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Reconstructing 1200 years of Hydroclimate Variability in the Southern Margins of the Arabian Desert: Insights From a Paleo-Lake in Southern Yemen

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Reconstructing 1200 years of Hydroclimate Variability in the Southern Margins of the Arabian Desert: Insights From a Paleo-Lake in Southern Yemen

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The climate of the Arabian Desert is not well documented during the past two millennia due to the scarcity of continuous and well-dated terrestrial archives in the region. Reliable interpretation from the climatic records from this region are pivotal for identifying periodicities of inter-annual to multi-decadal variability and trends driven by shifts in position of the Intertropical Convergence Zone (ITCZ) and the strength of the monsoons. A high-resolution multiproxy approach is presented for a ∼3.3 m composite core, GBW, from a karst lake located in Ghayl ba Wazir, southern Yemen. Sedimentary proxies, including particle size distribution, coupled with magnetic susceptibility (MS) and geochemistry (XRF), provide a comprehensive picture of sediment depositional changes that may be linked to climate and environmental variability over the southern Arabian Desert. The chronology of the GBW core is provided by five radiocarbon ( ¹⁴ C) dates from terrestrial macrofossils (wood and twigs) extracted from sediment samples and indicates the core extends to ∼900 CE. Our data indicates generally wetter conditions from 930 to 1400 CE corresponding to the “Medieval climate anomaly (MCA)” followed by arid phases during 1,410–1700 CE coinciding with the “Little Ice Age (LIA)”. Evidence for a drier LIA include high authigenic calcium precipitation [Ca/(Al + Fe + Ti)], decreased TOC/TIC values, and gypsum precipitation, whereas the wetter MCA is characterized by higher detrital element ratios (Ti/Al, K/Al, Rb/Sr), and increased TOC/TIC and deposition of finer sediments (EM1). Furthermore, end-member mixing analyses (EMMA) derived from the grain-size distribution (EM2 and EM3) corroborates the deposition of coarser silt sediment through wind erosion and production of carbonate sand during the LIA concurrently with low lake levels under generally dry conditions. Aridity during the LIA is consistent with evidence and theory for weakened boreal summer monsoons during intervals of northern hemisphere cooling.
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Reconstructing 1200 years of
Hydroclimate Variability in the
Southern Margins of the Arabian
Desert: Insights From a Paleo-Lake in
Southern Yemen
Shah Parth
1
*, James Russell
2
and Nicolas Waldmann
1
1
Dr. Moses Strauss Department of Marine Geosciences, Charney School of Marine Sciences, University of Haifa, Haifa, Israel,
2
Department of Earth, Environmental and Planetary Sciences, Brown University, Providence, RI, United States
The climate of the Arabian Desert is not well documented during the past two millennia due
to the scarcity of continuous and well-dated terrestrial archives in the region. Reliable
interpretation from the climatic records from this region are pivotal for identifying
periodicities of inter-annual to multi-decadal variability and trends driven by shifts in
position of the Intertropical Convergence Zone (ITCZ) and the strength of the
monsoons. A high-resolution multiproxy approach is presented for a 3.3 m composite
core, GBW, from a karst lake located in Ghayl ba Wazir, southern Yemen. Sedimentary
proxies, including particle size distribution, coupled with magnetic susceptibility (MS) and
geochemistry (XRF), provide a comprehensive picture of sediment depositional changes
that may be linked to climate and environmental variability over the southern Arabian
Desert. The chronology of the GBW core is provided by ve radiocarbon (
14
C) dates from
terrestrial macrofossils (wood and twigs) extracted from sediment samples and indicates
the core extends to 900 CE. Our data indicates generally wetter conditions from 930 to
1400 CE corresponding to the Medieval climate anomaly (MCA)followed by arid phases
during 1,4101700 CE coinciding with the Little Ice Age (LIA). Evidence for a drier LIA
include high authigenic calcium precipitation [Ca/(Al + Fe + Ti)], decreased TOC/TIC values,
and gypsum precipitation, whereas the wetter MCA is characterized by higher detrital
element ratios (Ti/Al, K/Al, Rb/Sr), and increased TOC/TIC and deposition of ner
sediments (EM1). Furthermore, end-member mixing analyses (EMMA) derived from the
grain-size distribution (EM2 and EM3) corroborates the deposition of coarser silt sediment
through wind erosion and production of carbonate sand during the LIA concurrently with
low lake levels under generally dry conditions. Aridity during the LIA is consistent with
evidence and theory for weakened boreal summer monsoons during intervals of northern
hemisphere cooling.
Keywords: lake sediment, paleoclimate, late holocene, Indian Summer Monsoon, XRF, Yemen, medieval climate
anomaly, little ice age
Edited by:
Davide Tiranti,
Agenzia Regionale per la Protezione
Ambientale (ARPA), Italy
Reviewed by:
Priyeshu Srivastava,
University of São Paulo, Brazil
Steven L. Forman,
Baylor University, United States
*Correspondence:
Shah Parth
pds.shah121@gmail.com
Specialty section:
This article was submitted to
Quaternary Science, Geomorphology
and Paleoenvironment,
a section of the journal
Frontiers in Earth Science
Received: 20 May 2021
Accepted: 19 November 2021
Published: 07 December 2021
Citation:
Parth S, Russell J and Waldmann N
(2021) Reconstructing 1200 years of
Hydroclimate Variability in the Southern
Margins of the Arabian Desert: Insights
From a Paleo-Lake in Southern Yemen.
Front. Earth Sci. 9:712443.
doi: 10.3389/feart.2021.712443
Frontiers in Earth Science | www.frontiersin.org December 2021 | Volume 9 | Article 7124431
ORIGINAL RESEARCH
published: 07 December 2021
doi: 10.3389/feart.2021.712443
INTRODUCTION
Large sub-tropical desert belts on Earth are formed due to a drastic
decline in the distribution of rainfall that results from changes in
atmospheric circulation (Edgell, 2006;Warner, 2009). Continuous
terrestrial records located near desert margins (e.g., lacustrine, uvial,
cave and aeolian) have provided valuable insights into past climate
and hydrological changes, which were often linked to uctuations in
the strength and latitudinal penetration of the summer monsoons
(Singhvi and Kar, 2004;Sinha et al., 2006;Lespez et al., 2011;
Wassenburg et al., 2016,amongothers).Lacustrinesediments,in
particular, have provided valuable paleoenvironmental records from
these regions (Abbott et al., 1997;Davies, 2006;Andersson et al.,
2011) as they combine continuity with very high resolution.
