Water level changes in Lake Van, Turkey, during the past ca. 600 ka: climatic, volcanic and tectonic controls

Abstract

Sediments of Lake Van, Turkey, preserve
one of the most complete records of continental
climate change in the Near East since the Middle
Pleistocene. We used seismic reflection profiles to
infer past changes in lake level and discuss potential
causes related to changes in climate, volcanism, and
regional tectonics since the formation of the lake ca.
600 ka ago. Lake Van’s water level ranged by as much
as 600 m during the past ca.600 ka. Five major
lowstands occurred, at ca.600, ca.365–340, ca.290–230,
ca.150–130 and ca.30–14 ka. During Stage A, between
about 600 and 230 ka, lake level changed dramati-
cally, by hundreds of meters, but phases of low and
high stands were separated by long time intervals.
Changes in the lake level were more frequent during
the past ca.230 ka, but less dramatic, on the order of a
few tens of meters. We identified period B1 as a time
of stepwise transgressions between*230 and 150 ka,
followed by a short regression between ca. 150 and
130 ka. Lake level rose stepwise during period B2,
until ca.30 ka. During the past ca.30 ka, a regression
and a final transgression occurred, each lasting about
15 ka. The major lowstand periods in Lake Van
occurred during glacial periods, suggesting climatic
control on water level changes (i.e. greatly reduced
precipitation led to lower lake levels). Although
climate forcing was the dominant cause for dramatic
water level changes in Lake Van, volcanic and
tectonic forcing factors may have contributed as well.
For instance, the number of distinct tephra layers,
some several meters thick, increases dramatically in
the uppermost*100 mof the sediment record (i.e. the
past ca.230 ka), an interval that coincides largely with
low-magnitude lake level fluctuations. Tectonic activ-
ity, highlighted by extensional and/or compressional
faults across the basin margins, probably also affected
the lake level of Lake Van in the past.

Full text

ORIGINAL PAPER
Water level changes in Lake Van, Turkey, during the past
ca. 600 ka: climatic, volcanic and tectonic controls
Deniz Cukur
•
Sebastian Krastel
•
Hans Ulrich Schmincke
•
Mari Sumita
•
Yama Tomonaga
•
M. NamıkC¸ag
˘
atay
Received: 2 February 2014 / Accepted: 29 July 2014
Ó Springer Science+Business Media Dordrecht 2014
Abstract Sediments of Lake Van, Turkey, preserve
one of the most complete records of continental
climate change in the Near East since the Middle
Pleistocene. We used seismic reflection profiles to
infer past changes in lake level and discuss potential
causes related to changes in climate, volcanism, and
regional tectonics since the formation of the lake ca.
600 ka ago. Lake Van’s water level ranged by as much
as 600 m during the past *600 ka. Five major
lowstands occurred, at *600, *365–340, *290–230,
*150–130 and *30–14 ka. During Stage A, between
about 600 and 230 ka, lake level changed dramati-
cally, by hundreds of meters, but phases of low and
high stands were separated by long time intervals.
Changes in the lake level were more frequent during
the past *230 ka, but less dramatic, on the order of a
few tens of meters. We identified period B1 as a time
of stepwise transgressions between *230 and 150 ka,
followed by a short regression between ca. 150 and
130 ka. Lake level rose stepwise during period B2,
until *30 ka. During the past *30 ka, a regression
and a final transgression occurred, each lasting about
15 ka. The major lowstand periods in Lake Van
occurred during glacial periods, suggesting climatic
control on water level changes (i.e. greatly reduced
precipitation led to lower lake levels). Although
climate forcing was the dominant cause for dramatic
water level changes in Lake Van, volcanic and
tectonic forcing factors may have contributed as well.
For instance, the number of distinct tephra layers,
some several meters thick, increases dramatically in
the uppermost *100 m of the sediment record (i.e. the
past *230 ka), an interval that coincides largely with
low-magnitude lake level fluctuations. Tectonic activ-
ity, highlighted by extensional and/or compressional
faults across the basin margins, probably also affected
the lake level of Lake Van in the past.
Keywords Lake Van  Lake level changes 
Climate  Tectonic activity  Volcanism
D. Cukur (&)  H. U. Schmincke  M. Sumita
GEOMAR Helmholtz Centre for Ocean Research Kiel,
Wischhofstr. 1-3, 24148 Kiel, Germany
e-mail: dcukur@geomar.de
S. Krastel
Institute of Geosciences, Christian-Albrechts-Universita
¨
t
zu Kiel, Otto-Hahn-Platz 1, 24118 Kiel, Germany
Y. Tomonaga
Department of Water Resources and Drinking Water,
Eawag, Swiss Federal Institute of Aquatic Science and
Technology, U
¨
berlandstrasse 133, 8600 Du
¨
bendorf,
Switzerland
Y. Tomonaga
Atmosphere and Ocean Research Institute, The University
of Tokyo, 5-1-5 Kashiwa-noha, Kashiwa-shi,
Chiba 277-8564, Japan
M. NamıkC¸ag
˘
atay
EMCOL and Department of Geological Engineering,
Istanbul Technical University, 34469 Maslak, Istanbul,
Turkey
123
J Paleolimnol
DOI 10.1007/s10933-014-9788-0

