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\DOI{10.5802/crgeos.240}
\datereceived{2023-07-04}
\daterevised{2023-10-09}
\dateaccepted{2023-10-10}
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\dateposted{2023-11-17}
\begin{document}

\begin{noXML}

%\makeatletter
%\def\TITREspecial{\relax}
%\def\cdr@specialtitle@english{Tribute to Jean Dercourt}
%%\def\cdr@specialtitle@french{Hommage \`a Jean Dercourt}
%\makeatother

\title{Data and models reveal humid environmental conditions during MIS
3 in two of the world's largest deserts}

\alttitle{Les donn\'{e}es et les mod\`{e}les r\'{e}v\`{e}lent des
conditions environnementales humides au cours du MIS 3 dans deux des
plus grands d\'{e}serts du monde}

\author{\firstname{Anne-Marie} \lastname{L\'{e}zine}\CDRorcid{0000-0002-3555-5124}\IsCorresp}
\address{Laboratoire d'Oc\'{e}anographie et du Climat - Exp\'{e}rimentations 
et Approches Num\'{e}riques (LOCEAN/IPSL), CNRS UMR 7159, 
Sorbonne Universit\'{e}, Paris, France}
\email[A.-M. L\'{e}zine]{anne-marie.lezine@locean.ipsl.fr}

\author{\firstname{Masa} \lastname{Kageyama}\CDRorcid{0000-0003-0822-5880}}
\address{Laboratoire des Sciences du Climat et 
de l'Environnement (LSCE/IPSL), UMR 8212 CEA, CNRS, 
UVSQ Orme des Merisiers, 91191 Gif-sur-Yvette cedex, France}

\author{\firstname{Franck} \lastname{Bassinot}\CDRorcid{0000-0003-2107-743X}}
\addressSameAs{2}{Laboratoire des Sciences du Climat et 
de l'Environnement (LSCE/IPSL), UMR 8212 CEA, CNRS, 
UVSQ Orme des Merisiers, 91191 Gif-sur-Yvette cedex, France}

\keywords{\kwd{MIS 3}
\kwd{Tropical Africa}
\kwd{North Africa}
\kwd{Arabian Peninsula}
\kwd{Continental hydrology}}

\altkeywords{\kwd{MIS 3}
\kwd{Afrique tropicale}
\kwd{Afrique du Nord}
\kwd{P\'{e}ninsule Arabique}
\kwd{Hydrologie continentale}}

\shortrunauthors

\thanks{European Research Council TracSymbols project
(Grant agreement no. 249587)}

\begin{abstract} 
MIS 3 environmental conditions in Africa north of the Equator and the
Arabian Peninsula have long been controversial due to data scarcity and
methodological caveats. In this paper we compare 245 continental
hydrological records and 11 long and continuous continental and marine
cores with results from the IPSL general circulation model to discuss
hydrological changes between 59 and 29~ka in North Tropical Africa,
North (Mediterranean) Africa and the Arabian Peninsula. Despite a
generally glacial context, wet conditions widely expanded giving place
to numerous lakes, rivers and wetlands. The major result of our study
is to show that humid conditions appeared much earlier and were more
prevalent in the Arabian Peninsula than in Africa, due to the
conjunction of monsoon rains in summer and Mediterranean rains in
winter.~The mechanisms driving MIS 3 humidity in our study area involve
global cooling factors such as greenhouse concentrations and ice
volume, which have impacted available moisture, orbital forcing, which
impacts monsoon circulation and amplitude and sensitivity to the state
of the Atlantic Meridional Overturning Circulation (AMOC).
\end{abstract}

\begin{altabstract} 
Les conditions environnementales du MIS 3 en Afrique au nord de
l'\'{e}quateur et dans la P\'{e}ninsule Arabique ont longtemps
\'{e}t\'{e} controvers\'{e}es en raison de la raret\'{e} des
donn\'{e}es et des limitations m\'{e}thodologiques. Dans cet article,
nous comparons 245 enregistrements hydrologiques continentaux et 11
carottes continentales et marines longues et continues avec les
r\'{e}sultats du mod\`{e}le de circulation g\'{e}n\'{e}rale de l'IPSL
pour traiter des changements hydrologiques entre 59 et 29~ka en Afrique
nord-tropicale, en Afrique du Nord (m\'{e}diterran\'{e}enne) et en
P\'{e}ninsule Arabique. Malgr\'{e} un contexte g\'{e}n\'{e}ral
glaciaire, les conditions humides \'{e}taient largement \'{e}tendues
donnant lieu \`{a} de nombreux lacs, rivi\`{e}res et zones humides. Le
r\'{e}sultat majeur de notre \'{e}tude est de montrer que les
conditions humides sont apparues beaucoup plus t\^{o}t et ont
\'{e}t\'{e} plus r\'{e}pandues en P\'{e}ninsule Arabique qu'en Afrique,
en raison de l'action conjointe des pluies de mousson d'\'{e}t\'{e} et
des pluies m\'{e}diterran\'{e}ennes d'hiver. Les m\'{e}canismes \`{a}
l'origine de l'humidit\'{e} du MIS 3 dans notre zone d'\'{e}tude
impliquent des facteurs de refroidissement global tels que les
concentrations de gaz \`{a} effet de serre et le volume de glace, qui
ont un impact sur l'humidit\'{e} disponible, le for\c{c}age orbital,
qui a un impact sur la circulation et l'amplitude de la mousson et la
sensibilit\'{e} \`{a} l'\'{e}tat de la circulation m\'{e}ridienne de
retournement Atlantique (AMOC).
\end{altabstract} 

\maketitle

\twocolumngrid

\end{noXML}

\section{Introduction}\label{sec1}
Increasing archaeological and paleogenetic evidence in desert areas of
northern Africa and the Arabian Peninsula shows that the period
spanning the time interval 59,000--29,000 years ago (i.e., Marine
Isotopic Stage 3) was crucial for human history with important
migration waves of  \textit{Homo sapiens}  from Africa into the Arabian
Peninsula and the Levant 
\citep[e.g.,][]{Drakeetal2013,Gracea2016,TimmermannFriedrich2016}.
However, the environmental conditions behind these migrations are
poorly known. The time interval corresponding to MIS 3 belongs to the
last glacial period (70--15~ka). The paucity of continental records
corresponding to this period has been interpreted as indicating the
absence of wet phases between MIS 5 and the Holocene throughout the
Sahara  \citep{Causseetal1988}. But that conclusion has been debated
ever since. Intense deflation during the last ice age 
\citep[e.g.,][]{Sarnthein1978} could have largely destroyed or severely
damaged lake or fluvial sediments, which could have reflected climatic
conditions favourable to the settlement or migration of human
populations.  

