Quantitative resolution of eolian continental crustal material and volcanic detritus in North Pacific surface sediment

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Abstract
Proxy records of continental climate and atmospheric circulation provided by analyses of eolian continental material extracted from marine sediment have resulted in significant new information concerning the behavior of these climate systems on various timescales. These studies, however, currently are limited to certain geographic areas because no chemical or physical extraction procedure provides an unambiguous separation of eolian continental crustal material from other contaminants like volcanic detritus. We employ a combined analytical and statistical procedure in an effort to extract a more refined eolian “signal” from areas that may be affected by volcanic detritus. Bulk surface sediment samples from 33 locations in the North Pacific were treated using a conventional sequential extraction procedure to remove the carbonate, silica and oxyhydroxide components, and the residue was analyzed by instrumental neutron activation analysis (INAA) for La, Ce, Sm, Eu, Yb, Lu, Hf, Sc, and Th. Q‐mode factor analysis of these data shows that > 99% of the variance is explained by two end‐members, which we interpret to be continental crustal material and volcanic detritus. Five least squares normative analysis models were evaluated to estimate the relative amount of these end‐members in each sample. The continental crustal component was approximated using a fine‐grained fraction of China loess and bulk loess. The volcanic component was approximated using the compositions of average Kurile‐Kamchatka volcanic material, a median Ocean Drilling Program (ODP) Leg 145 Ash, and a median Kurile basalt. The model based on average Kurile‐Kamchatka volcanic material and the fine loess fraction gives the most accurate results. Central and east Pacific samples typically contain up to 100% of the eolian continental crustal component, while samples near Japan, Kamchatka, and the Aleutians contain a majority of volcanic detritus. However, the highly variable composition of volcanic material can result in systematic errors up to 25% in samples dominated by volcanic detritus. The geographic distribution of the compositional end‐members is consistent with a continental dust source originating in Asia and being diluted by ash from the volcanic arcs of the Pacific rim. This improved identification and resolution of the eolian continental component realized in this approach should permit paleoclimatic reconstructions to be developed from sediments in significant portions of the world that were previously precluded from analysis because of limitations with chemical or physical extraction procedures.