Geochemistry

APPLIED SCIENCE

Oceanic metalic elements and their relative abundance

By MICHAEL JOHN UGLO
WELCOME to our final lecture on geochemistry.
After this lecture we go on to the applied sciences of robotics, biotechnology and artificial intelligence which pose a greater insight for a knowledge base for PNG students and advocates endeavoring to implement the Stem (science, technology, engineering and mathematics) curriculum.
This will be followed by the sciences of computers and technology to add further resource and substance.
Geochemistry should really help us to understand the involvement of geology and chemistry in furthering the refinement of our ideas and knowledge of the position of the planet earth in relation to the world around it in terms of its chemical and elemental composition.
The availability of trace metallic elements in the oceans are significant. The chemistry learnt in laboratories and classrooms can be extended to that of the external and outdoor applied learning of chemistry. Oxidation and reduction reactions to do with loosing and gaining electrons to form new products actually happens in the body of water, the ocean. The formation of chelates with ligands and the complex compounds happens in the ocean to maintain a less toxic reservoir for aquatic life to thrive instead of being an acidic or corrosive chemical dump that can deprive biological life.
The trace metallic elements that are seen to be available in the ocean are namely molybdenum, copper, cadmium, manganese, uranium, rhenium and vanadium. These trace elements form bonds with major ions known as the salts in the oceans such as carbonates, chlorides, sulfides and hydroxides.
In the oxidation and the reduction environments, cadmium can form CdCl+ (aq) in oxic water and CdS(s) in reduced environments. Particularly for the higher accumulation of the trace metallic element cadmium shows low potential for the redox reaction in the past climate and environment.
As an example drawn here, all the above remaining metals as molybdenum, copper both copper (I) and copper (II), cadmium, manganese, uranium and vanadium form complex chelates with ligands with these metals following the rules for redox reactions given an oxidative environment or a reduced environment.

The rules for redox reactions being in redox reactions, electrons are accepted by a most electronegative recipient reagent as donated from a more electropositive donor. The condition is for an electropositive substrate to attain a positive charge or positive charges while the recipient is negatively charged.
In the water bodies of the ocean and deeper lakes a vertical profile is seen to be created to exemplify the concentration of these trace elements. There are three categories of these profile and are namely conservative type, nutrient type and the scavenged type distributions. These three types of profiles for the trace elements have their different residence time in comparison to the microorganism in particular the planktons which dwell on them.
The category with the highest residence time is the conservative type to a period of 8 x 105 years for the trace element molybdenum. This trace metallic element that associates with is present as the molybdenite anion with a chemical formula for the anion as MoO42-. This is a negative ion. Molybdenum reacts weakly with other chemical particles in the ocean and hence display a more uniform vertical profile in the ocean. In terms of its interaction with the planktons in the ocean to form as a cofactor for the metallic enzyme is also not conducive.

The next group is the nutrient type distribution in which its residence time is bigger but not as high as the conservative type. This is the distribution type of the nutrients that are passing within the planktonic microorganisms. The trace elements are basically absorbed and assimilated from the top of the ocean. This organic matter undergoes dissolution and decomposition and it will have to take place right at the bottom of the ocean. Hence the residence time for such trace metallic elements as zinc takes several thousand to 100,000 years.
The next type of the vertical oceanic profile for the distribution of trace metallic elements is the scavenged type. A trace element in this category is aluminum whereby it interacts with other particles form the ocean. Therefore, its residence time is shorter on the distribution scale and it takes from 100 to 1000 years. The concentration of aluminum is greatest at the bottom of the ocean, as well as the hydrothermal vent and at the rivers. The source that feeds the supply of aluminum to the ocean is the atmospheric dust.

Iron and copper are the most scavenging trace metallic elements found in the sea. Iron is mostly concentrated with manganese at the hydrothermal vents up to a million times as those found in the ocean. Iron sulfides and iron oxyhydroxide occur as precipitates at the hydrothermal vents.
The bioactive trace elements bind with ligands and from complexes that avoid a toxic environment for some metals like copper to any toxic level. These bioactive metals include cadmium, zinc, cobalt, iron and copper. The ligands with the complexes formed create a toxic free environment for the planktonic microorganisms with other marine plants and animals to thrive.
My Prayer for PNG today is: “Blessed be the Lord, the God of mercy, the God who saves. I shall not fear the dark of night nor the arrow that flies by day.”
Next week: Robotics, biotechnology and artificial intelligence (AI)

• Michael Uglo is the author of the science textbook “Science in PNG, Pacific, Asia & Caribbean” and a lecturer in avionics, auto-piloting and aircraft engineering. Please email comments to [email protected]