In addition to the paucity of paleoenvironmental archives, there is a
major methodological limitation: due to the short half-life time of
$\mbox{}^{14}$C (5730 years) the radiocarbon dating method reaches its
limit of use around 50,000 years. Contamination of lake sediments by
older carbon from groundwater or detrital material, or
recrystallisation process cast doubt on the quality of the dating at
the limit of the method  \citep{FontesGasse1989}. In recent decades,
radiocarbon dating has been complemented by the increasing use of U/Th
or luminecence methods for dating continental sediments, thereby
improving significantly age reconstructions, despite the large
uncertainties that can be associated with these methods. Whenever they
are available, well-dated and continuous continental and marine records
can shed light on the chronology of climatic events which punctuated
MIS 3. However, these records are too scarce to provide a global view
of the evolution of climatic and environmental conditions over North
Africa and the Arabian Peninsula. In particular, they cannot address
the geographical spreading and retraction of humid areas. Thus, to
complement these few continuous records, we also collected published
data to build a comprehensive database of well-dated samples from wet
environments (lakes, paleosoils, river terraces, concretions and
travertines). We interpret the number of dated samples over 1000-year
time windows along the MIS 3 as an indicator of humidity. The
likelihood of collecting and dating those wet paleo-environmental
archives is higher for time intervals when humid conditions prevailed
over North Africa and the Arabian Peninsula, thus resulting in many
more sedimentation sites and higher chances that some of these archives
have reached us despite the intense deflation of the last ice age. The
large dating uncertainties of the continental samples do not allow us
to interpret the rapid variations seen in the high-resolution
continuous records, nor to confidently discuss leads and lags between
climate indicators at different sites. Thus, the main objective of this
article is limited to (i)~evaluating whether MIS 3 was drier or wetter
compared to the pre-industrial period, and (ii)~comparing the climatic
signals and their evolution over three regions of the northern
hemisphere: (1)~Tropical Africa, (2)~North Africa and (3)~East Africa
and the Arabian Peninsula  (Figure~\ref{fig1}). Our reconstructions are
compared with past climate simulations obtained with the climate model
from IPSL (IPSLCM5A-LR) in order to discuss the forcings and the
mechanisms involved in the climate system. 

\begin{figure*}
\includegraphics{fig01}
\vspace*{-3pt}
\caption{\label{fig1}Location map of the MIS 3 dated continental
records and long paleoclimatic records cited in the text. Grey arrows
indicate the strength and direction of the main 925 hPa monsoonal winds
during boreal summer (NCEP-DOE AMIP-II Reanalysis 
\citep{Kanamitsuetal2002}). Numbers refer to (1)~Tropical Africa, 
(2)~North Africa and (3)~Eastern tropical Africa and the Arabian
Peninsula. Continuous paleo-archives from tropical Africa and eastern
tropical Africa and the Arabian Peninsula are shown in 
Figures~\ref{fig4} and~\ref{fig5}, respectively.}
\vspace*{-6pt}
\end{figure*}

\section{Modern climate conditions}\label{sec2}
The monsoonal climate of tropical North Africa and the Arabian
Peninsula is characterised by seasonal reversal of the atmospheric
circulation and migration of the intertropical convergence zone (ITCZ)
associated withthe tropical rain belt. In summer, southwesterly surface
winds carry moisture from the Atlantic and Indian oceans to the
adjacent continents. Atlantic monsoon fluxes penetrate far northward
over northern Africa to the Tropic of Cancer and eastward to eastern
Sudan whereas the easternmost areas of northern Africa are mainly
subjected to the Indian monsoon influence. SW Indian monsoon fluxes
follow the southern Arabian coasts then penetrate eastward to southern
Iran, Pakistan and western India. In winter, the atmospheric
circulation reverses with the development of northeasterly winds
blowing toward the ocean and resulting in dry conditions over the
continents. Wet conditions are observed, however, over the Red Sea and
in the Arabo-Persian Gulf corridors owing to the penetration of
Mediterranean depressions during winter. 

\section{The data sets}\label{sec3}
In order to subdivide our dataset into internally consistent, climate
areas, three main regions have been distinguished based on the
respective influence of tropical and Mediterranean climates. These
three regions are: (1)~Tropical Africa (including the Eastern Atlantic)
from the Atlantic coast to the eastern border of Sudan which encompass
areas under the predominant influence of summer rains from the African
monsoon, (2)~North Africa influenced by winter rains from the
Mediterranean area and (3)~eastern tropical Africa (Ethiopia and
Dibouti) and the Arabian Peninsula (including the Arabian Sea and the
Red Sea), which are influenced by the Indian monsoon, and the
Mediterranean rains. Marine records from the \mbox{eastern} Mediterranean are
included in sector 3 because they are influenced by the Nile River,
whose watershed includes the Ethiopian highlands.

{\vspace*{-2pt}}

\subsection{Continuous continental and marine records}\label{sec3.1} 

{\vspace*{-2pt}}

\subsubsection{Tropical Africa, including eastern Atlantic Ocean
sites}\label{sec3.1.1}  

{\vspace*{-2pt}}

We selected long, published sequences from West Africa to provide us
with vegetation information (pollen, plant waxes, carbon isotopes) and
continental hydrology (pollen, sediments). From South to North 
(Figure~\ref{fig2}): 

\begin{figure*}
\includegraphics{fig02}
\vspace*{-3pt}
\caption{\label{fig2}MIS 3 in North Tropical Africa: From left to right
(A)~tree pollen percentages (Lake Bambili, Cameroon) 
\citep{Lezineetal2019}; (B)~tree pollen percentages (Core GIK 16856-2) 
\citep{DupontWeinelt1996}; (C)~$\rmdelta\mbox{}^{13}$C of plant leaf
waxes (Core GeoB9528-3)  \citep{Castanedaetal2009}; 
(D)~$\rmdelta\mbox{}^{13}$C of plant leaf waxes (Core ODP 659) 
\citep{Kuechleretal2013}; (E)~Humid Pollen Index (Core V22-196) 
\citep{LezineCasanova1991}; (F)~Humidity Index (Core GeoB7920.2) 
\citep{Tjallingiietal2008}. The blue band indicates the period
corresponding to MIS 3.}
\vspace*{-6pt}
\end{figure*}

