The impact of climate change on the development and
disintegration of Maya civilisation has long been debated. The lack of
agreement among existing palaeoclimatic records from the region has prevented
a detailed understanding of regional-scale climatic variability, its climatic
forcing mechanisms and its impact on the ancient Maya. We present two new
palaeo-precipitation records for the central Maya lowlands, spanning the
Pre-Classic period (1800 BCE–250 CE), a key epoch in the development of
Maya civilisation. A beach ridge elevation record from world's largest late
Holocene beach ridge plain provides a regional picture, while Lake Tuspan's
diatom record is indicative of precipitation changes at a local scale. We
identify centennial-scale variability in palaeo-precipitation that
significantly correlates with the North Atlantic
During the last decades, a wealth of new data has been gathered to understand human–environmental interaction and the role of climate change in the development and disintegration of societies in the Maya lowlands (e.g. Akers et al., 2016; Douglas et al., 2015, 2016; Dunning et al., 2012, 2015; Lentz et al., 2014; Turner and Sabloff, 2012). Previous studies have emphasised the impact of prolonged droughts and their possible link with social downturn, such as the Pre-Classic Abandonment and the Classic Maya Collapse (Ebert et al., 2017; Hoggarth et al., 2016; Lentz et al., 2014; Kennett et al., 2012; Medina-Elizalde et al., 2010, 2016; Haug et al., 2003; Hodell et al., 1995, 2001, 2005). Less attention has been given to episodes of excessive rain and floods that may also have severely impacted ancient Maya societies (e.g. Iannone, 2014). Evidence for such impacts is found in the fact that floods, as well as droughts, are an important theme depicted in the remaining ancient Maya codices (Fig. 1) (Thompson, 1972) and Maya mythological stories (Valásquez Garciá, 2006).
The image on p. 74 of the Dresden Codex depicts a torrential downpour probably associated with a destructive flood (Thompson, 1972).
A large part of the central Maya lowlands (outlined with a
black dashed line) is drained by the Usumacinta (Us.)
River
One of the main challenges in palaeoclimatic reconstructions is to unravel
climate from human-induced changes. Maya societies played a key role in the
formation of the landscape, but the degree of human-induced impact remains
highly debated (Hansen, 2017; Beach et al., 2015; Ford and Nigh, 2015). For
example, it is proposed that the increase in sedimentation rate after
1000 BCE at Lake Salpeten (Anselmetti et al., 2007) and Petén-Itzá
(Mueller et al., 2009) is related to human-induced soil erosion. However,
other high-resolution lake records from the area do not show a significant
increase in sedimentation rate during the Pre-Classic or Classic period (e.g.
Wahl et al., 2014), and past volcanic activity could have been responsible
for the deposition of smectite-rich clay layers in inland lakes (Tankersley
et al., 2016; Nooren et al., 2017a). Palynological records from the central
Maya lowlands (CML; Fig. 2) show no evidence of widespread land clearance and
agriculture before
In this paper, we present two new palaeo-precipitation records reflecting precipitation changes in the CML. The records span the Pre-Classic period (1800 BCE–250 CE), when Maya societies in the CML transformed from predominantly mobile hunter-gatherers in the Early Pre-Classic period (e.g. Inomata et al., 2015; Coe, 2011; Lohse, 2010) to complex sedentary societies that founded impressive cities like El Mirador by the later part of the Pre-Classic period (Hansen, 2017; Inomata and Henderson, 2016). The period of rapid growth in these centralised societies probably occurred much later than previously thought, sometime after the start of the Late Pre-Classic period around 400 BCE (Inomata and Henderson, 2016). This raises the question for the reason behind the delayed development of societies in this area, which was to become the core area of Maya civilisation during the following Classic period (250–900 CE). There is recent evidence that climate during the Middle Pre-Classic Period (1000–400 BCE) may have been less stable than recently reported (Ebert et al., 2017). We propose that anomalously wet conditions could have been unfavourable for the intensification of maize-based agriculture, which formed the underlying subsistence economy responsible for the development of many neighbouring Meso-American societies during this period.
The CML have been intensively studied, and several well-dated speleothem, palynological and limnological records have been obtained for this area (Díaz et al., 2017; Akers et al., 2016; Douglas et al., 2015; Wahl et al., 2014; Kennett et al., 2012; Mueller et al., 2009; Metcalfe et al., 2009; Domínguez-Vázquez and Islebe, 2008; Galop et al., 2004; Rosenmeier et al., 2002; Islebe et al., 1996) (Figs. 2 and A1). However, palaeo-precipitation signals from these records and those from adjacent areas in the Yucatán and central Mexico exhibit large differences among records (Fig. A2), making the reconstruction and interpretation of larger-scale precipitation for the region a challenge (Lachniet et al., 2013, 2017; Douglas et al., 2016; Metcalfe et al., 2015). Existing climate reconstructions mostly represent local changes and are predominantly based on oxygen isotope variability, although some new proxies have been introduced recently (e.g. Díaz et al., 2017; Douglas et al., 2015).
