Title : Marine Microbes at the Air–Sea Interface: From SML Ice-Nucleating Bacteria to Microbial Aerosols in the Indian Ocean

Abstract

Sea-spray aerosols (SSA) are a major natural source of cloud condensation nuclei (CCN) and ice-nucleating particles (INPs), yet the microbial drivers behind their production and variability remain poorly constrained. The sea-surface microlayer (SML), enriched in organic matter and microorganisms, acts as a selective interface that promotes the transfer of microbe-associated particles to the atmosphere. In this talk, I present two complementary studies that reveal a consistent role of specific marine bacterial lineages—particularly Flavobacteriia and Gammaproteobacteria—in shaping the composition and cloud activity of SSA. First, cultivation-based experiments in a coastal inlet of Japan identified SML bacteria from these groups exhibiting heat-labile, protein-associated ice-nucleating activity above –15 °C, demonstrating their potential as INP sources. Second, ocean-basin-scale microbial profiling during the research cruise across the Bay of Bengal and southeastern Indian Ocean showed that these same taxa are selectively aerosolized from particle-associated fractions, whereas coarse aerosol particles over the Bay of Bengal were more influenced by terrestrial intrusions. This highlights strong ecological and atmospheric controls on which marine microbes enter the air. Together, our findings indicate that microbe-rich SML communities—especially Flavobacteriia and Gammaproteobacteria—represent dynamic contributors to cloud-active aerosols, underscoring the need to integrate microbial ecology into predictions of ocean–atmosphere climate feedbacks. About the speaker: Professor Koji Hamasaki's research is focussed on understanding the microbial diversity and functions within surface ocean ecosystems and their critical roles in biogeochemical cycles. His group is notably recognized for pioneering studies on "actively growing bacteria" in natural seawater, employing advanced bromodeoxyuridine (BrdU) incorporation methods to investigate various metabolic processes, including bacterial photosynthesis, nitrogen fixation, and organic sulfur degradation. More recently, his research has concentrated on the specific role of microbial activity at the air-sea interface and its direct influences on climate processes.

Title : Multiple Emission-Line Diagnostics of the Accretion Process in Young Stars

Abstract

Young stars consist of a prestellar core, a circumstellar disk, and an envelope. Material from the envelope accretes to the disk, and through angular-momentum loss or removal, disk material is transported onto the central star. Circumstellar disks are therefore central to both stellar growth and planet formation, making them crucial for understanding the early stages of stellar evolution. In low-mass pre-main-sequence stars, accretion proceeds through magnetospheric funnels that channel disk material onto the stellar surface, generating accretion shocks that result in an excess emission in the UV region and strong emission lines. Classical T Tauri stars (CTTSs) show highly variable accretion across multiple timescales. The origins of this variability remain unknown. In this seminar, I will present a detailed analysis of a classical T Tauri star using multiple emission-line diagnostics to investigate its accretion properties and discuss various line diagnostics related to star-disk interaction processes.

Title : The Evolution of Granite-Greenstone Belts of the Western part of Dharwar Craton, Dharwar Craton, South India

Abstract

The evolution of granite-greenstone belts within the Western Dharwar Craton (WDC), a Paleoarchean-Neoarchean crustal accretion, represents the major Archean records of Early Earth. In this contribution, an integrating field relationships-whole-rock geochemistry (major/trace elements, REE patterns), and isotope systematics (Sm-Nd, Lu-Hf) depict an initial TTG-komatiite formation at 3400-3300 Ma linked to juvenile mantle inputs and elevated geothermal gradients, and a mixed tectonic setup. Subsequently, the dome-and-keel architectures emerge through subduction and plume tectonics represented by Sargur Group volcanics (~3.3 Ga), indicating high mantle potential temperatures and distinct tectonic manifestation of Archean Earth. While the younger Bababudan (~2.9 Ga) and Chitradurga (~2.7 Ga) greenstones hosting volcano-sedimentary assemblages reflect back-arc volcanism atop stabilised TTG basement, with two phases of 3.0Ga and 2.6 Ga. The Isotopic U-Pb zircon and radiogenic isotope data reveal episodic crustal growth, contrasting WDC's stable, thick (~42-51 km) core with major growth events at 3.35-3.25Ga, including TTG and Komatiitic Volcanism. Vertical tectonics dominate over nascent subduction, underscoring plume-driven nucleation of proto-cratons globally. Therefore, the eventual formation of granite greenstone belts of Western Dharwar Craton from a wide early Earth time window and proxies to investigate the sequential evolution of Archean cratonic units.