See
A CO2-Induced Increase in Subtropical North Atlantic Coccolithophore Abundance by Craig D. Idso of Cato.
"Coccolithophores are calcifying phytoplankton that comprise the
base of marine food webs all across the world ocean. They play an
important role in the cycling of carbon into the deep ocean and act as a
feedback to climate change. Anything that alters their function or
abundance, therefore, could have significant impacts on marine
ecosystems and global climate. Thus, it is no surprise that scientists
are interested in how coccolithophores will respond to future changes in
atmospheric CO2 and climate. And in this regard, Krumhardt et al.
(2016) say there has been “much speculation [that has] inspired
numerous laboratory and mesocosm experiments, but how they are currently
responding in situ is less well documented.” Working to provide just
such an in situ analysis, the team of four researchers thus set out to
analyze coccolithophore abundance in the subtropical North Atlantic over
the period 1990 to 2014.
To accomplish their objective, Krumhardt et al. used
coccolithophore pigment data collected at the Bermuda Atlantic
Time-series Study (BATS) site (located at 31.7°N, 64.2°W in the Sargasso
Sea) in conjunction with satellite estimates of surface chlorophyll and
particulate inorganic carbon as a proxy measure of coccolithophore
abundance. Results of their analysis revealed that “coccolithophore
populations in the North Atlantic subtropical gyre have been increasing
significantly over the past two decades. More specifically, they note
there was a 37 percent increase in euphotic zone-integrated (integrated
from 140 m depth) in coccolithophore pigment abundance at BATS and a
larger 68 percent increase in the upper 30 m of the water column (see
figure below). Such findings, in the words of the authors, add to those
of a growing number of studies showing that coccolithophores in the
North Atlantic “are increasing in abundance and are likely stimulated by
additional carbon from anthropogenic sources.”
The significance of Krumhardt et al.’s work is two-fold.
First, they note that the increased coccolithophore abundance they found
“is contrary to what numerous laboratory studies have predicted,
highlighting the importance of in situ observations,” as observations
clearly suggest that coccolithophores benefit from higher levels of atmospheric CO2. Second, for those who are concerned about the potential climatic impacts of CO2-induced
global warming, the increase in coccolithophore abundance is providing a
natural brake on increasing levels of atmospheric CO2, as more carbon is exported to the deep ocean with their increased abundance. What is more, Krumhardt et al.
note that in addition to transporting more carbon into the deep ocean,
coccolithophores produce dimethyl sulfide, a marine trace gas that
affects cloud formation and acts as a negative feedback to climate
warming (see Dimethyl Sulfide
for background on this topic). Thus, it is that the four researchers
conclude that overall increases in coccolithophore abundance will likely
induce “a multitude of effects on marine ecosystems in the North
Atlantic, as well as global carbon cycling and climate,” all of which,
we note, appear to be for the better.
Figure 1. Chlorophyll a (Chlahapto)
from haptophytes (planktonic group to which coccolithophores belong)
measured at BATS integrated from 30m (panel a) and 140m depth (panel b).
Adapted from Krumhardt et al. (2016).
Reference
Krumhardt, K.M., Lovenduski, N.S., Freeman, N.M. and Bates, N.R.
2016. Apparent increase in coccolithophore abundance in the subtropical
North Atlantic from 1990 to 2014. Biogeosciences 13: 1163-1177."
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