Ocean currents: How the Gulf Stream affects Europe’s fishing waters

Currents are undoubtedly at the heart of all life in the ocean and their importance in stabilising sea temperature, salinity and circulating nutrients and CO2 cannot be overstated. Changes in these currents can have a profound affect on the species, number and health of fish in the ocean so how would changes in the Gulf Stream impact on European fishing?

Whilst it is wind which drives the currents at the surface of the ocean, deep-sea currents flow many hundreds (or thousands) of metres below the surface. These circulatory, underwater rivers are one of the principle drivers for global climate and not only shape the face of the seas but also that of land. There are many currents in play across all of our oceans and each take their role in churning the waters to maintain a careful balance in salt levels, water temperature and phytoplankton. Collectively, they are known as the global conveyor belt because, fundamentally, that is the way they act.

The cycle starts in the North Atlantic where water is cooled by Arctic winds and the sea begins to freeze. The surface water that does not ice over has a high saline content (due to the fact that salt does not freeze) and as a result the dense (cold) water sinks to the bottom of the sea. Warmer surface water is then pulled on a current to replace the sink thus starting the chain of ocean circulation. The deep water currents cycle south between America and Europe where it eventually reaches the Antarctic and the, now warmer, water begns its second cold sink. Here in the Southern hemisphere the conveyor splits into two streams; one feeding into the Pacific Ocean and the other into the Indian Ocean. Both offshoots will cycle northwards to the equator where they will warm before eventually being pulled back to the North Atlantic to begin the cycle again. The process is a slow but steady one with deep currents moving at a pace of around 1-2cm per second vs tidal currents whose pace is more like 10-100cm per second. It is estimated that any body of one cubic meter of water will take approximately 1000 years to complete a full cycle on the global conveyor belt.

This process of churning the deep waters of our oceans is a vital one and is the primary driver behind, the global population, health and variety of, fish stocks. Without this constant cycling to provide nutrient rich cool waters, marine life would not thrive and the seas could not support the essential growth of seaweed and algae.

Many smaller currents are drawn under the influence of the phenomenon that is the global conveyor belt, including the Gulf Stream.

This current is mainly responsible for regulating the water temperature of the rich Atlantic fishing grounds. Whilst for the most part the Gulf Stream itself does not support much marine life of commercial interest (only Atlantic salmon, Bluefin tuna and flying fish) it does produce a unique effect when it reaches the waters of Northern Europe. When the warmer water meets the cooler waters it creates a turbulence which churns up nutrient salts in the ocean making these seas fertile ground for fishing.

The term global warming has been in use since 1975 and has come to cover the undeniable changes that are occurring in the planet’s climate. Whether the changes are man-made or an inevitable part of the ever-changing landscape of the Earth’s weather patterns is irrelevant; what is true is that there are changes being tracked in the cycles of our ocean currents and our ability to respond to this change is important.

Essentially, the increase in global temperatures appears to be speeding up the melting of the polar icecaps; in turn this means there is less salinity in these two regions which could disrupt the sinking of the cooler and denser water and thus slow down (and possibly halt) the conveyor process.

Whilst many scientists are still arguing over the possible implications of such a change as well as the possible rate at which this could happen, it does seem inevitable that changes will be seen in this century which will require the world, along with its fishing communities, to adapt.

Whether the increase in sea temperatures are man-made or an inexorable re-shaping of our planet’s climate is immaterial, what matters is that fish stocks are preserved and that fishermen remain adaptable to change.

Any shift in the global conveyor belt will have an impact on the species, distribution and numbers of fish available in Europe’s waters so equipping your fishing boat to accommodate such change is both forward-thinking and advantageous in commercial fishing.

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