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Ocean carbon sinks feeling the heat

By Matthew Knight for CNN
Evidence from the North Atlantic suggests some areas of the ocean are starting to soak up less carbon dioxide, say scientists
Evidence from the North Atlantic suggests some areas of the ocean are starting to soak up less carbon dioxide, say scientists
  • New study says warming climate is harming North Atlantic Ocean's ability to store CO2
  • Study examines nearly three decades of data from three distinct biological areas
  • Results enable clearer identification of underlying trends, say scientists
  • More data required on other oceans to determine if pattern is repeated worldwide

(CNN) -- The ability of oceans to soak up atmospheric carbon dioxide is being hampered by climate change, according to a new scientific study.

A fresh analysis of existing observational data taken from locations across the North Atlantic Ocean recorded over a period of almost three decades (1981-2009) has revealed that global warming is having a negative impact on one of nature's most important carbon sinks.

"Warming in the past four to five years has started to reduce the amount of carbon that large areas of the (North Atlantic) Ocean is picking up," said Galen McKinley, lead author and assistant professor of atmospheric and oceanic sciences at the University of Wisconsin-Madison.

According to the National Oceanic and Atmospheric Administration global ocean temperatures have risen by 0.74 degrees Celsius since the late 19th century.

The new study identified underlying trends in surface CO2 by examining data across three distinct biogeographic regions ("biomes") ranging from the subpolar gyre (circular ocean currents) in the north to two subtropical gyres further south.

Combined, these regions make up 87% of the total area of the North Atlantic Ocean, according to the paper published in the journal Nature Geoscience.

Data was collected from hundreds of scientific ships and container vessels equipped with special instrumentation.

Increases in atmospheric carbon dioxide have largely been matched by corresponding increases in dissolved CO2 in the seawater in the past three decades, according to the study.

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But there are also huge expanses of ocean where rising temperatures are slowing carbon absorption -- warmer water cannot hold as much CO2, say scientists.

"We are already seeing this in the North Atlantic subtropical gyre, and this is some of the first evidence for climate damping the ocean's ability to take up carbon from the atmosphere," McKinley said.

Marine life facing mass extinction

Previous scientific studies in this area have produced conflicting results caused by uncertainty over natural variability -- like North Atlantic oscillation and El Nino -- and its affects on CO2 absorption.

But McKinley says the breadth of this latest study cuts through this variability -- which often masks longer-term patterns of change -- enabling clearer identification of underlying trends in surface CO2 throughout the North Atlantic.

Climate warming would be a lot faster if not for these sinks, she says. Oceans worldwide currently soak up around a quarter of atmospheric carbon, while land-based sinks account for a similar percentage.

But manmade emissions continue to rise reaching record levels in 2010, according to the International Energy Agency.

Any changes in the efficiency of ocean sinks will have important implications for the planet and for policy-makers trying to tackle carbon emissions effectively, McKinley says.

"We need to continue to monitor this and see how things proceed because if humans are going to achieve some sort of stabilization of carbon in the atmosphere we really need to quantify what those sinks are going to be and how they are going to change with time," she said.