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Plutonium distribution was studied in an undisturbed sediment core sampled from the Tvaren bay in the vicinity of the Studsvik nuclear facility in Sweden. The complete analysis, including minor isotopes, of the Pu isotope composition (238Pu, 239Pu, oPu, 241Pu, 242Pu, and 244Pu) allowed us to establish the Pu origin in this area of the Baltic Sea and to reconstruct the Studsvik aquatic release history. The results show highly enriched 239Pu, probably originating from the Swedish nuclear program in the 1960s and 1970s and the handling of high burn-up nuclear fuel in the later years. In addition, the 244Pu/239Pu atomic ratio for the global fallout period between 1958 and 1965 is suggested to be (7.94 +/- 0.31)center dot 10-5. In the bottom layer of the sediment, dated 1953-1957, we detected a higher average 244Pu/239Pu ratio of (1.51 +/- 0.11)center dot 10-4, indicating the possible impact of the first US thermonuclear tests (1952-1958)., Funding Agencies|Swedish Radiation Safety Authority (SSM) [SSM2020-643]; Spanish Goverment (Ministerio de Ciencia, Innovaci?n y Universidades) [PGC2018-094546-B-I00]

Plutonium distribution was studied in an undisturbed sediment core sampled from the Tvaren bay in the vicinity of the Studsvik nuclear facility in Sweden. The complete analysis, including minor isotopes, of the Pu isotope composition (238Pu, 239Pu, oPu, 241Pu, 242Pu, and 244Pu) allowed us to establish the Pu origin in this area of the Baltic Sea and to reconstruct the Studsvik aquatic release history. The results show highly enriched 239Pu, probably originating from the Swedish nuclear program in the 1960s and 1970s and the handling of high burn-up nuclear fuel in the later years. In addition, the 244Pu/239Pu atomic ratio for the global fallout period between 1958 and 1965 is suggested to be (7.94 +/- 0.31)center dot 10-5. In the bottom layer of the sediment, dated 1953-1957, we detected a higher average 244Pu/239Pu ratio of (1.51 +/- 0.11)center dot 10-4, indicating the possible impact of the first US thermonuclear tests (1952-1958)., Funding Agencies|Swedish Radiation Safety Authority (SSM) [SSM2020-643]; Spanish Goverment (Ministerio de Ciencia, Innovaci?n y Universidades) [PGC2018-094546-B-I00]

Plutonium distribution was studied in an undisturbed sediment core sampled from the Tvaren bay in the vicinity of the Studsvik nuclear facility in Sweden. The complete analysis, including minor isotopes, of the Pu isotope composition (238Pu, 239Pu, oPu, 241Pu, 242Pu, and 244Pu) allowed us to establish the Pu origin in this area of the Baltic Sea and to reconstruct the Studsvik aquatic release history. The results show highly enriched 239Pu, probably originating from the Swedish nuclear program in the 1960s and 1970s and the handling of high burn-up nuclear fuel in the later years. In addition, the 244Pu/239Pu atomic ratio for the global fallout period between 1958 and 1965 is suggested to be (7.94 +/- 0.31)center dot 10-5. In the bottom layer of the sediment, dated 1953-1957, we detected a higher average 244Pu/239Pu ratio of (1.51 +/- 0.11)center dot 10-4, indicating the possible impact of the first US thermonuclear tests (1952-1958)., Funding Agencies|Swedish Radiation Safety Authority (SSM) [SSM2020-643]; Spanish Goverment (Ministerio de Ciencia, Innovaci?n y Universidades) [PGC2018-094546-B-I00]

Plutonium distribution was studied in an undisturbed sediment core sampled from the Tvaren bay in the vicinity of the Studsvik nuclear facility in Sweden. The complete analysis, including minor isotopes, of the Pu isotope composition (238Pu, 239Pu, oPu, 241Pu, 242Pu, and 244Pu) allowed us to establish the Pu origin in this area of the Baltic Sea and to reconstruct the Studsvik aquatic release history. The results show highly enriched 239Pu, probably originating from the Swedish nuclear program in the 1960s and 1970s and the handling of high burn-up nuclear fuel in the later years. In addition, the 244Pu/239Pu atomic ratio for the global fallout period between 1958 and 1965 is suggested to be (7.94 +/- 0.31)center dot 10-5. In the bottom layer of the sediment, dated 1953-1957, we detected a higher average 244Pu/239Pu ratio of (1.51 +/- 0.11)center dot 10-4, indicating the possible impact of the first US thermonuclear tests (1952-1958)., Funding Agencies|Swedish Radiation Safety Authority (SSM) [SSM2020-643]; Spanish Goverment (Ministerio de Ciencia, Innovaci?n y Universidades) [PGC2018-094546-B-I00]

