ALBERT

Description: The speciation of dissolved iron (DFe) in the ocean is widely assumed to consist almost exclusively of Fe(III)-ligand complexes. Yet in most aqueous environments a poorly defined fraction of DFe also exists as Fe(II), the speciation of which is uncertain. Here we deploy flow injection analysis to measure in situ Fe(II) concentrations during a series of mesocosm/microcosm/multistressor experiments in coastal environments in addition to the decay rate of this Fe(II) when moved into the dark. During five mesocosm/microcosm/multistressor experiments in Svalbard and Patagonia, where dissolved (0.2 µm) Fe and Fe(II) were quantified simultaneously, Fe(II) constituted 24 %–65 % of DFe, suggesting that Fe(II) was a large fraction of the DFe pool. When this Fe(II) was allowed to decay in the dark, the vast majority of measured oxidation rate constants were less than calculated constants derived from ambient temperature, salinity, pH, and dissolved O2. The oxidation rates of Fe(II) spikes added to Atlantic seawater more closely matched calculated rate constants. The difference between observed and theoretical decay rates in Svalbard and Patagonia was most pronounced at Fe(II) concentrations 〈2 nM, suggesting that the effect may have arisen from organic Fe(II) ligands. This apparent enhancement of Fe(II) stability under post-bloom conditions and the existence of such a high fraction of DFe as Fe(II) challenge the assumption that DFe speciation in coastal seawater is dominated by ligand bound-Fe(III) species.

Description: The iron(II) oxidation kinetic process was studied at 25 stations in coastal seawater of the Macaronesia region (9 around Cape Verde, 11 around the Canary Islands, and 5 around Madeira). In a physicochemical context, experiments were carried out to study the pseudo-first-order oxidation rate constant (k′, min-1) over a range of pH (7.8, 7.9, 8.0, and 8.1) and temperature (10, 15, 20, and 25 °C). Deviations from the calculated kcal′ at the same T, pH, and S were observed for most of the stations. The measured t1/2 (ln 2/k′, min) values at the 25 stations ranged from 1.82 to 3.47 min (mean 1.93 ± 0.76 min) and for all but two stations were lower than the calculated t1/2 of 3.21 ± 0.2 min. In a biogeochemical context, nutrients and variables associated with the organic matter spectral properties (CDOM and FDOM) were analyzed to explain the observed deviations. The application of a multilinear regression model indicated that k′ can be described (R = 0.921 and SEE = 0.064 for pH = 8 and T = 25 °C) from a linear combination of three organic variables, k′OM = kcal′-0.11∗ TDN + 29.9*bDOM + 33.4*C1humic, where TDN is the total dissolved nitrogen, bDOM is the spectral peak obtained from colored dissolved organic matter (DOM) analysis when protein-like or tyrosine-like components are present, and C1humic is the component associated with humic-like compounds obtained from the parallel factor analysis of the fluorescent DOM. Results show that compounds with N in their structures mainly explain the observed k′ increase for most of the samples, although other components could also play a relevant role. Experimentally, k′ provides the net result between the compounds that accelerate the process and those that slow it down.

Description: Highlights • Cu complexation was measured for the first time in the Fram Strait region. • Cu-binding ligand concentrations and binding strength varied longitudinally in the Fram Strait. • More than 99 % of dCu was organically complexed by strong ligands. • On the Greenland shelf the Transpolar Drift and the coastal processes were the main sources of Cu ligands. Abstract The Fram Strait represents the major gateway of Arctic Ocean waters towards the Nordic Seas and North Atlantic Ocean and is a key region to study the impact of climate change on biogeochemical cycles. In the region, information about trace metal speciation, such as copper, is scarce. This manuscript presents the concentrations and conditional stability constants of copper-binding ligands (LCu and log KcondCu2+L) in the water column of Fram Strait and the Greenland shelf (GEOTRACES cruise GN05). Cu-binding ligands were analysed by Competitive Ligand Exchange-Adsorptive Cathodic Stripping Voltammetry (CLE-ACSV) using salicylaldoxime (SA) as competitive ligand. Based on water masses and the hydrodynamic influences, three provinces were considered (coast, shelf, and Fram Strait) and differences were observed between regions and water masses. The strongest variability was observed in surface waters, with increasing LCu concentrations (mean values: Fram Strait = 2.6 ± 1.0 nM; shelf = 5.2 ± 1.3 nM; coast = 6.4 ± 0.8 nM) and decreasing log KcondCu2+L values (mean values: Fram Strait = 15.7 ± 0.3; shelf = 15.2 ± 0.3; coast = 14.8 ± 0.3) towards the west. The surface LCu concentrations obtained above the Greenland shelf indicate a supply from the coastal environment to the Polar Surface Water (PSW) which is an addition to the ligand exported from the central Arctic to Fram Strait. The significant differences (in terms of LCu and log KcondCu2+L) between shelf and coastal samples were explained considering the processes which modify ligand concentrations and binding strengths, such as biological activity in sea-ice, phytoplankton bloom in surface waters, bacterial degradation, and meltwater discharge from 79NG glacier terminus. Overall, the ligand concentration exceeded those of dissolved Cu (dCu) and kept the free copper (Cu2+) concentrations at femtomolar levels (0.13–21.13 fM). This indicates that Cu2+ toxicity limits were not reached and dCu levels were stabilized in surface waters by organic complexes, which favoured its transport to the Nordic Seas and North Atlantic Ocean and the development of microorganism.

