10 April - 22 May 2024 in the Indian Ocean (Colombo (Sri Lanka) - Singapore)

Aim: Quantification of the contribution of the different atmospheric aerosol sources and the input of mineral nutrients such as phosphorus, iron and other bio-relevant trace metals such as Cu, Zn, Mn, Cd in the Bay of Bengal

Participants: TROPOS-ACD, TROPOS-AMP; GEOMAR (Hermann Bange); Uni. Hamburg; University of Southern Denmark (SDU)

Instruments: Offline and online aerosol samplers and analysers (MAAP, CCN-Counter, SP-AMS...), SML sampling

Operated by: Arun Baba Suja, René Rabe, Shravan Deshmukh

Contact: Hartmut Herrmann, Manuela van Pinxteren


The SO305 BIOCAT-IIOE2 expedition

The scientific programme of expedition SO305 BIOCAT-IIOE2 aims to address fundamental questions about the formation and maintenance of oxygen minimum zones in the Bay of Bengal. It will also investigate the impact of air pollution transported from the Indian subcontinent.

Research will focus on microbiology, biogeochemistry and atmospheric chemistry.

During the expedition, our team of scientists, students and technicians will carry out measurements at various stations in the Eastern Indian Ocean and the Bay of Bengal to collect comprehensive data from the water column and the atmosphere. This will include studies of physical properties, microbial processes, trace elements and climate-relevant gases in the water column, as well as measurements of climate-relevant gases and aerosols in the atmosphere.

The results will contribute to two major international research programmes: the ongoing Second International Indian Ocean Expedition (IIOE II), and the Surface Ocean – Lower Atmosphere Study (SOLAS) research programme, which investigates the complex physical, chemical and biological exchange processes between the ocean and the atmosphere.

Week 1 (13 April 2024)

On 9 April 2024, 39 scientists from esteemed institutions such as the University of Hamburg, GEOMAR Helmholtz Centre for Ocean Research Kiel (GEOMAR), Helmholtz Centre hereon, University of Southern Denmark (SDU), and Leibniz Institute for Tropospheric Research (TROPOS) embarked on the research vessel Sonne for the BIOCAT-IIOE 2 (SO305) research expedition. The team comprises experts in marine biogeochemistry, microbiology, physical oceanography, and atmospheric chemistry.
The BIOCAT-IIOE 2 (SO305) expedition aims to decipher the biogeochemical processes occurring in the Bay of Bengal. This region, located in the northeast basin of the Indian Ocean, features a prominent oxygen minimum zone (OMZ) with dissolved oxygen concentrations nearing anoxic levels and experiences a heavily polluted atmosphere during spring. This research is an important contribution to the international programs 2nd International Indian Ocean Expedition (IIOE-2) and the Surface Ocean-Lower Atmosphere Study (SOLAS). Over the next five weeks, we will be investigating the efficiency of the biological pump, the nitrogen cycle within the OMZ, air-sea exchange fluxes of trace gases, and aerosol deposition.
Originally scheduled to depart from the Port of Colombo on 10 April, our departure was postponed due to the delayed arrival of our containers containing our materials and equipment. During this wait, we took the opportunity to get to know more our colleagues and explore the city of Colombo.
On 13 April 2024, with our containers finally in hand, we have set sail from the Port of Colombo, commencing our measurement campaign in the Bay of Bengal. We anticipate reaching the port of Singapore on 22 May 2024.
Stay tuned for updates as we navigate the challenges and discoveries that await us on SO305. As we embark on this important scientific expedition, we are excited to investigate the complexities of the Bay of Bengal’s biogeochemical processes. The collaboration between experts from various institutions promises a multidisciplinary approach that will yield valuable insights into this unique marine environment.
The Team of SO305

1st weekly report (9 - 14 April 2024), R/V Sonne voyage SO305 BIOCAT-IIOE2, Colombo (Sri Lanka) - Singapore



Scientists joining the BIOCAT- IIOE2 (SO305) expedition in front of the research vessel Sonne, with Prof. Dr. Hermann W. Bange (chief scientist, leftmost in the photo).

  • Loading of containers and R/V Sonne leaving the Port of Colombo. Source: FS Sonne / Expedition SO305

  • Loading of containers and R/V Sonne leaving the Port of Colombo. Source: FS Sonne / Expedition SO305

  • Loading of containers and R/V Sonne leaving the Port of Colombo. Source: FS Sonne / Expedition SO305

Week 2 (21 April 2024)

The World of Atmospheric Aerosols

by Dr. Arun Babu Suja

Greetings from the high seas by the TROPOS scientific team! Our mission during the BIOCAT-IIOE2 cruise is to delve into the fascinating world of atmospheric aerosols – those tiny particles suspended in the air – and unlock their secrets. These tiny particles suspended in the air hold immense significance in shaping our planet’s climate and ecosystems. Our mission is to unravel their mysteries, focusing on their interactions with clouds, radiation, and the ocean itself. Our adventure started with the collection of aerosol samples from the air around us. Using advanced techniques, we capture these minuscule particles and analyze their composition, size distribution, optical properties, and sources. It’s like discovering hidden treasures in the atmosphere, with each particle offering clues about its journey and the forces that shape our skies. But our exploration doesn’t end there.

We’re also investigating the sea surface microlayer (SML), the thin boundary between the ocean and the air above. Here, we’re taking samples to study how aerosols interact with the marine environment, unlocking insights into the complex relationship between the ocean and the atmosphere. Furthermore, our exploration encompasses measurements of black carbon (BC) concentrations, a potent climate-forcing agent with far-reaching impacts on atmospheric heating and regional climate variability. By quantifying BC emissions and their spatial distribution, we aim to elucidate their contributions to radiative forcing and regional climate trends. In our pursuit of a holistic understanding of aerosol-cloud interactions, we also conduct measurements of cloud condensation nuclei (CCN) concentrations. These microscopic aerosol particles serve as nuclei for cloud droplet formation, influencing cloud microphysics, precipitation patterns, and regional climate dynamics.

Moreover, our scientific voyage comprises investigations into ice nucleating particles (INPs), which play a pivotal role in cloud glaciation processes and precipitation formation. By characterizing INP concentrations and their ice nucleation efficiency, we aim to elucidate their contributions to cloud properties, precipitation regimes, and atmospheric circulation patterns. Through interdisciplinary collaboration and rigorous scientific inquiry, we endeavor to advance our understanding of aerosol science, thereby enhancing our capacity to address pressing environmental challenges and mitigate the impacts of global climate change. Every sample we collect and every measurement we take brings us closer to unlocking the secrets of aerosols and their impact on our planet.


2nd Weekly Report (15 - 21 April 2024), R/V SONNE cruise SO305 BIOCAT-IIOE2, Colombo (Sri Lanka) - Singapore

Photo: Riel Ingeniero, GEOMAR

  • Group photograph of the Leibniz Institute for Tropospheric Research (TROPOS) team onboard R/V Sonne. (Photo: Riel Ingeniero, GEOMAR).

  • Shravan with the aerosol mass spectrometer (photo by: Riel Ingeniero, GEOMAR)

  • View of a storm cloud from the hangar of R/V Sonne on April 19, 2024 (photo: Riel Ingeniero, GEOMAR).