Priyadarsi D Roy,1 Axel Rivero-Navarette,1 Nayeli Lopez-Balbiaux,2
Ligia L Pérez-Cruz,3 Sarah E Metcalfe,4 G Muthu Sankar5 and
Jose Luis Sánchez-Zavala1
AbstractProxy records of runoff, lake water salinity and aeolian activity, reconstructed by analyzing the concentrations of Ti, Ca and Zr/Ti in the sediments of
palaeolake Las Cruces, provide information about millennial-scale summer season palaeohydrological changes at the southern margin of Chihuahua Desert
over the last 8.4 cal. kyr BP. The data indicate generally higher-than-average runoff between c. 8.4 and 5 cal. kyr BP, correlative to the early Holocene
Thermal Maximum. Except for the c. 2.2–2 cal. kyr BP humid event, runoff was lower than average over the last c. 5 cal. kyr BP. Latitudinal shifts in average
position of the Inter-Tropical Convergence Zone (ITCZ) caused by long-term changes in summer insolation was the principal forcing behind the varying
summer season precipitation and El Niño Southern Oscillation (ENSO) activity may explain some of the hydrological variability (e.g. higher-than-average
summer precipitation during c. 2.2–2 cal. kyr BP). In general, the basin received more runoff during the periods of less frequent and weak ENSO, similar to
the modern response to ENSO activity of the region. Significant increases in lake water salinity and aeolian activity over the last 2 cal. kyr BP correspond
to stronger and more frequent ENSO during the late Holocene.
Received 3 September 2012; revised manuscript accepted 19 February 2013
Research paper
1106 The Holocene 23(8)
same location were attributed to less summer precipitation
(Brunelle et al., 2010). As the modern-day precipitation regimes in
the region are ENSO-modulated, Castiglia and Fawcett (2006)
associated the high lake stands identified in the Palomas Basin to an
increase in the magnitude and frequency of El Niño over the Holo-
cene. Menking and Anderson (2003) associated the mid-Holocene
droughts in the Estancia Basin to frequent La Niña events and
Asmerom et al. (2007) observed that the La Niña-like conditions
were frequent during intervals of higher solar activity.
Compared with the northern part of the Chihuahua Desert,
late-Quaternary records are absent from the central and southern
parts. In this paper, we present a new multiproxy record of Holo-
cene climatic variability from the southern margin. Geochemical
and mineral magnetic data from a new 226 cm long sediment
sequence from palaeolake Las Cruces were used to reconstruct
the millennial-scale hydrologic variability over the last 8.4 cal.
kyr BP. The proxy-based records of runoff, lake water salinity and
aeolian activity are compared with summer insolation at 20°N
(Huybers, 2006) and palaeo-archives that reflect shifts in the
average position of the ITCZ (Peterson and Haug, 2006) and
ENSO activity (Conroy et al., 2008; Moy et al., 2002) in order to
understand the possible forcing mechanisms.
Material and methods
Study site
The Chihuahua Desert spreads over at least five different states in
northern Mexico (Chihuahua, Coahuila, Durango, Zacatecas and
San Luis Potosi). Palaeolake Las Cruces is located at the southern
margin of the desert (22°39′20.2″N, 101°53′05.4″W; 2106 m
a.s.l., Figure 1a). This ephemeral and endorheic palaeolake is c. 2
km long and up to c. 0.8 km wide and is present in a NW–SE
trending tectonic basin (Figure 1b and c). The meteorological data
between AD 1977 and 2009 from a station located at c. 20 km
southeast of Las Cruces (Salinas de Hidalgo) recorded annual
rainfall varying between c. 130 and 1280 mm, with an average
annual precipitation of c. 380 mm (Source: CONAGUA, Mexico,
Figure 2a). An average 75% (c. 290 mm) of the precipitation
occurs during the summer months (May–September: average
temperature of 19–21°C), whereas the winter precipitation
(November–March: average temperature of 12–16°C) constitutes
less than 20% of the total.
