BACKGROUND OF U AND Th IN SEDIMENTS OF BEDROCK RIVERS

The Miño River is a good example of bedrock rivers, where sediment geochemistry is scarcely studied. Its urban reach when passing through the city of Ourense gathers some characteristics that provide interest to its sediments, like scarcity of fine sediments accumulation and the impact of several human activities. Sediments trapped by potholes and other rock cavities were considered. In order to evaluate society-nature interactions through sediment composition it is critical to determine the compositional background (in absence of human alterations), particularly when working with trace elements. This work presents an exploratory assay to determine background in sediments from bedrock rivers by using two uncommon elements, uranium (U) and thorium (Th). To determine their background different statistical techniques were applied in order to set the background composition value and calculate possible enrichments. Background was calculated by simple least squares lineal regression by using Al as independent variable (reference element) resulting in 8.7 mgU kg-1 and 5.6 mgTh kg-1. Enrichments were found in some particular samples and can be attributed to intrinsic microenvironment complexities inside rock cavities.

Trace elements in New Zealand ferromanganese nodules: implications for deep sea environments

<p>Ferromanganese nodules are authigenic marine sediments that form over millions of years from the precipitation of Fe oxyhydroxides and Mn oxides from seawater (hydrogenetic-type growth) and sediment pore-water (diagenetic-type growth). Fe-Mn (oxyhydr)oxides grow in layers about nuclei, effectively scavenging minor metals such as Ni, Cu and Co from the waters they grow in. The uptake of different elements into the ferromanganese nodules reflects their environment and mechanism of growth, and these deposits are of interest both as a potential source of metals of economic interest, and as records of changing ocean conditions. This study investigates the composition of 77 ferromanganese nodules from the seafloor around New Zealand. Samples analysed come from locations several thousand kilometres apart under the same water mass (Lower Circumpolar Deep Water – LCDW), but with varying depth, current velocity, and sediment type. The outermost 1 mm rim of each nodule, representing near-modern growth, was sampled to compare with modern environmental parameters including substrate sediment composition and chemical and physical oceanography. Major, minor, and trace element analysis of nodule rims were undertaken, and the authigenic and detrital components examined via leaching experiments to evaluate their relative influence on growth mechanisms. Overall, New Zealand ferromanganese nodules are hydrogenetic in origin. However, there are systematic variations in composition that reflect variable diagenetic influence. Hydrogenetic endmember compositions are defined by samples from two localities in the Southern Ocean that have no evidence for diagenetic influence. Diagenetic influence on nodule composition is exemplified by samples from the two locations in the Tasman Sea, but also include nodules from the Campbell nodule field. Nodules from the Campbell nodule field come from two transects perpendicular to the Campbell Plateau, and the Deep Western Boundary Current (DWBC). Both sediment composition and nodule rim chemistry vary systematically across both transects. Areas closest to the slope have sediment profiles indicating high energy, erosive environments, continental-sourced sand components, and are dominated by nodules with hydrogenetic chemical characteristics similar to those of the Southern Ocean. Further from the slope, the sediment profiles indicate silt dominated sediments of a more oceanic crustal provenance, lower energy environment, and increased influence of oxic diagenetic processes on the major, minor and trace element profiles of the nodules. No hydrothermal contribution was identified in the chemistry of any of the nodules analysed. The physical and chemical properties of the sediment, along with current velocities, were found to be the key influences in diagenetic enrichment in the nodules. The influence of seawater chemistry was difficult to determine due to the lack of direct analyses in the area. Ferromanganese nodule chemistry is a function of the nodule environment, including water body, sediment composition and depth. The authigenic components of nodules can therefore be used to investigate the deep-sea environment. The redox conditions of sediments and the productivity of the overlying water will affect the trace metal constituents of the pore-waters of a sediment (Kuhn et al., 2017). Sediments with a larger fraction of labile organic matter may result in trace element enrichment of the pore-water. Sediments below the CCD will be higher in trace elements than sediments below the CCD (U1413, U1406B, U1402, U1398, U1398, and U1378) due to carbonate matter acting as a dilutant that can limit the supply of trace elements mobilised in the pore-water during diagenesis (Glasby, 2006). Terrigenous clasts such as quartz (Chester, 1990), will also reduce trace element enrichment in the pore-water due to their low reactivity, e.g. for the sediment U1406B, which has a high lithic component (Table 3.2). Sediments with a higher biogenic silica component (such as U1373, U1374, and U1378) (Table 3.2, Table 3.4) are predicted to produce nodules with higher trace element contents (ISA, 2010). In contrast to both the CCZ and Indian Ocean nodules, the Campbell nodule field samples formed above the CCD, and hence in sediments that include a significant carbonate component. This minimises the trace element pore-water enrichment and can account for the lower Cu+Ni+Co contents observed in the Campbell nodule field nodules compared with those that formed below the CCD (CCZ and Indian Ocean).</p>