\begin{itemize}
\item \textbf{Gulf of Guinea}: 
Pollen data were used to reconstruct phases of forest expansions in
cores GIK 16856-2 (4.805 N, 3.40167 E)  \citep{DupontWeinelt1996} and
Bambili (5.93369 N, 10.24064 E)  \citep{Lezineetal2019} located off the
mouth of the Niger River and off the nearby Cameroon highlands,
respectively.  
\item \textbf{Off the Sahel and the Sahara}: 
The percentage of C$_{4}$ and C$_{3}$ vegetation as well as variations
in continental humidity were reconstructed from (i)~marine records of
the $\rmdelta\mbox{}^{13}$C of plant leaf waxes ($n$-alkanes) obtained
on core GeoB9528-3  [9.166 N, 17.6635 W,  \citealp{Castanedaetal2009}]
and ODP site 659 [18.083333 N, 21.033333 W; 
\citealp{Kuechleretal2013}] and (ii)~the pollen content of core V22-196 
[15.83333 N, 18.95 W;  \citealp{LezineCasanova1991}]. Continental
humidity over the Sahara was reconstructed based on the ratio of
hemi-pelagic mud to Aeolian dust in core GeoB7920.2  [20.7515 N,
18.581667~W;  \citealp{Tjallingiietal2008}].
\end{itemize}

\subsubsection{Eastern Africa, including sites from the Indian Ocean
and the Arabian Sea  (Figure~\myRef{fig3})}\label{sec3.1.2} 

\begin{figure*}
\includegraphics{fig03}
\vspace*{-3pt}
\caption{\label{fig3}MIS 3 in Eastern Africa and the Arabian Peninsula:
(A)~Lake Tana (Ethiopia) Ca/Ti ratio  \citep{Lambetal2018}; (B)~Nile
River record from core MS27PT Fe  \citep{Reveletal2010}; (C)~Moomi Cave
(Socotra Island)  $\rmdelta\mbox{}^{18}$O record 
\citep{Burnsetal2003,Burnsetal2004};  (D)~Stable hydrogen isotopic
composition of leaf waxes from Core RC09-166  \citep{Tierneyetal2017};
(E)~CaCO$_{3}$ from Core KL70  \citep{LeuschnerSirocko2000}.}
\end{figure*}

\begin{itemize}
\item \textbf{Eastern Africa:}
At Lake Tana in northwest Ethiopia (12 N, 37.25 E) 
\citep{Lambetal2018} the Ca/Ti ratio was used as a proxy for the lake
level change. Off the mouth of the Nile River in the Mediterranean Sea,
the Fe content of core MS27PT  [31.798333 N, 29.461667 E; 
\citealp{Reveletal2010}] was used to infer the Nile River discharges
and wet phases in its watershed including the Ethiopian highlands.
\item \textbf{The Arabian Sea:}
The $\rmdelta\mbox{}^{18}$O variations recorded in the stalagmite M1-2
from the Moomi Cave on Socotra Island  [12.498168 N, 54.209132 E; 
\citealp{Burnsetal2003,Burnsetal2004,Fleitmannetal2004}] were used to
infer past changes in precipitation in the Arabian Sea~area. Past
hydroclimatic variations in the Gulf of Aden and the Arabian Sea were
also deduced from the stable hydrogen isotopic composition of leaf
waxes from marine core RC09-166  [12.25 N,  44.0666667 E; 
\citealp{Tierneyetal2017}] and the \%CaCO$_{3}$ profile  of core KL70 
[17.5 N, 61.5 E;  \citealp{LeuschnerSirocko2000}].  
\end{itemize}

\subsection{Continental hydrological samples}\label{sec3.2}
Our data set contains 245 dated samples from lake sediments,
paleosoils, fluvial terraces, speleothems and travertines/springs
collected at 82 localities in North Africa and the Arabian Peninsula
and published in the litterature  (Figures~\ref{fig1} and~\ref{fig4}; 
Supplementary Table~1). We also examined seventy-four dated groundwater
samples from 27 localities. 

\begin{figure*}
\vspace*{-2pt}
\includegraphics{fig04}
\vspace*{-3pt}
\caption{\label{fig4}MIS 3 continental data in the three sectors shown
in Figure~\ref{fig1}. From left to right in each panel: the dated records and
corresponding box plot calculated in the mean age (error bars
excluded). The colours correspond to the different dating methods used:
U/Th in green, OSL/TL in yellow and radiocarbon in red.}
\vspace*{-2pt}
\end{figure*}

The age control is based on (i)~75 AMS and conventional radiocarbon
dates and Electron Spin Resonance dates (ESR) on lake carbonates,
remains of aquatic faunas and organic matter (ii)~61 luminescence (OSL,
TL, IRSL) dates on quartz grains and (iii)~46 Uranium--Thorium (U--Th)
dates on lake, spring and speleothem carbonates. All dates are
abbreviated ka BP.

Raw $\mbox{}^{14}$C dates were converted to calendar ages using the
CALIB 8.2 software  \citep{StuiverReimer1993}. Most of these dates
originate from isolated samples or discontinuous archives, as is usual
under predominantly arid climate conditions  \citep{Lezineetal2014}.
The  $\mbox{}^{14}$C dating of North Africa paleoarchives developed
following the pioneering work of  \citet{Gasse1975} in Djibouti, 
\citet{Street1979} in  Ethiopia and  \citet{Servant1983} in Chad. There
area total 42  $\mbox{}^{14}$C dates in MIS 3 paleoarchives of north
tropical Africa: Egypt (9), Chad (9), Ethiopia (4), Morocco (5), Libya
(6), Djibouti (6) and Sudan (3). In Arabia, there are 33 published
radiocarbon dates, 23 in Saudi Arabia, 8 in Oman, 1 in the United Arab
Emirates and 1 in Yemen. In Africa as in Arabia, the  $\mbox{}^{14}$C
dates are mainly from lake (47) and river (18) sediments. There are
only 5  $\mbox{}^{14}$C dates obtained on palustrine sediments
(including paleosoils) and 8 on speleothems. Hereafter in the text,
dates were calibrated and 
abbreviated ka BP.

Regarding the luminescence dating method, only dates on fluvial or
fluvio-lacustrine sediments were considered, as Aeolian (dune)
sediments from arid periods do not concern our study. It is in the
Arabian Peninsula that this method has been mostly used, since 
\citeauthor{Goodall1995}'s work  [\citeyear{Goodall1995}] at Sabkhat
Matti (United Arab Emirates) (1 date), with 22 additional dates in the
same sector, 16 in Oman, 5 in Saudi Arabia and 1 in Yemen. In Africa,
after the early work of  \citet{Whiteetal1996} at Oued es Seffia
(Tunisia) (1) the method has been developed in Morocco (18), Senegal
(3), Sudan (4), Mali (4), Ethiopia (3), Egypt (2) and Libya (2). 

