Limits on conservative behavior of Nd isotopes in seawater assessed from analysis of fish teeth from Pacific core tops

Keiji Horikawa; Ellen E. Martin; Yoshihiro Asahara; Takuya Sagawa

doi:10.1016/j.epsl.2011.07.018

Limits on conservative behavior of Nd isotopes in seawater assessed from analysis of fish teeth from Pacific core tops

Keiji Horikawa^*, Ellen E. Martin, Yoshihiro Asahara, Takuya Sagawa

^*Corresponding author for this work

Department of Natural and Environmental Science

Research output: Contribution to journal › Article › peer-review

45 Scopus citations

Abstract

Neodymium (Nd) isotopes have become an accepted water mass tracer for paleoceanographic reconstructions; however, high rates of radiogenic Nd input from volcanic islands/arcs in the western equatorial Pacific (WEP) and the subarctic North Pacific (SANP) can significantly alter the isotopic composition of ambient seawaters, leading to questions about the conservative nature of Nd isotopes in the Pacific. Here we present the first comprehensive study of Nd isotopes preserved in core-top fossil fish teeth/debris from 31 sites in the Pacific to define the vertical and horizontal distributions of seawater Nd isotopes and to test the reliability of Nd isotopes as a water mass tracer in the Pacific. We found that Nd isotopic values of northward-flowing Lower Circumpolar Deep Water (LCDW) are significantly modified in the western-central equatorial Pacific and the SANP as a result of local radiogenic inputs from young circum-Pacific island arcs. Consequently, 'modified LCDW' with ~-5 ε_Nd is created in the central equatorial Pacific, while recirculated North Pacific Deep Water (NPDW) acquires a radiogenic Nd isotope value (~-2 ε_Nd) in the SANP. Nd isotopic ratios of fish teeth/debris in the central North Pacific plotted against salinity (or phosphate concentration) from the overlying bottom water produce a mixing envelope between modified LCDW and NPDW, indicating that these Nd isotopic values represent the southern- and northern-sourced end member values for the central North Pacific and that mixing of these water masses defines vertical profiles of Nd isotopes in this region. In the eastern equatorial Pacific (EEP) three water masses (modified LCDW, NPDW_SANP, and NPDW_{western Pacific}) combine to produce Nd isotopic values that reflect this conservative mixture. Therefore, Nd isotopes behave as a conservative water mass tracer in the central North Pacific and the EEP, but high rates of lithogenic inputs from young circum-Pacific island arcs compromise the conservative behavior of Nd isotopes in the WEP and SANP.

Original language	English
Pages (from-to)	119-130
Number of pages	12
Journal	Earth and Planetary Science Letters
Volume	310
Issue number	1-2
DOIs	https://doi.org/10.1016/j.epsl.2011.07.018
State	Published - 2011/10/01

Keywords

Deep-water circulation
Fish teeth
LCDW
NPDW
Neodymium isotopes
Pacific Ocean

ASJC Scopus subject areas

Geochemistry and Petrology
Geophysics
Space and Planetary Science
Earth and Planetary Sciences (miscellaneous)

Access to Document

10.1016/j.epsl.2011.07.018

Cite this

@article{d0f67629bb01464890e7fe193cbbe295,

title = "Limits on conservative behavior of Nd isotopes in seawater assessed from analysis of fish teeth from Pacific core tops",

