Little is known about the climate evolution on the Kamchatka Peninsula during the last glacial–interglacial transition as existing climate records do not reach beyond 12 ka BP. In this study, a summer temperature record for the past 20 kyr is presented. Branched glycerol dialkyl glycerol tetraethers, terrigenous biomarkers suitable for continental air temperature reconstructions, were analyzed in a sediment core from the western continental margin off Kamchatka in the marginal northwest Pacific (NW Pacific). The record suggests that summer temperatures on Kamchatka during the Last Glacial Maximum (LGM) equaled modern temperatures. We suggest that strong southerly winds associated with a pronounced North Pacific High pressure system over the subarctic NW Pacific accounted for the warm conditions. A comparison with an Earth system model reveals discrepancies between model and proxy-based reconstructions for the LGM temperature and atmospheric circulation in the NW Pacific realm. The deglacial temperature development is characterized by abrupt millennial-scale temperature oscillations. The Bølling–Allerød warm phase and the Younger Dryas cold spell are pronounced events, suggesting a connection to North Atlantic climate variability.
During the Last Glacial Maximum (LGM; i.e., 24–18 ka BP; Mix et al.,
2001), when sea-level regression lead to the exposure of the Bering and
Chukchi shelves, the Bering Land Bridge connected Alaska and eastern Siberia
(Fig. 1). The resulting continuous landmass is commonly known as “Beringia”
(defined as the area extending from the Lena River in northeastern Russia to
the lower Mackenzie River in Canada; Hopkins et al., 1982). Beringia's
environmental history since the last glaciation is of particular interest
since having been unglaciated during the LGM, the landmass formed a glacial
refuge for arctic flora and fauna (Abbott und Brochmann, 2003; Nimis et al.,
1998; Guthrie, 2001) and allowed plants, animals and humans to migrate
between Asia and North America (e.g., Mason et al., 2001). Despite several
studies investigating the Beringian evolution of temperature, moisture
availability and vegetation (e.g., Lozhkin et al., 1993, 2007; Anderson et
al., 1996; Bigelow and Edwards, 2001; Bigelow and Powers, 2001; Pisaric et
al., 2001; Elias, 2001; Ager, 2003; Kienast et al., 2005; Sher et al., 2005;
Kurek et al., 2009; Elias and Crocker, 2008; Kokorowski et al., 2008a, b;
Berman et al., 2011; Fritz et al., 2012; Anderson and Lozhkin, 2015),
environmental change during the LGM-to-Holocene transition and the respective
climatic controls (e.g., rising atmospheric CO
The sparsity of continuous temperature records in Beringia also limits a comprehensive assessment of the geographic extent of abrupt deglacial climate reversals. There is consensus among sea surface temperature records from the northern Pacific (N Pacific) and its marginal seas that the deglaciation was characterized by abrupt warm–cold oscillations (e.g., Barron et al., 2003; Seki et al., 2009, 2014; Caissie et al., 2010; Max et al., 2012; Praetorius and Mix, 2014; Praetorius et al., 2015; Meyer et al., 2016), suggesting teleconnections with the North Atlantic realm (Manabe and Stouffer, 1988; Mikolajewicz et al., 1997; Okumura et al., 2009; Chikamoto et al., 2012). However, it is not fully understood how far this North Atlantic (N Atlantic) connection extended into Beringia. Records are inconsistent, suggesting both abrupt warm–cold oscillations (Anderson et al., 1990, 2002; Andreev et al., 1997; Pisaric et al., 2001; Bigelow and Edwards, 2001; Bigelow and Powers, 2001; Brubaker et al., 2001; Meyer et al., 2010; Anderson and Lozhkin, 2015) and continuous warming (Lozhkin et al., 1993, 2001; Anderson et al., 1996, 2002, 2003; Lozhkin and Anderson, 1996; Bigelow and Powers, 2001; Nowaczyk et al., 2002; Ager, 2003; Nolan et al., 2003; Kokorowski et al., 2008a, b; Kurek et al., 2009) throughout the deglaciation.
