Tiny ocean zooplankton could help tell if climate change targets are met

By Liz Gwynne for the ABC

Scientists have found some of the smallest animals in the ocean are having a big impact in the fight against climate change.

Microscopic phytoplankton are estimated to capture up to 20 billion tonnes of CO2 every year.

But it's what happens next that is important to removing CO2 from the atmosphere, according to zooplankton ecologist Svenja Halfter.

"Phytoplankton take up carbon. Because they do photosynthesis, zooplankton like to eat these micro algae and then store the carbon in their bodies and this is how it goes up the food chain," Dr Halfter explained.

"When these animals die, they take the carbon to the deep sea where it stays for a long time."

In fact, scientists believe the carbon can stay at the bottom of the ocean for hundreds, even thousands of years.

Current research - jointly conducted by the Institute for Marine and Antarctic Studies (IMAS) and CSIRO - has found zooplankton, which are not well represented in current CO2 capture models, play a much bigger role than previously thought.

However, their research - which is part of long-term ocean monitoring by the Integrated Marine Observing System (IMOS) - is also finding that the Southern Ocean is becoming warmer, fresher, less oxygenated and more acidic and this could, potentially, impact its ability to absorb atmospheric CO2.

CSIRO Research Scientist Elizabeth Shadwick explained more about the team's findings.

"We have been emitting CO2 into the atmosphere through the burning of fossil fuels, cement production, deforestation and the ocean is doing us a great service by absorbing about a third of those emissions," Dr Shadwick said.

"Understanding and quantifying the amount of carbon that is taken up by the ocean is really needed for us to make accurate predictions of climate change on decadal and century timescales.

"[It's] critical for us to observe and quantify the role the ocean is playing in taking CO2 out of the atmosphere and storing it in the deep sea.

"Australia has committed to reducing emissions, and we will see that in the atmosphere, but we have to be able to verify that what we are doing is actually making a difference."

How do they monitor the Southern Ocean?

Every 12 months, scientists on the CSIRO research vessel RV Investigator travel 36 hours south-west of Tasmania into the sub-Antarctic zone, to release sediment traps, attaching each to a deep-water mooring at a depth of 1000, 2000 and nearly 4000 metres.

On each sediment trap there are 21 cups, and these rotate under a big funnel to collect small particles that sink from ocean's surface, as IMAS' Cathryn Wynn-Edwards explained.

"We pick up a mooring that has been deployed a year earlier and put a new one in its place so it can continue to collect data," Dr Wynn-Edwards said.

"Some assumptions go into it when it comes to climate models, but we measure it directly and that's the value of this work.

"There's a lot of processes that happen in between, before this material that I analyse ends up at great depth, so it's a small fraction and a lot has happened to it before it ends up being organic material."

Continuous ocean monitoring has been in place for the past 20 years and scientists believe it will help validate the effect of the global CO2 emission reductions being made.

"Having observing platforms in place in the ocean where 30 per cent of the CO2 is going is really critical, not just for the doom and gloom of what's going to happen to the climate, but to be able to say: 'Look, we reduced our emissions. We met our targets'," Dr Shadwick said.

"Without a doubt, these observations are essential to increase our understanding about how climate variability is affecting us now and how it will likely affect us into the future.

"We need sustained observations over many years to understand what are natural variations and what are our own human imprints on those processes."

- ABC