The Koren Lab

The Bodélé Depression is the world's most intense dust source. One proposed explanation is wind amplification through an upwind mountain pass, the \u201cwind-lens\u201d effect, reflecting a Venturi-type acceleration. Using over 20 years of ERA5 reanalysis 10 m winds at the pass entrance and exit, together with Moderate Resolution Imaging Spectroradiometer Aerosol Optical Depth at the Bodélé, we show that winds nearly double as they traverse the pass. Two distinct dust-emission regimes emerge, separated by an exit-wind speed of ∼8 m/s. Under weaker winds, dust loading is low and largely independent of speed, while stronger winds produce sharply increasing dust and more aligned entranceexit flow. These regimes coincide with seasonal shifts: weak, variable summer winds contrast with a stronger, directionally aligned winter regime when dust events are frequent. The strongest emissions occur when exit winds cluster near 48° and entrance winds have a northern component, reflecting optimal alignment with the corridor.

The central Arctic is experiencing warming up to four times faster than the global average. This Arctic amplification is accompanied by large deviations in climate projections, making anticipation of high-impact, near-term regional biodiversity and climate change difficult. Several atmospheric processes contribute simultaneously to Arctic amplification and biodiversity change yet remain largely unstudied, not least because of the difficulty to access the central Arctic Ocean and conduct year-round studies. This article introduces the near-to mid-term objectives of the Tara Polar Station scoping group on "atmosphere-biosphere interactions," with a focus on identifying and quantifying the origin and genetic composition of local and long-range transported biogenic particles that can impact biodiversity and cloud formation, the role of the stratified boundary layer on vertical fluxes of cloud seeds, bioaerosols and nutrients, and the impact of clouds on atmospheric light transmission. The Tara Polar Station is a fortified research vessel built to drift in the Arctic sea ice throughout the next 20 years in ten Tara Polaris expeditions, each lasting one and a half years. The platform allows for year-round interdisciplinary studies targeted at understanding the central Arctic Ocean ecosystem functioning, biodiversity, and climate change at the ocean-ice-atmosphere nexus. This scoping group will deploy novel and automated instruments for in situ, real-time vertical and remote sensing observations of aerosols, clouds, and radiation. The link between the biosphere and atmosphere will be investigated specifically through bioand chemo-molecular sampling of air, clouds, ice, and water. We expect the early Tara Polaris expeditions to deliver insights that can be implemented into models for improved scenarios of Arctic change, in particular for the next few decades when we expect a regime shift in summer sea-ice presence.

Understanding the factors that influence the production of sea spray aerosols (SSA) is crucial for better understanding their impact on our climate. However, the role of oceanic microbial activity in contributing to SSA production is still underexplored. Here, we investigated the dynamics of SSA number concentration (N_SSA) during induced algal blooms within three airtight mesocosm enclosures. Monitoring algal abundance throughout a 24-day experiment revealed two main blooms: a mixed algal bloom followed by an extensive bloom of the coccolithophore Gephyrocapsa huxleyi and its subsequent demise. We observed two main patterns in N_SSA: (1) a diurnal variation with higher daytime emissions; and (2) a progressive decrease in N_SSAthroughout the bloom succession, with peak N_SSAduring the first mixed algal bloom and a decline during the G. huxleyi bloom and its demise. We hypothesize that photosynthetic processes could contribute to the observed diurnal changes, potentially through effects of enhanced bubble formation and subsequent SSA production. The suppression of N_SSAduring the G. huxleyi bloom and its demise correlates with the accumulation of particulate organic carbon and transparent exopolymer particles, which can act as surfactants and potentially suppress SSA production by altering surface tension dynamics. Our findings underscore the complex interplay between algal bloom dynamics and SSA production, with implications for understanding aerosol dynamics in marine environments, particularly under changing climate conditions.