The MIS 3 sediments dated by the U/Th method are only from Africa
(Libya, Morocco, Tunisia, Egypt and Algeria; 46 measurements). The
method was first applied to the Wadi Shati lacustrine deposits (Libya)
by  \citet{Gavenetal1981}. In addition,  \citet{Rogersonetal2019}
provided an extremely detailed chronology of MIS 3 from 35 U/Th
measurements of speleothems in Susah Cave, northern Lybia. We also put
in our database the ESR dates from the Kharga Oasis (Egypt) obtained on
fresh-water gastropod shells  \citep{Blackwelletal2012}.

In addition to the chronological control points listed above, we also
collected  $\mbox{}^{14}$C and U/Th measurements performed on African
and Arabian groundwaters falling within MIS 3. However, the groundwater
ages can be biased by the mixing of groundwaters from different layers
in the stratified
aquifers or the contributions of 
ancient carbon 
through the dissolution of carbonate minerals or the oxidation of old
organic matter in the soil  \citep{Froehlichetal2007}. While there are
several ways to estimate the initial  $\mbox{}^{14}$C activity, those
contamination processes remain a major source of uncertainty. Thus,
these mesurements should be considered with caution. \looseness=-1

Raw data were used to construct box-plot diagrams  (Figure~\ref{fig4}).
We also combined the dated hydrological archives over 1000~yr-long time
windows\unskip\break 
(Figure~\ref{fig7}). We interpret the number of dates per
interval as a proxy of climate humidity (see above). 

\vspace*{-4pt}
\subsection{IPSL climate model simulations}\label{sec3.3}
We have used the Institut Pierre-Simon Laplace (IPSL) Global Climate
Model IPSLCM5A-LR  \citep{Dufresneetal2013}. This model represents the
atmosphere, ocean, sea ice and land surface and their interactions, at
a resolution of  $3.5\text{\textdegree}\times2.75\text{\textdegree}$ 
in~longitude $\times$ latitude for the atmosphere  [LMDZ model, 
\citealp{Hourdinetal2013}] and land surface  \citep{Krinneretal2005}
and of  2\textdegree\ for the ocean  [for which the resolution is
refined in key regions,  \citealp{Madec2011}]. The state of this system
is computed as a function of the following external forcings:
atmospheric greenhouse gases  (CO$_{2}$, CH$_{4}$ and N$_{2}$O),
astronomical parameters (eccentricity, precession, obliquity) and
boundary conditions: continental distribution, land ice distribution,
bathymetry and topography. All simulations were run on supercomputers
Mercure and Curie at TGCC (Tr\`{e}s Grand Centre de Calcul du CEA). 
Table~\ref{tab1} summarises the forcing and boundary conditions for the
simulations analysed in the present work. The  pre-industrial
simulation (PI) is described in  \citet{Dufresneetal2013} and serves as
a reference simulation for past, historical and future climate
simulations. 

\begin{table*}
\caption{\label{tab1}Summary of the boundary conditions, forcings and
characteristics of the IPSLCM5A-LR simulations analysed in the present
work\vspace*{-2pt}}
\fontsize{8}{9.2}\selectfont\tabcolsep=2.5pt
\begin{tabular}{cccccc}
\thead
Simulation & PI & LGM & 
MIS 3---strong AMOC &  
MIS 3---weak AMOC & MIS 3 60~ka \\
\endthead
Period & 1850 & 21 ky BP & 46 ky BP & 46 ky BP & 60 ky BP \\ 
Ice sheet & Present & PMIP3 & ICE\_6G-C, 16~ka & ICE\_6G-C, 16~ka & ICE\_6G-C, 16~ka \vspace*{2pt}\\ 
\parbox[t]{2.3cm}{\centering Sea level anomaly w.r.t PI (m)} & 0 &
${-}$120 & ${-}$70 & ${-}$70 & ${-}$20  \vspace*{2pt}\\ 
Eccentricity & 0.016715 & 0.018994 & 0.01384268 & 0.01384268 & 0.018469 \\ 
Obliquity (degree) & 23.441 & 22.949 & 24.3548 & 24.3548 & 23.2329 \\ 
Precession ($\rmomega$---180\textdegree) & 
102.7 & 114.42 & 101.337 & 101.337 & 266.65 \\ 
CO$_{2}$ (ppm) & 284 & 185 & 205 & 205 & 200 \\ 
CH$_{4}$ (ppb) & 791 & 350 & 500 & 500 & 426 \\ 
N$_{2}$O (ppb) & 275 & 200 & 260 & 260 & 230 \\ 
Initial condition & 
\parbox[t]{2.3cm}{\centering
Previous piControl simuation} & 
\parbox[t]{2.3cm}{\centering
Previous 1000$+$ year-long LGM simulation, with strong AMOC} & 
\parbox[t]{2.8cm}{\centering
Previous MIS 3 simulation under same boundary conditions and forcings} & 
\parbox[t]{2.3cm}{\centering
MIS 3 AMOC on simulaton, year 79} & 
\parbox[t]{2.5cm}{\centering
Previous simulations under same boundary conditions and forcings} 
\vspace*{2pt}\\ 
\parbox[t]{2.3cm}{\centering
Run duration (years)} & 
250 & 350 & 200 & 250 & 210 
\vspace*{2pt}\\ 
\parbox[t]{2.3cm}{\centering
Years analysed (since start of run)} & 
150--249 & 300--349 & 
10--189 & 230--249 & 110--209 
\vspace*{2pt}\\ 
\parbox[t]{2.3cm}{\centering
Run reference on supercomputer Joliot-Curie} & 
\parbox[t]{2.3cm}{\centering
piControl2 years 2000--2099} & 
\parbox[t]{2.3cm}{\centering
lgm11f3 years 3350--3399} & 
\parbox[t]{2.3cm}{\centering
MS3I46K2 years 2320--2509} & 
\parbox[t]{2.3cm}{\centering
M3I46F02 years 2630--2649}  & 
\parbox[t]{2.3cm}{\centering
MIS4fB6 years 3100--3199} 
\vspace*{2pt}\\ 
\parbox[t]{2.3cm}{\centering AMOC (Sv) over the analysed period} & 
7--11.5 & 2.5--5  & 20--26  & 8.5--11 & \vspace*{2pt}
\botline
\end{tabular}
\tabnote{The AMOC value is defined as the maximum of the meridional
overturning stream function along the 30\textdegree\ S vertical
section. Minimum and maximum values of the AMOC are indicated.\vspace*{-3pt}}
\end{table*}

The boundary conditions used for the Last Glacial Maximum run presented
here are described in  \citet{Kageyamaetal2013a}.
These are compliant
with PMIP3  \citep{Otto-Bliesneretal2009,Braconnotetal2012}
recommendations, in particular in terms of ice sheets 
\citep{Abe-Ouchietal2015}. The run itself is a continuation of the LGM
simulation presented in  
\citet{Kageyamaetal2013a,Kageyamaetal2013b}, in which a
continuous 0.2~Sv fresh water flux is added to the North Atlantic and
the Arctic Ocean so as to decrease the Atlantic Meridional Overturning
Circulation to a more realistic LGM state (i.e. weak).

