High resolution EPICA ice core dust fluxes: intermittency, extremes and Holocene stability

Abstract. Recent research in climate variability as a function of temporal or spatial scale has shown that the majority of the variance power lies in what has up until now been considered an unimportant background with relatively little power in well-known frequencies, such as daily, seasonal, or orbital oscillations. Atmospheric variability as a function of scale can be divided in various dynamical "regimes" with alternating increasing and decreasing fluctuations: weather, macroweather, climate, macroclimate, megaclimate. Although a vast amount of data is available at small scales, the larger picture is not well constrained due to the scarcity and low resolution of long paleoclimatic time-series. Here, we analyse a unique centimetric resolution dust flux series from the EPICA Dome C ice-core in Antarctica that spans the past 800 000 years. The temporal resolution is 5 years over the last 400 kyrs, and 25 years over the last 800 kyrs, enabling the detailed statistical analysis and comparison of eight glaciation cycles. The main spectral peak of the complete record is superposed on a scaling (power law) process and accounts for only 4–15 % of the variability, the rest being in the scaling continuum, thus inverting the classical notions of foreground and background processes.

We analyzed the glacial-interglacial cycles using two definitions: a fixed duration of 100 kyrs (segments) and a variable duration defined by the interglacial dust minima (cycles). Segments and cycles were further divided into eight consecutive "phases". We found that the first two phases of each segment or cycle showed particularly large macroweather to climate transition scale T_c (around 2 kyrs), whereas later phases feature centennial transition scales (average of 250 kyr). This suggests that interglacials and glacial maxima are exceptionally stable when compared with the rest of a glacial cycle. The Holocene (with T_c ≈ 4 kyrs) had a particularly large T_c but it was not an outlier when compared with the phase 1 and 2 of other cycles. For each phase we quantified the drift, intermittency, and extremeness of the variability. Phases close to the interglacials (1, 2, 8) show low drift, moderate interm–7 display strong drift, weak intermittency, and weaker extremes.