Fig. 3: Temperature biases due to grain boundary diffusion in fossil benthic and planktonic foraminifera tests.
From: Rapid grain boundary diffusion in foraminifera tests biases paleotemperature records
The left y-axis shows the temperature bias induced by grain boundary diffusion on existing seawater paleotemperature reconstructions from bulk test oxygen isotopic compositions. Positive/negative values indicate that grain boundary diffusion has caused existing paleotemperature estimates to be too high/low and should therefore be subtracted by the indicated individual temperature correction. The parameters used to calculate these values are as follows: grain boundary fraction (FGB = 2.4%), seafloor temperature = 2.67 °C63, seawater δ18OVSMOW = 0‰, and a geothermal gradient = 0.053 °C/m. In boreholes with known geothermal gradients and seafloor temperatures, the known parameters were used in the calculations. Temperatures were calculated by multiplying the foraminifera δ18OLattice−δ18OBulk, shown on the right y-axis, by 4.81 °C/‰. The steep increase in benthic temperature biases at around 5 Mya is from foraminifera from Site 677, where the geothermal gradient is 0.208 °C/m63. Benthic foraminifera are from (1) Zachos et al. (2008)32, (2) Borrelli and Katz (2015)33, (3) Cramer et al. (2009)34, and (4) Huber et al. (2018)35. Planktonic foraminifera are from (4) Huber et al. (2018)35, (5) O’Brien et al. (2017)36, and (6) O’Connor et al. (2019)37.