In the modern era, enhanced subsidence over northern Mexico
and a southward shift in the ITCZ decrease summer rainfall and
cause drought conditions over most of Mexico during El Niño
years (Magaña and Quintanar, 1997; Magaña et al., 2003; Pavia et
al., 2006). Higher summer precipitation during La Niña years
results from a northward shift in the ITCZ, weaker subsidence
over the northern Mexico, a stronger monsoon and an increase in
the number of hurricanes in the Atlantic (Magaña et al., 2003).
This pattern is the opposite from that observed in the southwest-
ern USA and the extreme north and northwest of Mexico. In gen-
eral, the summer season rainfall (%) between AD 1977 and 2009
shows an inverse relationship with the Ocean Niño Index (ONI,
Source: National Weather Service, NOAA) (Figure 2b). Summer-
season precipitation contributed more than 85% of annual rainfall
Figure 1. Location of both continental and marine proxy records from the region (a). Palaeolake Las Cruces lying in a tectonic basin on the southern margin of the Chihuahua Desert (b), and the geology of the surroundings comprising Cretaceous, Tertiary and Quaternary volcanic and sedimentary rocks (c).
Roy et al. 1107
during the years of negative ONI indicative of La Niña condi-
tions (e.g. AD 1978, 1989–1990, 1995–1996, 1999–2000 and
2007–2008). During El Niño (positive ONI) years (e.g. AD 1982–
1983 and 1997–1998), summer precipitation decreased and com-
prised less than 50% of the annual precipitation.
The Las Cruces basin is surrounded by Cretaceous, Tertiary
and Quaternary volcanic as well as sedimentary rocks (Figure 1c).
Tertiary sandstone, polimictic conglomerate, rhyolite and rhyo-
litic tuff are the dominant rock types around the basin. Minor
exposures of Quaternary basalt and basaltic tuff are present in the
northern part of the basin, whereas Cretaceous andesite, sand-
stone and limestone are present in the southwestern part (Servicio
Geologico Mexicano, 2007).
Sampling and analysis
A number of pits were dug in the central and eastern parts of the
palaeolake Las Cruces during an expedition in May 2011 and
sampling was carried out in a pit from the central part of the
basin (Figure 1c). We restricted the sample collection to the
depth of 226 cm because of groundwater influx. The chronology
of the sedimentary sequence is based on four AMS 14C dates on
bulk organic matter present in the sediments collected at depths
of 17, 49, 81 and 221 cm. A total of 113 sediment samples were
collected continuously at an interval of 2 cm (i.e. 0–2 cm, 2–4
cm, 4–6 cm, etc.). All the samples were oven dried (40°C),
homogenised and ground with an agate pestle. Identification of
the minerals and their relative abundance were carried out in ten
bulk powdered samples collected at different depths using a Phil-
ips 1130/96 x-ray diffractometer (XRD).
The concentrations of total carbon (TC), total sulphur (TS)
and total nitrogen (TN) were measured in 23 samples (sampling
interval of 10 cm) in a Perkin Elmer Series II CHNS/O elemental
analyzer. The concentration of total organic carbon (TOC) was
measured in an elemental analyzer after removing the carbonates
by treating with 10% HCl. Total inorganic carbon (TIC) content
was calculated by subtracting the TOC from TC. Concentrations
of Ti, Fe, K, Ca and Zr were obtained in all 113 samples using a
(XRF) analyzer and corrected as per Roy et al. (2012a). The low
field magnetic susceptibility (K) was measured in all the samples
using a Bartington MSE High Resolution Surface Scanning Sen-
sor at a high spatial resolution (3.8 mm × 10.5 mm) at 2 kHz.
Results
Stratigraphy and mineralogy
The sediment column is divided into four different stratigraphic
units (Figure 3a). The mineralogical association and a qualitative
estimation of the relative abundance of each mineral in the differ-
ent stratigraphic units are presented by XRD diffractograms of
four different samples (Figure 3b). The basal unit IV (80–226 cm)
consists of massive brown-reddish silt with the presence of ran-
domly oriented gypsum lenses at some intervals. The gypsum
lenses are 5 to 10 cm long and partly developed into desert roses.
Quartz and gypsum are the most abundant minerals in this unit
and both are present in similar proportions. Halloysite, kaolinite
and calcite are present in trace amounts.
