Lithogenic influence from the Hawaiian Islands detectable up to Station ALOHA surface waters

8 September 2016

By coupling neodymium (Nd) and radium (Ra) isotopes and Rare Earth Element (REE) signals, Henning Fröllje and co-workers (2016, see reference below) show that the coastal Hawaiian waters are affected by a prominent lithogenic influence from the Hawaiian Islands. Rare earth patterns, radiogenic εNd signatures and high²²⁸Ra levels are clearly tracing this influence. Moreover, it is perceptible as far as ALOHA station (100 km north). This influence at ALOHA is most pronounced in February, when precipitation on the islands is highest and dust input from Asia is low. In summer, however, Nd isotopes are shifted towards the Asian dust endmember (εNd = -10), indicating seasonal dust influence overlying the Hawaiian background signal.

A close study of the rare earth distribution and speciation confirm that these elements are truly dissolved in seawater and that they are following water mass advection and mixing in the intermediate and deep central North Pacific Ocean.

16 Frolijel — **Figure:** Location of station ALOHA and sampling stations around Oahu, Hawaii, along with εNd and Nd concentration profiles. ALOHA full water column: εNd, Nd concentrations, and Radium-228 at ALOHA. Seasonal: seasonal εNd of the upper 800m, showing a shift to higher dust influence in June-August compared to February. Oahu: εNd and Nd concentration profiles at coastal sites around Oahu.

Reference:

Fröllje, H., Pahnke, K., Schnetger, B., Brumsack, H.-J., Dulai, H., & Fitzsimmons, J. N. (2016). Hawaiian imprint on dissolved Nd and Ra isotopes and rare earth elements in the central North Pacific: Local survey and seasonal variability. Geochimica et Cosmochimica Acta, 189, 110–131. doi:10.1016/j.gca.2016.06.001

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