Constraints on the use of long-chain diols as environmental proxies

Abstract

In order to better predict future climate change, we need knowledge on past oceanic and atmospheric responses to climate perturbations comparable to the current anthropogenic release of greenhouse gases. Accordingly, we rely on so-called climate archives of which tree rings, ice cores and marine and lacustrine sediments are typical examples. Especially, marine sediments are frequently used, in which we can measure climate proxies which are preserved entities providing indirect information on the climate when the sediments were deposited. This research has focused on organic geochemical proxies based on long-chain diols, which are organic molecules produced by micro-organisms in the ocean, and preserved in the sediment. It was previously observed that ratios of 1,13- and 1,15-diols show a strong relationship with surface seawater temperature, so that measuring these ratios in sediment cores might enable the reconstruction of past seawater temperature variations. In addition, 1,14-diols produced by diatoms typically thriving in upwelling regions, regions of high primary productivity induced by nutrient input from deep waters, may be applied as tracers of variations in past upwelling intensity. This thesis focuses on testing and validating the applicability of these proxies, and on the significance of long-chain diols as environmental indicators. We provide several new insights in the environmental controls determining the long-chain diol distributions we observe in marine sediments and show that long-chain diols can serve as valuable climate proxies for surface seawater temperature, upwelling and riverine input in coastal systems, though several constraints have to be considered before application.