An optimized scheme of lettered marine isotope substages for the last 1.0 million years, and the climatostratigraphic nature of isotope stages and substages

Abstract

A complete and optimized scheme of lettered marine isotope substages spanning the last 1.0 million years is proposed. Lettered substages for Marine Isotope Stage (MIS) 5 were explicitly defined by Shackleton (1969), but analogous substages before or after MIS 5 have not been coherently defined. Short-term discrete events in the isotopic record were defined in the 1980s and given decimal-style numbers, rather than letters, but unlike substages they were neither intended nor suited to identify contiguous intervals of time. Substages for time outside MIS 5 have been lettered, or in some cases numbered, piecemeal and with conflicting designations. We therefore propose a system of lettered substages that is complete, without missing substages, and optimized to match previous published usage to the maximum extent possible. Our goal is to provide order and unity to a taxonomy and nomenclature that has developed ad hoc and somewhat chaotically over the decades. Our system is defined relative to the LR04 stack of marine benthic oxygen isotope records, and thus it is grounded in a continuous record responsive largely to changes in ice volume that are inherently global.

Full text

An optimized scheme of lettered marine isotope substages for the last
1.0 million years, and the climatostratigraphic nature of isotope stages
and substages
L. Bruce Railsback
a
,
*
, Philip L. Gibbard
b
, Martin J. Head
c
, Ny Riavo G. Voarintsoa
a
,
Samuel Toucanne
d
a
Department of Geology, University of Georgia, Athens, GA 30602-2501, USA
b
Department of Geography, University of Cambridge, Downing Street, Cambridge CB2 3EN, England, UK
c
Department of Earth Sciences, Brock University, 500 Glenridge Avenue, St. Catharines, Ontario L2S 3A1, Canada
d
IFREMER, Laboratoire Environnements S
edimentaires, BP70, 29280 Plouzan
e, France
article info
Article history:
Received 9 September 2014
Received in revised form
15 December 2014
Accepted 16 January 2015
Available online
Keywords:
Substages
Stages
Marine isotope stages
MIS
Chronology
Chronostratigraphy
Climatostratigraphy
abstract
A complete and optimized scheme of lettered marine isotope substages spanning the last 1.0 million
years is proposed. Lettered substages for Marine Isotope Stage (MIS) 5 were explicitly defined by
Shackleton (1969), but analogous substages before or after MIS 5 have not been coherently defined.
Short-term discrete events in the isotopic record were defined in the 1980s and given decimal-style
numbers, rather than letters, but unlike substages they were neither intended nor suited to identify
contiguous intervals of time. Substages for time outside MIS 5 have been lettered, or in some cases
numbered, piecemeal and with conflicting designations. We therefore propose a system of lettered
substages that is complete, without missing substages, and optimized to match previous published usage
to the maximum extent possible. Our goal is to provide order and unity to a taxonomy and nomenclature
that has developed ad hoc and somewhat chaotically over the decades. Our system is defined relative to
the LR04 stack of marine benthic oxygen isotope records, and thus it is grounded in a continuous record
responsive largely to changes in ice volume that are inherently global.
This system is intended specifically for marine oxygen isotope stages, but it has relevance also for
oxygen isotope stages recognized in time-series of non-marine oxygen isotope data, and more generally
for climatic stages, which are recognized in time-series of non-isotopic as well as isotopic data. The terms
“stage”and “substage”in this context are best considered to represent climatostratigraphic units, and
thus “climatic stages”and “climatic substages”, because they are recognized from geochemical and
sedimentary responses to climate change that may not have been synchronous at global scale.
©2015 Elsevier Ltd. All rights reserved.
1. Introduction
As the complex history of Quaternary glaciation, climate, sea
level, and ocean circulation has become apparent over the past 60
years, the scientific community has developed a variety of systems
to identify intervals of time and glacio-climatic events. One of the
most widely applied systems has been that of numbered marine
oxygen isotope stages, or more generally oxygen isotope stages,
moving from the Holocene back in time as MIS 1, MIS 2, MIS 3, etc.,
where “MIS”refers to “marine isotope stage”. These isotope stages
have been divided in some cases into lettered substages, most
notably in MIS 5 as substages MIS 5a, 5b, 5c, 5d, and 5e, which were
formally defined as such by Shackleton (1969). In the past 20 years,
many publications have used lettered substages for intervals
outside MIS 5, from MIS 2a (Yelovicheva, 2006) to at least MIS 19c
(Tzedakis et al., 2012a,b). However, these lettered substages other
than those of MIS 5 have been named in many different papers, in
no coherent system, and sometimes with conflicting designations
of substages. Further, these lettered substages denoting intervals of
time are commonly interwoven if not confused with a numbered
system that was formulated to identify events rather than intervals,
as discussed below. As a result, researchers are left with an
*Corresponding author. Tel.: þ1 706 542 3453; fax: þ1 706 542 2652.
E-mail address: rlsbk@gly.uga.edu (L.B. Railsback).
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Quaternary Science Reviews
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Quaternary Science Reviews 111 (2015) 94e106

inconsistent and sometimes conflicting nomenclature originating
in a diverse and scattered literature.
In light of the usefulness of isotope stages and lettered sub-
stages, but also the piecemeal origin and disarray of the substage
nomenclature, we review the origins of Quaternary isotope chro-
nological schemes and tabulate the earliest reports of the lettered
isotope substages. We then present a scheme of lettered isotope
substages consistent with the previous scattered designations that
have appeared in the literature, with the hope that this scheme can
avoid further contradictions and provide a single unified source for
future researchers. This scheme is defined relative to the LR04 stack
of marine benthic oxygen isotope records, a continuous record that
largely represents changes in ice volume that are inherently global
and thus useful for global correlation.
2. Evolving concepts of stages and events
2.1. Named continental stages and substages (before 1940)
The concept of stages as deposits representing intervals of time,
which are formally known as “ages”(Salvador,1994), in Pleistocene
history (e.g., Cohen et al., 2013) derives from named stages, such as
Wisconsin and Kansan (Geikie, 1894; Chamberlin, 1895)(Table 1).
Those stages were defined by climatically significant continental
deposits, rather than by faunal zones, in the peculiarly Quaternary
paradigm (Flint, 1947, p. 209) now known as “climatostratigraphy”
(Mangerud et al., 1974; Harland, 1992; Gibbard, 2013). More recent
North American stages had named substages, such as the Iowan,
Tazewell, Cary, and Mankato substages of the Wisconsin (Leighton,
1933).
