&#948;11B and B/Ca ontogenetic variability within Globigerina bulloides
Authors: Buisson Matthieu , Louvat Pascale , Karancz Szabina , Tian Ruchen , Raitzsch Markus , Bijma Jelle , Rollion-Bard Claire 
Published: March 2020

&lt;p&gt;Understanding the atmosphere-continent-ocean carbon cycle and its associated oceanic carbon system is one of the keystones to face the Anthropocene&amp;#8217;s climate change. Since the 1990s the isotopic ratio of boron (&amp;#948;&lt;sup&gt;11&lt;/sup&gt;B) in calcitic shells of planktonic foraminifera has proven to be a powerful geochemical proxy to determine the oceanic paleo-pH and its link to atmospheric CO&lt;sub&gt;2&lt;/sub&gt; level over geological times&lt;sup&gt;1&lt;/sup&gt;, whereas the ratio B/Ca as proxy of the seawater carbonate chemistry is still questionable&lt;sup&gt;2,3&lt;/sup&gt;.&lt;/p&gt;&lt;p&gt;However, the use of planktonic foraminifera in paleoclimatic reconstructions requires calibrations of the pH &amp;#8211; &amp;#948;&lt;sup&gt;11&lt;/sup&gt;B relationships to correct what is known as &amp;#171;&amp;#160;vital effect&amp;#160;&amp;#187;&lt;sup&gt;4&lt;/sup&gt;: each species controls differently its calcification process and consequently slightly modifies the seawater chemistry during biomineralization&lt;sup&gt;5,6&lt;/sup&gt;. Moreover, shell size effect on &amp;#948;&lt;sup&gt;11&lt;/sup&gt;B has been reported for some symbiont-bearing species due to photosynthetic increase of pH&lt;sup&gt;7,8&lt;/sup&gt;.&lt;/p&gt;&lt;p&gt;Calibrations for the symbiont-barren &lt;em&gt;Globigerina bulloides&lt;/em&gt; have been already determined&lt;sup&gt;9,10 &lt;/sup&gt;but sparse data have been reported so far for the test size effect on &amp;#948;&lt;sup&gt;11&lt;/sup&gt;B &lt;sup&gt;11&lt;/sup&gt;.&lt;/p&gt;&lt;p&gt;Here we measured the &amp;#948;&lt;sup&gt;11&lt;/sup&gt;B of three different fractions (250-315, 315-400 and &gt;400 &amp;#956;m) of &lt;em&gt;G. bulloides&lt;/em&gt; sampled along the coretop PS97-122 from the Chilean margin (54.10&amp;#176;S, 74.91&amp;#176;W), by using a new protocol developed at IPGP and dedicated to small samples which couple a microsublimation technique and a micro-direct injection device (&amp;#956;-dDIHEN&lt;sup&gt;12&lt;/sup&gt;). Our preliminary results show significantly higher &amp;#948;&lt;sup&gt;11&lt;/sup&gt;B values for the large fractions compared to the small ones, as found for symbiont-bearing planktonic species such as &lt;em&gt;Globigerinoides sacculifer&lt;/em&gt;&lt;sup&gt;7&lt;/sup&gt; and &lt;em&gt;Globigerinoides ruber&lt;/em&gt;&lt;sup&gt;8&lt;/sup&gt;.&lt;/p&gt;&lt;p&gt;&amp;#160;&lt;/p&gt;&lt;ul&gt;&lt;li&gt;(1) Pearson &amp; Palmer, 2000, &lt;em&gt;Nature&lt;/em&gt; 406, 695-699&lt;/li&gt;
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