Lower oceanic 𝛿<sup>13</sup>C during the Last Interglacial compared to the Holocene

Abstract

Abstract. The last time in Earth’s history when the high latitudes were warmer than during pre-industrial times was the last interglacial (LIG, 129–116 ka BP). Since the LIG is the most recent and best documented warm time period, it can provide insights into climate processes in a warmer world. However, some key features of the LIG are not well constrained, notably the oceanic circulation and the global carbon cycle. Here, we use a new database of LIG benthic 𝛿13C to investigate these two aspects. We find that the oceanic mean 𝛿13C was ~ 0.2 ‰ lower during the LIG (here defined as 125–120 ka BP) when compared to the mid-Holocene (7–4 ka BP). As the LIG was slightly warmer than the Holocene, it is possible that terrestrial carbon was lower, which would have led to both a lower oceanic 𝛿13C and atmospheric 𝛿13CO2 as observed in paleo-records. However, given the multi-millennial timescale, the lower oceanic 𝛿13C most likely reflects a long-term imbalance between weathering and burial of carbon. The 𝛿13C distribution in the Atlantic Ocean suggests no significant difference in the latitudinal and depth extent of North Atlantic Deep Water (NADW) between the LIG and the mid-Holocene. Furthermore, the data suggests that the multi-millennial mean NADW transport was similar between these two time periods.

A global mean sea surface temperature dataset for the Last Interglacial (129–116 ka) and contribution of thermal expansion to sea level change

“…To investigate the impact of drift on SST reconstructions, we therefore used contemporary ocean circulation as a first-order approximation for the LIG. Whilst we acknowledge that there was likely a weakening of the Atlantic Meridional Overturning Circulation (AMOC) during the early LIG (Shackleton et al, 2020;Turney et al, 2020a;Thomas et al, 2020;Jones et al, 2017), subsequent recovery after 127 ka appears to have established a global circulation comparable to present day as suggested by recent ocean δ 13 C modelling results across the mid-interglacial (Bengtson et al, 2020). We performed an experiment with virtual particles in an eddy-resolving ocean model (the Japanese Ocean model For the Earth Simulator, OFES) (Masumoto et al, 2004), which has a 1/10 • horizontal resolution and near-global coverage between 75 • S and 75 • N (van Sebille et al, 2012).…”

“…Utilizing the 3D velocity field of the model, we used the Parcels code (http://oceanparcels.org/, last access: 4 December 2020; Lange and van Sebille, 2017) to compute the trajectories of more than 170 000 virtual planktic particles that end up at each of the sites by tracking them backwards in time, first simulating the sinking to these sites at 200 m d −1 and subsequently the advection at 30 m depth for a lifespan of 30 d; coral SSTs were not corrected for drift. Given the lifespan of most organisms that have been used to generate a temperature signal (Jonkers et al, 2015;Bijma et al, 1990), we consider a 30 d drift provides a reasonable estimate of the drift distance. Previous work has demonstrated comparable uncertainties between different models (van Sebille et al, 2015), providing confidence in the use of the OFES for the purposes of this study.…”