www.elsevier.com/locate/gloplacha

Global and Planetary Chan

Differential dissolution of Lake Baikal diatoms: correction factors

and implications for palaeoclimatic reconstruction

Richard W. Battarbeea,*, A.W. Mackaya, D.H. Jewsonb, D.B. Ryvesa,c, M. Sturmd

aEnvironmental Change Research Centre, Department of Geography, University College London, 26 Bedford Way, London WC1H 0AP, UKb96, Desertmartin Road, Magherafelt, County Derry, BT45 5HE, Northern Ireland, UKcDepartment of Geography, Loughborough University, Loughborough, LE11 3TU, UK

dSedimentology Section/Surface Waters, EAWAG, Uberlandstrasse 133, CH-8600 Dubendorf, Switzerland

Abstract

In order to assess how faithfully the composition of diatom assemblages in the recent sediments of Lake Baikal represents

the composition of the planktonic diatom populations in the lake, we have compared the flux of diatoms from the water column

(i.e., bexpectedQ in the sediment) with the accumulation rates of the same diatom taxa (i.e., bobservedQ in the sediment) from

BAIK 38, a sediment core collected in the south basin of the lake. Whilst there are many uncertainties, the results indicate that

only approximately 1% of the phytoplankton crop is preserved in the sediment and some species are more affected by

dissolution than others. These findings are comparable to similar studies undertaken in the marine environment. In terms of

differential dissolution, our studies suggest that the endemic taxa (e.g., Cyclotella minuta and Aulacoseira baicalensis) are the

most resilient, whereas cosmopolitan taxa such as Nitzschia acicularis and Synedra acus are the least resilient. N. acicularis

dissolves in the water column, but for other taxa, most dissolution takes place at the surface sediment–water interface. We use

the data to develop a series of species-specific correction factors that allow the composition of the source populations to be

reconstituted, and we argue that failure to take these processes into account can undermine the use of the diatom and biogenic

silica record in Lake Baikal for palaeo-productivity and palaeoclimate reconstruction.

D 2004 Elsevier B.V. All rights reserved.

Keywords: Lake Baikal; Planktonic diatoms; Diatom dissolution; Palaeoclimate reconstruction

1. Introduction

The sediments of Lake Baikal contain a diatom

archive useful for assessing changes in water quality

(Mackay et al., 1998), tracing the evolution of the lake’s

0921-8181/$ - see front matter D 2004 Elsevier B.V. All rights reserved.

doi:10.1016/j.gloplacha.2004.11.007

* Corresponding author. Tel.: +44 20 7679 7582; fax: +44 20

7679 7565.

E-mail address: r.battarbee@ucl.ac.uk (R.W. Battarbee).

endemic biota (Khursevich et al., 2001), reconstructing

the history of the lake (cf. Bradbury et al., 1994) and

reconstructing past climate change both on Holocene

(Qui et al., 1993; Karabanov et al., 2000; Mackay et al.,

2005-this issue) and Pleistocene time-scales (Colman

et al., 1995; Edlund and Stoermer, 2000; Rioual et al.,

2005-this issue; Swann et al., 2005-this issue).

The potential of the record for Holocene climate

change studies is especially important as for most of

ge 46 (2005) 75–86

R.W. Battarbee et al. / Global and Planetary Change 46 (2005) 75–8676

this period diatom assemblages consist of taxa that

still occur in the lake at the present day. It is

consequently possible to develop a detailed under-

standing of their ecology and life-cycle strategies with

respect to the physical environment that potentially

enhances their use as indicators of climate change in

the past (cf. Bradbury et al., 1994). Recent studies of

the main taxa both in culture (e.g., Richardson et al.,

2000; Jewson unpublished, but see Mackay et al.,

2000, for summary results) and in the lake water

column (Granin et al., 2000; Verkhozina et al., 2000)

show how water temperature, ice cover, snow cover

on the ice and thermal stratification exert controlling

influences on the life-cycle strategies of these mainly

endemic taxa.