The overlying unit III (50–80 cm) comprises massive brown-
reddish silt and lacks gypsum lenses. However, randomly ori-
ented millimetre-scale evaporite crystals are visible in this unit.
Sediments of this unit contain abundant quartz, minor calcite and
gypsum, and trace amounts of halloysite and kaolinite. The sedi-
ments of unit II (18–50 cm) are massive calcareous grey silty-clay
with randomly oriented angular calcrete nodules (1–2 cm long).
Quartz is the most abundant mineral, followed by minor calcite
and gypsum. Plagioclase, halloysite and kaolinite are present in
trace amounts. The uppermost unit I (0–18 cm) consists of mas-
sive grey silty-sand with remnants of plant roots and vertical des-
iccation fissures (up to 5 cm long). Quartz and gypsum are the
most abundant minerals followed by calcite. Halloysite and
kaolinite are present in trace amounts. Trace amounts of magne-
tite are identified only in the sediments of units I and II.
Age model
The age model was constructed after calibrating the AMS 14C
dates using the IntCal 09 curve and Calib 6.0 program (Reimer et
al., 2009) (Table 1). The age versus depth diagram (Figure 4) was
generated by using the calibrated ages in the free software R (R
Development Core Team, 2009) and includes uncertainties
between 88 and 130 years between the tie points. The rate of sedi-
mentation (calculated between two consecutive dates) varies
between 0.009 and 0.073 cm/yr. Age of the samples present
between depths of 17 and 221 cm was estimated by interpolating
the sedimentation rates calculated between the consecutive 14C
dates. The base of the sediment column (226 cm) was assigned an
age of c. 8.4 cal. kyr BP by extrapolating the sediment rate calcu-
lated between sediments present at depths of 81 and 221 cm. As
the basin remains dry for an extended period during every year
and aeolian deflation causes erosion of the surface sediments, the
topmost part of the sampled sediment column may not represent
Figure 2. (a) Average monthly precipitation (dark bars) and temperature (dotted line) registered at the meteorological station located at Salinas de Hidalgo (see Figure 1b). (b) Comparison between summer season precipitation (solid line) and Ocean Niño Index (ONI, dotted line) during AD 1977–2009.
1108 The Holocene 23(8)
Figure 3. (a) Stratigraphy of the sediment core collected from Las Cruces and location of the four AMS 14C dates along the depth. (b) The mineralogical association and relative abundance of each mineral is presented by the XRD diffractograms.
kyr BP). The sediments representing the last c. 1 cal. kyr BP are
characterized by the highest TOC (1.0–1.3%).
Sediments show total nitrogen (TN) concentration of
0–0.2%. The relative dominance of terrestrial or lacustrine
plants on the bulk organic carbon is identified by the TOC/
TN (C/N) ratios (Meyers and Ishiwatari, 1995; Talbot and
Johannessen, 1992). Organic matter sourced from the aquatic
plants is characterized by C/N values <10 as nitrogen is
enriched in the cellulose lacking phytoplankton, whereas ter-
restrial plants with woody tissue and cellulose have lower
concentrations of nitrogen and their increasing dominance
results in higher C/N values. The sediments of Las Cruces
have C/N values between 1.6 and 30 (Figure 5). Higher C/N
values (17–30) are indicative of the greater influence of ter-
restrial plants on the organic matter deposited during c. 7.5–7
cal. kyr BP and lower values of C/N (<10) suggest that the
Table 1. Radiocarbon dates of the sediments collected at different depths from palaeolake Las Cruces, southern Chihuahua Desert.
the present day. Similarly, the occurrence of deflation events dur-
ing other drier intervals over the last 8.4 cal. kyr BP cannot be
ruled out. Within the limitations of this age model, we consider
that the sediments of stratigraphic unit I are representative of last
c. 1.7 cal. kyr BP. Sediments of unit II were deposited during c.
2.2–1.7 cal. kyr BP, unit III is constrained between c. 5.3 and 2.2
cal. kyr BP and the gypsum lenses present in unit IV were depos-
ited during c. 8.4–5.3 cal. kyr BP.