The Kamchatka Peninsula (attached to Siberia, Fig. 1a) is among the areas in western Beringia where the least is known about environmental conditions during the LGM-to-Holocene transition since terrestrial archives on Kamchatka do not reach beyond 12 ka BP (e.g., Dirksen et al., 2013, 2015; Nazarova et al., 2013; Hoff et al., 2014, 2015; Klimaschewski et al., 2015; Self et al., 2015; Solovieva et al., 2015). Kamchatka is an important location to study deglacial changes in regional atmospheric and oceanic circulation in the northwestern Pacific realm. Protruding into the northwestern Pacific (NW Pacific, Fig. 1a), the peninsula responds to variations in these regional climate controls in addition to global or supraregional climate drivers, e.g., summer insolation or teleconnections with the N Atlantic realm, as has been shown for the Holocene (Savoskul, 1999; Dirksen et al., 2013; Nazarova et al., 2013; Andrén et al., 2015; Brooks et al., 2015; Hammarlund et al., 2015; Self et al., 2015).
In this study, we analyzed branched glycerol dialkyl glycerol tetraethers (brGDGTs), terrigenous biomarkers as recorders of continental air temperature (Weijers et al., 2006a, 2007), in a marine sediment core retrieved at the eastern continental margin off Kamchatka and the NW Pacific (site SO201-2-12KL, NW Pacific; Fig. 1a, b). We present a continuous, quantitative record of summer temperature for the past 20 kyr and infer changes in atmospheric circulation. The findings are compared to an Earth system model (ESM).
The Kamchatka Peninsula is situated south of the Koryak Uplands and separates
the Sea of Okhotsk from the NW Pacific and the Bering Sea (Fig. 1a). It is
characterized by strong variations in relief with lowlands in the coastal
areas (western lowlands and eastern coast) and mountain ranges further inland
(Fig. 1b). The mountain ranges, the Sredinny and the eastern ranges, encircle
the lowlands of the Central Kamchatka Depression (CKD, Fig. 1b). The CKD is
the largest watershed of the peninsula and is drained by the Kamchatka River,
the largest river of Kamchatka. The river discharges into the Bering Sea near
56
The mountainous terrain with strongly variable relief results in pronounced
climatic diversity on the peninsula (Fig. 1b). The coastal areas, the western
lowlands and the eastern coast are dominated by marine influences. In the
coastal areas, summers are cool and wet and winters are relatively mild.
Precipitation is high along the coast and in the mountains throughout the
year (Kondratyuk, 1974; Dirksen et al., 2013). Being protected from marine
influences by the mountain ranges, the CKD has more continental conditions
with less precipitation and a larger annual temperature range than in the
coastal areas (Ivanov, 2002; Dirksen et al., 2013; Kondratyuk, 1974; Jones
and Solomina, 2015). Mean temperatures averaged for the entire peninsula
range from
Within a joint German–Russian research program (KALMAR Leg 2), core
SO201-2-12KL (Fig. 1a, b) was recovered with a piston-corer device during
cruise R/V
Average Holocene, deglacial and glacial sedimentation rates are 39, 79 and
59 cm ka
For this study we used the same samples as Meyer et al. (2016). These authors sampled the core in 10 cm steps, providing an average temporal resolution of approximately 200 years. For GDGT (glycerol dialkyl glycerol tetraether) analyses, freeze-dried and homogenized sediment samples (approximately 5 g) were extracted and processed according to Meyer et al. (2016).
GDGTs were analyzed by high-performance liquid chromatography (HPLC) and a
single quadrupole mass spectrometer (MS). The systems were coupled via an
atmospheric pressure chemical ionization (APCI) interface. The applied method
was slightly modified from Hopmans et al. (2000). Analyses were performed on
an Agilent 1200 series HPLC system and an Agilent 6120
mass selective detector (MSD).