Accurate reconstruction, however, also depends on

an understanding of taphonomic (i.e., what happens,

in this case to the diatoms, from their death, burial and

subsequent recovery) and sedimentological processes,

in particular the extent to which the sediment record

faithfully records variations in diatom populations and

the degree to which the sediment record is impaired

by problems such as the presence of turbidites and

discontinuities, which in Lake Baikal are well known

(e.g., Nelson et al., 1995). Of importance here is the

ability to detect such sediment accumulation anoma-

lies before diatom interpretations are undertaken

(Mackay et al., 1998).

The critical issue considered here, therefore, is the

problem of differential diatom preservation and the

extent to which it might bias environmental, espe-

cially climate, reconstructions (cf. Mackay et al.,

2003, 2005-this issue). From sediment trap studies,

Ryves et al. (2003) have already shown that some

frustule dissolution, e.g., for the most fragile taxa such

as Nitzschia acicularis W. Smith and Synedra acus

(Kutz.) Hustedt, takes place in the water column, and

that further dissolution of more robust taxa occurs at

the surface sediment–water interface. Intriguingly,

levels of dissolution were comparable to those found

in marine environments. For example, Ryves et al.

(2003) suggest that only about 1% of valves are

finally preserved in the Lake Baikal sedimentary

record, with most dissolution occurring at the surface

sediment–water interface. This value is similar to a

recent study, which sought to make a re-assessment of

the silica balance in the world’s oceans (Treguer et al.,

1995). A global average of c. 3% preservation was

determined, although this figure hides spatial varia-

bility, which ranges from almost 24% in the Southern

Ocean, with almost no preservation in sub-tropical

regions (Treguer et al., 1995). In another study, Kato

et al. (2003) looked at the transport of planktonic

diatoms through the water column in Omura Bay,

western Japan ad found that only c. 3% valves were

preserved, whilst in the Atlantic Ocean, only c. 1%

valves were found to make it into the sedimentary

record (Treppke et al., 1996). Both these latter two

studies also reported differential dissolution between

taxa, with lightly valves species being affected to a

much greater degree than more heavily silicified

valves. These observations are therefore especially

important in a palaeoclimate context, as they suggest

bias will occur in reconstructions.

Given the importance of the location of Lake

Baikal for palaeoclimate reconstructions, i.e., its mid

continental setting, far from oceanic influences, here,

we have attempted to quantify dissolution losses both

for the total diatom crop and for individual taxa by

comparing diatom fluxes through the water column

with diatom accumulation rates (DAR) in recent

sediments. We take the premise that these values

should be equal if there is no dissolution, sediment

focussing or resuspension. The observed difference

between the expected and observed fluxes can then in

theory be used to derive a series of correction factors

for each taxon to calculate the probable composition

of the source population.

2. Sites and methods

For the purpose of this study, we have used mainly

existing data sets both for water column phytoplankton

sampling and for sediment cores. The phytoplankton

samples were collected monthly in the southern basin

of Lake Baikal at three sites along a transect between

Lystvyanka and Tanhoi (Fig. 1) between 1994 and

1998. Samples were collected from water depths of 0,

5, 10, 15, 25, 50, 100, 150, 250, 500, 750, 1000 and

1200 m. The data used in this study were from the

central location on the transect, close to a sediment trap

array (water depth=1390m; Fig. 1) (Ryves et al., 2003).

The sediment cores were collected at a number of sites

throughout the lake during various expeditions

between 1992 and 1994 (see Table 1 in Mackay et

Fig. 1. Map of Lake Baikal showing location of cores, sediment trap array and plankton sampling location.

R.W. Battarbee et al. / Global and Planetary Change 46 (2005) 75–86 77

al., 1998 for full location details). In this study, we used

data from BAIK 38 (51834V06WN; 104831V43WE), acore collected from a 690-m-deep site in the south

basin, relatively close to both the phytoplankton

sampling sites and the sediment trap array (cf. Ryves

et al., 2003). Diatom accumulation rates from a series

of other cores (BAIK 19, 22, 25 and 29), collected

throughout the lake (Fig. 1), have also been used for

comparison. In calculating the bexpectedQ flux of

diatoms to the sediment, we have used annual maxima

cell counts for each taxa. The bobservedQ diatom

accumulation rates are taken from data of Mackay et

al. (1998). For details of sediment coring, dating and

diatom counting methods, see Appleby et al. (1998)

and Mackay et al. (1998). Finally, we have also

attempted to estimate errors for the derived correction

factors of the five main plankton species, based on

Maher’s (1972) nomogram equations.