2.2. Numbered marine stages, and their substages (1952e1969)
The more recent concept of numbered and marine, rather than
named and continental, climatostratigraphic stages arose with the
work of Arrhenius (1952). In plotting the concentration of CaCO
3
in
marine sediment cores, Arrhenius (1952) made correlations using
stages and substages numbered in decimal style, with the upper-
most and therefore most recent stage designated “1”and followed
by “2”,“3.1”,“3.2”,“4”and “5”.Arrhenius (1952) recognized that his
odd-numbered stages represented interglacial periods and his
even-numbered stages represented glacial periods, and he thought
it “probable”that his youngest four glacial stages corresponded to
the Nebraskan, Kansan, Illinoian, and Wisconsin “Ice Ages”
(Arrhenius, 1952, p. 200). His Fig. 3.4.2 recognized 18 stages over
the last 1.0 millionyears, which was then considered the entirety of
the Pleistocene. Today, more stages are identified over both of those
intervals (e.g., Lisiecki and Raymo, 2005), but the system of stages
generated by Arrhenius (1952) provided a conceptual framework
that was used when isotopic, rather than compositional, analysis of
marine cores (e.g., Emiliani, 1955) began soon after his work.
Within that system, his stages numbered with integers clearly
referred to intervals of sediment or time (e.g., in his Fig. 3.4.2), but
his only illustration showing substages numbered in decimal style
(his Fig. 1.2.4) used lines pointing to peaks in his data, implying that
these chronological features numbered in decimal style were
viewed as events as much as intervals (Fig. 1A), a distinction that
would become critical by the 1980s.
Emiliani (1955), in characterizing the variability of his oxygen
isotope data from deep-sea cores, adopted the system of stages
initiated by Arrhenius (1952).Emiliani (1955) recognized 14
numbered “core stages”in his Figs. 3 and 15, in analogy to and for
correlation with continental glacial stages, as in his Table 15.
Emiliani (1955) in some cases wrote about the “thickness”of stages
(his p. 554) and elsewhere used time terms (e.g., “preceded by”on
his p. 566 and “earlier”on his p. 557) to characterize stages. Emi-
liani's Fig. 1 clearly labeled stages with a time, rather than depth or
thickness, axis. He thus made the transition from “stage”as a term
for sediments deposited during an interval of time to “stage”as a
term for an interval of time. The use of “stage”rather than “age”
(Table 1) as a term for time in isotopic stratigraphy has persisted,
with implications discussed in Section 5.2.
Emiliani (1955) designated the present and previous in-
terglacials as MIS 1, 5, 7, 9, 11, etc., with MIS 3 as an interval that is
no longer considered an interglacial (e.g., Sirocko et al., 2007). That
usage has persisted to the present, despite its imperfection as an
arithmetic series, and its persistence illustrates the extent to which
the system of isotope stages is a matter of consistent communica-
tion, rather than of contemporary geological reasoning. Its persis-
tence as a mathematically flawed but widely used chronological
system is paralleled by the even more widespread persistence of
numbers used to identify years before (BCE) or after (CE) a datum
now acknowledged to have been misplaced by about five years
(Teres,1984; Maier, 1989). In both cases, the need for consistency of
usage has triumphed over logic and purity of system.
Emiliani (1955) designated no marine substages, despite
explicitly noting continentally-defined intervals such as the Allerød
and Two Creeks that he called “substages”.Emiliani (1961) followed
his earlier publication (Emiliani, 1955) in recognizing 14 numbered
stages in his Fig. 9, and in his Fig. 10 he subdivided Stage 5 into five
un-labeled intervals of isotopic maxima and minima of lesser
relative magnitude than those defining stages. Shackleton (1969)
explicitly labeled those five intervals as “isotope sub-stages”with
letters “a”to “e”in his Fig. 1, and he discussed “Substage 5e”
extensively. Fig. 1 of Emiliani (1955) explicitly conceptualized
stages as intervals of time with boundaries at changes in temper-
ature, and Fig. 10 of Emiliani (1961) and Fig. 1 of Shackleton (1969)
implicitly but clearly followed that model with substages as suc-
cessive contiguous intervals of time (Fig. 1B), in contrast to later
schemes.
From the 14 isotope stages first recognized by Emiliani (1955,
196 6) extended the system of isotope stages back to Stage 17 in
his Fig. 6, and Shackleton and Opdyke (1973) extended it to Stage 22
in their Fig. 9. Van Donk (1976) extended the system back to MIS 42
in his Fig. 1, Ruddiman et al. (1989) extended the system of MIS
stages to MIS 63 in their Fig. 7, and Raymo et al. (1989) extended it
Table 1
Geochronologic intervals and their stratigraphic equivalents, with examples.
Geochronologic
(time) interval
a
Chronostratigraphic
(time-rock) interval
a
Global chrono-stratigraphic
example
b
Climato-stratigraphic
regional continental example
b
Climato-stratigraphic marine
isotopic example
b
Period System Quaternary
Epoch Series Pleistocene
Age Stage Calabrian
c
Wisconsin MIS 7
Subage Substage Mankato MIS 7b
a
For the significance of this distinction, see Fig. 5 and Section 5.2, and more generally Salvador (1994).
b
Note that these examples are not time-equivalents (e.g., Wisconsin is not Calabrian, and Mankato is not 7b).
c
Cita et al. (2012).
L.B. Railsback et al. / Quaternary Science Reviews 111 (2015) 94e106 95

from MIS 63 to MIS 116 in their Fig. 6 (but see also Shackleton et al.,
1990). Shackleton et al. (1995) extended the system back to the
Miocene, and thus to give a total of 220 marine isotope stages, in
their Fig. 7. These stages beyond MIS 5e were designated only with
integers, and no substages were recognized, and thus neither let-
ters nor decimal-style numbers were used. Shackleton et al. (1995)
did, however, remark that “lettered substages”might eventually be
useful in the early stages that they defined.
In the lineage from Arrhenius (1952) to Shackleton (1969)
described above, a transition was made from the non-isotopic
substages with decimal-like numbers of the former to the
lettered isotopic substages of the latter. Shackleton (1969) cited
Arrhenius (1952) but made no mention of the numbered substages
in that paper, leaving the previous use of decimal-style numbers by
Arrhenius seemingly forgotten, and thus leaving decimal-style
numbers free for application to isotopic “events”recognized in
marine cores in the 1980s.
2.3. Events (1984e1994)
Prell et al. (1986, p.138) explicitly rejected the substage concept
of Shackleton and Opdyke (1973) because stages and substages, as
intervals, were argued to not provide the distinct control points
needed to construct age models. Instead, Prell et al. (1986) used
decimal-style numbers to label “events”, which were much briefer
intervals at “maxima, minima, or rapid changes”in the oxygen
isotope record (Fig. 1C). The end of one event was commonly not
the beginning of the next, so that intervals of time between suc-
cessive events were left without designation. Numbers such as 2.0,
3.0, 4.0, etc., indicated boundaries, rather than intervals, and they
marked the boundaries of the isotope stages of Emiliani (1955).
