Stable isotopes in surface waters of the Atlantic Ocean: Indicators of ocean-atmosphere water fluxes and oceanic mixing processes

Publisher's version (útgefin grein)The surface ocean hydrological cycle is explored based on ∼300 new δ18O and δD measurements from surface waters of the Atlantic Ocean and the Mediterranean Sea over the period 2010–2016. Our approach combines these surface observations with salinity (S) and stable isotope measurements of atmospheric water vapor. The distinct regional S‐δ distributions are used to identify different surface water masses and their horizontal advection. Moreover, based on assumptions on the δ‐S characteristics of seawater sources and the isotope composition of the evaporative (δe) and meteoric water (δMW) fluxes, the δ‐S distribution is used to indicate the relative importance of evaporation (E) and meteoric water inputs (MW). Here δe is estimated from the Craig and Gordon's equation using 120 days of measurements of the ambient air above the Atlantic Ocean collected during three cruises. To provide quantitative estimates of the E:MW ratio, we use the box model from Craig and Gordon (1965). This identifies the subtropical gyre as a region where E:MW ∼2 and the tropical ocean as a region were MW:E ∼2. Finally, we show that the δ18O‐δD distribution is better represented by a linear fit than the δ‐S relationship, even in basins governed by different hydrological processes. We interpret the δ18O‐δD distribution considering the kinetic fractionation processes associated with evaporation. In the tropical region where MW exceeds E, the δ18O‐δD distribution identifies the MW inputs from their kinetic signature, whereas in regions where E exceeds MW, the δ18O‐δD distribution traces the humidity at the sea surface.The Picarro equipment was purchased with support from different French institutions, in particular by IPSL, LOCEAN, LMD, and LATMOS. Work during Strasse on R/V Thalassa and Pirata FR24 on R/V Suroit was supported by three LEFE/IMAGO INSU grants (Strasse, Strasse/SPURS, and PIRATA), with additional support for equipment from IPSL and from OSU Ecce Terra. The authors gratefully acknowledge the association “Les Amis du Jeudi et du Dimanche” for the measurements aboard the RARA AVIS. The authors thank the TOSCA‐SMOS program whose founding was used for installing the SBE45 onboard the RaRa Avis Vessel. The Suratlant Project, as well as the data collection from the Toucan, Colibri and Cap San Lorenzo, are supported by SO SSS in France. Data collection onboard Ovide‐2010 (doi:10.3334/CDIAC/OTG.CLIVAR_OVIDE_2010) and Ovide‐2012 (doi:10.3334/CDIAC/OTG.CLIVAR_OVIDE_2012) cruises was supported by LEFE‐INSU. We also acknowledge Philipe Poupon and Cedric Courson for the sampling aboard the sailing boat Fleur Austral, Tara Expéditions for the sampling aboard the sailing boat Tara, CSIC for the sampling aboard the Sarmiento de Gamboa during the Midas Cruise and MOOSE program (ALLENVI‐INSU) for the sampling onboard R/V L'ATALANTE during the MOOSE‐GE2016 cruise (doi:10.17600/16000700). The authors thank the National Power Company of Iceland Landsvirkjun for their contribution to this research. The data are shared with the free Global Seawater Oxygen‐18 database [Schmidt et al., 1999].Peer reviewe

Relation between the water isotopic composition in the North Atlanticmarine boundary layer and the boundary layer dynamic

Publisher's version (útgefin grein)Water isotopes are powerful tracers of the hydrological cycle and can be used to serve many purposes in climateresearch. Here, we use water isotopic measurements – in the vapour and in the precipitations – from Bermudaand Iceland measurement facilities, as well as from the Infrared Remote Sensing Interferometer (IASI), toinvestigate the feedback between evaporation and the boundary layer development through shallow convection.Icelandic Research Institute (no. 152229)Peer reviewe

The Surtsey volcano geothermal system: An analogue for seawater-oceanic crust interaction with implications for the elemental budget of the oceanic crust

