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Biology

Feeling the heat: how do plankton respond to glacial melting?

The paper:

Sommaruga, R. (2015). When glaciers and ice sheets melt: consequences for planktonic organisms. Journal of Plankton Research37(3), 509-518 DOI: 10.1093/plankt/fbv027

Introduction:

Our global climate is changing and has been for the last century. In that time, temperature and atmospheric CO2 have dramatically risen, causing major issues for Earth’s ecosystems (More climate change information). One of the most prominent signs of climate change is the rapid retreat of glaciers and ice sheets on land. Glaciers are dense (thousands of feet thick) accumulations of ice and snow that move under their own weight and can be hundreds of miles long. Glaciers naturally shrink and rebuild over time, but current climate effects have significantly sped up glacial melting. The retreat of glaciers and ice sheets is a global phenomenon and several locations such as the Alps, Greenland and the Central and Southern Andes are particularly vulnerable (Check out this amazing glacial retreat caught on film in Western Greenland).

Lakes

Figure 1: Diagram showing the conditions within glacial lakes over time. Turbidity, nutrients and UV radiation change with time and shape the plankton community in glacial lakes.

The rapid melting of glaciers has some major consequences. As glaciers melt, natural freshwater is released from the ice. Nearly 70% of the Earth’s freshwater is stored within glaciers, so increased melting could greatly alter the hydrological cycle and lead to more flooding in many parts of the world. In addition to releasing freshwater, current glacial melting facilitates the transport of different inorganic and organic molecules, as well as pollutants that have been trapped for decades. For instance, melting of glaciers in the mountain areas of the Alps has dramatically increased levels of nickel and other metals in nearby lakes, leaving them undrinkable.

Freshwater runoff from land glaciers allows for the creation of proglacial and ice-contact lakes (Fig. 1). Newly created lakes are often on unstable land and thus are susceptible to sudden flooding events. Newly built lakes are not rare. For example, in northern Patagonia total glacial lake area has increased by 65% since 1945. Though quite numerous, not much is known about the animal life within glacial lakes, especially at the microscopic level. Tiny plankton  produce vital oxygen, form the base of food webs and coincidentally are the first colonizers of glacial lakes. By studying glacial lakes, we can better understand how the melting of glaciers may influence the plankton community. Below is a discussion of previous work in the field focusing on the conditions within glacial lakes and how this relates to the plankton that live there.

What makes these lakes so unique?

Ice-contact lakes and coastal oceans receiving glacial meltwater are full of highly concentrated mineral particles. These particles, so-called glacial flour, form by erosion that occurs underneath the glacier as it moves over the underlying bedrock. Just try and imagine a tightly packed, mile-deep glacier moving along the continent and scraping up the ground below. As the glacier melts, particles (about the size of fine silts or clays) are picked up and deposited into new lakes or coastal oceans, creating a “cloudy” appearance in the water (Fig. 2). The environmental effects caused by mineral-rich meltwater are amplified in lakes because they are much smaller bodies of water with less mixing compared to the ocean.

Picture1

Figure 2: A) Glacial lake with high amounts of glacial flour discharged by nearby glacier. B) Closer look at glacial flour particles.

How do plankton organisms deal with this environment?

Microscopic plankton have a lot to deal with besides their obvious size disadvantage. Plankton require adequate sunlight, nutrients, and other plankton to eat (if you are a predator). The success of plankton in young glacial lakes is hard to measure. High concentrations of glacial flour will make it challenging for filter-feeding plankton organisms to feed, especially if they cannot discriminate between mineral particles and their planktonic prey. Mineral particles do not provide any nutritional benefit to herbivorous plankton and have been shown to lower their survival rates. Physical factors such as water temperature can also negatively impact plankton communities in glacial lakes. Glacial meltwater is cold (surprise, surprise) when it first reaches a lake, which can reduce growth in plankton populations.

On the other hand, new glacial lakes offer some benefits for plankton. Though glacial flour minimizes the amount of sunlight that can penetrate into the water column, it does give autotrophic (sunlight dependent) plankton and bacteria a break from harmful UV radiation. In addition, meltwater from glaciers carries large amounts of inorganic and organic nutrients (like nitrogen and phosphorous) that may help plankton compensate for low sunlight and temperature. In fact, autotrophic bacteria have been shown to survive in new glacial lake environments regardless of high glacial flour. Ultimately, these “cloudy” glacier-fed lakes provide contrasting growth conditions for plankton that colonize them.

Discussion and Significance:  

Need evidence for climate change? Look no further than the current melting of glaciers across the world. Glaciers discharge meltwater and can create unstable and highly turbid lakes on land. Over time, glacial lakes become more visible, warm up and support plankton life. The question remains…how will plankton in the coastal oceans and beyond respond to input from glacial meltwater? Glacial ice and meltwater that enters the ocean may contribute to a change in the chemistry and physics of the oceanic environment, as it has already been shown to alter lake systems on land. Regardless of how large it may seem, life in the ocean can be sensitive to change (i.e. ocean acidification, pollution, overfishing). Plankton are the tiny giants that power our oceans, so changes in the plankton community have ramifications for Earth’s climate. Further research on plankton in glacial-fed lakes is critical to understanding how plankton may respond to future meltwater scenarios in the ocean.

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