Iceberg. Photo: Simon Berger, pexels.com
This week I have been learning about how ice shapes the seafloor, a new concept for me. Part of my job is recognising patterns deep below our oceans, interpreting what caused them, and then understanding if those processes are still happening, or are likely to happen again soon.
Iceberg. Photo: Jean-Christophe André, pexels.com
The patterns caused by ice in the sediments and rock that make up the bottom of our oceans are beautiful and complex. They tell stories spanning thousands of years, or even more if we look below the surface. So how does this happen?
Most of us probably don’t tend to think much about icebergs down here in New Zealand, unless we are pondering the disastrous voyage of the Titanic in 1912. We also sometimes see in the news when enormous chunks of ice detach through calving from the Antarctic ice sheet, or when discussions of our changing climate are brought to the forefront.
Janine Krippner
When an iceberg forms and becomes a solitary chunk of floating ice, it is then carried by wind and water currents where it can slowly melt or break apart into smaller chunks. This process might be quick, or last decades for the larger ones. The shapes and sizes are diverse, from expansive flat-topped “tabular” giants to small growlers and “bergy bits”. Yes, that is a technical term, and perhaps my new favourite.
We have all seen the sort of inspirational posters that point out that most of an iceberg’s mass is below the surface. What we see above the water is only about 10 per cent of the total volume. Sometimes these massive structures scrape along the seafloor, leaving scars, and as this happens, sand, mud, and boulders are pushed aside to form ridges.
Some areas are covered in crisscrossing scours (also called gouges or furrows) from where the bottoms of many icebergs (the keel) ploughed through the seabed.
These scours can be kilometres long, on the order of tens to hundreds of meters wide, and meters deep. This is a significant process across the seafloor, especially when you think of critical infrastructure like cables across the seafloor at high latitudes where these processes still take place today.
Scientists who study these patterns can learn about past ocean and climate patterns, uncovering the clues left behind long ago by these fleeting, icy giants. Some of the more interesting scours can be spiral shaped where currents carried the icebergs in circular motions, and others form lines of pits where an iceberg was lifted up and down by tides, puncturing the deep sediments.
Understanding how deep the ocean was at a particular location and time allows an estimation of how large an iceberg was. Scientists have found evidence of “mega-bergs” scraping along the seafloor down to 1 km water depth.
To think that icebergs are the final part of the long, slow journey of glacial ice that formed potentially many thousands of years prior, floating across the ocean and becoming part of the global water cycle. Most never leave a trace that we are aware of, while others have scribbled their signatures in deep waters for us to uncover.
Iceberg. Photo: Simon Berger, pexels.com
