Blame it on the rain

Daniela Turk and co-authors have discovered that rain turns vast expanses of ocean into carbon sinks. (Danny Abriel Photo)

Rain falls in the Western Equatorial Pacific Ocean. Lots of it.

As part of the Western Pacific Ocean region called the warm pool, and home to that enfant terrible of weather, El Niño, this is an important stretch of water for climate change researchers.

Most scientists had seen this ocean as a source of CO2 emissions, but Dalhousie Oceanography Research Scientist Daniela Turk and her co-authors just discovered something quite amazing: the rain here turns vast expanses of ocean into carbon sinks capable of absorbing CO2.

Their discovery could affect how we calculate greenhouse gas levels in all tropical waters.

“It’s just, rain is so common and not to look at it, I mean, we count rain all the time,” Dr. Turk says incredulously. Of course, she is quick to point out that scientists have looked at rain and CO2 emissions from the ocean before, but no one had ever noted its ability to change bodies of water from sources to sinks.

“Rain does different things,” says Dr. Turk, “Rain affects the physics and it also affects the chemistry. Maybe some people have looked at physics separately, or chemistry separately, but nobody has included all the factors. They are all important together.”

Tank

Two years ago, Dr. Turk began her research with scientists at the Lamont-Doherty Earth Observatory in New York, where she is an adjunct associate research scientist. They used a large tank of water to simulate the effects of wind and rain on CO2 fluxes.

“We kind of thought about how would we apply this to the real world,” she says. Dr. Turk looked for a place to use as model to test their discoveries in the tank and thought of the Western Equatorial Pacific where she worked on her Phd.

“There’s a lot of rain there and good rain data available from Tropical Atmosphere Ocean buoy. The other important thing is that the winds are pretty low,” she says.

On the North Atlantic, for instance, this would likely have a smaller effect. Strong winds would dominate over the rain’s effects on CO2 fluxes. 

Rain water must be able to sit on the surface of the ocean like a thin film of fresh water for the chemical change to take place. Dr Turk calls this rainwater a lens. Lenses are big, approximately 200 square kilometres. As the fresh water lens slowly dilutes into the salt water over the course of several days, it lowers the CO2 content in the surface water, creating the proper atmospheric environment for a carbon sink to exist.

It’s an important discovery, with all sorts of scientific repercussions. Dr. Turk sees many researchers proposing study grants on this heels of this paper.

'Taste of what's coming'

“This is just a taste of what’s coming,” she says, smiling.

Future research directions for her and her colleagues involves examining how long sink conditions last and how to apply this to global greenhouse gas level.

“What is difficult to do is to go out and do this in the real world,” she says. Taking measurements outside the lab is both expensive and difficult, but it is an adventure.

“You have to go out on a small ship and catch rain. It’s not logistically easy to do. On an expedition, you think you will catch an event like wind or rain, and then it doesn’t happen. Or something else new happens.”

Dr. Daniela Turk’s paper is currently in press and will be published in the journal Geophysical Research Letters. 

LINK: Geophysical Research Letters