Introduction
Lacustrine sediments can provide important insights
into past lake levels (Smith 1991). Major changes in
lake level, in turn, represent a powerful tool for
understanding paleoenvironmental and paleoclimatic
conditions in continental regions (Machlus et al. 2000;
Adams et al. 2001). Former lake levels can be
recognized from seismic reflection data using several
indicators such as erosional surfaces, changes in stratal
geometries (downward shifts in coastal onlap), and
distinctive features such as prograding clinoforms
(Aksu et al. 1992; Anselmetti et al. 2006; McGlue
et al. 2008; Moernaut et al. 2010; Lyons et al. 2011).
These cited studies, however, cover relatively short
time periods, not exceeding 150 ka.
Interest in the paleoclimate record of Lake Van
(Fig. 1) grew following the pioneering studies of
Degens and Kurtman (1978) and Landmann et al.
(1996) and culminated in the ICDP (International
Continental Scientific Drilling Program) PaleoVan
Deep-Drilling Project, carried out in 2010. The aim
was to recover the entire sediment archive of Lake Van
(Litt et al. 2011, 2012). Previous studies attempted to
quantify past lake levels and their relationship to
climate forcing (Landmann et al. 1996; Kempe et al.
2002; Kuzucuog
˘
lu et al. 2010). These lake level
reconstructions were based on the elevation of onshore
terraces above the present water surface of Lake Van
(up to ?110 m), but had limited temporal constraints,
or were inferred from geochemical analyses of the
porewater in short cores. These reconstructions have
recently been challenged in light of the new ICDP
PaleoVan core data (Litt et al. 2009), which encom-
passes the[600-ka history of Lake Van since its origin
as a closed-basin lake (Litt et al. 2011, 2012;
Stockhecke et al. 2014a, b). Moreover, past lake
levels, inferred from onshore terraces, were ques-
tioned by Sumita and Schmincke (2013a) because of
problems with stratigraphic correlation and dating of
tephra deposits underlying some terraces. No study
has yet inferred past lake stands below the modern lake
Fig. 1 Lake Van and surrounding areas. Lake Van is located in
the eastern part of Turkey. Two volcanoes, Nemrut and Su
¨
phan,
are situated close to the lake. The Bitlis Massif in the south
towers up to 3,500 m a.s.l. The Mus Basin lies in the
southwestern part of the lake. Seven rivers contribute inflow
water to the lake, but the lake has no outflow at present
J Paleolimnol
123