Description: Surface-to-bottom seawater sampling for total alkalinity (AT), total inorganic carbon (TIC) and dissolved oxygen determination were performed in archipelagic coastal waters of the Macaronesia region during the POS533 cruise (from February 28 to March 19, 2019) on board the RV Poseidon. The Macaronesia region show a high variability due to its location in a coupling area between the Canary Upwelling System along the Northwest African coast and the oligotrophic open-ocean waters of the Northeast Atlantic subtropical gyre and the influence of the island interaction with the Canary Current. Thus is a key zone in terms of CO2 distribution, natural and anthropogenic carbon inventory and air-sea exchange and requires the develop of regional-scale field studies. The water-column sampling was carried out in leeward coastal stations located in the archipelagos of Cape Verde, Canary and Madeira, as well as in the Cape Verde Ocean Observatory (CVOO) and the European Station for Time-Series in the Ocean of the Canary Islands (ESTOC). A bottle rosette sampler containing twelve 10 L Niskin bottles was used for depth water sampling. The obtained dataset includes temperature, salinity, AT, TIC and dissolved oxygen. The temperature and salinity were monitored by using a CTD placed in the rosette. The AT and TIC was determined on board from the depth water samples using a VINDTA 3C and following Mintrop et al., (2000). Samples were potentiometrically titrated with HCl for AT determination, while TIC was coulometrically determined. Both AT and TIC values were corrected using certified reference material (CRM) bottles (batch 177, provided by A. Dickson at Scripps Institution of Oceanography), giving values with an accuracy of ±1.5 and ±1.0 µmol kg-1, respectively. The dissolved oxygen was determined from the seawater samples collected in pre-calibrated glass wide neck bottles by using the WINKLER method, introduced by Winkler (1888) and optimized by Carpenter (1965) and Carrit and Carpenter (1966). A Metrohm 888 Titrando operated with the software Tiamo and an amperometric electrode to determine the end point was used for the titration (Culberson and Huang, 1987). These in-situ collected data improve the knowledge about the biogeochemistry in eastern boundary transitional areas and allows a better understanding of the role in the climate change of archipelagic waters, coastal regions and island/continental shelves. The provided datasets can be used in further biogeochemical studies in the Macaronesia region and in the entire Northeast Atlantic. The monitoring and data collection received fundings from the Atmosphere-Ocean-Islands-Biogeochemical interactions in the Macaronesian Archipelagos of Cabo Verde, the Canaries and Madeira project (AIMAC project) and the European Union's Horizon 2020 research and innovation program under grant agreement Nº 820989 (COMFORT project). In this case, the measurements complemented those done for iron study (Santana-Casiano and Quack, 2021).