Plutonium distribution was studied in an undisturbed sediment core sampled from the Tvaren bay in the vicinity of the Studsvik nuclear facility in Sweden. The complete analysis, including minor isotopes, of the Pu isotope composition (238Pu, 239Pu, oPu, 241Pu, 242Pu, and 244Pu) allowed us to establish the Pu origin in this area of the Baltic Sea and to reconstruct the Studsvik aquatic release history. The results show highly enriched 239Pu, probably originating from the Swedish nuclear program in the 1960s and 1970s and the handling of high burn-up nuclear fuel in the later years. In addition, the 244Pu/239Pu atomic ratio for the global fallout period between 1958 and 1965 is suggested to be (7.94 +/- 0.31)center dot 10-5. In the bottom layer of the sediment, dated 1953-1957, we detected a higher average 244Pu/239Pu ratio of (1.51 +/- 0.11)center dot 10-4, indicating the possible impact of the first US thermonuclear tests (1952-1958)., Funding Agencies|Swedish Radiation Safety Authority (SSM) [SSM2020-643]; Spanish Goverment (Ministerio de Ciencia, Innovaci?n y Universidades) [PGC2018-094546-B-I00]

This study explores for the first time the possibilities that the U-233/U-236 atom ratio offers to distinguish waters of Atlantic or Pacific origin in the Arctic Ocean. Atlantic waters entering the Arctic Ocean often carry an isotopic signature dominantly originating from European reprocessing facilities with some smaller contribution from global fallout nuclides, whereas northern Pacific waters are labeled with nuclides released during the atmospheric nuclear testing period only. In the Arctic Ocean, U-233 originates from global fallout while U-236 carries both, a global fallout and a prominent nuclear reprocessing signal. Thus, the U-233/U-236 ratio provides a tool to identify water masses with distinct U sources. In this work, U-233 and U-236 were analyzed in samples from the GN01 GEOTRACES expedition to the western Arctic Ocean in 2015. The study of depth profiles and surface seawater samples shows that: (a) Pacific and Atlantic waters show enhanced signals of both radionuclides, which can be unraveled based on their U-233/U-236 signature; and (b) Deep and Bottom Waters show extremely low U-233 and U-236 concentrations close to or below analytical detection limits with isotopic ratios distinct from known anthropogenic U sources. The comparably high U-233/U-236 ratios are interpreted as a relative increase of naturally occurring U-233 and U-236 and thus for gradually reaching natural U-233/U-236 levels in the deep Arctic Ocean. Our results set the basis for future studies using the U-233/U-236 ratio to distinguish anthropogenic and pre-anthropogenic U in the Arctic Ocean and beyond., Funding Agencies|ETH Zurich Research GrantETH Zurich [ETH-06 16-1]; Swiss National Science FoundationSwiss National Science Foundation (SNSF)European Commission [PRIMA SNF PR00P2_193091]; Spanish Government (Ministerio de Ciencia, Innovacion y Universidades)Spanish Government [PGC2018-094546-B-I00]

This study explores for the first time the possibilities that the U-233/U-236 atom ratio offers to distinguish waters of Atlantic or Pacific origin in the Arctic Ocean. Atlantic waters entering the Arctic Ocean often carry an isotopic signature dominantly originating from European reprocessing facilities with some smaller contribution from global fallout nuclides, whereas northern Pacific waters are labeled with nuclides released during the atmospheric nuclear testing period only. In the Arctic Ocean, U-233 originates from global fallout while U-236 carries both, a global fallout and a prominent nuclear reprocessing signal. Thus, the U-233/U-236 ratio provides a tool to identify water masses with distinct U sources. In this work, U-233 and U-236 were analyzed in samples from the GN01 GEOTRACES expedition to the western Arctic Ocean in 2015. The study of depth profiles and surface seawater samples shows that: (a) Pacific and Atlantic waters show enhanced signals of both radionuclides, which can be unraveled based on their U-233/U-236 signature; and (b) Deep and Bottom Waters show extremely low U-233 and U-236 concentrations close to or below analytical detection limits with isotopic ratios distinct from known anthropogenic U sources. The comparably high U-233/U-236 ratios are interpreted as a relative increase of naturally occurring U-233 and U-236 and thus for gradually reaching natural U-233/U-236 levels in the deep Arctic Ocean. Our results set the basis for future studies using the U-233/U-236 ratio to distinguish anthropogenic and pre-anthropogenic U in the Arctic Ocean and beyond., Funding Agencies|ETH Zurich Research GrantETH Zurich [ETH-06 16-1]; Swiss National Science FoundationSwiss National Science Foundation (SNSF)European Commission [PRIMA SNF PR00P2_193091]; Spanish Government (Ministerio de Ciencia, Innovacion y Universidades)Spanish Government [PGC2018-094546-B-I00]