R.W. Battarbee et al. / Global and Planetary Change 46 (2005) 75–8678

3. Results

3.1. Observed versus expected fluxes

3.1.1. Expected flux—water column phytoplankton

The flux of diatoms to the sediments has been

estimated from phytoplankton populations sampled on

a monthly basis from 1994 to 1998. Although some

losses occur by sedimentation and grazing through the

year, these are thought to be relatively small (Ryves et

Fig. 2. Phytoplankton counts (cells) per square meter (thousands) plotted

scales.

al., 2003). The annual fluxes of each species to the

sediment are then assumed to correspond to the

respective peaks of each phytoplankton crop through

the year (Fig. 2) and are also assumed to be

representative of populations throughout the south

basin. Table 1 shows these data expressed in terms of

valves per square centimeter for each species for each

of the 5 years and in total.

The data (Fig. 2) show that there were very large

year to year variations in species abundance both

on a log scale against year of sampling. Note differences in y-axis

Table 1

Diatom phytoplankton crop maxima for 1994–1998 (cells cm�2)

A. skvortzowii A. baicalensis C. minuta Stephanodiscus meyerii S. acus v. radians N. acicularis Total

1998 6345 31572 230236 0 465593 36178 826021

1997 8060791 5277069 200600 53167 2955977 2053 16621949

1996 514791 121314 840000 3631803 15283388 15190 20411422

1995 51447 56926 523653 1724701 19618 17304358 19683940

1994 605966 1389636 133249 377367 4834 50968 2565829

R.W. Battarbee et al. / Global and Planetary Change 46 (2005) 75–86 79

between species and in total, with 1994 dominated by

Aulacoseira baicalensis (Meyer) (Simonsen), 1995

dominated by Nitschia acicularis, 1996 by Synedra

acus, 1997 by A. baicalensis and 1998 again by S.

acus. These major inter-annual fluctuations in species

composition are well known for Lake Baikal (e.g.,

Rychkov et al., 1989; Bondarenko, 1999; Popov-

skaya, 2000), and probably are responses to inter-

annual variations in weather patterns and zooplankton

grazing. Indeed, Popovskaya (2000) specifically links

the shift of cold-water endemic diatoms to cosmopol-

itan taxa more tolerant of warmer waters (in recent

decades) to the trend towards global warming and

consequent effects on ice formation and break-up,

movement of water masses and nutrient recycling in

the lake.

Our previous work (Ryves et al., 2003) has

shown that diatom phytoplankton populations sedi-

ment rapidly through the water column towards the

sediment surface. Except for Nitschia acicularis,

which quite clearly dissolves in the water column,

and to some extent Synedra acus which partially

dissolves in the water column (Ryves et al., 2003)

almost all the populations are quantitatively

recorded in the bottom sediment traps only weeks

after their population maxima in the upper water

column. In 1997, the Aulacoseira baicalensis

bloom was recorded in the upper (c. 550 m) and

lower (c. 1300 m) sequencing traps implying

sedimentation rates of between at least 64 and

100 m day�1.

Unfortunately, due to bioturbation, the bottom

sediments do not retain the structure of the seasonal

and annual fluxes recorded by the traps. Even the

Table 2

Diatom accumulation rates for the surface sediment of core BAIK 38 (no

B38 A. skvortzowii A. baicalensis C. minuta S.

1994 12942 38038 35562 32

cores with the most rapid sediment accumulation, and

that are sampled at high resolution (2 mm) show little

short time-scale variability, suggesting that these input

diatom fluxes are effectively mixed at the sediment

surface either from bioturbation or from resuspension.

However, we should mention here recent work by

Boes et al. (2005-this issue) who do demonstrate

variations in the grey scale of Lake Baikal sediments

at 20 Am resolution, which they suggest is indicative

of regional climate changes with a pluriannual

resolution. To assess the extent of dissolution by

comparison between the plankton flux and the sedi-

ment diatom accumulation rate it is necessary there-

fore to smooth the plankton data. Table 1 shows

averages for the total and for each taxon for the full 5-

year record as well as data for each year.

