 absorbed by the ocean and leads to ocean acidification (OA, Doney et al, 2009;Orr et al, 2005). In addition to absorption of excess CO 2 , upwelling, eutrophication, and river discharge affect carbonate chemistry in coastal waters and contribute to coastal acidification (Cai et al, 2011;Feely et al, 2008;Vargas et al, 2016;Wallace et al, 2014). Localized and regional acidification of coastal waters is not well understood due to its complexity and limited spatial and temporal observations and model estimates (Hofmann et al, 2011;Strong et al, 2014).…”

Coastal ocean acidification and increasing total alkalinity in the northwestern Mediterranean Sea

“…Variability in coastal carbonate chemistry stems from both physical (e.g., upwelling, river discharge; Feely et al, 2008;Vargas et al, 2016) and biological processes (e.g., primary production, respiration, net calcification). Within watersheds, coastal carbonate chemistry is affected by eutrophication (Borges and Gypens, 2010;Cai et al, 2011), groundwater supply (Cai et al, 2003), and land use and rain influence on river alkalinity (Raymond and Cole, 2003;Stets et al, 2014).…”