Pre-print (óritrýnt handrit)Surtsey is a young volcanic island in the offshore extension of Iceland's southeast rift zone that grew from the seafloor during explosive and effusive eruptions in 1963–1967. In 1979, a cored borehole (SE-1) was drilled to 181 m depth and in 2017 three cored boreholes (SE-2a, SE-2b and SE-3) were drilled to successively greater depths. The basaltic deposits host a low-temperature (40–141 °C) seawater-dominated geothermal system. Surtsey provides an ideal environment to study water-rock interaction processes in a young seawater geothermal system. Elemental concentrations (SiO2, B, Na, Ca, Mg, F, dissolved inorganic carbon, SO4, Cl) and isotope contents (δD, δ18O) in borehole fluids indicate that associated geothermal waters in submarine deposits originated from seawater modified by reactions with the surrounding basalt. These processes produce authigenic minerals in the basaltic lapilli tuff and a corresponding depletion of certain elements in the residual waters. Coupling of measured and modelled concentrations investigates the effect of temperature and associated abundance of authigenic minerals on chemical fluxes from and to the igneous oceanic crust during low-temperature alteration. The annual chemical fluxes calculated at 50–150 °C range from −0.01 to +0.1×1012 mol yr−1 for SiO2, +0.2 to +129×1012 mol yr−1 for Ca, −129 to −0.8×1012 mol yr−1 for Mg and −21 to +0.4 × 1012 mol yr−1 for SO4 where negative values indicate chemical fluxes from the ocean into the oceanic crust and positive values indicate fluxes from the oceanic crust to the oceans. These flux calculations reveal that water-rock interaction at varying water-rock ratios and temperatures produces authigenic minerals that serve as important sinks of seawater-derived SiO2, Mg and SO4. In contrast, water rock interaction accompanied by dissolution of basaltic glass and primary crystal fragments provides a significant source of Ca. Such low-temperature alteration could effectively influence the elemental budget of the oceanic igneous crust and ocean waters. The modeling provides insights into water chemistries and chemical fluxes in low temperature MOR recharge zones. Surtsey also provides a valuable young analogue for assessing the chemical evolution of fluid discharge over the life cycles of seamounts in ridge flank systems.Funding for this project was provided by the University of Iceland Recruitment fund, the International Continental Scientific Drilling Program (ICDP) through a grant to the SUSTAIN project, the Icelandic Science Fund, ICF-RANNÍS, the Bergen Research Foundation and K.G. Jebsen Centre for Deep Sea Research at University of Bergen, Norway, the German Research Foundation (DFG), and DiSTAR, Federico II, University of Naples, Federico II, Italy. The University of Utah, USA and the two Icelandic power companies Reykjavík Energy and Landsvirkjun, contributed additional funds. The authors would like to thank P. Bergsten, A.M. di Stefano, C.F. Gorny, J. Gunnarsson-Robin, G.H. Guðfinsson, Þ. Högnadóttir, E.W. Marshall, R. Ólafssdóttir, D.B. Ragnarsson and Þ.M. Þorbjarnardóttir for their contribution and assistance during sampling, sample preparation, analyses and data evaluation. The authors would like to thank M. E. Böttcher for careful editorial handling. Two anonymous reviewers and J. Alt are thanked for their thoughtful and valuable reviews

Atmospheric and oceanic stable isotope signatures of a cold-air outbreakin Iceland during YOPP SOP1 and IGP

Publisher's version (útgefin grein)North-Atlantic Cold-air outbreaks are weather events characterised by extensive fluxes of latent heat to theatmosphere. Understanding the water budget of these weather events is important for the weather impact indownstream coastal areas. We use here observations of the stable isotopic composition of water vapour andprecipitation, expressed by the quantities dD, d18O, d17O and the secondary parameters d-excess and 17O-excess,to extract information about the origin and condensation history of water vapour evaporating during a period ofcold-air outbreaks north of IcelandIcelandic research institute (RANNÍS 152229

Freshwater exports from Arctic to the Labrador and Greenland shelf andslope.

Publisher's version (útgefin grein)We investigate whether one can detect changes in the freshwater contributions to the North Atlantic subpolar gyre(SPG), in light of the observed recent decrease of salinity in the region. We focus on two important conduits offreshwater from the Arctic to the interior North Atlantic subpolar gyre: the Coastal Labrador Current and thesouthern Greenland shelf, and use a dataset of different freshwater tracers from a set of cruises over the period2010-2014.Icelandic research institute (RANNÍS no. 152229)Peer reviewe

Origin of 14C in Icelandic Groundwater

We report the first attempt to date Icelandic groundwater by the radiocarbon dating technique. We propose that boron concentrations of the water samples can be taken as a measure of the amount of dead CO2 in the groundwater leached from rock. By assuming that the ratio of boron to CO2 is the same in the rock and groundwater it is possible to correct the 14C concentration for the contribution of rock-derived carbon in the groundwater and thus calculate the initial (undiluted) 14C concentration. When this correction is applied, the values for the cold and warm waters lie in the range 60 to 110 pMC, which is in accordance with the estimated residence time for the groundwater. We have also calculated the fractions of atmospheric and organic carbon in the water, based on the delta-13C measurements, and the results agree well with the general hydrology and vegetational cover of the areas. Results from geothermal systems indicate that it is possible to use 14C to estimate relative age differences of the water in a particular geothermal areaThis material was digitized as part of a cooperative project between Radiocarbon and the University of Arizona Libraries.The Radiocarbon archives are made available by Radiocarbon and the University of Arizona Libraries. Contact [email protected] for further information.Migrated from OJS platform February 202

