Apatite nanoparticles in 3.46–2.46 Ga iron formations: Evidence for phosphorus-rich hydrothermal plumes on early Earth

Phosphorus is an essential nutrient that is thought to have regulated primary productivity in global oceans after the advent of oxygenic photosynthesis. The prime source of seawater phosphorus is regarded to be continental weathering of phosphate minerals. Ancient seawater phosphorus concentrations have been constrained using the phosphorus content of iron-rich chemical sediments—banded iron formations (BIFs); however, the removal processes and depositional phases remain unclear. Here we report that nanometer-sized apatite crystals (<500 nm) are ubiquitous in 3.46–2.46 Ga BIFs and cherts from the Kaapvaal (South Africa) and Yilgarn and Pilbara (Western Australia) cratons. The apatite is uniformly dispersed in a chemical sediment comprising greenalite nanoparticles, which were encased in very early diagenetic silica cement that limited compaction and chemical reactions. The lack of organic carbon (below detection; <0.3 wt%) and absence of primary iron oxides implies that the phosphorus was not derived from the degradation of organic matter or seawater scavenging by oxide particles. Instead, the occurrence of apatite in sediments derived from hydrothermally sourced Fe2+ and SiO2(aq) suggests that phosphorus too was derived from vent plumes. Today, seawater P is rapidly removed from vent fluids due to scavenging by oxidized Fe2+. However, prior to the Great Oxidation Event (2.45–2.32 Ga), dissolved phosphorus released during anoxic alteration of seafloor basalts escaped the iron-oxidation trap. Our results point to the existence of a submarine hydrothermal flux of dissolved phosphorus that supplied nutrients to the early anoxic oceans. High amounts of seawater P may help to explain why phosphorus is ubiquitous in cell biology—it was not limiting during the origin and early evolution of life.

Ecotoxicological testing of sediments and dredged material: an overlooked opportunity?

Purpose Basing decisions for the management of contaminated sediments on ecotoxicological data is still often met with skepticism by European stakeholders. These concerns are discussed as they pertain to bioassays to show how ecotoxicological data may provide added value for the sustainable management of sediment in aquatic systems. Materials and methods Five “concerns” are selected that are often raised by stakeholders. The ecotoxicological practice is discussed in light of the knowledge gained in recent decades and compared with chemical sediment analysis and chemical data. Results and discussion Common assumptions such as a higher uncertainty of biotest results for sediments compared to chemical analyses are not supported by interlaboratory comparisons. Some confusion also arises, because the meaning of biotest data is often misunderstood, questioning their significance in light of a limited number of organisms and altered test conditions in the lab. Because biotest results describe a sediment property, they should not be directly equated with an impact upon the biological community. To identify a hazard, however, the possibility of false-negative results due to the presence of contaminants that are not analyzed but are toxic is lower. Conclusions The cost of increased investment in ecotoxicological tests is, in our view, small compared with that of making false-negative assessments of sediment/dredged material that can ultimately have long-term environmental costs. As such, we conclude that ecotoxicological testing is an opportunity for sediment management decision-making that warrants more attention and confidence in Europe.

Archean to Paleoproterozoic seawater halogen ratios recorded by fluid inclusions in chert and hydrothermal quartz

Past changes in the halogen composition of seawater are anticipated based on the differing behavior of chlorine and bromine that are strongly partitioned into seawater, relative to iodine, which is extremely depleted in modern seawater and enriched in marine sediments due to biological uptake. Here we assess the use of chert, a chemical sediment that precipitated throughout the Precambrian, as a proxy for halide ratios in ancient seawater. We determine a set of criteria that can be used to assess the primary nature of halogens and show that ancient seawater Br/Cl and I/Cl ratios can be resolved in chert samples from the 2.5 Ga Dales Gorge Member of the Brockman Banded Iron Formation, Hamersley Group, Western Australia. The values determined of Br/Cl ~2 × 10-3 M and I/Cl ~30 × 10-6 M are comparable to fluid inclusions in hydrothermal quartz from the 3.5 Ga North Pole area, Pilbara Craton, Western Australia, that were the subject of previous reconstructions of ancient ocean salinity and atmospheric isotopic composition. While the similar Br/Cl and I/Cl values indicate no substantial change in the ocean halide system over the interval 2.5–3.5Ga, compared to modern seawater, the ancient ocean was enriched in Br and I relative to Cl. The I/Cl value is intermediate between bulk Earth (assumed chondritic) and the modern seawater ratio, which can be explained by a smaller organic reservoir because this is the major control on marine iodine at the present day. Br/Cl ratios are about 30% higher than both modern seawater and contemporary seafloor hydrothermal systems, perhaps indicating a stronger mantle buffering of seawater halogens during the Archean.