3.1.2. Observed flux—DAR in the sediment

The accumulation rates for both the total and the

five dominant planktonic diatoms for the surface

sediment sample of BAIK 38 are shown in Table 2,

whilst Table 3 shows total diatom accumulation rates

for a range of other cores for which data are available

(Mackay et al., 1998) (with BAIK 38 for comparison).

The procedure for calculating DAR for individual

cores for recent sediments, i.e., those that can be dated

by 210Pb dating is quite accurate (cf. Appleby et al.,

1998; Battarbee et al., 2001). However, the extent to

which the DAR in any one core might be expected to

record accurately the input fluxes from the water

column directly above the coring site depends on a

number of factors including the intensity of sediment

focussing in the lake and processes responsible for

lateral movement of sediments. Table 3 illustrates

. cm�2 year�1)

meyerii S. acus v. radians N. acicularis Total

64 5514 0 112540

Table 3

Surface sediment diatom accumulation rates for five cores from

Lake Baikal (from Mackay et al., 1998)

Core code Location Water

depth (m)

Average

DAR

BAIK 19 Buguldieka Saddle 342 118411

BAIK 22 Middle basin 1624 824132

BAIK 25 Academician Ridge 307 181689

BAIK 29 North basin 910 17752

BAIK 38 South basin 690 112540

See Fig. 1 for locations.

R.W. Battarbee et al. / Global and Planetary Change 46 (2005) 75–8680

there is some spatial variability among cores, which

may be partly explained by comparing core locations,

their different water depths and different sedimento-

logical provinces, whilst Ryves et al. (2003) found

little evidence of large scale resuspension close to the

lake bottom.

BAIK 19 is taken from the Bugyldieka Saddle, an

intra-basin high (water depth 342 m) opposite the

shallow waters of the Selenga Delta, whilst BAIK 38

was taken from an isolated elevated plateau in the

south basin (water depth 690 m). Charlet et al. (2005-

this issue) outline how these isolated highs may prove

to be the best coring locations, as they are far from

fluvial input and isolated from bottom water currents

(a major source of turbidites in Lake Baikal). BAIK

22, on the other hand, was extracted from basin floor

in the middle basin, a region prone to turbidite activity

(Vologina et al., 2003). Therefore, whilst BAIK 22 has

the highest DAR values, Appleby et al. (1998)

determined that this core has an unusual sedimentary

sequence, with several non-monotonic features in the

upper layers. It is likely therefore that the rapid

accumulation seen at this location is most probably

due to turbidite currents (Mackay et al., 1998). BAIK

25 was taken from another intra-basin, underwater

high (the Academician Ridge) which separates the

north and middle basins of Lake Baikal. Here,

Table 4

Annual average of the 5-year (1994–1998) totals for the main planktonic d

BAIK 38

A. skvortzowii A. baicalensis C. minu

Average 1994–1998 1847868 1375303 385548

BAIK 38 (1994) 12942 38038 35562

Preservation factor 0.007 0.027 0.092

Preservation factors are calculated as the ratio of the two. NA=not applic

sediment rates are some of the lowest found in the

lake (Appleby et al., 1998). Finally, BAIK 29 was

taken from the abyssal plain in the north basin, and

has the lowest DAR values. These low values reflect

lower overall production rates between the north and

south basins in general; long-term numbers of diatoms

are five times higher in the south basin than in the

north, whilst biomass is c. 3.5 times higher in the

south than the north (Popovskaya, 2000). Possible

reasons for this include the fact that there is a longer

growth period in the south basin than the north, and

that the more nutrient rich waters of the Selenga River

flow into both the south and middle basins, but not the

north basin (Shimaraev et al., 1994; Popovskaya,

2000).

3.1.3. Comparison between input fluxes and the

diatom accumulation rates for BAIK 38

Table 4 shows comparisons between the fluxes of

diatoms to the sediment from the water column and

DAR for BAIK 38. Assuming these figures are

directly comparable, the proportion of the total diatom

crop preserved in the sediment record is about 1%.

