Papers by Melchor Gonzalez Davila
Biogeosciences, 2021
We present a new natural carbon dioxide (CO 2 ) system located off the southern coast of the isla... more We present a new natural carbon dioxide (CO 2 ) system located off the southern coast of the island of La Palma (Canary Islands, Spain). Like CO 2 seeps, these CO 2 submarine groundwater discharges (SGDs) can be used as an analogue to study the effects of ocean acidification (OA) on the marine realm. With this aim, we present the chemical characterization of the area, describing the carbon system dynamics, by measuring pH, A T and C T and calculating aragonite and calcite. Our explorations of the area have found several emission points with similar chemical features.
Underway physical oceanography and carbon dioxide measurements during QUIMA cruise QUIMA20060211
Deep-Sea Research II 49 (2002) 4145–4161 The carbon dioxide system in the Strait of Gibraltar
During the CANIGO Project pHT and total alkalinity (AT) and continuous underway fugacity of carbo... more During the CANIGO Project pHT and total alkalinity (AT) and continuous underway fugacity of carbon dioxide (fCO2) measurements were carried out in the Strait of Gibraltar in September 97 and February 98. The pH values describe the most representative water masses in the area, including the Levantine Intermediate Water (7.86) and West Mediterranean Deep Water (7.89). The linear relationships between the alkalinity (at all depths) and TIC (below the euphotic zone) with salinity were determined (AT 2353 (70.4)+92.28 (70.31) (S36.0), r2 0:998 and CT 2119 (71.4)+79.52 (70.76) (S–36.0), r2 0:991). A net alkalinity outflow of –1.9070.04mol yr1 was estimated. The normalised alkalinity and total inorganic carbon were higher in the Mediterranean waters than in the Atlantic. The Mediterranean seawater in the 200–400m range shows higher CT values East (2323mmol kg 1) rather than the West (2301mmol kg1) of the Strait of Gibraltar, which is related to mixing processes through the interface layer....
Underway carbon dioxide in the Atlantic Ocean of Quima cruise QUIMA20050821
Ciencias Marinas, 2000
Seawater was sampled from different depths in the North Atlantic Ocean (Canary Islands region) an... more Seawater was sampled from different depths in the North Atlantic Ocean (Canary Islands region) and distributed among three different labs for the determination of titration alkalinity. Analysis was performed by potentiometric methods, involving titration in a closed cell, titration in an open cell and a two end-point acid addition method. The precision, which is the sample reproducibility taken from the mean standard deviation for replicate measurements, was between 0.45 and 0.90 µmol · kg–1 for the individual labs. Accuracy, here taken as the deviation for the values of a lab from the mean of all three, was mostly below 1 µmol · kg–1 and never exceeded 0.1% of the sample value. Mean standard deviation for all labs and all samples was 0.87 µmol · kg–1, once the individual methods were calibrated using certified reference material (CRM). Without CRM calibration, the mean standard deviation would increase to 2.8 µmol · kg–1. The conclusion is that current high precision methods for al...
Experimentación en química marina. Parte II : química marina : manual de laboratorio
International Journal of Remote Sensing, 2014
Submarine volcanic eruptions took place at the island El Hierro (Canary Islands) between October ... more Submarine volcanic eruptions took place at the island El Hierro (Canary Islands) between October 2011 and March 2012. The event produced plumes of discoloured waters due to the discharge of volcanic matter, magmatic gases, and hydrothermal fluids. The expelled materials, which behaved like oceanic tracers, were detected from the site of the volcano to the open sea by remote-sensing techniques using different level-2 (L2) products of the Moderate Resolution Imaging Spectroradiometer (MODIS) sensor. In order to assess the effect of the anomalous turbidity, three atmospheric correction schemes were evaluated: SeaWiFS Data Analysis System (SeaDAS) standard, near-infrared-shortwave-infrared (NIR-SWIR), and Management Unit of the North Sea Mathematical Models (MUMM). The comparison between them verified that the SeaDAS standard atmospheric correction was the most suitable. The downwelling diffuse attenuation coefficient at 490 nm (K d ( )) was used as a measure of plume intensity in comparison with other submarine volcanic eruptions. The MODIS-derived K d (490) values verified that the intensity of the El Hierro plume was moderate. Only in some specific situations did the values barely exceed 0.4 m -1 . The remote-sensing reflectance (R rs ) was used for the characterization of the affected waters. The R rs spectra also allowed a comparison with other volcanic and sulphide events reported in previous studies. Similarities were found, both with submarine volcanic eruptions in the southwestern Pacific and with sulphide events at the Namibian coast, in composition and properties of optically active water constituents. A classification schema based on K d (490) values and R rs ratios was developed and used in connection with MODIS red-green-blue (RGB) composites as well as surface current velocities from altimeter missions to investigate the spatio-temporal development of the volcanic plume. The spreading and transport of volcanic material observed at the ocean surface was caused by the predominant surface currents coupled with different mesoscale eddies. Discoloured waters were identified more than 200 km away from the eruption site. Field data from oceanographic surveys verified the high concentration of sulphur compounds in affected waters and confirmed the overestimation by the MODIS default algorithm of chlorophyll-a concentrations in the volcanic plume.