Organic carbon (TOC) and C/N
The total organic carbon (TOC) concentration varies between 0.1
and 1.3% (Figure 5): it remains homogeneous and low (0.1–0.3%)
in the lower part of the sediment profile (stratigraphic units III
and IV, c. 8.4–2.4 cal. kyr BP) and shows a gradual increasing
trend (0.5–1.3%) in the upper part (units II and I, last c. 2.4 cal.
Roy et al. 1109
organic matter was sourced dominantly from lacustrine algae
in the rest of the sequence.
Carbonate (CaCO3) and sulphate (CaSO4)
As calcite is the only carbonate mineral and gypsum is the only
sulphate mineral present in the sediments of Las Cruces, we
expressed total inorganic carbon (TIC) as calcite (CaCO3) and
total sulphur (TS) as gypsum (CaSO4) (Figure 5). The calcite con-
tent varies between 1.7 and 13.4% with higher values observed in
the sediments deposited during c. 4.5–3.5 cal. kyr BP (7.3–7.9%)
and over the last c. 2 cal. kyr BP (9.6–13.4%). In the rest of the
sediments, calcite shows an abundance of 1.7–5.7%. The gypsum
content fluctuates between 0 and 3% and higher values are
observed in the sediments of c. 8–6 cal. kyr BP (up to 3%), c. 2.5
cal. kyr BP (2.5%) and c. 1 cal. kyr BP (2.1%). The varying abun-
dance of calcite and gypsum suggests that the brine composition
changed between Ca-HCO3 and Ca-SO4 rich conditions through
time. Both Ca and HCO3 were derived from the weathering of
sandstone, limestone and volcanic rocks exposed in the catchment
of the basin, whereas SO4 could be partially from the bedrocks and
partially oceanic (Eugster and Hardie, 1978). The salt assemblage
indicates an inflow with composition of Ca>HCO3. After the cal-
cite precipitation, the subsequent brine evolution yielded precipi-
tation of Ca-bearing sulphate (gypsum) (Cohen, 2003). We do not,
however, have sufficient data resolution to make high-resolution
interpretations from the abundance of evaporite minerals.
Magnetic susceptibility
Magnetic susceptibility (K) of the sediments varies between 10.1 and
21.9×10−5 SI. Sediment of units I (16.7–21.9×10−5 SI) and II (19.4–
26.3×10−5 SI) show higher values compared with the sediments of
units III (10.1–16.5×10−5 SI) and IV (12.1–19.8×10−5 SI) (Figure 6).
Lower K values are associated with silt-dominated sediments with or
without gypsum lenses deposited during c. 8.4–2.2 cal. kyr BP.
Higher K values are associated with the silty-clay and silty-sand
dominated sediments deposited over the last c. 2.2 cal. kyr BP.
The abundance and type of magnetic minerals affect K-values
measured in the bulk sediments and the presence of ferromagnetic
minerals has a dominant influence over the diamagnetic and para-
magnetic minerals (Blanchet et al., 2007; Thompson and Old-
field, 1986; Urrutia-Fucugauchi, 1981; Urrutia-Fucugauchi et al.,
1997). Except for the trace amounts of ferromagnetic magnetite
identified in the sediments of units I and II, the sediments of the
palaeolake show a mineralogical assemblage dominated by dia-
magnetic quartz, calcite and gypsum. Paramagnetic halloysite and
kaolinite are present in trace amounts and their occurrence does
not show any significant variation in the sediment profile. Higher
K-values are observed with the sediments of stratigraphic units I
and II showing presence of magnetite.
Multi-element concentrations
The concentration of Ti varies between 0.18 and 0.30%, Fe fluc-
tuates between 1.8 and 3.0%, K varies from 2.0 to 3.0%, Ca
shows variation between 1.3 and 6.0% and Zr fluctuates between
146 and 235 ppm along the depth profile (Figure 6). The distribu-
tions of Ti, Fe and K are similar (R2=0.7–0.8) and Ca shows a
distribution opposite to Ti (R2= −0.8) and Fe (R2= −0.9). The dis-
tribution of Zr is similar to Ti (R2= −0.2) in some parts of the
profile and comparable with Ca (R2=0.4) in others.