However, such records are only partially preserved or totally
missing in the mid-and low-latitude desert belts.
Lakes situated near major global atmospheric circulation systems
are likely to be highly susceptible to subtle changes in climate over
time. The Arabian Peninsula is one of these locations as its northern
areas are impacted by the Northern Westerlies Wind belt, while the
southern margins are inuenced by the Indian Summer Monsoon
(ISM) circulation, with the latter linked to latitudinal changes in the
Inter-Tropical Convergence Zone (ITCZ) position (Staubwasser
et al., 2002;Gupta et al., 2003). Mechanisms inuencing the
current precipitation in the SW margins of the Arabian
Peninsula are linked to shifts in the Red Sea Trough (RST),
which is a low-pressure semi-permanent active zone over the Red
Sea that generates local convective rainfall (Farquharson et al., 1996;
Al-ameri et al., 2014). However, the precipitation pattern in the
region is also modulated by the ISM, which brings moisture towards
the southern Arabian Peninsula associated with northwards
migrations of the ITCZ (Rodwell and Hoskins, 1996;Enzel et al.,
2015). Holocene climate reconstruction from Yemen shows
signicant changes in the hydrological balance, probably as a
response to the magnitude of monsoonal precipitation over time
(Davies, 2006;Lézine et al., 2010;Berger et al., 2012). However, the
existing lacustrine records are of relatively low temporal resolution.
Other records, such as isotope data from speleothems, have proved
to be valuable archives of climate change at high resolution, although
with less continuity (Shakun et al., 2007;Fleitmann et al., 2011;Van
Rampelbergh et al., 2013).
Hemispheric to global reconstructions have shown that
warmth during the last two millennium reached a peak during
the Medieval Climate Anomaly (MCA; from 950 to 1350 CE;
Gayo et al., 2012), followed by increased cooling conditions
during the Little Ice Age (LIA; 1,500 to 1800 CE; Matthews
and Briffa, 2005;Miller et al., 2012), and anthropogenic post-
industrial warming (Levitus et al., 2001). In fact, these two climate
intervals (MCA and LIA) are dened in terms of temperature
changes in the northern hemisphere; however, the temperature
shifts in sub-tropical and tropical regions probably triggered
changes in the moisture balance, which in turn gauged the
amount and intensity of precipitation (Trenberth et al., 2003).
The causes for the MCA and LIA have been widely discussed and
linked to natural mechanisms, including solar and volcanic
forcing as well as anthropogenic processes such as land cover
decrease (Shindell et al., 2001;Ruddiman, 2013; among others).
However, disagreement continues on the exact timing of both
MCA and LIA intervals, which appear desynchronized worldwide
(Crowley and Lowery, 2000;Broecker, 2001;Neukom et al.,
2019), with many studies pointing to profound differences in
temperature and precipitation gradients (e.g., Cronin et al., 2010;
Jomelli et al., 2016). For example, while tropical East Africa
experienced arid conditions during the MCA due to weak East
African monsoons (Tierney et al., 2011), drier conditions
associated with a positive phase of the North Atlantic
Oscillation (NAO) characterizes the southern Levant during
the same interval (Toker et al., 2012;Kushnir and Stein,
2019). Thus, there is a need to increase information density
from climate archives around the globe to produce a reliable
dataset for understanding the mechanisms and modalities of
these two climate systems (MCA and LIA). The current study
aims to enhance our understanding of the impact of these two
climate phases by exploring sub-tropical hydrologic changes
recorded in Gayal el Bazal, a lacustrine sedimentary sequence
from southern Yemen, and its the relation with tropical
monsoonal circulation.
STUDY AREA
Gayal el Bazal is located in the town of Ghayl Ba Wazir, at 85 m
above mean sea level, in the southern part of the Hadhramwat
province, between the base of the Jabal Hasusah mountain cliffs
and the Arabian Sea (Figure 1A). The geology of the region
includes the Ghabar Group, which consists of metamorphic to
anchi-metamorphic units, namely sandstone, greywacke,
conglomerate, rhyolite, and quartzite rocks (As-Saruri and
Wiefel, 2012). The region is characterized by several karstic
sinkholes developed as a result of the dissolution of gypsum
and limestone units from the Cretaceous Rus Formation
(Hehmeyer et al., 2002). Lake Gayal el Bazal has occupied one
of these sinkholes until very recently when it was reduced to small
residual pools (Figure 1D), likely resulting from human
groundwater withdrawal and agriculture. Currently, the small
lake area (0.1 km
2
,Figure 1C) is utilized by local communities for
agriculture, mainly tobacco and palm plantations. The
hydrological balance of the Gayal el Bazal is primarily
controlled by summer precipitation (with an estimated mean
of 56 mm/yr) that falls over the main feeding Wadi Huwairah
watershed (Figure 1B) and by an unknown amount of
groundwater inltration from the local aquifers. This limited
precipitation amount promotes conditions of extreme pluvial
events, with ash oods leaving a dramatic effect on local social
and economic sustainability (Llasat et al., 2010). As for the water
output balance, evaporation accounts for the sole estimated water
output with unknown rates.
The climate of the studied area is characterized by extremely
hot and dry conditions, with a monthly average ranges from 40°C
to 43°C during summer and 28°C31°C during winter (Bakhlah
and Hassan, 2012). A hyper-arid desert dominates the east and
north of our site (Almazroui, 2012), while the south part is
slightly more temperate due to the Arabian Sea proximity
(Hadden, 2012). Some minimal moisture appears to pass
Frontiers in Earth Science | www.frontiersin.org December 2021 | Volume 9 | Article 7124432
Parth et al. Late-Holocene Paleoclimatic Record From Yemen
across the Hadhramaut Mountains to the north (that reach
1,300 m) as a consequence of local orographic uplift and to
reach the Arabian Desert, although the rates of this humidity are
mostly unknown (Fleitmann et al., 2007). Most of the seasonal
precipitation (60%) over the region of Gayal el Bazal occurs
during the spring months of March-April-May (MAM) through
RST (Figure 2B;Baseer et al., 2019). During the summer season
June-July-August (JJA), the moisture (30%) is contributed by
the ISM (Figure 2C;Fleitmann and Matter, 2009), and limited
moisture is provided in the form of the winter season as a result of
increasing outbreaks of North Westerly (NW) circulation
(Figure 2D;Hasanean and Almazroui, 2015).
