Search for: All records

Abstract. Meeting internationally agreed-upon climate targets requirescarbon dioxide removal (CDR) strategies coupled with an urgent phase-down offossil fuel emissions. However, the efficacy and wider impacts of CDR arepoorly understood. Enhanced rock weathering (ERW) is a land-based CDRstrategy requiring large-scale field trials. Here we show that a low 3.44 t ha−1 wollastonite treatment in an 11.8 ha acid-rain-impacted forested watershed in New Hampshire, USA, led to cumulative carbon capture by carbonic acid weathering of 0.025–0.13 t CO2 ha−1 over 15 years. Despite a 0.8–2.4 t CO2 ha−1 logistical carbon penalty from mining,grinding, transportation, and spreading, by 2015 weathering together withincreased forest productivity led to net CDR of 8.5–11.5 t CO2 ha−1. Our results demonstrate that ERW may be an effective, scalableCDR strategy for acid-impacted forests but at large scales requiressustainable sources of silicate rock dust. 

Mercury isotopic compositions of amphipods and snailfish from deep-sea trenches reveal information on the sources and transformations of mercury in the deep oceans. Evidence for methyl-mercury subjected to photochemical degradation in the photic zone is provided by odd-mass independent isotope values (Δ¹⁹⁹Hg) in amphipods from the Kermadec Trench, which average 1.57‰ (±0.14,n= 12, SD), and amphipods from the Mariana Trench, which average 1.49‰ (±0.28,n= 13). These values are close to the average value of 1.48‰ (±0.34,n= 10) for methyl-mercury in fish that feed at ∼500-m depth in the central Pacific Ocean. Evidence for variable contributions of mercury from rainfall is provided by even-mass independent isotope values (Δ²⁰⁰Hg) in amphipods that average 0.03‰ (±0.02,n= 12) for the Kermadec and 0.07‰ (±0.01,n= 13) for the Mariana Trench compared to the rainfall average of 0.13 (±0.05,n= 8) in the central Pacific. Mass-dependent isotope values (δ²⁰²Hg) are elevated in amphipods from the Kermadec Trench (0.91 ±0.22‰,n= 12) compared to the Mariana Trench (0.26 ±0.23‰,n= 13), suggesting a higher level of microbial demethylation of the methyl-mercury pool before incorporation into the base of the foodweb. Our study suggests that mercury in the marine foodweb at ∼500 m, which is predominantly anthropogenic, is transported to deep-sea trenches primarily in carrion, and then incorporated into hadal (6,000-11,000-m) food webs. Anthropogenic Hg added to the surface ocean is, therefore, expected to be rapidly transported to the deepest reaches of the oceans.

 

Abstract. Meteoric 10Be (10Bemet) concentrations insoil profiles have great potential as a geochronometer and a tracer of Earthsurface processes, particularly in fine-grained soils lacking quartz thatwould preclude the use of in situ produced 10Be (10Bein situ). Oneprerequisite for using this technique for accurately calculating rates anddates is constraining the delivery, or flux, of 10Bemet to a site.However, few studies to date have quantified long-term (i.e., millennial)delivery rates, and none have determined a delivery rate for an erodingsoil. In this study, we compared existing concentrations of 10Bein situ with new measurements of 10Bemet in eroding soils sampledfrom the same depth profiles to calibrate a long-term 10Bemetdelivery rate. We did so on the Pinedale (∼ 21–25 kyr) and BullLake (∼ 140 kyr) glacial moraines at Fremont Lake, Wyoming(USA), where age, grain sizes, weathering indices, and soil properties areknown, as are erosion and denudation rates calculated from 10Bein situ. After ensuring sufficient beryllium retention in each profile,solving for the delivery rate of 10Bemet, and normalizing forpaleomagnetic and solar intensity variations over the Holocene, we calculate10Bemet fluxes of 1.46 (±0.20) × 106 atoms cm−2 yr−1 and 1.30 (±0.48) × 106 atoms cm−2 yr−1 tothe Pinedale and Bull Lake moraines, respectively, and compare these valuesto two widely used 10Bemet delivery rate estimation methods thatsubstantially differ for this site. Accurately estimating the 10Bemetflux using these methods requires a consideration of spatial scale andtemporally varying parameters (i.e., paleomagnetic field intensity, solarmodulation) to ensure the most realistic estimates of10Bemet-derived erosion rates in future studies.