Atlantic Meridional Overturning Circulation and δ13C Variability During the Last Interglacial

A Kessler,U S Ninnemann,E V Galaasen,D M Roche,N Bouttes,J Tjiputra

doi:10.1029/2019pa003818

Abstract

AbstractThe Atlantic Meridional Overturning Circulation (AMOC) is thought to be relatively vigorous and stable during Interglacial periods on multimillennial (equilibrium) timescales. However, recent proxy (δ13C benthic) reconstructions suggest that higher frequency variability in deep water circulation may have been common during some interglacial periods, including the Last Interglacial (LIG, 130–115 ka). The origin of these isotope variations and their implications for past AMOC remain poorly understood. Using iLOVECLIM, an Earth system model of intermediate complexity (EMIC) allowing the computation of and direct comparison to proxy reconstructions, we perform a transient experiment of the LIG (125–115 ka) forced only by boundary conditions of greenhouse gases and orbital forcings. The model simulates large centennial‐scale variations in the interior of the North Atlantic similar in timescale and amplitude to changes resolved by high‐resolution reconstructions from the LIG. In the model, these variations are caused by changes in the relative influence of North Atlantic Deep Water (NADW) and southern source water (SSW) and are closely linked to large (∼50%) changes in AMOC strength provoked by saline input and associated deep convection areas south of Greenland. We identify regions within the subpolar North Atlantic with different sensitivity and response to changes in preformed of NADW and to changes in NADW versus SSW influence, which is useful for proxy record interpretation. This could explain the relatively large δ13C gradient (∼0.4%0) observed at ∼3 km water depth in the subpolar North Atlantic at the inception of the last glacial.

Highlights

Variation in the Atlantic Meridional Overturning Circulation (AMOC) is one of the major driving force controlling climate changes as it affects the distribution of heat and carbon in the ocean, influencing regional climate and atmospheric CO2 concentrations (Ganachaud & Wunsch, 2000)
In order to compare and contrast our simulation with data records, we focus our discussion to the locations of the two high-resolution proxy records MD03-2664 (Galaasen et al, 2014) and Integrated Ocean Drilling Program (IODP) Site U1304 (Hodell et al, 2009), which depict centennial-scale δ13C perturbations during the Last Interglacial (LIG)
We simulate a transient experiment from the last interglacial period (125–115 ka) using an Earth system model of intermediate complexity (EMIC) allowing the computation of δ13CDIC, an oceanic tracer for the ocean circulation, and biogeochemical processes used in paleoclimate reconstruction

Summary

Introduction

Variation in the Atlantic Meridional Overturning Circulation (AMOC) is one of the major driving force controlling climate changes as it affects the distribution of heat and carbon in the ocean, influencing regional climate and atmospheric CO2 concentrations (Ganachaud & Wunsch, 2000). This has made AMOC changes a key concern in future projections, with models suggesting it will likely decrease in response to buoyancy gain in the deep-water formation regions but the extent to which remains highly uncertain (Bakker et al, 2016; Stocker et al, 2014). Reconstructions of millennial-timescale variability indicate that vigorous North Atlantic Deep Water (NADW) production persisted on millennial timescales (Adkins et al, 1997; Oppo et al, 1997), simulztaneously as southern source waters (SSWs) expanded

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