The boundary conditions used for the MIS 3 runs are described in 
\citet{Woillezetal2014} and  \citet{LeMezoetal2017}. They used smaller
ice sheets than for the LGM (ICE\_6G-C 16 ky BP ice sheet
reconstructions from  \citet{Peltieretal2015} available at the time of
running, which corresponded to the same global sea level as MIS 3), and
intermediate atmospheric greenhouse values between those known for the
pre-industrial and for the LGM, as documented by ice cores. All these
runs use the same boundary conditions but differ in terms of the
astronomical and greenhouse gas forcings. The ``MIS 3---strong AMOC''
and ``MIS 3---weak AMOC'' runs used 46~ka astronomical parameters and
greenhouse gas concentrations while the ``MIS 3 60~ka'' uses 60~ka
astronomical parameters and greenhouse gas concentrations  [in  
\citealp{LeMezoetal2017},  this ``MIS 3 60~ka'' simulation is named
MIS4F,  it actually sits at the boundary between MIS 3 and  MIS 4]. The
``MIS 3---weak AMOC'' simulation is obtained by imposing a 0.2 Sv fresh
water flux into the North Atlantic and Arctic Oceans to weaken the AMOC
which is strong in the ``MIS 3---strong AMOC'' simulation. Indeed, this
simulation was designed to study the sensitivity of the MIS 3 climate
to the AMOC state. The AMOC ranges between 20 and 26 Sv in the MIS 3
strong AMOC run, while it stays between 8.5 and 11 Sv in the MIS 3 weak
AMOC simulation  (Table~\ref{tab1}). We have included simulations with
a weak and a strong AMOC because MIS~3 is characterised by AMOC
instabilities which have been shown to have an impact on the African
and Asian monsoons  \citep{Zhangetal2022}. Even though the \mbox{resolution}
of most records does not allow to depict climate changes in
relationship with the AMOC instabilities, their potential impact on the
recorded continental climate cannot be ignored, hence the approach of
considering both states in the experimental design of the numerical
experiments.

\section{Results}\label{sec4} 

\subsection{Tropical Africa and North Africa}\label{sec4.1}  

\subsubsection{Long paleoclimatic records}\label{sec4.1.1}
Marine cores and long continental series from West Africa between 
5\textdegree\ and 20\textdegree~45 N reveal a coherent picture of
higher humidity during MIS 3 than during
MIS 4 and MIS 2. Such a higher humidity is\unskip\break 
responsible for the development of plant cover and is
therefore readily seen in pollen and leaf wax records 
(Figure~\ref{fig2}).  \citet{LezineCasanova1991} and 
\citet{Castanedaetal2009} observed a wet period between 51 (52) and 44
(45) ka with the expansion of C$_{3}$ plants in the Sahel 
\citep{Castanedaetal2009}. In addition,  \citet{Kuechleretal2013} noted
the expansion of C$_{4}$ herbaceous plants in the Sahara, between 61
and 40~ka with a peak at 51~ka. High-resolution analyses show that the
climate was highly variable with significant phases of climatic
degradation punctuating MIS 3, coeval with the Heinrich events of
northern latitudes \citep{Tjallingiietal2008}.
In the highlands of Cameroon  \citep{Lezineetal2019}, forest trees
around Lake Bambili increased as early as 53~ka and reached a maximum
between 46 and 41~ka with a peak at 43.9~ka. The forest phase that
extended up to 30.9~ka was punctuated by phases of disruptions at
48--46~ka (H~5), 41--39~ka (H~4), 37--34.5~ka and then 26--30~ka (H~3).

\subsubsection{Continental records}\label{sec4.1.2}
Continental data from MIS 3 are extremely rare in tropical Africa west
of Chad  (Figure~\ref{fig1}), which gave substance to the assumption by
\citet{Causseetal1988} that there were no wet phases between MIS 5 and
the Holocene throughout the Sahara. However, the unique  $40\pm20$~a
U/Th age initially measured by  \citet{Gavenetal1981} at Wadi Shati,
Southern Libya, was later confirmed by  \citet{Armitageetal2007} who
\mbox{provided} an OSL age of  $52.8\pm6.3$~ka on lake deposits in the same
area. In Senegal and Mali, OSL ages measured on fluvial deposits in the
Fal\'{e}m\'{e} River  \citep{Lebrunetal2017,Mayoretal2018}
and at Ounjoungou  \citep{Rasseetal2004} fall within the interval
38--25~ka and  52--33~ka, respectively. As expected, given the
limitations of the method and the old origin of the data 
\citep{Gasse1975,Street1979,Servant1983,PachurHoelzmann1991,Szaboetal1995}, 
the radiocarbon measurements do not extend beyond 47~ka. 
Two intervals around 40 and 31~ka show a high density of 
dates obtained in sediments from Chad, Egypt, Sudan and 
East Africa (Djibouti and Ethiopia). The oldest ages are 
recorded in Chad (45~ka) and Egypt (47~ka), while the oldest 
records from Eastern Africa only date from 37.6~ka (Ethiopia) 
and 41~ka (Djibouti). In Ethiopia, the  
$\mbox{}^{14}$C age provided by  \citet{Street1979} in the Ziway-Shala
Basin (31.5~ka) is of the same order as those recently provided by 
\citet{Viehbergetal2018} at Lake Chew Bahir by both  $\mbox{}^{14}$C
(33.8 and 37.6~ka) and OSL methods (40, 38.6 and 37.2~ka). In North
Africa (Libya and Morocco), radiocarbon dates clearly show two
wellidentified periods: an early one in Libya at 48.5--47~ka 
\citep{GraceaGiraudi2006}, and another one common to both countries at
34.5--29.2~ka
\citep{Giraudi2005,GraceaGiraudi2006,Mercieretal2009,Barichetal2010}.
In addition,  \citet{Occhiettietal1994} note an age of 40.7~ka in the
Souss river valley (Morocco).  