Despite its publication date, Prell et al. (1986) was the cited
source of systems used in Imbrie et al. (1984) and Pisias et al.
(1984).Imbrie et al. (1984) adopted a system of decimal-style
numbered “events”, with boundaries at 2.0, 3.0, 4.0, etc., like that
of Prell et al. (1986).Pisias et al. (1984) used a similar series of
decimal-style numbered “events”and cited Prell et al. (1986) as a
source, but they moved further from the model of Emiliani (1955),
Imbrie et al. (1984), and Prell et al. (1986) by using 1.0, 2.0, 3.0, etc.
to label events that were intervals of non-zero duration (Fig. 1D),
rather than to label boundaries as Prell et al. (1986) had done.
Martinson et al. (1987) cited Pisias et al. (1984) as the source of
their system of decimal-style numbered events. However, Fig. 18 of
Martinson et al. (1987) suggests that each of that publication's
events, whether at transitions or at peaks or troughs, had no sig-
nificant duration in time (Fig. 1E), in contrast to the bracketed
events of measurable duration shown by Prell et al. (1986).
Martinson et al. (1987) joined Pisias et al. (1984) in taking some
Fig. 1. Six different published styles of dividing Pleistocene time series, with the middle four from founding papers in the field of marine isotope stratigraphy discussed in Sections
2.2 and 2.3. The curve shown, and all of the letters and numbers, are arbitrary creations to illustrate the various schemes: “6”and “8”only suggest even numbers assigned to glacial
periods; “7”only suggests odd numbers assigned to interglacials; etc. Dashed lines are boundaries between intervals; brackets identify short intervals; solid lines point to events of
very short duration.
L.B. Railsback et al. / Quaternary Science Reviews 111 (2015) 94e10696

decimal-style designations to two places, as for example with
Events 5.51 and 5.53 within Event 5.5 in Fig. 18 of Martinson et al.
(1987). The series of publications from Prell et al. (1986) to Pisias
et al. (1984) and Imbrie et al. (1984) to Martinson et al. (1987)
thus presents an evolving number-based scheme of events, rather
than contiguous intervals, different in intent and form from the
lettered substages of Shackleton (1969).
Bassinot et al. (1994) continued this tradition by extending the
system of numbered events back to MIS 22 in their Fig. 7, and they
maintained that tradition's focus on isolated peaks, rather than on
continuity of contiguous intervals, by not designating an Event 6.4
between their Events 6.3 and 6.5, and likewise by not designating
an Event 17.2 between their Events 17.1 and 17.3. Bassinot et al.
(1994) consistently referred to integer-numbered stages (e.g.,
“Stage 19”), decimal-style numbered events (e.g., “Isotopic Event
19.1”), and decimal-style numbered stage boundaries (e.g., “Isotope
stage boundary 23.0”), completely consistent with the conceptual
separation of lettered substages and decimal-style numbered
events arising from the papers discussed above. However, later
workers would not maintain that distinction in using the decimal-
style numbers established by Bassinot et al. (1994).
2.4. Hybridization and modification (~1990 to present)
Despite the distinction between stages and events established in
the 1980s, later workers have gone on to hybridize these schemes.
For example, Plagnes et al. (2002), Wang et al. (2008), Kitaba et al.
(2011), and Muhs et al. (2014) used decimal-style numbers to one
place to identify substages, rather than events (Fig. 1F). Bühring
et al. (2004) used decimal-style numbers to two places to identify
substages and drew these numbers from those used to identify
events by Imbrie et al. (1984) in some cases and by Martinson et al.
(1987) in others. Poli et al. (2012) likewise used decimal-style
numbers to two places to identify substages, but they drew the
numbers from those used to identify events by Bassinot et al.
(1994). In their text, Bühring et al. (2004) innovated further by
using substage designations with two decimal-style dots, as in their
substages 5.3.1 and 5.3.3. In a more complex hybrid, Jahns et al.
(1998) combined decimal-style numbers and letters in identifying
single substages when they referred to “
d
18
O-substage 12.2h”, and
Desprat et al. (2007) combined lettered and numbered substages
(e.g., 8.2, 9e, and 11.3) in one series in their Fig. 25.3.
Meanwhile, other workers challenged some of the original
premises of earlier schemes. For example, Melles et al. (2007) and
Vaks et al. (2010) extended the use of numbers with Substage 6.1,
and Melles et al. (2007) wrote of Substage 8.1, whereas none of the
founding papers of the 1960se1990s discussed above had referred
to an event or substage 2.1, 4.1, 6.1, or the like. That prior convention
presumably prevailed because an even-numbered and therefore
glacial stage was not expected to end with a warm (odd-numbered)
phase prior to a typically abrupt termination.
2.5. Shackleton's valedictory perspective (2006) and beyond
Nicholas Shackleton (1937e2006) was the author of the first
paper identifying lettered isotope substages (Shackleton, 1969) and
a co-author of the papers establishing the systems of numbered
events (Imbrie et al., 1984; Pisias et al., 1984; Prell et al., 1986;
Martinson et al., 1987; Bassinot et al., 1994), and a co-author on
many of the works cited in Section 3of this paper. In his INQUA
Presidential Address published as an “unfinished”paper in 2006,
Shackleton reiterated the difference between, on the one hand,
substages representing bounded intervals that collectively account
for all of past time and, on the other hand, numbered events rep-
resenting points in time between which some intervals of time are
undesignated (Shackleton, 2006). He concluded that “the two
systems are not interchangeable”.
We concur that the two systems are not interchangeable, for
two reasons. The first reason, a conceptual one, is the contradiction
above between contiguous intervals and discrete events that was
presented by Shackleton (2006) and that was implied in the explicit
rejection of stages and substages by Prell et al. (1986). The second
reason, a practical one, is that the assumption that the number “1”
means “a”,“2”means “b”, etc., fails when one encounters an in-
terval numbered “X.0”(as in Wang et al., 2008 and Kitaba et al.,
2011) because zero has no analog among letters. Thus one cannot
assume that “readers will know what we meant”when the
nomenclature of numbered events is applied to time intervals. In
fact, the example from Fig. 8 of Kitaba et al. (2011) is additionally
instructive because that figure identifies two successive substages,
22.0 and 22.2, with no intervening 22.1, a designation compatible
with the numbering of events but incompatible with a succession
of stages.
One recent and well-expressed example of the two systems can
be seen in Figs. 3e6ofHern
andez-Almeida et al. (2012). These
figures show the extent of MIS 20 to 30 in blue and white bands
between which there are no gaps, consistent with the notion of
stages presented by Emiliani (1955) and Shackleton and Opdyke
(1973). The figures also show decimal-style numbered events in
red bands that are not contiguous. Events 24.1 and 29.1 are intervals
of short duration in the middles of MIS 24 and 29, respectively, and
Event 30.1 is an event of short duration at the beginning of MIS 30.
