Reconstructing Late Holocene North Atlantic atmospheric circulation changes using functional paleoclimate networks

Jasper G Franke,Johannes P Werner,Reik V Donner

doi:10.5194/cp-13-1593-2017

Abstract

Abstract. Obtaining reliable reconstructions of long-term atmospheric circulation changes in the North Atlantic region presents a persistent challenge to contemporary paleoclimate research, which has been addressed by a multitude of recent studies. In order to contribute a novel methodological aspect to this active field, we apply here evolving functional network analysis, a recently developed tool for studying temporal changes of the spatial co-variability structure of the Earth's climate system, to a set of Late Holocene paleoclimate proxy records covering the last two millennia. The emerging patterns obtained by our analysis are related to long-term changes in the dominant mode of atmospheric circulation in the region, the North Atlantic Oscillation (NAO). By comparing the time-dependent inter-regional linkage structures of the obtained functional paleoclimate network representations to a recent multi-centennial NAO reconstruction, we identify co-variability between southern Greenland, Svalbard, and Fennoscandia as being indicative of a positive NAO phase, while connections from Greenland and Fennoscandia to central Europe are more pronounced during negative NAO phases. By drawing upon this correspondence, we use some key parameters of the evolving network structure to obtain a qualitative reconstruction of the NAO long-term variability over the entire Common Era (last 2000 years) using a linear regression model trained upon the existing shorter reconstruction.

Highlights

The increasing availability of high-resolution paleoclimate archives and resulting proxy records allows to study local climate variability before the beginning of the instrumental period and associated spatial structures at least at a regional level
By comparing the time-dependent inter-regional linkage structures of the obtained functional paleoclimate network representations to a recent multi-centennial North Atlantic Oscillation (NAO) reconstruction, we identify co-variability between southern Greenland, Svalbard, and Fennoscandia as being indicative of a positive NAO phase, while connections from Greenland and Fennoscandia to central Europe are more pronounced during negative NAO phases
These are located in southern Greenland (SG), Fennoscandia (FS), and central Europe (CEU) and cover all of the Common Era

Summary

Introduction

The increasing availability of high-resolution paleoclimate archives and resulting proxy records allows to study local climate variability before the beginning of the instrumental period and associated spatial structures at least at a regional level. Corresponding studies have commonly been performed using linear multivariate statistical methods like empirical orthogonal function (EOF) analysis (Gouirand et al, 2008; Mann et al, 1998) or, more recently, Bayesian hierarchical modelling (Luterbacher et al, 2016). At the conceptual level, many of the classical statistical approaches have considerable problems in analysing paleoclimate data. The appealing alternative of data interpolation can lead to a systematic bias and large uncertainties in the resulting reconstructions of spatial patterns of past climate variability (Rehfeld et al, 2011). Many previously applied methods rely on some kind of linearity and/or orthogonality assumption, which might result in some unrealistic representation of the climatic processes or phenomena under study

Objectives

Methods

Results

Discussion

Conclusion