Ocean circulation and climate

Oceanic overturning circulation transports heat, salt and carbon between the low and high latitude oceans and between the surface and the deep ocean.

Overview

Because of its role in moving heat and carbon, overturning strongly influences the partitioning of carbon and heat between the atmosphere and ocean and therefore influences global climate.

GNS records past climate variability using many locations around the South West Pacific, other parts of the Southern Ocean, such as the Indian Sector and the Ross Sea.

We’re researching how the strength of the overturning circulation has changed in the past. We are also researching the climate changes associated with this variability and how these far-away changes can affect climate in the South West Pacific and across the wider Southern Ocean. This will give us a better understanding of what might happen in the near future because of human-induced climate change.

The project

How ocean circulation affects climate

The global ocean overturning circulation transports heat, salt and carbon between the low and high latitude oceans and between the surface and the deep ocean. Because of its role in moving heat and carbon, overturning strongly influences the partitioning of carbon and heat between the atmosphere and ocean, thereby influencing global climate.

What happens if this circulation slows?

Climate models predict a slowing of the Atlantic overturning circulation over the 21st century due to atmospheric warming. A reduced air/sea temperature gradient slows the release of heat to the atmosphere from the northward moving currents, and increasing rain and ice melt also freshens the North Atlantic, reducing the buoyancy difference between water masses.

These changes are likely to deliver an impact on the climate system. A slowed North Atlantic overturning circulation would not transport as much heat as it presently does to Northern Europe, offsetting temperature rises from other factors such as increasing greenhouse gases. Slowed formation of North Atlantic Deep water will slow the removal of anthropogenic heat and carbon from the upper ocean and accelerate the rate of heat and carbon increase from human activities in the atmosphere.

It is not expected that over the 21st century the Atlantic meriodional overturning circulation will experience a major collapse and reorganisation, as it has during periods of rapid climate change in the geological past. However, beyond the 21st century, major changes, including a strengthening and stabilisation of the overturning circulation in both the Southern and Northern hemispheres, or a shifting dominance to North Pacific overturning, cannot be ruled out.

Giuseppe Cortese Paleoclimate Scientist

I was born in Reggio Calabria, a Greek colony founded in 600 BC at the very tip of Italy’s boot, just opposite Sicily: only 3 km away, quite practical if you can walk on water. After a lot of close brushes with Mesozoic rocks during my University years, I specialized in modern radiolarians, the plankton group that controlled the silica cycle in the ocean for a long time, until diatoms stole their show… I’ve worked on fjords, the Nordic Seas and their oceanography, morphometry of microfossils, temperature and sea ice reconstructions, silica cycle, polar paleoclimate, iron fertilization and all things Southern Ocean. I moved to New Zealand in January 2009, where I keep on studying the Southern Ocean, the SW Pacific and the Tasman Sea, particularly their recent past climate history. As fitting for my Greek heritage and geological background, I married my own rock (Meera) on a caldera rim, in Santorini. I have way too many hobbies to cleanse my brain, including riding motorbikes, cooking, playing keyboards, fishing/boating, travelling and experiencing the world, learning languages, and gaming.

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