Ti, Fe, K and Zr are present in the detrital minerals such as sili-
cates and oxides sourced from the erosion of rocks present in the
catchment of the basin. Higher sediment–water interaction during the
transportation of primary minerals and lower oxidation-reduction
potential (Eh) in the water column causes dissolution of a part of the
Fe and K present in the detrital minerals (Cohen, 2003; Mason and
Moore, 1982). The released Fe and K re-precipitate as secondary clay
minerals and authigenic carbonates and evaporites (Cohen, 2003).
The similar distribution of Ti, Fe and K suggests that the sediment–
water interaction was low and the basin did not have anoxic condi-
tion of deposition. The different distribution of Zr compared with Ti,
Fe and K could be due to the fact that different geomorphological
processes (i.e. pluvial and aeolian) were associated with the transpor-
tation of Ti, Fe and K-bearing and Zr-bearing minerals into the basin.
We present Zr/Ti as a proxy to demarcate the intervals with higher
influx of Zr-bearing minerals compared with Ti-bearing ones into the
basin (Figure 6). Abundance of Zr-bearing minerals is higher in the
sediments of the last c. 5 cal. kyr BP (stratigraphic units I, II and III)
compared with the sediments deposited during c. 8.4–5 cal. kyr BP
(stratigraphic unit IV) and the highest values are associated with the
sediments deposited over the last c. 2 cal. kyr BP.
The positive coefficient of correlation between Ca and TIC
(R2=0.8) suggests that higher Ca-values are associated with sedi-
ments with more calcite precipitation and represent intervals of
more saline lake water and arid conditions. The similar distribu-
tion of Zr/Ti and Ca (R2=0.8) suggests that the Zr-bearing miner-
als were deposited during arid intervals and hence transported
into the basin by aeolian processes. The negative coefficient of
correlation between Zr/Ti and Ti suggests that Ti, Fe and
K-bearing minerals were transported into the basin during humid
intervals by pluvial discharge (runoff). It is interesting to observe
that the magnetic susceptibility is comparable with Ti in some
parts of the sequence and similar to Zr/Ti and Ca in other parts
(Figure 6). This suggests that the magnetic minerals were trans-
ported both by pluvial and aeolian processes into the basin.
Discussion
Proxy interpretations and palaeohydrological
reconstructions
Over the last c. 8.4 cal. kyr BP, the variations in climatic condi-
tion at the southern margin of the Chihuahua Desert (palaeolake
Figure 4. Age model (age versus depth) created from the calibrated AMS 14C dates in the free software R (R Development Core Team, 2009). The age model has uncertainties of 88 to 130 years between the tie points.
1110 The Holocene 23(8)
Las Cruces) are documented using proxies for runoff, lake water
salinity and aeolian activity. The abundance of Ti-bearing min-
erals estimated from Ti concentration in the sediments of Las
Cruces is interpreted as a proxy for runoff of detrital minerals
into the basin and therefore an estimation of regional summer
precipitation. The intervals of higher Ti values reflect periods of
more summer rainfall and vice versa for intervals of lower Ti
values (e.g. Haug et al., 2001; Metcalfe et al., 2010; Roy et al.,
2012a, 2012b). The abundance of calcite (CaCO3) estimated
from the Ca concentration is interpreted as a proxy for carbonate
precipitation and therefore an estimation of lake water salinity.
The intervals of higher Ca values demarcate periods of higher
lake water salinity and vice versa. Similarly, Zr/Ti values
estimate the abundance of Zr-bearing minerals deposited in the
basin by aeolian processes and higher Zr/Ti values demarcate
the periods with enhanced aeolian activity in the basin surround-
ings. Magnetic susceptibility is considered as a proxy to identify
the intervals of higher influx of magnetic minerals into the basin
both by pluvial and aeolian processes. The proxy records are
standardized (e.g. Kirby et al., 2010) by subtracting the mean
value and dividing by the standard deviation of the distribution
from the measured proxy value in order to document the inter-
vals with hydrological conditions different from the average of
last c. 8.4 cal. kyr BP (Figure 7). For example, positive Ti excur-
sions represent periods of higher than the average runoff and
vice versa.
Figure 5. Concentrations of total organic carbon (TOC), C/N, CaCO3 and CaSO4 in the sediments against depth (cm) and age (cal. kyr BP) (for the stratigraphic description see Figure 3).