MATERIALS AND METHODS
Sample Collection
Three sites were cored in the Gayal el Bazal paleo-lake system
aiming to retrieve a spatial coverage of the different sedimentary
facies. The cores named Yemen-GBW01-2A (IGSN:
CDR0000GK), Yemen-GBW01-2B (IGSN: CDR0000GL),
Yemen-GBW01-3B (IGSN: CDR0000GM) were retrieved
during a eld campaign in December 2001 using a Livingstone
piston corer, and cores measured 271, 95, and 108 cm
(respectively) and were transported to the LacCore repository
facility in Minnesota (United States) for curation and
preservation.
Lab Measurements
Once in the lab, the cores were submitted to a set of non-
destructive measurements, including magnetic susceptibility
using a Bartington loop mounted to a Geotek multi-sensor
core logger at a 5 mm (2.5 mm up and down) resolution and
the data smoothed over 50 data points. Following this step, the
cores were cut lengthwise into two halves (working and archive).
While the archive halves were used for lithological description,
imaging, and measurement of the elemental content using an
ITRAX μX-Ray Fluorescence (XRF) core scanner, the working
halves were used for destructive measurements (physical
sampling). XRF measurements were done at a 0.5 cm
resolution with the Cr and Mo tubes for identifying lighter
and heavier elements, respectively (Croudace et al., 2006). The
scanner generates element-related X-ray uorescence peaks,
and intensity is expressed in counts per second (cps),
reecting each given elemental concentrations (Löwemark
et al., 2011;Rothwell, 2015;Chawchai et al., 2016). A semi-
FIGURE 1 | (A) A SRTM 30 m elevation map of the SW part of the Arabian Peninsula with the studied area in Southern Yemen highlighted in a black square. (B)
Geological map of the studied area marked in (a), highlighting the Wadi Huwairah watershed (red polygon) and the location of Gayal el Bazal (black square) (modied after
Pollastro et al., 1999). The black square stands for the Gayal el Bazal area. (C) Detailed map of the Gayal el Bazal area. Black polygon marks the Gayal el Bazal Lake
watershed with the riverine network system. The lake location is marked by a red polygon (Google Earth image, 2004). (D) Field photograph showing lake setting
and core collection using Livingstone piston corer.
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Parth et al. Late-Holocene Paleoclimatic Record From Yemen
quantitative analysis of the elements can be performed by
normalizing element counts with total counts or Al to make
a better comparison within intervals. Considering the
parameters used during the XRF measurements, Al counts
were reliable and were selected for normalization.
X-ray diffraction (XRD) measurements were carried out using
a Rigaku Miniex X-ray Diffractometer for the mineralogical
study of the sediments. The mineral identication was carried out
using PDXL 2 software, which uses a prole- and peak-based
search approach based on detailed peak information. The
quantitative analysis using reference intensity ratio determined
the relative abundance of individual minerals.
Further destructive measurements include total inorganic and
total organic carbon (TIC and TOC, respectively) at a 3cm
resolution using a Skalar Primacs Series Total carbon analyzer.
The samples were freeze-dried, weighed, and homogenized before
the measurement. TIC was determined by acidication in the IC
compartment at low temperature (100°C), which releases CO
2
to
measure the abundance of inorganic carbon in the sediments. For
TOC, dried sediments were treated with 1N HCl in order to
remove carbonates, followed by heating the sample in the TC
compartment at 700°C in the presence of pure Oxygen resulting
in CO
2
releasing and generation of the abundance of organic
carbon in the sediments.
Granulometric analysis was conducted using a Beckman
Coulter LS 13 320 mw laser diffraction particle size analyzer
on the same sampling resolution (3 cm; n 139). The sediments
were pretreated with 10 ml H
2
O
2
(30%) for organic matter
removal and followed by acidifying using 1N HCl for removal
of carbonate from the sediments (Murray, 2002;Vaasma, 2008).
The solution containing digested sediments was washed with
distilled water several times to remove the extra oxidizing
reagents. The solution was homogenized with an ultrasonic
bath prior to measurement. The grain size distribution was
calculated for 100 grain size classes (particles sizes between
0.04 and 2000 µm), and the analytical error was less than 1%.
The chronology was established using AMS radiocarbon (
14
C)
dating carried out at PoznańRadiocarbon Laboratory, Poland, on
FIGURE 2 | The proportion of rainfall (19702010) by seasons: (A) winter (Dec-Feb), (B) spring (Mar-May), (C) summer (Jun-Aug), and (D) fall (Sept-Nov) (Source:
WorldClim 2021).
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Parth et al. Late-Holocene Paleoclimatic Record From Yemen
wood and plant remains. Samples were selected from 5 different
layers representing the whole composite core and weighed
between 515 mg for sufcient precision of
14
C dating. The
raw AMS radiocarbon dates were calibrated using the OxCal
program (Bronk Ramsey, 2009) with the most recent IntCal20
calibration curve (Reimer et al., 2020).
Statistical Approaches
For XRF data interpretation, a statistical approach was applied to
understand possible grouping and disentangle complex signals
out of the dataset. Further statistical analyses of the data [such as
calculation of the principal component analysis (PCA)] were
carried out using princomp function in R-Studio software
(Mardia et al., 1979;Venables and Ripley, 2002). PCA is an
important tool used for reducing the multivariate data into fewer
dimensions and can help aid the interpretation of multiple
elements. PCA transforms an original set of N-variables into a
new set of N-principal components, which are orthogonal to each
other (Xue et al., 2011). Each component is weighted in light of a
linear combination of the original variables.
End-member mixing analysis (EMMA) was applied on the
grain size parameters to understand the sediment mixtures in a
series of sedimentary components (end members) reecting the
transport mechanisms and sediment sources (Dietze et al., 2012,
2013;Mishra et al., 2019). End member mixing analysis is a
statistical tool that can disentangle the modes of transport of the
sediments from polymodal particle size distribution (Weltje,
1997). The number of modes of transportation was selected
based on a best-t model for grain size distribution,
representing the relation between the number of end members
and the coefcient of determination (r
2
). After optimizing all the
parameters (n, q, l), the statistical analysis was performed using
EMMA function based on EMMAgeo-package, in R-language
(Dietze et al., 2012).
RESULTS
Stratigraphy and Lithology
A composite core record was generated based on correlation of
the different cores sequences and through a detailed identication
of the same lithology units and layers in all sections. The
composite core GBW reaches 3.26 m in length, and three
different lithological units are established (LU-1 to LU-3) and
distinguished by distinct sedimentary facies (Figure 3).
