Some comments on cliIllatic reconstructions froIll ice cores drilled in ...

Journal qfGlaciology, Vo!. 43, No. 143, 1997
<strong>Some</strong> <strong>comments</strong> on cliIllatic reconstructions froIll ice cores
drilled in areas of high Illelt
Roy M. KOERNER
Terrain Sciences Division, Geological SUTVey qfCanada, Ottawa, Ontario K1A OE8, Canada
ABSTRACT. Poor considerati on has been given in many Arctic circum-polar ice-core
studies to the effect of summer snow m elt on chemistry, stable-isotope concentrations and
time-scales. Many of these cores are drilled close to the firn line wh ere m elt is intense.
<strong>Some</strong> come from below the Grn line where accumulation is solely in the form of superimposed
ice. In all cases, seasonal signa ls are reduced or removed and, in some, time gaps
develop during periods of excessive m elting which situate the drill site in the ablation
zone. Consequently, cross correlations of assumed sy nchronous events among the cores
are invalid, so that time-scales along the same cores differ between authors by factors of
over 2. Many so-call ed climatic signals a re imaginary ra ther than real. By reference to
published a nalyses of cores from the superimposed ice zone on Devon Ice Cap (Koerner,
1970) and Meighen Ice Cap (Koerner a nd PatersOJ1, 1974), it is shown how m elt affects all
the normally well-es ta blished ice-core proxies and leads to their misinterpretation.
D espite these limitations, the cores can give valuable low-resolution records for all or
part of the Holocene. T hey show that the thermal maximum in the circum-polar Arctic
occurred in the early H olocene. This m aximum, effected negative balances o n all th e ice
caps and removed the smaller ones. Cooler conditions in the second half of the H olocene
have caused the rcgrowth of these sam e ice caps.
INTRODUCTION
M ajor contributions to the study of climate change h ave
been made over the past two decades by the study of ice
cores from the world's two great ice sheets of Greenland
a nd Anta rctica (e.g. D ansgaard and others, 1985, 1993;
Lorius and others, 1985; Barnola and others, 1987). These ice
sheets provide areas where there is positive balance and no
m elting. Consequently, continuous record s of climate
cha nge are preserved. Studies of cores from ice caps on
Spitsberge n (e.g. Gordienko and others, 1981; Punning a nd
Tyugu, 1991; Sin'kevich, 1992; Tarussov, 1992) the Severnaya
Zemlya archipelago (e.g. Kotlyakov a nd others, 1991) and
Meighen Ice Cap (e.g. Koerner and Paterson, 1974) in the
Canadian Arctic are less well known. With one exception,
these records are restricted to the Holocene peri od. H owever,
recognition of a climatic signal a nd development of
time-scales in some of these cores is difficult and, a t times
impossibl e, due to heavy summer melting and the presence
of time gaps in the record formed during long periods of
negative balance at the drill site. Unfortunately, m a ny of
these studies have not given due considerati on to the mode
of accumulation and melt at the drill-site locations and its
effect on the derivation of time-scales, or the interpretation
of ice-core chemi stry, ice texture and stable-isotope ratios in
the cores. Many of these problems h ave already been discussed
and published in work based on a core from M eighen
l ee Cap (Koerner, 1968; Paterson, 1968; Koerner and
others, 1973; Koerner a nd Paterson, 1974). I wish, therefore,
to re-address the problem of ice-core analysis in cores taken
from a reas of high melt la rgely by reference to that work.
Benson's (1959; see a lso Paterson, 1994) Grn-facies terms will
be used throughout.
DRILL-SIT E CHARACT ERISTICS
The location, elevation and surface cha racteristi cs of the
drill sites to be di sc ussed are shown in Table 1 and Figure I.
Published results from these cores are shown in Figures 2-4.
Apart from the results from M eighen and Agassiz Ice Caps,
the values plotted in the fig ures are derived from digitization
of published diagrams referred to in this tex t. Timescale
are those determi ned by the authors of the various
publications.