level in a quantitative way, because of a lack of high-
quality seismic and borehole data. Seismic evidence of
past lake levels, combined with sediment core anal-
yses, provide a robust method for characterizing past
lake level changes in Lake Van during the last 600 ka.
We used high-resolution seismic reflection profiles
to reconstruct past water level in Lake Van. We
discuss the possible causes of lake level fluctuations,
as such changes have important implications for
interpreting local and/or global paleoclimate. Our
interpretations are supported by ground-truth data
from sediment core analyses that better constrain
seismic facies and the lake level history. The study
area includes the Northern, Tatvan, and Deveboynu
Basins, which are separated from one another by
basement ridges, as well as the so-called Northern
Ridge and the Ahlat Ridge (Fig. 2).
Study site
Lake Van (38.5°N, 43.0°E) is located in eastern
Anatolia, Turkey, at an altitude about 1,650 m a.s.l.
(Fig. 1). Lake Van is the deepest (maximum water
depth [450 m) and largest lake in Turkey and is the
fourth largest terminal lake in the world (*650 km
3
).
The lake has a WSW-ENE length of 130 km and
covers an area of *3,600 km
2
.
The drainage basin covers about 16,000 km
2
(Kempe et al. 1978) and encompasses the eastern part
of the Mus¸ Basin. The south shore is formed by the
Bitlis Massif, towering more than 3,500 m a.s.l. and
consisting of metamorphic rocks of Paleozoic age
(Fig. 1). Two large active stratovolcanoes, Nemrut
(2,948 m a.s.l.) and Su
¨
phan (4,058 m a.s.l.), border
the lake to the west and north. Their tephra deposits
(*450 layers according to our most recent estimate;
Schmincke and Sumita, unpubl.) make up as much as
*20 % of the lake sediment volume. A large hyal-
oclastite cone, Incekaya [400 m above present lake
level (a.p.l.l.)], has grown at the southwestern shore of
the lake.
The modern climate of the area is governed by
continental conditions. Winds blow mainly from the
southwest, providing the moist air responsible for
rainfall during winter and spring. Summers are dry,
with winds from the north and average daytime
temperatures of 20 °C in July and August (Kadioglu
et al. 1997). Annual rainfall varies from \400 mm in
the northern and eastern part of the lake to [600 mm
in the south (Kadioglu et al. 1997). Most precipitation
in the drainage basin falls during the winter season as
snow.
The major rivers entering Lake Van today are the
Karasu, Morali, and Engil near the city of Van, the
Fig. 2 Bathymetry of Lake
Van and distribution of
seismic data and ICDP drill
locations (AR: Ahlat Ridge
drill site; NB: Northern
Basin drill site). Bathymetry
was constructed from
seismic data used in this
study. Contours are water
depths in meters
J Paleolimnol
123

Gu
¨
zel near Tatvan, the Zilan, Delicay, and Bendimahi
near Ercis, and the Papicek near Ahlat (Fig. 1). More
than 50 % of the annual water discharge to the lake is
provided by the Zilan, Bendimahi and Engil Rivers
(Reimer et al. 2008). River discharge (*2km
3
/year;
Reimer et al. 2008) and evaporation (*3.8 km
3
/year;
Reimer et al. 2008) represent the most important
processes controlling annual lake level fluctuations,
which can range as high as 0.9 m (Kaden et al. 2010).
Materials and methods
Our data comprise more than 1,500 km of migrated
seismic reflection profiles, and lithologic and tephra
age data from the Ahlat Ridge drill site [*220 m b.l.f.
(below lake floor)], which was drilled in 2010 within
the framework of the ICDP PaleoVan Project (Litt
et al. 2011, 2012; Fig. 2). The multi-channel seismic
reflection datasets were collected in 2004 and 2012
with similar acquisition systems. A 16-channel (100-
m-long) analogue streamer was used in 2004 and a
48-channel (100-m-long) digital streamer was used in
2012. A Mini-GI-Gun with a frequency of 80–500 Hz
was used as a source for both surveys. Data processing
included editing of bad traces, geometry setup,
binning, velocity analysis, NMO correction, stacking,
and time migration. For the common mid-point (CMP)
stacks, bin distances of 10 and 3 m were chosen for the
2004 and 2012 data, respectively. The IHS Kingdom
Suite software was used for seismic data interpretation
and mapping. For seismic-to-well tie we assumed
speeds of sound in water and sediments of 1,455 and
1,500 m/s (Wong and Finckh 1978), respectively.
Results
Interpretation of seismic reflection data
Chronostratigraphy
We identified 19 seismic unit boundaries or unconfo-
rmities (SUB1–SUB19), including the top of the
acoustic basement, throughout the lake basin (Figs. 3,
4; Cukur et al. 2014). The top of the acoustic basement
is the deepest coherent reflector observed in the
seismic sections. The seismic unit boundaries are
defined by erosional truncation, toplap, onlap or
downlap surfaces. Approximate ages for these uncon-
formities are based on single crystal
40
Ar/
39
Ar ages,
varve chronology, magnetostratigraphy, radiocarbon
dating, and cosmogenic isotope dating in the ICDP
bore holes (Table 1; Sumita and Schmincke unpubl.;
Stockhecke et al. 2014a). Seismic units bounded by
these unconformities are referred to as SU1–SU19,
from oldest to youngest.
Seismic facies analysis
Five seismic facies (SF) are identified throughout the
Lake Van Basin (Fig. 5; Cukur et al. 2014) based on
seismic reflection amplitude and continuity, the inter-
nal/external reflection character, and the data from
drill cores. SF1 is characterized by high-amplitude
reflections with good continuity, which are interpreted
as resulting from undisturbed, finely laminated lacus-
trine sedimentation (laminated clayey silt interbedded
with distal turbidites and tephra layers) during warm
periods. SF2 consists of low-amplitude reflections
with good continuity, and is represented in the cores as
banded to massive packages of clayey silt deposited
under lacustrine conditions during cold periods. SF1
and SF2 are found mostly in the deeper parts of the
lake, away from terrigenous sources (Fig. 6). SF3,
characterized by irregular and highly chaotic internal
reflections, and interpreted as mass-transport deposits,
dominates in the southern part of the lake (Fig. 6).
SF4, characterized by low-to-moderate amplitude
with oblique- and/or complex-oblique-shaped external
form, is interpreted as deltas (Fig. 3, seismic section in
Fig. 3 is *4 km from the Ahlat Ridge drill site)
similar to the delta lobes described by McGlue et al.
(2008) in Lake Tanganyika, by Lindhorst et al. (2010)
in Lake Ohrid, and by Lyons et al. (2011) in Lake
Malawi. SF5, characterized by variable amplitude
with poor to moderate continuity, is interpreted as
fluvial deposits. SF4 and SF5 occur in the slope and
shelf areas.
Reconstruction of past lake levels
We calculated past lake levels at the end of each
seismic unit (Table 2) using depths of topset-foreset
point (roll-over point) of prograding clinoforms and
onlap surfaces (Fig. 3). The roll-over point marks the
wave base, which, for a lake like Lake Van could be at
J Paleolimnol
123

