Yale Scientific Interviewed Dr Mario Lebrato about his Paper on Seawater Chemistry and the Variability Found in its Elemental Composition

Yale Scientific Magazine (the oldest college magazine in the USA), has published an article on the seawater chemistry and the variability found in its elemental composition, overturning a 130-year-old assumption in ocean knowledge, mentioning our Station Manager and Chief Scientist, Dr. Mario Lebrato, and referring to his research, as he is the first author of the paper published in August 2020. Dr. Lebrato is commenting on the study process as he is being interviewed by Yale Scientific, explaining what inspired the project and how the paper came together.

The PNAS paper, ‘Global variability in seawater Mg:Ca and Sr:Ca ratios in the modern ocean’, challenges the elemental stability of the ocean and the timeline of the ocean’s development, which has been widely accepted by the science community for over one-hundred years. This work is the result of nine-year study led by Kiel University in Germany and GEOMAR Helmholtz Centre for Ocean Research, to which BCSS contributed significantly. The study includes analysis of 1100 samples from 14 different ecosystems, ranging from the water surface to 6000 meters deep, collected on 79 ship expeditions.

Journal cover for the PNAS article “Global variability in seawater Mg:Ca and Sr:Ca ratios in the modern ocean

Modern ocean global variability in seawater Mg:Ca and Sr:Ca ratios divided by depth and water masses.

Modern ocean seawater Mg:Ca and Sr:Ca ratios as cross plot to understand how ocean processed impact the ratios distribution. 

Snippets from the PNAS article – tap to enlarge. 

Coral reef ecosystems are areas where there is active exchange between seawater and the coral themselves during the bio-calcification process. Corals use Ca, Mg, and Sr to build their skeletons, removing it from the seawater. Photo by Helen Walne

Coral reef ecosystems in deep waters are exposed to open ocean water masses with a direct impact from the composition of those waters. Seawater composition above a shallow reef and a deep reef tends to differ based on how much water exchange is with the open ocean.  Photo by Orlando Mirando + Salvador Colvee

Related: Ocean Observatory continuous seawater sampling

Currently, BCSS is running a seawater sampling project as part of the Ocean Observatory, where sampling is conducted on a weekly basis with the aim to understand how seawater Mg:Ca and Sr:Ca ratios change in coral reefs and offshore waters, month to month. There is a particular interest in breaking down the global patterns into time-series, in order to investigate the impact of ecosystems on the seawater itself on smaller time scales. Besides collecting seawater, corals and invertebrates are being sampled to measure skeleton calcium carbonate and aragonite Mg:Ca, Sr:Ca, and Ba:Ca to couple seawater with the calcification process. In parallel, meta-data on ocean physics, chemistry and biology, as well as weather data, are being compiled to understand how the whole system works monthly. There is currently no information on a regional to local scale on how seawater fluctuates in composition, because it has always been assumed that most elements remain conservative. Yet, owing to the discovered variability (published), we are re-assessing this notion by considering local conditions as well as the main drivers in the ecosystem. Join BCSS in our Scientific Training Program to get involved with scientific diving, coral sampling, and learn about ocean chemistry, in our research station in the Bazaruto Archipelago.

A conductivity, temperature, and depth (CTD) instrument in action, recovering samples from 4000 m depth in the Atlantic Ocean. Photo by Mario Lebrato

BCSS is also coordinating seawater sampling in the 2024-2025 recently announced sailing transatlantic cruise from Spain to Antarctica and back to further measure the seawater in the transit from coastal areas to the open ocean, and at different latitudes and longitudes. It will give a very solid snapshot of seawater composition over a very small amount of time. 

Seawater samples in the open ocean are normally recovered using a conductivity, temperature, and depth (CTD) instrument, which consists of a metal frame rosette with bottles that can be triggered from a computer. This traps seawater at desired study depths, and then the water is brought back to the surface to sample it. The CTD is often deployed with several physics, chemistry and biology sensors to further measure the water column. 

The place where the ocean and the land meet is very active in elementals transfer and exchanges. Seawater ratios in these mixed areas tend to be very variable, often impacted by land sources. Photo by BCSS

Contribute to BCSS’s mission and ambitious projects by enrolling in the Scientific Training Program or joining our 5-Star PADI Dive Center, and dive into the world of marine science and conservation. 

For questions about this article, please contact:
Mario Lebrato, Bazaruto Center for Scientific Studies

Bazaruto Center for Scientific Studies
Host of the first permanent Ocean Observatory focused on multi-ecosystem time series research in Africa, the Bazaruto Center for Scientific Studies (BCSS) was established in 2017 as in independent, non-profit organisation with a mission to protect and support the fragile ecosystems of the Bazaruto Archipelago, Mozambique. The research station is located on Benguerra Island, off the coast of Mozambique.

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