Canadian Arctic
Meighen Ice Cap is a small ice cap th at an ice core, drilled
in 1964, showed to have accumulated a lmost entirely
through the formation of superimposed ice (K oerner and
Paterson, 1974). Mass-ba lance measurements have bee n
made almost annually since 1959 and show a mean an nual
balance for the ice cap of - 13.2 g cm 2 a \. The same period
has effected a slightly negative balance of - 27 111m ice a - \ on
the dome where the ice core was drilled. \80 results from
this core are shown in Figure 5.
Six surface-to -bedrock cores have been drilled from
Agassiz Ice Cap in an area that li es within the percolation
zone. This paper uses the combined record of two cores
drilled at the LOp of the Ilowline in 1984 and 1987 as a reference
far climatic change (Koerner and Fi sher, 1990; Fisher
and Koerncr, 1994; Fisher and others, 1995) as the area does
not suffer the limitations for ice-core interpretati on discussed
in this paper.
Svalbard
The cores on Sva lbard have been drilled by the former Soviet
Union (3) and theJ apancse (1). TheJ apanese core is from the
90

Koerner: Climatic reconstructions from ice cores in areas qf high melt
Table 1. Melt (in parentheses, column 5) is the j)roduct if melt j)er cent and annual accumulation, nol halance. H owevel; annual
accumulation equals balance above theJirn line. The melt values are only directly comparable between the sites if the sites lie above
the saturation Line. Below this, run-wocCllrs, i.e. melt may exceed 100% ifmeLting extends into underlying annual layers. The Iwo
valuesjor balance on HfJghetta include the valuejor the last 20 years and (in parentheses) the valueJor the 1959- 63 period. The
latter is the one used to date the core; Fujii and others (1990) identified recurrent layers qf this thickness at depth and considered
them annual la)eTS . • Stiivenard and others (1996) believed the isotopic signature qf a 37- 60 cm layer if ice sandwiched between
Jro;::en sediments underlying a more recent Vavilov core rejJTesents Pleistocene ice. <strong>Some</strong>what contentious, it must at best represent ice
that may have survived the early Holocene by ils burial underj)rotective debris. The "trend"colwnn rifers to whether tlte trend in
either (j 18 0 or melt between 7 and 0.5 ka is significant
Site ELevation Ice depth klean (i'BO lee mel!/Huen! Balance nrn Pieis!ocene ice) Trend
/JffWlt
thickn ess
.,
ma.s. 1.
m o 7 ka gem - mmw.e. a m
Agassiz'
M eighcn 2 3
H oghctta
Fr/Gron'
Lomonsov S
Austfonna 6
Vav ilm,7
Akad. :\'auk'
1730
268
1200
450
1000
700
720
810
127
121
85.6
213
220
566
+67
761
27.1
21.2
- 11.3
- 1+.2
17.0
20.0
- 21.0
2.9 (6) 98 60 YeS Yes
100 (172) 0 0 :\'0 No
100 (200) 47 0 No No
(200)
750 + No )lo
820 27 30 1\0 )10
67 (532) 794 30+0 :':0 Yes
41 (205) 113 < 10 No' No
cl·7 (154) 315 Ycs Yes
I: Fisher and others, 1995; 2: Koerner and Paw'son, 1974; 3: Fuj ii a nd Olhcrs. 1990; 4 : Punning and 01 hers, 1980; 5: Gordicnko and others, 1981; 6: Tarussov, 1992;
Zagorodnov and Arkhipov. 1989; 7: K otl yako,' and olhers, 1991.
H oghetta ice dome on Spitsbergen (Fig. I). No direct measurements
of mass balance have been made in the vicinity of
the drill site but, as rhe ice core drilled from there consists
entirely of superimposed ice, the d rill site must lie within rhe
superimposed ice zo ne (FLUii and others, 1990).
