Heat and Salt Budgets

Heat Budget

What is the Heat Budget?

The heat budget of the ocean refers to the balance between the heat energy absorbed and released by the ocean. Oceans act as heat engines that absorb surplus insolation (solar radiation) and release energy during periods of heat deficit, thereby regulating the temperature and climate of the Earth. Despite receiving about 25% of all insolation on the Earth-Atmospheric System, oceans do not continuously get warmer or cooler. Instead, they maintain their temperature through a delicate balance of heat exchange.

How Does the Heat Budget Work?

The amount of insolation received by the ocean is denoted as Q_i.

As oceans maintain a constant temperature overall, the heat budget equation is represented as: Qi + Q{LW} + Qs + Q{LH} + QB + Q{average} = 0

Where:

• Q_i : Insolation received by the ocean
• Q_{LW}: Longwave radiation loss
• Q_s : Sensible heat transfer (transfer of heat due to temperature differences)
• Q_{LH}: Latent heat transfer (heat absorbed or released during evaporation or condensation)
• Q_B: Bottom heat transfer
• Q_{average}: Overall average heat flux

Radiational Heat Exchange

• Oceans are, on average, 0.3°C warmer than the atmosphere across all latitudes.
• Both longwave radiation (QLW) and sensible heat transfer (Qs) result in a net loss of energy from the ocean.
• During evaporation, oceans absorb heat, whereas during condensation, they release heat.

The heat balance for the ocean as a whole can be simplified as: Qi = Q{LW} + Qs + Q{LH}

Mechanism of Heat Balance

• Heat is not lost instantaneously but is instead redistributed over time, contributing to a balanced temperature across the ocean.
• The balance varies by latitude, as the influx and outflux of heat are not evenly matched everywhere.
• Human activities can disturb this delicate heat balance, leading to changes in sea surface temperatures and effects like ocean acidification.

Salt Budget

What is the Salt Budget?

The salt budget of the ocean refers to the balance between the addition and removal of salts, ensuring that the total salinity remains relatively constant. The ocean’s salt content follows the Law of Conservation.

Principles Governing the Salt Budget

1. Total Salts of the Ocean are Constant: Despite processes adding and removing salts, the total quantity remains unchanged.
2. Principle of Constant Proportion of Salts (Froschhammer’s Principle): Regardless of the total salt content, the relative proportion of individual salts remains constant.

Sources and Processes Involving Salt

Processes Adding Salts:

• Vulcanism: Volcanoes release salts into the ocean through volcanic eruptions.
• Denudation Agents: Rivers and streams erode rocks, carrying salts to the ocean.

Processes Removing Salts:

• Biological Processes: Organisms remove calcium and other minerals, which precipitate and eventually become part of ocean deposits.
• Chemical Reactions: These precipitate salts, removing them from the water.

Key Observation: Sodium salts have the highest residence time, making up 78% of all salts in the ocean.

Calculation and Measurement of Total Salts

• The total salt content of the ocean is approximately 5×10^19 kg.
• Salts added by vulcanism and rivers amount to 3×10^12 kg annually, but this represents only about 1 in 17 million parts of the ocean’s total salt content.
• Advanced instruments can currently detect changes in salinity at 0.003 parts per thousand, but detecting actual additions requires instruments 1,500 times more sensitive. Hence, for practical purposes, the ocean’s total salt budget is assumed to be constant.

Sea Surface Salinity

What is Sea Surface Salinity?

Surface salinity refers to the concentration of dissolved salts in the upper layers of the ocean. It varies across different regions due to multiple factors such as evaporation, precipitation, and freshwater input.

How Does Salinity Vary?

• High Salinity:
  • Found in the center of ocean basins away from river mouths.
  • More concentrated in subtropical regions due to high evaporation rates, clear skies, little rainfall, and prevailing winds.
• Low Salinity:
  • Present in coastal and equatorial regions where precipitation exceeds evaporation.
  • Enclosed or landlocked seas in arid regions may have high salinity due to evaporation.

Tracking Sea Surface Salinity

Salinity acts as a surface tracer for freshwater inputs and outputs in the ocean, such as:

• Precipitation and Evaporation
• Soil Moisture and Atmospheric Water Vapor
• Sea Ice Extent

Why Is Salinity Important?

By tracking sea surface salinity, scientists can monitor changes in:

• The water cycle
• Land runoff
• Sea ice freezing and melting
• Evaporation and precipitation over oceans

These changes help understand variations in the global Earth system and detect natural or human-induced changes.

Conclusion

The heat and salt budgets of the ocean play critical roles in regulating Earth’s climate, oceanic processes, and marine ecosystems. Understanding these processes is vital for predicting climate change impacts and managing the Earth’s water and heat distribution.

1. How do the heat budget and heat exchange processes of the ocean influence global climate patterns, and what role does human interference play in altering this balance? (250 words)
2. Discuss the significance of the principle of constant proportion in maintaining the ocean’s salt budget. How do natural processes regulate the addition and removal of salts? (250 words)
3. Explain how tracking sea surface salinity helps scientists understand the Earth’s water cycle and the impact of climate change on oceanic processes. (250 words)