Earth Syst. Sci. Data, 12, 2647–2663, 2020 https://doi.org/10.5194/essd-12-2647-2020 © Author(s) 2020. This work is distributed under the Creative Commons Attribution 4.0 License. ARIOS: a database for ocean acidification assessment in the Iberian upwelling system (1976–2018) Xosé Antonio Padin, Antón Velo, and Fiz F. Pérez Instituto de Investigaciones Marinas, IIM-CSIC, 36208 Vigo, Spain Correspondence: Xosé Antonio Padin ([email protected]) Received: 13 March 2020 – Discussion started: 24 April 2020 Revised: 21 August 2020 – Accepted: 30 August 2020 – Published: 4 November 2020 Abstract. A data product of 17 653 discrete samples from 3343 oceanographic stations combining measure- ments of pH, alkalinity and other biogeochemical parameters off the northwestern Iberian Peninsula from June 1976 to September 2018 is presented in this study. The oceanography cruises funded by 24 projects were primarily carried out in the Ría de Vigo coastal inlet but also in an area ranging from the Bay of Biscay to the Por- tuguese coast. The robust seasonal cycles and long-term trends were only calculated along a longitudinal section, gathering data from the coastal and oceanic zone of the Iberian upwelling system. The pH in the surface waters of these separated regions, which were highly variable due to intense photosynthesis and the remineralization of organic matter, showed an interannual acidification ranging from −0:0012 to −0:0039 yr−1 that grew towards the coastline. This result is obtained despite the buffering capacity increasing in the coastal waters further inland as shown by the increase in alkalinity by 1:1±0:7 and 2:6±1:0 µmol kg−1 yr−1 in the inner and outer Ría de Vigo respectively, driven by interannual changes in the surface salinity of 0:0193±0:0056 and 0:0426±0:016 psu yr−1 respectively. The loss of the vertical salinity gradient in the long-term trend in the inner ria was consistent with other significant biogeochemical changes such as a lower oxygen concentration and fertilization of the surface waters. These findings seem to be related to a growing footprint of sediment remineralization of organic matter in the surface layer of a more homogeneous water column. Data are available at https://doi.org/10.20350/digitalCSIC/12498 (Pérez et al., 2020). 1 Introduction absorption of atmospheric CO2 by the oceans decreases sea- water pH, causing ocean acidification, which conditions the Emissions of anthropogenic origin CO2 (fossil fuels, land use buffering capacity of seawater and in turn the exchange of and cement manufacturing) into the atmosphere are the main CO2 between the ocean and the atmosphere (Caldeira and cause behind the warming of the Earth due to the greenhouse Wickett, 2003; Raven et al., 2005). The Intergovernmental effect (IPCC, 2013). Given the constant exchange of gases Oceanographic Commission of the UNESCO identified the through the air–sea interface, the oceanic reservoir plays a chemical change in seawater brought about by ocean acid- key role as a sink for about 31 % of anthropogenic CO2 emis- ification as an indicator of a stressor on marine ecosystems sions (Sabine et al., 2004), controlling the partial pressure of with a negative impact on socio-economic activities such as carbon dioxide in the atmosphere and regulating global tem- fishing and shellfish farming. Hence, it was necessary for the peratures. oceanography community to observe and gather data about The CO2 uptake by the oceans produces changes in the in- pH and other parameters of the marine carbon system to organic carbon system in spite of being partially dampened conduct accurate measurements of pH and ancillary param- by the seawater buffering capacity. This ability of seawater to eters and provide data products to help a sustainable man- withdraw anthropogenic CO2 becomes more limited as more agement of the marine resources. The effect of ocean acid- CO2 is absorbed, which will make it difficult to stabilize at- ification on marine ecosystems has stimulated impetus in mospheric CO2 in the future (Orr et al., 2009). The gradual Published by Copernicus Publications. 2648 X. A. Padin et al.: ARIOS the international community for gathering high-quality time- series measurements of the marine inorganic carbon system (Hofmann et al., 2011; Andersson and MacKenzie, 2012; McElhany and Busch, 2013; Takeshita et al., 2015; Wahl et al., 2016) and for predicting the future evolution of the pH caused by climate change. The threat for oceanic acidification of marine ecosystems is especially significant in regions like coastal upwelling ar- eas, which are more sensitive and appear to respond faster to anthropogenic perturbations (Feely et al., 2008; Gruber et al., 2012; Lachkar, 2014; Hauri et al., 2013). These ecosystems are characteristic for their complex physical and biogeo- chemical interactions and for sustaining enormous biologi- cal productivity and productive fisheries (Pauly and Chris- tensen, 1995; Haury et al., 2009). The photosynthetic activ- ity in these regions is also an important mechanism for the seawater CO2 uptake, converting