Separation of the individual GDGTs was performed on a Prevail Cyano column
(Grace, 3
GDGTs were quantified by peak integration and the obtained response factor
from the C
The Cyclisation of Branched Tetraethers index (CBT) and Methylation of
Branched Tetraether index (MBT) were introduced as proxies for soil pH (CBT)
and mean annual air temperature (MAT, CBT–MBT) by Weijers et al. (2007). We calculated the CBT
index after Weijers et al. (2007). For calculating the MBT index we used a
modified version, the MBT', which excludes GDGTs IIIb and IIIc and was
introduced by Peterse et al. (2012). From repeated measurements of a lab
internal standard sediment extract (
Although terrestrial soils are supposed to be the main source of brGDGTs
(Weijers et al., 2007), brGDGT can also be produced in situ in marine water
systems (Peterse et al., 2009; Zhu et al., 2011; Zell et al., 2014) as well
as in freshwater environments (Tierney et al., 2010; Zell et al., 2013; De
Jonge et al., 2014; Dong et al., 2015). As in situ production can bias
temperature reconstructions, particularly in marine settings where the input
of terrigenous GDGTs is low (Weijers et al., 2006b; Peterse et al., 2009,
2014; De Jonge et al., 2014), the contribution of terrigenous brGDGTs to the
marine sediments needs to be estimated prior to any paleoclimatic
interpretation of temperatures derived from CBT–MBT
In order to compare inferences for atmospheric circulation during the summer
months to general circulation model outputs, model simulations for the
climate were performed with the ESM COSMOS for preindustrial
(PI)
(Wei et al., 2012) and LGM conditions (Zhang et al., 2013). The model
configuration includes the atmosphere component ECHAM5 at T31 resolution
(
External forcing and boundary conditions are imposed according to the
protocol of PMIP3 for the LGM (available at
For both, PI and LGM conditions the climate model was integrated twice for 3000 model years and provides monthly output (Wei et al., 2012; Wei and Lohmann, 2012; Zhang et al., 2013). Here, anomalies in sea-level pressure (SLP), wind directions (1000 hPa level) and surface air temperature (SAT) between the LGM and preindustrial conditions were analyzed for the boreal summer season – June, July and August (JJA). We focus on the summer season as in high latitudes brGDGTs seem to reflect summer temperature instead of the annual mean (Rueda et al., 2009; Shanahan et al., 2013; Peterse et al., 2014). All produced figures show climatological mean characteristics averaged over a period of 100 years at the end of each simulation.
The summed concentration of all nine brGDGTs (
The fractional abundance of all nine brGDGTs, calculated relative to the
Fractional abundances of all nine brGDGT in core 12KL, given in
percentage relative to the amount of
Comparison of proxy- and model-based inferences regarding glacial
anomalies in temperature and atmospheric circulation over the N Pacific and
Beringia relative to present.
The temperatures derived from CBT–MBT
Model simulations for SLP (JJA) are shown Fig. 4a. The LGM simulation is
characterized by strong positive anomalies in SLP over the North American
continent (Fig. 4a). Positive SLP anomalies also occur over the Arctic Ocean.
Negative SLP anomalies occur south of 50
The positive SLP anomalies over North America are associated with pronounced
anticyclonic anomalies in the wind directions, which expand to the
Chukchi Sea and to the formerly exposed Bering Land Bridge (Fig. 4a). Over
western Beringia as well as the adjacent Arctic Ocean, small northerly
anomalies are present. Between 100 and 110
Model simulations for SAT (JJA) are shown in Fig. 4b. The model predicts
widespread negative SAT anomalies over Beringia,
eastern Asia, North America, the Arctic Ocean and the entire N Pacific
(Fig. 4b). However, in small parts of the formerly exposed Bering Land Bridge
conditions that are
slightly warmer than present occur. On the arctic shelf there is a
small band where temperature is similar to the PI conditions (the SAT anomaly
falls in the window of
Considering that brGDGTs are thought to be synthesized by terrestrial
bacteria that thrive in peats and soils (e.g., Weijers et al., 2006b), it is
most likely that the major origin of brGDGTs in the marine sediments of the
Bering Sea and NW Pacific would be the Kamchatka Peninsula. However, BIT
values from core 12KL range between 0.08 and 0.2 (Meyer et al., 2016)
throughout the entire record, indicating that marine-derived GDGTs dominate
the total GDGT composition and that terrigenous input is low (Fig. 2c).
Marine settings where terrigenous input is low are particularly sensitive to
bias from in situ production (e.g., Weijers et al., 2006b; Peterse et al.,
2009; Zhu et al., 2011); thus, non-soil-derived brGDGTs potentially have a
considerable effect on the temperature reconstruction at site 12KL. However,
the concentrations of
Although the CBT–MBT paleothermometer has been suggested to generally record
mean annual air temperatures (Weijers et al., 2007), it is assumed to be
biased to the summer months and ice-free season in high latitudes (Rueda et al.,
2009; Shanahan et al., 2013; Peterse et al., 2014). According to the Klyuchi
climate station (for location see Fig. 1b), mean annual air temperatures in
the northern CKD are
The finding that LGM summers were as warm as during the Holocene contrasts
with the general understanding of the glacial climate, according to which the
extratropics were significantly colder than today, as documented by several
proxy-based temperature reconstructions and general circulation model
simulations (e.g., MARGO compilation or PIMP, and others; see Kutzbach et
al., 1998; Kageyama et al., 2001, 2006; Kim et al., 2008; Waelbroeck et al.,
2009; Braconnot et al., 2012; Alder and Hostetler, 2015). Generally cooler
LGM temperatures are thought to result from low summer insolation, reduced
carbon dioxide concentrations in the atmosphere and extensive continental ice
sheets (Berger and Loutre, 1991; Monnin et al., 2001; Kageyama et al., 2006;
Shakun et al., 2012). Therefore, one may expect that the Kamchatka Peninsula
would experience a glacial–interglacial warming trend. As MAT
In previous studies, the warm Siberian summers during the LGM were attributed
to increased continentality, which would arise from the exposure of the
extensive Siberian and Chukchi shelves at times of lowered sea level
(Fig. 1a; e.g., Guthrie, 2001; Kienast et al., 2005; Berman et al., 2011).