Unit LU-1 (326191 cm) is characterized by clayey silt and
sandy silt beds separated by minor erosional contacts. The
FIGURE 3 | The lithology of Gayal el Bazal sediment core showing the magnetic susceptibility (MS), the XRF (Ca counts), the XRD data (calcite, gypsum and quartz
abundance), and TOC/TIC values.
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Parth et al. Late-Holocene Paleoclimatic Record From Yemen
mineralogical composition is dominated by calcite which is
the most abundant mineral (range 16100%), followed by
gypsum (038%) and quartz (026%). There are increases in
quartz minerals at 217208 cm, 267250 cm, and
295286 cm intervals; Figure 3. The MS values in LU-1
range from 2.78 to 11.57 ×10
7
SI and average 5.46 ×10
7
SI. MS decreases at 326265 cm and 251224 cm and
increases from 205 to 200 cm, where the highest values
are observed for this unit (Figure 3). The Ca abundance
displays a similar pattern or curve with MS values for those
intervals (r 0.93; Figure 3). TOC/TIC content in the LU-1
unit varies between 0.07 and 0.92, with higher values of
TOC/TIC in specic layers (217208 cm, 237222 cm,
267250 cm, and 295286 cm) (Figure 3).
Unit LU-2 (19171 cm) is marked by silty sand and sandy
silt and the appearance of gypsum. The sediments in the
unit mainly contain calcite (0.4100%) and gypsum
(0100%) abundance minerals with a trace amount of
quartz (036%). The MS values range from 2.5 to 11.2 ×
10
7
SI with an average of 5.7 ×10
7
SI, and higher values are
for intervals from 102 to 99 cm, 136139 cm. The higher
value of MS is also marked by higher values of Ca counts,
coarser grain size (silty sand layers), and increased gypsum
abundance (Figure 3). TOC/TIC values range from 0.04 to
0.86 and average 0.25 in the LU-2 unit. Lower TOC/TIC are
observed for intervals 9893 cm, 146126 cm, and
191174 cm (Figure 3). The LU-2 unit is also marked by
deposition of clayey silt sediments at 90.587.5 cm and
125121 cm (Figure 3).
Unit LU-3 (711 cm) consists of clayey silts and sandy silts
with abundant quartz compared to the rest of the sequence.
Specically, the interval 291 cm is marked by a clayey silt
bed with increased quartz mineral for that interval
(Figure 3). The MS values uctuate from 3.3 to 11.2 ×
10
7
SI and average 5.34 ×10
7
SI. Lower values of MS are
observed from interval 291cm (Figure 3). TOC/TIC
content in this unit varies between 0.23 and 0.57 and
showing lower values of TOC/TIC are observed from 63
to 50 cm (Figure 3).
Geochemistry and Statistical Analysis
XRF analyses document considerable variations in the counts
formajorelementslikeAl,Si,S,Cl,K,Ca,Ti,Mn,Fe,Srand
minor elements like Rb and Zr, which we interpret to reect
FIGURE 4 | Major XRF data presented in the paper and compared with a high-resolution core image of GBW. The elemental variability of Ca/(Al + Fe + Ti), S counts,
Ti/Al, K/Al, and Rb/Sr is shown (see text for more details).
Frontiers in Earth Science | www.frontiersin.org December 2021 | Volume 9 | Article 7124436
Parth et al. Late-Holocene Paleoclimatic Record From Yemen
relative abundance changes. Element abundance and ratios
like Ca/(Al + Fe + Ti), S counts, Ti/Al, K/Al, and Rb/Sr show
signicant variability through the whole GBW composite
core (Figure 4). The element ratios like Ti/Al, K/Al, and
Rb/Sr exhibits similar stratigraphic patterns. Unit LU-1
records the higher values of Ti/Al, K/Al, and Rb/Sr from
217 to 208 cm, 237222 cm, 267250 cm, and 295286 cm
(Figure 4). Unit LU-2 also shows sharp spikes in Ti/Al, K/Al,
and Rb/Sr from 90.5 to 87.5 cm and 125121 cm (Figure 4).
However, Ca/(Al + Fe + Ti) sharply increases at 9893 cm,
146126 cm, and 191174 cm and higher values of S counts
from 126 to 146 and 162191 (Figure 4). In Unit LU-3, Ti/Al,
K/Al, and Rb/Sr increases from 35 to 1 cm. Additionally, Ca/
(Al + Fe + Ti) shows increase trend interval between
5934 cm (Figure 4).
The principal component (PC) analysis reveals two
components explaining 69% variability in the dataset
(Figure 5A). PC1 receives positive loading from Ti, K, Fe, Si,
Rb, Al, and Zr and negative loading from Ca (Figure 5B). The
PC2 has positive loading from S and Sr but negative loading from
Cl (Figure 5C). The biplot of PC1 and PC2 shows elements like
Ti, K, Fe, and Rb are oppositely associated with Ca, Sr, and S
(Figure 5A).
Grain Size Distribution and Statistical
Approach
The clastic grain size distribution of the GBW composite core is
largely characterized by silt with minor variations of sand and
clayey silt fractions. The mean grain size of the core ranges from
3.1 to 7.1 ϕand the coarsest grain size fraction is found at
152144 cm and nest fraction at 260 to 253 cm (Figure 6). The
overlay of all grain size data from all samples revealed a
polymodal distribution, and hence end-member analysis has
been applied. The EMMA of grain size distribution in GBW
core yielded an optimal model with ve end members and
explained 65% variability of the total dataset. End member 1
(EM1) represents the nest particle fraction in the core with the
dominant modal grain size of 7.1 and is in the range of clayey silt.
For EM2, the dominant modal grain size is 4.8 and lies in the
range of medium to coarser silt. Furthermore, EM3 (mode 3.2
ϕ), EM4 (mode 1.4 ϕ) and EM5 (mode 0.65 ϕ) are in the range
of ne, medium and coarse sand, respectively. Unit LU-1 is
marked by the increased relative abundance of EM1 from 216
to 209 cm and 269265 cm and a higher abundance of EM2
between 278276 cm and 305296 cm (Figure 6). Unit LU-2
represents higher contribution from EM3, EM4 and EM5 for
FIGURE 5 | Statistical analyses of the XRF data. (A) Principal Component Analysis (PCA) and biplot between PC1 and PC2 showing the geochemical parameters of
composite core GBW. (B) Loadings of principal components (PC1) derived from elemental data. (C) Loadings of principal components (PC2) derived from
elemental data.