Trace elements in New Zealand ferromanganese nodules: implications for deep sea environments

<p>Ferromanganese nodules are authigenic marine sediments that form over millions of years from the precipitation of Fe oxyhydroxides and Mn oxides from seawater (hydrogenetic-type growth) and sediment pore-water (diagenetic-type growth). Fe-Mn (oxyhydr)oxides grow in layers about nuclei, effectively scavenging minor metals such as Ni, Cu and Co from the waters they grow in. The uptake of different elements into the ferromanganese nodules reflects their environment and mechanism of growth, and these deposits are of interest both as a potential source of metals of economic interest, and as records of changing ocean conditions. This study investigates the composition of 77 ferromanganese nodules from the seafloor around New Zealand. Samples analysed come from locations several thousand kilometres apart under the same water mass (Lower Circumpolar Deep Water – LCDW), but with varying depth, current velocity, and sediment type. The outermost 1 mm rim of each nodule, representing near-modern growth, was sampled to compare with modern environmental parameters including substrate sediment composition and chemical and physical oceanography. Major, minor, and trace element analysis of nodule rims were undertaken, and the authigenic and detrital components examined via leaching experiments to evaluate their relative influence on growth mechanisms. Overall, New Zealand ferromanganese nodules are hydrogenetic in origin. However, there are systematic variations in composition that reflect variable diagenetic influence. Hydrogenetic endmember compositions are defined by samples from two localities in the Southern Ocean that have no evidence for diagenetic influence. Diagenetic influence on nodule composition is exemplified by samples from the two locations in the Tasman Sea, but also include nodules from the Campbell nodule field. Nodules from the Campbell nodule field come from two transects perpendicular to the Campbell Plateau, and the Deep Western Boundary Current (DWBC). Both sediment composition and nodule rim chemistry vary systematically across both transects. Areas closest to the slope have sediment profiles indicating high energy, erosive environments, continental-sourced sand components, and are dominated by nodules with hydrogenetic chemical characteristics similar to those of the Southern Ocean. Further from the slope, the sediment profiles indicate silt dominated sediments of a more oceanic crustal provenance, lower energy environment, and increased influence of oxic diagenetic processes on the major, minor and trace element profiles of the nodules. No hydrothermal contribution was identified in the chemistry of any of the nodules analysed. The physical and chemical properties of the sediment, along with current velocities, were found to be the key influences in diagenetic enrichment in the nodules. The influence of seawater chemistry was difficult to determine due to the lack of direct analyses in the area. Ferromanganese nodule chemistry is a function of the nodule environment, including water body, sediment composition and depth. The authigenic components of nodules can therefore be used to investigate the deep-sea environment. The redox conditions of sediments and the productivity of the overlying water will affect the trace metal constituents of the pore-waters of a sediment (Kuhn et al., 2017). Sediments with a larger fraction of labile organic matter may result in trace element enrichment of the pore-water. Sediments below the CCD will be higher in trace elements than sediments below the CCD (U1413, U1406B, U1402, U1398, U1398, and U1378) due to carbonate matter acting as a dilutant that can limit the supply of trace elements mobilised in the pore-water during diagenesis (Glasby, 2006). Terrigenous clasts such as quartz (Chester, 1990), will also reduce trace element enrichment in the pore-water due to their low reactivity, e.g. for the sediment U1406B, which has a high lithic component (Table 3.2). Sediments with a higher biogenic silica component (such as U1373, U1374, and U1378) (Table 3.2, Table 3.4) are predicted to produce nodules with higher trace element contents (ISA, 2010). In contrast to both the CCZ and Indian Ocean nodules, the Campbell nodule field samples formed above the CCD, and hence in sediments that include a significant carbonate component. This minimises the trace element pore-water enrichment and can account for the lower Cu+Ni+Co contents observed in the Campbell nodule field nodules compared with those that formed below the CCD (CCZ and Indian Ocean).</p>