We present a regional-scale palaeo-precipitation record for the CML,
extracted from world's largest late Holocene beach ridge sequence at the Gulf
of Mexico coast (Fig. 2b). The beach ridge record captures changes in river
discharge resulting from precipitation patterns over the entire catchment of
the Usumacinta River and thus represents regional changes in precipitation
over the CML (Nooren et al., 2017b). Currently the annual discharge of the
Usumacinta river is approximately 2000 m
The coastal beach ridges consist of sandy material originating from the
Grijalva and Usumacinta rivers, topped by windblown beach sand (Nooren et
al., 2017b). Although multiple factors determine the final elevation of the
beach ridges, it has been shown that during the period
Summarised proxy record of Lake Tuspan sediment core C. In the
lithological column black lines represent large flood layers and grey boxes
turbidites. Ca and Si (in cps: counts per second) are presented here as a
percentage of total counts. Vertical lines (red) in the (amorphous) Si graphs
indicate the 1 standard deviation threshold above the mean. For the diatom
record only the relative abundance of “key” diatom species are shown here.
During dry periods, a reduced riverine input of freshwater and a lowering of the lake level enhance the effect of evaporation and increase the salinity of the lake water. Diatom communities within oligo- to hypersaline lakes are strongly influenced by lake water salinity (Reed, 1998; Gasse et al., 1995), and we therefore determined diatom assemblage changes within the Lake Tuspan sediment record (Fig. 3) to reconstruct palaeosalinities of the lake water, reflecting palaeo-precipitation in the lake's catchment via changes in the balance of precipitation and evaporation.
Beach ridges elevations were extracted from a digital elevation model (DEM)
of the coastal plain along the transects indicated in Fig. 2 (Nooren et al.,
2017b). The DEM is based on lidar data originally acquired in April–May 2008
and processed by Mexico's National Institute of Statistics and Geography
(INEGI), Mexico. The relative beach ridge elevation is defined as the
difference between the beach ridge elevation and the long-term (
Two parallel cores, Tuspan cores B and C, were taken with a Russian corer (type GYK) in shallow water near the inflow of the Dulce River (not to be confused with the Dulce River that drains lake Izabal in eastern Guatemala), not far from core A, which has been studied for pollen (Galop et al., 2004). Semi-quantitative analyses of Si, S, K, Ca, Ti, Mn and Fe were conducted on both cores with an X-ray fluorescence core scanner (type AVAATECH) at 0.5 cm intervals. Deposits of large floods were identified on the basis of elevated concentrations of Si, Fe, Ti and Al (Davies et al., 2015), with peak concentrations exceeding a 1 standard deviation threshold above the mean.
Core C was investigated for amorphous silica, charred plant fragments and
diatoms (Figs. 3, A4 and A5). The core was subsampled at 4–12 cm contiguous
intervals, each interval representing 25–80 years. In addition, 37 1 cm
samples (representing
Slides were prepared from the remaining material. Diatoms were identified,
counted and reported as percentages of the total diatom sum, excluding the
small and often dominant
The age–depth model for core C is based on seven AMS radiocarbon-dated
terrestrial samples and stratigraphical correlation with core A (Fleury et
al., 2014). We used a linear regression between the available
radiocarbon-dated samples (Fig. A7), which is comparable with the age–depth
model of Fleury et al. (2014) for the time window between
The relation between our beach ridge and diatom record and other
palaeo-precipitation records from the Maya lowlands and nearby regions
(Figs. A1 and A2) were investigated by wavelet transform coherence
(WTC) analyses
using the software developed by Grinsted et al. (2004). We also applied WTC to compare our record with North Atlantic ice drift record (Bond et al.,
2001) and the Northern Hemisphere atmospheric
As described above, when beach ridge elevation is largely driven by the
discharge of the Usumacinta River, periods of relative high (low) beach
ridges correspond to relatively drier (wetter) conditions in the Usumacinta
catchment (Fig. 2). The beach ridge record shows clear centennial-scale
variability, with an exceptionally dry phase centred around
The sediment stratigraphy of core C can be divided into two main units. Below 4.3 m the core is clearly laminated, and 0.5–4 cm thick dark palaeo-flood layers contrast with the predominantly light-coloured calcareous deposits. The flood layers are characterised by elevated detrital input, resulting in elevated concentrations of Si, amorphous silica, and charred plant fragments. The average recurrence time of large floods was approximately 50 years. Sediments from 0.25 to 4.3 m depth are vaguely laminated, with three distinct decimetre-thick turbidite layers (Fig. 3).