This study explores for the first time the possibilities that the U-233/U-236 atom ratio offers to distinguish waters of Atlantic or Pacific origin in the Arctic Ocean. Atlantic waters entering the Arctic Ocean often carry an isotopic signature dominantly originating from European reprocessing facilities with some smaller contribution from global fallout nuclides, whereas northern Pacific waters are labeled with nuclides released during the atmospheric nuclear testing period only. In the Arctic Ocean, U-233 originates from global fallout while U-236 carries both, a global fallout and a prominent nuclear reprocessing signal. Thus, the U-233/U-236 ratio provides a tool to identify water masses with distinct U sources. In this work, U-233 and U-236 were analyzed in samples from the GN01 GEOTRACES expedition to the western Arctic Ocean in 2015. The study of depth profiles and surface seawater samples shows that: (a) Pacific and Atlantic waters show enhanced signals of both radionuclides, which can be unraveled based on their U-233/U-236 signature; and (b) Deep and Bottom Waters show extremely low U-233 and U-236 concentrations close to or below analytical detection limits with isotopic ratios distinct from known anthropogenic U sources. The comparably high U-233/U-236 ratios are interpreted as a relative increase of naturally occurring U-233 and U-236 and thus for gradually reaching natural U-233/U-236 levels in the deep Arctic Ocean. Our results set the basis for future studies using the U-233/U-236 ratio to distinguish anthropogenic and pre-anthropogenic U in the Arctic Ocean and beyond., Funding Agencies|ETH Zurich Research GrantETH Zurich [ETH-06 16-1]; Swiss National Science FoundationSwiss National Science Foundation (SNSF)European Commission [PRIMA SNF PR00P2_193091]; Spanish Government (Ministerio de Ciencia, Innovacion y Universidades)Spanish Government [PGC2018-094546-B-I00]

U-233 (T-1/2 = 0.159 My) has aroused much interest in the last few years because of the potential of U-233/U-236 to inform about anthropogenic U sources. The reported U-233/U-238 atom ratios in general environmental samples are in the 10(-12)-10(-6) range. We demonstrate that U-233/U-238 abundance sensitivities at the 5 x 10(-11) level can be achieved at the 1 MV Accelerator Mass Spectrometry system at the Centro Nacional de Aceleradores (CNA, Seville, Spain). Unresolved U-234, U-235 and Th-232 molecular fragments are identified as the main U-233 background contributors and procedures to subtract them are proposed. U-233/U-238 and U-236/U-238 atom ratios were analysed in the IAEA reference materials coded Soil-6, 300, 385, 410, and 412 at the CNA and at the 600 kV ETH AMS system for intercomparison. U-233/U-238 atom ratios for samples 412 and 385 were only reported by the ETH., Funding Agencies|Spanish Government (Ministerio de Ciencia, Innovacion y Universidades) [PGC2018-094546-B-I00]

