The Koren Lab

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.

The CloudCT mission aims to enhance climate predictions by studying warm clouds using a sensor network based on self-organizing small satellites. Warm clouds play a crucial role in the Earth's radiative budget and the transport of heat, humidity, pollutants, and aerosols from the boundary layer to the free atmosphere. This mission employs ten cooperating nano-satellites to perform polarization sensitive computed tomography (CT) of cloud interiors, using backscattered sunlight. The satellite formation faces the challenge of cooperative attitude and orbit control, as well as camera payload coordination. To address these, the attitude and orbit control system (AOCS) features a modular design and uses a leader-follower configuration for joint cloud observation, which enables autonomous distribution of target information between the satellites. This autonomy reduces pre-processing and operational requirements on the ground and streamlines mission management. Planned for launch in 2026 the mission is in implementation phase and currently undergoing intensive ground performance tests. These tests employ adaptive control models to simulate noisy multi-view space borne images, optimizing CT strategies, and data acquisition. The satellites' AOCS undergoes extensive testing, involving several simulators and hardware-in-the-loop (HIL) testbeds to ensure reliable operation in-orbit. In the article, the developed AOCS is presented, covering crucial aspects like its mode design, a rule-based, hierarchic redundancy and fault detection, isolation and recovery (FDIR) software approach and the test strategy and environments. The interdisciplinary CloudCT mission combines atmospheric modeling, image processing, and satellite formation flying to improve climate and weather predictions.