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Parth et al. Late-Holocene Paleoclimatic Record From Yemen
intervals 8684 cm, 175167 cm, 180178 cm, 189186 cm and
signicant contribution from EM2 for 10995 cm, 118115 cm,
129126 cm, and 161158 cm (Figure 6). Unit LU-3 has
pronounced contribution from EM1 from 29 to 1 cm and
EM2 from 57 to 50 cm. For EM3, EM4, and EM5,
representing coarser particle size fractions are higher for
4135 cm in the unit (Figure 6).
Chronology
The age model for GBW is based on ve accelerator mass
spectrometry (AMS) radiocarbon dates on terrestrial
fragments (wood, twig, and plant remain) picked from
intervals 62, 112, 157, 242, and 325 cm depth of the GBW
composite core. The radiocarbon dates can also be affected by
the reservoir effect, which can skew results such that older
radiocarbon ages can appear than the equivalent age of the
sample (Philippsen, 2013). However, in the GBW composite
core, radiocarbon ages are based on the most reliable material,
including terrestrial macrofossils (short-lived twigs remains) for
younger sediments in the lake (Marshall et al., 2007).
Calibration of obtained
14
C dates was done with the IntCal20
calibration curve (Table 1;Reimer et al., 2020), and the age-
depth model was carried out using a Poisson process model
deposition (P_Sequence; Ramsey, 2008)(Figure 7).
DISCUSSION
Variability of Allochthonous vs
Autochthonous Depositional Patterns
in GBW
The elemental analysis documents a series of processes occurring
in the lake environment, including changes in the origin and
FIGURE 6 | Overlay of the grain size distribution of all samples and particle distribution through down-core sediments and ve end members with their relative
abundance plotted against the composite depth.
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Parth et al. Late-Holocene Paleoclimatic Record From Yemen
provenance of particles (e.g., allochthonous vs autochthonous),
oxidation/reduction conditions in the lake bottom, water
velocities and depth variabilities through time (Engstrom and
Wright, 1984;Zolitschka et al., 2002;Boyle, 2005;Weltje and
Tjallingii, 2008;Löwemark et al., 2011). These can in turn, reect
changes in climatic and limnological conditions. We interpret
that the inorganic geochemical compositions of the GBW core are
primarily controlled by both allogenic processes (uvial (wadi)
discharge and aeolian input) coupled with authigenic processes
(i.e. precipitation of evaporite minerals).
The statistical analyses of the elemental record (PC1) carried out
on the XRF data show that Ti, K, Si, Rb, and Zr follow the same
behavior, with elements like Mn and Fe partially following the same
positive axis (Figures 5A,B). Previous studies carried out on similar
settings points that Ti and K are geochemically stable lithogenic
elements, which are hosted by resistant minerals and are conservative
in most geochemical environments, and thus reect detrital input into
the lake (Boës et al., 2011). Changes in the concentration of Ti and K
can be related to either stronger catchment runoff, which reects
wetter conditions, or enhanced aeolian deposition, hence a low
precipitation regime (Hou et al., 2017). In the studied core, we
observe a direct association of Ti and K with the clayey silt or
ner fraction (EM1) of the sediment (r 0.78, Figure 8)and
hence these elements probably represent detrital origin. Many studies
done in lakes dominated by the siliciclastic type of sedimentation have
shownthatFeandMncanoriginate from detrital input and
catchment runoff, though they can often be related to redox
conditions in the sediment/water interface (Davison, 1993).
Therefore, interpretation of their temporal behavior in the
depositional system should carefully be considered in light of
variability occurring in the other measured elements. In GBW,
PC1 data reveals that Fe is alignedwithdetritalelements(Ti,K);
hence we estimate that it also represents an allogenic provenance
(Figures 5A,B). Although many studies use Si to estimate diatom
blooms (Schettler et al., 2006), which may occur during episodes of
increase in nutrient input from aeolian transport or volcanoclastic
materials (Peinerud, 2000) however, our statistical analysis shows a
close association of Si with Ti and K, which is carried by the silicate
fraction and may indicate a terrigenous source for Si (Figures 5A,B).
Rb appears to be associated with ne-grained siliciclastic rocks
(Kylander et al., 2011). In our core, this element shows a positive
correlation with Al and K (Figures 5A,B); hence can be used to
measure the amount of siliciclastic material depositing in the
basin. The Rb/Sr ratio is often associated with the chemical
weathering of catchment rock and can be interpreted as the
changes in uxes of dissolved materials within from catchment
(Miriyala et al., 2017). This behavior suggests positive loading on
PC1 indicates detrital inux into the lake system. Ca is on the
negative axis of PC1, and hence we estimate that it shows a non-
detrital origin; therefore, it indicates authigenic processes
occurring in the lake (Figures 5A,B)(Zhao et al., 2010). We,
accordingly, suggest that the elemental ratios of Ti/Al, K/Al, and
Rb/Sr (or PC1 score) are well suited for estimating changes in the
terrestrial sediment supply through time and can hence be used to
reconstruct past uvial discharge (Neugebauer et al., 2016).
PC2 is dened by positive loading of Sr and S and negative
loading of Cl (Figure 5C); hence this principal component
appears to indicate in-situ precipitation of carbonates.
Moreover, Ca indicates authigenic origin due to its negative
loading with PC1 (Figure 5B) and has no major correlation
with S and Sr (Figure 5C). However, there is a possibility of
allogenic sources of Ca to the lake basin cannot be omitted, and
could consist of both uvial and aeolian origins. Detailed XRD
TABLE 1 | Radiocarbon ages for the GBW core based on OxCal calibration (Reimer et al., 2020).
Composite Depth (cm) AMS
14
C(BP)Calibrated
14
C(CE)Error Lab no
62.5 200 ±30 1768 30 Poz-127874
112.5 370 ±30 1,565 30 Poz-120224
157.5 400 ±30 1,481 30 Poz-127875
242.5 675 ±30 1,326 30 Poz-120852
325.5 1,140 ±30 914 30 Poz-120852
FIGURE 7 | Age-depth model for the GBW core with grey lines indicating
condence limits and blue curve showing age-depth interpolation.