This includes diatoms lost both in the water column

and at the sediment surface. The extent of the loss

varies differentially from species to species, as might

be expected, in relation to the silica content and

specific surface area of the cell wall. Nitschia

acicularis is an important planktonic taxon, dominat-

ing the diatom crop in some years, but it is an

exceptionally delicate diatom and is not recorded in

the sediment. Synedra acus is the next most vulner-

able species, partially dissolving in the water column

(Ryves et al., 2003) and massively under-represented

in the sediment with only one in a thousand valves

being preserved. The best-preserved taxa are Cyclo-

tella minuta (Skv.) Antipova and Aulacoseira baica-

lensis, but in both cases less than one tenth of the

population is preserved. It should be noted here,

iatom taxa compared with annual diatom accumulation rates of core

ta S. meyerii S. acus N. acicularis Total

1157408 3745882 3481749 12021832

3264 5514 0 112540

0.003 0.001 NA 0.009

able.

R.W. Battarbee et al. / Global and Planetary Change 46 (2005) 75–86 81

however, that we have not made any distinction

between the late spring valves of A. baicalensis,

which are formed as mixing depth increases, and

valves formed under the ice. The former are more

silicified, and therefore likely to preserve better in the

sediments, whereas the latter valve type are thinner,

being similar in thickness to valves of Aulacoseira

skvortzowii Edlund, Stoermer and Taylor) and more

likely therefore to dissolve.

3.2. Expected versus observed percentages

The water column diatom data and the surface

sediment data can also be compared on the basis of

percentage composition. Indeed, diatom counts from

sediments are most often expressed as percentage

values, and palaeolimnologists generally base their

environmental reconstructions on the assumption that

the percentage composition of diatoms in sediment

assemblages accurately reflects the relative abundance

of different taxa across the different living commun-

ities in the lake. Table 5 shows a comparison of the

water column data and surface sediment data

expressed as percentages. Based on a count sum of

452 valves for BAIK 38 surface sample, confidence

limits at p=0.95 have been calculated (Maher, 1972).

Table 5 also indicates that there are major differ-

ences between the expected and observed percentage

values. Whilst some of the difference could be due to

mismatches between the period of phytoplankton

collection and the time period represented by the

surface sediment sample, this effect is likely to be

minor, as the percentage composition of the BAIK 38

diatom assemblage is very similar to other samples in

the upper part of the core and similar to the surface

sediment samples of other cores (Mackay et al.,

1998). The most extreme difference is for Nitschia

acicularis, a taxon that does not appear in the

sediment record, but over the 5-year phytoplankton

Table 5

Comparison of the percentage composition of the diatom assemblage in t

A. skvortzowii A. baicalensis C. min

Observed % 11.5 33.8 31.6

Max 14.77 38.28 36.03

Min 8.88 29.59 27.48

Expected % 15.37 11.44 3.21

sampling period was responsible for approximately

29% of the cells produced in the water column.

Synedra acus is also poorly represented in the

sediment with approximately 5% observed and 31%

expected. Other taxa show greater similarity, but the

relatively more robust taxa such as Cyclotella minuta

(32%) and Aulacoseira baicalensis (34%) that dom-

inate the sediment assemblage, only comprise 11%

and 3%, respectively, in the aggregate water column

sample.

It is clear from these data that the high relative

abundance of Cyclotella minuta and Aulacoseira

baicalensis in Lake Baikal sediments over recent

decades is due to the more rapid differential loss of

other taxa, some of which are not preserved at all and

some of which are badly preserved, rather than to their

dominance in the water column. These processes may

therefore largely account for the mismatch between

the recent diatom sediment record and longer-term

phytoplankton records, which document increasing

concentrations of these finely silicified, cosmopolitan

taxa (e.g., Bondarenko, 1999; Popovskaya, 2000).

3.3. Correction factors

In view of the significant differential loss of taxa

and the potential bias that the loss processes introduce

into the palaeoenvironmental record, it is useful to

attempt to quantify the loss rates and introduce

corrections to the sediment data. This is especially

important for (1) validating recent sediment invento-

ries with long-term monitoring records, and (2)

transfer function development (cf. Mackay et al.,

2003) as these are constructed on the basis of

percentage data. Correction factors for the main taxa

can be calculated from the estimates of the ratio of

diatoms produced in the water column to diatoms

preserved in the sediment (Table 6). Possible max-

imum and minimum correction factors determined

he water column and in the surface sediment of BAIK 38

uta S. meyerii Synedra acus N. acicularis

2.9 4.9 0

4.89 7.30 0.84

1.71 3.26 0.00

9.63 31.16 28.96

Table 6

Comparison of data from Table 5 expressed in terms of correction factors for the different taxa

