A Novel Paleo Sea Surface Nutrient Proxy Based on Long Chain Alkyl Diols: Nutrient Diol Index (NDI)

Abstract

During recent years, several diol-based indices have been introduced to provide information on past climatic and environmental conditions. Here, we investigated the distribution of long chain diols (LCDs) using suspended particulate matter (SPM) collected along a south-north transect ranging from the East Sea of Korea to the Bering Sea in the northwestern Pacific region. Our results shed light on the spatial distribution pattern of LCDs in the Pacific Ocean, showing that both saturated and unsaturated C28 and C30 1,14-diols were dominant in most SPM samples. The principal component analysis (PCA) results indicated that the C28:1 and C30:1 1,14-diols were positively associated with nutrient concentrations. However, only the C28:1 1,14-diol in addition to the C28 1,14-diol was positively associated with nutrient concentrations in the global surface sediment data set previously published, while the C30:1 1,14-diol was related to sea surface temperature (SST). Based on these observations, we developed the nutrient diol index (NDI) as follows:

Nutrient diol index (NDI) =([C_28 1,14]+[C_(28:1) 1,14])/([C_28 1,14]+[C_(28:1) 1,14]+[C_30 1,14]+[C_(30:1) 1,14]+[C_28 1,13]+[C_30 1,13]+[C_30 1,15] )

The NDI was positively associated with the ocean atlas values of surface water phosphate and nitrate concentrations for the SPM and surface sediment data sets (Fig. 1). Accordingly, the results of our study showed that the NDI has potential as a quantitative nutrient proxy for estimating sea surface phosphate (or nitrate) changes. Definitely, more works are needed to assess the NDI applicability for reconstructing surface water nutrient variations in the past, by analysing more SPM and sediment cores collected from various oceanic settings.