Climate change clues from tiny marine algae -
ancient and modern
04 February 2013
Microscopic ocean algae called
coccolithophores are providing clues about the impact of climate
change both now and many millions of years ago. The study found
that their response to environmental change varies between species,
in terms of how quickly they grow.
Coccolithophores, a type of plankton, are not
only widespread in the modern ocean but they are also prolific in
the fossil record because their tiny calcium carbonate shells are
preserved on the seafloor after death – the vast chalk cliffs of
Dover, for example, are almost entirely made of fossilised
coccolithophores.
The fate of coccolithophores under changing
environmental conditions is of interest because of their important
role in the marine ecosystem and carbon cycle. Because of their
calcite shells, these organisms are potentially sensitive to
ocean acidification, which occurs when rising atmospheric carbon
dioxide (CO2) is absorbed by the ocean, increasing its
acidity.
There
are many different species of coccolithophore and in an article,
published in Nature Geoscience this week, the scientists
report that they responded in different ways to a rapid climate
warming event that occurred 56 million years ago, the
Palaeocene-Eocene Thermal Maximum (PETM).
The study, involving researchers from the University of
Southampton, the National Oceanography Centre and University
College London, found that the species Toweius pertusus
continued to reproduce relatively quickly despite rapidly changing
environmental conditions. This would have provided a competitive
advantage and is perhaps why closely-related modern-day species
considered to be its descendants, (such as Emiliana
huxleyi) still thrive today.
In contrast, the species Coccolithus
pelagicus grew more slowly during the period of greatest
warmth and this inability to maintain high growth rates may explain
why its descendants are less abundant and less widespread in the
modern ocean.
"This work provides us with a whole new way of
looking at living and fossil coccolithophores," said lead author Dr
Samantha Gibbs, Senior Research Fellow at University of Southampton
Ocean and Earth Science.
By comparing immaculately preserved and
complete fossil cells with modern coccolithophore cells, the
researchers could interpret how different species responded to the
sudden increase in environmental change at the PETM, when
atmospheric CO2 levels increased rapidly and the oceans
became more acidic.
"We use knowledge of how coccolithophores
build their calcite skeletons in the modern ocean to interpret how
climate change 56 million years ago affected the growth of these
microscopic plankton,” said co-author Dr Alex Poulton, a Research
Fellow at the National Oceanography Centre.
"This is a significant step forward and allows
us to view fossils as cells rather than dead 'rocks'. Through this
we can begin to understand the environmental controls on oceanic
calcification, as well as the potential effects of climate change
and ocean acidification."
The study was primarily supported by the UK
Ocean Acidification Research Programme, which is jointly funded by
the Natural Environment Research Council (NERC), the Department of
Environment, Food and Rural Affairs (Defra) and the Department of
Energy and Climate Change (DECC).