A. skvortzowii A. baicalensis C. minuta S. meyerii S. acus N. acicularis Total

Average 1994–1998 1847868 1375303 385548 1157408 3745882 3481749 12021832

BAIK 38 (1994) 12942 38038 35562 3264 5514 0 112540

Correction factor 142.78 36.16 10.84 354.6 679.34 NA 106.82

Max 111.16 31.92 9.51 210.41 456.09 NA

Min 184.95 41.30 12.46 602.79 1020.30 NA

R.W. Battarbee et al. / Global and Planetary Change 46 (2005) 75–8682

from assessing confidence intervals of the observed

diatom abundances in BAIK 38 are also shown

(Maher, 1972). Confidence limits on correction

factors are estimated, as we have not included error

from added microsphere ratios or from plankton

counts.

Table 6 shows that correction factors vary from

approximately 10 for Cyclotella minuta to ca. 680 for

Fig. 3. Percentage diatom diagram for BAIK 38 showing only the dominan

of dissolution; (b) corrected for dissolution using correction factors from

Synedra acus. Although the accuracy of these values

is unknown as there are many uncertainties both in

the estimates of fluxes from the water column and in

the accumulation rates in the sediment, confidence

limits can at least be calculated (Maher, 1972). There

are also uncertainties due to the difference in time

period represented by the two data sets. In BAIK 38,

the surface 5 mm accumulated over a period of

t planktonic taxa referred to in the text, (a) uncorrected for the effects

Table 6.

R.W. Battarbee et al. / Global and Planetary Change 46 (2005) 75–86 83

4 years (Appleby et al., 1998), and therefore because

the surface sediment used here is 0–2 mm, our

sample represents the couple of years just before core

collection in 1994. In addition, this approach cannot

take into account problems associated with the almost

complete loss of Nitschia acicularis for which a

correction factor tending to infinity might be needed,

and cannot be applied easily to earlier sediments

containing taxa not growing in the water column at

the present day, such as Stephanodiscus flabellatus

Khursevich and Loginova, a taxon abundant in the

early Holocene, but which now may be extinct.

Despite these problems, the correction factors can be

useful as they probably reflect reasonably accurately

the relative differences in preservation rate between

the dominant taxa growing in the lake today. By

applying them to the diatom concentration data in the

sediment, new values for the total diatom concen-

tration in the sediment sample can be reconstructed

and new species percentages can then be calculated

to generate a dissolution-corrected diatom diagram

(Fig. 3).

In the uncorrected profile, from c. 1980 up to 1994,

the sediment profile is dominated by endemic taxa,

which grow best in the colder waters of the pelagic

region of the lake (i.e., Aulacoseira baicalensis and

Cyclotella minuta). In this profile, the cosmopolitan

taxa Syned. acus is not very common. However, the

corrected profile suggests that in the early 1980s,

Synedra acus was the dominant species at least near

the eastern shore of the south basin of Lake Baikal,

but that from the mid 1980s up to 1994, abundances

of this species declined, although there are only small

increases in other taxa at this time, such as the

endemic Aulacoseira skvortzowii. Other taxa, includ-

ing C. minuta, seem now to have been only a very

minor component of the phytoplankton of Lake

Baikal since at least the 1980s. These trends are

much closer to changes in relative abundances of C.

minuta in the phytoplankton record between 1994 and

1998.

4. Discussion

Diatom dissolution is a significant process in Lake

Baikal occurring in the water column for very delicate

taxa, such as Nitschia acicularis, but mainly at the

sediment–water interface for other more robust taxa.