The greater northward extent of the Beringian landmass (approximately
Intriguingly, U
If oceanic circulation alone is unlikely to have caused the warm temperatures
on Kamchatka, atmospheric circulation may have exerted an important control
on glacial summer temperatures in the region. In terms of atmospheric
circulation, the summer climate of Kamchatka is largely determined by the
strength and position of the NPH over the N Pacific (Mock et al., 1998). As
the southerly flow at the southwestern edge of the NPH brings warm and moist
air masses to Kamchatka, summers on the peninsula become warmer when the NPH
and the associated warm southerly flow increase in strength (Mock et al.,
1998). This modern analogue suggests that the LGM NPH over the subarctic
NW Pacific was stronger than today
and the resulting warming effect may have balanced the cooling effects of
CO
These inferences contrast with results from the climate simulations with
COSMOS. For JJA, the model predicts a decrease in SLP over the NW Pacific,
suggesting that the southerly flow at the western edge of the NPH was reduced
rather than strengthened (Fig. 4a). The weakening of the southerly flow is
also discernable in the anomaly of the major wind patterns over the NW
Pacific (Fig. 4a) as a small northerly anomaly occurs north of Kamchatka,
over the peninsula itself and along the Asian coast (Fig. 4a). The weakening
of the NPH is in agreement with several other general circulation models (GCMs),
which consistently predict a reduction in SLP over the N Pacific (Kutzbach
and Wright, 1985; Bartlein et al., 1998; Dong and Valdes, 1998; Vettoretti et
al., 2000; Yanase and Abe-Ouchi, 2007; Alder and Hostetler, 2015). It has
been suggested that a pronounced positive SLP anomaly and a persistent
anticyclone over the North American continent resulted in reduced SLP over the
western northern Pacific (Yanase and Abe Ouchi, 2010). The positive SLP anomaly
and the strong anticyclonic tendencies are clearly present in the COSMOS
simulation of SLP and wind patterns (Fig. 4a) and were also simulated by
several other GCMs (e.g., Yanase and Abe-Ouchi, 2007, 2010; Alder and
Hostetler, 2015). Its development was attributed to the presence of extensive
ice sheets on the North American continent (Yanase and Abe-Ouchi, 2010), which
would have caused severe cooling of the overlying atmosphere. Considering the
consistency of different GCMs, the anticyclonic anomalies over North America
as well as resulting cyclonic anomalies over the N Pacific seem to be a
robust feature of the glacial atmospheric circulation. Therefore, it is
unlikely that the increased influence of the NPH over Kamchatka (as inferred
from MAT
Interestingly, the general patterns of temperature change over Beringia and
the N Pacific (as inferred from the proxy compilation, Fig. 4c)
suggest that the LGM thermal gradient between western and central Beringia and
the N Pacific was increased relative to today (Fig. 4c). While warm
summers were widespread in western Beringia (Alfimov and Berman, 2001;
Kienast, 2002; Kienast et al., 2005; Sher et al., 2005; Berman et al., 2011),
the majority of SST records from the open N Pacific and the Bering Sea
indicate colder conditions during the LGM (Fig. 4c; de Vernal and Pedersen,
1997; Seki et al., 2009, 2014; Kiefer and Kienast, 2005; Harada et al., 2004,
2012; Maier et al., 2015; Meyer et al., 2016). Under the assumption that
alkenone-based reconstructions of LGM SST in the Sea of Okhotsk (Seki et al.,
2004, 2009; Harada et al., 2004, 2012) are biased, the Sea of Okhotsk
may also have been significantly colder than at present, as suggested by
TEX
The distribution of temperature anomalies in the COSMOS simulation shows a
different pattern than the proxy compilation (Fig. 4b and c). The model
predicts a widespread cooling over Siberia and Kamchatka where the majority
of proxy data suggest warmer or equal temperatures relative to present.