abstract = "Neodymium (Nd) isotopes have become an accepted water mass tracer for paleoceanographic reconstructions; however, high rates of radiogenic Nd input from volcanic islands/arcs in the western equatorial Pacific (WEP) and the subarctic North Pacific (SANP) can significantly alter the isotopic composition of ambient seawaters, leading to questions about the conservative nature of Nd isotopes in the Pacific. Here we present the first comprehensive study of Nd isotopes preserved in core-top fossil fish teeth/debris from 31 sites in the Pacific to define the vertical and horizontal distributions of seawater Nd isotopes and to test the reliability of Nd isotopes as a water mass tracer in the Pacific. We found that Nd isotopic values of northward-flowing Lower Circumpolar Deep Water (LCDW) are significantly modified in the western-central equatorial Pacific and the SANP as a result of local radiogenic inputs from young circum-Pacific island arcs. Consequently, 'modified LCDW' with ~-5 εNd is created in the central equatorial Pacific, while recirculated North Pacific Deep Water (NPDW) acquires a radiogenic Nd isotope value (~-2 εNd) in the SANP. Nd isotopic ratios of fish teeth/debris in the central North Pacific plotted against salinity (or phosphate concentration) from the overlying bottom water produce a mixing envelope between modified LCDW and NPDW, indicating that these Nd isotopic values represent the southern- and northern-sourced end member values for the central North Pacific and that mixing of these water masses defines vertical profiles of Nd isotopes in this region. In the eastern equatorial Pacific (EEP) three water masses (modified LCDW, NPDWSANP, and NPDWwestern Pacific) combine to produce Nd isotopic values that reflect this conservative mixture. Therefore, Nd isotopes behave as a conservative water mass tracer in the central North Pacific and the EEP, but high rates of lithogenic inputs from young circum-Pacific island arcs compromise the conservative behavior of Nd isotopes in the WEP and SANP.",

keywords = "Deep-water circulation, Fish teeth, LCDW, NPDW, Neodymium isotopes, Pacific Ocean",

author = "Keiji Horikawa and Martin, {Ellen E.} and Yoshihiro Asahara and Takuya Sagawa",

note = "Funding Information: We kindly thank G. Kamenov for laboratory assistance at UF and C. Basak for valuable discussions. The manuscript benefited from comments by Gideon Henderson (editor) and three anonymous reviewers. K.H acknowledges financial support from JSPS (Japan Society for the Promotion of Science) Research Fellowships for Young Scientist (No. 206613 ) and JSPS Excellent Young Researchers Overseas Visit Program . Sediment samples used in this study were retrieved by the Geological Survey of Japan, New Energy and Industrial Technology Development Organization (NEDO), Ocean Research Institute (University of Tokyo) cruises, R/V Marion Dufresne the IMAGES VII WEPAMA (2001) cruise, and D/V Chikyu cruise CK05-04. We are grateful to the captains, officers, crew, and scientists involved in these research cruises for their sample collection.",

year = "2011",

month = oct,

day = "1",

doi = "10.1016/j.epsl.2011.07.018",

language = "英語",

volume = "310",

pages = "119--130",

journal = "Earth and Planetary Science Letters",

issn = "0012-821X",

publisher = "Elsevier B.V.",

number = "1-2",

}

TY - JOUR

T1 - Limits on conservative behavior of Nd isotopes in seawater assessed from analysis of fish teeth from Pacific core tops

AU - Horikawa, Keiji

AU - Martin, Ellen E.

AU - Asahara, Yoshihiro

AU - Sagawa, Takuya

N1 - Funding Information: We kindly thank G. Kamenov for laboratory assistance at UF and C. Basak for valuable discussions. The manuscript benefited from comments by Gideon Henderson (editor) and three anonymous reviewers. K.H acknowledges financial support from JSPS (Japan Society for the Promotion of Science) Research Fellowships for Young Scientist (No. 206613 ) and JSPS Excellent Young Researchers Overseas Visit Program . Sediment samples used in this study were retrieved by the Geological Survey of Japan, New Energy and Industrial Technology Development Organization (NEDO), Ocean Research Institute (University of Tokyo) cruises, R/V Marion Dufresne the IMAGES VII WEPAMA (2001) cruise, and D/V Chikyu cruise CK05-04. We are grateful to the captains, officers, crew, and scientists involved in these research cruises for their sample collection.