In this study, we attempt to quantify dissolution losses

both for the total diatom crop and for individual

planktonic taxa. We have assumed that diatoms are

quantitatively transferred to the sediment surface by

sedimentation from the water column directly above

the sediment core location, and that the water column

flux derived from the phytoplankton counts is the

same at the BAIK 38 core location as for the

phytoplankton sampling location. The first assump-

tion is not valid for many lakes as deep water

sediments usually over-represent water column pro-

duction owing to processes such as sediment focus-

sing (sediment transport from shallow, more marginal

regions to deep basins) or potentially under-represent

it in small lakes where water retention rates are low

and where significant plankton loss can occur through

the outflow. But in Lake Baikal, whilst these

processes obviously occur, we can argue that they

are relatively unimportant. The long residence time of

water in the lake (between c. 377 and 400 years;

Gronskaya and Litova, 1991) ensures that almost all

diatoms produced are retained in the lake, with losses

through the outflow being minimal. Moreover, BAIK

38 was taken from an isolated high to the east of the

south basin, ensuring that the location is far from

fluvial influences such as the Selenga River, and too

isolated to be affected by turbidites and sediment

focussing.

An indication that resuspension from marginal

areas occurs in Lake Baikal, but is relatively unim-

portant, is the low abundance of benthic diatoms in

the deep-water sediments. Benthic diatoms are excel-

lent tracers of sediment transport from marginal areas,

and they account for less than 10% of all diatoms in

deep-water cores (Mackay et al., 1998). In the

sediment traps exposed during 1996–1997, they

accounted for approximately 5% of the total cells

counted (Ryves et al., 2003).

A further question is the extent to which the

planktonic data set and the core data are comparable.

Plankton data are only available from 1994 onwards,

but BAIK 38 was collected in 1994. For the purposes

of this study, therefore, we have assumed that the

averaged plankton crop data for the five years from

1994 to 1998 is a reasonable approximation of diatom

plankton production in the lake not only for those

years but also for the time period before 1994 that is

R.W. Battarbee et al. / Global and Planetary Change 46 (2005) 75–8684

represented by the uppermost sediments of BAIK 38

(c. 2–4 years; Appleby et al., 1998). The inter-annual

variability of the water column diatom production

(Table 1) suggests that it is necessary to be cautious in

using a mean value based on a 5-year period, but

longer phytoplankton records over the last five

decades suggest that they may be more similar

(Kozhova and Izmest’eva, 1998). It is worth noting

here that during years of low diatom biomass, summer

picoplankton biomass increases (especially the blue-

green Synechocystis limnetica Popovskaya) but in

years of high diatom biomass, picoplankton concen-

trations remain low (Popovskaya, 2000).

If we allow for these assumptions and uncertain-

ties, we can argue that the results of this study indicate

a clear mismatch between diatom accumulation rates

in the sediment and diatom fluxes from the water

column due to diatom dissolution. Comparison with

the sediment trap data (Ryves et al., 2003) indicates

that, except for Nitschia acicularis, dissolution mainly

occurs at the surface sediment. On the figures

presented here only 1% of the crop accumulates in

the permanent sediment and dissolution losses are

differential between species (compare the global value

of 3% preservation efficiency in oceans (Treguer et

al., 1995) and mean 2.8% in coastal marine environ-

ments of the western Japan (Kato et al., 2003)). Both

these conclusions have considerable implications for

the use of the Lake Baikal diatom record for palae-

olimnological and palaeoclimate reconstruction.

Growth rate experiments of the main taxa in

culture indicate that Synedra acus and Stephanodiscus

meyerii Genkal and Popovskaya have broader temper-

ature ranges, in contrast to Aulacoseira baicalensis

and Cyclotella minuta that appear to be exclusively

cold-water taxa (Jewson, unpublished, but see

Mackay et al., 2000, for summary results). A.

baicalensis in particular is a cold-water adapted

diatom growing beneath the ice in spring and avoiding

warmer waters in early summer by sinking rapidly

into cooler (4 8C) mid water depths of between 50 and

250 m. Thicker walls in, e.g., A. baicalensis resting

cells are associated with surviving dissolution in

deeper water, which in turn may be an adaptation to

bacterial mediated dissolution (which in itself is

temperature dependent) (Bidle and Azam, 1999); the

importance of bacterial populations to the general

ecology of Lake Baikal is increasingly being realised

(Kozhova and Izmest’eva, 1998; Straskrabova et al.,

2005-this issue). Nevertheless, the obvious conclusion

is that dissolution strongly biases the composition of

the preserved diatom assemblages towards cold-water

restricted taxa. Treppke et al. (1996) came to a similar

conclusion from sequential trap experiments used to

investigate diatom transport and dissolution in the

eastern equatorial Atlantic. They found that species

present in the water column that are indicative of

equatorial upwelling (e.g., the finely silicified Nitz-

schia bicapitata Cl.) were not found in the surface

sediments, although spring, autumn and winter taxa

were represented.