most of these areas into at- mospheric CO2 sinks (Pérez et al., 1999; Cobo-Viveros et al., 2013). However, the high physical/chemical variability in short temporal and spatial scales of upwelling systems and the lack of regular sampling in these waters prevents a com- plete picture of the acidification of these ecosystems. In the Iberian upwelling system, the researchers of the In- stituto de Investigaciones Marinas (IIM-CSIC) since 1976 commenced accurate measurements of marine inorganic car- bon system and associated parameters. As a result, a collec- tion of pH observations and ancillary biogeochemical infor- mation along the Galicia coast (40 and 45◦ N, 11◦ W) has been gathered under the framework of different projects over Figure 1. Map of all stations (red dots) including the geographi- the past 40 years. The current database, hereinafter called the cal areas selected to classify the ARIOS database from isobath of ARIOS (Acidification in the Rías and the Iberian Continen- 250 m (dark blue line) and 75 m (light blue line), latitudinal crite- tal Shelf) database, holds biogeochemical information from rion (green lines), and geographical lines (black lines). 3357 oceanographic stations, giving 17 653 discrete sam- ples. This unique collection is a starting point (i) for evalu- ating the ocean acidification in the Iberian upwelling system characterized by intense biogeochemical interactions as an Water (ENACW) (Ríos et al., 1992). Under these condi- observation-based analysis or (ii) for use as inputs in a cou- tions, the Rías Baixas act as an extension of the continen- pled physical–biogeochemical model to disentangle these in- tal shelf (Rosón et al., 1995; Souto et al., 2003; Gilcoto et teractions at the ecosystem level. al., 2017), where upwelling filaments extending westward export primary production from the coast into the ocean (Álvarez-Salgado et al., 2001). In the opposite direction, the 2 Data provenance prevalence of northward winds (Blanton et al., 1984) moves 2.1 Data spatial coverage the surface waters towards the coast, where they accumu- late, sink and thus isolate the coast. This process, known as The main characteristic of the Galician coastline, located in downwelling, is typical during the autumn–winter along with the northwest of the Iberian Peninsula, is the Rías Baixas, other characteristics such as the warm, salty waters from the four long coastal estuaries or rias (> 2.5 km3) between 42 Iberian Poleward Current (IPC) of subtropical origin (Fraga and 43◦ N (Fig. 1). The water exchange between the Rías et al., 1982; Alvarez-Salgado et al., 2006) that flows con- Baixas and open waters is drastically affected by the coastal strained to the Iberian shelf break (Frouin et al., 1990). The wind pattern as part of the Canary Current upwelling system runoff from local rivers also contributes to the presence of (Wooster et al., 1976; Fraga 1981; Arístegui et al., 2004). river plumes over the shelf (Otero et al., 2008). These hy- Under the predominance of northeasterly winds (Blanton et drodynamic conditions, the meteorological forcings and the al., 1984) during spring–summer, the surface offshore trans- alternation of periods of upwelling and downwelling (Ál- port of surface waters leads to a rising cold, nutrient-rich, varez, 1999; Gago et al., 2003c; Cobo-Viveros et al., 2013) deep water mass called the Eastern North Atlantic Central stimulate the development of intense primary production and Earth Syst. Sci. Data, 12, 2647–2663, 2020 https://doi.org/10.5194/essd-12-2647-2020 X. A. Padin et al.: ARIOS 2649 high rates of recycling and downward carbon export (Alonso- scale, summer and autumn were the preferred seasons to ad- Pérez and Castro, 2014). The result of this biogeochemical dress the different research purposes, with 37 % and 36 % of variability in terms of air–sea CO2 exchange is that the sur- the total samples respectively. The observations taken dur- face waters act as a net CO2 sink that is especially intense ing less favourable winter conditions, especially aboard the and variable over the shelf compared to offshore or in the coastal vessels usually available, only accounted for the 10 % inner Rías Baixas (Padin et al., 2010). of the ARIOS database. Besides the short-term and seasonal variability, signifi- cant changes in the long-term scale have been reported in 2.3 Data sources this region. In addition to changes such as the weakening and shortening of the upwelling events (Lemos and Sansó, The ARIOS database is a compilation of biogeochemical 2006; Pérez et al., 2010; Alvarez-Salgado et al., 2008), the properties with discrete measurements of temperature, salin- warming (González-Pola et al., 2005; Pérez et al., 2010), and ity, oxygen, nutrients, alkalinity, pH and chlorophyll that changes in the composition of phytoplankton (Bode et al., were sampled in waters off the northwest of the Iberian 2009; Pérez et al., 2010), the acidification in the first 700 m Peninsula from 1976 to 2018 and measured by IIM-CSIC for the geographical area from the Iberian Peninsula to the (Table 1).