Scientia Marina, 2001
During the cruise F/S Poseidon 212/3 (September 30-October 8, 1995) determination of carbon syste... more During the cruise F/S Poseidon 212/3 (September 30-October 8, 1995) determination of carbon system variables was carried out over the section of La Palma-La Graciosa and at the ESTOC station in the Canary Island area. Total alkalinity and pH in the total scale at 25ºC were determined at 24 stations from surface to bottom. In this area, the presence of different water masses can be traced by the carbon system variables. NACW is defined by a strong gradient of A T and pH from 150 to 750 m. MW is characterised by high values of A T and pH between 1000 to 1200 m and AAIW signals are found at around 900 m in the strait between Gran Canaria and Fuerteventura with low A T , low pH and a maximum of fCO 2 . Assuming an atmospheric mean value of fCO 2 of 360 µatm and an average surface value of 393±7 µatm, we can conclude that during this cruise this oceanic area tends to release CO 2 into the atmosphere, acting as a weak source with a carbon flux towards the atmosphere of +8.0±1.8 mmol•m -2 d -1 . The saturation levels in the Canary Island area have been found to be higher than 3600 m for calcite and 2700 m for aragonite. The inorganic carbon/organic carbon ratio (IC/OC) varies from 0.07 at 300 m to 0.5 at 3000 m. The IC/OC ratio shows that about a 34% increase in the C T of the deep water is contributed by the inorganic CaCO 3 dissolution. The IC at 300 m is around 7 µmol kg -1 , increasing with depth to 37.5 µmol kg -1 at 3700 m.
Scientia Marina, 2010
The measurement of the surface molar fraction of CO 2 (atmosphere and sea water) and water column... more The measurement of the surface molar fraction of CO 2 (atmosphere and sea water) and water column pH T , total alkalinity, A T , nutrients and oxygen were carried out in spring 2000 at the European Station for Time Series in the Ocean at the Canary Islands (ESTOC) and in the area located south of the Canary Islands. The significant eddy field strongly affecting the pattern of the chemical and carbonate system variables is presented and discussed. A mixing model based on the thermohaline properties of the water masses was established. The model explained over 97% of the variability found in the distribution of the chemical variables. Intermediate waters to the south of the Canary Islands show a high contribution of Antarctic waters with about 5% of pure Antarctic Intermediate Water. Moreover, the surface structure affected the atmosphere-ocean carbon dioxide exchange, making the area act as a CO 2 sink taking up 9.1 mmol m -2 week -1 , corresponding to 0.03 Mt of CO 2 which were taken up by the area in a week at the end of March 2000.
Marine Chemistry, 1995
Metal ions become adsorbed to algal surface groups and complexed to organic material released by ... more Metal ions become adsorbed to algal surface groups and complexed to organic material released by algae at all growth stages influencing their distribution in the seawater. In this study, the differential pulse anodic stripping voltammetry (DPASV) technique was used to evaluate the adsorption and the interaction between the exudates excreted by the marine algae Dunaliella tertiolecta and Pb 2+. The adsorption process has been studied in seawater as a function of pH (2 to 8), temperature (5 to 45"C), salinity (5 to 36), biomass and the presence of a second metal, copper. The rate of adsorption was found to occur in two steps: first a relatively fast adsorption step (10 min) and second, a slow, diffusion-controlled uptake into the cells. A two-site model which considers the presence of two major functional groups, namely: highaffinity binding and low-affinity binding was used to fit the experimental data. The values for the stability constants of * Pb2+ on these two groups were log K t,, = 8.40 & 0.18 and log *@H,2 = 7.25 & 0.31. The high-affinity constant is similar to the complexing capacity of the exudates (log *K$ = 8.40 f 0.05) produced by the alga showing that extracellular ligands play an important role in buffering the concentration of the free metal concentration. A decrease in the temperature and salinity result in lower adsorption of Pb2+ to the algae and a higher complexation of lead with the exudate. The presence of copper decreases the lead complexation to the algal surface by 70%.
