When did the Last Interglacial end?

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  • QU.4T'ERNARY RESEARCH 4, 246-252 (1974)

    When Did the Last Interglacial End?

    R. P. SUGGATE~

    Received April 1, 1974

    Disagreement on the time of the end of the Last Interglacial stems from lack of an agreed definition of an Interglacial. Although strictly a climatic episode, Interglacial as commonly used is essentially a chronologic unit equivalent to an Age, corresponding in time range to the chronostratigraphic unit Stage.

    The name Last Interglacial has gained a global connotation so that its definition must take into account global rather than local effects of temperature fluctuations. An Interglacial begins with a warming to full interglacial warmth (as warm as the present day). It continues until a cooling of full glacial severity occurs, and includes any lesser toolings within a period of fluctuating climate. Such lesser toolings are recorded, particu- larly in deep-sea cores, following a period of warmth about 125,000 y.a. The cooling that led to the next full glacial cold began about 50,000 yr later. The Last Interglacial lasted from about 123,000 to 73,000 yr BP, equivalent to stage 5 of Shackleton and Opdyke.

    INTRODUCTION

    Amidst the wealth of important papers given to a symposium concerned with the timing of the end of the present intergla- cial, published in Quaternary Research 2, 1972, there lies a total confusion as to when the Last Interglacial can be said to have ended. The guest editorial by Kukla et al. (1972) emphasized the contrasts in previ- ously published assignments of duration of the Last Interglacial and asserted (p, 263) that lL. . . . at least for the purposes of the meeting the concept similar to the practice of European palynologists was tacitly adopted. The term interglacial is under- stood here to mean an uninterrupted warm interval, in which the environment on a global scale reached at least the present level of warmth. The editorial indicated that this symposium adopted the period

    1 New Zealand Geological Survey, P.O. Box 30368, Lower Hutt, New Zealand.

    *The first letters of the words Last Intergla- cial need to be in capitals to indicate the effec- tively formal use of the term.

    about 128,000-116,000 yr BP, for the Last Interglacial. Yet no such generalization is apparent in the published papers. Several authors did not define the Last Interglacial even though they used it as an analogy for the present one ; others did not need to define it. The following contrasts are found in the dating of its end:

    116,000 yr BP-Fairbridge (1972: 294) Kukla and Kukla (1972:

    42) 97,000 yr BP-Morner (1972, Figs. 1, 2;

    pp. 342-343) 73,000 yr BP--McIntyre and Ruddiman

    (1972: 350).

    Wright (1972: 280) clearly stated one rea- son for divergency, The 70,000 yr date [for the end of the Last Interglacial] is now challenged by evidence of a low stand of sea level (-71 m) in Barbados and thus presumably extensive glaciation between 125,000 and 105,000 yr BP, according to thorium dates. This cold period is referred to as the 110,000 YBP event by Sancetta

    246 Copyright @ 1974 by University of Washingcon. All rights of reproduction in any form reserved.

  • WHEN DID THE LAST INTERGLACIAL END? 1i

    et al. (1972: 366), and is correlated with a northern hemisphere winter insolation minimum by Kukla and Kukla (1972, Fig. 3). Sancetta et al. (lot. tit.) stated that The cooling associated with the 110,000 YBP event represents, in the [North Atlan- tic] core studied, two-thirds of a swing towards full glacial conditions, and was considerably more intense than that associ- ated with the younger event at 92,000 YBP. Although both events are recorded in the Camp Century ice core (Dansgaard et al., 1972, Fig. l), the magnitude of the earlier one is not known because of a break in the record. In this ice core, the events appear to have been of exceedingly short. duration.

    The period of 127,000-71,000 yr BP ap- parently had three temperature maxima separated by two minima, although Emi- liani (1972, Fig. 1A) appears to have dated these climatic episodes in the range of lOO,OOO-70,000 yr BP. The first tempera- ture maximum was almost certainly the warmest, probably warmer than the present day, and the later two may have been as warm as or a little less warm than the pres- ent day. The question is-should the whole period be regarded as one interglacial (cf. McIntyre and Ruddiman, 1972: 350), as one interglacial followed by two stadials and two interstadials of the Last Glaciation (cf. Fairbridge, 1972, Fig. 7)) or as three interglacials? The question needs to be answered in the most globally useful man- ner, without undue weight being given to any particular local sequence, especially if that sequence is far from oceans that pro- vide a global means of smoothing the ex- tremes of local fluctuations.