Frontiers in Earth Science | www.frontiersin.org December 2021 | Volume 9 | Article 7124439
Parth et al. Late-Holocene Paleoclimatic Record From Yemen
measurements reveal that the GBW core contains calcite and
gypsum, with the occasional appearance of quartz. The studies
also show that calcite might constitute a major percentage of dust
particles in the Arabian desert (Al-Dousari and Al-Awadhi, 2012;
Al-Dousari et al., 2013). In general, Ca represents an arid
environment; hence, to estimate the authigenic deposition of
Ca, the ratio between Ca/(Al + Fe + Ti) might represent a reliable
proxy of precipitation changes in the region (Mueller et al., 2009).
Higher values of this ratio can imply an increase in lake water
salinity coupled with lower runoff from the catchment, which
might point to dry conditions. S counts show a good correlation
with gypsum abundance (r 0.73, Figure 8), and their down-core
shifts in the sediment can be associated with lower lake levels or
shallow water depths, indicating dry climatic conditions in the
region.
Correlation of Magnetic Susceptibility, Total
Inorganic Carbon/Total Organic Carbon
With Elemental Proxies
The magnetic susceptibility (MS) properties of sediments are
inuenced by the presence of Fe-bearing ferromagnetic minerals
and serve as a proxy to disentangle the abundance of paramagnetic
and diamagnetic minerals, such as carbonates, quartz, and clays
(Bareille et al., 1994;Schnurrenberger et al., 2003). Previous studies
have shown that MS can be a reliable indicator of both external
processes (e.g., weathering magnitude and volcanism) and internal
chemical cycling in the lacustrine environment, particularly the
oxidation state in the sediment-water interface that can inuence
magnetite dissolution or formation (Rawat et al., 2021). In GBW, MS
values are relatively low (averaging 5.6 ×10
7
SI) compared to
carbonate rich lakes (Wünnemann et al., 2010;Pleskot et al., 2018),
which can be associated to an increase in the presence of diamagnetic
minerals or due to presence of negative magnetic susceptibility
values of rocks in the catchment area (e.g. sandstone, greywacke,
conglomerate, quartzite and carbonates). The MS values in the GBW
sediments are mainly controlled by the minerals of Ca in the
sediment as a high correlation is observed between Ca counts
and MS values (r 0.82, Figure 3 and Figure 8). Our GBW
core is highly enriched in calcite (a typical diamagnetic mineral)
with frequent intercalations of gypsum (least diamagnetic mineral),
and we nd that the layers enriched by gypsum have relatively higher
values of MS compared with those enriched by calcite (Ivakhnenko
et al., 2015). Furthermore, studies have shown that sediment
consisting of higher carbonate or organic matter can dilute the
concentration of magnetic minerals, also leading to low MS values
FIGURE 8 | A Pearson correlation matrix of elemental abundance and ratios, mineral abundance, different end members of grain size, MS, and TOC/TIC data of the
GBW composite core.
Frontiers in Earth Science | www.frontiersin.org December 2021 | Volume 9 | Article 71244310
Parth et al. Late-Holocene Paleoclimatic Record From Yemen
(Hounslow and Maher, 1999). In several previous studies, MS values
have been shown to increase with decreasing grain-size fraction
(Thompson and Morton, 1979;Dessai et al., 2009). However, in
GBW high values of MS are not necessarily associated with changes
in the grain size distribution. The MS values are also lower for higher
detrital inux events where quartz is found due to its diamagnetic
properties, however it doesntshowanysignicant variation
throughout the GBW core.
The Total Carbon (TC) budget of a lake is primarily controlled by
chemical and biochemical processes associated with the balance
between the water input and the evaporation of lake water
(Håkanson and Jansson, 1983). TIC is primarily controlled clastic
sediment input or precipitation/evaporation processes, depending
on whether carbonate minerals are allogenic or authigenic. In turn,
TIC can serve as a proxy for temperature and precipitation changes
(Yanhong et al., 2007). We estimate that TIC values increases during
drier conditions due to the increased carbonaceous dust inux as it
correlates quite well with calcite mineral abundance (r 0.7). Hence
for those intervals, lower values of TOC/TIC reect intervals with
sandy silt units. TOC indicates the productivity of the lake, oxic state
of the bottom waters and can also be used to track changes in the
organic deposition conditions through the sedimentary sequence
(Chen et al., 2001;Xu et al., 2007). The organic matter in the lake can
be derived from the allochthonous input through catchment runoff
or wadi inux and from autochthonous sources. However, in
general, low productive lakes get the signicant contribution of
organic matter from the allochthonous terrestrial sources (Dean and
Gorham, 1998). Hence, the primary source of TOC for the paleo-
lake Gayal el Bazal is the terrigenous sediment supply during the
relatively wetter condition in the region. The TIC and TOC data thus
are complex to interpret due to uncertainty in the sources of these
materials to the sediment through time. Nevertheless, the TOC/TIC
data used in conjunction with other proxies (e.g., Ti/Al, K/Al, and
Rb/Sr or PC1 score) provide information about different
sedimentary processes, such as uvial vs. aeolian input to the
lake, and thus reect rainfall changes. We further suggest that the
high preservation conditions of the organic matter result from
relatively fast burial processes, which in turn might indicate
deposition during intense oods.
Deposition and Transport Mechanism of
Sediments
The depositional patterns of lake sediment are controlled by
sediment transport mechanisms such as uvial inows, aeolian
transport, and turbid inows (Solohub and Klovan, 1970;Sly,
1994;Lou et al., 2000;Stuut et al., 2002). These different transport
mechanisms and depositional conditions can yield high
variability in grain size distribution and grain morphology
(e.g., sphericity and roundness; Håkanson and Jansson, 1983;
McLaren and Bowles, 1985;Sun et al., 2002;Last, 2005;
Vandenberghe, 2013). Processes like these can create complex
distributions in the particle size variation; thus, disentangling the
sources is a must. To un-mix the modes of deposition into the
lake system, end-member mixing analysis (EMMA) is applied to
provide meaningful end members associated with various
depositional processes. This approach, applied on the GBW
core, resulted in ve particle populations of modes attributed
to different transport mechanisms. EM1 is the nest grain size
fraction (7.1 ϕ), which a large majority falls under the clayey silt
class and reects the uvial or wadi inux into the lake. Previous
studies have shown that during pluvial events in arid
environments, clayey silt is deposited in the basin, mostly due
to surface runoff (Lézine et al., 1998,2007). Furthermore, heavy
elements (e.g., Ti, K, and Rb) and PC1 score are closely associated
with EM1 variation, which are introduced to the basin also
through surface runoff (r 0.8; Figure 8). Hence, ner
fraction EM1 along with other proxies (detrital elements and
PC1) are interpreted as increased precipitation in the region. EM2
consists of medium to coarse silt (4.8 ϕ) and reveals the aeolian
mode of transport of sediments into the basin. It is consistent with
available records showing that the southern Arabian Peninsula is
highly inuenced by aeolian processes (Khalaf and Al-Hashash,
1983;Al-Dousari et al., 2013). The greater abundance of EM2
reects coarser aeolian dust advected from proximal sources, as it
is larger in size than the dust particles from distal source (Crouvi
et al., 2008). EM3 is situated around a ne sand fraction (3.1 ϕ)
which would have formed due to the lowering of lake level or
shallow near the shore. Hence, this end member, along with
increased authigenic Ca precipitation (Ca/(Al + Fe + Ti)) in the
lake, represents dry episodes with shallow water conditions,
characterized by higher hydraulic energy conditions and
deposition of coarser sediments in the lake. The greater
abundance of EM3 is attributed to lower lake stands that
probably resulted from periods of increased aridity and
decreased water supply from the wadi catchment. EM4 (mode
1.4 ϕ) and EM5 (mode 0.65 ϕ) represent the coarsest
sediment fraction and indicate extreme erosional events. Those
intervals with a high abundance of EM4 and EM5 are followed by
a higher abundance of EM1 (clayey silt). Hence we suggest that
these two end members are indicative of coarser erosional
material from the catchment.