5–10 m. However, as the wave base is not known in
the area, the roll-over point was taken as 0 m. We
grouped the lake level changes of Lake Van into two
stages: Stage A and Stage B (Fig. 7c). Stage A
(*600–230 ka) is characterized by high-amplitude
lake level fluctuations, whereas Stage B (*230 ka to
present) consists mainly of low-amplitude fluctua-
tions. Stage B, on the basis of magnitude and
frequency of lake level changes, was further subdi-
vided into two transgressive sub-phases (B1,
*230–150 ka and B2, *130–30 ka) separated by a
moderate regression (P12, *150–130 ka).
Discussion
Depositional and lake-level history of Lake Van
The 19 seismic units (SU1-SU19) represent 19 distinct
phases (P1–P19) of the depositional and lake-level
history of Lake Van (Fig. 7c). Below, we describe and
discuss only major regressive and transgressive phases
of Stage A and Stage B. All phases not explicitly
mentioned in the following also correspond to lake
level fluctuations, but are small compared to the major
changes described below.
Fig. 3 W–E regional
seismic profile showing 19
unconformities or seismic
unit boundaries (SUB1–
SUB19), including the top of
the acoustic basement.
Seismic units bounded by
these unconformities are
referred to as SU1–SU19
from oldest to youngest. The
seismic profile also shows
past lake level markers such
as well-developed
prograding clinoforms
(shaded by colors) and onlap
surfaces at different depths,
suggesting significant lake-
level fluctuations. (Color
figure online)
J Paleolimnol
123