Successful AMS 14C Dating of Non-Hydraulic Lime Mortars from the Medieval Churches of the Åland Islands, Finland

Fifteen years of research on accelerator mass spectrometry (AMS) radiocarbon dating of non-hydraulic mortar has now led to the establishment of a chronology for the medieval stone churches of the land Islands (Finland), where no contemporary written records could shed light on the first building phases. In contrast to other material for dating, well-preserved mortar is abundantly available from every building stage. We have gathered experience from AMS dating of 150 land mortar samples. Approximately half of them have age control from dendrochronology or from 14C analysis of wooden fragments in direct contact with the mortar. Of the samples with age control, 95% of the results agree with the age of the wood. The age control from dendrochronology, petrologic microscopy, chemical testing of the mortars, and mathematical modeling of their behavior during dissolution in acid have helped us to define criteria of reliability to interpret the 14C results when mortar dating is the only possibility to constrain the buildings in time. With these criteria, 80% of all samples reached conclusive results, and we have thus far been able to establish the chronology of 12 out of the 14 churches and chapels, while 2 still require complementary analyses.The Radiocarbon archives are made available by Radiocarbon and the University of Arizona Libraries. Contact [email protected] for further information.Migrated from OJS platform February 202

Stable isotopes in surface waters of the Atlantic Ocean: Indicators of ocean-atmosphere water fluxes and oceanic mixing processes

International audienceThe surface ocean hydrological cycle is explored based on ~ 300 new $\delta^{18}$O and $\delta^{18}$D measurements from surface waters of the Atlantic Ocean and the Mediterranean Sea over the period 2010–2016. Our approach combines these surface observations with salinity (S) and stable isotope measurements of atmospheric water vapor. The distinct regional S-$\delta$ distributions are used to identify different surface water masses and their horizontal advection. Moreover, based on assumptions on the $\delta$-S characteristics of seawater sources and the isotope composition of the evaporative ($\delta_e$) and meteoric water ($\delta_{MW}$) fluxes, the $\delta$-S distribution is used to indicate the relative importance of evaporation (E) and meteoric water inputs (MW). Here $\delta_e$ is estimated from the Craig and Gordon’s equation using 120 days of measurements of the ambient air above the Atlantic Ocean collected during three cruises. To provide quantitative estimates of the E:MW ratio, we use the box model from Craig and Gordon (1965). This identifies the subtropical gyre as a region where E:MW ~ 2 and the tropical ocean as a region were MW:E ~ 2. Finally, we show that the $\delta^{18}$O-$\delta$D distribution is better represented by a linear fit than the $\delta$-S relationship, even in basins governed by different hydrological processes. We interpret the $\delta^{18}$O-$\delta$D distribution considering the kinetic fractionation processes associated with evaporation. In the tropical region where MW exceeds E, the $\delta^{18}$O-$\delta$D distribution identifies the MW inputs from their kinetic signature, whereas in regions where E exceeds MW, the $\delta^{18}$O-$\delta$D distribution traces the humidity at the sea surface

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From the 16th International Radiocarbon Conference held in Gronigen, Netherlands, June 16-20, 1997.We report an age-depth profile for the sediments of the Lake Hestvatn, southern Iceland, based on 14C analyses of the organic fraction of bulk sediment samples, molluscs and foraminifera. Our age-depth curve is supported by the occurrence of the well-dated Vedde ash in the lowermost part of the sediments. Comparison of foraminifera dates with the age of the Vedde ash indicates a reservoir age of ca. 400 yr. The results suggest that the sediments at Hestvatn accumulated in a marine environment until ca. 8700 BP and thereafter in freshwater. Owing to the lack of terrestrial macrofossils and the low concentration of molluscs and foraminifera, we were forced to attempt to date most of the core with the organic fraction of the bulk sediment samples. We found, however, that this fraction is not homogeneous in density or 14C age. We believe that during sample pretreatment we managed to isolate a light organic fraction, which closely represents the true age of the sediment, whereas the denser fraction yields ages that are too high. This age diversity may to some extent be explained by the large drainage area of the lake, from which plant remains of different ages may have been washed into the lake.This material was digitized as part of a cooperative project between Radiocarbon and the University of Arizona Libraries.The Radiocarbon archives are made available by Radiocarbon and the University of Arizona Libraries. Contact [email protected] for further information.Migrated from OJS platform February 202