García-Ibáñez
Maribel I.
García-Ibáñez
Maribel I.
No Thumbnail Available
3 results
Search Results
Now showing
1 - 3 of 3
-
ArticleNitrate supply routes and impact of internal cycling in the North Atlantic Ocean inferred from nitrate isotopic composition(American Geophysical Union, 2021-04-02) Deman, Florian ; Fonseca-Batista, Debany ; Roukaerts, Arnout ; García-Ibáñez, Maribel I. ; Le Roy, Emilie ; Thilakarathne, E. P. D. N. ; Elskens, Marc ; Dehairs, Frank ; Fripiat, FrancoisIn this study we report full-depth water column profiles for nitrogen and oxygen isotopic composition (δ15N and δ18O) of nitrate (NO3−) during the GEOTRACES GA01 cruise (2014). This transect intersects the double gyre system of the subtropical and subpolar regions of the North Atlantic separated by a strong transition zone, the North Atlantic Current. The distribution of NO3− δ15N and δ18O shows that assimilation by phytoplankton is the main process controlling the NO3− isotopic composition in the upper 150 m, with values increasing in a NO3− δ18O versus δ15N space along a line with a slope of one toward the surface. In the subpolar gyre, a single relationship between the degree of NO3− consumption and residual NO3− δ15N supports the view that NO3− is supplied via Ekman upwelling and deep winter convection, and progressively consumed during the Ekman transport of surface water southward. The co-occurrence of partial NO3− assimilation and nitrification in the deep mixed layer of the subpolar gyre elevates subsurface NO3− δ18O in comparison to deep oceanic values. This signal propagates through isopycnal exchanges to greater depths at lower latitudes. With recirculation in the subtropical gyre, cycles of quantitative consumption-nitrification progressively decrease subsurface NO3− δ18O toward the δ18O of regenerated NO3−. The low NO3− δ15N observed south of the Subarctic Front is mostly explained by N2 fixation, although a contribution from the Mediterranean outflow is required to explain the lower NO3− δ15N signal observed between 600 and 1500 m depth close to the Iberian margin.
-
ArticleThe Ra-226–Ba relationship in the North Atlantic during GEOTRACES-GA01(Copernicus Publications on behalf of the European Geosciences Union, 2018-05-17) Le Roy, Emilie ; Sanial, Virginie ; Charette, Matthew A. ; van Beek, Pieter ; Lacan, Francois ; Jacquet, Stéphanie H. M. ; Henderson, Paul B. ; Souhaut, Marc ; García-Ibáñez, Maribel I. ; Jeandel, Catherine ; Perez, Fiz F. ; Sarthou, GeraldineWe report detailed sections of radium-226 (226Ra, T1∕2 = 1602 years) activities and barium (Ba) concentrations determined in the North Atlantic (Portugal–Greenland–Canada) in the framework of the international GEOTRACES program (GA01 section – GEOVIDE project, May–July 2014). Dissolved 226Ra and Ba are strongly correlated along the section, a pattern that may reflect their similar chemical behavior. Because 226Ra and Ba have been widely used as tracers of water masses and ocean mixing, we investigated their behavior more thoroughly in this crucial region for thermohaline circulation, taking advantage of the contrasting biogeochemical patterns existing along the GA01 section. We used an optimum multiparameter (OMP) analysis to distinguish the relative importance of physical transport (water mass mixing) from nonconservative processes (sedimentary, river or hydrothermal inputs, uptake by particles and dissolved–particulate dynamics) on the 226Ra and Ba distributions in the North Atlantic. Results show that the measured 226Ra and Ba concentrations can be explained by conservative mixing for 58 and 65 % of the samples, respectively, notably at intermediate depth, away from the ocean interfaces. 226Ra and Ba can thus be considered conservative tracers of water mass transport in the ocean interior on the space scales considered here, namely, on the order of a few thousand kilometers. However, regions in which 226Ra and Ba displayed nonconservative behavior and in some cases decoupled behaviors were also identified, mostly at the ocean boundaries (seafloor, continental margins and surface waters). Elevated 226Ra and Ba concentrations found in deepwater in the West European Basin suggest that lower Northeast Atlantic Deep Water (NEADWl) accumulates 226Ra and Ba from sediment diffusion and/or particle dissolution during transport. In the upper 1500 m of the West European Basin, deficiencies in 226Ra and Ba are likely explained by their incorporation in planktonic calcareous and siliceous shells, or in barite (BaSO4) by substitution or adsorption mechanisms. Finally, because Ba and 226Ra display different source terms (mostly deep-sea sediments for 226Ra and rivers for Ba), strong decoupling between 226Ra and Ba were observed at the land–ocean boundaries. This is especially true in the shallow stations near the coasts of Greenland and Newfoundland where high 226Ra ∕ Ba ratios at depth reflect the diffusion of 226Ra from sediment and low 226Ra ∕ Ba ratios in the upper water column reflect the input of Ba associated with meteoric waters.
-
ArticleUncertainty sources for measurable ocean carbonate chemistry variables(Association for the Sciences of Limnology and Oceanography (ASLO), 2023-12-14) Carter, Brendan R. ; Sharp, Jonathan D. ; Dickson, Andrew G. ; Alvarez, Marta ; Fong, Michael B. ; Garcia-Ibanez, Maribel I. ; Woosley, Ryan J. ; Takeshita, Yuichiro ; Barbero, Leticia ; Byrne, Robert H. ; Cai, Wei-Jun ; Chierici, Melissa ; Clegg, Simon L. ; Easley, Regina A. ; Fassbender, Andrea J. ; Fleger, Kalla L. ; Li, Xinyu ; Martin-Mayor, Macarena ; Schockman, Katelyn M. ; Wang, Zhaohui AleckThe ocean carbonate system is critical to monitor because it plays a major role in regulating Earth's climate and marine ecosystems. It is monitored using a variety of measurements, and it is commonly understood that all components of seawater carbonate chemistry can be calculated when at least two carbonate system variables are measured. However, several recent studies have highlighted systematic discrepancies between calculated and directly measured carbonate chemistry variables and these discrepancies have large implications for efforts to measure and quantify the changing ocean carbon cycle. Given this, the Ocean Carbonate System Intercomparison Forum (OCSIF) was formed as a working group through the Ocean Carbon and Biogeochemistry program to coordinate and recommend research to quantify and/or reduce uncertainties and disagreements in measurable seawater carbonate system measurements and calculations, identify unknown or overlooked sources of these uncertainties, and provide recommendations for making progress on community efforts despite these uncertainties. With this paper we aim to (1) summarize recent progress toward quantifying and reducing carbonate system uncertainties; (2) advocate for research to further reduce and better quantify carbonate system measurement uncertainties; (3) present a small amount of new data, metadata, and analysis related to uncertainties in carbonate system measurements; and (4) restate and explain the rationales behind several OCSIF recommendations. We focus on open ocean carbonate chemistry, and caution that the considerations we discuss become further complicated in coastal, estuarine, and sedimentary environments.