Stage A
Phase 1 (SU1; ca. [600 ka). P1 corresponds to the
deposition of the oldest sediments (SU1) in Lake Van
above the acoustic basement (Figs. 3, 4, 8a). The
toplap depth of the prograding delta (Fig. 3) suggests
that the lake level at this time was *610 m b.p.l.l.
(Fig. 8a). The presence of a prograding delta sitting
directly on top of the acoustic basement further
suggests major flooding at the beginning of the
formation of the lake. This prograding delta extends
towards the Ahlat Ridge (Fig. 6; SF4) and its upper-
most sediment layers were penetrated by the ICDP
PaleoVan drilling (Fig. 7a). The drilled sediments
consist of coarse sand and gravel, reflecting initial lake
formation under shallow, freshwater conditions (Litt
et al. 2011). During that time, sedimentation only
occurred in the deeper parts of the basin. As a result,
deposits of SU1 are missing in the shallower parts of
the present lake, where deposition did not occur or
there was erosion during the early stage of lake
formation (Fig. 8a).
Phase 3 (SU3, ca. 485–420 ka). The initiation of
SU3 deposition in the lake corresponds to a major lake
transgression (Fig. 8b). Reconstruction of lake level
suggests a rise to * 265 m b.p.l.l. Seismic profiles
show that SU3 is characterized by uniform, chaotic to
transparent seismic facies throughout the lake (Figs. 3,
4). At Ahlat Ridge, SU3 consists of up to 20-m-thick,
disrupted and deformed laminated sediments, capped
by a megaturbidite (deformed unit, DU; Stockhecke
et al. 2014b, Fig. 7a). The uniform, almost basin-wide
zone of chaotic reflections, together with evidence
from the ICDP drill cores, indicate that it was
Fig. 4 N-S regional
seismic profile (a) and its
interpretation (b) Seismic
profile showing the seismic
unit boundaries (SUB1–
SUB19) and the seismic
units (SU1–SU19) identified
in the study area. The box
indicates the portion of the
profile shown in Fig. 7a
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123

deformed in situ, possibly by seismic shaking. Similar
deformational structures are also observed in onshore
lacustrine deposits of Lake Van (U
¨
ner et al. 2010).
Based on field observations, U
¨
ner et al. (2010)
interpreted such deformation structures as caused by
seismic shaking during strong earthquakes.
Phase 5 (SU5; ca. 365–340 ka). The upper bound-
ary of SU5 represents a major regressive surface and
lowstand (Fig. 8c). This regression was accompanied
by erosion, as shown by truncations of older units
(SU4) towards the eastern shelf area (Figs. 3, 8c). We
relate this phase to marine isotope stage 10 (MIS10
glacial maximum; Fig. 7d) as the ages are comparable.
We estimate that lake level fell at this time to *560 m
b.p.l.l.
Phase 6 (SU6; ca. 340–290 ka). This phase corre-
sponds to the deposition of SU6 and represents a
major, rapid rise of lake level, immediately following
the lowstand of Phase 5 (Fig. 8d). We relate it to
marine isotopic stage 9 (MIS9) in the global record
(Fig. 7d). The lake level rose during this period to
200 m b.p.l.l. (Fig. 8d). Slow, undisturbed lacustrine
sedimentation prevailed in the lake, episodically
interrupted by mass-transport processes, possibly
synignimbrite turbidites.
Phase 7 (SU7; ca. 290–230 ka). The end of SU7
corresponds to a lake lowstand (down to 470 m b.p.l.l.;
Fig. 8E). SU7 was deposited between ca. 290 and
230 ka BP, during MIS8. The seismic character of
SU7 (low-amplitude, high-continuity reflections) is in
good agreement with the core data, as indicated by the
presence of massive to banded lacustrine sediments,
implying cold climate conditions (Stockhecke et al.
2014b). Very thick (up to *8 m) volcaniclastic
deposits (possibly synignimbrite turbidites) are pres-
ent within this unit (Fig. 7b).
Stage B
Phase 8 (SU8; ca. 230–190 ka). This phase corre-
sponds to the deposition of SU8 (Fig. 8f). Unit SU8
provides evidence for another cycle of lake level rise.
This is also reflected by the increased abundance of
carbonates (Stockhecke et al. 2014b). We estimate the
lake level rose at this time to 275 m b.p.l.l., and we
tentatively correlate this phase to the beginning of
MIS7. Inferred rising lake levels are in part supported
by lower porewater salinities in the core-catcher
samples of the ICDP PaleoVan Project at Ahlat Ridge
(Y. Tomonaga, pers. commun.). The onset of these
lower salinities has not yet been dated, but lower
salinities in a closed lake basin represent clear
evidence for a larger water volume. SU8 consists of
prograding clinoforms in the east, suggesting
increased sediment input that might have resulted
from a period of increased runoff. Throughout the
basin, undisturbed laminated lacustrine sedimentation
prevailed.
Phase 12 (SU12; ca. 150–130 ka). The top of SU12
represents a major erosive event in Lake Van
Table 1 Age versus depth at Ahlat Ridge site (from Stock-
hecke et al. 2014a)
Depth
(mblf)
Age
(*ka)
Error
(ka)
Depth
(mblf)
Age
(*ka)
0.00 35.5 77.98
0.36 0.6 0.048 36.0 79.17
1.58 2.67 0.025 40.6 84.97
2.29 4.33 0.078 44.6 90.03
2.90 6.01 0.06 48.5 104.03
3.26 6.89 0.069 50.7 108.27
4.39 11.65 53.1 115.40
5.99 12.85 56.9 128.40
6.10 14.01 57.9 131.00
6.70 14.64 61.3 136.00
8.91 18.59 0.062 95.6 189.50
11.0 23.29 99.3 198.80
13.4 27.73 104.0 216.00
14.1 28.85 107.6 222.20
14.8 32.45 0.25 113.2 241.80
18.3 33.69 118.1 250.00
18.9 35.43 121.6 259.41
19.8 38.17 130.1 276.53
20.6 40.11 135.2 291.00
21.0 41.41 136.1 297.00
21.7 43.29 144.4 336.00
22.7 46.81 147.8 351.00
23.4 49.23 158.0 392.00
24.6 54.17 160.8 407.00
25.2 55.75 163.7 413.28
26.2 58.23 186.1 480.07
26.6 59.0 187.8 488.50
30 64.05 195.0 528.00
31.8 69.58 200.6 556.00
33.3 72.28 206.7 579.00
34.8 76.40 210.8 595.21
J Paleolimnol
123

