Oil on troubled water, ice on rough seas

I came across this brilliant Deep Sea News blog post about oil on troubled waters. It talks at length about how a surface film of oil damps out higher frequency surface waves and only the low frequency waves can propagate. The net effect is the sea feels calmer as the breaking waves are damped out.

The same thing happens in rough seas when ice forms. I took the picture below in Bellingshausen Sea.

A grease ice slick in the Bellingshausen Sea Antarctica
A grease ice slick in the Bellingshausen Sea Antarctica

What you are looking at is very thin slick made up of sea ice crystals in the open ocean (called grease ice). The layer of crystals only allows the low frequency waves to propagate - so you see these odd looking slowly propagating ripples.

It does look like there is oil on the surface doesn’t it.

When the wind picks up slightly and it "tears" the grease ice slick, instantly tiny wind generated waves start to form

A frazil ice slick damping out tiny wind generated ripples

A frazil ice slick damping out tiny wind generated ripples

The effect is very clear. The next picture is an enlargement of the boundary showing the high frequency wind generated wave being damped out - and refraction at the boundary between the open water and the ice/ocean mix.

Refraction at the ice open water interface
Refraction at the ice open water interface

This damping out means (as you can see) that the reflectivity of the ocean surface  is very different between areas that are open water, and areas that are ice covered.

That means you can easily observe it from space using satellites with radar sensors in the same way that for example oil slicks as sea can be observed. For example this shows an oil slick.

TerraSAR-X image of the month: Oil disaster off the Australian coast
Oil slick from the Montara offshore oil platform in the Timor Sea. TerraSAR-X image of the month: Oil disaster off the Australian coast

The oil spill shows up as dark - just as the sea ice does in such imagery.

There are some very interesting science papers in this area, and several pdfs showing how you can observe this effect from space

 

 

3 thoughts on “Oil on troubled water, ice on rough seas

    1. Mark Brandon

      Post author

      Oh that is lovely!
      I think it likely is. A thin biological film on the surface damping the waves. I think it would be weird to see if not cold...

      Reply
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