Dust Deposition to the Bermuda Region: A Comparison of Estimates Using Seasonally-resolved Measurements of Aluminum in Water-column, Aerosol, and Rain Samples

• Main Authors: Williams, Tara, Sedwick, Peter, Sohst, Bettina, Resing, Joe, Buck, Kristen, Caprara, Salvatore, Johnson, Rod, Ohnemus, Dan, Twining, Ben, Tagliabue, Alessandro
• Format: Text
• Language: unknown
• Published: ODU Digital Commons 2023
• Subjects: Biogeochemistry; Geochemistry; Oceanography; North Atlantic
• Online Access: https://digitalcommons.odu.edu/gradposters2023_sciences/18; https://digitalcommons.odu.edu/cgi/viewcontent.cgi?article=1000&context=gradposters2023_sciences

Dust deposition is a major source of bioactive trace elements to the surface ocean, yet this flux remains difficult to constrain. Previously, time-averaged dust flux has been estimated using surface ocean dissolved aluminum (DAl) concentrations, assumed values for aerosol aluminum solubility (%AlS), and the residence time of DAl in the surface mixed layer (SML). We apply this method to estimate dust deposition in the Bermuda Atlantic Time-series Study (BATS) region using water-column DAl data from cruises in 2019, which is compared with direct flux estimates from contemporaneous measurements of aluminum in aerosols and rain collected on Bermuda. Seasonal DAl inventories over the upper 200 m (our observed maximum SML depth) yield flux estimates that follow the expected seasonality of dust deposition in Bermuda, with ranges of 9.9-13 g/m2/y and 4.7-6.1 g/m2/y, using %AlS values derived from aerosol leaches using ultrapure water and 25% acetic acid, respectively. These values are ~5-10 times higher than our estimates based on aluminum in aerosols and rain, which average ~1.18 g/m2/y over our 318 day sampling period and are in accord with previous estimates of dust deposition at Bermuda. This discrepancy may reflect uncertainties in aerosol deposition velocity (assumed 1 cm/s), lateral advection of DAl in the region (assumed negligible), and, most likely, the residence time of DAl in the upper water column (assumed 5 years). The two different estimates can be brought into agreement if the residence time of DAl in the upper 200 m is increased to ~49 years or ~23 years, for %AlS values estimated by leaching aerosols with ultrapure water or 25% acetic acid, respectively. Such residence times for DAl in the upper 200 m are greater than a recent estimate for the North Atlantic based on thorium supply but appear compatible with values extracted from a recent data-assimilation modeling study. https://digitalcommons.odu.edu/gradposters2023_sciences/1000/thumbnail.jpg