Temperature variations during the
past 20 ka at Huguangyan Maar Lake in tropical China and dynamic link
Qi Li1,2, Qing
Sun3, Manman Xie3, Yuan
Ling4, Zeyang Zhu1, Qingzeng
Zhu1, Nan Zhan3, Guoqiang
Chu1,5,6
1Institute of
Geology and Geophysics, Chinese Academy of Sciences, Beijing 100029,
China.
2 University of Chinese Academy of Sciences, Beijing
100049, China.
3 National Research Center of Geoanalysis, Beijing
100037, China.
4 Institute of Geology, Chinese Academy of Geological
Sciences, Beijing 100037, China.
5 CAS Center for Excellence in Life and
Paleoenvironment, Beijing 100044, China.
6 Innovation Academy for Earth Science, Chinese
Academy of Sciences, Beijing 100029, China.
Corresponding author:
G. Chu (chuguoqiang@mail.igcas.ac.cn) and Q. Sun (sunqing1616@yahoo.com)
Key Points:
- A temperature record over last 20 ka from Huguangyan Maar Lake in
tropical China based on brGDGTs
- The Holocene temperature evolution at Huguangyan Maar Lake
characterized with a regional-scale temperature change
- Ice volume may be main driving force on the temperature change of
Huguangyan Maar Lake region from the Last Glacial Maximum to Holocene
Abstract
Discrepancies exist in global temperature evolution from the Last
Glacial Maximum to the present between model simulations and proxy
reconstruction. This debate is critical for understanding and evaluating
current global warming on a longer timescale. Here we report a branched
GDGTs-based temperature reconstruction from the sediments of Huguangyan
Maar Lake in southeast China and validate it using historical
documentary evidence and instrumental data. The reconstructed mean
annual air temperature (MAAT) indicates distinct changes during the last
deglaciation (Oldest Dryas, Bølling-Allerød, Younger Dryas). During the
Holocene, temperatures gradually increased from the end of the Younger
Dryas to ~7.0 ka BP, followed by a decrease in recent
decades. However, our terrestrial temperature record differs with model
simulations and proxy sea surface temperature records of the Holocene.
We conclude that ice volume or ice sheet is the most prominent forcing
that controlled the regional temperature evolution from the Last Glacial
Maximum to the beginning of the middle Holocene; while the temperature
variations during the middle and late Holocene were mainly regulated by
several possible factors, such as oceanic and atmospheric circulation,
and external drivers (solar and volcanic activity).
1 Introduction
There is an ongoing debate about the Holocene temperature record of the
extratropical Northern Hemisphere. Proxy records show a general
long-term cooling trend since the early Holocene (Marcott et al., 2013),
while model simulations indicate a warming trend over the past
~12,000 years (Liu et al., 2014). Models play an
important role in understanding how climate systems respond to various
forcing factors and boundary conditions. However, many dynamic processes
are not well computed or weighted in the model simulations, such as
external forcing factors (solar irradiance and explosive volcanism), and
the internal variability of the climate system (e.g., ENSO, PDO, AO, and
the monsoon). Moreover, proxy-based temperature reconstructions are
often of low resolution and have relatively large uncertainties in proxy
calibration and dating, as well as regional or seasonal biases. Hence,
more regional proxy-based paleoclimate time series are needed to verify
the climatic record of the Holocene and to understand the differences
between model simulations and paleoclimate reconstructions.
In this study, we present a high resolution branched glycerol dialkyl
glycerol tetraethers (brGDGTs) membrane lipids-based temperature
reconstruction (0-10 ka BP) combined with previously published data
(10-20 ka BP) from the sediments of Huguangyan Maar Lake (21º9´N,
110º17´E) in tropical China (Chu et al., 2017), with the aim of
obtaining a regional terrestrial temperature record and to understand
its dynamic links.
Our paleotemperature proxy is based on brGDGTs, which comprise two
dialkyl chains with different amounts of methyl and cyclopentane
moieties (Damsté et al., 2009; Hopmans et al., 2004; Naafs et al., 2017;
Sanchi et al., 2014; Schouten et al., 2000; Schouten et al., 2013; Sun
et al., 2011; Tierney & Russell, 2009; Weijers et al., 2007). The
physical and biological mechanisms of the temperature sensitivity of
brGDGTs could be due to their membrane components maintaining membrane
fluidity via methyl and cyclopentane moieties (Damsté et al., 2002;
Huguet et al., 2007; Weijers et al., 2007). The methylation index of
branched tetraethers (MBT) and the cyclization ratio of branched
tetraethers (CBT) have previously been used to reconstruct terrestrial
paleotemperatures from lacustrine sediments, soils, and peat sequences
(Ding et al., 2015; Naafs et al., 2017; Peterse et al., 2012; Weijers et
al., 2007; Yang et al., 2014).
Numerous studies have confirmed that brGDGTs-based indices from
lacustrine sediments can be used to reconstruct terrestrial
paleotemperatures (De Jonge et al., 2014; Hu et al., 2016; Kaiser et
al., 2015; Loomis et al., 2012; Martin et al., 2020; Naafs et al., 2017;
Pearson et al., 2011; Russell et al., 2018; Sun et al., 2011; Tian et
al., 2019; Tierney et al., 2010; Weijers et al., 2007; Zink et al.,
2016). However, several interpretational uncertainties remain, such as
regarding the relative contributions of aquatic sources and soil sources
to brGDGTs because the calibration functions from soils and lakes are
quite different. Huguangyan Lake is a small, hydrologically-closed lake
with no inflows and a small watershed area, and therefore the
sedimentary organic matter originates mainly in the water column (Chu et
al., 2017; Hu et al., 2016). The within-lake origin of the sedimentary
organic matter, which is also supported by the relatively low
sedimentary TOC/N ratios since ~20 ka BP (Chu et al.,
2002), substantially reduces this source of uncertainty in
paleotemperature reconstruction. Previous brGDGTs-based MAAT
reconstructions during the last deglaciation from the sediments of
Huguangyan Maar Lake demonstrated a distinctive pattern of temperature
changes from during the Oldest Dryas, Bølling-Allerød, Younger Dryas,
and the onset of the Holocene (Chu et al., 2017).
2 Materials and Methods
2.1 Study site
Maar lakes are recognized as ideal sites for preserving high-resolution
sedimentary archives because they are closed basins with a relatively
simple hydrological system and they provide continuous sedimentary
sequences (Yancheva et al., 2007). Huguangyan Maar Lake is a closed
basin without stream inputs located in the Leizhou Peninsula in the
tropical region of South China. The surface area is 2.3 km2,
the maximum water depth is 22 m,
and the watershed area is 3.2 km2 (Figure 1) (Chu et al., 2002; Yancheva
et al., 2007). The area has a mean annual air temperature of 23.4℃ and a
temperature difference between winter and summer of 11.9℃ (1964–2004;
data from Zhanjiang meteorological station). Overlapping piston cores
were collected from near the center of the lake in a water depth of 14
m. The cores were sliced at a 1-cm interval and then freeze dried for
GDGTs extraction.