The interpretation of PC-1 (Fig. 3) as an indicator of lake salinity and
hence relative dryness (see the “Methods” section) is supported by the fact
that low or negative PC-1 values are driven by relatively high percentages of
A drastic change from dry to wet conditions occurred around 4.3 m depth
(
Comparison of the Lake Tuspan and beach ridge record
WTC analysis (Grinsted et al., 2004) indicates in-phase coherence between the
beach ridge record and the recently extended and revised calcite
Both beach ridge and diatom records indicate that the onset of the Early Pre-Classic period was relatively dry (Fig. 4). Despite the predominantly dry conditions, large floods still occurred, as demonstrated by the repetitive input of fluvial material into Lake Tuspan. Periods with the highest fluvial sediment input coincided with periods of increased input of charcoal into Lake Petén-Itzá (Schüpbach et al., 2015) (Fig. A2). Because the CML were still sparsely populated during the Early Pre-Classic period (Inomata et al., 2015) we relate the presence of charcoal to the occurrence of wildfires.
After a transition to wetter conditions between 1500 and 1400 BCE, we
observe a drying trend that culminated in a prolonged dry period at the end
of the Early Pre-Classic period centred around
Both the beach ridge and the Lake Tuspan diatom records indicate a change to
wetter conditions around 1000–850 BCE, causing major changes in
hydrological conditions in the CML (Fig. 4). The diatom assemblages in the
Lake Tuspan record show a major change in composition. Species indicative of
meso- to poly-saline water almost completely disappear and are replaced by
species indicating freshwater conditions (Fig. 4). In the lake sediments,
this transition is also marked by a lithological shift from clearly to
vaguely laminated sediments that lack repetitive large flood layers, while
charred plant fragments are almost absent until
Both beach ridge and diatom record (Fig. 4) indicate that a relatively dry
period occurred by the onset of the Late Pre-Classic period, which has not
been identified in other proxy records from the region (Fig. A2), although
high
The observed general drying trend over the last few thousand years is probably related to the southward shift of the Intertropical Convergence Zone (ITCZ) during the late Holocene. The shift occurred in response to orbitally forced changes in insolation (Haug et al., 2001), causing a gradual Northern Hemisphere cooling versus Southern Hemisphere warming (Fig. 4), thereby shifting the ITCZ towards the warming Southern Hemisphere (Schneider et al., 2014). Wetter conditions during the Middle Pre-Classic period may reflect a more northerly position of the ITCZ, which may be related to stronger easterly trade winds and the less frequent occurrence of winter season cold fronts, as beach ridge morphological changes suggest (Nooren et al., 2017b).
The coherence between the beach ridge record and the relatively well-dated
Macal Chasm speleothem record gives us confidence that these records reflect
regionally coherent variability at centennial timescales during the
Pre-Classic period. Interestingly, the beach ridge record is significantly in
anti-phase with the North Atlantic ice drift record (Bond et al., 2001) and
the Northern Hemisphere atmospheric
Wavelet transform coherence (WTC) analysis between the beach ridge
record and the Northern Hemisphere atmospheric
The coherence with fluctuations in solar irradiance is most evident during
the 850 BCE (2.8 ka) event, related to the Homeric Grand Solar Minimum. At
that time, a strong decrease in the total solar irradiance resulted in higher
atmospheric
It has previously been suggested that there was a coherent response to the late Holocene southward shift of the ITCZ in both northern South America and the Maya lowlands (Haug et al., 2003), implying that the beach ridge record should be in-phase with the Cariaco Ti record (Haug et al., 2001). Although the Cariaco record indicates large centennial-scale variability in precipitation over northern South America (Fig. 4), this variability is not significantly correlated with the beach ridge record. The correlation improved slightly using an updated age–depth model for Cariaco (Fig. A9) but remains insignificant, probably as a consequence of uncertainties in the chronological control of both records or because of a more prominent influence of the North Atlantic climatic forcing mechanisms in the Maya lowlands.
