Aerosol iron was examined in Saharan dust plumes using a combination of iron near-edge X-ray absorption spectroscopy and wet-chemical techniques. Aerosol samples were collected at three sites located in the Mediterranean, the Atlantic, and Bermuda to characterize iron at different atmospheric transport lengths and time scales. Iron(III) oxides were a component of aerosols at all sampling sites and dominated the aerosol iron in Mediterranean samples. In Atlantic samples, iron(II and III) sulfate, iron(III) phosphate, and iron(II) silicates were also contributors to aerosol composition. With increased atmospheric transport time, iron(II) sulfates are found to become more abundant, aerosol iron oxidation state became more reduced, and aerosol acidity increased. Atmospheric processing including acidic reactions and photoreduction likely influence the form of iron minerals and oxidation state in Saharan dust aerosols and contribute to increases in aerosol-iron solubility.
Polyphosphate (polyP) was examined within the upper water column ( 150 m) of Station ALOHA (228 45 0 N, 1588 00 0 W) during two cruises conducted in May-June 2013 and September 2013. Phosphorus molar ratios of particulate polyP to total particulate phosphorus (TPP) were relatively low, similar to previously reported values from the temperate western North Atlantic, and did not exhibit strong vertical gradients, reflecting a lack of polyP recycling relative to other forms of TPP with depth. Furthermore, relationships among polyP:TPP, soluble reactive phosphorus (SRP), and alkaline phosphatase activity (APA) were also consistent with previous observations from the Atlantic Ocean. To ascertain potential mechanisms of biological polyP production and utilization, surface seawater was incubated following nutrient additions. Results were consistent with polyP:TPP enrichment under opposite extremes of APA, suggesting diverse polyP accumulation/retention mechanisms. Addition of exogenous polyP (45 6 5 P atoms) to field incubations did not increase chlorophyll content relative to controls, suggesting that polyP was not bioavailable to phytoplankton at Station ALOHA. To clarify this result, phytoplankton cultures were screened for the ability to utilize exogenous polyP. PolyP bioavailability was variable among model diatoms of the genus Thalassiosira, yet chain length did not influence polyP bioavailability. Thus, microbial community composition may influence polyP dynamics in the ocean, and vice versa.Phosphorus (P) is a vital nutrient present in major biomolecules such as nucleic acids, phospholipids, and adenosine 5 0 -triphosphate (ATP). P is considered the ultimate limiting nutrient in the ocean over geologic timescales (hundreds to millions of years) because its abundance is regulated by relatively slow processes such as continental weathering and the burial of authigenic calcium phosphate minerals in marine sediments. However, revised estimates of marine P removal have decreased the residence time of P in the ocean (Ruttenberg 1993;Benitez-Nelson 2000;Ruttenberg 2014), and recent discoveries have revealed surprising aspects of microbial P metabolism (Yang and Metcalf 2004;Karl et al. 2008;Van Mooy et al. 2009; Martinez et al. 2012;Van Mooy et al. 2015), which highlights a need and growing interest to better understand the cycling of marine P on a wide range of timescales (Karl 2014).Polyphosphate (polyP) is a biopolymer consisting of at least three and up to thousands of phosphate molecules joined by phosphoanhydride (PAOAP) bonds. PolyP has historically been under-recognized in the study of ocean biogeochemistry (Bj€ orkman 2014). However, recent evidence suggests that polyP may play a key role in the marine P cycle over both modern and geologic timescales. For example, in sediments polyP may participate in long-term P sequestration by facilitating the formation of authigenic apatite phases (Schulz and Schulz 2005;Diaz et al. 2008). Over shorter timescales, polyP in surface waters may represent a source o...
Biological productivity in many ocean regions is controlled by the availability of the nutrient phosphorus. In the Mediterranean Sea, aerosol deposition is a key source of phosphorus and understanding its composition is critical for determining its potential bioavailability. Aerosol phosphorus was investigated in European and North African air masses using phosphorus near-edge X-ray fluorescence spectroscopy (P-NEXFS). These air masses are the main source of aerosol deposition to the Mediterranean Sea. We show that European aerosols are a significant source of soluble phosphorus to the Mediterranean Sea. European aerosols deliver on average 3.5 times more soluble phosphorus than North African aerosols and furthermore are dominated by organic phosphorus compounds. The ultimate source of organic phosphorus does not stem from common primary emission sources. Rather, phosphorus associated with bacteria best explains the presence of organic phosphorus in Mediterranean aerosols.
Abstract:The composition and oxidation state of aerosol iron were examined using synchrotron-based iron near-edge X-ray absorption spectroscopy. By combining synchrotron-based techniques with water leachate analysis, impacts of oxidation state and mineralogy on aerosol iron solubility were assessed for samples taken from multiple locations in the Southern and the Atlantic Oceans; and also from Noida (India), Bermuda, and the Eastern Mediterranean (Crete). These sampling locations capture iron-containing aerosols from different source regions with varying marine, mineral dust, and anthropogenic influences. Across all locations, pH had the dominating influence on aerosol iron solubility. When aerosol samples were approximately neutral pH, iron solubility was on average 3.4%; when samples were below pH 4, the iron solubility increased to 35%. This observed aerosol iron solubility profile is consistent with thermodynamic predictions for the solubility of Fe(III) oxides, the major iron containing phase in the aerosol samples. Source regions and transport paths were also important factors affecting iron solubility, as samples originating from or passing over populated regions tended to contain more soluble iron. Although the acidity appears to affect aerosol iron solubility globally, a direct relationship for all samples is confounded by factors such as anthropogenic influence, aerosol buffer capacity, mineralogy and physical processes.
Iron has a key role in controlling biological production in the Southern Ocean, yet the mechanisms regulating iron availability in this and other ocean regions are not completely understood. Here, based on analysis of living phytoplankton in the coastal seas of West Antarctica, we present a new pathway for iron removal from marine systems involving structural incorporation of reduced, organic iron into biogenic silica. Export of iron incorporated into biogenic silica may represent a substantial unaccounted loss of iron from marine systems. For example, in the Ross Sea, burial of iron incorporated into biogenic silica is conservatively estimated as 11 mmol m À 2 per year, which is in the same range as the major bioavailable iron inputs to this region. As a major sink of bioavailable iron, incorporation of iron into biogenic silica may shift microbial population structure towards taxa with relatively lower iron requirements, and may reduce ecosystem productivity and associated carbon sequestration.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.