¹⁰Be/⁹Be Ratios Reveal Marine Authigenic Clay Formation

Abstract

As reverse weathering has been shown to impact long‐term changes in atmospheric CO2 levels, it is crucial to develop quantitative tools to reconstruct marine authigenic clay formation. We explored the potential of the beryllium (Be) isotope ratio (10Be/9Be) recorded in marine clay‐sized sediment to track neoformation of authigenic clays. The power of such proxy relies on the orders‐of‐magnitude difference in 10Be/9Be ratios between continental Be and Be dissolved in seawater. On marine sediments collected along a Chilean margin transect we chemically extracted reactive phases and separated the clay‐sized fraction to compare the riverine and marine 10Be/9Be ratio of this fraction. 10Be/9Be ratios increase fourfold from riverine to marine sediment. We attribute this increase to the incorporation of Be high in 10Be/9Be from dissolved biogenic opal, which also serves as a Si‐source for the precipitation of marine authigenic clays. 10Be/9Be ratios thus sensitively track reverse‐weathering reactions forming marine authigenic clays.

Evolution of the Global Carbon Cycle and Climate Regulation on Earth

“…Subsequently, both field (e.g., Baldermann et al, 2013;Baldermann et al, 2015;Ehlert et al, 2016;Ku & Walter, 2003;Mackenzie et al, 1981;Mackin & Aller, 1984, 1986März et al, 2015;Michalopoulos et al, 2000;Michalopoulos & Aller, 1995, 2004Presti & Michalopoulos, 2008;Rahman et al, 2016Rahman et al, , 2017Ristvet, 1978;Solomon et al, 2008;Tatzel et al, 2015;Wallmann et al, 2008) and laboratory studies (Loucaides et al, 2010;Michalopoulos & Aller, 1995) investigating the mineralogy and porewater chemistry of modern marine sediments and their evolution with depth have provided convincing evidence for the operation of this process in the natural environment, prompting greater acceptance within the broader community. Most recently, studies of stable Si (Ehlert et al, 2016), cosmogenic Si (Rahman et al, 2016(Rahman et al, , 2017 and beryllium (Be) (Bernhardt et al, 2020) isotopes have been developed as a tracer for fingerprinting Si uptake during authigenic clay formation in marine sediments. Similar to marine weathering, reverse weathering has been observed to take place in both marine sediments (e.g., Ehlert et al, 2016) and oceanic crust (e.g., Chan et al, 1992;Chan et al, 2002;Chan & Kastner, 2000).…”

Initial measurement of beryllium‐9 using high‐resolution inductively coupled plasma mass spectrometry allows for more precise applications of the beryllium isotope system within the Earth Sciences

“…1,4 Eventually, the reactive and dissolved Be contained within rivers, which equilibrate to have approximately identical 10 Be/ 9 Be ratios, is discharged to the ocean where it mixes with the meteoric 10 Be introduced directly from the atmosphere, the reactive phase of which becomes deposited in marine sediments. 5 The measurement of 10 Be and 9 Be in the reactive phase of soils and sediments or the dissolved phase in rivers and seawater has elucidated a wide range of Earth system processes. The authigenic phase of sediments, the dissolved phase of seawater and Fe-Mn crusts have been used to quantify denudation rates, erosion rates or the degree of weathering on both regional 2,[6][7][8][9] and global 1,4,5,10 scales.…”

“…[19][20][21][22][23] Concerning the measurement of 10 Be/ 9 Be ratios for the aforementioned purposes, only Be in the chemically precipitated or dissolved form is of use as the high abundance of 9 Be from primary silicate minerals, which is not relevant to these processes, needs to be excluded. 4 The reactive (authigenic) Be therefore needs to be extracted from sedimentary material as this reflects the 10 Be/ 9 Be ratio of the overlying water column at the time of deposition. 2,11 This has led to a series of reductive leaching techniques aimed at extracting the Fe-Mn oxyhydroxide component of sediments.…”

“…Alternatively, a solution of hydrogen peroxide (H 2 O 2 ) and/or 0.5 to 6 M hydrochloric acid (HCl) has been utilised. 2,14,18,27 After leaching, a small aliquot (10%) of the sample solution is used for 9 Be determination, the remainder of which undergoes 10 Be measurement using accelerator mass spectrometry (AMS). 2,11 Beryllium-9 analysis is generally conducted by either standard addition methods using atomic absorption spectrophotometry (AAS) 11,17,[21][22][23]28 or calibration methods using inductively coupled plasma (ICP) optical emission (OES) or mass spectrometry (MS), 2,14,15,26 achieving a precision of 5% and 2 to 5%, respectively.…”

“…Here, we present the first 9 Be analysis of five geochemical reference materials by high-resolution inductively coupled plasma mass spectrometry (HR-ICP-MS) using a Thermo® ELEMENT XR instrument. Although not directly compared, results suggest that using HR-ICP-MS can improve precision over AAS, ICP-OES or ICP-MS measurements reported in the literature.…”