The Soviet ice cores are from Vestfonna (Punning and
1)' ugu, 1991; Sin'kevich, 1992), Austfonna (Zagorodno\' and
A rkhipov, 1989; Ta rrusov, 1992), the ice divide between
G ro nfj ord a nd Frid tj ov Gl acie rs, w hich I will call the
GronG ord ice core (Punning a nd o thers, 1980) and Lo monosO\'
Ridge (Gordienko and others, 1981). While accumulati
o n rates are high, mel ting in summer soaks most or all of
th e a nnual layer (L omonosov, Vestfo nna and Austfonna ) or
occasiona ll y removes the annual layer (G ronG ord ). Thus,
the d rill sites are generally in the saturati on zone w he re
melt percolates deeper than the current annual layer and,
D
Fig. 1. D riLL sites rifened to in text. l. GRIP and GISP2; 2. Devon Ice Cap; 3. rlgassi;:: fee Cap; 4. Meighen Ice Caj); 5. Academii
Nauk; 6. Vavilov lee Caj); 7. H @ghetta, GrfJrifjord, Lomonosov; 8. Allsifonna, Vestfonna; 9. Penny lee Call; 10. Fran;::] osif.
91

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...................
Journal qfGlaciology
Balance near equilibrium line
50
40
30
~
'ca 20
ai 10
~ 0
E -10
E
-20
Q)
()
c -30
ca
(ij
-40
CD -50
-60
-70
-80
..................... , .. . ............ : ................... :
.... ..... .. ........ ~
. .
: . . . . . . . . . . . . .. . ..
: : r-----~----~-,
............ ..:.......... ......... ~ .. ...... .. .....; -- Devon 1050 m asl
.. .. ........... j .................( .. ..... .. .... : - Meighen 268 m asl
......... ~ ,.. ........... ~ ..............." .. ~ ............... ....: ...................,' , ..
. . .
.. .. .. ..........(........,..,...... -1 -' ................ ~ .....,............. ~ .. .. .... ......... ':' .. ...... ,........ ~ .. ......... .. .....
...........,..................:.. .... .... .... .....;........ ....... ...
60 65 70 75 80 85 90 95
Year
Fig. 2. Stable isotopes on a depth scale: Meighen Ice Cap ( Koerner and Patmon, 1974), Lomonosov ( Gordienko and others, 1981)
and GronJJord/ Fridtjqf ( Punning and others, 1980) ice cores. Values from the Soviet ice cores are from digitization cif the published
records. M eighen and GmnJJord data sll1jace to bedrock, Lomonosov suiface to 20 m above the bed.
in the case of Gr0nfjord, occasionally in the abl ation zone.
Stable-i so tope d ata from the G ronfj ord and Lo m onosov
cores a re shown in Figure 2 and melt from Austfo nna is
shown in Figure 4.
Severnaya Z ernlya
The Severnaya Zemlya archipelago has been the centre of
deep drilling by the former Soviet Uni on since 1975 (Kotlyakov
a nd others, 1991). Six boreholes on the Vavilov ice
dome (460- 557 m ) and one on Academii Nauk ice dome
(AN ) (761 m ) have been drilled to bedrock. Both ice caps
ri se above the firn line (Kotlyakov a nd others, 1991; Barkov
and others, 1992) but the accumulati on undergoes substantial
summer melt. The to ps of both ice caps probabl y li e
within the saturation zone as the AN ice core consists, on
average, of 42% melt ice and Vavilov ice core (from Kotlya-
J
0
co
re
Stable Isotopes, Svalbard, Arctic Canada
-5
,
-7 ................ .... ..
-9
-11 ... ;.
-13
-15
-1 7
-19
-21
-23 ......... ;.. . .. ,: ..
-25
o 40 80 120 160 200 240
Depth (m)
Fig. 3. Stable isotopes, Academii Nauk, Vavilov ( Kotlyakov
and others, 1991) and Agassiz ( Fisher and others, 1983) Ice
Caps. Valuesfol' Academii Nauk and Vavilov al'eJrom digitization
cif the published diagrams. R un -won Vavilov ( B al'kov
and others, 1992) has probably afficted this record.
kov a nd others, 1991) 48% melt ice. M elt-ice percentage a nd
stab le-isotope data from Soviet cores a re shown in Figures
2- 4.
