African biomass burning is a substantial source of phosphorus deposition to the Amazon, Tropical Atlantic Ocean, and Southern Ocean

The deposition of phosphorus (P) from African dust is believed to play an important role in bolstering primary productivity in the Amazon Basin and Tropical Atlantic Ocean (TAO), leading to sequestration of carbon dioxide. However, there are few measurements of African dust in South America that can robustly test this hypothesis and even fewer measurements of soluble P, which is readily available for stimulating primary production in the ocean. To test this hypothesis, we measured total and soluble P in long-range transported aerosols collected in Cayenne, French Guiana, a TAO coastal site located at the northeastern edge of the Amazon. Our measurements confirm that in boreal spring when African dust transport is greatest, dust supplies the majority of P, of which 5% is soluble. In boreal fall, when dust transport is at an annual minimum, we measured unexpectedly high concentrations of soluble P, which we show is associated with the transport of biomass burning (BB) from southern Africa. Integrating our results into a chemical transport model, we show that African BB supplies up to half of the P deposited annually to the Amazon from transported African aerosol. This observational study links P-rich BB aerosols from Africa to enhanced P deposition in the Amazon. Contrary to current thought, we also show that African BB is a more important source of soluble P than dust to the TAO and oceans in the Southern Hemisphere and may be more important for marine productivity, particularly in boreal summer and fall

Data for Interannual variability in the source location of North African dust transported to the Amazon

Here, we present the data and MixSIAR code that corresponds to the manuscript “Interannual variability in the source location of North African dust transported to the Amazon.” African dust is seasonally transported to the western Tropical Atlantic Ocean (TAO) and South America (SA), including the Amazon Basin. Leading hypotheses suggest that either the Western North African potential source area (PSA) or the Central North African PSA (e.g., Bodélé Depression) is the main source of dust transported to the Amazon. However, these notions remain largely untested with geochemical data. Here, we present a more nuanced hypothesis: both PSAs contribute dust to SA with precipitation and wind patterns determining the dominant source. Our premise is based upon two years of isotopic measurements (strontium and neodymium) of African dust collected in SA integrated into a statistical model in a Bayesian framework. With this approach, we identified strong interannual variability: while the Central PSA supplied 48% in winter 2016, a region within the Western PSA, which we suggest may be located near Niger, Mali, and Algeria accounts for 54% of transport in winter 2014. We propose the variability is due to the strength of the Libyan High and differing amounts of precipitation in the Gulf of Guinea and TAO between the two years. We anticipate that our work will lead to better constraints of dust nutrient deposition and subsequent carbon sequestration in the TAO and Amazon as well as improved model predictions of dust transport. Due to the connection between dust, precipitation, and wind patterns, our work can be used to link changes in climate with past changes in the source and magnitude of dust transported to the Amazon and TAO.This data is associated with the article: Barkley, A.E., Pourmand, A., Longman, J., Sharifi, A., Prospero, J.M., Panechou, K., Bakker, N., Drake, N., Guioiseau, D., Gaston, C.J. Interannual variability in the source location of North African dust transported to the Amazon. Submitted to the Proceedings of the National Academy of Sciences.## Description of the datasets The `data/` folder contains three data sets. `ds01` contains the data collected in this study from 34 samples including the dates of collection and Sr and eNd isotopic ratios. ## Metadata of the trajectory file ds01 is a *csv* file that contain 12 columns. Column 1 presents the date in the format ‘MM:DD:YYYY’ (e.g., 01-30-2014) that sample collection was initiated. Column 2 presents the date ‘MM:DD:YYYY’ (e.g., 01-31-2014) sample collection ended. Column 3 shows the mean 87Sr/86Sr ratio (unitless) measured and Column 4 shows the 95% confidence interval (CI) for each sample run in triplicate. Column 5 shows the 143Nd/144Nd isotopic ratio reported as epsilon neodymium (unitless) and Column 6 presents the 95% CI of the mean epsilon Nd. Columns 7, 9, and 11 show the lead (Pb) isotopic ratios normalized to 204Pb with their corresponding 95% CI in Columns 8, 10, and 12

Interannual Variability in the Source Location of North African Dust Transported to the Amazon

International audienceAfrican dust is transported to South America (SA) every winter and spring. Hypotheses suggest that either Western or Central North Africa (e.g., Bodélé Depression) is the main source of transported dust, yet these notions remain largely untested with geochemical data. Using 2 years of isotopic measurements (strontium and neodymium) of African dust collected in SA integrated into a statistical model, we identified strong interannual variability in dust source region. Central North Africa supplied 44% of long-range transported dust in winter 2016 while the Western region accounted for 53% of dust in winter 2014. We propose the variability is due to differences in the strength of the Libyan High and precipitation over the Gulf of Guinea and Atlantic Ocean between the 2 years. Our findings can improve constraints of dust nutrient deposition and predictions of how changes in climate impact the source and magnitude of dust transported to the Amazon