The decimal-style numbered events are thus consistent with the
spirit of Pisias et al. (1984), Imbrie et al. (1984), Prell et al. (1986),
and Martinson et al. (1987) in marking isolated points in time.
However, any attempt to convert these decimal-style numbered
events to substages would fail, because substages designated “1”or
(more appropriately) “a”should be at the end, rather than middles
or beginnings, of the sequence of substages in a stage.
3. Extension of lettered substages to time other than MIS 5,
and resulting problems
In the last four decades, the system of lettered substages has
been extended to time other than Shackleton's (1969) MIS 5 sub-
stages (Table 2). However, that extension has been accomplished
largely in an ad-hoc fashion wherein lettered substages were
denoted, but not defined, in order to meet the needs of the subject
matter of specific papers, some of which dealt with terrestrial
rather than marine deposits (Table 2). In some papers, substage
designations were used in figures but not mentioned in text, and in
some cases substage designations were mentioned in text but not
illustrated in figures (e.g., Ninkovich and Shackleton, 1975). In
almost no cases were boundary lines between substages like those
of Shackleton (1969) (Fig. 1B) drawn on isotope time-series plots.
Our compilation in Table 2 shows that the first occurrences, and in
some cases only occurrences, of use of these lettered substages
outside MIS 5 are scattered across at least 19 papers. Despite this
proliferation, some substages remain without explicit identification
amidst substages that have been labeled (e.g., Substages 13b and
16b).
In the midst of this piecemeal extension of lettered substages,
contradictions have developed (Fig. 2). Some examples, presented
only to illustrate the hazards of this ad-hoc way of creating a
chronology, include the following:
1) Lundberg and McFarlane (2007) designated three substages of
MIS 6 (6c, 6b and 6a), and they specifically defined MIS 6c as
“the first cold period of MIS 6”. On the other hand, Sun and An
(2005) discussed five substages of MIS 6 (6e, 6d, 6c, 6b and
L.B. Railsback et al. / Quaternary Science Reviews 111 (2015) 94e106 97

6a), of which MIS 6e was the earliest of three MIS 6 cold sub-
stages in their Fig. 7. Meanwhile, Kawamura et al. (2007)
designated five MIS 6 substages as MIS 6f, 6e, 6d, 6c and 6b,
with MIS 6f as the earliest cold substage and no MIS 6a at all in
their Fig. 2, a usage later employed by Railsback et al. (2014).
2) Ninkovich and Shackleton (1975) designated the earliest sub-
stage of MIS 7 as MIS 7c, Bussell and Pillans (1997) made the
same designation (citing the decimal-style numbered events of
Imbrie et al.,1984 and Martinson et al., 1987 as their source), and
Zazo (1999) similarly identified MIS 7c and 7a as the two
highstands of MIS 7, whereas Tzedakis et al. (1997) designated
the earliest substage of MIS 7 as MIS 7e, a usage subsequently
followed by Schreve (2001), Robinson et al. (2002), Siddall et al.
(2007, their Table 7.1), and Compton (2011).
3) Bassinot et al. (1994) identified as Isotopic Event 8.5 the peak
that Tzedakis et al. (1997) designated as MIS 9a, a contradiction
not only of substages but of stages.
4) Bussell and Pillans (1992), Bradley (1999, 2015),andSiddall
et al. (2007) labeled the earliest peak in MIS 9 as MIS 9c,
whereas Tzedakis et al. (1997) designated that peak as MIS 9e,
and it was subsequently identifiedasMIS9eonthe
Quaternary chronostratigraphical charts of Gibbard and
Cohen (2008) and Cohen and Gibbard (2011) and in
Fig. 25.3 of Desprat et al. (2007). On the other hand, Fig. 3 of
Westaway (2011) presented a detailed series of substages
from MIS 5a to MIS 15e in which all of MIS 9 was labeled only
“9”without subdivision.
5) Prokopenko et al. (2001) and Schreve (2001) referred to MIS 11e,
and Ashton (2010) similarly referred to MIS 11d and MIS 11e,
although Tzedakis et al. (1997) had defined MIS 11c as the
earliest substage of MIS 11. On the other hand, de Abreu et al.
(2005) referred to MIS 7e and 9e, evidently finding these
lettered substages of use, in a paper focused on MIS 11 in which
they found no reason to refer to any substages of MIS 11 at all.
Fig. 3 of Westaway (2011) likewise presented a detailed series of
substages from MIS 5a to MIS 15e in which all of MIS 11 was
labeled only “11”without subdivision.
6) Tzedakis et al. (2012a,b) labeled the earliest substage of MIS 15
as MIS 15c, whereas it had been identified as MIS 15e by
Khursevich et al. (2001) and Westaway (2011) and on the
Quaternary chronostratigraphical charts of Gibbard and Cohen
(2008) and Cohen and Gibbard (2011).
Table 2
First designations of lettered substages.
Substage Earliest known use
a
MIS literature cited Record
b
2ae2h Yelovicheva (2006)
,
c
None Non-marine sediments
3a and 3b Wright et al. (1995) None Marine CaCO
3
3c Wu et al. (2004) None
d
18
O of Tibetan ice
3d and 3e Yelovicheva (2006) None Non-marine sediments
4ae4c Yelovicheva (2006) None Non-marine sediments
5ae5e Shackleton (1969) Emiliani (1961) Marine
d
18
O
6ae6e Sun and An (2005) None Loess
6f Kawamura et al. (2007) Tzedakis et al. (2004) Dome Fuji
d
18
O
7a, 7b, 7c Ninkovich and Shackleton (1975) Emiliani (1955, 1966); Shackleton (1969) Marine
d
18
O
7d Prokopenko et al. (2001);Imbrie et al. (1984) Lacustrine silica
Khursevich et al. (2001) None Lacustrine silica
Forsstr€
om (2001) None Vostok
d
D
7e Tzedakis et al. (1997) Imbrie et al. (1984); Prell et al. (1986);
Martinson et al. (1987)
Marine
d
18
O
8ae8c None found ee
9a, 9b, 9c Bussell and Pillans (1992) Imbrie et al. (1984) Marine
d
18
O
9d Prokopenko et al. (2001);Imbrie et al. (1984) Lacustrine silica
Khursevich et al. (2001) None Lacustrine silica
9e Tzedakis et al. (1997) Imbrie et al. (1984); Prell et al. (1986);
Martinson et al. (1987)
Marine
d
18
O
10a, 10b, 10c Lundberg and McFarlane (2007) None Cave deposits
11a and 11c Tzedakis et al. (1997, 2001) Imbrie et al. (1984); Prell et al. (1986);
Martinson et al. (1987)
Marine
d
18
O
11b Ashton et al. (2008)
,
d
Tzedakis et al. (2001); Prokopenko et al. (2001) Marine
d
18
O
11d Ashton (2010)
,
d
11e Prokopenko et al. (2001) Imbrie et al. (1984) Lacustrine silica
12a, 12c, 12e Sun and An (2005) None Loess
12b Voelker et al. (2010) None Marine
d
18
O
13a Westaway (2010) None Bithynia ala/ser
e
13c Voelker et al. (2010) None Marine
d
18
O
13b, 13d, 13e None found ee
14a, 14b, 14c None found ee
15a, 15b, 15c, 15d, 15e Khursevich et al. (2001) None Lacustrine silica
16a, 16c Sun and An (2005) None
16b, 16d None found ee
17a, 17b, 17c, 17d, 17e None found ee
18a, 18b, 18c None found ee
19a, 19b, 19d, 19e None found ee
19c Tzedakis et al. (2012a); None Marine
d
18
O
Tzedakis et al. (2012b) None EPICA C
d
D
20ae28c None found ee
a
This list shows the earliest use reported in searches of Web of Science, with earlier additions from the authors' knowledge.