EFFECTS OF MELT ON ICE-CORE ANALYSIS
Stable is otopes
Sta ble iso topes (6 18 0 , 6D ) are used as proxy tem perature
indicators in ice-cor e a nalyses. The tra nsfer functi on (6/
tempe rature) is based on empirical rela tionships drawn
from globally distributed data (D a nsgaard and others,
1973)_ The most impo rtant effect is tha t of cooling of the
water vapour as it moves from its ocean source to the locati
o n where it condenses close to the ice-core site. While limitations
of the transfer function have been well disc ussed in
terms of ice cores from above th e percolati on line (Paterson,
1994), they are less well known for ice cores fro m a reas of
very heavy melt. The most important (a nd additiona l to
those th at apply above the percolatio n line) have been discussed
by Koerner a nd others (1973) a nd are as foll ows.
L
E a rly summer melt will cause melting of the very negative
(cold )-6 winter/spring snow which lies near the surface.
The meltwa ter then percola tes down to refreeze
within, or at the base of, th e current annual snowpack.
Further melt may cause run-o fT of less negati ve (wa r­
m er)-8 snow deposited during the early winter/fall period.
A very negative (cold)-8 snowpack remains.
2. L a te summer melt will cause m elting of surface snow
depo ited during the early summer period. This m ay
p ercolate and refreeze in the annua l snowpack. The early
spring/winter snow is then ex posed at the surface a nd
further melting m ay cause this snow to leave the ice cap
as run-off. A less negative (wa rme r )-6 snow pack renla
ms.
3. Cool summers, with very little melt but accumulati on of
summer snow, will add a layer ofless negative warmer-6
snow at the surface. This will give a disproportionately
wa rm 8 value fo r the annual layer.
92

Koemer: Climatic reconstructionsJrom ice cores in areas rifhigh melt
-20
-22
-24
~ -26
0 -28
Cl)
?o -30
-32
-34
-36
-38
-17
~
Cl)
o
f
-25
0 2 4 6
Years before present (x 1000)
8 10 12
Fig. 4. Melt recordforAcademii Nauk ( Kotlyakov and others, 1991) Ausifonna ( "lCLrllSSOV, 1992) and Agassiz lee Caps ( Koemer
and Fis/w; 1990). AI/el! expressed as gem 2 a I based on accumulation mtes alld melt jJelu ntages jmblished by the authors and, ill
the case if Academii Nauk, and Ausifonna, digitizedJrom the published diagram. Time-scales are those if the authoTS. In the case
qf Ausifonna, both a theoretical and stratigraj)hic time-scale aregiven (.:(agorodnov and Arkhij)ov, 1989). I lIse the theoretical that
gives the bed an age rif 6000- 7000 )lears. The stratigraphic gives a basal ice age qf 3000 4000 )Iears.
4. M elting of the snow cover and subsequent percolation
through rec rystallizing snow causes isotopic fractionation
a nd enrichment in 18 0 of the soli d phase at the exp
ense of the meltwater (Arnason, 1969).
Chemistry and wind-blown dust
Melting causes leaching of ions in the snowpaek. T his postdepositional
eHect homogeni zes the snow chemistry, thereby
red ucing the seasonal variations often use d to detect
annua l layering and to date the core. Furthermore, J ohannesse
n a nd others (1977), J ohan nessen a nd H enriksen
(1978), Goto-Az uma a nd others (1993) a nd Gj ess ing and
othe rs (1993) among others have shown that so me ions,
such as sulphates, are preferentially leached from th e sno"v.
This means that, ifmcltwater leave the drill site, the melt-
')'
E
u
Cl
~
::E
')'
E
u
Cl
~
::E
90
r
80
70
60
50
40 -l"
25
20
15
10
Melt
Austfonna
.......... ...... __....
..... ... .... .............
.... ........ ....•.. ...
