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The water surface microlayer (SML) serves as a boundary through which microbes can be exchanged. To evaluate exchanges of microbes, this study compared microbial communities within different reservoirs, with an emphasis on the water SML and aerosols. Additionally, the microbial communities during a sewage spill and perigean tides were evaluated and the results were compared to times without these events. Results show that during perigean tides and during the sewage spill, levels of culturable bacteria were highest and showed an increase via sequencing in potential pathogenic bacteria (Corynebacterium and Vibrio, which increased from 3.5%-1800% depending on sample type). In the aerosol samples, Corynebacterium (average of 2.0%), Vibrio (1.6%), and Staphylococcus (10%), were the most abundant genera. Aerosolization factors, which were used to examine the transfer of the microbes, were high for these three genera. Measurements of general marine bacteria (GMB) by culture showed a weak but significant correlation between culturable GMB in aerosol samples versus in water and in the SML. More research is needed to evaluate the exchange of pathogens between the SML and air, given the increase in potentially pathogenic microbes within the SML during rare events and evidence that suggests that microbes maintain viability during transfers across reservoirs.

The number concentration and properties of aerosol particles serving as cloud condensation nuclei (CCN) are important for understanding cloud formation, particularly in the tropical Atlantic marine boundary layer (MBL) where marine cumulus clouds reflect incoming solar radiation and obscure the low-albedo ocean surface. Studies linking aerosol source, composition, and water uptake properties in this region have been conducted primarily during summertime dust transport, despite the region receiving a variety of aerosol particle types throughout the year. In this study, we compare size-resolved aerosol chemical composition data to the hygroscopicity parameter κ derived from size-resolved CCN measurements made during the EUREC4A and ATOMIC campaigns from January to February 2020. We observed unexpected periods of wintertime long-range transport of African smoke and dust to Barbados. During these periods, the accumulation mode aerosol particle and CCN number concentrations as well as the proportions of dust and smoke particles increased while the average κ slightly decreased (κ = 0.45+0.1) from marine background conditions (κ = 0.52+0.08) when the particles were mostly composed of marine organics and sulfate. Size-resolved chemical analysis shows that smoke particles were the major contributor to the accumulation mode aerosol during long-range transport events, indicating that smoke is mainly responsible for the observed increase in CCN number concentrations. Earlier studies conducted at Barbados have mostly focused on the role of dust on CCN, but our results show that aerosol hygroscopicity and CCN number concentrations during wintertime long-range transport events over the tropical North Atlantic are affected by African smoke more than dust. Our findings highlight the importance of African smoke for atmospheric processes and cloud formation over the Caribbean.

African mineral dust is transported many thousands of kilometres from its source regions and, because of its ability to nucleate ice, it plays a major role in cloud glaciation around the globe. The ice-nucleating activity of desert dust is influenced by its mineralogy, which varies substantially between source regions and across particle sizes. However, in models it is often assumed that the activity (expressed as active sites per unit surface area as a function of temperature) of atmospheric mineral dust is the same everywhere on the globe. Here, we find that the ice-nucleating activity of African desert dust sampled in the summertime marine boundary layer of Barbados (July and August, 2017) is substantially lower than parameterizations based on soil from specific locations in the Saharan desert or dust sedimented from dust storms. We conclude that the activity of dust in Barbados’ boundary layer is primarily defined by the low K-feldspar content of the dust, which is around 1 %. We propose that the dust we sampled in the Caribbean was from a region in West Africa (in and around the Sahel in Mauritania and Mali), which has a much lower feldspar content than other African sources across the Sahara and Sahel.

The article of record may be found at https://doi.org/10.1575/1912/27821 The Surface Ocean – Lower Atmosphere Study (SOLAS) (http://www.solas-int.org/) is an international research initiative focused on understanding the key biogeochemical-physical interactions and feedbacks between the ocean and atmosphere that are critical elements of climate and global biogeochemical cycles. Following the release of the SOLAS Decadal Science Plan (2015-2025) (Brévière et al., 2016), the Ocean-Atmosphere Interaction Committee (OAIC) was formed as a subcommittee of the Ocean Carbon and Biogeochemistry (OCB) Scientific Steering Committee to coordinate US SOLAS efforts and activities, facilitate interactions among atmospheric and ocean scientists, and strengthen US contributions to international SOLAS. In October 2019, with support from OCB, the OAIC convened an open community workshop, Ocean-Atmosphere Interactions: Scoping directions for new research with the goal of fostering new collaborations and identifying knowledge gaps and high-priority science questions to formulate a US SOLAS Science Plan. Based on presentations and discussions at the workshop, the OAIC and workshop participants have developed this US SOLAS Science Plan. The first part of the workshop and this Science Plan were purposefully designed around the five themes of the SOLAS Decadal Science Plan (2015-2025) (Brévière et al., 2016) to provide a common set of research priorities and ensure a more cohesive US contribution to international SOLAS. This report was developed with federal support of NSF (OCE-1558412) and NASA (NNX17AB17G). This report was developed with federal support of NSF (OCE-1558412) and NASA (NNX17AB17G).

The science guiding the EUREC4A campaign and its measurements is presented. EUREC4A comprised roughly 5 weeks of measurements in the downstream winter trades of the North Atlantic – eastward and southeastward of Barbados. Through its ability to characterize processes operating across a wide range of scales, EUREC4A marked a turning point in our ability to observationally study factors influencing clouds in the trades, how they will respond to warming, and their link to other components of the earth system, such as upper-ocean processes or the life cycle of particulate matter. This characterization was made possible by thousands (2500) of sondes distributed to measure circulations on meso- (200 km) and larger (500 km) scales, roughly 400 h of flight time by four heavily instrumented research aircraft; four global-class research vessels; an advanced ground-based cloud observatory; scores of autonomous observing platforms operating in the upper ocean (nearly 10 000 profiles), lower atmosphere (continuous profiling), and along the air–sea interface; a network of water stable isotopologue measurements; targeted tasking of satellite remote sensing; and modeling with a new generation of weather and climate models. In addition to providing an outline of the novel measurements and their composition into a unified and coordinated campaign, the six distinct scientific facets that EUREC4A explored – from North Brazil Current rings to turbulence-induced clustering of cloud droplets and its influence on warm-rain formation – are presented along with an overview of EUREC4A's outreach activities, environmental impact, and guidelines for scientific practice. Track data for all platforms are standardized and accessible at https://doi.org/10.25326/165 (Stevens, 2021), and a film documenting the campaign is provided as a video supplement.