Tropical vegetation response to Heinrich Event 1 as simulated with the UVic ESCM and CCSM3

D Handiani,X Zhang,M Prange,A Paul,U Merkel,L Dupont

doi:10.5194/cp-9-1683-2013

Abstract

Abstract. We investigated changes in tropical climate and vegetation cover associated with abrupt climate change during Heinrich Event 1 (HE1, ca. 17.5 ka BP) using two different global climate models: the University of Victoria Earth System-Climate Model (UVic ESCM) and the Community Climate System Model version 3 (CCSM3). Tropical South American and African pollen records suggest that the cooling of the North Atlantic Ocean during HE1 influenced the tropics through a southward shift of the rain belt. In this study, we simulated the HE1 by applying a freshwater perturbation to the North Atlantic Ocean. The resulting slowdown of the Atlantic Meridional Overturning Circulation was followed by a temperature seesaw between the Northern and Southern Hemispheres, as well as a southward shift of the tropical rain belt. The shift and the response pattern of the tropical vegetation around the Atlantic Ocean were more pronounced in the CCSM3 than in the UVic ESCM simulation. For tropical South America, opposite changes in tree and grass cover were modeled around 10° S in the CCSM3 but not in the UVic ESCM. In tropical Africa, the grass cover increased and the tree cover decreased around 15° N in the UVic ESCM and around 10° N in the CCSM3. In the CCSM3 model, the tree and grass cover in tropical Southeast Asia responded to the abrupt climate change during the HE1, which could not be found in the UVic ESCM. The biome distributions derived from both models corroborate findings from pollen records in southwestern and equatorial western Africa as well as northeastern Brazil.

Highlights

Hydrology and Earth SystemHeinrich events in general are aSssocciieatnedcweitsh layers of icerafted debris (IRD) in the sediments of the North AtlanticOcean dated between 70 ka BP and 14 ka BP (Heinrich, 1988; Broecker, 1994).The Heinrich event 1 O(HEc1e, acan. 1S7.c5 ikea nBPc)eis the most recent of these distinctive cold periods in the North Atlantic region
If the percentage is over 50 %, the plant functional types (PFTs) potential is set equal to the dominant PFT
If it is less than 50 %, the grid cell is designated as mixed trees if it is dominated by tree PFTs, as mixed vegetation if non-trees PFTs are dominant, as open vegetation if all PFTs are between 20 % and 50 % and as desert if all PFTs together are less than 20 % (Crucifix et al, 2005)

Summary

Introduction

Heinrich events in general are aSssocciieatnedcweitsh layers of icerafted debris (IRD) in the sediments of the North Atlantic. Paleoceanographic evidence suggests a connection between the abrupt climate changes during these events and the variability of the North Atlantic Deep Water (NADW) formation and the Atlantic Meridional Overturning Circulation (AMOC, Sarnthein et al, 199S4;oMlicdMaEnuasretthal., 2004). A change in the AMOC during the HE1 is invoked to explain an unusual hydrological cycle in the tropics and a southward shift of the Intertropical Convergence. Since vegetation and climate are tightly coupled, tropical climate changesTinhfleuenCcerythoestrpophicearlevegetation patterns. This is demonstrated by pollen proxy records, which exhibit changes in the tropics simultaneous with the North

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Conclusion