Data for atmospheric transport of North African dust-bearing supermicron freshwater diatoms to South America: implications for iron transport to the equatorial North Atlantic Ocean

The equatorial North Atlantic Ocean (NAO) is a nutrient-limited ecosystem that relies on the deposition of long-range transported iron (Fe)-containing aerosols to stimulate primary productivity. Using microscopy, we characterized supermicron and super-coarse mode African aerosols transported to the western NAO in boreal winter/spring. We detected three particle types including African dust, primary biological aerosol particles, and freshwater diatoms (FDs). FDs contained 4% Fe by weight due to surficial dust inclusions that may be susceptible to chemical processing and dissolution. FDs were typically larger than dust particles and comprised 38% of particles between 10 and 18 μm in diameter. The low density, high surface-area-to-volume ratio, and large aspect ratios of FD particles suggest a mechanism by which they can be carried great distances aloft. These same properties likely increase the residence time of FDs in surface waters thereby increasing the time for Fe dissolution and their potential impact on marine biogeochemical cycles.## Metadata of the trajectory file ds01 is a *csv* file that contain 7 columns. Column 1 names the sampling location, whereby 'CAY' represents Cayenne, French Guiana. Column 2 and 4 show the start and end date of collection, respectively, and is in the format dd-mmm-yy (e.g. 04-feb-16). Columns 3 and 5 show sample collection start and stop time, respectively, and is in local time to Cayenne, French Guiana (GMT-3) in the format 'HH:MM' (e.g. 14:33). NA represents data that is not available. Column 6 shows the total air volume pulled for each sample and is in meters cubed (m^3). Column 7 shows dust mass concentration for each sample (micrograms per meter cubed (ug m^-3). ds02 is a *csv* file that contains 3 columns. The first column names the particle type. The second column gives particle length along the longest axis (Dmax) in micrometers (um). Column 3 shows projected area diameter (Dpa) in micrometer (um). Column 4 shows aerodynamic diameter (Da) in micrometer. Further discussion of Dmax, Dpa, and Da is located in Section S2.2 in the Supporting Information. ds03 is a *csv* file that contains 3 columns. Column 1 contains particle type. Column 2 shows particle length along the longest axis (Dmax) in micrometer (um) and the width (W) of the particle at the longest axis that is perpendicular to Dmax in micrometer (um).## Description of the datasets The `data/` folder contains three data sets. `ds01` contains information regarding sampling collection dates and times. `ds02` contains particle diameters for each particle analyzed in this study. `ds03` contains the data used to make Figure 4 in the main manuscript

Determining the source location of African dust transported to the Amazon and its associated Fe speciation

The Amazon and Tropical Atlantic Ocean (TAO) are both nutrient-depleted ecosystems where primary productivity is controlled in part by the atmospheric deposition aerosols. The primary nutrient-laden aerosol is African dust, which is transported in boreal winter and spring, and an important source of iron (Fe) to the Amazon and TAO. Determining the source location of transported dust would provide key insights into the mineralogy and nutrient content of transported dust. Additionally, Fe mineralogy and speciation associated with this dust have not well characterized despite being important predictors of Fe bioavailability. Using strontium, neodymium, and lead isotopes as well as elemental analysis, we characterized two years of transported African aerosols collected in Cayenne, French Guiana, which is located adjacent to the Amazon and western TAO. Our isotopic analysis revealed no evidence of transport from the El-Djouf region. Instead, our results show that the majority of the dust originates from present day southern Algeria and northern Niger. We also confirm with isotopic evidence that the Amazon and western TAO are impacted by the deposition of biomass burning aerosols in the boreal summer and fall when dust transport is low. Further investigation of mineralogy and Fe oxidation state of transported Saharan dust showed the presence of hematite, goethite, and small amounts of Fe(II), which is the most soluble form of Fe and immediately usable by biota. These results integrate source location, mineralogy, and Fe speciation, which yield a more complete view of how African dust impacts marine and terrestrial ecosystems

Atmospheric Transport of North African Dust-Bearing Supermicron Freshwater Diatoms to South America: Implications for Iron Transport to the Equatorial North Atlantic Ocean