U/Th dating is mainly concentrated in North Africa from Morocco to
Egypt and is distributed over the entire MIS 3. The periods where U/Th
ages are most concentrated are between 45 and 38~ka 
[Egypt---\citealp{Hamdam2000};
\citealp{Sultanetal1997,Szaboetal1989,Churcheretal1999};
Algeria---\citealp{Fontesetal1992};
Tunisia---\citealp{Causseetal1989,Causseetal2003};
Lybia---\citealp{Macklinetal2002,Gavenetal1981};
Morocco---\citealp{Mercieretal2009}] and around 30~ka 
[Morocco---\citealp{Boudadetal2003,Mercieretal2009,Rousseauetal2008};
Tunisia---\citealp{Causseetal2003}; Libya---\citealp{BarichGarcea2008,Barichetal2010}].
In addition to these fluviatile and lacustrine records, 
\citet{Rogersonetal2019} published a well-dated U/Th series on a
speleothem from northern Libya showing three major periods of
speleothem growth at 56, 51 and 36~ka. 

OSL dating is divided into four major groups at 53--52~ka 
[Mali---\citealp{Rasseetal2004}; Libya---\citealp{Armitageetal2007};
Morocco---\citealp{Mercieretal2009}], at 47~ka 
[Mali---\citealp{Rasseetal2004}; Morocco---\citealp{Mercieretal2009};
Tunisia---\citealp{Whiteetal1996}]; between 42 and 37~ka with a peak at
39~ka 
[Morocco---\citealp{Mercieretal2009,Weisrocketal2006,Thorpetal2002};
Libya---\citealp{Macklinetal2002}] then between 34 and 30~ka
[Morocco---\citealp{Mercieretal2009,Weisrocketal2006};
Senegal---\citealp{Lebrunetal2017}; Mali---\citealp{Rasseetal2004}].

\vspace*{-4pt}
\subsection{Eastern Africa, the Arabian Peninsula and the Indian
Ocean}\label{sec4.2} 

\subsubsection{Long paleoclimatic records}\label{sec4.2.1} 
In Eastern Africa and the Arabian Peninsula, the Ca/Ti ratio at Lake
Tana \citep{Lambetal2018} clearly shows two phases of high lake level
at 54~ka and then between 42 and 31~ka, which is consistent with the
periods of strong Nile River discharges recorded in core MS27TP between
60 and 50~ka and then between 38 and 30~ka  \citep{Reveletal2010}. A
wet period between 53.4 and
40.4~ka also isat the origin of the
formation of the Moomi stalagmite on Socotra Island 
\citep{Burnsetal2003,Burnsetal2004}. This early humid phase is also
recorded in core RC09-166 showing two wet phases in the Gulf of Aden,
between 57.7 and 50.8~ka, then around 41.9~ka \citep{Tierneyetal2017}. 

In detail, high-resolution studies of the Arabian Sea 
[KL70---\citealp{LeuschnerSirocko2000}; Moomi 
Cave---\citealp{Burnsetal2003,Burnsetal2004}] show that environmental
variability during MIS 3 is consistent with the Greenland 
$\rmdelta\mbox{}^{18}$O ice record. In these high-resolution records,
Dansgaard--Oeschger cycles and Heinrich Events were
identified and H 4, in particular, revealed a strong peak in wind
activity in the Red Sea  \citep{Rohlingetal2008}.

\begin{figure*}
\includegraphics{fig05}
\vspace*{-3pt}
\caption{\label{fig5}Mean seasonal cycle of continental precipitation
(mm/month) over regions 1, 2 and 3, as simulated by the IPSLCM5A-LR
climate model for the five sets of forcings and boundary conditions
summarised in Table~\ref{tab1}.
The results for months 13 to 18 replicate those
for months 1 to 6, in order to better show the seasonal cycle for
region 2, which peaks during the winter season.}
\vspace*{-6pt}
\end{figure*}

\subsubsection{Continental records}\label{sec4.2.2} 
Regarding continental data, early studies in Arabia, since 
\citet{Mcclure1976}  \cite[in e.g.,][and reference
therein]{Sanlaville1992},
provided radiocarbon dates for MIS 3 lacustrine deposits
distributed across the Peninsula between 18 and  31\textdegree\ N and
ranging from 40.5~ka at Mundafan  \citep{Mcclure1976} to 27.7~ka at
Harrat Nawasif  \citep{Zotl1984}. The   $\mbox{}^{14}$C ages obtained
on speleothems from Oman by  \citet{ClarkFontes1990} also fall within
this interval and range from 39.2 to 29.3~ka. However, most of these 
$\mbox{}^{14}$C dates have probably been subject to contamination
processes by younger  $\mbox{}^{14}$C that would have resulted in
considerable age rejuvenation. At Mundafan (Saudi Arabia), 
\citet{Rosenbergetal2011} obtained OSL dates that challenge the older 
$\mbox{}^{14}$C measurements from  \citet{Mcclure1976,McCLure1978} 
and place the Pleistocene Lake of Mundafan during MIS 5. 

OSL ages on fluvio-lacustrine sediments indicate humid environmental
conditions between 61--55~ka around the Aqaba paleolake (UAE) 
\citep{Partonetal2013}: and between 59--42~ka at Wadi Mistal (Oman) 
\citep{Hoffmannetal2015}. However, younger ages spanning the
radiocarbon period are also recorded in the easternmost sector of the
Arabian Peninsula in Al Ain, Liwa  \citep{GlennieSinghvi2002} (31~ka)
and Jebel Faya  \citep{Bretzkeetal2013} (34~ka) as well as in southern
Oman, in the Dhofar region  \citep{Roseetal2019} (30~ka) and in Yemen
at Wadi Dawan  \citep{Amirkhanov2020} (33~ka).

\vspace*{-3pt}
\subsection{Model simulations}\label{sec4.3}
The results of the IPSLCM5A-LR climate model simulations show that for
all the conditions
summarised in Table~\ref{tab1}, the seasonal cycles of
continental precipitation are characterised by a summer,
monsoon-related peak for sectors 1 and 3, which contrasts with no
precipitation in December and January, while for sector 2, the cycle is
dominated by a wet winter and a dry summer, which still receives 
some\unskip\break
rain. 

