This glacial valley could fertilise northern fjords

Imagine the following: You are a grain of sand trapped under the ice. A lot of ice – in fact, let us say, 100 metres of glacier ice. How does it feel, how does it sound down there?

You may hear the ice cracking, but sounds from the outside do not reach you, because the thick ice insulates so well. It is likely going to be cold, but also quite a stable temperature, because the ice buffers changes in outside air temperature. 

If you are not in a meltwater channel, you are probably also quite isolated from the nutrient inputs that come from snow and rain, and generally just snug and stable in your glacial sediment bed.

All of a sudden, one day in late summer, light reaches you through the ice. After a while, meltwater starts dripping. Before you realise it, the glacial ice that used to cover your neighbourhood of sand grains is all gone as the glacier has retreated back up the valley. "What is happening?" you may think.

From now on, a new era of your existence begins. In the coming years, the summers feel warm, and in autumn and winter, temperatures cycle between freezing and thawing. 

It is now dry in summer and wet in spring, and rain, snow, and dust from the air bring new compounds and new microbes to your neighbourhood. Perhaps the soil water tastes a bit sour from the changes in pH.

What has happened to you is, of course, glacial retreat and exposure to the world outside the glacier. 

Nutrients on the move

In recent decades, glacial retreat has escalated, leaving large surfaces of sediment exposed to rain, temperature fluctuations, and chemical-biological input from the atmosphere. With time, microbial activity builds up organic matter and nutrients in the surface sediment. 

Some of the nutrients are released into soil water, either directly, or when the soil thaws. This means that during rain and snowmelt, the built-up nutrients can be moved with water running through the soil. They can for example end up in the glacial river, and from there in the fjord. In the fjord, algae and other microbes use nutrients to survive.

The question is, however, whether the faster glacial retreat will cause the much larger surfaces to release more nutrients, so that the transport of nutrients will be much larger and fertilise the fjords, disturbing fragile ecosystems? 

This is what we are trying to understand in Steindalen valley in Lyngen, Troms.

Studying soil water nutrients from sediments

Here, the local glacier has retreated fast since the 1970s (see above, Fig. 1). We have therefore set up study sites to measure soil water nutrient contents from sediments. The sediments have different ages, because they were exposed within the last 10-15 years, 30 years, 70 years, and more than 150 years ago. 

We take the soil water samples throughout a whole year so we can measure the effect of freezing and thawing on the nutrient release.

We use the soil water samples, together with river water samples from the glacial river, to understand:

1. How much of the nutrients the sediments of different ages contain throughout the year.
2. How much of those nutrients end up in the glacial rivers, and at what time of the year.

This will help us understand how much of the nutrients will be transported into the fjords as the glaciers keep retreating. And it will help your grain of sand understand what is happening to its world.

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