Heinrich Events

Session 1: The Terrestrial Fingerprint of a Heinrich Event

Session Description

This session will focus on Heinrich events as recorded in the ice-core records and other terrestrial sites. We will investigate the importance of chronological uncertainties and how they might affect our understanding of synchroneities (or not) in climate signals from disparate locations.

Session Talks
Keynote

The signature of Heinrich Events in ice cores and other terrestrial records, and their relationship to Dansgaard-Oeschger cycles

Eric Wolff

Heinrich Events are of course an observational phenomenon in the marine realm. They are generally assumed to have some relationship to the much more numerous Dansgaard-Oeschger (DO) events that are so prominent in Greenland ice cores, and by extension, to the related Antarctic Isotopic Maxima (AIM). I will describe the characteristics of DO events and AIM in ice cores, and their related signatures in greenhouse gas records. I will then assess how the expression of DO events and AIM that are contemporary with Heinrich Events differ from the rest in ice core records. I will take a brief look at contemporary records of continental climate (pollen, speleothems). Finally I will discuss ideas about the common or distinct causes of Heinrich and DO climate variability, and its role in triggering glacial terminations.

Revising and extending the INTIMATE event stratigraphy: a proposal for how to count Greenland stadials and interstadials

Sune Olander Rasmussen


Sune Olander Rasmussen, Anders Svensson, Bo Vinther, Henrik B. Clausen, Inger Seierstad

Centre for Ice and Climate, Niels Bohr Institute, University of Copenhagen, Denmark


In exploring past climate conditions and in the search for the triggers, processes, and feedbacks responsible for past climate change, ice cores have been instrumental, providing a highly attractive combination of long records, high temporal resolution, and good dating control. Over the past two decades, high-resolution examination of the GRIP, GISP2, NGRIP and the current NEEM ice cores have provided new insights into both interglacial and glacial climate behaviour, and the best-resolved of these records make it possible to reconstruct variations in the climatic régime of the North Atlantic region on annual scale or better.


Since the very first ice core records showed the existence of alternating cold and warm periods during the last glacial, these variations have been assigned names and numbers to identify the oscillations and promote correlation and comparison between the ice core records and other types of sediment profiles. The most widely scheme, based on GRIP data in Dansgaard et al. (1993) used the terms stadials (cold) and interstadials (warm) and numbers assigned to the interstadials only. Björck et al. (1998) formalised the numbering and added numbers to the stadials as part of the so-called INTIMATE event stratigraphy, which aimed at setting up a framework for robust correlation of climate records as part of the project INTegrating Ice core, MArine, and TErrestrial records. Subsequent updates and extensions by Walker et al. (1999), Lowe et al. (2008), and Blockley et al. (2012) sticked to this numbering strategy which is widely used although it is not the only scheme proposed (Rousseau et al., 2006).


With the increase in resolution of ice core records and the advent of a coherent dating framework for the Greenland ice cores, the Greenland Ice Core Chronology 2005 - GICC05, the current numbering scheme is become insufficient as Greenland climate is being analysed in several cores in parallel in still finer detail. The presentation will introduce a proposal on how to assign numbers to the interstadials and stadials that allow unique labelling of climate events also of shorter duration than what is included in the current numbering system, while maintaining the maximum degree of compatibility with the existing system. While the new scheme in itself hardly represents significant new scientific insight, the detailed study of stadial-interstadial variability in several parallel co-dated cores provides information on the nature of the mechanisms governing millennial-scale climate change, and the improved numbering scheme is hoped to ease robust correlation of different records of past climate.


References:

Björck et al. (1998), An event stratigraphy for the Last Termination in the North Atlantic region based on the Greenland ice-core record: a proposal by the INTIMATE group, Journal of Quaternary Science 13, p. 283-292.

Blockley et al. (2012), Synchronisation of palaeoenvironmental records over the last 60,000 years, and an extended INTIMATE1 event stratigraphy to 48,000 b2k, Quaternary Science Reviews 36, p. 2-10.

Dansgaard et al. (1993), Evidence for general instability of past climate from a 250-kyr ice-core record, Nature 364, p. 218-220.

Lowe et al. (2008), Synchronisation of palaeoenvironmental events in the North Atlantic region during the Last Termination: a revised protocol recommended by the INTIMATE group, Quaternary Science Reviews 27, p. 6-17.

North Greenland Ice Core Project members (2004), High-resolution record of Northern Hemisphere climate extending into the last interglacial period, Nature 431, p. 147-151.

Rousseau et al. (2006), What is what in the ice and the ocean? Quaternary Science Reviews 25 (2006) p. 2025-2030.

Walker et al. (1999), Isotopic 'events' in the GRIP ice core: a stratotype for the Late Pleistocene, Quaternary Science Reviews 18, p. 1143-1150.

Detection of Heinrich event impacts in southern European vegetation records

William Fletcher

William Fletcher


Quaternary Environments and Geoarchaeology, Geography, School of Environment and Development , The University of Manchester


Long sedimentary sequences from southern Europe (both terrestrial and marine) provide important archives for examining the terrestrial impacts of Heinrich events. Several long pollen records (e.g. ODP site 976, MD95-2043, Tenaghi Philippon) now show an unambiguous one-to-one match with the Greenland "template" of Dansgaard-Oeschger variability, and many others display characteristic signals of millennial-scale variability. These patterns reflect the sensitive response of Mediterranean vegetation to rapid glacial climate variability, with abrupt changes within inter-sample resolution of 100-300yr. Glacial stadials are typically characterised by development of semi-desert steppe vegetation across southern Europe, reflecting arid and possibly cold conditions. More severe conditions for stadials associated with Heinrich events is detected at select locations (e.g. Alboran Sea, NW Greece) where ecological conditions permit differences in stadial intensity to be resolved. Work on Iberian margin records furthermore identifies recurrent climatic structures within Heinrich event stadials, including a multi-centennial scale shift from cold-wet to cold-dry atmospheric conditions. Future directions should include increased sample resolution across Heinrich Events, quantitative climate reconstructions incorporating both plant physiological responses to low carbon dioxide and constraints from non-pollen proxies, and modelling of vegetation feedbacks on climate.

Dr. Jennifer D. Stanford, Geography & Environment, University of Southampton