(Fig. 8g). We interpret this discontinuity as indicative
of a lake level drop to *310 m b.p.l.l., which can be
associated with MIS6 (Fig. 7d). The lake floor in the
eastern shelf area appears to have been subaerially
exposed and subsequently incised by fluvial process
(Fig. 8g). Erosion in the shelf area was directly related
to coarse detrital inputs derived from the eastern
inflows (i.e. the Karasu, Morali, and Engil Rivers). To
the west and south, mass-transport deposits dominate.
At Ahlat Ridge, SU12 is characterized by banded
clays, providing evidence for a cold climate.
Phase 13 (SU13; ca. 130–85 ka). Lake level rose up
to *170 m b.p.l.l. during MIS5, following the low-
stand period (P12) (Fig. 8h). The incised channels
resulted from a previous lowstand period filled with
sediments of SU13 (Fig. 8h). The prograding clino-
forms developed in the east suggest a major increase in
sediment input. Finely laminated sediments are com-
mon in SU13 in Ahlat Ridge drill cores, indicating
strong seasonality and high lake levels (Stockhecke
et al. 2014b). Mass-transport processes became more
pronounced during this period, suggesting increased
tectonic activity along the southern margin of the lake.
Phase 18 (SU18; ca. 30–14 ka). The end of SU18 is
characterized by a major regressive surface (Fig. 8i).
During that time, the lake level dropped to about
210 m b.p.l.l. This phase can be attributed to the Last
Glacial Maximum (LGM) (Fig. 7d), when dry
Fig. 5 Seismic facies identified throughout the lake and their geological interpretation (modified from Cukur et al. 2014)
J Paleolimnol
123

