Assessing the statistical uniqueness of the Younger Dryas: a robust multivariate analysis

Henry Nye,Alan Condron

doi:10.5194/cp-17-1409-2021

Abstract

Abstract. During the last glacial period (ca. 120–11 kyr BP), dramatic temperature swings, known as Dansgaard–Oeschger (D–O) events, are clearly manifest in high-resolution oxygen isotope records from the Greenland Ice Sheet. Although variability in the Atlantic Meridional Overturning Circulation (AMOC) is often invoked, a unified explanation for what caused these “sawtooth-shaped” climate patterns has yet to be accepted. Of particular interest is the most recent D–O-shaped climate pattern that occurred from ∼ 14 600 to 11 500 years ago – the Bølling–Allerød (BA) warm interstadial and the subsequent Younger Dryas (YD) cold stadial. Unlike earlier D–O stadials, the YD is frequently considered a unique event, potentially resulting from a rerouting and/or flood of glacial meltwater into the North Atlantic or a meteorite impact. Yet, these mechanisms are less frequently considered as the cause of the earlier stadials. Using a robust multivariate outlier detection scheme – a novel approach for traditional paleoclimate research – we show that the pattern of climate change during the BA/YD is not statistically different from the other D–O events in the Greenland record and that it should not necessarily be considered unique when investigating the drivers of abrupt climate change. In so doing, our results present a novel statistical framework for paleoclimatic data analysis.

Highlights

First noted in 1985 by Willi Dansgaard as “violent oscillations” in Greenland’s DYE-3 and Camp Century oxygen isotope (δ18O) records, Dansgaard–Oeschger (D–O) events are well-known examples of abrupt climate change during the last glacial period (Dansgaard, 1985)
The BA/Younger Dryas (YD) appears not to strictly follow the trend of the seven time series lines or mean line in the two Antarctic record overlays (EDML δ18O and CO2), which indicates that further study is required to determine how the BA/YD might constitute an exceptional event from the perspective of these records
Using four chemical records commonly included in assessments of general D–O behavior – δ18O and CH4 from NGRIP (Greenland), δ18O from EDML (Antarctica), and compiled CO2 from multiple Antarctic records – we employ a holistic approach that captures the shape of each D–O cycle in terms of multiple variables

Summary

Introduction

First noted in 1985 by Willi Dansgaard as “violent oscillations” in Greenland’s DYE-3 and Camp Century oxygen isotope (δ18O) records, Dansgaard–Oeschger (D–O) events are well-known examples of abrupt climate change during the last glacial period (ca. 120–11 kyr BP) (see Fig. 1) (Dansgaard, 1985). 120–11 kyr BP) (see Fig. 1) (Dansgaard, 1985) These events are characterized by abrupt warmings of ∼ 8–16 ◦C and a subsequent centennial- to millennial-length period of relative warmth (i.e., an interstadial), followed by a gradual, and sometimes abrupt, shift to cooler (stadial) conditions (Rasmussen et al, 2014). Since their discovery 3.5 decades ago, countless mechanisms have been proposed to explain D–O cycles (see Li and Born, 2019, for a review). Given that D–O events provide compelling evidence that the global climate can rapidly switch from one state to another, it is imperative that we determine the causes of this variability if we are to accurately predict future climate

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