This study explores for the first time the possibilities that the U-233/U-236 atom ratio offers to distinguish waters of Atlantic or Pacific origin in the Arctic Ocean. Atlantic waters entering the Arctic Ocean often carry an isotopic signature dominantly originating from European reprocessing facilities with some smaller contribution from global fallout nuclides, whereas northern Pacific waters are labeled with nuclides released during the atmospheric nuclear testing period only. In the Arctic Ocean, U-233 originates from global fallout while U-236 carries both, a global fallout and a prominent nuclear reprocessing signal. Thus, the U-233/U-236 ratio provides a tool to identify water masses with distinct U sources. In this work, U-233 and U-236 were analyzed in samples from the GN01 GEOTRACES expedition to the western Arctic Ocean in 2015. The study of depth profiles and surface seawater samples shows that: (a) Pacific and Atlantic waters show enhanced signals of both radionuclides, which can be unraveled based on their U-233/U-236 signature; and (b) Deep and Bottom Waters show extremely low U-233 and U-236 concentrations close to or below analytical detection limits with isotopic ratios distinct from known anthropogenic U sources. The comparably high U-233/U-236 ratios are interpreted as a relative increase of naturally occurring U-233 and U-236 and thus for gradually reaching natural U-233/U-236 levels in the deep Arctic Ocean. Our results set the basis for future studies using the U-233/U-236 ratio to distinguish anthropogenic and pre-anthropogenic U in the Arctic Ocean and beyond., Funding Agencies|ETH Zurich Research GrantETH Zurich [ETH-06 16-1]; Swiss National Science FoundationSwiss National Science Foundation (SNSF)European Commission [PRIMA SNF PR00P2_193091]; Spanish Government (Ministerio de Ciencia, Innovacion y Universidades)Spanish Government [PGC2018-094546-B-I00]

This study explores for the first time the possibilities that the U-233/U-236 atom ratio offers to distinguish waters of Atlantic or Pacific origin in the Arctic Ocean. Atlantic waters entering the Arctic Ocean often carry an isotopic signature dominantly originating from European reprocessing facilities with some smaller contribution from global fallout nuclides, whereas northern Pacific waters are labeled with nuclides released during the atmospheric nuclear testing period only. In the Arctic Ocean, U-233 originates from global fallout while U-236 carries both, a global fallout and a prominent nuclear reprocessing signal. Thus, the U-233/U-236 ratio provides a tool to identify water masses with distinct U sources. In this work, U-233 and U-236 were analyzed in samples from the GN01 GEOTRACES expedition to the western Arctic Ocean in 2015. The study of depth profiles and surface seawater samples shows that: (a) Pacific and Atlantic waters show enhanced signals of both radionuclides, which can be unraveled based on their U-233/U-236 signature; and (b) Deep and Bottom Waters show extremely low U-233 and U-236 concentrations close to or below analytical detection limits with isotopic ratios distinct from known anthropogenic U sources. The comparably high U-233/U-236 ratios are interpreted as a relative increase of naturally occurring U-233 and U-236 and thus for gradually reaching natural U-233/U-236 levels in the deep Arctic Ocean. Our results set the basis for future studies using the U-233/U-236 ratio to distinguish anthropogenic and pre-anthropogenic U in the Arctic Ocean and beyond., Funding Agencies|ETH Zurich Research GrantETH Zurich [ETH-06 16-1]; Swiss National Science FoundationSwiss National Science Foundation (SNSF)European Commission [PRIMA SNF PR00P2_193091]; Spanish Government (Ministerio de Ciencia, Innovacion y Universidades)Spanish Government [PGC2018-094546-B-I00]

The aim of this study was to assess the potential of combining the conservatively behaving anthropogenic radionuclides U-236 and Np-237 to gain information on the origin of water masses tagged with liquid effluents from Nuclear Reprocessing Plants. This work includes samples collected from three full-depth water columns in two areas: i) the Arctic Ocean, where Atlantic waters carry the signal of Sellafield (United Kingdom) and La Hague (France) nuclear reprocessing facilities; and ii) the western Mediterranean Sea, directly impacted by Marcoule reprocessing plant (France). This work is complemented by the study of the particle-reactive Pu isotopes as an additional fingerprint of the source region. In the Canada Basin, Atlantic waters showed the highest concentrations and Np-237/U-236 ratios in agreement with the estimated values for North Atlantic waters entering the Arctic Ocean and tagged with the signal of European Nuclear Reprocessing Plants. These results may reflect the impact of the documented releases for the 1990s. In the Mediterranean Sea, an excess of U-236 presumably caused by Marcoule is reflected in the lower Np-237/U-236 ratios compared to the Global Fallout signal in all the studied samples. On the contrary, the Pu-239,Pu-240 profiles were mainly governed by the Global Fallout. The impact of Marcoule as a local source is further corroborated when comparing the temporal evolution of these ratios between 2001 and 2013. The lowest Np-237/U-236 ratios observed in 2001 at the surface reflect a previous local input that is no longer observed in 2013 as it had been homogenized through the whole water column. This work presents the use of Np-237 as a new ocean tracer. A more accurate characterization of the main sources is still needed to optimize the use of U-236-Np-237 as a new tool to understand transient oceanographic processes. (C) 2020 Elsevier B.V. All rights reserved., Funding Agencies|Spanish Government (Ministerio de Economia y Competitividad) [FIS2015-69673-P, PGC2018-094546-B-I00]; Spanish Government (Ministerio de Ciencia, Innovacion y Universidades) [FIS2015-69673-P, PGC2018-094546-B-I00]; U.S. National Science FoundationNational Science Foundation (NSF) [OCE 1439319]; Fundacion Camara Sevilla