When we take into account approximate correc-

tion factors, and recalculate abundances of the main

planktonic taxa in the sedimentary record, our

results are (encouragingly) similar to long-term

monitoring, as outlined by Popovskaya (2000).

Although she describes phytoplankton trends going

back to the 1950s, here, only trends going back to

the early 1980s are relevant, as depicted in BAIK

38. The majority of the planktonic diatoms in our

record grow under the ice in spring, before reaching

peak numbers when ice breaks up. The exception to

this is Cyclotella minuta, which although it can be

found growing in small numbers beneath the ice

(e.g., Ryves et al., 2003), given prevailing ecological

conditions, by far the majority of its net growth is in

autumn, after summer stratification. Uncorrected

diatom abundances in BAIK 38 suggests that in

the south basin at this time, C. minuta has been one

of the most important species driving production

within the lake. However, we know from monitoring

studies that phytoplankton biomass in spring under

the ice usually determines overall productivity of the

lake (Popovskaya, 2000). The corrected abundances

for BAIK 38, therefore, are more similar to

monitoring phytoplankton records than the uncor-

rected profile (Fig. 3). Bondarenko (1999) highlights

that between the 1950s and 1970s, S. acus was

abundant in the lake, blooming after peaks in

Aulacoseira baicalensis, otherwise known as Melo-

sira years. From the BAIK 38 record, at c. 1980, S.

acus is indeed the dominant species, but since the

mid 1980s, Bondarenko (1999) shows that S. acus

became less common in the lake due to increasing

numbers of Nitschia acicularis. Whilst decreasing

abundances of S. acus are suggested to occur in the

R.W. Battarbee et al. / Global and Planetary Change 46 (2005) 75–86 85

lake from the BAIK 38 record, there are no

concomitant increases in N. acicularis—but this is

to be expected given that we now know that almost

100% of frustules of this taxa dissolve before being

incorporated in the sedimentary record (Ryves et al.,

2003). Given these findings, namely the improved

relationship between recent monitoring and sediment

records, we can have more confidence that the

application of correction factors to recently depos-

ited sediments in Lake Baikal are worthwhile, and

improved reconstruction inferences that can be

made. A longer-term application of these correction

factors can be found in Mackay et al. (2005-this

issue) who also apply the correction factors to

improve the development of inference models of

snow cover on the lake spanning the last 1000

years.

These results allow dissolution effects to be

quantitatively taken into account in environmental

reconstructions covering most of the Holocene

period where the assemblages are dominated by

diatoms that still occur in the plankton today. For

previous time periods, allowance for dissolution

effects needs to be considered in a more qualitative

way, as taxa often abundant in the past are now

extinct (e.g., during the Kazantsevo Interglacial

(Eemian equivalent) (Rioual et al., 2005-this issue),

and Marine Isotope Stage 3 (Swann et al., 2005-this

issue)). Finally and more generally, these results

suggest that caution should be exercised in simply

using the biogenic silica record as a record of lake

productivity and climate change (cf. Colman et al.,

1995). Whilst the general shape of the biogenic silica

record across glacial and interglacial cycles probably

does accurately reflect the broad pattern of climate

variability through the Quaternary period much of

the detail in that record may simply be a signature of

varying preservation rates.

Acknowledgements

We are grateful to the UK Natural Environment

Research Council (Grant GR3/10529), the EU

CONTINENT programme (EVK2-CT-2000-0057),

the UK Royal Society, under the auspices of the

Baikal International Centre for Ecological Research

(BICER) and to the Swiss Government (EAWAG-

GEOPASS 96-97.37) for funding. We would also

like to thank the Limnological Institute in Irkutsk,

especially its director M.A. Grachev for the provi-

sion of ship time and laboratory facilities. Elanor

McBay’s and Helene Coleman’s help in the prepa-

ration of the manuscript is also warmly acknowl-

edged. Finally, we would like to thank the two

reviewers, whose comments have helped to improve

the manuscript.

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