The equatorial North Atlantic Ocean (NAO) is a nutrient-limited ecosystem that relies on the deposition of long-range transported iron (Fe)-containing aerosols to stimulate primary productivity. Using microscopy, we characterized supermicron and supercoarse mode African aerosols transported to the western NAO in boreal winter/spring. We detected three particle types including African dust, primary biological aerosol particles, and freshwater diatoms (FDs). FDs contained 4% Fe by weight due to surficial dust inclusions that may be susceptible to chemical processing and dissolution. FDs were typically larger than dust particles and comprised 38% of particles between 10 and 18 μm in diameter. The low density, high surface-area-to-volume ratio, and large aspect ratios of FD particles suggest a mechanism by which they can be carried great distances aloft. These same properties likely increase the residence time of FDs in surface waters thereby increasing the time for Fe dissolution and their potential impact on marine biogeochemical cycles

Characterizing and Quantifying African Dust Transport and Deposition to South America: Implications for the Phosphorus Budget in the Amazon Basin

These data were obtained in support of a research program whose objective was to characterize and quantify the amounts of African dust that are carried in the Trade Winds to the Amazon Basin region and to South America at large. To this end, established an aerosol sampling station in Cayenne on a hill at a coastal site (4.948936N, 52.309692W). In this paper we compare 10 months of mineral dust data to concurrent measurements of PM10 that are made by the agency in charge of the air quality monitoring program in Cayenne, ATMOS-Guyane. Using this data, we show that concentrations of PM10 above about 15 - 20 ug/m3 can be directly linked to the advection of African dust into the region. On this basis we can use the entire (15 year) PM10 measurement record made in Cayenne to characterize the long term transport of African dust.Hi-Vol Filter Sampling: In early 2014 a high-volume aerosol filter sampling system was installed at a site situated on the top of a 67-meter wooded hill (4.948936N, ‑52.309692W) located directly on the coast that lies northeast of the city of Cayenne (population 57,000) (see Fig. 1). The site is a fenced and gated government radar facility with restricted access. Cayenne lies in the Trade Wind belt and winds have a very strong NE component all year long. Figure S2 shows selected seasonal wind roses from a site 1.3 km SE of the sampling site. Sampling is carried out on a cooperative basis by personnel of ATMO. Samples are changed on a nominal 24-hour cycle starting around local noon although the start and end times are variable, depending on the workload of the personnel. Exposed filters are replaced with a new filter the following morning except over weekends and holidays when multi-day samples are taken. Most 3-day filter samples in the archive are weekend samples that were begun on a Friday morning and terminated on a Monday morning. Also, because of work schedule limitations and holidays, some filter changes may be missed during the week or extend over longer times. Note that the filter change cycle starts approximately at local noon and, thus, the schedule is not precisely coordinated with the daily PM measurement cycle which starts at midnight. Samples are collected by drawing air through 20cm x 25cm Whatman 41 filters (W41) at a flow rate of about 0.75 m-3 min‑1. In the marine boundary layer, the collection efficiency of W-41 filters is greater than 95% for dust (Kitto & Anderson, 1988; Arimoto et al., 1990). W-41 filters yield consistently low blank values for a wide range of elements and they are routinely used for aerosol trace element sampling in ocean environments (Morton et al., 2013). Exposed filters are periodically returned to Miami where all analyses are carried out. For mineral dust analyses, a quarter section of each filter is extracted with three aliquots of water and then placed in a muffle furnace for about 14 hours (i.e., overnight) at 500°C. Earlier studies on Barbados show that the soluble components consist primarily of sea salt aerosol (Savoie et al., 2002; Savoie, Prospero, & Saltzman, 1989). The ash residue weight (less filter blank) is assumed to be mineral dust. The ash blanks yield a standard error in the mineral dust concentration that is essentially constant at ±0.1 µg m-3 for concentrations less than 1 µg m-3; at higher levels, the standard error is about ±10%. The filter ash weight underestimates the true dust concentration because of the loss of soluble soil salts associated with the minerals during the extraction procedure (e.g., halides, CaCO3, CaSO4), and during the subsequent heating through the volatilization of bound water and various species and the breakdown of other components including organic matter. Based on an early assessment (Savoie & Prospero, 1977) we developed a canonical adjustment factor, 1.3, to compensate for those losses. In later work, the concentration of 19 elements was measured by neutron activation (Arimoto et al., 1995) in aliquots of 1349 dust-laden filter samples collected at Barbados. A scatter plot of Al vs the ash weights of aliquots of these same filters (obtained as described above) yields an average Al concentration of 10.4%. When we apply the canonical factor, 1.3, we obtain an Al concentration of 8.0%. This value is close to the average abundance of Al in the upper continental crust: 8.15%, (Rudnick & Gao, 2003). With this normalization method, a large suite of elements is found to be present in Barbados dust at ratios close to crustal abundances (e.g., Trapp et al., 2010; Bozlaker et al., 2017.PM10 Measurements. Aerosol concentrations are measured with ThermoFisher Scientific TEOM 1400 series instruments. Measurements are made in two size classes: PM2.5 and PM10. The TEOM is a gravimetric instrument that continuously weighs the collection filter and measures particle mass concentrations. The TEOM is an EPA equivalent method for measuring PM2.5 and PM10 particulate matter and is used worldwide in air quality programs (Nosratabadi, Graff, Karlsson, Ljungman, & Leanderson, 2019). The instruments at Cayenne are operated and maintained by ATMO-Guyane, a non-profit organization (https://www.atmo-guyane.org/qui-sommes-nous/statuts/ ) responsible for monitoring air quality in FG following French national air quality requirements and protocols (https://www.atmo-guyane.org/). Sampling is carried out at various fixed sites in the Cayenne region and also at mobile sites as needed. Data is stored as 15-minute averages. In this work, we use the daily means of values between midnight to midnight. Data can be downloaded at https://www.atmo-guyane.org/donnees/open-data/Column 1: Date of sample Column 2. Mineral dust concentration as determined from filter samples. In the case of multi-day samples, the concentration is copied over the span of the days sampled. Colored blocks identify multi-day time span. Column 3: The number of days that the filter sample was exposed for collection of aerosol. Column 4: TEOM PM10 concentrations (ug/m3). This is the average of all stations in operation during that specific day. Column 5: PM10 concentrations (ug/m3) where the daily sample values are averaged over the time range of the multi-day filter samples

