Carbon dioxide pumped into the air
since the Industrial Revolution appears to have changed the way the coastal
ocean functions, according to a new analysis
published this week in Nature. A comprehensive review of research
on carbon cycling in rivers, estuaries and continental shelves suggests that
collectively this coastal zone now takes in more carbon dioxide than it
releases. The shift could impact global models of carbon’s flow through the
environment and future predictions related to climate change.
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“We need to better understand the
role of the coastal ocean in carbon dioxide exchange between the atmosphere and
the ocean,” said study co-author Wei-Jun Cai,
professor of oceanography in the University of Delaware’s School of Marine
Science and Policy within the College of
Earth, Ocean, and Environment. “That will give us a much better
capacity to predict future global carbon budgets and fluxes due to climate
change and other anthropogenic factors.”
Cai and other environmental
scientists have been examining the complex dynamics that move different forms
of carbon through coastal waters. Numerous variables, from rainfall to
temperature to plant photosynthesis, can influence how much carbon is present in
water at any given time.
“Carbon is not stationary,” Cai
said. “It flows and changes among its different forms.”
The multiple sources and processes
at play make coastal carbon challenging to study, however, and Cai said it has
traditionally been overlooked in global carbon budget calculations. The annual
estimate of how much anthropogenically-released carbon dioxide is trapped by
land, for example, has been determined by subtracting the amount taken up by
the ocean from the amount put into the air.
“If there is another reservoir —
the coastal ocean — that also takes up carbon dioxide, then that changes the
balance,” Cai said.
The coastal zone may be relatively
small compared to the open ocean, but the researchers point out that it
represents a disproportionately large amount of the carbon dioxide exchanged
between air and water.
That suggests that the coastal
ocean may have its own mechanism for holding carbon dioxide — something Cai
first suspected in 2005 on a cruise off the coast of Georgia. There he was
surprised to see that sea surface carbon dioxide levels were about the same as
10 years prior, even though there were significantly greater amounts of the
greenhouse gas in the atmosphere.
Conventional wisdom would hold that
sea surface carbon dioxide should rise in tandem with levels in the atmosphere,
as is the case in most of the ocean basin.
Read more at the University
of Delaware.
Foaming
beach image via Shutterstock.