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Two of Earth’s Ocean Carbon Sinks Shrinking, Studies Show

New research reveals that mangroves and kelp forests, crucial for carbon storage and cycling, are under threat from development and climate change

By Katherine Bagley

Apr 7, 2011
Kelp forest

It is well known that deforestation is shrinking the carbon storage capacity of tropical forests, one of the world's great land-based carbon sinks. Now a pair of studies confirms that two key marine CO2 stores — mangroves and kelp forests — are also in peril from human activity.

The findings, scientists say, highlight the need to protect carbon- and biodiversity-rich ocean forests from development and global warming by including them in existing forest-conservation programs.

Mangrove forests — trees and shrubs that thrive in brackish waters — have declined 30 to 50 percent in the past 50 years, according to one out this week in the journal Nature Geoscience.

The seaside carbon sinks are generally being razed for coastal development such as houses, roads, railways, as well as to turn wetlands into farmland and expand fishing. Towns built on coasts nearby can also leach toxins into the forests and poison sediment, harming life-giving root systems.

Mangroves suck up carbon through the atmosphere during photosynthesis and store it in their leaves, branches and above-ground roots. Because their thick, mucky soils have fairly low oxygen levels, the natural decay of the biomass is slow, resulting in a steady but heavy buildup of carbon over time.

For the first time, scientists have crunched the numbers on the carbon sequestered in these trees, dead organic matter and soil in 25 sites across Micronesia, Indonesia and Bangladesh — which house a large portion of Earth's mangroves — and gleaned insight into salty forests worldwide.

The international team, led by Daniel Donato, an ecologist with the in Hilo, Hawaii, said soils account for a massive 45 to 98 percent of carbon storage in mangrove ecosystems. Because of this, "coastal mangrove forests store more carbon than almost any other forest on Earth," the research station .

Earlier by Steven Bouillon, a mangrove ecologist with Catholic University of Leuven in Belgium, estimated that the world's mangroves take in more than 200 million metric tons of carbon dioxide annually, with some of it being stored and the rest getting cycled through to nourish other ecosystems.

Uproot the trees and degrade the soil, and the carbon gets spewed back into the atmosphere, the new study affirms. In total, mangrove destruction releases as many as 120 million metric tons of carbon dioxide annually, it finds — an amount nearly equivalent to the yearly emissions of Norway, Finland and Sweden combined.

The emissions footprint of clearing mangroves is disproportionate to their presence. While mangroves encompass only 0.7 percent of the world's tropical rainforests, their discharge of stored carbon accounts for roughly 10 percent of all deforestation-related emissions, Donato said in an interview. In total, forest loss is responsible for nearly a fifth of the greenhouse gases blamed for climate change.

Kelp Forests At Risk from Climate-Related Storms

Kelp plants, known as the "underwater forest," are another vital ecosystem at risk, though for different reasons, according to published online on Mar. 24 in the journal Global Change Biology.  

The large beds of seaweed, which can grow up to 50 feet high, are scattered across the globe in temperate and polar regions, including the entire west coast of North America. They are widely considered one of the most productive ecosystems on Earth because of a high rate of carbon cycling, the process by which carbon travels through the ecological community. 

In giant kelp plants, most cycling of carbon works this way: the seaweed takes in carbon through photosynthesis; marine life such as sea urchins graze on the kelp to provide them life, inhaling the carbon. It then moves through the food web relatively quickly as one organism consumes another.

Sequestered Carbon

During the Jurassic (and other early periods) atmospheric CO2 content many times higher than today's supported a vast proliferation of life. Greenhouse growers understand the benefits of elevated CO2 as well - that's why they pump it into their greenhouses. Recent experiments with elevated CO2 show that food crops respond well and increase productivity.

It seems the real problem today is that too much CO2 has been sequestered in sea beds and coal seams so that life cannot access it. With a mere 0.038% CO2 remaining in our atmosphere, life is starved for it.

Why are we afraid of releasing some of the CO2 that was sequestered away? The benefits of elevating CO2 are rather obvious.

Life loves a greenhouse, not a glacier.

Think About It

Where do human beings fit

Where do human beings fit into the Jurassic? Think about it again.

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