b
The record used to define the substage, which may not have been the kind of record studied.
c
Yelovicheva (2006) explicitly labeled her eight substages as “MIS”.Murari et al. (2014) identified five monsoonal HimalayaneTibetan stages (MOHITS) from 2A to 2E
correlative with MIS 2, and Dortch et al. (2013) identified six semi-arid western HimalayaneTibetan stages (SWHTS) from 2A to 2F correlative with MIS 2.
d
Jahns et al. (1998) referred to “Pollen subzones”11b and 11d in “oxygen isotope stage 11”, but they did not explicitly refer to substages designated 11b and 11d.
e
Ratio of the amino acids alanine and serine in opercula of the freshwater gastropod Bithynia.
L.B. Railsback et al. / Quaternary Science Reviews 111 (2015) 94e10698

Meanwhile, attempts at numbered substages have fared no
better. For example, Wang et al. (2008) identified as Substage 7.0
the same interval that Bühring et al. (2004) designated as MIS 6.6.
Similarly, Vaks et al. (2010) identified the youngest substage of MIS
6 as MIS 6.1, whereas Ruddiman (2006) had identified it as MIS 6.2.
All eight examples combine to illustrate the confusion that can arise
when no single system exists to divide time series.
4. A proposed system of lettered substages
The long history of repeated attempts to label parts of Cenozoic
time series at fine scale shows that this is a useful and desirable
component of communication about Earth history. However, the
piecemeal and ad-hoc approach to substages and its resultant
contradictions (Fig. 2) imply that a systematic development of
substage taxonomy and nomenclature would be more useful. We
therefore propose the complete scheme of lettered substages
shown in Fig. 3. Our goals in preparing this scheme have included
the following:
1) Definition of substages relative to a marine isotope record,
rather than a terrestrial one. This follows logically from the
expression “Marine Isotope Stage”, and it is consistent with the
objective of identifying time intervals that are meaningful at
global, rather than regional, scale. Fig. 3 therefore shows three
marine records, and its substages are defined relative to the
LR04 stack of marine benthic oxygen isotope records of Lisiecki
and Raymo (2005). However, Fig. 3 additionally includes four
non-marine records that provide a basis for comparison with
less complete non-marine records from which some substages
may be missing. The seven records in Fig. 3 combine to provide
depositional diversity (marine sediments, glacial ice, lacustrine
silica and pollen, and loess) and geographic diversity (Northern
and Southern Hemispheres, and Atlantic and Pacific). The re-
cords are also diverse in their applicability, in that the Lake
Baikal silica record of Prokopenko et al. (2006) characterizes
substages of interglacial stages clearly, whereas the Chinese
loess record of Sun et al. (2006) conversely characterizes sub-
stages of glacial stages clearly. Nonetheless, using benthic
foraminiferal isotope records to define our scheme means that it
should substantially reflect global ice volume changes and
therefore be applicable across both hemispheres.
2) A scheme as consistent as possible with previous designations of
substages, so as to minimize conflict with the previous litera-
ture. This requires the following:
2a) Stages that end with a substage designated “a”, and earlier
substages are designated with the sequence of letters of the
Latin alphabet, consistent with the first lettered substages
defined by Shackleton (1969). This system precludes the
interposition of additional substages by later workers but
avoids the confusion that would be inherent in a system
with missing letters that were subsequently inserted
piecemeal.
2b) Substages that have been defined by their apparent paleo-
environmental significance, and therefore by human in-
spection. One might argue for a scheme in which substages,
and by necessity stages as well, were identified by a
mathematical or statistical algorithm, seemingly indepen-
dent of human judgment. Alternatively, one might argue for
a theoretical approach in which substages and stages were
defined according to Milankovi
c insolation cycles. However,
either approach would eliminate any continuity with the
previous literature, because MIS 5 would become MIS 3, as
discussed in Section 2.2, and MIS 5e would become MIS 3e if
not MIS 3c. With an algorithmic or theoretical approach, the
earlier substages of MIS 18 would likely become substages
of MIS 19, which would, with the elimination of present MIS
3 and 4, become MIS 17. Similarly, an algorithmic or theo-
retical approach would likely designate MIS 24 as a sub-
stage of one stage consisting of present Stages 23e25, all of
which would, with the elimination of present MIS 3 and 4,
become MIS 21 eand the result would be great confusion
between previous and future publications.
2c) Substages that are consistent with designations by previous
workers (Table 2) to the maximum extent possible.
3) Assignment of all intervals of time to stages and substages, in
accord with Fig. 1 of Emiliani (1955) and in contrast to the
schemes of Pisias et al. (1984) and Prell et al. (1986) for events.
4) Explicit divisions between, and thus definition of, each substage,
as shown for the stages of Fig. 1 of Emiliani (1955) and the
Fig. 2. Some examples of the contradictory designations of isotope substages used in the published literature from 1997 to 2015, as discussed in Section 3. Each gray box indicates
assignments from one system of one publication. Red highlights the earliest substage of MIS 6, for which five different designations have been used in the literature. (For inter-
pretation of the references to color in this figure legend, the reader is referred to the web version of this article.)