Unraveling the Medieval Climate Anomaly
and Little Ice Age in Yemen
The sedimentary record from the GBW core reveals the past
1,200 yearsclimatic changes in the southern Arabian Peninsula
and is divided into three stages based on the down-core variation
(Figure 9).
Unit LU-1 (9201400 CE)
Unit LU-1 is dominated by detrital inux to the lake, as is marked
by a higher PC1 score and an increase in TOC/TIC interpreted as
resulting from augmentation in catchment runoff during pluvial
episodes (Figure 9). The intervals from 9301000 CE, 1,0601110
CE, 1,1401200 CE, 1,2201280 CE, and 1,3301400 CE are
sustained periods of wetness as represented by increased
catchment erosion and augmentation of the clayey silt fraction
(EM1 score) (Figure 9). These periods coincide with the Medieval
Climate Anomaly (MCA; 9001350 CE; Gayo et al., 2012),
which is an interval characterized by a shift in atmospheric
circulation in the northern hemisphere that has left signals in
sedimentary archives around the globe (Graham et al., 2011;
Frontiers in Earth Science | www.frontiersin.org December 2021 | Volume 9 | Article 71244311
Parth et al. Late-Holocene Paleoclimatic Record From Yemen
Lüning et al., 2018). The synchroneity and extent of the climate
pattern during this period are debated (Mann et al., 2009), yet it is
widely recognized as a relatively warming interval in the northern
hemisphere. However, it appears that the MCA interval in our
record does not uniformly represent wet conditions but shows the
inception of a major wet interval probably associated with
increase warmth and humid conditions. Enhanced
precipitation in the region during the MCA is consistent with
regional records (Gupta et al., 2003;Fleitmann et al., 2004). The
possible causes of the MCA are debatable as different forcing
mechanisms, such as solar, volcanic, greenhouse gases, and land
cover/use changes, occurred individually, and their combination
all likely inuenced this climatic shift. The simulation provided
by Community Earth System Model-Last Millennium Ensemble
(CESM-LME) captures globally warmer conditions during the
MCA due to weaker volcanic forcing relative to radiative forcing
that characterized the Little Ice Age (LIA; 1,5001800 CE, Otto-
Bliesner et al., 2016). Fluctuations in the regional climate during
the MCA can also be attributed to changes in the intensity of solar
irradiance and thus inducing enhanced wet conditions in the
region, which led to an increase in the input of allogenic materials
into the lake (Figure 9). We estimate that this anomaly could
have been triggered by the northward migration of the ITCZ
linked to increased solar forcing (Broccoli et al., 2006;Kuhnert
and Mulitza, 2011), which led to an increase in humidity in the
southern margins of the Arabian Peninsula during the MCA.
Unit LU-2 (1,4001720 CE)
The LU-2 unit is dened by increased Ca/(Al + Fe + Ti), gypsum
abundance, and higher EM2 abundance, which we believe
represent an increase in the evaporite formation and aeolian
inux to the lake basin. During 1,4101450 CE, 1,5001580 CE,
and 1,6401690 CE, higher values of Ca/(Al + Fe + Ti) and
increased abundance of gypsum indicate periods of decline in lake
level, which exemplify for dry climatic conditions in the region
(Figure 9). In fact, the EM2 abundance from 1,430 to 1670 CE
signicantly increases due to drier conditions. These dry episodes
appear to prevail during the LIA when coarser silt sediments were
brought into the lake and were consequently winnowed under
lower lake levels. Aridity during the LIA is consistent with
regional evidence (Felis et al., 2018) and follows proposed
theories for weakened boreal summer monsoons during an
interval of northern hemisphere cooling (Feng and Hu, 2008;
Figure 9).
Conversely to the MCA interval, with a southward migration
of the ITCZ during the inception of the LIA, an increase in the
interhemispheric temperature contrast and enhanced high-
latitude ice cover resulted in arid climatic conditions on the
southern margins of the Arabian Peninsula (Schneider et al.,
2014). Hence precipitation changes in Yemen during both the
MCA and LIA anomalies were possibly driven by changes in the
mean position of ITCZ. However, we infer that the LIA was not
extremely dry, as we do not see evidence for compete desiccation
of the lake and formation of soils.
Unit LU-3 (17202000 CE)
This unit consists of post-LIA sediments and is dened by higher
detrital input to the lake post-1900 CE. These intervals are
dened by higher values of PC1 score and ner sediment
(EM1 score) fraction but lower values of TOC/TIC (Figure 9).
The unit is also marked by a higher aeolian inux due to an
increase in the abundance of EM2 (Figure 9). However,
uncertainty in our age-depth model is high for this section, as
it is difcult to accurately constrain the timing of initial inux of
detrital material to the lake. However, it occurred after the LIA
and is marked by the inception of wetter conditions. Several
FIGURE 9 | Multiproxy data obtained from Gayal el Bazal from 900 CE to 2000 CE showing three units (marked by blue and red stripes) indicating wet and dry
intervals, respectively (Steinhilber et al., 2012).
