Zinc plays an overlooked role in ocean processes

The significant role of the Southern Ocean in global biological processes and the carbon cycle has been reconfirmed by a recent study published in the journal Science. The research reveals the overlooked importance of inorganic zinc particles.

Zinc and dissolved silica 

The Southern Ocean significantly contributes to global phytoplankton productivity, absorbing atmospheric carbon dioxide. 

Zinc, although present in trace amounts in seawater, is a crucial micronutrient – especially for polar phytoplankton blooms. When phytoplankton blooms die off, zinc is released, playing a critical role in ocean processes.

Historically, scientists have noted a puzzling disconnection between zinc and phosphorus, despite both nutrients being co-located in phytoplankton regions. Instead, they discovered a strong and unexplained correlation between zinc and dissolved silica.

Understanding the ocean’s zinc cycle 

Professor Alakendra Roychoudhury from Stellenbosch University, a co-author of the study, argued that scientists can now confidently explain the biogeochemical processes driving the ocean’s zinc cycle. 

Since 2013, Roychoudhury’s team has participated in expeditions on South Africa’s polar research vessel, the SA Agulhas II, collecting sea water and sediment samples across the Southern Ocean.

“Processes occurring in the Southern Ocean are imprinted on water masses which are then transported to the Atlantic, Indian, and Pacific Oceans,” said co-lead author Ryan Cloete, a scientist at LEMAR in France. Collaborating with a team of international researchers, the scientists used X-ray spectroscopic techniques to analyze samples at the atomic and molecular levels.

Replenishment of dissolved zinc

The findings indicate that higher productivity in summer increases the availability of zinc in the surface ocean’s organic fraction for phytoplankton uptake. However, they also found high concentrations of zinc associated with debris from rocks, earth, and atmospheric dust. 

This interplay between zinc’s association or dissociation from particles is crucial for replenishing dissolved zinc to support marine life.

“In winter, poor growing conditions cause zinc particles to be ‘scavenged’ by inorganic solids like silica, iron, and aluminum oxides, explaining the strong association between zinc and silica in the oceans,” Cloete explained. 

Coupling between biochemical processes

Zinc bound to organic ligands is easily absorbed by marine life, whereas zinc in mineral form is not readily available, leading to its eventual sinking to the deep ocean and becoming inaccessible to phytoplankton.

“A warmer climate increases erosion, leading to more atmospheric dust and more scavenging of zinc particles, reducing zinc availability for marine life,” noted Roychoudhury. 

According to Cloete, such an approach to studying the oceanic zinc cycle opens the door to investigating other micronutrients, like copper, cadmium, and cobalt, which could also experience climate-induced changes.

“Our findings are a prime example of the coupling between biochemical processes at the molecular level and global processes like planetary warming,” Roychoudhury concluded.

Why is zinc important to marine life?

Zinc is a vital micronutrient that supports numerous physiological and biochemical functions in marine life.

Zinc is involved in the activity of over 300 enzymes, many of which are critical for the metabolism and overall health of marine organisms. 

Protein synthesis

Zinc plays a crucial role in the synthesis and stabilization of proteins. It helps in the formation of structural proteins, enzymes, and other important molecules.

Gene expression

Zinc is involved in the regulation of gene expression by influencing the activity of transcription factors. This regulation is vital for cellular functions and responses to environmental changes.

Immune function 

Zinc is important for the proper functioning of the immune system. It helps marine organisms resist infections and recover from illness.

Growth and reproduction 

Adequate zinc levels are necessary for the growth and reproductive health of marine organisms. Zinc deficiency can lead to stunted growth and reproductive issues.

Antioxidant defense

Zinc contributes to the antioxidant defense system by protecting cells from oxidative damage caused by free radicals.

Development

Zinc is crucial during the development stages of marine organisms, influencing everything from embryonic development to the growth of larvae and juveniles.

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