Introducing GloRiSe – a global database on river sediment composition

Rivers transport dissolved and solid loads from terrestrial realms to the oceans and between inland reservoirs, representing major mass fluxes on Earth's surface. The composition of river water and sediment provides clues to a plethora of Earth and environmental processes, including weathering, erosion, nutrient and carbon cycling, environmental pollution, reservoir exchange, and tectonic cycles. While there are documented, publicly available databases for riverine dissolved and suspended nutrients, there is no openly accessible, georeferenced database for riverine suspended sediment composition. Here, we present a globally representative set of 2828 suspended and bed sediment compositional measurements from 1683 locations around the globe. This database, named Global River Sediments (GloRiSe) version 1.1, includes major, minor and trace elements, along with mineralogical data, and provides time series for some sites. Each observation is complemented by metadata describing geographic location, sampling date and time, sample treatment, and measurement details, which allows for grouping and selection of observations, as well as for interoperability with external data sources, and improves interpretability. Information on references, unit conversion and references makes the database comprehensible. Notably, the close to globe-spanning extent of this compilation allows the derivation of data-driven, spatially resolved global-scale conclusions about the role of rivers and processes related to them within the Earth system. GloRiSe version 1.1 can be downloaded from Zenodo (https://doi.org/10.5281/zenodo.4485795, Müller et al., 2021) and GitHub (https://github.com/GerritMuller/GloRiSe, last access: 26 May 2021), where updates with adapted version numbers will become available, along with a technical documentation and an example calculation in the form of MATLAB scripts, which calculate the sediment-flux-weighted major element composition of the annual riverine suspended sediment export to the ocean and related uncertainties.

Mapping of Sediment on the Waters Around Panjang Island, Banten Bay, Indonesia

This study was conducted to map the surface sediment conditions in the waters around Panjang Island, Banten Bay. The survey method was conducted in February 2015 by taking sediment samples using a grab sampler at 15 stations. Sediment analysis was conducted to determine the grain size using the granulometry method which was then processed using the KUMMOD-SEL software to obtain the composition and texture of the sediment. The results of processing sediment samples at each station obtained that the grain size of sediments in the waters around Panjang Island ranged from -0.7 to 2.6 in the phi (φ) scale. Sediment composition consists of sand and gravel, with sand dominance of 89.1 %. Sediment textural classification consists of only 4 categories i.e. very coarse sand, coarse sand, medium sand, and fine sand. In general, the pattern of sediment distribution follows the pattern of water depth, where fine sand occupies deeper areas. Meanwhile, medium sand dominates surface sediment distribution in the study area.

Temporal change in molluscan assemblages (bivalves and gastropods) of Frobisher Bay, Nunavut, Canada, over fifty years

Long-term studies provide an effective way to assess the ecological impacts of decades-long environmental change in Arctic coastal benthic environments but are undertaken rarely in the Canadian Arctic. In light of this, historical datasets can be compared with modern samples to examine temporal differences in benthic community structure. Frobisher Bay, Nunavut provides a unique opportunity to use a historical census to examine the impacts that long-term environmental change have had on the marine benthos. Between 1967-1976 and in 2016, infaunal samples were collected in inner Frobisher Bay and were compared to determine how the molluscan assemblages have changed between the two time periods. Molluscan assemblages in two regions of inner Frobisher Bay (Iqaluit and Cairn Island) were examined to minimize sampling discrepancies between the two time periods. A long-term increase in mean annual air temperature and a decline in the length of the ice cover season were observed. Both regions exhibited some change in sediment composition and quality and in molluscan assemblage between the two time periods and species diversity indices also indicated some change between time periods. Both the 1967-1976 and 2016 molluscan datasets provide a baseline for future long-term studies in a changing Arctic.