Preferential Riverine Export of Fine Volcanogenic Particles to the Southeast Australian Margin

Abstract

We report on rare earth element and neodymium isotopic compositions in a series of grain-size fractions separated from river suspended matter in the Murray-Darling Basin (MDB) and a nearby marine sediment core (MD03-2607) offshore southeastern Australia. This source-to-sink approach was used to further investigate the extent to which sediment sorting may control the geochemistry of suspended loads in rivers, and to provide constraints on the source of the detrital sediment material exported to the ocean. Our results provide further compelling evidence that significant sizedependent geochemical decoupling can occur in river systems, accounting here for Nd isotopic (ε Nd) differences of up to eight epsilon-units between silt (>25 µm) and colloidal (0.2−0.006 µm; 0.006−0.003 µm) fractions. All suspended particulate samples from the River Murray watershed display a trend toward more radiogenic (higher ε Nd) Nd signatures with decreasing grain-size, in addition to differing REE signatures, which collectively point toward a preferential volcanogenic origin for the fine-grained inorganic particles transported by MDB rivers. Furthermore, we show that the same river-borne volcanogenic material dominates in the fine-grained detrital fractions extracted from core MD03-2607 at the southeastern Australian margin; a finding corroborated by REE signatures in a series of copepod fecal pellet separates from the same core. Collectively, our results suggest that river sediment discharge is accompanied by preferential export of fine-grained volcanogenic particles to the ocean. This potential source of bioavailable trace metals and nutrients in ocean surface waters could impact marine productivity.

The Study of Peri-Urban Soil Contamination in the Kenitra Region, Morocco – Characterization and Assessment Using a Statistical Approach

“…The correlation between the fine fraction (< 63 µm) and most metals is quite good (r > 0.60). This result supports previous studies stating that metals preferentially associate with the finest fraction of the sediment (Bayon et al, 2020;Gunalan et al, 2018). Lead, copper and cadmium show an affinity with carbonates (calcite) and organic carbon (r > 0.50).…”

A global survey of radiogenic strontium isotopes in river sediments

“…Additionally, recent studies based on Nd isotopes have documented the preferential presence of radiogenic volcanogenic particles (i.e. characterized by relatively high  Nd signatures) in the finest size fractions of river suspended loads (e.g., Bayon et al, 2020b). To investigate whether such effect could partially account for the observed size-dependent Sr isotope decoupling in the rivers draining mixed lithologies,  87 Sr/ 86 Sr Clay-Silt is plotted against  Nd clay-silt , i.e.…”

Mixed carbonate-siliceous hydrothermal chimneys ahead of the Asal propagating rift (SE Afar Rift, Republic of Djibouti)

“…The behavior of REE during basalt alteration has been investigated in previous studies, showing that weathered volcanogenic products are typically associated with development of a pronounced negative Ce anomaly (Price et al, 1991;Prudencio et al, 1995;Martin and McCulloch, 1999). The development of Ce-anomalies during basalt weathering is thought to relate to preferential Ce oxidation and sequestration relative to its neighboured trivalent REE (Prudencio et al, 1995); a process which can result in the development of negative Ceanomalies in weathering products subsequently formed in soils and exported to river systems (Bayon et al, 2020).…”