A multi-decade record of high quality fCO2 data in version 3 of the Surface Ocean CO2 Atlas (SOCAT)

The Surface Ocean CO2 Atlas (SOCAT) is a synthesis of quality-controlled fCO2 (fugacity of carbon dioxide) values for the global surface oceans and coastal seas with regular updates. Version 3 of SOCAT has 14.7 million fCO2 values from 3646 data sets covering the years 1957 to 2014. This latest version has an additional 4.6 million fCO2 values relative to version 2 and extends the record from 2011 to 2014. Version 3 also significantly increases the data availability for 2005 to 2013. SOCAT has an average of approximately 1.2 million surface water fCO2 values per year for the years 2006 to 2012. Quality and documentation of the data has improved. A new feature is the data set quality control (QC) flag of E for data from alternative sensors and platforms. The accuracy of surface water fCO2 has been defined for all data set QC flags. Automated range checking has been carried out for all data sets during their upload into SOCAT. The upgrade of the interactive Data Set Viewer (previously known as the Cruise Data Viewer) allows better interrogation of the SOCAT data collection and rapid creation of high-quality figures for scientific presentations. Automated data upload has been launched for version 4 and will enable more frequent SOCAT releases in the future. High-profile scientific applications of SOCAT include quantification of the ocean sink for atmospheric carbon dioxide and its long-term variation, detection of ocean acidification, as well as evaluation of coupled-climate and ocean-only biogeochemical models. Users of SOCAT data products are urged to acknowledge the contribution of data providers, as stated in the SOCAT Fair Data Use Statement. This ESSD (Earth System Science Data) “living data” publication documents the methods and data sets used for the assembly of this new version of the SOCAT data collection and compares these with those used for earlier versions of the data collection (Pfeil et al., 2013; Sabine et al., 2013; Bakker et al., 2014). Individual data set files, included in the synthesis product, can be downloaded here: doi:10.1594/PANGAEA.849770. The gridded products are available here: doi:10.3334/CDIAC/OTG.SOCAT_V3_GRID

MicroSub: Diversidade microbiana e bioxeoquímica agochadas nas augas subterráneas costeiras dos parques nacionais mariños

Poster.-- Close Encounters IIM (3rd Kind), Vigo, 23 June 2022Dous achados recentes revelaron o papel ecolóxico dos acuíferos como reservorios de diversidade e como mediadores de transformacións bioxeoquímicas que poden impactar nos ecosistemas mariños circundantes: - As augas subterráneas albergan unha gran diversidade de microorganismos en moitos casos descoñecidos para a ciencia - A descarga de auga subterránea ao mar achega grandes cantidades de nutrientes que poden afectar á calidade e a función ecolóxica dos ecosistemas mariños. MicroSub reúne un equipo altamente interdisciplinar, con especialistas en hidroxeoloxía costeira, na detección e medida de fluxos de auga subterránea ao mar, na caracterización das transformacións bioxeoquímicas e no estudo da ecoloxía microbiana acuática O obxectivo do proxecto é analizar a diversidade microbiana e xeoquímica de acuíferos costeiros prístinos e o seu impacto no mar circundante. Estes datos servirán de liña de base e como indicadores dos cambios que os ecosistemas dos parques poidan sufrir nos próximos anos por mor do cambio climático actual que poderían causar grandes cambios hidrolóxicos, biolóxicos e xeoquímicos nos acuíferos e nos medios mariños afectados por elesO proxecto MicroSub recibiu financiación do Organismo Autónomo Parques Nacionales e do Ministerio para la Transición Ecológica y el Reto Demográfico a través das subvencións para a realización de proxectos de investigación na rede de parques nacionais 2020 (Ref 2595 2020)N

Collapse of the tropical and subtropical North Atlantic CO₂ sink in boreal spring of 2010

