Lower oceanic &amp;lt;i&amp;gt;δ&amp;lt;/i&amp;gt;&amp;lt;sup&amp;gt;13&amp;lt;/sup&amp;gt;C during the last interglacial period compared to the Holocene

Lise Missiaen,Fortunat Joos,Shannon A. Bengtson,Laurie C. Menviel,Carlye D. Peterson,Katrin J. Meissner,Lorraine E. Lisiecki

doi:10.5194/cp-17-507-2021

Abstract

Abstract. The last time in Earth's history when high latitudes were warmer than during pre-industrial times was the last interglacial period (LIG, 129–116 ka BP). Since the LIG is the most recent and best documented interglacial, 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 Holocene (7–2 ka BP). A lower terrestrial carbon content at the LIG than during the Holocene could have led to both 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 Holocene. Furthermore, the data suggest that the multi-millennial mean NADW transport was similar between these two time periods.

Highlights

The most recent and well documented warm time period is the last interglacial period (LIG), which is roughly equivalent to Marine Isotope Stage (MIS) 5e (Past Interglacials Working Group of PAGES, 2016; Shackleton, 1969)
We present a new compilation of benthic δ13C covering the periods 130–118 and 8–2 ka BP
The lowest δ13C values are in the deep South Atlantic (> 4000 m) because the Antarctic Bottom Water (AABW) end member is much lower than its North Atlantic Deep Water (NADW) counterpart

Summary

Introduction

The most recent and well documented warm time period is the last interglacial period (LIG), which is roughly equivalent to Marine Isotope Stage (MIS) 5e (Past Interglacials Working Group of PAGES, 2016; Shackleton, 1969). The LIG was globally warmer than the pre-industrial period (PI, ∼ 1850–1900; IPCC, 2013; Shackleton et al, 2020), with PI estimated to be ∼ 0.4 ◦C cooler than the peak of the Holocene (10–5 ka BP) (Marcott et al, 2013). We seek to constrain the mean LIG ocean circulation and estimate the global oceanic mean δ13C. As greenhouse gas concentrations were comparable to the Holocene, the LIG was most likely relatively warm because of the high boreal summer insolation (Laskar et al, 2004). During the LIG, the atmospheric CO2 concentration was relatively stable around ∼ 280 ppm (Bereiter et al, 2015; Lüthi et al, 2008), while during the Holocene CO2 first decreased by about 8 ppm starting at 11.7 ka BP before increasing by ∼ 17 to 277 ppm at ∼ 2 ka BP (Fig. 1a) (Köhler et al, 2017). CH4 and N2O peaked at ∼ 700 and ∼ 267 ppb, respectively, during both the LIG and the Holocene

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