Frontiers in Earth Science | www.frontiersin.org December 2021 | Volume 9 | Article 71244312
Parth et al. Late-Holocene Paleoclimatic Record From Yemen
studies have reported warm and wet conditions following the LIA
(Kotlia et al., 2012;Lüning et al., 2019), and our GBW record
follows a similar trend. We suggest that this pattern is promoted
by an active Red Sea Trough system that enhances precipitation
over the southern Arabian Peninsula (Almazroui, 2012;Baseer
et al., 2019).
Climate Variability in the Region
Based on the multiproxy approach of this study, high rainfall
intervals were identied during 9301400 CE, with lower
magnitudes occurring during 1,4101700 CE (Figure 9). A
similar precipitation trend is witnessed in other well-dated sites
from NW Arabia and eastern Africa, suggesting warm and humid
conditions during the MCA followed by a cold and dry condition
during the LIA (Lüning et al., 2017). A late Holocene study from
Shuaiba Lagoon, Saudi Arabia, reveals high paleo-tidal elevation as
shown by enrichment in δ
13
CandδDofSorites orbiculus indicating
wet climatic condition during 1,0001550 CE followed by aridity
from 1,550 to 1850 CE due to MCA and LIA inuence in the region
(Figure 10A;Abu-Zied and Bantan, 2015). Furthermore, marine
records retrieved on the Arabian Sea also report increased
monsoonal activity 7501150 CE and a weaker monsoon during
1,3501550 CE (Figures 10D,E), which correlate well with two large
temperature excursions during the late Holocene (Anderson et al.,
2010). Additional records from Mount Kenya (Figure 10C)and
Lake Turkana (Figure 10F) report cooler on average temperatures
during the LIA but no indication of the MCA (Fastook et al., 1999;
Berke et al., 2012). In contrast, a study based on sea surface
temperature (SST) reconstruction from the Gulf of Aden using
GDGTs shows no major indication for substantial temperature
change during the MCA and LIA (Figure 10G;Tierney et al.,
2015). This pattern can potentially be arguable due to major cold
upwelling in the Arabian Sea that results from stronger Indian
Summer Monsoons (SW winds) that brings colder, nutrient-rich
waters from the Indian Ocean. The relationship between cold
upwelling conditions during higher solar irradiance was already
established by a previous study from the Oman margin (Figure 10E;
Gupta et al., 2005), showing strong SW monsoons during the MCA
(equivalent to a solar maxima interval) and weaker strengths during
the LIA (solar minima). Hence, both climatic anomalies are well
documented in many segments of East Africa, Saudi Arabia, and the
Arabian Sea which most likely are triggered by changes in solar and
volcanic forcing and ocean cycles.
CONCLUSION
This study integrated magnetic susceptibility, geochemical, and
TOC/TIC analyses, coupled with end-member mixing analysis
derived from particle size measurements carried out on a 3.3 m
long core retrieved from Gayal el Bazal (southern Yemen) utilized
to understand the late Holocene climatic uctuations in the
region. The current study shows that sediment accumulating
in the lake comprises of allochthonous material (derived during
pluvial events through surface runoff), precipitation of authigenic
evaporite minerals (formed following changes in water
composition and inow strength during dry intervals), and
aeolian activity (indicated by an increase in EM2 and calcite
minerals). The multiproxy investigation displays enhanced
precipitation during the MCA, marked by an increase in
FIGURE 10 | Comparison of the GBW record with other regional pale oclimatic data. (A) δ
13
Cand(B) TOC, both from Shuaiba Lagoon (Saudi Arabia; Abu-Zied and
Bantan, 2015), (C) TOC values from Naro Moru Tarn (Mount Kenya; Fastook et al., 1999), (D) G. Bulloides from core RC2735 (Anderson et al., 2010) and (E) G. Bulloides
from core ODP Hole 723A (Gupta et al., 2003), both from the Arabian Sea (Oman margin). (F) TEX86 temperature reconstruction from Lake Turkana (Berke et al., 2012).
(G) δD
wax
data for the past millennium from a Gulf of Aden core (Tierney et al., 2015).
Frontiers in Earth Science | www.frontiersin.org December 2021 | Volume 9 | Article 71244313
Parth et al. Late-Holocene Paleoclimatic Record From Yemen
detrital elements, higher TOC/TIC content, and dominance of
EM1 (clayey silt fraction), which represent higher surface runoff
in the lake watershed. Additionally, the higher contribution of
EM2 (coarser silt fraction) appears to indicate aeolian input,
coupled with increased gypsum production during the LIA,
which indicate drier conditions. Our results show that the
evolution of the Gayal el Bazal Lake has been mainly
controlled by climatic factors (Solar and volcanic forcing), as
the MCA and LIA are well imprinted in the sedimentary record.
We further suggest that the Gayal el Bazal sedimentary archive
has reliably responded to centennial-scale latitudinal variability of
the ITCZ and associated with ISM. Comparison with other
marine and terrestrial records from the Arabian Peninsula and
Eastern Africa shows a similar climate pattern during the LIA and
MCA intervals. We conclude that this work documents, for the
rst time, a continuous lacustrine record from southern Yemen
that reliably responds to climate variability associated with the
MCA and the LIA. Our work also proposes that the regions
hydroclimate balance is sensitive to changes in solar activity, and
thus if an extended solar minimum prevails in the future, it could
affect the region, causing increased drought.
DATA AVAILABILITY STATEMENT
The original contributions presented in the study are included in
the article/Supplementary Material, further inquiries can be
directed to the corresponding author.
AUTHOR CONTRIBUTIONS
SP, JR, and NW designed the study. JR collected the samples, SP
performed the measurements and carried out analysis on the
samples, drafted the manuscript, and designed gures. NW and
JR supervised the project made a substantial contribution to the
concept or design of the article. All authors provided critical
feedback and helped shape the research, analysis, and manuscript.
FUNDING
This research was supported by grants from PBC Fellowship
program for International PhD students offered by the Council
for Higher Education of Israel to SP.
ACKNOWLEDGMENTS
We are thankful to LacCore (National Lacustrine Core Facility),
Department of Earth Sciences, University of Minnesota, for
providing the sediments for the project. The authors
acknowledge assistance with eldwork from Douglas
Schnurrenberger, who led eldwork, and Prof. Juris Zarins.
The American Institute for Yemeni Studies is thanked for
their assistance with eld logistics and project permitting. The
authors warmly thanks Nimer Taha for assistance with grain size,
XRD, and TOC/TIC measurements.
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