Description: Surface underway physicochemical measurements were performed in open-ocean and archipelagic coastal waters of the Macaronesia region during the POS533 cruise (from February 28 to March 19, 2019) on board the RV Poseidon. The Macaronesia region show a high variability due to its location in a coupling area between the Canary Upwelling System along the Northwest African coast and the oligotrophic open-ocean waters of the Northeast Atlantic subtropical gyre and the influence of the island interaction with the Canary Current. Thus is a key zone in terms of CO2 distribution, natural and anthropogenic carbon inventory and air-sea exchange and requires the develop of regional-scale field studies. The autonomous monitoring was carried out through the vessel track mainly downwind in the archipelagos of Cape Verde, Canary and Madeira and through the latitudinal transects that connect them. The obtained dataset includes sea surface temperature (SST), salinity (SSS) and pH values with a temporal frequency of data collection of 5 minutes. The SST and SSS were monitored by using a SeaCat SBE21 termosalinograph placed at the same location of the seawater immersed pump (main seawater intake of the RV Poseidon) with an accuracy of 0.01 ºC and 0.001, respectively. A spectrophotometric pH sensor (SP101-SM) developed by the QUIMA group (IOCAG-ULPGC) and SensorLab (González-Dávila et al., 2014; 2016) and based on the method described by Clayton and Byrne (1993) was run in continuous and used for the surface pH monitoring. The SP101-SM pH sensor uses 4 wavelengths analysis for the m-cresol purple, includes auto-cleaning steps, performs a blank for pH calculation immediately after the dye injection and removes any dye effect in each pH reading (the accuracy with respect to a TRIS seawater buffer was ±0.002 units). These in-situ collected data improve the knowledge about the biogeochemistry in eastern boundary transitional areas and allows a better understanding of the role in the climate change of archipelagic waters, coastal regions and island/continental shelves. The provided datasets can be used in further biogeochemical studies in the Macaronesia region and in the entire Northeast Atlantic. The monitoring and data collection received fundings from the Atmosphere-Ocean-Islands-Biogeochemical interactions in the Macaronesian Archipelagos of Cabo Verde, the Canaries and Madeira project (AIMAC project) and the European Union's Horizon 2020 research and innovation program under grant agreement Nº 820989 (COMFORT project). In this case, the measurements complemented those done for iron study (Santana-Casiano and Quack, 2021).

Description: The data includes carbonate system variables (pH, total dissolved inorganic carbon, total alkalinity and pCO2) measured in the water column of the European Station for time series in the Ocean, ESTOC, located at 29º10'N and 15º30'W in the northeast Atlantic Ocean, together with temperature and salinity. The period of ESTOC data started in February 1994 but the carbonate variables started on October 1995. Data for ESTOC until year 2010 were already included in PANGAEA (see related datasets).This new dataset includes all available water column measured carbonate variables from 2011 to April 2023 and new data for two visits before 2010, one in October 2007 and March 2008. A total of 626, 392 and 626 new samples are included, respectively, for total alkalinity (AT), pH in total scale (pHT) and total dissolved inorganic carbon (CT). Until 2011, sampling was done every two months. During 2012 and 2013, ship operations were stopped and re-started on February 2014, keeping since, seasonal visits to ESTOC. In 2016, a surface buoy with physical and biochemical sensors was included in ESTOC. Starting on February 2019, a General OceanicTM GO 8050 continuous underway pCO2 system with four calibration gasses together with sea surface temperature and salinity sensors (Curbelo-Hernández et al., 2021; doi:10.1016/j.scitotenv.2021.145804) was included in a volunteer observing ship (CanOA VOS line, ICOS-ERIC, https://meta.icos-cp.eu/labeling/ last visited 07/05/2023) passing close to ESTOC (25-30 km to the East). This pCO2 system has provided a total of 1502 data starting on February 2nd, 2019. For the pH in total scale, a potentiometric system was used during the first 2 years, calibrated again TRIS-artificial seawater buffers at 25ºC. After 1996, an automatic spectrophotometric pH system was developed using m-cresol purple with a precision of ± 0.0015 (n=15 for different batches of certified reference material, CRM) (González-Dávila et al., 2003). Samples for AT were potentiometrically titrated with HCl in a close cell to the carbonic acid endpoint until 2004, as described in detail in Mintrop et al. (2000; doi:10.7773/cm.v26i1.573). Since 2004, AT and CT were measured for the same 500 ml borosilicate glass bottle sample using a VINDTA 3C system (González-Dávila et al., 2010; doi:10.5194/bg-7-3067-2010) with coulometric determination. Sample accuracy for any of the three measured variables (pH ±0.0015; AT ±1.5 µmol kg-1, CT ± 1.0 µmol kg-1) has been maintained by routine analysis of seawater certified reference materials (CRMs; prepared and acquired to Andrew Dickson, UCSD). After 2019, the surface molar fraction of CO2 (xCO2) has been measured using a GO 8050 system described in detail in Curbelo-Hernández et al. (2021; Doi: 10.1016/j.scitotenv.2021.145804).

Description: Discrete seawater samples in a Weddell Sea coastal polynya along the Ekström Ice Shelf were collected from two sets of repeat CTD casts, capturing tidal variability in the water column. One set was collected during RV POLARSTERN expedition PS89, between 8 and 11 January 2015. The second set was collected during RV POLARSTERN expedition PS117, between 11 and 12 January 2019. Dissolved inorganic carbon (DIC) and total alkalinity (TA) were measured using coulometric titration and potentiometric titration, respectively, on a VINDTA 3C system. DIC and TA have been normalised to salinity: nDIC and nTA. Nutrients were measured with UV-Vis spectrophotometry and a continuous gas-segmented flow auto-analyser.