Academii Nauk
5 ... .. ........... ! .......... ....... !.... ·· ·· ······ ... i-
0 .. - . .. .. ...:.
o 2000 4000 6000 8000 10000 12000
Years before present
Fig. 5. Annual mass balance at the drill site on j\!/eighen Ice
Cal) and at a Slake sitl/ated close to the equilibrium line on the
northwest side if Devon Ice Cap.
water is su Ipha te-enriched a nd the remaining ice co re is
sulphate-depleted . We have found in work on Canadia n
High Arctic ice caps tha t, whi le chlorides are much less
affected than sulphates by th is process, intense melting will
alter th e position and/or a mplitude of chl oride spring peaks
to rende r them unusable fo r recogni zing a nnual laye rs;
some investi gators have relied on the seasonal variations of
chlorides to date cores (e.g. Punning and Tyug u, 1991). High­
Iyacid laycrs, formed from distant volcanic eruptions a nd
used lo cl a te ice co res drilled from above the p ercolation
li ne (Fi sher a nd oth er , 1983), may also be a lte red ufficientl
y in m agnitude to ma ke them unusable fo r dating purposes
(Fujii a nd others, 1990).
Insolub le micropanicles te nd to coll ect at a melting
surface. \lVith melting this produces a small peak in conce
ntratio n s (K oerner, 1977). H owever, none of the core
analyses cl iscussecl here expl oits the use of microparticles
for dating purposes. [n . ome cases, this was clue to a lack
of adequa lc equipment (e.g. a Coulter counte r ) and in
others (e.g. M eighen Ice Cap) because melting and ru n­
off removecl the seasona l cycles. Small er ice caps a re also
likely to receive high inputs of wind-blown dust from the
surrou ndi ng ice-free terrai n. Th is is particul a rl y true during
winters of very low snow accumulation. <strong>Some</strong> of these
particles may be soluble a nd wi ll affec t the ice chemistry
during summer melt. Part of the increasing pH/time
trend in the H oghetta core (FlU ii and others, 1990) may be
attributable to a n increased input of buffering wind-blown
dust with inc reasing depth. K oerner and Paterson (1974)
related dust-layer concentrations in the M eig hen core to
the chang i ng size of the ice cap. Expan ion of the ice cap,
for exam plc by loweri ng of the fi rn line to ice-free grou nd
beyond the ice-cap margins, increases the drill site-to-dust
source dista nce; dirt-Iaye,- concentrati on in the core then
dec reases (Fig. 5; Koerner, 1968). Thus, reduction of dust
concentrations may be a reOecti on of increased g lacieri zation
of the surrounding land.
The melt-layer transfer function and ice texture
The distribution of melt layers and the variations of ice tex-
93

Journal qfGlaciology
ture in ice cores can be u sed as summe r-temperature
proxies. The cl im ate-related transfer functi on depends, in
the case of ice layers, on wa rmer summers causing a higher
percentage of mclt ice in the a nnual layer. The transfer function
is dependent on empirical relati on hips found in the
a rea of investi gati on. Fo r exampl e, K oerner and Fi she r
(1990) used an ice per cent/elevati on/temperature relationship
in the Canadi an High Arctic ice caps (Koerner, 1977)
to calculate a 2°C temper ature change in the Holocene
from the changing melt percentage in the Agassiz cores.
The transfer functi on has two thres holds. The upper threshold
is crossed when the zone of superimposed ice extends
into the drill-site a rea. In this zo ne, all summers causing
comple te melting of the annua l snow layer will leave a
100 % melt-i ce section, whether run-o ff occurs or not. A
summer with much Hill-off will be warmer than one with
little or none. However, the ice-core record will show a fl at,
100 % melt-ice record, regardless of how much run-off occurred.
The lower threshold is crossed when the clima te
causes the dry-snow line to drop below the drill site. In this
case, no melt layers are formed and there is no melt record.
Both situations can be seen in two of the cores presented
here; they will be disc ussed later. In fact, Alley and Anandakrishnan
(1995) have extended this technique to dry-snow
areas. By very careful examinati on of the GRIP Gree nland
core, they have developed a m elt record from a core with a n
average of only one 2- 3 mm thick ice laye r every 200 years!
