Pollen and non‐pollen palynomorphs of Lake Chalco as indicators of paleolimnological changes in high‐elevation tropical central Mexico since MIS 5

High‐quality records of hydroclimate variability in central Mexico during the last 2000 years are necessary to better understand human–environment interactions in Mesoamerica. Of particular interest are the climatic conditions during the Epiclassic period (ad 600–900), as droughts have been associated with a cultural demise occurring around ad 900–1000. We reconstruct the hydroclimate history of the last 2000 years based on a sediment record from a drought‐sensitive lake located near one of the most important Epiclassic city‐states in Mesoamerica. Titanium concentrations, pollen and diatoms give a consistent environmental signal of five droughts occurring at about: (i) ad 50–250, (ii) ad 700–950, (iii) ad 1200–1300, (iv) ad 1450–1550 and (v) ad 1760–1820. Some droughts were associated with cooler climatic conditions, and all of them framed major historical events. Our results show that the great cultural development of the Epiclassic period ( ad 600–900) was framed by a scenario of drought conditions followed by abandonment at ad 900–1000. A brief return to moister conditions is recorded before another drought during the time of the fall of the city‐state of Tula (1200). European contact (1521) and the War of Independence (1810–20) also occurred during times of drought.

Section: Resultsmentioning

confidence: 99%

Droughts during the last 2000 years in a tropical sub‐humid environment in central Mexico

Caballero-Miranda

Lozano‐García

Romero

et al. 2023

“…Moreover, an increasing abundance of the algae Botryococcus could be indicative of increasingly alkaline conditions. Palynological Zone C, included in sub‐zone 3.1, is also characterised by increasing concentrations of the unknown spherical non‐pollen palynomorph referred to as ‘Type‐TXA’, which has been associated with alkaline–highly alkaline (pH 9–10) and hyposaline (TDS 3–20 g/L) lake water conditions (Torres‐Rodríguez et al ., 2018). The total ostracod abundance increased to 735 valves/g, the highest total abundance in our record.…”

Section: Discussionmentioning

confidence: 99%

Late Pleistocene and Holocene palaeoecological reconstruction of Lake Texcoco (Basin of Mexico) based on its ostracod record

Chávez-Lara

Lozano‐García

Ortega‐Guerrero

et al. 2022

We present a palaeohydrological reconstruction of Lake Texcoco over the last 32.7 cal ka based on ostracod records consisting of two species, Candona patzcuaro and Limnocytherina axalapasco. Overall, the presence of these species suggests that Lake Texcoco was highly saline and experienced occasional desiccation periods. Moreover, this work helps improve our knowledge of L. axalapasco, an endemic species of central Mexico; their eggs could remain dormant‐resting to survive long dry periods. Four ostracod zones reflect the main environmental changes that occurred during the Late Pleistocene and Holocene. From 32.7 to 30 cal ka bp (Zone 4), Lake Texcoco's water levels were stable and alkaline with saline conditions. Zone 3, representing the period from 30 to 18 cal ka bp, includes a period of enhanced precipitation (greatest abundance of C. patzcuaro) from 30 to 26 cal ka bp. From 26 to 18 cal ka bp, an abundance of L. axalapasco reflects shallower and more saline conditions. The Last Glacial Maximum was characterised by cold and humid conditions with enhanced runoff, especially at 25.3, 21.9, and 20.7 cal ka bp. Zone 2 (18–7 cal ka bp) represents the driest period on record. Finally, shallow and saline lake conditions have prevailed over the last 7 cal ka (Zone 1).

“…Several sediment sequences from ancient Lake Chalco have been collected near the depocenter of the lake. In this paper, we present the detailed diatom record of the CHA08 sequence from 17.5 to 122.4 m. Note, however, that in previous works the CHA08 sequence was integrated with the CHA11‐VII core, which covers the uppermost 18 m to produce a master sequence from which facies analysis, geochemical, magnetic mineralogy, summary diatom groups and charcoal records have been published previously (Torres‐Rodríguez et al 2015, 2018, 2022, Ortega‐Guerrero et al 2017, 2020, Martínez‐Abarca et al 2021a). In this work, nevertheless, we present the CHA08 sequence and the previously published diatom data from the 26‐m‐long Cha‐B core (Caballero & Ortega‐Guerrero 1998, Caballero et al 2019).…”

Section: Methodsmentioning

confidence: 96%

Response of diatom assemblages to orbital‐ and millennial‐scale climatic variability since the penultimate glacial maximum in the northern limit of the Neotropics

Avendaño

Caballero-Miranda

Ortega‐Guerrero

et al. 2023

Lake Chalco, in Central Mexico, has a long diatom record which provides an excellent opportunity to document the biotic and hydrological responses of this ecosystem to orbital‐ and millennial‐scale climatic variability during the last 150 ka. Detrended correspondence analysis was used to evaluate the ecological turnover and to identify diatom species associations throughout the sequence. Millennial‐scale climatic fluctuations were identified as peaks in freshwater (mostly small Fragilariaceae spp.) or as peaks in salt‐tolerant species. At orbital scales, species turnover involved changes between freshwater assemblages dominated by Stephanodiscus spp. – small Fragilariaceae spp. – Cocconeis placentula, present during low‐evaporation, cool intervals [late Marine Isotope Stage (MIS)6, MIS5d, MIS2] against salt‐tolerant taxa, dominated by Stephanocyclus and Cyclotella spp., in higher evaporation, higher salinity conditions (MIS5e, MIS5c–a, MIS4, MIS3, early MIS1). Comparatively, MIS6 and MIS5d seem to have been cooler (~ −6 to −7 °C) and wetter than MIS2 (~ − 4 to −5 °C). In contrast, MIS5e and early MIS1 (11.5–6 ka) had similar warmer, low lake level, saline conditions. In addition, MIS5 was a period of intense climatic change associated with wide‐amplitude orbital forcing that favored a Stephanocyclus–Cyclotella spp. ecological succession (S. meneghinianus, C. tlalocii, C. poyeka, S. quillensis). In contrast, smaller temperature changes were inferred during MIS4 and MIS3.