L.B. Railsback et al. / Quaternary Science Reviews 111 (2015) 94e106 99

3.0
3.5
4.0
4.5
5.0
5.5 2
3a
3b
3c
4
5a
5b
5c
5d
5e
6a
6b
6c
6d
6e
7a
7b
7c
7d
7e
8a
8b
8c
9a
9b
9c
9d
9e
10a
10b
10c
11a
11b
11c
11e
11d
12a
12b
12c
13a
13b
13c
14a
14b
14c
14d
15a
15b
15c
15d
15e
16a
16b
16c
17a
17b
17c
17d
17e
18a
18b
18c
18d
18e
19a
19b
19c
20a 20c
20d
b
21a
21b
21c
21e
21d
21f
21g
22
23a
23b
23c
24
25a
25c
25b
25d
25e
26
27
28a
28b
28c
29
1
0 50 100 150 200 250 300 350 400 450 500 550 600 650 700 750 800 850 900 950 1000 1050
III IIIA III IV VVI VII VIII IX XXI XII
18O (‰ vs. VPDB)
LR04 marine stack
7b
11a
11b
13a
13b
13c
15a
15b
15c
15d
15e
26
27 28b
28a
28c
29
Elderfield et al. (2012) ODP 1123 SW Pacific marine record
3.0
3.5
4.0
4.5
5.0
5.5
18O (‰ vs. VPDB)
2.0
2.5
3.0
3.5
4.0
4.5
5.0
18O (‰ vs. VPDB)
3a
3b
3c
14a
14b
14c
15a
15b
15c
15d
15e
Hodell et al. (2008) U1308 North Atlantic marine record
18a
18b
18c
18d
18e
20a
20c
b21a
b
21g
d
ce
f
Jouzel et al. (2007) EPICA Dome C
ice record using chronology of Veres
et al. (2013) and Bazin et al. (2013)
7b 9d
10a
10b
10c 11b
11c
11d
11e
12a
12b
12c
13a
13b
13c
15a
15b
15c
15d
15e
16a
16b
16c
D (‰ vs. VSMOW)
-440
-420
-400
-380
-360
0
10
20
30
40
% biogenic silica
0
20
40
60
80
100
% arboreal pollen
-0.2
0.0
0.2
0.4
0.6
0 50 100 150 200 250 300 350 400 450 500 550 600 650 700 750 800 850 900 950 1000 1050
6a 6e
7a
7b
7c
7d
7e
8a
8b
8c
9a
9b
9c
9d
9e 11c
11e
11a
13a
13b
13c
14a
14b
14c
17a 17c
17e
18a
18b
18c
18d
18e Prokopenko et al. (2006)
Lake Baikal record
25a
25c
25b
d
25e
26
27
28b
28a 28c
3a
3b
3c
7d 8a
8b
8c 10a
10b
10c
12a
12b
12c
13a 13c
18a
18b
18c
18d
18e Tzedakis et al.
(2006) Tenaghi Phillipon
pollen record, Greece
26
6a 6c
6e
7d 10a 12a
12b
12c
13a
13c
13b
16a
16b
16c Sun et al.(2006)
Chinese loess record
20a
22
24
26
29
Mean grain size of quartz
particles (normalized)
Thousands of years B.P.
Fig. 3. Proposed scheme of marine isotope substages for the last 1.0 million years, defined relative to the LR04 stack of marine benthic foraminiferal
d
18
O data of Lisiecki and Raymo
(2005). Horizontal bars indicate the length of each substage. Many substages come from the sources listed in Table 2. However, many papers only labeled a peak or trough on a time-
series diagram, with no indication of boundaries, and some papers only named the substage(s) in the text with no illustrative time series. The stages are taken from Shackleton and
Opdyke (1973), Ruddiman et al. (1989), and Lisiecki and Raymo (2005). Roman numerals indicate terminations (Broecker and van Donk, 1970) or transitions (Jouzel et al., 2007) from
glacial to interglacial stages, with Termination IIIA from Cheng et al. (2009). Six other time-series of data are shown to illustrate the relevance of the substages in those data. Criteria
used in constructing this scheme are discussed in Section 4.

substages of Fig. 1 of Shackleton (1969) but rarely shown in
subsequent publications.
5) No substages that are left unidentified (e.g., no “b”s left unused
or merely implicit between “a”s and “c”s), in contrast to many
designations of substages prior to MIS 5e.
Applying these goals has led us to the scheme of substages
shown in Fig. 3. No substages are designated for MIS 1 (the Ho-
locene), MIS 2, and MIS 4 for three reasons: they are all brief
stages, they are stages for which substages have never been
designated in marine records, and they are in the time interval in
which numbered Greenland Stadials and Greenland Interstadials
(Dansgaard et al., 1993; Eiríksson et al., 2000) are now widely
applied in recognizing substage-scale periods (e.g., Schulz et al.,
1998). For MIS 3, which is almost as long as MIS 1, 2 and 4 com-
bined, the three substages are those recognized by Carey et al.
(2005) in East Pacific Core V19-30 and by Wright et al. (2009) in
the North Atlantic, and they are similar to those of Wu et al. (2004)
in data from Tibetan ice. They are evident in LR04 and further
supported by the Tenaghi Philippon record of Tzedakis et al.
(2006). The five substages of MIS 5 shown are those of
Shackleton (1969), which he defined relative to a generalized
oxygen isotope record. The five substages of MIS 6, which were
first designated by Sun and An (2005), are easily recognized in the
LR04 record, and are further supported by the Chinese loess record
of Sun et al. (2006) (Fig. 3). The five substages of MIS 7 and 9,
which are easily recognized in LR04, are those designated by
Tzedakis et al. (1997). The three substages of MIS 8 are clearly
recognized in the LR04 record and further supported by the Lake
Baikal and Tenaghi Philippon records of Prokopenko et al. (2006)
and Tzedakis et al. (2006), respectively. The three substages of
MIS 10 are easily recognized in LR04, are strongly supported by
Antarctic ice and Tenaghi Philippon records in Fig. 3, and are in
accord with the MIS 10a, 10b, and 10c discussed but not illustrated
by Lundberg and McFarlane (2007). The substages of MIS 11 can be
recognized in LR04 and are strongly supported by the Antarctic
and Lake Baikal records. The three substages of MIS 12 are most
readily recognized in the marine record of Hodell et al. (2008). The
three stages of MIS 13 are readily evident in the marine records of
Fig. 3 and additionally supported by the Antarctic ice, Tenaghi
Philippon pollen, and Chinese loess records. The three substages of
MIS 14 are readily evident in the marine record of Hodell et al.
(2008). The five substages of MIS 15 first designated by
Khursevich et al. (2001) can be recognized in the LR04 record and
are also evident in the marine record of Hodell et al. (2008) and
the Antarctic ice record of Jouzel et al. (2007). The three substages
of MIS 16 first designated by Sun and An (2005) are recognizable
in the marine records of Hodell et al. (2008) and Fig. 2 of Naafs
et al. (2011), and they are further supported by the Antarctic ice
record of Jouzel et al. (2007) and the Chinese loess record of Sun
et al. (2006) (Fig. 3). The five stages of MIS 17 are evident in
LR04 and supported by the Lake Baikal record of Prokopenko et al.
(2006). The five substages of MIS 18 are evident in LR04 and the
marine record of Hodell et al. (2008), and they are supported by
the Lake Baikal record of Prokopenko et al. (2006). The three
substages of MIS 19 were first designated by Tzedakis et al.