Our records indicate that the Early Pre-Classic period in the CML was
relatively dry. During that period, the CML were still sparsely populated by
moving hunter-gatherers. It is highly likely that before maize became
sufficiently productive to sustain sedentism, the karstic lowlands were less
attractive for humans than the coastal wetlands along the Gulf of Mexico and
Pacific coast, where natural resources were abundantly present to
successfully sustain a hunting–gathering subsistence system (Inomata et al.,
2015). Reliance on cultivated crops, most notably maize, rapidly increased
after the onset of the Middle Pre-Classic period around 1000 BCE (Rosenswig
et al., 2015). Between 1000 and 850 BCE, under still dry conditions, there
is evidence for increased maize agriculture in the Pacific flood basin
(Rosenswig et al., 2015) and within the Olmec area on the Gulf of Mexico
coast (Arnold, 2009), and maize grains (AMS
For the first time a regional palaeo-precipitation record has been reconstructed for the central Maya lowlands (CML), based on an exceptionally well-dated high-resolution beach ridge record. This record indicates centennial-scale precipitation fluctuations during the Pre-Classic period that are not always registered in local records, adding valuable new insights into larger-scale climatic forcing mechanisms for the CML. The generally poor correlation between the regional and local palaeo-precipitation reconstructions are probably related to spatial precipitation variability and chronological uncertainties of many records. Additional research of beach ridge formation processes are needed to extend this regional precipitation reconstruction to the Classic and Post-Classic period.
We have also generated a local-scale palaeo-precipitation record using diatoms preserved in a core from Lake Tuspan, thereby adding an alternative proxy to the relatively high number of local reconstructions predominantly based on oxygen isotope variability. We recognise, however, that diatom preservation is often poor in the carbonate lakes across the wider region. As a result, the correlation between these two reconstructions is variable through time.
Although the occurrence of a prolonged drought during the end of the Early Pre-Classic period, which we report here, is evident in other palaeo-precipitation reconstructions from the CML, the subsequent wet period during the Middle Pre-Classic period, registered in both our new records, is less evident elsewhere. Although many researchers have focused on the impact of drought on the development and disintegration of Maya societies, one should consider this prolonged wet period as potentially unfavourable for the development and intensification of agriculture in the CML, particularly in the wetter areas. We cannot be certain about the impact of wetter conditions on the Maya. However, owing to the lack of development at this time, we theorise that the wet period could have created poor growing conditions for maize in the CML. In order to test this theory, we advocate the use of process-based modelling approaches which capture heterogeneous environmental constraints on crop growth for given climate boundary conditions, such as the approach applied by Dermody et al. (2014).
Our results provide evidence that North Atlantic atmospheric–oceanic forcing plays an important role in the modulation of the observed centennial-scale precipitation variability; however, further studies are required which compare well-dated terrestrial reconstructions that capture regional signals with solar and oceanic reconstructions to gain a better understanding of climate forcing mechanisms, both in the CML and across the wider region.
The relative beach ridge elevation record, spanning the Pre-Classic period, as well as the complete PC-1, amorphous silica, charred plant fragments and flood layer record of lake Tuspan core C (Fig. 4a), are available at the PANGAEA website (Nooren et al., 2018).
Location of proxy records indicated in Fig. A2 and/or mentioned in
the main text.
Age–distance model for beach ridge transect B. We refer to Nooren et al. (2017b) for further details.
Diatom record for lake Tuspan core C. Diatom concentrations (
Detailed diatom record around one of the larger flood events
Age–depth model for Tuspan core C. The age–depth model is based on
a linear interpolation between calibrated ages of radiocarbon-dated
terrestrial macro-remains from core A (Galop et al., 2004) and core C (Fleury
et al., 2014). The model is most reliable for ages between
Wavelet transform coherence (WTC) analysis between the beach ridge
record and the Macal Chasm
Mean annual discharge of the Usumacinta river at Boca del Cerro (Banco Nacional de Datos de Aguas Superficiales, 2017) compared with the total solar irradiance (TSI). The TSI is comprised of the reconstruction from 1700 to 2004 (Krivova et al., 2007), concatenated with observations from the Total Irradiance Monitor (TIM) on NASA's Solar Radiation and Climate Experiment (SORCE) from 2005 to 2011 (Kopp and Lean, 2011). In total, 4.56 W is added to the TIM measurements as previous reconstructions were calibrated against less accurate measuring equipment, compared with the TIM instrument, which led to an overestimation of TSI.
Updated age–depth model for Cariaco core 1002D. Original model
(Haug et al., 2001) has been based on a linear interpolation of calibrated
ages. We applied a fourth-order polynomial fit through modelled ages
calculated with a P_sequence model (Oxcal 4.2) (Bronk Ramsey, 2009, 2016):
The authors declare that they have no conflict of interest.
This research is supported by the Netherlands Organization for Scientific Research (NWO-grant 821.01.007). The lidar data were generously provided by INEGI, Mexico. We acknowledge Philippe Martinez, Jacques Giraudeau and Pierre Carbonel for the XRF core scan measurements, and we would like to thank Peter Douglas, Pete Akers and Gerald Haug for providing their data. We thank Konrad Hughen for valuable suggestions for updating the age–depth model for Cariaco's sediment core 1002D. We thank Ton Markus for improving the figures and Mark Brenner and an anonymous reviewer for their valuable comments for improving the paper. Edited by: Alessio Rovere Reviewed by: Mark Brenner and one anonymous referee