Detecting paleoclimate transitions with Laplacian Eigenmaps for
Recurrence Matrices (LERM)
Abstract
Paleoclimate records can be considered low-dimensional projections of
the climate system that generated them. Understanding what these
projections tell us about past climates and changes in their dynamics is
the main goal of time series analysis on such records. Linear techniques
provide insight into changes in the periodic behavior of the climate,
but are intrinsically limited. Novel tools from nonlinear time series
analysis allow us to examine changes in other kinds of behavior that are
reflected in these records. Laplacian Eigenmaps of Recurrence Matrices
(LERM) is one such technique, providing information about when
fundamental shifts in climate dynamics have occurred. This is done by
leveraging time delay embedding to construct a manifold that is mappable
to the attractor of the climate system; this manifold can then be
analyzed for significant dynamical transitions. Through numerical
experiments with observed and synthetic data, LERM is applied to detect
both gradual and abrupt regime transitions. Our paragon for gradual
transitions is the Mid-Pleistocene Transition (MPT). We observe that
LERM is robust in detecting gradual MPT-like transitions for
sufficiently high signal-to-noise ratios, though it tends to occur
towards the later stages of the transition. Our paragon of abrupt
transitions is the 8.2ka event; we find that LERM is generally robust at
detecting 8.2ka-like transitions for sufficiently high signal-to-noise
ratios, though edge effects become more influential. We conclude that
LERM can usefully detect dynamical transitions in paleogeoscientific
time series. An associated Python package is proposed to ease its use in
the fields of paleoclimatology and paleoceanography.