The aim of this study was to assess the potential of combining the conservatively behaving anthropogenic radionuclides U-236 and Np-237 to gain information on the origin of water masses tagged with liquid effluents from Nuclear Reprocessing Plants. This work includes samples collected from three full-depth water columns in two areas: i) the Arctic Ocean, where Atlantic waters carry the signal of Sellafield (United Kingdom) and La Hague (France) nuclear reprocessing facilities; and ii) the western Mediterranean Sea, directly impacted by Marcoule reprocessing plant (France). This work is complemented by the study of the particle-reactive Pu isotopes as an additional fingerprint of the source region. In the Canada Basin, Atlantic waters showed the highest concentrations and Np-237/U-236 ratios in agreement with the estimated values for North Atlantic waters entering the Arctic Ocean and tagged with the signal of European Nuclear Reprocessing Plants. These results may reflect the impact of the documented releases for the 1990s. In the Mediterranean Sea, an excess of U-236 presumably caused by Marcoule is reflected in the lower Np-237/U-236 ratios compared to the Global Fallout signal in all the studied samples. On the contrary, the Pu-239,Pu-240 profiles were mainly governed by the Global Fallout. The impact of Marcoule as a local source is further corroborated when comparing the temporal evolution of these ratios between 2001 and 2013. The lowest Np-237/U-236 ratios observed in 2001 at the surface reflect a previous local input that is no longer observed in 2013 as it had been homogenized through the whole water column. This work presents the use of Np-237 as a new ocean tracer. A more accurate characterization of the main sources is still needed to optimize the use of U-236-Np-237 as a new tool to understand transient oceanographic processes. (C) 2020 Elsevier B.V. All rights reserved., Funding Agencies|Spanish Government (Ministerio de Economia y Competitividad) [FIS2015-69673-P, PGC2018-094546-B-I00]; Spanish Government (Ministerio de Ciencia, Innovacion y Universidades) [FIS2015-69673-P, PGC2018-094546-B-I00]; U.S. National Science FoundationNational Science Foundation (NSF) [OCE 1439319]; Fundacion Camara Sevilla

The aim of this study was to assess the potential of combining the conservatively behaving anthropogenic radionuclides U-236 and Np-237 to gain information on the origin of water masses tagged with liquid effluents from Nuclear Reprocessing Plants. This work includes samples collected from three full-depth water columns in two areas: i) the Arctic Ocean, where Atlantic waters carry the signal of Sellafield (United Kingdom) and La Hague (France) nuclear reprocessing facilities; and ii) the western Mediterranean Sea, directly impacted by Marcoule reprocessing plant (France). This work is complemented by the study of the particle-reactive Pu isotopes as an additional fingerprint of the source region. In the Canada Basin, Atlantic waters showed the highest concentrations and Np-237/U-236 ratios in agreement with the estimated values for North Atlantic waters entering the Arctic Ocean and tagged with the signal of European Nuclear Reprocessing Plants. These results may reflect the impact of the documented releases for the 1990s. In the Mediterranean Sea, an excess of U-236 presumably caused by Marcoule is reflected in the lower Np-237/U-236 ratios compared to the Global Fallout signal in all the studied samples. On the contrary, the Pu-239,Pu-240 profiles were mainly governed by the Global Fallout. The impact of Marcoule as a local source is further corroborated when comparing the temporal evolution of these ratios between 2001 and 2013. The lowest Np-237/U-236 ratios observed in 2001 at the surface reflect a previous local input that is no longer observed in 2013 as it had been homogenized through the whole water column. This work presents the use of Np-237 as a new ocean tracer. A more accurate characterization of the main sources is still needed to optimize the use of U-236-Np-237 as a new tool to understand transient oceanographic processes. (C) 2020 Elsevier B.V. All rights reserved., Funding Agencies|Spanish Government (Ministerio de Economia y Competitividad) [FIS2015-69673-P, PGC2018-094546-B-I00]; Spanish Government (Ministerio de Ciencia, Innovacion y Universidades) [FIS2015-69673-P, PGC2018-094546-B-I00]; U.S. National Science FoundationNational Science Foundation (NSF) [OCE 1439319]; Fundacion Camara Sevilla