Figure 6. Distribution of magnetic susceptibility (K) and concentrations of Ti, Fe, Zr, Ca and Zr/Ti against depth (cm) and age (cal. kyr BP) in the sediments of palaeolake Las Cruces (for the stratigraphic description see Figure 3).
Roy et al. 1111
Characterized by millennial-scale variations, the sediments
between 226 and 75 cm have generally average and higher than aver-
age Ti concentrations and represent an interval of higher runoff into
the basin during c. 8.4–5 cal. kyr BP. This interval of more than aver-
age summer rainfall is contemporary to the Holocene Thermal Maxi-
mum (Haug et al., 2001). The palaeohydrological variations during
this interval are reflected by gypsum precipitation at certain depths as
intervals of lower rainfall and increasing salinity and evaporation.
Lower than average runoff are identified at c. 7.5 (183–187 cm), 7
(147–150 cm) and 6.2–6 (111–123 cm) cal. kyr BP. The positive val-
ues of standardized Ca indicate that lake water salinity was higher
than average at c. 7 cal. kyr BP and c. 6.2–6 cal. kyr BP. Similarly, the
average to lower than average Zr/Ti mirrors the weak aeolian activity
in the surroundings of Las Cruces during the entire interval.
Except for the c. 2.2–2 cal. kyr BP interval, the sediments
deposited over the last c. 5 cal. kyr BP (75–0 cm) have lower than
average Ti and represent a period of lower than average summer
precipitation (Figure 7). However, the runoff into the basin was
relatively higher and the lake water salinity lower between c. 5
and 2.3 cal. kyr BP compared with the last 2 cal. kyr BP. This is
suggested by the relatively higher Ti and lower Ca in the sedi-
ments at depths of 75–50 cm compared with 30–0 cm. The abun-
dance of calcite is also lower between c. 4.5 and 3.5 cal. kyr BP
compared with the last c. 2 cal. kyr BP. Transportation of Zr-bearing
minerals into the basin by aeolian processes increased post c. 5
cal. kyr BP. The dominant aeolian activity over the last 2 cal. kyr
BP corresponds to an interval of lowest runoff (i.e. Ti) and highest
calcite abundance (i.e. Ca) (Figure 7). An abrupt increase in Ti at
depths between 50 and 33 cm suggests higher-than-average sum-
mer precipitation during c. 2.2–2 cal. kyr BP. During this event,
increased runoff transported magnetic minerals into the basin and
the dilute lake water precipitated less than average calcite.
Possible forcing mechanisms
We compared the runoff record of Las Cruces with summer inso-
lation variation at 20°N (Huybers, 2006) and palaeorecords of
latitudinal shifts in the position of ITCZ (Peterson and Haug,
2006) and ENSO activity (Conroy et al., 2008; Moy et al., 2002)
in order to understand the possible forcing mechanisms (Figure 8).
Palaeoreconstructions suggest higher summer precipitation in the
Northern Hemisphere during the intervals of solar insolation
modulated northward ITCZ and vice versa (Haug et al., 2001;
Hodell et al., 1991). Based on Ti concentrations in sediments of
the Cariaco Basin (Figure 1a), Haug et al. (2001) and Peterson
and Haug (2006) reported a northward shift in the mean position
of ITCZ between c. 10.5 and 5.4 cal. kyr BP and a gradual south-
ward shift with millennial-scale fluctuations post c. 5.4 cal. kyr
BP (Figure 8). The proxy record of runoff from Las Cruces shows
a first order positive relationship with the position of the Inter-
Tropical Convergence Zone (ITCZ) and summer insolation. Gen-
erally higher than average runoff (c. 8.4–5 cal. kyr BP) occurred
during the interval of higher summer insolation and northerly
ITCZ. Except for the c. 2.2–2 cal. kyr BP event, the lower than
average runoff over the last c. 5 cal. kyr BP is similar to the grad-
ual reduction in summer insolation and southerly shifting of ITCZ
over the middle and late Holocene. This suggests that the summer
season precipitation at the southern margin of the Chihuahua Des-
ert over the Holocene was mainly controlled by the summer inso-
lation driven latitudinal shifts in the average position of ITCZ.