(2012a,b) and can be recognized in LR04. The four substages of
MIS 20 are evident in the marine record of Hodell et al. (2008).
The seven substages of MIS 21 are evident in the marine records of
Hodell et al. (2008) and Fig. 2 of Naafs et al. (2011), and less clearly
but arguably in LR04. They also parallel the seven numbered
substages recognized by Ferretti et al. (2010). MIS 22, 24, 26, and
27 are sufficiently brief and invariant that there is little justifica-
tion for designating substages within them. On the other hand, the
three substages of MIS 23 and five substages of MIS 25 can be
recognized in LR04, and the latter are supported by the Lake Baikal
record of Prokopenko et al. (2006).
We have extended this scheme back 1.0 million years, and thus
to MIS 28, because marine isotope stages before that time are both
sufficiently short and their oxygen isotope data are sufficiently
uniform internally that substages seem unnecessary at the present
state of knowledge. Furthermore, UeTh dating has made detailed
chronologies possible over the last 550,000 years and thus has
necessitated substages back to MIS 14, but the use of substages
before MIS 14 will presumably be less extensive. The compilation of
usage in the literature shown in Table 1 suggests little applicability
of substages before MIS 20 at about 800 ka, further suggesting little
need to define substages before 1.0 million years ealthough it is
implicit that the scheme proposed herein could in the future be
extended further backwards if found desirable.
As isotopic records are further refined in the future, workers
may also find it useful to define shorter-term oscillations in the
marine record and thus to subdivide the marine isotope substages.
With regard to marine isotope records, one step in that direction
was taken by Bauch and Erlenkeuser (2008), who within MIS 5e
recognized one interval, MIS 5e-ss, where “ss”represented “sensu
stricto”. That interval may have been similar to the MIS 5e “plateau”
noted by Shackleton et al. (2003), which falls within the limits of
MIS 5e. However, neither designation was part of a larger system of
contiguous intervals within MIS substages, and the current state of
marine isotopic and other records may make any attempt at such
refinement premature now. Outside the realm of marine isotope
stages, but in parallel with their usage, Dansgaard et al. (1993) and
Greenland Ice Core Project (GRIP) Members (1993) recognized
subdivisions of MIS 5e that they designated “MIS 5e1 to 5e5”in the
GRIP
d
18
O record. For the marine isotope record, we recommend
the same scheme for labeling the subdivisions of substages.
5. The diversification of names and applications of stages,
and its implications
5.1. Diversification
In the mid-1980s, the “stages”of Arrhenius (1952),“core stages”
of Emiliani (1955, 1966), and then “isotope stages”of Shackleton
(1969) and Shackleton and Opdyke (1973) progressed to “
18
O
stages”and “
d
18
O stages”(Kukla, 1977) and “oxygen isotope stages”
(e.g., Prell et al., 1986) and “marine isotope stages”(e.g. Porter,
1987), and most thoroughly to “marine oxygen isotope stages”
(Scott et al., 1983). This was a progression toward greater specificity,
as is shown by Fig. 4. However, time-series of isotopic data from
marine sediments are so dominated by oxygen isotope data that
“marine isotope stage”and “marine oxygen isotope stage”are
nearly synonymous (Fig. 4), leading to the frequent and familiar use
of “Marine Isotope Stage”and thus “MIS”.
The material to which the terminology of marine isotope stages
has been applied has also evolved, in that stages that were defined
in oxygen isotope data from marine sediments have been used to
label intervals in time-series of very different parameters from very
different materials in very different settings. Examples include
“oxygen isotope stages”applied to time-series of
10
Be concentra-
tion data in Fig. 4 of Eisenhauer et al. (1994),“oxygen isotope
stages”applied to time-series of pollen data in Fig. 5 of
Seidenkrantz et al. (1996),“isotope stages”applied to time-series of
data about ice-rafted debris in Fig. 3 of Forsstr€
om (2001), and
“marine isotope stages”applied to time-series of
d
18
O data from
CaCO
3
of stalagmites in Fig. 1 of Wang et al. (2008) and to time-
series of deuterium concentrations in the EPICA Dome C ice core
in Antarctica in Fig. 4 of Hur et al. (2013). Even more strikingly, “MIS
5e1 to 5e5”were defined relative to an ice-core record, rather than a
L.B. Railsback et al. / Quaternary Science Reviews 111 (2015) 94e106 101

marine record (Greenland Ice Core Project (GRIP) Members, 1993,
their Fig. 2).
5.2. Implications for chronostratigraphy
The blurring of distinctions in materials and settings discussed
above can mask differences in timing that can result from different
time lags of different proxies, from different latitudinal settings,
and from locations in different ocean basins (Fig. 5). For example, a
transition defining the end of a substage or stage may progress in
time from a low-latitude marine sedimentary record to mid-
latitude stalagmite records (each with different time lags
imposed by different rates of groundwater movement) to a high-
latitude pollen record or an alpine ice-core record. Even within
one type of data, benthic foraminiferal
d
18
O records, Skinner and
Shackleton (2005) found a 4-kyr Atlantic lead over the Pacific for
the last deglaciation, caused by a local or basin-restricted compo-
nent of this signal. Hodell et al. (2013, their paragraph 50) have
pointed out similar lags in marine
d
18
O records. It follows that
numbered Quaternary stages (packages of sediment characterized
by data recovered from them) are less ages (intervals of time) than
facies (packages of sediment that may be deposited at slightly
different times in different places in response to moving sets of
depositional conditions and/or locally anomalous conditions)
(Table 1). Indeed, the International Stratigraphic Guide (Salvador,
1994, p. 10) would consider these isotopic stages as zones akin to
the range zones and assemblage zones of biostratigraphy or to the
polarity zones of magnetostratigraphy. If we were to start isotope
chronostratigraphy anew, as Wright et al. (2009) aspired when they
proposed the use of “marine isotope chron”and thus “MIC”as a
time term, we would call these units “marine isotope zones”
labeled “MIZ”ebut the desirability of nomenclatural stability
dictates continued use of the customary, if technically incorrect,
“marine isotope stage”.
Because of the possibility of time mismatches caused by dif-
ferences in kinds of data and by contrasting hydrographic settings,
some authors may have been wise when, for example, they chose to
call the MIS-like numbered intervals “climatic stages”when
applied to time-series of paleomagnetic data (Raffalli et al., 1996)
and to time-series of
d
D and dust data (Delmonte et al., 2004)
(Fig. 4). Even Cesare Emiliani himself referred to the isotopically-
defined intervals as “climatic stages”(Gartner and Emiliani, 1976).