Marine Chemistry, 1997
The uptake of iron by the marine diatom Thalassiosira weissflogii and the green algae Dunaliella ... more The uptake of iron by the marine diatom Thalassiosira weissflogii and the green algae Dunaliella tertiolecta in seawater has been investigated. Computations were made of the rate constants for the binding of iron to specific cell surface-associated transport ligands and the subsequent slow active uptake into the cytoplasm of the cells. Although both algae transport Fe, the sorption constants and the kinetic parameters are markedly different and temperature dependent. The sorption constants, which are one order of magnitude higher for T weissjlogii versus D. tertiolecta (2.5 X 10m9 1 cell-' vs. 1 cell-') at 2X, give us a measure of the theoretical number of transport sites needed by each cell. The effects on the iron speciation and on the rate of iron uptake due to the addition of different concentrations of Zn(II), Al(II1) and Cd(D) have also been determined. The results confirm that while iron is taken up via specific sites on the cell surfaces, synergistic and antagonistic effects on the iron rate uptake for T. weissflogii and D. tertiolecta, respectively, have been found and evaluated. 0 1997 Elsevier Science B.V.
Marine Chemistry, 2014
Spectrophotometric study of catechol oxidation by aerial O 2 in alkaline aqueous solutions contai... more Spectrophotometric study of catechol oxidation by aerial O 2 in alkaline aqueous solutions containing Mg(II) ions. Spectrosc. Lett. 31,[327][328][329][330][331][332][333] The authors also wish to replace Eqs. ( ), (3), and (4) with Fe(II) + O 2 •-→ Fe(III) + H 2 O 2 Fe(II) + H 2 O 2 →Fe(III) + OH • + OH - Fe(II) + OH • →Fe(III) + OH -.
Geochimica et Cosmochimica Acta, 1990
Environmental Science & Technology, 2005
The oxidation of Fe(II) by molecular oxygen at nanomolar levels has been studied using a UV-Vis s... more The oxidation of Fe(II) by molecular oxygen at nanomolar levels has been studied using a UV-Vis spectrophotometric system equipped with a long liquid waveguide capillary flow cell. The effect of pH (6.5-8.2), NaHCO 3 (0.1-9 mM), temperature (3-35 °C), and salinity (0-36) on the oxidation of Fe(II) are presented. The first-order oxidation rates at nanomolar Fe(II) are higher than the values at micromolar levels at a pH below 7.5 and lower than the values at a higher pH. A kinetic model has been developed to consider the mechanism of the Fe(II) oxidation and the speciation of Fe(II) in seawater, the interactions between the major ions, and the oxidation rates of the different Fe(II) species. The concentration of Fe(II) is largely controlled by oxidation with O 2 and O 2 •-but is also affected by hydrogen peroxide that may be both initially present and formed from the oxidation of Fe(II) by superoxide. The model has been applied to describe the effect of pH, concentration of NaHCO 3 , temperature, and salinity on the kinetics of Fe(II) oxidation. At a pH over 7.2, Fe(OH) 2 is the most important contributing species to the apparent oxidation rate. At high levels of CO 3 2-and pH, the Fe(CO 3 ) 2 2-species become important. At pH values below 7, the oxidation rate is controlled by Fe 2+ . Using the model, log k i values for the most kinetically active species (Fe 2+ , Fe(OH) + , Fe(OH) 2 , Fe(CO 3 ), and Fe(CO 3 ) 2 2-) are given that are valid over a wide range of temperature, salinity, and pH in natural waters. Model results show that when H 2 O 2 concentrations approach the Fe(II) concentrations used in this study, the oxidation of Fe(II) with H 2 O 2 also needs to be considered.
