https://ogma.newcastle.edu.au/vital/access/ /manager/Index ${session.getAttribute("locale")} 5 https://ogma.newcastle.edu.au/vital/access/ /manager/Repository/uon:50135 Tue 04 Jul 2023 14:02:38 AEST ]]> https://ogma.newcastle.edu.au/vital/access/ /manager/Repository/uon:33010 SO₄ =(mSO₄/mCO₃)_solid/(mSO₄/mCO₃)_solution. High crystal growth rates (driven by either pH or saturation state) encouraged higher values of D_SO₄ because of an increasing concentration of defect sites on crystal surfaces. At low growth rates, D_SO₄ was reduced due to an inferred competition between sulphate and bicarbonate at the calcite surface. These experimental results are applied to understand the incorporation of sulphate into speleothem calcite. The experimentally determined pH-dependence suggests that strong seasonal variations in cave air PCO₂ could account for annual cycles in sulphate concentration observed in stalagmites. Our new experimentally determined values of D_SO₄ were compared with D_SO₄ values calculated from speleothem-drip water monitoring from two caves within the Austrian and Italian Alps. At Obir cave, Austria, D_SO₄ (×10⁵) varies between 11.1 (winter) and 9.0 (summer) and the corresponding figures for Ernesto cave, Italy, are 15.4 (winter) and 14.9 (summer). These values approximate predicted D_SO₄ values based on our chamber experiments containing both low (2 ppm) and high (20 ppm) sulphate concentrations. Our experimental values of D_SO₄ obtained at crystal growth rates typical of stalagmites, closely match those observed in other cave sites from around the world. This validates the universality of the controls behind D_SO₄ and will enhance the use of speleothem CAS as a palaeoenvironmental proxy.]]> Tue 03 Sep 2019 18:19:27 AEST ]]> https://ogma.newcastle.edu.au/vital/access/ /manager/Repository/uon:12517 DIC values are already higher (by about 1‰) than those of soil water due to dissolution of the carbonate rock. A subsequent systematic shift to even higher δ¹³C values, from −11.5‰ in the cave drips to about −8‰ calculated for the solution film on top of stalagmites, is related to degassing on the stalagmite top and equilibration with the cave air. Mass-balance modelling of C fluxes reveals that a very small percentage of isotopically depleted cave air CO₂ evolves from the first phase of dripwater degassing, and shifts the winter cave air composition toward slightly more depleted values than those calculated for equilibrium. The systematic ¹³C-enrichment from the soil to the stalagmites at Grotta di Ernesto is independent of drip rate, and forced by the difference in pCO₂ between cave water and cave air. This implies that speleothem δ¹³C values may not be simply interpreted either in terms of hydrology or soil processes.]]> Sat 24 Mar 2018 08:16:02 AEDT ]]> https://ogma.newcastle.edu.au/vital/access/ /manager/Repository/uon:10263 Sat 24 Mar 2018 08:13:06 AEDT ]]> https://ogma.newcastle.edu.au/vital/access/ /manager/Repository/uon:11476 Sat 24 Mar 2018 08:10:27 AEDT ]]> https://ogma.newcastle.edu.au/vital/access/ /manager/Repository/uon:10909 Sat 24 Mar 2018 08:07:41 AEDT ]]> https://ogma.newcastle.edu.au/vital/access/ /manager/Repository/uon:19953 Sat 24 Mar 2018 07:58:32 AEDT ]]> https://ogma.newcastle.edu.au/vital/access/ /manager/Repository/uon:6876 Sat 24 Mar 2018 07:49:46 AEDT ]]> https://ogma.newcastle.edu.au/vital/access/ /manager/Repository/uon:6877 Sat 24 Mar 2018 07:49:46 AEDT ]]> https://ogma.newcastle.edu.au/vital/access/ /manager/Repository/uon:27242 100 nm) of soils, but in the fine colloidal (< 100 nm) and nominally dissolved (< 1 nm) fractions of dripwaters. The concentration of Cu, Ni and Co in dripwater samples across all sites were well correlated (R2 = 0.84 and 0.70, Cu vs. Ni, Cu vs. Co, respectively), indicating a common association. Furthermore, metal ratios (Cu:Ni, Cu:Co) were consistent with NICA-Donnan n1 humic binding affinity ratios for these metals, consistent with a competitive hierarchy of binding affinity (Cu > Ni > Co) for sites in colloidal or dissolved NOM. Large shifts in Cu:Ni in dripwaters coincided with high fluxes of particulate OC (following peak infiltration) and showed increased similarity to ratios in soils, diagnostic of qualitative changes in NOM supply (i.e. fresh inputs of more aromatic/hydrophobic soil organic matter (SOM) with Cu outcompeting Ni for suitable binding sites). Results indicate that at high-flows (i.e. where fracture-fed flow dominates) particulates and colloids migrate at similar rates, whereas, in slow seepage-flow dripwaters, particulates (> 1 μm) and small colloids (1–100 nm) decouple, resulting in two distinct modes of NOM–metal transport: high-flux and low-flux. At the hyperalkaline drip site PE1 (in Poole's Cavern), high-fluxes of metals (Cu, Ni, Zn, Ti, Mn, Fe) and particulate NOM occurred in rapid, short-lived pulses following peak infiltration events, whereas low-fluxes of metals (Co and V > Cu, Ni and Ti) and fluorescent NOM (< ca. 100 nm) were offset from infiltration events, probably because small organic colloids (1–100 nm) and solutes (< 1 nm) were slower to migate through the porous matrix than particulates. These results demonstrate the widespread occurrence of both colloidal and particulate NOM–metal transport in cave dripwaters and the importance of karst hydrology in affecting the breakthrough times of different species. Constraints imposed by soil processes (colloid/particle release), direct contributions of metals and NOM from rainfall, and flow-routing (colloid/particle migration) are expected to determine the strength of correlations between NOM-transported metals in speleothems and climatic signals. Changes in trace metal ratios (e.g. Cu:Ni) in speleothems may encode information on NOM composition, potentially aiding in targeting of compound-specific investigations and for the assessment of changes in the quality of soil organic matter.]]> Sat 24 Mar 2018 07:29:08 AEDT ]]> https://ogma.newcastle.edu.au/vital/access/ /manager/Repository/uon:22573 Sat 24 Mar 2018 07:14:48 AEDT ]]>