The aim of this study was to assess the potential of combining the conservatively behaving anthropogenic radionuclides U-236 and Np-237 to gain information on the origin of water masses tagged with liquid effluents from Nuclear Reprocessing Plants. This work includes samples collected from three full-depth water columns in two areas: i) the Arctic Ocean, where Atlantic waters carry the signal of Sellafield (United Kingdom) and La Hague (France) nuclear reprocessing facilities; and ii) the western Mediterranean Sea, directly impacted by Marcoule reprocessing plant (France). This work is complemented by the study of the particle-reactive Pu isotopes as an additional fingerprint of the source region. In the Canada Basin, Atlantic waters showed the highest concentrations and Np-237/U-236 ratios in agreement with the estimated values for North Atlantic waters entering the Arctic Ocean and tagged with the signal of European Nuclear Reprocessing Plants. These results may reflect the impact of the documented releases for the 1990s. In the Mediterranean Sea, an excess of U-236 presumably caused by Marcoule is reflected in the lower Np-237/U-236 ratios compared to the Global Fallout signal in all the studied samples. On the contrary, the Pu-239,Pu-240 profiles were mainly governed by the Global Fallout. The impact of Marcoule as a local source is further corroborated when comparing the temporal evolution of these ratios between 2001 and 2013. The lowest Np-237/U-236 ratios observed in 2001 at the surface reflect a previous local input that is no longer observed in 2013 as it had been homogenized through the whole water column. This work presents the use of Np-237 as a new ocean tracer. A more accurate characterization of the main sources is still needed to optimize the use of U-236-Np-237 as a new tool to understand transient oceanographic processes. (C) 2020 Elsevier B.V. All rights reserved., Funding Agencies|Spanish Government (Ministerio de Economia y Competitividad) [FIS2015-69673-P, PGC2018-094546-B-I00]; Spanish Government (Ministerio de Ciencia, Innovacion y Universidades) [FIS2015-69673-P, PGC2018-094546-B-I00]; U.S. National Science FoundationNational Science Foundation (NSF) [OCE 1439319]; Fundacion Camara Sevilla

The aim of this study was to assess the potential of combining the conservatively behaving anthropogenic radionuclides U-236 and Np-237 to gain information on the origin of water masses tagged with liquid effluents from Nuclear Reprocessing Plants. This work includes samples collected from three full-depth water columns in two areas: i) the Arctic Ocean, where Atlantic waters carry the signal of Sellafield (United Kingdom) and La Hague (France) nuclear reprocessing facilities; and ii) the western Mediterranean Sea, directly impacted by Marcoule reprocessing plant (France). This work is complemented by the study of the particle-reactive Pu isotopes as an additional fingerprint of the source region. In the Canada Basin, Atlantic waters showed the highest concentrations and Np-237/U-236 ratios in agreement with the estimated values for North Atlantic waters entering the Arctic Ocean and tagged with the signal of European Nuclear Reprocessing Plants. These results may reflect the impact of the documented releases for the 1990s. In the Mediterranean Sea, an excess of U-236 presumably caused by Marcoule is reflected in the lower Np-237/U-236 ratios compared to the Global Fallout signal in all the studied samples. On the contrary, the Pu-239,Pu-240 profiles were mainly governed by the Global Fallout. The impact of Marcoule as a local source is further corroborated when comparing the temporal evolution of these ratios between 2001 and 2013. The lowest Np-237/U-236 ratios observed in 2001 at the surface reflect a previous local input that is no longer observed in 2013 as it had been homogenized through the whole water column. This work presents the use of Np-237 as a new ocean tracer. A more accurate characterization of the main sources is still needed to optimize the use of U-236-Np-237 as a new tool to understand transient oceanographic processes. (C) 2020 Elsevier B.V. All rights reserved., Funding Agencies|Spanish Government (Ministerio de Economia y Competitividad) [FIS2015-69673-P, PGC2018-094546-B-I00]; Spanish Government (Ministerio de Ciencia, Innovacion y Universidades) [FIS2015-69673-P, PGC2018-094546-B-I00]; U.S. National Science FoundationNational Science Foundation (NSF) [OCE 1439319]; Fundacion Camara Sevilla