INOPEX

The Innovative North Pacific Experiment (INOPEX)

research cruise (SO-202) sailed in July-August 2009 around

the Pacific subarctic gyre sampling seawater and ocean sediments

Chief Scientist: Rainer Gersonde (Alfred Wegener Institute)

Boundary Scavenging: Measurements of dissolved ²³⁰Th and ²³¹Pa, which

are insoluble products of natural uranium decay in the ocean, across the lateral productivity

gradients found along the INOPEX cruise track, test the hypothesis that insoluble elements are removed by scavenging

(adsorption onto sinking particles) preferentially at ocean margins. This study concludes that the contrast in scavenging

is much stronger across the subarctic-subtropical gyre boundary than within the subarctic itself, and has implications for the

biogeochemical cycles of other insoluble elements, such as micronutrient trace metals. [C. T. Hayes, R. F. Anderson,

S. L. Jaccard, R. François, M. Q. Fleisher, M. Soon, R. Gersonde; in press, Earth and Planetary Science Letters, 2013]

Chemical Fractionation of ²³¹Pa/²³⁰Th in the Pacific Ocean: The ratio of ²³¹Pa/²³⁰Th in sediments has been used

as a proxy for a variety of ocean processes in paleoceanography based on relatively few observations in the modern

Ocean. In this study, measurements of excess ²³¹Pa/²³⁰Th in surface sediments from the INOPEX cruise track in

direct comparison to the overlaying seawater, allow calculation of the degree to which the ²³¹Pa/²³⁰Th ratio is influenced

by the chemical composition of the sediments. These measurements included in a basin-wide survey of available data

offer perspectives for interpreting sedimentary ²³¹Pa/²³⁰Th records in the Pacific primarily in terms of the contrast in

biogeochemical provinces. [C. T. Hayes, R. F. Anderson, M. Q. Fleisher, R. Gersonde in prep.]

Quantifying lithogenic inputs to the Ocean using the long-lived thorium isotopes: Measurements of ²³⁰Th

combined with the major isotope of thorium (²³²Th), allow an accurate estimate of the supply of soluble trace elements due to

the dissolution of aerosol dust or other lithogenic sources. This method applied to INOPEX water column profiles produces estimates

of dust deposition which average over several years within the subarctic Pacific, a region in which biological productivity is debatably

limited by aerosol-derived Fe. The long-lived thorium isotopes offer new insights into lithogenic material transformations in the ocean

which complement more traditional tracer elements. [C. T. Hayes, R. F. Anderson, M. Q. Fleisher, R. Gersonde, in prep.]

Funding for this project from the National Science Foundation is acknowledged.

Sampling for dissolved (left) and surface sediment (right)

radionuclides in the subarctic Pacific (2009)

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