The origin and biogeochemical impact of North African dust transported to South America

The long-range transport of African dust to South America in the boreal winter and spring is thought to provide nutrients, such as iron and phosphorus (e.g., Fe and P), that can fertilize both the nitrogen-limited Tropical Atlantic Ocean and the P-limited Amazon rainforest. The source location of transported African dust determines both the magnitude and mineralogy and, therefore, the biogeochemical impact of dust deposited to marine and terrestrial ecosystems. Dust has been postulated to originate from Central North African sources, such as the Bodele Depression, and Western North Africa; however, few measurements exist that can elucidate the source and nutrient-content of African dust. Here we present two years of continuous measurements of dust mass concentrations and associated nutrient content of transported African aerosols collected at a coastal site in Cayenne, French Guiana in South America. We couple our bulk chemical measurements with single particle measurements in addition to dust isotopic fingerprinting to assess the origin of North African dust. Our results indicate that the source of North African dust transported to South America fluctuates on seasonal and interannual timescales potentially due to meteorological patterns that determine both the strength and location of dust emission. Further, our results indicate that North African dust provides nutrients to South America year-round. In addition to dust, we show that wildfire combustion from African biomass burning aerosols play a substantial role in supplying both P and Fe to the ocean and Amazon rainforest. Overall, our results suggest that several long-standing hypotheses regarding the origin of wintertime African dust transport to South America and its role as the sole provider of nutrients to the Amazon and Tropical Atlantic Ocean need to be revised to accurately characterize the role of African aerosol transport and deposition on marine and terrestrial biogeochemical cycles and climate

The impact of African aerosol transport on biogeochemical cycles

The long-range transport of African dust is of great interest due to its impact on biogeochemical cycles in the Amazon Basin and the Tropical Atlantic Ocean. Despite interest in this topic, few measurements exist to document this phenomenon and quantify its impacts on biogeochemical cycles. Here we will discuss measurements collected at the University of Miami's Barbados Atmospheric Chemistry Observatory (BACO) and a site in Cayenne, French Guiana located on the coast of the Tropical Atlantic Ocean which receives only long-range transported and sea spray aerosol. Therefore, Cayenne is ideal for determining the impact of long-range transport on the aerosol burden in South America. We will discuss seasonal variations in nutrient loadings and aerosol sources during active and non-active dust transport periods, and single particle measurements of the mixing state of iron (Fe) and phosphorus (P) containing particles. Our measurements reveal that in addition to dust, other particle sources are also important for supplying nutrients to these ecosystems. In particular, we elucidate the underappreciated role of biomass burning transport in supplying nutrients. Overall, our measurements demonstrate the importance of both bulk and single-particle characterization for describing particulate contributions to biogeochemical cycles and for quantifying the deposition of nutrients from different aerosol sources. Further, it is important to continue and expand long-term measurement records to fully quantify the impact of aerosol deposition on ecosystem health and climate