International audienceFollowing the 2009 Pacific El Niño, a warm event developed in the tropical and subtropical North Atlantic during boreal spring of 2010 promoted a significant increase in the CO2 fugacity of surface waters. This, together with the relaxation of the prevailing wind fields, resulted in the reversal of the atmospheric CO2 absorption capacity of the tropical and subtropical North Atlantic. In the region 0–30°N, 62–10°W, this climatic event led to the reversal of the climatological CO2 sink of −29.3 Tg C to a source of CO2 to the atmosphere of 1.6 Tg C from February to May. The highest impact of this event is verified in the region of the North Equatorial Current, where the climatological CO2 uptake of −22.4 Tg for that period ceased during 2010 (1.2 Tg C). This estimate is higher than current assessments of the multidecadal variability of the sea-air CO2 exchange for the entire North Atlantic (20 Tg year−1), and highlights the potential impact of the increasing occurrence of extreme climate events over the oceanic CO2 sink and atmospheric CO2 composition. Anthropogenic CO2 emission to the atmosphere is widely considered the main cause of current climate change. Since the industrial revolution, the oceans have absorbed about 40–50% of all the anthropogenic CO2 emissions 1,2 , thus mitigating its effects over the Earth climate system. Nevertheless, studies have suggested that the oceanic C sink may be decreasing for the last 50 years 3,4. Whether these changes are caused from anthropogenic climate change or internal climate variability is still uncertain 4–6 , but they could significantly impact future atmospheric CO2 levels. The North Atlantic north of 18°N is one of the oceanic regions of strongest CO2 uptake (420 ± 110 Tg C y−1) representing 30% of the global oceanic CO2 sink 7 , and an estimated interannual and multidecadal CO2 uptake variability of 20 Tg C yr −1 7–9. The area of the North Atlantic with CO2 uptake that is most sensitive to climate forcing (changes in sea surface temperature (SST) and wind speed) is the subtropical North Atlantic 10. There, the sea-air CO2 exchange is mainly controlled by sea surface temperature (SST) changes due to its permanent oligotrophic conditions outside upwelling areas, thus presenting the strongest seasonal variability in the sea-air CO2 exchange of this ocean 10. Recent warming identified in the region, partially linked to anthropogenic forcing, is already reducing its CO2 uptake 11. Large-scale climate modes such as the North Atlantic Oscillation (NAO), the Atlantic Multidecadal Oscillation (AMO) and the El Niño-Southern Oscillation (ENSO) can mitigate or exacerbate anthropogenic-driven SST increase in the North Atlantic and its effects over the sea-air CO2 exchange 12. In 2009, a strong El Niño event occurred in the Pacific. ENSO events are known to promote positive SST anomalies in the northern tropical Atlantic through a teleconnection driven through the troposphere with a time lag of a few months 13. In boreal spring of 2010, this event coincided with a strong positive AMO resulting in a strong positive SST anomaly associated with negative wind speed anomalies in the tropical Atlantic 14,15 (Fig. 1). Its impact in the equatorial Atlantic sea-air CO2 exchange has been explored by Lefèvre et al. 14 , who showed that during this period the Intertropical Convergence Zone (ITCZ) was shifted northward compared to its climatological position, associated with a significant reduction of rainfall. The CO2 undersaturation promoted by the intense rainfall associated with the ITCZ was thus significantly reduced and, consequently, CO2 outgassing in this area increased. As their study mainly focused on the Western equatorial Atlantic, the impact of this climatic event in the sea-air CO2 exchange in the North Atlantic is currently unknown

Evidence for enhanced primary production driving significant CO2 drawdown associated with the Atlantic ITCZ

