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<article language="en">
	<journal>
		<journal_title>Climate of the Past Discussions</journal_title>
		<journal_url>www.clim-past-discuss.net</journal_url>
		<issn>1814-9340</issn>
		<eissn>1814-9359</eissn>
		<volume_number>6</volume_number>
		<issue_number>2</issue_number>
		<publication_year>2010</publication_year>
	</journal>
	<doi>10.5194/cpd-6-257-2010</doi>
	<article_url>http://www.clim-past-discuss.net/6/257/2010/</article_url>
	<abstract_html>http://www.clim-past-discuss.net/6/257/2010/cpd-6-257-2010.html</abstract_html>
	<fulltext_pdf>http://www.clim-past-discuss.net/6/257/2010/cpd-6-257-2010.pdf</fulltext_pdf>
	<start_page>257</start_page>
	<end_page>294</end_page>
	<publication_date>2010-03-04</publication_date>
	<article_title content_type="html">Perturbing phytoplankton: a tale of isotopic fractionation in two coccolithophore species</article_title>
	<authors>
		<author numeration="1" affiliations="1,4">
			<name>R. E. M. Rickaby</name>
			<email>rosr@earth.ox.ac.uk</email>
		</author>
		<author numeration="2" affiliations="2,3">
			<name>J. Henderiks</name>
		</author>
		<author numeration="3" affiliations="1">
			<name>J. N. Young</name>
		</author>
	</authors>
	<affiliations>
		<affiliation numeration="1" content_type="html">Department of Earth Sciences, Oxford University, Parks Road, Oxford, OX1 3PR, UK</affiliation>
		<affiliation numeration="2" content_type="html">Department of Geology and Geochemistry, Stockholm University, Sweden</affiliation>
		<affiliation numeration="3" content_type="html">now at: Department of Earth Sciences, Paleobiology Program, Uppsala University, Villavägen 16, 75 236 Uppsala, Sweden</affiliation>
		<affiliation numeration="4" content_type="html">Invited contribution by R. E. M. Rickaby, one of the EGU  Outstanding Young Scientist Award winners 2008.</affiliation>
	</affiliations>
	<abstract content_type="html">No two species of coccolithophore appear to respond to perturbations
of carbonate chemistry in the same way. Here, we show that the degree of
malformation, growth rate and stable isotopic composition of organic matter
and carbonate produced by two contrasting species of coccolithophore
(&lt;i&gt;Gephyrocapsa oceanica&lt;/i&gt; and &lt;i&gt;Coccolithus pelagicus&lt;/i&gt; ssp. &lt;i&gt;braarudii&lt;/i&gt;) are
indicative of differences between their photosynthetic and calcification
response to changing dissolved inorganic carbon (DIC) levels (ranging from
~1100 to ~7800 μmol kg&lt;sup&gt;&amp;minus;1&lt;/sup&gt;) at constant pH
(8.13&amp;plusmn;0.02). &lt;i&gt;G. oceanica&lt;/i&gt; thrived under all
conditions of DIC, showing evidence of increased growth rates at higher DIC,
but &lt;i&gt;C. braarudii&lt;/i&gt; was detrimentally affected at
high DIC showing signs of malformation, and decreased growth rates. The
carbon isotopic fractionation into organic matter and the coccoliths
suggests that &lt;i&gt;C. braarudii&lt;/i&gt; utilises a common
internal pool of carbon for calcification and photosynthesis but
&lt;i&gt;G. oceanica&lt;/i&gt; relies on independent supplies for
each process. All coccolithophores appear to utilize bicarbonate as their
ultimate source of carbon for calcification resulting in the release of a
proton. But, we suggest that this proton can be harnessed to enhance the
supply of aqueous dissolved carbon dioxide (CO&lt;sub&gt;2&lt;/sub&gt;(aq)) for
photosynthesis either from a large internal bicarbonate ion
(HCO&lt;sub&gt;3&lt;/sub&gt;&lt;sup&gt;-&lt;/sup&gt;) pool which acts as a pH buffer
(&lt;i&gt;C. braarudii&lt;/i&gt;), or pumped externally to aid the
diffusive supply of CO&lt;sub&gt;2&lt;/sub&gt; across the membrane from the abundant
HCO&lt;sub&gt;3&lt;/sub&gt;&lt;sup&gt;-&lt;/sup&gt; (&lt;i&gt;G. oceanica&lt;/i&gt;), likely
mediated by an internal and external carbonic anhydrase, respectively. Our
simplified hypothetical spectrum of physiologies may provide a context to
understand different species response to changing pH and DIC, the
species-specific &lt;i&gt;ε&lt;/i&gt;&lt;sub&gt;&lt;i&gt;p&lt;/i&gt;&lt;/sub&gt; and calcite &quot;vital effects&quot;, as well as accounting for geological trends in coccolithophore
cell size.</abstract>
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</article>