The effect of tilapia Oreochromis niloticus addition on the sediment of brackish low-salinity ponds to white shrimp Penaeus vannamei farming system during the wet and dry season

The present study was carried out to determine the effect of tilapia Oreochromis niloticus on the physical and chemical sediment parameters on an earthen pond in monoculture (shrimp Penaeus vannamei) and co-culture (tilapia-shrimp) during the dry and wet seasons in a commercial farm during the period from mid-September to end-December 2017 and February to mid-May 2018. Chemical and physical analyses were realized on sediment samples from brackish water ponds representing shrimp farms in San Blas Nayarit, Mexico. Concentrations of organic carbon, nitrogen, potassium, magnesium and calcium were higher in co-culture ponds, and there was a tendency to a higher concentration of phosphorus and sodium in the sediment of monoculture ponds. The texture of the ponds showed a tendency in the dry season to increase the percentage of clay in co-culture due to the effect of bioturbation caused by tilapia. There was no evidence of poor development of sediment quality in any treatment. It was found that tilapia was a factor that affected sediment quality, differences in growth between shrimp monoculture and tilapia-shrimp co-culture can be explained, at least in part, by differences in their sediment.

Chemical sediment variables from the Faroe area: Organic content, Nitrogen, Phosphorus, Zinc, and Copper / Evnafrøðiligar bleytbotnsdátur á føroyskum havøki: lívrunnið tilfar, nitrogen, fosfor, sink og kopar

<p><strong>Ú</strong><strong>r</strong><strong>t</strong><strong>ak</strong>: Havlívfrøðiliga royndarstøðin hevur síðan 1998 gjørt regluligar kanningar av botnsigi í føroyskum firðum. Kanningarnar fevndu um fylgjandi evnafrøðiligu brigdlar: nøgd av lívrunnum tilfari (gløðitap), sinki, kopari og heildarnøgd av køvievni og fosfori. Greinin viðger broytni av hesum og fevnir um 229 staksýni.</p><p>Í hesi grein eru eisini savnað úrslit, sum onnur hava almannakunngjørt um somu evnafrøðiligu broytlar.</p><p>Úrslitini eru bólkað eftir dýpi og eftir hvørjum slagi av botnsigi, ið tað snýr seg um. Eisini verður hugt eftir, hvussu virðini eru inni við land og borið verður saman við, hvussu tað er útiá.</p><p>Inni við land var nøgdin av lívrunnum tilfari, nitrogeni, fosfori, sinki og kopari í botnsiginum ávikavist: 0,5-13,0 %, 0,14-4,01 g/kg, 0,43-2,02 g/kg, 12-98 mg/kg og 14-120 mg/kg. Útiá var innihaldið av lívrunnum tilfari millum 1,3 og 5,6 %, meðan innihaldið av sinki og kopari vóru 13-47 mg/kg og 5-38 mg/kg.</p><p><strong>A</strong><strong>bstract</strong>: Since 1998 Kaldbak Marine Biological Laboratory (KMBL) has regularly performed seabed surveys in Faroese fjords. The analyses performed on the sediments included the chemical variables: Organic content (loss on ignition), total nitrogen, total phosphorus, zinc and copper. This paper deals with the variability of the variables in the Faroe area.</p><p>The results of 229 seabed samples are included. Inshore data are compared and related to depth intervals and according to sediment types. Sediment data from inshore waters are compared to sediment data from offshore localities.</p><p>Also included in this paper are eight reports that include data on the above mentioned chemical variables.</p><p>From inshore waters the concentration of organic matter, total nitrogen, total phosphorous, zinc and copper in the sediments was, respectively: 0.5-13.0 %, 0.14-4.01 g/kg, 0.43-2.02 g/kg, 12-98 mg/kg and 14-120 mg/kg. Organic content from offshore localities showed values from 1.3 to 5.6 % while the content of zinc and copper were 13-47 mg/kg and 5-38 mg/kg, respectively.</p>