| 28 Apr 2026
Variations in Arctic aerosol iron solubility in relation to leaching methodology, air mass characteristics, and seasonality
Abstract. Atmospheric deposition of the essential micronutrient, iron (Fe), can have an important influence on primary production and marine biogeochemistry. In the Arctic Ocean, the ongoing shift towards seasonal ice coverage means that summertime atmospheric deposition increasingly takes place direct to the surface ocean, rather than onto sea ice. As a result, atmospheric deposition of material emitted from natural and anthropogenic sources may become a more relevant Fe input to the region. As part of the U.S. GEOTRACES GN01 section, aerosols and precipitation samples were collected to quantify the atmospheric delivery of Fe and other trace elements to the Arctic Ocean. Aerosol Fe solubility was assessed using three different leaching approaches. The readily soluble fraction, determined by rapid exposure leaches with ultrapure water (UPW) and filtered seawater (SW) was low throughout GN01, averaging 0.7 % and 1.4 %, respectively. Solubility determined using a more aggressive acetic acid (HAc) leach as an upper limit estimate of post-deposition aerosol Fe bioavailability averaged 44 %. Comparison to Fe UPW-solubility data from winter (median 6.5 %) and springtime (median 1.9 %) aerosol samples collected during the MOSAiC expedition suggests a strong seasonality to Arctic aerosol Fe solubility, potentially associated with winter/springtime Arctic haze. Iron stable isotope analysis of GN01 total Fe (d56FeTot = +0.10 ± 0.13 ‰) and UPW-soluble Fe (d56FeSol = −0.17 ± 0.33 ‰) indicate the low summertime total Fe loading was dominated by mineral aerosols, albeit with anthropogenic contributions to the small soluble Fe fraction in some samples. Bulk deposition fluxes, calculated using the beryllium-7 method, were estimated at 0.8 ± 1.2 nmol m-2 d-1 UPW-soluble Fe, 1.8 ± 1.9 nmol m-2 d-1 SW-soluble Fe, and 46 ± 48 nmol m-2 d-1 HAc-soluble Fe, with the UPW-soluble Fe flux around an order of magnitude lower than that measured during the winter months.
This article combines together fe solubility measurements in the Arctic Ocean and, for the first time, explores the seasonal variability of both bulk deposition and relative solubility of fe transported and deposited via aerosol deposition. The Arctic provides a unique template for aerosol exploration given the year-round sea ice coverage that prevents complete deposition into the seawater where fe is likely to have the largest impact on biology. The authors do a very complete comparison with other aerosol studies in the Arctic from the same cruises they focus on (GEOTRACES GN01 and the MOSAiC expedition). Ultimately, they conclude that deposition of soluble Fe is more substantial in winter due in part to increased anthropogenic emissions despite lower atmospheric depositional rates. The authors also make some guesses of how this pattern may evolve or shift with projected reduced sea ice cover in the Arctic.
I enjoyed reading this manuscript and have no major comments or revisions for the authors, only a few questions and small technical corrections.
Minor comments:
Figure 5/Lines 461-462: I think the data shown in the FIgure 5 inset does not support the statement that no inverse pattern is noticeable within the Arctic data. I think there is a slight inverse pattern with the MOSAiC data. The Arctic data falls squarely within the range of previous data, particularly in the Atlantic datasets. I think you are trying to emphasize the very limited range in concentration compared to Atlantic/Pacific aerosols but I would rephrase this sentence.
Lines 519-520: repeated use of "resulting", sounds a bit messy.
Lines 609-612: Same thing, both sentences here start with "As a result". I would do a careful read through of the manuscript to make sure phrases like "as a result" and "suggests/suggesting" aren't over-used in quick succession.
Conclusions: I thought this discussion was pretty brief. I wonder if the authors could comment on whether Fe making it to open water may relieve potential emerging Fe limitation in the Eurasian sector (Rijkenberg et al., 2018) or whether larger scale shifts in atmospheric weather patterns (like the Arctic Oscillation Index) may exert a control on summer vs winter deposition.