We woke this morning having left the English Channel and are now steaming across the Celtic Sea. The wind picked up overnight giving much greater swell and an early test for the team’s sea legs.
I have been thinking a lot about why we are here today, probably because the wind picked up and the swell left me feeling nauseous all day – “what am I doing here??”. To understand this, we first need a bit of background about the OSMOSIS project.
What does OSMOSIS stand for?
The project name stands for “Ocean Surface Mixing – Ocean Submesoscale Interaction Study”. This explains why we simply refer to it as OSMOSIS. Although it is not related to the chemical process of osmosis, it investigates a mixing process which happens in the upper ocean.
Surface mixing is important in the Earth’s climate system as it is where the ocean and atmosphere communicate with each other. Mixing in this area can move properties of the atmosphere down into the ocean – or properties of the ocean up into the atmosphere.
An important example of this is heat. For example, a large storm at sea might mix colder water from depth up into the surface ocean, leading to a cooler surface layer. This colder water can then chill the air above it, leading to cooler air temperatures. Another important example is CO2. In many places surface layer water has a high concentration of CO2 which it has absorbed from the atmosphere. If this surface layer water is mixed downwards it may be replaced by water which has a low concentration of CO2. This water with low concentration can then absorb more CO2 from the atmosphere, reducing the amount available to cause the greenhouse effect. However, some speculate that this mixing process has gone into reverse in other periods of Earth’s climate and so increased the greenhouse effect.
What are ‘submesoscales’ then?
The flows in the ocean have different sizes or ‘scales’. These scales include the ‘basin-scale’ which refers to currents that extend over thousands of kilometres of an ocean basin such as the Atlantic or Indian Oceans. They also include small-scale processes such as the waves you see on the surface.
In between these two scales lies the ‘mesoscale’ where the word ‘meso’ is derived from the Greek word for the middle. The mesoscale refers to the ocean eddies with a horizontal length of 50 – 150 km. The mesoscale is thought to be the most important in controlling many aspects of ocean flows and is responsible for the swirling motions in this animation from NASA.
Submesoscale then refers to the next largest size of motions, so they are ‘sub-meso’. They can be thought of as ‘eddies-on-eddies’. Oceanographers think they may be important in linking the very small scale processes with the mesoscale. Historically, the submesoscale has not been well studied because studies have tended to focus on either large or small scale features or the. The OSMOSIS project has been designed to investigate this gap in our knowledge by deploying an array in the North Atlantic which we will describe in more detail in a later post.
As for me, I eventually found my sea legs today. Once that happened it was magnificent to be out on deck with the ship riding the 5 metre waves. As we crested one wave the surface seemed as far below as it would from the deck of a ferry, but seconds later, sinking into that trough, the next wave loomed so large that we had to look upwards to its breakers. And then we crest that wave only for the next valley to reveal a lone gannet alongside skimming across the waves with its wing tips almost touching the breakers.