conditions prevailed in the region (Sarikaya et al.
2008; Litt et al. 2009). This dry period is reflected in
the low-amplitude reflections observed in the seismic
data, a consequence of low acoustic contrasts. Facies
analysis of drill cores also suggests rather homogenous
sedimentation, with an absence of laminations during
the cold lake period (Stockhecke et al. 2014b). Further
evidence for a cold and dry climate is provided by
palynological data that indicate cold and semi-desert
steppe vegetation (Wick et al. 2003; Litt et al. 2009).
The sudden decrease of mass-flow deposits along the
southern margin (Figs. 6, 8I) may indicate a signifi-
cant decrease in sediment supply from the south,
which in turn suggests reduced tectonic activity across
the southern boundary fault.
Phase 19 (SU19; ca. 14 ka—present). The most
recent phase of deposition in Lake Van is represented
by SU19, which is characterized by well-stratified
seismic facies that indicate quiescent lake conditions
(Fig. 8j). After the lowstand period, the lake level rose
to its present elevation within the last 14 ka. Modern
lake conditions appear to have started at the beginning
of this phase, as confirmed by the presence of
laminated sediments at Ahlat Ridge (Stockhecke
et al. 2014b). During this period, the lake basin has
been seismically inactive, with only limited small-
scale mass-transport processes.
Climatic, tectonic, and volcanic influences on lake
level fluctuations
Climatic and/or tectonic/volcanic forcing might have
played a role in controlling lake level fluctuations in
Lake Van. Low-magnitude variations in lake levels
may be attributable to gradual subsidence in the lake
basin, which is inferred from the bottom morphology
and the steep normal faults (Fig. 4). The normal faults
in the lake suggest extensional tectonics; Lake Van has
Fig. 6 Interpreted seismic
facies along the seismic
profile shown in Fig. 4.In
the southern part of the
Tatvan Basin, SU1–SU17
are dominated by SF3
(mass-transport deposits).
SF4 is seen in SU1. In the
entire basin, SU18 is
characterized by SF2 (cold-
climate, undisturbed
lacustrine sediments/
turbidites and tephra
deposits), whereas SU19
consists of SF1
Table 2 Past lake levels in Lake Van reconstructed from
seismic reflection profiles
Seismic unit
boundary (SUB)
Age
(ka)
Past lake levels, meters below
present lake level (m b.p.l.l.)
SUB19 *14 -210
SUB18 *30 -85
SUB17 *40 -70
SUB16 *60 -87
SUB15 *80 -125
SUB14 *85 -170
SUB13 *130 -310
SUB12 *150 -145
SUB11 *155 -160
SUB10 *170 -175
SUB9 *190 -275
SUB8 *230 -470
SUB7 *290 -200
SUB6 *340 -560
SUB5 *365 -185
SUB4 *420 -265
SUB3 *485 -480
SUB2 *600 -610
SUB1 Top of the acoustic basement
J Paleolimnol
123

been extended *2 km in an E–W direction since its
formation (Cukur et al. 2012). The reverse faults in the
lake further suggest compressional movement (uplift)
(Fig. 4). The role of tectonic activity is further
evidenced by deposition of various mass-flow deposits
in the lake basin (Fig. 6) as well as micro-deforma-
tional structures, seen in sediment cores (Litt et al.
2012). Therefore, we suggest that tectonic activity
(subsidence/uplift) along the lake margins might have
induced small-scale lake level fluctuations.
Volcanic activity is also likely to have caused low-
magnitude variations in lake level, as briefly discussed
by Sumita and Schmincke (2013c) (Fig. 1). A major
reason is the fact that two major active volcanoes
Fig. 7 a Seismic-to-well tie at the Ahlat Ridge drill site. For
time-depth conversion, a sound velocity of 1,455 m/s for water
and 1,500 m/s for sediments was used. b Lithology of the Ahlat
Ridge drill site adopted from Stockhecke et al. (2014b).
c Reconstructed lake levels (below present lake level; b.p.l.l.)
at the end of each seismic unit boundary. The depths of the lake
levels were estimated using delta offlap breaks and coastal onlap
surfaces. Solid circles represent past lake levels above present
water depths reconstructed by Kuzucuog
˘
lu et al. (2010).
d Comparison of marine isotope stages (MIS; Cohen and
Gibbard 2011) and lake level changes for particular climate
intervals. The apparent correlation between major lowstands
and glacial periods implies that climatic changes controlled
formation of these features
J Paleolimnol
123

border Lake Van to the west and northwest: Nemrut
rising 1,300 m a.p.l.l. and Su
¨
phan 2,400 m a.p.l.l.
However, the lower flanks of both structures extend to
the lake bottom and deeper. It is well known that
volcanoes grow as much or even more from the inside
by intrusion than by surface accumulation. Hence,
volcano expansion prior to an eruption may have
caused a lake-level rise, which could have been further
boosted by a subsequent extensive tephra deposition
on the lake floor during and after the eruption [in some
cases more than 15 m; e.g. AP1 tephra magma
volume, exceeding 30 km
3
(Sumita and Schmincke
2013a)]. Tephra input into the lake has increased
during the past *230 ka (Sumita and Schmincke
2013a, b, c), an interval largely coinciding with low-
magnitude lake-level fluctuations.
Large-magnitude changes, on the other hand, can
best be explained by water imbalance related to
climatic changes. The abrupt lowstands and high-
stands of the lake coincide rather well with marine
isotope stages (Fig. 7d), suggesting that climate
change was most likely the dominant factor determin-
ing the total water budget of Lake Van. Similar
massive lake level fluctuations (over 300 m) have
been documented in Lake Baikal (Romashkin and
Williams 1997), Lake Malawi (Finney et al. 1996),
Fig. 8 Schematic illustration of the depositional and lake-level history of Lake Van. See text for details
J Paleolimnol
123