PY - 2011/10/1

Y1 - 2011/10/1

N2 - Neodymium (Nd) isotopes have become an accepted water mass tracer for paleoceanographic reconstructions; however, high rates of radiogenic Nd input from volcanic islands/arcs in the western equatorial Pacific (WEP) and the subarctic North Pacific (SANP) can significantly alter the isotopic composition of ambient seawaters, leading to questions about the conservative nature of Nd isotopes in the Pacific. Here we present the first comprehensive study of Nd isotopes preserved in core-top fossil fish teeth/debris from 31 sites in the Pacific to define the vertical and horizontal distributions of seawater Nd isotopes and to test the reliability of Nd isotopes as a water mass tracer in the Pacific. We found that Nd isotopic values of northward-flowing Lower Circumpolar Deep Water (LCDW) are significantly modified in the western-central equatorial Pacific and the SANP as a result of local radiogenic inputs from young circum-Pacific island arcs. Consequently, 'modified LCDW' with ~-5 εNd is created in the central equatorial Pacific, while recirculated North Pacific Deep Water (NPDW) acquires a radiogenic Nd isotope value (~-2 εNd) in the SANP. Nd isotopic ratios of fish teeth/debris in the central North Pacific plotted against salinity (or phosphate concentration) from the overlying bottom water produce a mixing envelope between modified LCDW and NPDW, indicating that these Nd isotopic values represent the southern- and northern-sourced end member values for the central North Pacific and that mixing of these water masses defines vertical profiles of Nd isotopes in this region. In the eastern equatorial Pacific (EEP) three water masses (modified LCDW, NPDWSANP, and NPDWwestern Pacific) combine to produce Nd isotopic values that reflect this conservative mixture. Therefore, Nd isotopes behave as a conservative water mass tracer in the central North Pacific and the EEP, but high rates of lithogenic inputs from young circum-Pacific island arcs compromise the conservative behavior of Nd isotopes in the WEP and SANP.

AB - Neodymium (Nd) isotopes have become an accepted water mass tracer for paleoceanographic reconstructions; however, high rates of radiogenic Nd input from volcanic islands/arcs in the western equatorial Pacific (WEP) and the subarctic North Pacific (SANP) can significantly alter the isotopic composition of ambient seawaters, leading to questions about the conservative nature of Nd isotopes in the Pacific. Here we present the first comprehensive study of Nd isotopes preserved in core-top fossil fish teeth/debris from 31 sites in the Pacific to define the vertical and horizontal distributions of seawater Nd isotopes and to test the reliability of Nd isotopes as a water mass tracer in the Pacific. We found that Nd isotopic values of northward-flowing Lower Circumpolar Deep Water (LCDW) are significantly modified in the western-central equatorial Pacific and the SANP as a result of local radiogenic inputs from young circum-Pacific island arcs. Consequently, 'modified LCDW' with ~-5 εNd is created in the central equatorial Pacific, while recirculated North Pacific Deep Water (NPDW) acquires a radiogenic Nd isotope value (~-2 εNd) in the SANP. Nd isotopic ratios of fish teeth/debris in the central North Pacific plotted against salinity (or phosphate concentration) from the overlying bottom water produce a mixing envelope between modified LCDW and NPDW, indicating that these Nd isotopic values represent the southern- and northern-sourced end member values for the central North Pacific and that mixing of these water masses defines vertical profiles of Nd isotopes in this region. In the eastern equatorial Pacific (EEP) three water masses (modified LCDW, NPDWSANP, and NPDWwestern Pacific) combine to produce Nd isotopic values that reflect this conservative mixture. Therefore, Nd isotopes behave as a conservative water mass tracer in the central North Pacific and the EEP, but high rates of lithogenic inputs from young circum-Pacific island arcs compromise the conservative behavior of Nd isotopes in the WEP and SANP.

KW - Deep-water circulation

KW - Fish teeth

KW - LCDW

KW - NPDW

KW - Neodymium isotopes

KW - Pacific Ocean

UR - http://www.scopus.com/inward/record.url?scp=80054052698&partnerID=8YFLogxK

U2 - 10.1016/j.epsl.2011.07.018

DO - 10.1016/j.epsl.2011.07.018

M3 - 学術論文

AN - SCOPUS:80054052698

SN - 0012-821X

VL - 310

SP - 119

EP - 130

JO - Earth and Planetary Science Letters

JF - Earth and Planetary Science Letters

IS - 1-2

ER -

Limits on conservative behavior of Nd isotopes in seawater assessed from analysis of fish teeth from Pacific core tops

Abstract

Keywords

ASJC Scopus subject areas

Access to Document

Fingerprint

Cite this