A
B
C
Fig. 5. Three hypothetical sets of time series data illustrating chronological errors
possible in identifying stages (blue) or events (red) from time-series data of different
kinds, as discussed in Section 5.2. A and B combine to illustrate how differential time
lags can cause faulty correlations in time of both stages and events; B and C combine to
illustrate how difference in latitude or altitude can cause faulty correlations in time of
stage boundaries. Comparison of B and C also illustrates why the dating of termina-
tions may be more disputed than the dating of maxima or minima in some isotopic
curves, supporting the preference of Prell et al. (1986) for use of events, rather than
stages, for correlation to absolute time scales. The figure illustrates some aspects of the
argument by Gibbard (2013) that “isotope stratigraphy is not strictly a chronostratig-
raphy”. (For interpretation of the references to color in this figure legend, the reader is
referred to the web version of this article.)
Fig. 4. Euler diagram showing different kinds of time-series data and the kinds of
stages that would be identified from them, as discussed in Section 5.1.
L.B. Railsback et al. / Quaternary Science Reviews 111 (2015) 94e106102

His usage is a reminder that all numbered Quaternary stages,
whether identified in marine isotopic records, spelean isotopic re-
cords, pollen records, etc., have potentially diachronous transitions
controlled by individual responses to changing climate, and they
are therefore “climatic stages”in the climatostratigraphic para-
digm. Thus, to use the example in Fig. 5, our proposed scheme of
lettered substages (Fig. 3) attempts to eliminate confusion in the
literature between Substage na and Substage nc, but no such
scheme can eliminate the possibility that the transition from Sub-
stage nb to Substage na occurred at slightly different times in
different places and/or in different records.
6. Consideration of potential problems in application to
other records
The widespread designation of marine isotope substages dis-
cussed in Sections 2 and 3 suggests that the concept of substages is
applicable to many records, both marine and non-marine. One
might question how applicable this concept can be to discontin-
uous records from which some substages are missing, but exami-
nation of the Tianmen Cave (Cai et al., 2010) and Kesang Cave
(Cheng et al., 2012) spelean records demonstrates that substages
can be applied in radiometrically dated records with missing in-
tervals. The Tianmen Cave stalagmites from the Tibetan Plateau
were deposited over only about 30,000 of the last 120,000 years,
but U-series dates combined with changes in
d
18
O allowed clear
assignment of stalagmite intervals to Marine Isotope Substages 5a,
5c, and 5e (Cai et al., 2010). Similarly, the Kesang Cave stalagmites
from northwestern China were deposited over only about 80,00 0 of
the last 130,000 years, but U-series dates and variation in
d
18
O
allowed recognition of Marine Isotope Stages 1 and 3 and of Sub-
stages 5a, 5c, and 5e (Cheng et al., 2012). In this respect, it is
fortunate that speleothems, the paleoclimate records whose
sensitivity to climate change makes them most prone to hiatuses
(Railsback et al., 2013), are the records most readily dated by
radiometric methods.
One might also question whether antiphasing might cause
confusion in recognition of substages, in that a cold substage in one
hemisphere might be a warm substage in the other. However,
several considerations combine to suggest that antiphasing should
not be a major concern. First, our use of a benthic oxygen isotope
record to define substages means that the substages are largely a
function of changes in global ice volume (Shackleton, 2000;
Elderfield et al., 2012), which is inherently an interhemispherical
signal changing at time scales considerably greater than the mixing
time of the oceans (Broecker and Peng, 1982). Secondly, modeling
of changing ice volume suggests that, although antiphasing may
have been an issue prior to about 1 million years ago, it has not been
significant over the last million years (Raymo et al., 2006), although
it is acknowledged that the harmonics of precession are significant
features of some North Atlantic benthic oxygen isotope records
(Ferretti et al., 2010), raising issues of potential antiphasing. Thirdly,
the magnitude in offsets in DansgaardeOeschger events between
northern and southern polar regions of 200e400 years (Hinnov
et al., 2002) and in the bipolar see-saw with its offset of
150 0e3000 years (Blunier and Brook, 2001) is sufficient to cause
the sort of lags discussed in Section 5but not sufficient to cause
antiphasing of substages, given that our scheme of 94 substages
across 1.0 million years gives an average duration for substages of
more than 10 thousand years.
The arguments in the preceding paragraph apply mainly to
benthic marine records and to records from high-latitude accu-
mulations of ice. On the other hand, mid-latitude continental re-
cords and planktonic marine records may be more subject to
antiphasing that would complicate application of substages. In the
middle latitudes, fluctuations of continental climate are commonly
linked to monsoonal variations, and increases in northern or
southern hemisphere insolation can shift the Inter-Tropical
Convergence Zone to the north or south and lead to more exten-
sive monsoonal rainfall in the northern or southern hemispheres,
respectively (e.g., Janicot, 2009). For example, Partridge et al. (1997)
found an antiphase relationship in the North African and South
African monsoons at orbital (precession) time scales. These longer-
term antiphase relationships among various individual continental
records may further demonstrate the importance of defining global
substages relative to stacked marine benthic records.
7. Summary
Careful examination of the literature reveals that later Cenozoic
time has been identified by two alphanumeric systems arising from
the division of deep-sea sediment sequences, one identifying
contiguous intervals by the use of numbered stages divided into
lettered substages (Fig. 1B), and the other identifying non-
contiguous events by the use of decimal-style numbers
(Fig. 1CeE). However, because the lettering of substages other than
those of MIS 5 has never been formally defined, many conflicting
designations and systems have been used for substages over the
last twenty years (e.g., Fig. 2). We therefore propose one complete
scheme (Fig. 3), with no internal contradictions and as compatible
as possible with previous usage, for use henceforth in identifying
substages in time-series of isotopic, as well as other, data (Fig. 4).
This scheme, defined relative to the LR04 stack of marine benthic
oxygen isotope records, extends designation of substages back to
MIS 28, and thus back in time 1.0 million years.
Acknowledgments
The manuscript was improved by the comments of Dr. Alan G.
Smith of the Department of Earth Sciences of the University of
Cambridge and Dr. Kim Cohen of the Faculty of Geosciences of
Utrecht University. It benefited also from the advice of Dr. Jeroen
Groeneveld of the Department of Geosciences of the University of
Bremen, Dr. Youbin Sun of the Institute of Earth Environment of the
Chinese Academy of Sciences in Xian, Dr. Martin Melles of the
Faculty of Mathematics and Natural Sciences of the University of
Cologne, and Dr. Andreas Koutsodendris of the Institute of Earth
Sciences of Ruprecht-Karls-Universit€
at in Heidelberg. Professor
Polychronis Tzedakis of the Department of Geography of University
College, London, kindly provided the otherwise unavailable pollen
data for Tenaghi Philippon. The manuscript was greatly improved
by a review for QSR by Professor Lorraine Lisiecki of the University
of California at Santa Barbara.
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