Modelled glacier equilibrium line altitudes during the mid-Holocene in the southern mid-latitudes

C Bravo,M Rojas,B M Anderson,P I Moreno,E Sagredo,A N Mackintosh

doi:10.5194/cp-11-1575-2015

Abstract

Abstract. Glacier behaviour during the mid-Holocene (MH, 6000 years BP) in the Southern Hemisphere provides observational data to constrain our understanding of the origin and propagation of palaeoclimate signals. In this study we examine the climatic forcing of glacier response in the MH by evaluating modelled glacier equilibrium line altitudes (ELAs) and climatic conditions during the MH compared with pre-industrial time (PI, year 1750). We focus on the middle latitudes of the Southern Hemisphere, specifically Patagonia and the South Island of New Zealand. Climate conditions for the MH were obtained from PMIP2 model simulations, which in turn were used to force a simple glacier mass balance model to simulate changes in ELA. In Patagonia, the models simulate colder conditions during the MH in austral summer (−0.2 °C), autumn (−0.5 °C), and winter (−0.4), and warmer temperatures (0.2 °C) during spring. In the Southern Alps the models show colder MH conditions in autumn (−0.7 °C) and winter (−0.4 °C), warmer conditions in spring (0.3 °C), and no significant change in summer temperature. Precipitation does not show significant changes but exhibits a seasonal shift, with less precipitation from April to September and more precipitation from October to April during the MH in both regions. The mass balance model simulates a climatic ELA that is 15–33 m lower during the MH compared with PI conditions. We suggest that the main causes of this difference are driven mainly by colder temperatures associated with the MH simulation. Differences in temperature have a dual effect on glacier mass balance: (i) less energy is available for ablation during summer and early autumn and (ii) lower temperatures cause more precipitation to fall as snow rather than rain in late autumn and winter, resulting in more accumulation and higher surface albedo. For these reasons, we postulate that the modelled ELA changes, although small, may help to explain larger glacier extents observed by 6000 years BP in South America and New Zealand.

Highlights

Deciphering the climate signals and glacial history of the mid-latitudes of the Southern Hemisphere (Fig. 1) during the Holocene is key to unravelling the mechanism of climate change that occurred during this period
We explore the differences in the climatic equilibrium line altitudes (ELAs) between MH and PI conditions, using a degree day model with data based on Paleoclimate Modelling Intercomparison Project Phase 2 (PMIP2) climate models output in the Southern Alps in New Zealand and the Patagonian Andes in South America (Fig. 1)
A glacier mass balance model forced with PMIP2 simulations showed that southern mid-latitude glacier ELAs during the mid-Holocene (MH) were lower compared to preindustrial (PI) conditions

Summary

Introduction

Deciphering the climate signals and glacial history of the mid-latitudes of the Southern Hemisphere (Fig. 1) during the Holocene is key to unravelling the mechanism of climate change that occurred during this period. Solomina et al (2015) recently provided a global review of Holocene glacier activity. Periods of renewed glacial activity, known as neoglaciations (Porter and Denton, 1967), were initially identified in the North-. During the last decades, numerous studies have shown evidence of glacial advances, as well as climate variability during this period in the Southern Hemisphere (approximately between 35 and 55◦ S). Most of these studies have focused on Patagonia Most of these studies have focused on Patagonia (e.g. Clapperton and Sugden, 1988; Porter, 2000; Rodbell et al, 2009; Strelin et al, 2014) and in the Southern Alps in New Zealand (e.g. Gellatly et al, 1988; Porter, 2000; Schaefer et al, 2009; Putnam et al, 2012; Kaplan et al, 2013)

Objectives

Methods

Results

Discussion

Conclusion