Southern deep ocean carbon chemistry changes along the mid-Pleistocene transition evidenced an increase in carbon storage starting from stage 22

The Mid-Pleistocene Transition (MPT), from ~ 1.2 to 0.6 million years is characterized by glacial interglacial cycles periodicity shifting from 41 kyr to ~100 kyr with larger amplitude variations (Pisias et Moore, 81; Imbrie et al., 93). This transition cannot be explained as a direct consequence of the astronomical forcing. Among the different mechanisms that has been suggested to explained this change in periodicity, a number involve a long-term decrease in atmospheric carbon, linked to greater carbon sequestration in the ocean. Various processes may have caused this carbon sequestration in the ocean (Paillard, 207; Willeit et al., 2019), including ocean temperature decrease, increased productivity in the Southern Ocean (Martinez-Garcia et al., 2011), and changes in deep ocean circulation (Raymo et al., 1997, Peña et Goldstein, 2012, Hasenfratz et al., 2019). For some processes, reconstructions indicate  different timings, with mean surface temperature decrease occurring before 1.2 Myr (Snyder 2016) while ocean circulation changes started after 0.95 Myr (Raymo et al., 1997, Peña et Goldstein, 2012, Hasenfratz et al., 2019). Here we present the evolution of CO₃^2- concentration along the MPT, in the Pacific sector of the Southern Ocean, that is linked to carbon accumulation. This record has been reconstructed from benthic foraminifera B/Ca ratio (Yu and Elderfield, 2007) from 1.25 to 0.45 Myr. While the two records from the Atlantic Ocean, North (Sosdian et al. 2018) and South (Farmer et al., 2019), indicate a reduction in CO₃^2-, thus an increase in carbon accumulation, starting with the deep Atlantic Ocean circulation change at ~0.95 Myr (Raymo et al., 1997, Peña et Goldstein, 2012), these new South Pacific data indicate a delayed decrease by ~100kyr in agreement with a Pacific tropical record (Qin et al., 2022) obtained from changes in normalized weights of planktic foraminifera. This different timing, even within the Southern Ocean, questions the role of the balance between the dissolution/accumulation of carbonates between the Atlantic and Pacific basins.

 

Hasenfratz et al.,2019, Science, 363, 1080–1084.

Imbrie J. et al., 1993, Paleoceanography, https://doi.org/10.1029/93PA02751

Paillard, D., 2017, Clim. Past, 13, 1259-1267.

Peña L.D & Goldstein S.L., 2014, Science 345 (6194):318-22.

Pisias, N.G. and T.C. Moore, 1981, EPSL, 52, 450-458, https://doi.org/10.1016/0012-821X(81)90197-7

Qin, B. et al. (2022). Geophysical Research Letters, 49, e2021GL097121. https://doi. org/10.1029/2021GL097121

Raymo, M.E. et al., 1997, Paleoceanography 12, 546–559. 15. 16.

Snyder C.W., 2016, Nature, 538,226-228

Sosdian, S. et al., (2018), Paleoceanography and Paleoclimatology, 33, 546–562., https://doi.org/10.1029/2017PA003312

Willeit et al., 2019, Sci. Adv. 5 : eaav7337.

Yu, J., & Elderfield, H. (2007), Earth and Planetary Science Letters, 258(1–2), 73–86. https://doi.org/10.1016/j.epsl.2007.03.025