Such a study demand a ver y hi gh-quality ice core but extends
the applicability of the method.
In the second case, i. e. in the zone of superimposed ice,
where there is 100 % melt ice (Meighen a nd H0ghetta ), a
cli mate transfer fun cti on has to be developed from ice-tex ture
changes and is useable in only very genera l terms. The tra nsfer
function is based on the dependency of g rain-size in the
newly forming ice, on the degree of meltwater saturati on of
the snow cover and the temperature of the winterlspring
snowpack a nd underlying ice during the early stages of
melting (Koerner, 1970; see a lso Waka ha m a and others,
1976). At one end of the sp ectrum, meltwater standing o n
the surface at the end of the melt season freezes slowly to
form very coarse-grained ice. At the other end of th e sam e
spectrum, incompletely saturated snow forms fin e-grained ,
bubbly, ice. On Devon Ice Cap, there is a gradual transition
in the superimposed ice zone, from fine-g rained, bubbly ice
just below the firn line to coarser-grained, clear ice just
above the equilibrium line (K oerner, 1970). This cha nge is
related to the summer temperature/eleva ti on rel ati onship.
A simple ice-core model, based on this relati onship equa tes
fin e-g rained bubbly ice with cold summers a nd coarse, clear
ice with warmer summers. H owever, the warmest summers
a re unrepresented as a negati ve balance removes all or part
of the a nnual accumulation. The transfer function therefore
has limited applicati on.
By similar processes, g ra in-size/bubble-concentra tion
vari ations at one site each year may produce recognizable
a nnual layers in the superimposed ice zone. These layers
have been studied on Vestfonna by Palosuo (1987) and used
by J onsson and H ansson (1990), toge ther with chemi cal and
mic ro pa rticle sig natures, to d ate a sh a llow core from
Storoya ice cap (a sm all island off the east coast of Nord­
Austlandet). The latter is the only work I a m aware of that
has made a careful study of annual layering in superimposed
ice and applied it to the development of a ti mc-scale
in the superimposed ice zone. H owever, co ntinuous suites of
recognizable annual laye rs through periods of past climatic
warming must be uncommon at sites now situated near the
urn line. Any peri od of wa rmer clim ate will c reate a sequence
with seasons and/or complete annua l layers mi ssing.
Furthermore, if at any time during the history of the
ice cap, the firn line com es close to the drill site, melting
will also add a layer of ice to the continuous ice under the
firn (6 m dep th on the northwest side of D evon Ice Cap
(Koerner, 1966)). In this se nse, the resolution of core sections
deposited just above the firn line can never be better
than about 6 m .
Koerner a nd Paterson (1974), although unabl e to detect
continuous sequences of annua l layers, made quantitati ve
measurem ents of bubble concentrati ons in the Meighen
core to draw inferences about climatic and slope changes at
the drill site. For example, the bubbly, fin e-gra i ned ice texture
of secti ons of the ice core 22- 44 m from the surface suggested
they formed during years with very cold summers.
They were attributed to the Little Ice Age, despite stableisotope
val ues that were less negati ve than the enclosing
ice. Other studies have used qualitativcly rather than quantitative
ly derived measure m e nts of ice texture to detect
climate sign als (e.g. Kotlyakov and others, 1991).
High variability of the accumulation rate
"Vhile the snow-accumulatio n rate may not var y much close
to the firn line, th e speciuc m ass balance does, due to fluclUati
ons in the melt rate each summer. The 1961- 93 massbalance
records taken close to the mean equilibrium line
on Devon a nd Meighen Ice Caps illustrate this (Fig. 5).
O ver the sam e period, the a nnual equilibrium line on Devon
Ice Cap has moved b etween 1500 m a.s. l. (above the
urn line) in 1962 and 1000 m.
