Greenland, a vast island largely covered by ice, harbors a dynamic aquatic world often unseen. Within this icy landscape, various lakes form on and beneath the massive ice sheet. These water bodies, though seemingly small in comparison to the expansive ice, are active components of Greenland’s changing environment. Their presence and evolution offer unique insights into the intricate processes shaping the region.
Formation and Characteristics of Greenland Lakes
Greenland’s lakes primarily fall into two categories: supraglacial and subglacial, each forming through distinct mechanisms. Supraglacial lakes, or meltwater lakes, appear on the ice sheet’s surface during warmer months. They form as meltwater from snow and ice accumulates in natural depressions on the ice, appearing as bright, turquoise features in satellite imagery. These lakes can range in size from a few meters to tens of kilometers in area and reach several meters in depth. They are common in lower elevations at the start of the melt season and expand further inland as melting progresses.
Many supraglacial lakes are temporary, draining rapidly through cracks or fractures in the ice, sometimes within hours. This rapid drainage, known as hydrofracturing, can transport large volumes of water to the base of the ice sheet. Some supraglacial lakes can persist through winter by forming an insulating ice lid. The presence of these surface lakes also reduces the ice’s reflectivity, leading to more sunlight absorption and further melting, creating a feedback loop.
Subglacial lakes, in contrast, exist hidden beneath the immense ice sheet, forming at the boundary between the ice and the underlying bedrock. Liquid water can persist here due to the pressure from the overlying ice, which lowers the melting point of water, and geothermal heating from below. Water in these lakes can remain isolated from the external environment for extended periods. Greenland has fewer subglacial lakes than Antarctica, with approximately 20 active ones identified. These subglacial lakes are often smaller than their Antarctic counterparts due to steeper ice-surface slopes and stronger hydraulic gradients.
Influence on the Greenland Ice Sheet
The presence and behavior of both supraglacial and subglacial lakes influence the dynamics of the Greenland Ice Sheet. Meltwater from supraglacial lakes often drains through vertical shafts called moulins, which are conduits extending from the ice surface to its base. This water flow to the ice-bedrock interface can lubricate the base of the ice sheet, reducing friction and allowing the ice to slide faster towards the ocean. This process can accelerate the movement of glaciers, particularly during the summer melt season.
Rapid drainage events from large supraglacial lakes can trigger the formation of new moulins, even in areas distant from existing ice crevasses. This mechanism means that more regions of the ice sheet, including higher elevations, can become susceptible to accelerated movement. The increased water pressure from these drainage events can cause the ice sheet to lift and slip horizontally, contributing to faster ice flow. While the impact of subglacial lakes on ice dynamics is less directly understood than surface lakes, their activity can also affect the timing and rate of freshwater flow through the subglacial system, influencing water delivery to the ocean.
Scientific Insights from Greenland Lakes
Scientists closely monitor Greenland’s lakes to gain insights into the complex dynamics of the ice sheet and its response to climate change. Satellite monitoring provides broad observations of lake formation, drainage, and evolution, helping researchers understand how these features change over time. Direct measurements and field observations offer detailed information about water levels, ice movement, and subglacial conditions. This data helps to refine models that predict how the ice sheet will behave under future warming scenarios.
Research on Greenland’s lakes contributes to broader climate models and predictions about global sea level rise. For example, studies have shown that the “brownification” of lakes in West Greenland, caused by extreme heat and rain, led them to shift from absorbing carbon dioxide to emitting it. This change occurred in less than a year. Such rapid transformations highlight the sensitivity of Arctic ecosystems and the importance of continued monitoring to understand the ice sheet’s stability and its contribution to global sea levels.