    CURRENT NOMENCLATURE OF SEQUENCES IN THE

    LATER QUATERNARY

    Several schemes of subdivision, based on climatic change inferred from data derived from different sediment types, were used by contributors to the symposium. As well as more or less traditional schemes such as the

    Flandrian-Weichselian-Eemian sequence, three numerical or alphabetical sthemes were used :

    Author of srheme of

    subdivision Sourvc of data Subdivisions Emiliani 1 kcp-sea (ores ;,I . *; 1 < .,I 1

    ( lSkj,i I

    Ericson et ~2. Ikep-sea cores s I ,z (1!)61)

    Kukln (1961) Loess stratigraphy H A

    The 2 = 1 = A subdivision is the post- glacial; prior to that the status of units varies. Beca.use the dating of t.he X/Y boundary is not agreed (89,500 yr BP, Kennett and Huddlestun 1972: 391; 72,000, Kukla et nl., 1972: 264), the correlation implied above between the Ericson and Emiliani units is not quite certain. Further- more Emiliani (197, Fig. 1) dated the be- ginning of his core stage 5 at about 100,000 yr BP whereas the beginning of Ericsons pelagic zone S is at about 130,000 yr; the discrepancy resul t.s almost certainly from difficulties of dating deep sea-cores rather than from difficulties of correlatng between cores. It may be noted that the numerical stages of Shackleton and Opdyke (1973) are those of Emiliani, but their date for the beginning of stage 5 is 128,000 yr BP.

    Subdivisions of Ericsons units were made by Kennett and Huddlestun (1972: 386) who numbered the subunits backward in tirnc progrcssivcly in the snn~e dir&ion as Ericsons main units. Emilianis unit 5 was subdivided alphabetically backward in time by Shackleton (1969)) in the direction opposite to the numbering by Emiliani. Kuklas units were subdivided numerically forumrtl in time by Kukla and KoFi (1972: 3771 in the direction opposite to t,hat of Kuklas alphabetical progression of main units.

    These detailed contrasts in usage are reflected also in the three main systems themselves and have a parallel in the con- trast b&m-een the forward nurnbc~ring of the

  • 248 R. P. SUGGATE

    Mallorca interglacial high-sea-level se- quence (Tyrrhenian-I being older than Tyrrhenian-II and Tyrrhenian-III) by Butser and Cuerda (1962) and the baclc- ward numbering of the Barbados sequence (Barbados-I being younger than Barba- dos-11 and Barbados-III) by Mesolella et al. (1969). Another forward numbering sys- tem is that of pollen zones in northwest Europe and another backward numbering system is that of the Terminations of glacial cycles of Broecker and van Donk (1970).

    Clearly the various conflicting practices make it difficult to comprehend the litera- ture easily. Whereas the problem of the direction of numbering could be resolved by simple agreement-preferably by number- ing forward in time in the direction of the sequence of events, the problem of the status of units is more difficult. Of the nu- merical or alphabetical units, only those of Ericson et al. (1961) are of Interglacial and Glacial status, in the sense that they are intended to be equivalent to major half- cycles within full climatic cycles.3 In order to begin to systematize the various ap- proaches to subdivision on a climatic basis, agreement should be sought for interpreta- tion in terms of major units of this status, with minor half-cycles within full climatic cycles as subunits. It is probable that some pollen sequences, from which comes one concept of an Interglacial (cf. Jessen and Milthers, 1928) record minor half-cycles rather than major ones.

    THE DEFINITION OF INTERGLACIAL [AGE]

    An interglacial episode between two gla- ciations can strictly have taken place only in regions that were glaciated, and its dura-

    The term climatic cycle seems preferable to that of glacial cycle used by Kukla et al. (1972) and Fairbridge (1972) since both the inter- glacial and glacial parts of the cycle need to be included; the use of cycle for a half-cycle, by Wright (1972: 275) and MGrner (1972: 345) is wrong.

    tion will have varied from place to place according to location relative to areas of ice accumulation and ice limits; its time boundaries are accordingly time-transgres- sive. The term Interglacial has, however, been extended widely to nonglaciated regions, to refer to a warm episode between two cold ones that correspond to those with truly glacial effects at higher latitudes or altitudes. To be of value for interregional correlation, it is necessary to define units with boundaries that are not time-trans- gressive, and the regions beyond the ice limits, including the oceans, can provide critical data. The time between the begin- ning and end of such units constitutes an Interglacial Age (a chronologic unit) and the rocks formed during that period of time form an Interglacial Stage (a chrcno- stratigraphic unit).

    The distinction between the time-trans- gressive climatic episode and the chrono- logic and chronostratigraphic units that are not time-transgres

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