Relatively warm summers in western and central Beringia (as inferred from the
proxy data) have been explained by increased continentality due to the
exposure of the Siberian, Bering and Chukchi shelves during the LGM (Guthrie,
2001; Kienast et al., 2005; Berman et al., 2011). In the model the impact of
continentality may be comparable to the proxy world over the eastern Siberian
and the northern Chukchi shelves since SAT anomalies are between
Given the discrepancies between proxy-based temperature reconstructions for Siberia and the ESM, the thermal gradient between western Beringia and the subarctic NW Pacific may also differ. In the model simulation the thermal contrast between land and ocean tends to become smaller since the negative temperature anomaly over western Beringia for the most part is more pronounced than over the subarctic N Pacific (Fig. 4b). This contrasts with the proxy compilation, according to which the thermal gradient may have been increased relative to the present gradient (Fig. 4c). As the model predicts a reduction of the thermal gradient the preconditions for the increased landward airflow are not given. In contrast, a reduced thermal gradient would support a northerly anomaly, which is in accordance with the simulated wind patterns over Kamchatka (Fig. 4a). Hence, the discrepancies between proxies and model outputs concerning glacial summer temperature over western Beringia potentially explain the mismatch between model- and proxy-based reconstructions of the atmospheric circulation patterns over the NW Pacific.
The deglacial millennial-scale variability resembles the climate development
in the N Atlantic as MAT
While the western Bering Sea was likely already coupled to the N Atlantic
prior to
The presence of a YD cold reversal on Kamchatka is in agreement with
palynological data from the lakes Dolgoe, Smorodynovoye, Ulkhan Chabyda and
El'Gygytgyn (Fig. 1a; Pisaric et al., 2001; Anderson et al., 2002; Kokorowski
et al., 2008b), suggesting that the N Atlantic climate signal was transmitted
to these sites (Kokorowski et al., 2008b). By contrast, a climatic reversal
equivalent to the YD is often absent in records from northeast Siberian Lake
Jack London, Lake Elikchan 4, Lake El'Gygytgyn and Wrangel Island (Fig. 1a;
Lozhkin et al., 1993, 2001, 2007; Lozhkin and Anderson, 1996; Nowaczyk et
al., 2002; Nolan et al., 2003; Kokorowski et al., 2008a, b; Andeev et al.,
2012). Compiling deglacial records from Beringia, Kokorowski et al. (2008b)
identified an east–west gradient across western Beringia with a YD-like
climatic reversal being present west of 140
Although not quite pronounced in magnitude, the long-term MAT
Based on the CBT–MBT
LGM summers were as warm as at present. The warm summers may result from stronger-than-present southerly winds over Kamchatka as a result of a stronger-than-present anticyclone over the subarctic NW Pacific. The temperature reconstruction as well as the inferences for atmospheric circulation contrast with model simulations, which predict widespread cooling over Siberia and Kamchatka and a weakening of the NPH over the NW Pacific, together with a reduction of southerly winds over Kamchatka. These discrepancies underline the need for further investigations of the LGM climate in the NW Pacific realm using environmental indicators and GCMs.
Abrupt millennial-scale fluctuations characterize the deglacial temperature development and represent the most prominent changes in summer temperature during the past 20 kyr. A first abrupt cooling event at 18 ka BP marks the end of the warm LGM conditions and was likely caused by regional climate change, the origin of which cannot be identified yet. From around 15 ka onwards, the temperature variations seem to be linked to climate change in the N Atlantic, presumably via atmospheric teleconnections as the B–A interstadial and the YD cold reversal are present. Discrepancies with northeastern Siberian records are possibly related to the position of the westerly jet.
The biomarker data obtained in this study are available at
Sites and references for the data compiled in Fig. 4c. BLB: Bering Land Bridge.
The authors declare that they have no conflict of interest.
The study was part of a PhD project funded by the Helmholtz Association
through the President's Initiative and Networking Fund and is supported by
GLOMAR – Bremen International Graduate School for Marine Sciences. Core
SO201-2-12KL was recovered during cruise SO201-2, which took place in 2009
within the framework of the German–Russian research project “KALMAR –
Kuril–Kamchatka and Aleutian Marginal Sea Island Arc Systems: Geodynamic and
Climate Interaction in Space and Time”. We thank the Master and the crew of
R/V