The Surprising Role of Sublimation in Glacial Ice Mass Balance: An Energy Balance Perspective

Glaciers are one of the most important sources of freshwater on Earth, and their mass balance (the balance between ice accumulation and loss) is a key indicator of the health of our planet’s cryosphere. A positive mass balance occurs when the amount of ice gained by a glacier exceeds the amount lost through melting, calving, and other processes. While it may seem counterintuitive, sublimation-the process by which ice converts directly to water vapor without passing through the liquid phase-can actually contribute to positive mass balance in certain situations. In this article, we will explore how and why sublimation can have a positive impact on glacier mass balance.

Explaining sublimation as a process

Sublimation is a process that occurs when a solid (such as ice) is exposed to air with low relative humidity. When this happens, the solid begins to turn into a gas without first melting into a liquid. This is because the energy required to break the bonds holding the solid together is less than the energy required to form new bonds between the solid and liquid phases. The opposite of sublimation is deposition, which occurs when water vapor in the atmosphere condenses directly into ice without first forming liquid droplets.
Sublimation is an important process in the Earth’s water cycle because it contributes to the movement of water between land, oceans, and the atmosphere. In the case of glaciers, sublimation can occur when the air temperature is below freezing and the air is very dry. Under these conditions, ice at the surface of a glacier can turn directly into water vapor and be carried away by the wind. This process can occur even when the air temperature is below freezing because the heat required to sublimate the ice comes from the ice itself, which cools as it sublimates and can keep the surface below the air temperature.

How sublimation can contribute to positive mass balance

At first glance, it may seem that sublimation would lead to a negative mass balance because it removes water from the glacier system. However, sublimation can actually contribute to positive mass balance in two ways.

First, sublimation can remove ice that is already at the surface of the glacier, which is typically the least dense and most porous ice. This ice is often referred to as “surface ice” and can be several centimeters thick. Because this ice is not as densely packed as the ice deeper in the glacier, it has a lower density and contains less mass per unit volume. When this ice sublimates, it removes mass from the glacier without reducing its volume, which can result in a net gain in mass.
Second, sublimation can increase the albedo (reflectivity) of the glacier surface by removing the darker, less reflective ice from the surface. This can reduce the amount of solar radiation absorbed by the glacier, which can slow the rate of melting and contribute to positive mass balance. In addition, as sublimation occurs, the ice surface becomes smoother, which can further increase the albedo and reduce the amount of solar radiation absorbed.

It is important to note that the positive effect of sublimation on glacier mass balance is limited by several factors. First, sublimation is most effective in cold, dry environments, which are becoming increasingly rare due to climate change. Second, sublimation can only remove a limited amount of ice from a glacier’s surface and cannot compensate for large-scale melting or other forms of ice loss. Finally, the positive effect of sublimation on mass balance may be diminished by other factors, such as increased melting due to rising temperatures.

Implications for Earth science and energy balance

Understanding the role of sublimation in glacier mass balance is important for several reasons. First, glacial mass balance is a key indicator of climate change, and changes in glacial mass balance can have significant impacts on water resources, sea level rise, and other aspects of the Earth system. Second, sublimation is an important process in the Earth’s water cycle, and understanding how it contributes to glacial mass balance can improve our understanding of global water resources and the climate system.

In terms of energy balance, sublimation can have important implications for the amount of solar radiation absorbed by the Earth’s surface. As mentioned above, sublimation can increase the albedo of glacier surfaces, which can reduce the amount of solar radiation absorbed by the glacier and reflected back into the atmosphere. This can have a cooling effect on the Earth’s surface, which can help offset some of the warming caused by greenhouse gas emissions. In addition, sublimation can contribute to the movement of water vapor between the land, oceans, and atmosphere, which can have important implications for the Earth’s energy balance and climate.
It is important to note that while sublimation can have a positive effect on glacier mass balance and the Earth’s energy balance, its overall effect is limited by a variety of factors, including the availability of dry air, air temperature and humidity, and the amount of ice on the glacier surface. In addition, the positive effect of sublimation on glacier mass balance may be overwhelmed by other factors, such as increased melting due to rising temperatures. Therefore, it is important to continue studying the role of sublimation in glacial mass balance and the Earth’s energy balance to better understand their complex interactions and implications for the future of our planet.

FAQs

1. What is sublimation and how does it work?

Sublimation is the process by which a solid, such as ice, transforms directly into a gas, such as water vapor, without passing through the liquid phase. This occurs when the energy required to break the bonds holding the solid together is less than the energy required to form new bonds between the solid and liquid phases. Sublimation is an important process in the Earth’s water cycle, as it allows water to move between the land, oceans, and atmosphere.

2. How can sublimation contribute to positive mass balance in glaciers?

Sublimation can contribute to positive mass balance in glaciers in two ways. First, sublimation can remove ice that is already at the surface of the glacier, which is typically the least dense and most porous ice. When this ice sublimates, it removes mass from the glacier without reducing its volume, which can lead to a net gain in mass. Second, sublimation can increase the albedo (reflectivity) of the glacier surface by removing the darker, less reflective ice from the surface. This can reduce the amount of solar radiation absorbed by the glacier, which can slow down the rate of melting and contribute to positive mass balance.

3. Are there any limitations to the positive impact of sublimation on glacial mass balance?

Yes, the positive impact of sublimation on glacial mass balance is limited by several factors. First, sublimation is most effective in cold, dry environments, which are becoming increasingly rare due to climate change. Second, sublimation can only remove a limited amount of ice from the surface of a glacier, and cannot compensate for large-scale melting or other forms of ice loss. Finally, the positive impact of sublimation on mass balance may be mitigated by other factors, such as increased melting due to rising temperatures.

4. What is the relationship between sublimation and albedo?

Sublimation can increase the albedo (reflectivity) of the glacier surface by removing the darker, less reflective ice from the surface. This can reduce the amount of solar radiation absorbed by the glacier, which can slow down the rate of melting and contribute to positive mass balance. Additionally, as sublimation occurs, the ice surface becomes smoother, which can further increase the albedo and reduce the amount of solar radiation absorbed.

5. What is the importance of understanding the role of sublimation in glacial mass balance?

Understanding the role of sublimation in glacial mass balance is important for several reasons. First, glacial mass balance is a key indicator of climate change, and changes in glacial mass balance can have significant impacts on water resources, sea level rise, and other aspectsof the Earth system. Second, sublimation is an important process in the Earth’s water cycle, and understanding how it contributes to glacial mass balance can improve our understanding of global water resources and the climate system. Finally, sublimation can have important implications for the Earth’s energy balance, as it can increase the albedo of glacier surfaces and reduce the amount of solar radiation absorbed by the Earth’s surface, which can have a cooling effect on the planet and help to offset some of the warming caused by greenhouse gas emissions.

6. Can sublimation compensate for large-scale melting or other forms of ice loss?

No, sublimation can only remove a limited amount of ice from the surface of a glacier and cannot compensate for large-scale melting or other forms of ice loss. While sublimation can contribute to positive mass balance in certain situations, it is not a solution to the larger problem of glacial melt and ice loss due to climate change.

7. How can we continue to study the role of sublimation in glacial mass balance and the Earth’s energy balance?

We can continue to study the role of sublimation in glacial mass balance and the Earth’s energy balance through a variety of methods, including field studies, satellite observations, and computer models. By improving our understanding of the complex interactions between sublimation, glacial mass balance, and the Earth’s energy balance, we can better predict the impacts of climate change on glaciers and the wider Earth system, and develop strategies to mitigate these impacts and adapt to a changing climate.