The intense rainfall associated with the Intertropical Convergence Zone (ITCZ), a narrow zone of confluence of the northeast and southeast trades, can significantly alter sea surface salinity, the chemistry of inorganic C and the resulting sea-air CO2 exchange in the tropics. We have analyzed extensive underway data collected from 2008 until 2014 and recorded by an autonomous CO2 system installed on a commercial ship that crosses the central tropical Atlantic (5°S to 15°N, 18°W to 36°W) to disentangle the effects of the ITCZ over the carbonate system there. Based on statistically significant linear co-variance of sea surface fugacity of CO2 (fCO2sw) and sea surface salinity in the areas affected by the ITCZ, we calculated CO2 drawdown rates associated with the impact of the ITCZ in the central tropical Atlantic ranging from 0.11 ± 0.02 to 2.35 ± 0.08 mmol m−2 d−1. These were calculated by comparing the observed fCO2sw with that expected without surface seawater carbonate system dilution and increase in gas transfer caused by the ITCZ. The observed decrease in fCO2sw associated with the freshening caused by the ITCZ is much larger than expected from thermodynamics alone. 59.1 ± 4.1 % of the total observed CO2 drawdown associated with the ITCZ cannot be explained by abiotic processes. Instead, we found significant negative correlations between underway sea surface salinity and remote-sensed chlorophyll a in the areas affected by the ITCZ. Different to other tropical oceanic basins, the tropical Atlantic receives large amounts of continental dust originated from Africa. Wet dust deposition driven by the ITCZ appears associated with the interannual variability of the CO2 drawdown associated with the ITCZ. Fertilization driven by the ITCZ seems to enhance primary production in the otherwise oligotrophic tropical Atlantic, thus significantly lowering CO2 emissions to the atmosphere

Does Nitrate Enrichment Accelerate Organic Matter Turnover in Subterranean Estuaries?

18 pages, 1 table, 11 figures.-- This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY)Due to the widespread pollution of coastal groundwaters with fertilizers, submarine groundwater discharge (SGD) is often thought to be a large dissolved inorganic nitrogen (DIN) source to the ocean. Whether this N is autochthonous or allochthonous to the subterranean estuary (STE), the availability of large quantities of DIN can nevertheless interact with the cycling of other elements, such as carbon (C). In previous studies, we documented the discharge of large quantities of freshwater and NO3– from the mouth of an STE into the Ria Formosa lagoon (SW Iberian Peninsula). For the period covered in this study (2009–2011), the same STE site was dominated by recirculating seawater due to a prolonged fall in piezometric head in the coupled coastal aquifers. Total SGD rates remained similarly high, peaking at 144 cm day–1 at the lower intertidal during fall. We observed a progressive increase of NO3– availability within the STE associated with the recovery of piezometric head inland. Interestingly, during this period, the highest SGD-derived dissolved organic C and DIN fluxes (112 ± 53 and 10 ± 3 mmol m–2 day–1, respectively) originated in the lower intertidal. NO3– enrichment in the STE influences the benthic reactivity of fluorescent dissolved organic matter (FDOM): when seawater recirculation drives STE dynamics, only small changes in the benthic distribution of recalcitrant humic-like FDOM are observed (from −2.57 ± 1.14 to 1.24 ± 0.19 10–3 R.U. “bulk” sediment h–1) in the absence of DIN. However, when DIN is available, these recalcitrant fractions of FDOM are actively generated (from 1.32 ± 0.15 to 11.56 ± 3.39 10–3 R.U. “bulk” sediment h–1), accompanied by the production of labile protein-like FDOM. The results agree with previous studies conducted with flow-through reactor experiments at the same site and suggest that DIN enrichment in the STE enhances the metabolic turnover of sedimentary organic matter up to the point of discharge to surface waters. DIN pollution of coastal aquifers may therefore promote a contraction of the residence time of particulate organic C within the STE, driving carbon from continental storage into the seaData collection and sample analysis were funded by the Portuguese Foundation for Science and Technology (FCT), the EU (FEDER), and the Portuguese Government through grant contract SFRH/BD/39170/2007 and project NITROLINKS [NITROgen loading into the Ria Formosa through Coastal Groundwater Discharge (CGD) – Pathways, turnover, and LINKS between land and sea in the Coastal Zone, PTDC/MAR/70247/2006]. Data analysis and manuscript preparation were funded by project SUBACID [SUBmarine Groundwater Discharge (SGD) impact on coastal ACIDification processes in contrasting European Atlantic Shores: toward securing ecosystem services and food production], funded by the Irish Research Council and the European Union’s Horizon 2020 Research and Innovation Program under the Marie Skłodowska-Curie grant agreement no. 713279 through the CAROLINE program (CLNE/2017/210)Peer reviewe

