Seki et al . ( 2010 ) published new pCO 2 estimates from the boron isotope and alkenone proxies from a site not included in the Pagani et al . ( 2010 ) study , but the same time range . The top panel shows previous pCO 2 estimates for the period ( colour bands are selected sites from Pagani et al . 2010 ; black diamonds are bulk organic � 13 C estimates from Raymo et al ., 1996 ; red circles are stomatal estimates from Kurschner et al ., 1996 ; and blue diamonds are the old boron isotope data from Pearson and Palmer , 2000 ; the green line at the left is the ice core air bubble data from Luthi et al ., 2008 ). Panel b is new boron isotope estimates from the species G . ruber with different assumptions about alkalinity ( the different symbols ) and panel c is the alkenone data both uncorrected ( red band ) and corrected ( between the red squares ) for changing cell size effect . It can be seen from this that the Pliocene boron estimates are mostly in the 300-350 ppm range but just exceed 400 ppm around 3 Ma given certain assumptions . The alkenone estimates exceed 400 ppm for a few values around 5 Ma but only if the size correction is taken into account .
vii . Bartoli et al . ( 2011 )
Fig . 7 . Boron isotope , δ 18 O and pCO 2 reconstruction by Bartoli et al . ( 2011 ). Red line added .
This record is from boron isotopes in the planktonic foraminifer G . sacculifer . The estimates are shown on the bottom panel together with some previous ( mostly alkenone ) records for comparison as