Organic complexation in karst cave systems: implications for transition metal incorporation into speleothems
type: CreativeWork
description: The accurate prediction of future climate scenarios heavily relies on the robust understanding of the magnitude and drivers of past climate variability. Amongst the various materials used to study historic climate beyond the instrumental record, secondary cave carbonate deposits, or speleothems, have proven to present particularly valuable archives of numerous environmental processes over a range of temporal and spatial scales. In this context, trace elements included in speleothems are increasingly used to bolster speleothem-based records of past climates and environments (often primarily based on stable isotope proxies), with Mg/Ca and Sr/Ca ratios presenting the most widely interpreted elemental signatures indicative of hydrological processes in the karst. More recently, however, a novel proxy system based on the concentrations of first-row transition metals in stalagmites has been proposed to potentially offer a first means to quantitatively reconstruct past cave drip rates, and hydroclimate by extension. The transport from the surface to the site of speleothem formation of transition metals, such as Co, Ni, or Cu, is understood to be largely governed by the formation of organic metal complexes (OMCs) with ligands present in natural organic matter (NOM). This organic association can evidently facilitate the deposition of organically-complexed metals in response to strong infiltration events, however, has also been suggested to enable a mechanistically distinct and largely undefined inclusion pathway for metals into calcite. Specifically, the availability of transition metals at speleothem surfaces for partitioning into the crystal phase may arguably be driven by the rate-dependant dissociation (or ‘decay’) of OMCs, which is in turn predicted to depend on their residence time at speleothem surfaces. OMC decay kinetics may thus present a potentially viable link between metal concentrations in stalagmites, and the residence time of OMCs at their surfaces. This thes…
abstract: The accurate prediction of future climate scenarios heavily relies on the robust understanding of the magnitude and drivers of past climate variability. Amongst the various materials used to study historic climate beyond the instrumental record, secondary cave carbonate deposits, or speleothems, have proven to present particularly valuable archives of numerous environmental processes over a range of temporal and spatial scales. In this context, trace elements included in speleothems are increasingly used to bolster speleothem-based records of past climates and environments (often primarily based on stable isotope proxies), with Mg/Ca and Sr/Ca ratios presenting the most widely interpreted elemental signatures indicative of hydrological processes in the karst. More recently, however, a novel proxy system based on the concentrations of first-row transition metals in stalagmites has been proposed to potentially offer a first means to quantitatively reconstruct past cave drip rates, and hydroclimate by extension. The transport from the surface to the site of speleothem formation of transition metals, such as Co, Ni, or Cu, is understood to be largely governed by the formation of organic metal complexes (OMCs) with ligands present in natural organic matter (NOM). This organic association can evidently facilitate the deposition of organically-complexed metals in response to strong infiltration events, however, has also been suggested to enable a mechanistically distinct and largely undefined inclusion pathway for metals into calcite. Specifically, the availability of transition metals at speleothem surfaces for partitioning into the crystal phase may arguably be driven by the rate-dependant dissociation (or ‘decay’) of OMCs, which is in turn predicted to depend on their residence time at speleothem surfaces. OMC decay kinetics may thus present a potentially viable link between metal concentrations in stalagmites, and the residence time of OMCs at their surfaces. This thes…
author: Höpker, Sebastian Niels
keywords: Carbonate, Climate, Geochemistry, Cave, South Pacific, Trace metal, Organic matter
license: https://researchcommons.waikato.ac.nz/bitstreams/26e0a104-ab6f-456c-84f5-95c33ab6df18/download
date published: 2024
date modified: 2026-07-24T05:57:52Z
provider: University Waikato
publisher: Networked Digital Library of Theses and Dissertations
type: WebPage
source organization: The University of Waikato