A new study reveals how ocean currents are key to the journey of microscopic organisms to the depths


Microscopic organisms utilize ocean currents as a "highway" to the depths, as revealed by a recent study conducted by researchers at the Mediterranean Institute for Advanced Studies (IMEDEA CSIC-UIB). This study, published in the Proceedings of the National Academy of Sciences (PNAS), sheds light on how these organisms exploit marine currents as a kind of "highway", allowing them to travel from the sunlit surface to the darkest depths of the ocean. In these deep regions, microscopic organisms play a vital role in chemical processes and in maintaining the balance of the marine ecosystem.

The CALYPSO project (Coherent Lagrangian Pathways from the Ocean Surface to the Interior), funded by the U.S. Office of Naval Research (ONR), has been instrumental in this discovery. The study focuses on the Mediterranean Sea as an example of a subtropical region and unravels the mystery of how some unicellular organisms, such as phytoplankton and bacteria, manage to venture beyond 100 meters deep, where sunlight is scarce and living conditions are challenging.

Marine currents, known as intrusions, act as true life carriers, transporting a diversity of organisms and significantly contributing to the redistribution of carbon in the ocean. According to Dr. Freilich, these intrusions not only alter the composition of available food in the ocean depths but also play a crucial role in transporting a considerable amount of carbon from the water's surface, thereby enriching the complexity of the marine depths ecosystem.

"Vertical exchange between the surface and the interior of the ocean affects carbon export. With this work, we have demonstrated the importance of mesoscale intrusions (which occur at a spatial scale of between 10 and 100 km)," Dr. Ananda Pascual.

The study challenges conventional conceptions of how carbon reaches ocean depths. Previously, it was thought that sinking carbon-rich particles were the sole mechanism responsible for this process. However, the findings reveal that intrusions play a crucial and hitherto underestimated role in this transport.

"The published work also represents an example of the benefits of international scientific collaboration between researchers from Europe and the USA to address such challenges in observing physical-biological coupling processes in the ocean. By combining scientific knowledge and advanced observation and analysis technologies, we have been able to obtain and analyze unprecedented simultaneous physical and biogeochemical parameter information, allowing us to quantify carbon transport associated with these intrusions," Dr. Simón Ruiz.

In addition to its ecological impact, this study raises significant implications regarding climate change. It is expected that as the oceans warm, the proportion of carbon in these microscopic cells will increase, potentially altering the dynamics of intrusions and, ultimately, the global carbon cycle in a changing climate. This multidisciplinary study was made possible through collaboration between Spanish researchers from IMEDEA and SOCIB ICTS in Mallorca, and Italian scientists from ISMAR and CMRE. Through the use of advanced sampling and genetic analysis tools, the characteristics and behavior of oceanic intrusions could be thoroughly examined.




3D intrusions transport active surface microbial assemblages to the dark ocean

Mara A. Freilich,  Camille Poirier,  Mathieu Dever,  Eva Alou-Font , John Allen,  Andrea Cabornero, Lisa Sudek, Chang Jae Choi, Simón Ruiz, Ananda Pascual, J. Thomas Farrar, T. M. Shaun Johnston, Eric A. D’Asaro, Alexandra Z. Worden, Amala Mahadevan