Denitrification-nitrification process in permeable coastal sediments: An investigation on the effect of salinity and nitrate availability using flow-through reactors

12 pages, 7 figures, 2 tablesPermeable coastal sediments act as a reactive node in the littoral zone, transforming nutrients via a wide range of biogeochemical reactions. Reaction rates are controlled by abiotic factors, e.g., salinity, temperature or solute concentration. Here, a series of incubation experiments, using flow-through reactors, were conducted to simulate the biogeochemical cycling of nitrate (NO −3 ) and phosphorus (P) in permeable sediments under different NO −3 availability conditions (factor I) along a salinity gradient (admixture of river and seawater, factor II). In an oligotrophic scenario, i.e., unamended NO −3 concentrations in both river and seawater, sediments acted as a permanent net source of NO −3 to the water column. The peak production rate occurred at an intermediate salinity (20). Increasing NO −3 availability in river water significantly enhanced net NO −3 removal rates within the salinity range of 0 to 30, likely via the denitrification pathway based on the sediment microbiota composition. In this scenario, the most active removal was obtained at salinity of 10. When both river and seawater were spiked with NO3, the highest removal rate switched to the highest salinity (36). It suggests the salinity preference of the NO −3 removal pathway by local denitrifiers (e.g., Bacillus and Paracoccus) and that NO −3 removal in coastal sediments can be significantly constrained by the dilution related NO −3 availability. Compared with the obtained variation for NO −3 reactions, permeable sediments acted as a sink of soluble reactive P in all treatments, regardless of salinity and NO −3 input concentrations, indicating a possibility of P-deficiency for coastal water from the intensive cycling in permeable sediments. Furthermore, the net production of dissolved organic carbon (DOC) in all treatments was positively correlated with the measured NO −3 reaction rates, indicating that the DOC supply may not be the key factor for NO −3 removal rates due to the consumption by intensive aerobic respiration. Considering the intensive production of recalcitrant carbon solutes, the active denitrification was assumed to be supported by sedimentary organic matterPeer reviewe

Microbiota for Nitrogen Removal in Wastewater Treatments and Marine Environments: Advocating Communication and Interactive Research

5 pages, 1 table, 1 figure.-- This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY)Nitrogen (N) is essential for life as all organisms need N for growth. Due to the intensive application of the Haber-Bosch process and cultivation of N-fixation crops on a global scale, the reactive N (mainly as nitrate, nitrite and ammonium) is increasingly accumulated in terrestrial systems worldwide (Zhang et al., 2020). To eliminate the environmental stress and negative ecological feedbacks caused by redundant N, N removal reactions are deemed to be a key factor in its cycling and receive great attention from the scientific community, managers and stakeholders. To avoid further human-derived N enrichment of ecosystems, N removal in wastewater treatment is also pivotal. Currently, different technologies based on a wide range of N processing microbiota, mainly derived from nitrification, anaerobic/aerobic denitrification, anaerobic ammonium oxidation (Anammox) have been used for reducing N content in sewage (Cao et al., 2021), such as single reactor for high activity ammonia removal over nitrite (SHARON), completely autotrophic nitrogen removal over nitrite (CANON) and oxygen-limited autotrophic nitrification and denitrification (OLAND). Nevertheless, N accumulation is still frequently observed in urban and rural areas and a significant quantity of reactive N produced from anthropogenic activities enters into marine systems via surface loadings, submarine groundwater discharge and atmospheric deposition (Jiang et al., 2021a). In marine environments, N excess is rapidly removed via biogeochemical reactions, such as biological assimilation in the euphotic zone, aerobic/anaerobic denitrification and dissolved oxygen (DO) dependent Anammox in both water parcels and sediments (Jiang et al., 2021b). In fact, the microbial strains for N removal used in wastewater treatments could be frequently observed in marine environments, e.g., Thiosphaera pantotropha in denitrification or Candidatus Brocadia sinica in Anammox. As research subjects with great similarity, valuable N reaction information from researchers in marine environments and wastewater treatments is barely shared and microbiota involved in N removal process is also limitedly exchanged between subjects. Active communication between academics likely enhances the understanding on a series of key issues in both subjects, such as the efficiency of N removal in brackish wastewater, low temperature conditions and carbon-limited scenarios, as well as in-situ N removal along coastal belts. Here, we demonstrate the similarity of N removal in wastewater treatments and marine environments and highlight causal linkages between each other. Furthermore, we advocate the necessity and benefits derived from communication and interactions among scientists in both subjects in the futurePeer reviewe