and Lake Titicaca (D’Agostino et al. 2002), and have
been attributed to climate forcing.
Large-magnitude changes could also be explained
by extreme tectonic events in the catchment (De Batist
et al. 2002). Tectonic activity in the catchment area,
but not in the lake basin itself, may possibly have
altered the shape and size of the catchment on longer
timescales, and this could have significantly affected
the hydrological balance of the lake, leading to long-
term changes in riverine input, and in closed-basin
Lake Van, to changes in water level. Such changes in
the morphology of the catchment, however, would be
expected to produce long-term shifts in the hydro-
chemical signature of Lake Van. The porewater
salinity profile, measured in core-catcher samples of
the ICDP PaleoVan Project, indicates that a steady-
state salinity of about 21 g/kg prevailed for hundreds
of thousands of years (Y. Tomonaga, pers. commun.).
Hence, it is unlikely that the source area that provided
salts to Lake Van via riverine discharge, changed
significantly since the lake became a closed-basin
system [600 ka ago.
Lake Van had higher lake levels in the past, as
documented by the onshore terraces (Fig. 7c, dark
circles; Kuzucuoglu et al. 2010). The onshore terraces
suggest high lake stands at times [105 ka BP,
\100 ka BP, and *26–24.5 ka BP, reaching
*110 m above present lake level. However, the ages
of some of these terraces, reconstructed from under-
lying tephra deposits, were recently questioned by
Sumita and Schmincke (2013a). In addition, we
cannot identify thin reflectors in seismic data because
of the limited vertical resolution, i.e. a few meters.
Therefore, although the lake might have had higher
periods in the past, the available seismic data do not
resolve such periods.
Conclusions
Water level in Lake Van, Turkey, changed dramati-
cally during the past ca. 600 ka, by as much as 600 m,
based on high-resolution seismic reflection profiles
that show erosional surfaces, changes in stratal
geometries such as downward shifts in coastal onlap,
and distinctive features such as prograding clinoforms.
Since the formation of Lake Van as a closed-basin
system, we recognize a total of 19 lake-level changes
with alternating regressions and transgressions. Only
10 of those, however, represent major lake level
changes. Major regression events occurred around
*600 ka (Phase 1, P1), 365–340 ka (Phase 5, P5),
290–230 ka (Phase 7, P7), 150–130 ka (Phase 12,
P12), and 30–14 ka (Phase 18, P18) BP. We recognize
two major periods (or stages) using frequency and
intensity of lake level changes. During Stage A
(600–230 ka), we recognize three major lowstands
(P1, P5 and P7), which were especially pronounced
between 290 and 230 ka. The transgressive phases
between these lowstands show stepwise rises. During
Stage B, we recognize only two moderate regressions
(P12 and P18), separated from each other by relatively
small-scale transgressions. Because major lowstands
coincide with changes in the marine records, major
lake-level fluctuations in Lake Van are likely a
consequence of climate changes. However, in the
tectonically active area of Lake Van, extensional
faulting, basin subsidence, uplift and volcanism could
also have induced variations in lake level.
Acknowledgments We thank the PaleoVan team for support
during collection and sharing of data. The authors acknowledge
funding of the PaleoVan drilling campaign by the International
Continental Scientific Drilling Program (ICDP), the Deutsche
Forschungsgemeinschaft (DFG; Grants KR2222-9 and KR2222/
15), the Swiss National Science Foundation (SNF Grants
200020_121853, 200021_124981, and 200020_143340), the
Scientific and Technological Research Council of Turkey
(Tu
¨
bitak), and the EU Seventh Framework Programme for
Research and Technological Delopment (Marie Curie
International Outgoing Fellowship, Contract PIOF-GA-2012-
332404). We thank editor Mark Brenner and two anonymous
reviewers for their constructive comments. We also thank Prof.
Sefer O
¨
rcen and Dr. Aysegu
¨
l Feray Meydan from the Yu
¨
zu
¨
ncu
¨
Yil University of Van, Turkey, for their cooperation and support
and making the boat available during the seismic campaign.
Special thanks go to our captains, Mete Orhan and Mu
¨
nip
Kanan for their untiring commitment during the seismic data
acquisition.
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