For all sectors, the amplitude of the wet season is strongly sensitive
to the boundary conditions and forcings for the different periods. The
driest period is the LGM for all three sectors. In Tropical Africa
(sector 1) the precipitation values for the MIS 3---weak AMOC run are
close to the PI values, peaking at about 80~mm/month, whereas the MIS
3---strong AMOC run and the MIS 3 60~ka run are much larger than the PI
values, in particular during spring and summer. The peak value for the
MIS 3 60~ka run reaches more than 100~mm/month. The largest differences
with the PI control simulations are for the month of June, for which
the precipitation doubles in MIS 3 60~ka compared to PI 
(Figure~\ref{fig5}). This corresponds to a northward extension of the
monsoon region, in particular for the MIS 3 strong AMOC and MIS 3 60~ka
simulations  (Figure~\ref{fig6}).

\begin{figure*}
\includegraphics{fig06}
\caption{\label{fig6}Number of months, in the average seasonal cycle of
continental precipitation, with precipitation larger than 3~mm/month.
The results are shown in absolute value for the PI simulation (top
left) and as anomalies with respect to this reference for all other
simulations.}
\end{figure*}

\begin{figure*}
\includegraphics{fig07}
\caption{\label{fig7}Number of dated records (vertical axis) of
humidity during MIS 3 by 1000-year time steps. Ages are considered with
their error bars (horizontal axis) in the three sectors shown in 
Figure~\ref{fig1}. Underground waters are not shown in this figure.}
\end{figure*}

For East Africa and the Arabian Peninsula (sector 3) all MIS 3
simulations show wetter conditions than for PI, from June to August for
the MIS 3 strong and weak AMOC runs, and all year round for the MIS 3
60~ka run. The MIS 3 strong AMOC simulation shows a lengthening of the
precipitation season until November. The MIS 3 60~ka results are much
wetter than for all other simulations, with a maximum at 50~mm/month
for August, w.r.t. between 20 and 30~mm/month for the other MIS
simulations, less than 20~mm/month for the PI run and less than 10
mm/month for the LGM run. These wetter conditions in the MIS 3
simulations are due to a northward extension of the monsoon region on
both sides of the Red Sea and the southern part of the Arabian
Peninsula, as well as a southward extension of the rainbelt extending
eastward from the Mediterranean Sea, which results in wetter conditions
in the northern part of the Arabian Peninsula  (Figure~\ref{fig6}).
This corresponds to autumn and winter precipitation (not shown).

Over North Africa (sector 2), the precipitation seasonal cycle is
dominated by fall, winter and spring rainfall  (Figure~\ref{fig5}). The
maxima are reached in December, with values of 8~mm/month for the PI
run, between 10 and 11~mm/month for MIS 3 strong and weak AMOC and
between 11 and 12~mm/month for MIS 3 60~ka. In addition to showing the
strongest winter values, MIS 3 60~ka also displays the longest rainy
season in spring. The spring season is the one for which there are most
differences between the simulations, with low values for LGM and PI,
and higher and higher values for MIS 3 weak AMOC, MIS 3 strong AMOC,
and maximum values for MIS 3 60~ka. This longer duration of the rainy
season is also illustrated in  Figure~\ref{fig6}.

\section{Discussion}\label{sec5}
Despite the scattered nature of the records and the large chronological
uncertainties, continental sediment dating and long paleoclimate series
allow us to identify several key aspects:

\medskip\noindent(1)
Numerous indicators of wetness (lakes, playas, rivers{\ldots}) are
recorded in Africa north of the Equator and in the Arabian Peninsula
during MIS 3. 

\medskip\noindent(2)
A clearly differentiated distribution of these humid indicators is
observed between sector 3 (Eastern Africa and the Arabian Peninsula),
on the one hand and the two other sectors of Tropical Africa (sector~1)
and North Africa (sector 2), on the other hand\unskip\break 
(Figure~\ref{fig7}). 

\begin{itemize}
\item
In sector 3 the onset of humid conditions during MIS 3 occurred earlier
than in sectors 1 and 2, starting at 64~ka in Eastern Arabia and about
10~ka later in tropical and North Africa. Wet conditions were also
probably more intense during the first half of MIS 3, as shown by the
number of dated records. These wet conditions lasted until the end of
MIS 3. These results are consistent with previous observations from 
\citet{Preusseretal2002} who noticed the absence of aeolian
remobilisation in the ``Wahiba sands'' area (Oman) between 64 and 22~ka
reflecting a long, wet period. At Lake Chew Bahir (Ethiopia), 
\citet{Viehbergetal2018} also noticed a long period of climatic
stability between 58 and 32~ka allowing the maintenance of a lake
despite intense evaporation. Although our study shows that humid
indicators were continuously present throughout MIS 3, this period was
climatically far from stable. Two periods of marked humidity emerge:
(1)~an early wet phase is attested by the peak of OSL-dated records
between 59 and 48~ka; (2)~a second wet phase is revealed by the
distribution of  $\mbox{}^{14}$C records from both Eastern Africa and
the Arabian Peninsula between 42 and 29~ka with a maxium between 39 and
34~ka. This second wet phase is confirmed by  $\mbox{}^{14}$C ages on
groundwaters at Liwa (South-Eastern Arabian Peninsula) starting from 43
ka and peaking ca. 30~ka  \citep{WoodImes1995}. These results are also
consistent with the Lake Tana (Ethiopia) and the eastern Mediterranean
records  \citep{Lambetal2018,Reveletal2010,Langgutetal2018} which
reveal two periods of enhanced humidity in eastern Africa and the
Levant at 54~ka (56--44) then between 42 and 30~ka, bracketing a dry
period peaking ca. 44--42~ka. Marine cores from the Arabian Sea and the
Red Sea (KL11 and 70KL), as well as the Socotra stalagmite show that
climatic variability also occurred at a shorter timescale, resulting in
a succession of wet and arid periods that seem to mimic
Dansgaard/Oeschger events at high latitudes although chronological
uncertainties do not currently allow to correlate them unambiguously 
\citep{Svenssonetal2008}.  
\item 
In Tropical Africa and North Africa (sectors 1 and 2) there is a near
absence of dated wet records prior to 53~ka  (Figure~\ref{fig7}). 
\item
In North Africa, the number of OSL and U/Th dates increases steadily
after 52~ka, reaching a peak between 42 and 37~ka (OSL) and 36--32~ka
(U/Th). Radiocarbon dates, in limited number, show two humid periods
between 51 and 44~ka and then between 35 and 29~ka. These results are
consistent with U/Th measurements from Susah Cave in northern Libya 
\citep{Rogersonetal2019}. This record shows that humid conditions
started from 53~ka and that the major phase of speleothem growth was
dated from 36~ka that closely corresponds to the last period of aquifer
recharge in northern Africa 
\citep{EdmundsWright1979,Guendouzetal1997,Abouelmagdetal2014}. 
\item
In Tropical Africa, two peaks of humidity are distinctly identified:
the first peak is\unskip\break 
revealed by U/Th and OSL-dated continental deposits
at Wadi Shati and in Egypt/Sudan between 47 and 37~ka, the second peak
is observed in the distribution of OSL-dated deposits in Senegal and
Mali between 36 and 30~ka, consistent with the  $\mbox{}^{14}$C
records in both Chad and Egypt/Sudan. These results are consistent with
groundwater records, which show two major phases of aquifer recharge
between 55 and 42~ka in Eastern Egypt, 
\citep{Sultanetal1997,Osmondetal1999} and in the Taoudenni basin 
\citep{Huneauetal2011} then between 39 and 29~ka in Niger 
\citep{DodoZuppi1999},  Burkina Faso  \citep{Huneauetal2011}, Nigeria 
\citep{Edmundsetal1998} and Egypt 
\citep{Pattersonetal2005,Froehlichetal2007}. The long sedimentary
series from the Sahara and Sahel reveal an increase in humidity and
vegetation cover between about 55-53 and 42~ka, coeval with a reduced
Aeolian circulation over the Sahara  [Core MD03
2705---\citealp{Matsuzakietal2011}]. Near the equator, this wet period
lasted until 30~ka, albeit to a lesser degree. There were several
variations responsible for the degradation of the forest cover. They
are coeval with Heinrich events in northern latitudes (H 5, 4 and 3).
High amplitude climate variability in the eastern Atlantic domain
during MIS 3 is moreover confirmed by \citet{Tjallingiietal2008}.
\end{itemize}