In order to explain the higher-than-average summer precipita-
tion during c. 2.2–2 cal. kyr BP and observe the influence of ENSO
on the precipitation variation in the southern Chihuahua Desert, we
compared the proxy runoff record with the palaeo-ENSO archives
of Moy et al. (2002) and Conroy et al. (2008) (Figure 8). The pal-
aeo-ENSO records were obtained from the inorganic clastic
Figure 7. Standardized proxy records indicating variations in clastic input (K), runoff into the basin (Ti), lake water salinity (Ca) and aeolian activity (Zr/Ti) over the last c. 8.4 cal. kyr BP. The positive values indicate more than average and vice versa.
1112 The Holocene 23(8)
laminae in a sediment core from Laguna Pallcacocha (southern
Ecuador, Figure 1a) and sand content in another sediment core
from the El Junco Crater Lake (Galápagos Islands). The Laguna
Pallcacocha record documents millennial-scale moderate-to-strong
El Niño events. It records the first statistically significant ENSO
activity at c. 7 cal. kyr BP and maximum ENSO frequency at c. 1.2
cal. kyr BP (Moy et al., 2002). The record from the El Junco Crater
Lake indicates an increase in the frequency and magnitude of
Figure 8. Comparison of the runoff (precipitation) record at Las Cruces (a) with palaeo-archives indicating latitudinal shift in the mean position of ITCZ (b, Peterson and Haug, 2006), summer insolation at 20°N (c, Huybers, 2006), palaeo-ENSO archives obtained from Laguna Pallcacocha (d, Moy et al., 2002) and El Junco Crater Lake (e, Conroy et al., 2008).
Figure 9. Comparison of the proxy record of summer precipitation in the southern Chihuahua Desert with other regional continental (Babicora: Roy et al. (2012a); San Bernardino Ciénega: Brunelle et al. (2010); Yuma: Bacon et al. (2010); Guadalupe Mountains: Asmerom et al. (2007); and Estancia Basin: Menking and Anderson (2003)) and marine records from the Gulf of California (Gonzalez-Yajimovich et al., 2005; Pérez-Cruz, 2012) and Gulf of Mexico (Poore et al., 2004).
Roy et al. 1113
ENSO after c. 4.2 cal. kyr BP and highest ENSO variance during
2–1.5 cal. kyr BP (Conroy et al., 2008). Despite the discrepancies,
both the records suggest weak or non-existent ENSO during the
early part of the middle Holocene and an increase in ENSO fre-
quency and amplitude over the late Holocene. The runoff record of
palaeolake Las Cruces shows a first-order negative correlation with
the palaeo-ENSO archive obtained from Laguna Pallcacocha.
More than average runoff during c. 8.4–5 cal. kyr BP and c. 2.2–2
cal. kyr BP corresponds to the intervals of weak or non-existent
moderate-to-strong ENSO. Less than average runoff between c. 5
and 2.3 cal. kyr BP occurred during an interval of gradual increase
in the frequency of El Niño. Arid conditions with the lowest sum-
mer precipitation over the last c. 2 cal. kyr BP coincide with the
period of highest ENSO frequency and amplitude towards the late
Holocene (i.e. dominant El Niño state). The inverse relationship
between the proxy records of summer precipitation in the southern
Chihuahua Desert and ENSO activity suggests that the ENSO forc-
ing on regional precipitation was present throughout the
Holocene.