Radon prevalence in domestic water in the Ría de Vigo coastal basin (NW Iberian Peninsula)

14 pages, 7 figures, 1 table.-- This article is licensed under a Creative Commons Attribution 4.0 International LicenseThe Ría de Vigo catchment is situated in the largest radon-prone area of the Iberian Peninsula. High local indoor radon (222Rn) levels are the preeminent source of radiation exposure, with negative effects on health. Nevertheless, information on radon levels of natural waters and the potential human exposure risks associated with their domestic use is very sparse. To elucidate the environmental factors increasing human exposure risk to radon during domestic water use, we undertook a survey of local water sources, including springs, rivers, wells, and boreholes, over different temporal scales. Continental waters were highly enriched in 222Rn: activities ranged from 1.2 to 20.2 Bq L−1 in rivers and levels one to two orders of magnitude higher were found in groundwaters (from 8.0 to 2737 Bq L−1; median 121.1 Bq L−1). The geology and hydrogeology of local crystalline aquifers support one order of magnitude higher 222Rn activities in groundwater stored in deeper fractured rock compared to that contained within the highly weathered regolith at the surface. During the mean dry season, 222Rn activities nearly doubled in most sampled waters in comparison to the wet period (from 94.9 during the dry season to 187.3 Bq L−1 during wet period; n = 37). Seasonal water use and recharge cycles and thermal convection are postulated to explain this variation in radon activities. The high 222Rn activities cause the total effective dose of radiation received from domestic use of untreated groundwaters to exceed the recommended 0.1 mSv y−1. Since more than 70% of this dose comes from indoor water degassing and subsequent 222Rn inhalation, preventative health policy in the form of 222Rn remediation and mitigation measures should be implemented prior to pumping untreated groundwater into dwellings, particularly during the dry periodOpen Access funding provided thanks to the CRUE-CSIC agreement with Springer Nature. Financial support was provided by the SUBACID project (SUBmarine groundwater discharge (SGD) impact on coastal ACIDification processes in contrasting Atlantic Shores: towards securing ecosystem services and food production), funded by the Irish Research Council and the European Union’s Horizon 2020 research and innovation program under the Marie Skłodowska-Curie grant agreement No713279 through the CAROLINE program (CLNE/2017/210)Peer reviewe

Seasonal and interannual variability of sea-air CO₂ fluxes in the tropical Atlantic affected by the Amazon River plume

International audienc

Geochemical tracers in submarine groundwater discharge research: Practice and challenges from a view of climate changes

17 pagesSubmarine groundwater discharge (SGD), the flux of porewater from permeable seabed or karst conduits to surface water bodies, delivers a significant quantity of land-borne solutes to coastal oceans. This input of land-derived solutes is frequently linked with eutrophication, harmful algae blooms, and benthic hypoxia, and hence has the potential to trigger great economic losses. Geophysical and geochemical tracers, including salinity, temperature, water stable isotopes, and radioactive elements, have been widely applied in SGD studies for more than 50 years to, amongst others, identify water sources, estimate residence times, and quantify discharge rates. Here we review advantages and shortcomings of these tracers in the study of SGD. Application requirements are outlined based on previous research and combined tracer approaches in karst environments, permeable coasts, and estuaries are illustrated under the view of climate changes. Current challenges with the use of geochemical tracers in SGD studies are highlighted and opportunities to develop these tracers for improved coastal management showcasedPeer reviewe