Environmental Science & Technology, 1992
las Pamas G.C.• P.O. Box 550. Span • The lindane ~experimenb oonducted using ehitin u an adsorben... more las Pamas G.C.• P.O. Box 550. Span • The lindane ~experimenb oonducted using ehitin u an adsorbent in seawater show that the partitioo coerrlCienta decrease as adsorbent concentration increases and that sorption and deeorption are not completely reversible at chitin concentrations lower than 10 gIL. Tbese two effectl have been anaI)'%ed in tenos oC a revenible-resistant tWOoCOmponent model oC sorptiondeaorption. Further at.udielI varying the temperature (from 5 lo oi5 DC) and salinity (Cmm 15 lo 361.) were carried out 10 dariCy the mechanUllllS responsible Cor these effectl. Tbe partition coefficients Cor tbe resistant and reversible components are Cound 10 behave quite regularly in all the elperimental conditMms: the reversible oomponent is Cairly constant in the range ol45:!: 4 L/k¡ wbereas tbe resistant oomponent partition coetrlcient is inven¡e in relation 10 the ehitin concentration, and it approaches zero wben tbe chitin concentration is held at values bigber than lO gIL. Tbe temperature and salinity do not affect tbe reversible component partition coefficient, and it is sbown tbat the resistant component decreases botb as temperature increases and as salinity decreases. Lindane sorption in different types of sites ond lo differing degrees can acoount Cor tbe observed effects.
Binding of Cu(II) to the Surface and Exudates of the Alga Dunaliella tertiolecta in Seawater
Environmental Science & Technology, 1995
Binding of Cu(ll) to the Surface ... MELCHOR GONZALEZ-DAVILA,* J. MAGDALENA SANTANA-CASIANO, AND ... more Binding of Cu(ll) to the Surface ... MELCHOR GONZALEZ-DAVILA,* J. MAGDALENA SANTANA-CASIANO, AND JESUS PEREZ-PENA Departamento de Quimica, Facultad de Ciencias del Mar, Uniuersidad de Las Palmas de Gran Canaria, Las Palmas 35071, Spain
Trends in North Atlantic sea-surface fCO2 from 1990 to 2006
Deep Sea Research Part II: Topical Studies in Oceanography, 2009
... In the last few years there has been a rapid increase in the published observations of air–se... more ... In the last few years there has been a rapid increase in the published observations of air–sea ΔfCO 2 over large regions of the North Atlantic (Bates, 2007; Corbière et al., 2007; Lefevre et al., 2004; Omar and Olsen, 2006; Santana-Casiano et al., 2007; Schuster and Watson ...
Collection of Czechoslovak Chemical Communications, 1989
Infrared and Raman spectra of 2-mercaptoimidazole and 2-mercaptothiazole in solid state as well a... more Infrared and Raman spectra of 2-mercaptoimidazole and 2-mercaptothiazole in solid state as well as i.r. spectra of 2-mercaptothiazole in HCCl3 and CS2 0.05M solutions have been investigated. A general assignment of all the observed bands is proposed for both fundamental vibrations and for overtone and combination bands. For 2-mercaptothiazole, the thiocarbonyl-form, intermolecularly hydrogen-bonded dimers in solid state, and unassociated molecules in dilute solutions of inert solvents have been established. Finally, based on this data, thermodynamic functions have been computed.
Vibrational spectra and thermodynamic properties of thiazole, 2-aminothiazole, 2-amino-[2H]-thiazole and 2-amino-[2H2]-thiazole
Collection of Czechoslovak Chemical Communications, 1989
Infrared and Raman spectra of thiazole have been reinvestigated with new assignments of overtone ... more Infrared and Raman spectra of thiazole have been reinvestigated with new assignments of overtone and combination bands being proposed. Infrared spectra in the solid phase and in different solutions for 2-aminothiazole and 2-amino-[2H2]-thiazole, as well as Raman spectrum of microcrystalline powder for 2-aminothiazole were also studied and a general assignment for all the observed bands have been proposed. The present assignment satisfies the isotopic product rule for i.r. fundamentals. On this basis thermodynamic functions have been computed.
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Papers by Melchor Gonzalez Davila