NPI seminar: Reconstructing the leading mode of multi-decadal North Atlantic climate variability over the last two millennia using functional paleoclimate network analysis

Speaker: Reik Donner, Potsdam Institute for Climate Impact Research.

The increasing availability of high-resolution North Atlantic paleoclimate proxies allows to not only study local climate variations in time, but also temporal changes in spatial variability patterns across the entire region possibly controlled by large-scale coherent variability modes such as the North Atlantic Oscillation (NAO) and Atlantic Multidecadal Oscillation.

In this study, we use the recently developed tool of functional paleoclimate network analysis[1][2] to investigate changes in the statistical similarity patterns among an ensemble of Late Holocene high-resolution paleoclimate records covering vast parts of Europe. Specifically, we construct complex networks capturing the mutual statistical similarity of inter-annual temperature variability recorded in different types of continuous archives within centennial time windows. The observed patterns of co-variability are ultimately connected to multidecadal-to-centennial scale changes in the North Atlantic climate variability, most prominently expressed in terms of the NAO.

Based on the inferred network representations, we study the dynamical similarity between regional clusters of archives defined according to present-day inter-annual temperature variations across the study region. Our analysis particularly highlights those time-dependent inter-regional linkages that are most informative about the leading-order North Atlantic climate variability according to a recent NAO reconstruction for the last millenium[3]. Based on these linkages, we extend the existing reconstruction backwards in time to obtain qualitative information on the leading mode of multidecadal-to-centennial scale North Atlantic climate variability over the last two millenia. In general, we find a tendency towards conditions expected for a dominance of a positive NAO phase during most time periods, which appear to have been interrupted by distinct intervals of negative NAO. Relatively rapid transitions between both types of behavior coincide with well-known climate periods including the Little Ice Age, the Medieval Climate Anomaly and the Late Antique Little Ice Age. The obtained qualitative reconstruction of North Atlantic climate variability agrees well with independent sources like historical documents indicating sustained drought periods in different parts of the continent.

References

  1. K. Rehfeld, N. Marwan, S.F.M. Breitenbach, J. Kurths. 2013. Late Holocene Asian summer monsoon dynamics from small but complex networks of paleoclimate data. Climate Dynamics 41, 3–19.
  2. J.L. Oster, N.P. Kelley. 2016. Tracking regional and global teleconnections recorded by western North American speleothem records. Quaternary Science Reviews 149, 18–33.
  3. P. Ortega, F. Lehner, D. Swingedouw, V. Masson-Delmotte, C.C. Raible, M. Casado, P. Yiou. 2015. A model-tested North Atlantic Oscillation reconstruction for the past millenium. Nature 523, 71-74.