Any site located within this ra nge, including those in the
lower reaches of the firn zone, will have exp erienced years
of accumulation by superimposed ice or firn, a nd yea rs of
mass loss. This means tha t som e of the drill si tes cited in
Table 1 will include c1iscontinuities, or time gaps.
TIME-SCALES AND DISCONTINUITIES
The main problems facing the derivati on of time-scales in
cores drilled cl ose to the firn line may be summarized as
follows:
1. Gaps in the reco rd produced during periods of negative
balance a nd the high variability of the drill-site annual
mass bala nce limit the use of flow modcls (e.g. Nye, 1960)
and make detail ed cross-correlation between cores highly
cO I!i ectural (e.g. Punning and oth ers, 1980; Kotlyakov
and others, 1991).
2. Detection of seasonal variations of ions, microparticles
and sta ble isotopes b ecom es conj ectura l due to the effects
of p ercolating m eltwater (e.g. G ordienko a nd
others, 1981; Punning a ncl Tyugu, 1991).
3. Cross-correlation of volca nic events with the well-dated
Greenl a nd cores (H ammer, 1983; H ammer a nd others,
1985) is frustrated by m eltwater alteration of the original
signal strength of these events (e.g. Fujii and others,
1990).
94

Koem er: Climatic reconstrllctionsJrom ice cores in areas (J/ Iziglz meLt
Koerner and Paterso n (1974, fi g. 2) drew attention to proba
bl e time gaps in the Meighen core and did not develop an
overall time-scale. However, a general lack of understanding
of the significance of time gaps in ice cores is common
in some of the other studies. :1"or exa mple, }

JournaloJGlaciology
light of the melt and (iISO profiles from Agassiz, Academii
Nauk and Austfonna Ice Caps (Figs 4 and 5) which show
warmer conditions than present during the first half of the
Holocene. It means that very n egative bala nces ex isted
throughout the first half of the Holocene in the ci rcum-polar
region. This was the period that saw the fin al demise of the
great Pleistocene ice sheets. I would suggest that highly negative
balances removed not only the great ice sheets but also
many small ice caps in the circum-polar region in the early
Holocene. This would explain the absence of Pleistocene ice
in most of the records discussed in this paper (see l ilble I).
There is other work which lends support to this argum
ent. Li ch e nometric a nd lake-sediment analyses by
'''!erner (1988) in the west Spitsbergen area are strongly supportive
of late Holocene glacier regrowth in that region.
Similarly, Bradley's (1990) synthesis of palaeoclimate studies
in the Canadian High Arctie also presents a st rong
body of evidence for late Holocene cooling in that region.
Kotlyakov and others (1991) cited evidence for restricted
ice-cap extent in the Severnaya Zemlya region in the early
Holocene, although they extend ed this period back into the
late glacial as well.
CONCLUSIONS
Ice cores drilled in areas of hig h melt req uire g reat caution
wh en attempting to derive pa laeoclimatic information from
them. Because melting can introduce time gaps and remove
good seasonal signals, time-scales can be difficu lt or impossible
to evaluate. However, I should stress tha t techniques
for core analysis have improved enorm ously since many of
these cores were studied. IlTlproved detection limits of ionanalysis
equipment, the use of modern microparticle CO LII1-
ters and also of the solid electrical conductivity method associated
with continuous pH, liquid conductivity and laser!
microparticle measurements (originally discussed by Hammer
(1980); H a mmer, 1983) could make the study of new
cores from some of these areas a n importa nt addition to
the stud y of cl imatic change in the circum-polar area. The
exceptiona lly careful work of Alley and Anandakrishnan
(1995) has also shown that the "cold threshold" of melt-layer
anal ysis can be pushed further down th e temperature scale
to include high-elevation Greenland cores, thereby providing
further opportunities for cross-correlation with absolutely
dated cores from that area.
ACKNOWLEDGEMENTS
I should like to thank two anonymous reviewers and B. Lefauconnier
10r very thorough reviews of the m a nuscript.
Their suggestions have substa ntiall y improved the paper.
This is Geological Survey o f Canada contribution No.
43895.
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