\medskip\noindent(3)
Modelling results are broadly consistent with the data showing a wet
MIS 3 in all three sectors, despite the fact that this period was
globally colder and drier than the pre-industrial period. In fact,
favourable obliquity (for MIS 3 strong and weak AMOC runs) or
precession parameter (MIS 3 60~ka) outweigh the impact of these
globally colder and drier environment and favour strong monsoons both
over West Africa and East Africa and the Arabian Peninsula. This
confirms results obtained by other models for periods close to those
analysed here  \citep[e.g.][]{Jenningsetal2015,SingarayerBurrough2015}.
The impact of the AMOC strength is clearly visible for both regions, a
strong AMOC being favourable to stronger monsoon. This was already
shown in several earlier works \mbox{performed} with different types of
climate models, e.g.~\citet{Tjallingiietal2008} with the CLIMBER Earth
System Model of Intermediate Complexity (EMICs), or in the review by 
\citet{Kageyamaetal2013a,Kageyamaetal2013b}, 
based on Global General Circulation models
and EMICs. Compared to these works, the simulations presented here,
performed with a GCM for different periods within MIS 3, are either
more detailed  \citep[compared to][]{Tjallingiietal2008} or using a
more realistic set up for MIS 3  [the experiments analysed by 
\citealp{Kageyamaetal2013a,Kageyamaetal2013b} 
used the Last Glacial Maximum as a 
reference]. \citet{SingarayerBurrough2015} insist on multiple factors
forcing the response of the African monsoon. This is also the case
here, with the combined effects of the orbital parameters, ice sheet
state and AMOC state which result in the MIS 3 simulation with a weak
AMOC showing wetter conditions than for the pre-industrial, for
instance. The conditions at the start of MIS 3 are particularly
favourable to both monsoons too, in particular for East Africa and the
Arabian Peninsula, as found by the previous studies cited above. This
brings an explanation for the record of wet conditions for this period
compiled here. For Tropical Africa, the model simulates slightly wetter
conditions for the beginning of MIS 3 than for the middle of this
period, but the differences between the periods are not as large as for
East Africa and Arabia. In North Africa, the reasons for MIS 3 being
wet are associated with a strengthening of the winter rain and an
extension of the rainy season over spring for the wettest periods (MIS
3 strong AMOC and beginning of MIS 3). This could be due to a southern
position of the mid-latitude jet stream, which would have to be
confirmed by further analyses. All in all, these simulations offer
possible explanations for the recorded wet conditions over tropical
Africa, northern Africa, East Africa and the Arabian Peninsula during
MIS 3. Additional feedbacks (e.g. vegetation and lake cover) could
enhance the simulated response to astronomical parameters, greenhouse
gas and ice sheets depicted by the simulations
shown here.

\section{Conclusion}\label{sec6}
Our results show that, contrary to what had been concluded in previous
studies, MIS 3 was a relatively wet period in tropical Africa, North
Africa and the Arabian Peninsula compared to MIS 4 and MIS 2. This
brings important environmental constraints when trying to understand
the migratory waves of \textit{Homo sapiens} from Africa to the Arabian
Peninsula and the Levant. Our results show in particular that there are
significant differences between regions, with a clear East--West
contrast. The most striking breakthrough of our study is to show that
eastern tropical Africa and the Arabian Peninsula were particularly
humid from the end of MIS 4 already, thus well ahead of the
humidification that took place over western Africa. 

Numerical simulations are in agreement with the data and make it
possible to specify the processes at work. From a hydrological point of
view, MIS 3 in the Arabian Peninsula is characterised by a lengthening
of the rainy season due to the combined effects of the Indian monsoon
and Mediterranean depressions. These evolutions are, in the first
place, linked to the orbital forcing. Model results suggest that
precession had a major impact on monsoon intensity through its control
of the northern hemisphere, low latitude summer insolation. But the
simulations also suggest that obliquity may have played an important
role as well, through its impact on the AMOC. The available data do not
currently allow us to test this hypothesis but the question of AMOC
impact on the precipitation dynamics during MIS 3 will have to be
addressed in the years to come.

\section*{Declaration of interests}
The authors do not work for, advise, own shares in, or receive funds
from any organization that could benefit from this article, and have
declared no affiliations other than their research organizations.

\section*{Acknowledgements}
We would like to thank the editors of this special volume in honour of
Professor J. Dercourt for inviting us to contribute. The computing time was
provided by GENCI (Grand Equipement National de Calcul Intensif) and
the simulations were performed using Curie at TGCC (Tr\`{e}s Grand
Centre de Calcul du CEA). M.-N. Woillez and P. Le M\'{e}zo are thanked
for taking part in this endeavour, as part of their post-doctoral and
PhD projects, respectively. The MIS 3 60~ka simulation was initially
run for the European Research Council TracSymbols project led by C.
Henshilwood and F. D'Errico (Grant no.~249587).

\CDRGrant[European Research Council TracSymbols]{249587}

\back{}

\section*{Supplementary data}
Supporting information for this article is available on the journal's
website under \printDOI\ or from the author. 

\CDRsupplementaryTwotypes{supplementary-material}{\cdrattach{Table-S1.xlsx}}

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