Comparison with regional records
Figure 9 compares the Las Cruces record with both continental
and marine palaeoclimatic archives from the region (see Figure
1a for locations). Higher summer precipitation over the early part
of the middle Holocene and its gradual decrease over the middle
to late Holocene are registered in marine sediments from the Gulf
of Mexico and Gulf of California (Gonzalez-Yajimovich et al.,
2005; Pérez-Cruz, 2012; Poore et al., 2004, 2005). Based on the
planktonic foraminifer G. sacculifer in cores from the Gulf of
Mexico, Poore et al. (2005) suggested an enhanced North Ameri-
can Monsoon during c. 7–4.7 cal. kyr BP and severe multicentury
drought centered at c. 1.6 cal. kyr BP. Similarly, the mass accumu-
lation rate and terrigenous input in the Alfonso Basin located in
the southern Gulf of California also indicate gradually reducing
summer precipitation as a result of solar insolation controlled
southward movement of ITCZ over the last 6 cal. kyr BP (Gonza-
lez-Yajimovich et al., 2005; Pérez-Cruz, 2012). We observe
remarkable similarity between the palaeohydrological conditions
at Las Cruces and the forest fire record obtained from the domi-
nantly summer precipitation-fed San Bernardino Ciénega located
in southeastern Arizona and northern Sonora (Brunelle et al.,
2010). The rare fire occurrence between c. 8.1 and 5.3 cal. kyr BP
was related to higher regional summer precipitation and the
increase in forest fire frequency post c. 5.3 cal. kyr BP was associ-
ated with higher winter-precipitation taxa. The interval of more-
than-average summer precipitation at Las Cruces during c. 2.2–2
cal. kyr BP is contemporary with the high magnitude flooding
events occurring between c. 2.4 and 1.1 cal. kyr BP at the San
Bernardino Ciénega. Similarly, the events of lower precipitation
at c. 7.5, 3 and 1 cal. kyr BP are contemporary to the drought
conditions/desiccations observed at palaeolake Babicora (north-
ern Mexico) (Chávez-Lara et al., 2012; Roy et al., 2012a).
The proxy records indicating variations in regional winter pre-
cipitation are in contrast to the observations from Las Cruces
(Figure 9). For example, Menking and Anderson (2003) reported
drought conditions at the Estancia Basin between c. 7 and 5 cal.
kyr BP and related those to a La Niña-like state. Bacon et al.
(2010) observed 900 years of alluvial aggradation during c. 3.2–
2.3 cal. kyr BP near Yuma (southwestern Arizona). A centennial-
scale speleothem record from the Guadalupe Mountains (New
Mexico) recorded less winter precipitation during c. 8–7 cal. kyr
BP and at c. 2.2–2 cal. kyr BP (Asmerom et al., 2007). The contri-
bution of winter moisture to mean annual precipitation increased
over the late Holocene (i.e. at c. 3.3 and c. 2.7 cal. kyr BP).
Although the records are of different resolutions, the c. 6.2–6 cal.
kyr BP event is registered both at Las Cruces (lower summer pre-
cipitation) and Guadalupe Mountains (higher winter moisture).
ConclusionsHigh resolution proxy-based palaeoclimatic records are scarce in
the central and southern parts of the Chihuahua Desert. Poor pres-
ervation of biological indicators and the presence of hiatuses in
the sediment sequences are some of the major obstructions to the
reconstruction of Holocene climate of the region. We provide use-
ful information about the summer season palaeohydrological con-
ditions over the last 8.4 cal. kyr BP at the southern margin of the
Chihuahua Desert by studying multi-element concentrations and
magnetic susceptibility of sediments from palaeolake Las Cruces.
Our main conclusions can be summarized as:
• Variation in summer season precipitation at the southern
margin of Chihuahua Desert is mainly driven by long-
term changes in solar insolation and associated latitudinal
shifts in the average position of ITCZ and ENSO activity.• Higher-than-average summer season precipitation between
c. 8.4 and 5 cal. kyr BP occurred during an interval of
northerly ITCZ and weak to non-existent ENSO.• Over the last c. 5 cal. kyr BP, the lower-than-average summer
precipitation was caused by southward movement of the
average position of ITCZ and increasing ENSO activity.• Higher summer precipitation during c. 2.2–2 cal. kyr BP is
contemporary to an interval of weak or non-existence of
moderate to strong ENSO. However, it is interesting that
the event is observed only in the continental records from
the region and not in the marine sediments.
Acknowledgements
We are thankful to the staffs of Presidencia Municipal and Casa de
Cultura of Salinas de Hidalgo (SLP) for their help during the sam-
pling expeditions. The critical comments and observations of both
anonymous reviewers are gratefully acknowledged. Technical as-
sistance was provided by Marcela Patricia Charles-Polo, Rufino
Lozano Santacruz, Victor Lemus and Susana Sosa-Najera.
Funding
The data presented in this paper were generated with financial
support from the Papiit-UNAM project (IN100413) to PDR.
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