Question

Which of the following dissolved gases enters ocean water both from the atmosphere and from organisms that photosynthesize? A. carbon C. hydrogen B. nitrogen D. oxygen

Short answer

D. oxygen

Step-by-step solution

Understand the question

We need to determine which dissolved gas can enter ocean waters both from the atmosphere and from organisms. This means the gas can be introduced through two distinct sources: atmospheric exchange and biological processes via photosynthesis.

Identify possible gases from atmospheric exchange

Consider the gases that can dissolve into ocean water from the atmosphere. These typically include oxygen ( O_{2} ), nitrogen ( N_{2} ), carbon dioxide ( CO_{2} ), and possibly others. Recall that hydrogen does not typically dissolve from the atmosphere into the ocean.

Identify gases produced via photosynthesis

Photosynthesis produces oxygen as a byproduct, which is released into the surrounding water. Organisms like phytoplankton in ocean water perform photosynthesis, contributing oxygen to the environment.

Determine common dissolved gas in both scenarios

Since oxygen is both a significant component of the atmosphere that can dissolve into ocean water and is also a byproduct of photosynthesis, it satisfies both conditions mentioned in the question.

Key concepts

Dissolved Gases

Dissolved gases in oceanography refer to gases that are mixed into ocean waters from their gaseous state. The ocean acts as a giant solution where various gases from the atmosphere can be held in dissolved form. These dissolved gases play critical roles in supporting marine life and various oceanic processes.

Some of the main gases found dissolved in ocean water include:

• Oxygen ( O_{2} ): Crucial for the respiratory activities of marine organisms.
• Nitrogen ( N_{2} ): Although less reactive, it's present due to its abundance in the atmosphere.
• Carbon Dioxide ( CO_{2} ): Important for the processes such as photosynthesis and ocean acidification effects.

Newer gases like hydrogen have minimal impact in their dissolved form compared to these dominant gases. Understanding these gases is essential for comprehending marine biology and chemical oceanography.

Photosynthesis

Photosynthesis is a process where organisms convert light energy, usually from the sun, into chemical energy stored in glucose. In the ocean, this process is primarily carried out by microorganisms called phytoplankton. These are microscopic, photosynthetic organisms that float in the sunlit waters of the ocean surface.

During photosynthesis, phytoplankton use sunlight, carbon dioxide (CO_{2}), and water to produce glucose, a type of sugar that stores energy, and oxygen as a byproduct. The formula for photosynthesis can be represented as:\[6CO_{2} + 6H_{2}O + light \rightarrow C_{6}H_{12}O_{6} + 6O_{2}\]Phytoplankton serve as the foundation for the marine food web, providing energy to a wide array of ocean organisms. While generating oxygen during photosynthesis, they also help remove carbon dioxide from the atmosphere, playing a crucial role in the earth’s carbon cycle.

Biological Processes

Biological processes in the ocean involve the chemical activities performed by marine organisms that are necessary for life. These processes are essential for nutrient cycling and energy flow throughout marine ecosystems.

In the context of dissolved gases:

• Respiration: Most marine organisms, like fish, use respiration to derive energy, consuming oxygen and releasing carbon dioxide.
• Photosynthesis: As mentioned earlier, it's a critical process performed by phytoplankton, contributing oxygen and consuming carbon dioxide.
• Decomposition: The breakdown of dead organic matter releases carbon dioxide and other nutrients back into the water, which are then reused by other living organisms.

These biological processes maintain the balance of gases in the ocean and are crucial for sustaining life as they recycle nutrients and energy across various trophic levels.

Atmospheric Exchange

The exchange of gases between the ocean and the atmosphere is a key process in regulating both oceanic and atmospheric compositions. This process occurs mainly through diffusion, where gases move from areas of higher concentration to areas of lower concentration.

How Atmospheric Exchange Works:

• Equilibrium: Over time, the concentration of gases becomes balanced between the atmosphere and the ocean surface, owing to the diffusion process.
• Factors Affecting Exchange: Temperature, wind speed, and water movements influence the rate and direction of this gas exchange. Warmer waters, for instance, generally hold less gas than colder water.

Oxygen (O_{2} ) frequently enters ocean waters from the atmosphere, providing essential support for aquatic life. Conversely, carbon dioxide (CO_{2} ) is often absorbed by the ocean, helping modulate global climate impacts through carbon sequestration. Atmospheric exchange forms the foundation of the ocean's capability to sustain life and influence climatic patterns worldwide.