The Indonesian Throughflow (ITF) is the only low-latitude connection between two ocean basins and an important component of the global ocean circulation. Every second, it transports approximately 15 million cubic meters of water from the Pacific into the Indian Ocean. Today, the ITF is thought to transport mainly waters of North Pacific origin. Even though the significance of the ITF for the global ocean circulation and climate has long been established, little is known about the hemispheric origin of the water masses contributing to its overall transport in the past.
To study the hemispheric origin of the ITF source waters, an international team led by Prof. Markus Kienast from Dalhousie University (Halifax, Canada) measured nitrogen isotopes (δ15N) in a sediment core from the Banda Sea, Indonesia – located at the heart of the ITF. “The isotopic compositions of subsurface nitrate in the Northern and Southern Hemisphere source waters of the ITF are substantially different and by measuring δ15N in the Banda Sea core, we could detect the contribution of these waters to the ITF through time,” explains Dr. Martina Hollstein, corresponding author of the study. “Our results show a remarkable long-term stability of the nitrogen cycle all along the equatorial Pacific, with Southern Hemisphere-sourced subsurface waters contributing significantly to the total ITF transport during the last 800,000 years.”
The study reveals that the Southern Hemisphere contribution has been much higher than previously thought. “This is an important finding. Because it implies a relevant and direct conduit by which high southern Pacific climate signal is transmitted to the Indonesian Seas and from there, to the Indian and Atlantic Oceans,” says PD Dr. Mahyar Mohtadi from MARUM and Faculty of geosciences at the university of Bremen, also corresponding author of the study.
The transport of elements within the water column and towards the ocean floor is also being investigated further as part of the Cluster of Excellence “The Ocean Floor – Earth’s Uncharted Interface”, which is currently based at MARUM and the Institute of Marine Chemistry and Biology (ICBM) at the University of Oldenburg. The aim is to estimate their budget under current and past conditions of the Earth system.
More information
Working group Low-Latitude Climate Variability https://www.marum.de/en/Low-Latitude-Climate-Variability.html
Contact
Dr. Martina Hollstein
Low-Latitude Climate Variability
MARUM – Center for Marine Environmental Sciences at the University of Bremen
Email: mhollstein@marum.de
PD Dr. Mahyar Mohtadi
Low-Latitude Climate Variability
MARUM – Center for Marine Environmental Sciences at the University of Bremen
Email: mmohtadi@marum.de
Participating Institutions
• Department of Oceanography, Dalhousie University, Halifax (Canada)
• MARUM – Center for Marine Environmental Sciences, University of Bremen, Germany
• Faculty of Geosciences, University of Bremen, Germany
• Institute for Marine and Antarctic Studies, University of Tasmania (Australia)
• College of Marine Science, University of South Florida (USA)
• College of Marine Geosciences, Ocean University of China (China)
• Institute of Earth Sciences, National Taiwan Ocean University (Taiwan)
MARUM produces fundamental scientific knowledge about the role of the ocean and the ocean floor in the total Earth system. The dynamics of the ocean and the ocean floor significantly impact the entire Earth system through the interaction of geological, physical, biological and chemical processes. These influence both the climate and the global carbon cycle, and create unique biological systems. MARUM is committed to fundamental and unbiased research in the interests of society and the marine environment, and in accordance with the Sustainable Development Goals of the United Nations. It publishes its quality-assured scientific data and makes it publicly available. MARUM informs the public about new discoveries in the marine environment and provides practical knowledge through its dialogue with society. MARUM cooperates with commercial and industrial partners in accordance with its goal of protecting the marine environment.
Nature Communications
Significant Southern Hemisphere contribution to the Indonesian Throughflow over the last 800,000 years
14-Apr-2026