Pengantar Oseanografi - Komposisi Kimia Air Laut

Summary

This lecture provides an in-depth overview of the chemical composition of seawater and its significance in oceanography. It explores the roles of major, minor, and trace elements in marine ecosystems, focusing on their contributions to salinity, nutrient cycles, and biochemical processes. Key elements such as chloride, sodium, phosphorus, and nitrogen are discussed, alongside their sources, interactions, and impacts on marine life. The concept of resident time is introduced, highlighting how long different elements stay in the ocean. The lecture emphasizes the importance of understanding these processes for environmental and biological studies in the ocean.

Takeaways

• 😀 The chemical composition of seawater is complex and plays a vital role in various oceanic processes.
• 😀 Seawater elements can be categorized into major, minor, and trace elements based on their concentration levels.
• 😀 Major elements, such as chloride, sodium, sulfate, magnesium, calcium, and potassium, determine seawater salinity and are considered conservative.
• 😀 Minor elements have lower concentrations but contribute significantly to chemical processes in the ocean and are classified as non-conservative.
• 😀 Trace elements, present in very low concentrations, contribute minimally to salinity but are crucial for biochemical reactions.
• 😀 Elements in seawater come from both external sources, such as the atmosphere and rivers, and internal sources like underwater volcanic activity and tectonic processes.
• 😀 Resident time refers to the average duration an element stays in the ocean before being removed. Major elements have long resident times, while others like iron have shorter times.
• 😀 Macronutrients, including nitrogen, phosphorus, and silicon, are essential for marine organism growth, particularly for phytoplankton.
• 😀 Nutrient cycles, like the nitrogen and phosphorus cycles, describe how elements are transformed and recycled in marine ecosystems.
• 😀 Nutrient concentrations are highest at depths of 500-1000 meters due to remineralization, while surface waters are often nutrient-depleted.
• 😀 Oxygen concentrations are higher at the surface but decrease with depth, in contrast to nutrient levels that are generally higher deeper in the ocean.

Q & A

What are the three categories of elements found in seawater?

The three categories of elements found in seawater are major elements, minor elements, and trace elements.

What is the role of major elements in seawater?

Major elements, such as chloride, sodium, sulfate, magnesium, calcium, and potassium, constitute the largest portion of seawater's salinity and play a critical role in determining its properties, such as salinity.

What distinguishes conservative elements from non-conservative elements?

Conservative elements, such as the major elements in seawater, maintain a constant proportion in the ocean, despite changes in salinity. Non-conservative elements, such as minor elements, have variable concentrations because they are more reactive and influenced by chemical and biological processes.

How do minor elements contribute to the ocean's ecosystem?

Minor elements, though present in small quantities (less than 1%), play vital roles in chemical processes, support marine life as nutrients, and can act as pollutants in some cases. Examples include phosphorus, nitrogen, and iron.

What is the significance of trace elements in seawater?

Trace elements are found in very low concentrations but are essential for various biochemical functions in marine organisms. They are mostly present in complex compounds and can be critical for specific biological processes.

What is 'residence time' in the context of oceanography?

Residence time refers to the average time an element remains in seawater before being removed or transferred elsewhere. Elements with longer residence times, like sodium and chloride, stay in the ocean longer, while others, like iron, have shorter residence times.

What factors determine the residence time of an element in the ocean?

The residence time of an element is primarily determined by its reactivity. Elements that are less reactive, like sodium and magnesium, tend to have longer residence times, while more reactive elements, like iron, have shorter residence times.

How do nutrient cycles, like the nitrogen and phosphorus cycles, affect marine life?

Nutrient cycles, such as the nitrogen and phosphorus cycles, are crucial for the growth of marine organisms like phytoplankton. These nutrients undergo processes like nitrogen fixation and nitrification, and when organisms die, their nutrients are recycled back into the ocean.

Why is the concentration of nutrients low at the ocean's surface?

Nutrient concentrations are low at the surface due to high consumption by organisms like phytoplankton. The limited input of new nutrients at the surface, combined with their consumption, leads to a nutrient-poor upper layer.

How does the vertical distribution of nutrients vary in the ocean?

Nutrient concentrations are lowest at the ocean's surface and increase with depth due to the process of remineralization. At deeper levels, nutrients are replenished through the decomposition of organic matter, whereas oxygen follows an opposite trend, being highest at the surface.