Search

Carbon isotopes (δ13Corg) in biomass, carbon (δ13Ccarb) and oxygen (δ18Ocarb) isotopes in authigenic calcite and estimations of chemical weathering of siliciclastic minerals (chemical index of alteration [CIA] and plagioclase index of alteration [PIA]) in lacustrine sediments of the ephemeral Babicora Basin, located within the core region of the North American Monsoon at northwest Mexico, helped to evaluate the source of biomass, variations in hydrological balance and sediment–water interactions during three different marine isotope stages (late MIS 4: ≥65.4–59.5 cal ka BP, MIS 3: ~59.5–28 cal ka BP and MIS 2: ~28–15 cal ka BP) of the last glacial. Comparisons of δ13Corg with previously published records of C/N, diatom abundance and fossil pollen indicate that biomass of the late MIS 4 was sourced from C3 aquatic and land plants. During the MIS 3, the C3 plants continued to contribute biomass and the influence of lacustrine algae, however, increased during its later part. The water column experienced more evaporation compared to two other MIS stages and sediment–water interactions varied between minimal to moderate (CIA: 49–68). Sediments were transported for longer distances during the wetter intervals and eroded from nearby lithologies during the drier intervals. Interactions between sediments and inflowing water (CIA: 59–65) remained homogeneous during the MIS 2. Source of the biomass, however, was variable. Lacustrine algae and C3 land plants contributed biomass during the early MIS 2 (~28–19 cal ka BP) and contributions from the C4 and CAM vegetation slightly increased towards the deglaciation (~19–15 cal ka BP). [ABSTRACT FROM AUTHOR]

Anthropogenic global warming might cause expansion of the drylands and trigger socio‐economic challenges in the water‐deficit subtropical regions. Changes in hydroclimate during the intervals of variable global temperature over the recent geological past, however, could provide useful information about the possible responses of these arid ecosystems to the near future warmer conditions. We evaluated hydroclimates of two different parts of subtropical North America by generating new records of surface processes and regional vegetation from drought‐prone northeast Mexico and subsequently compared them with the paleoclimate of the central‐southern United States. Our study suggests that congruent changes occurred in both parts during ~13.5–9.5 cal ka BP, an interval with no warm pool in the northern Gulf of Mexico. The precipitation and erosion responded to temperature‐modulated variations in positions of the Inter‐Tropical Convergence Zone (ITCZ). Conditions were wetter than today in the subsequent warmer interval (~9.5–8.2 cal ka BP) with generally stable ITCZ and the highest summer insolation. Hydroclimate changes of both parts lacked congruency during ~8.2–6.8 cal ka BP as the northern Gulf of Mexico began hosting a warm pool. Similar to the modern conditions, this warm pool might have modified trajectories of the tropical storms. Erosion and abundance of C3 plants decreased in northeast Mexico. Higher wetness in the Mississippi River Basin and the southern Great Plains during this interval suggested that the storms made landfall more frequently in the central‐southern United States. © 2019 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Sediments deposited in the Etzatlán-Magdalena Basin were analyzed to reconstruct the paleohydrological variations and generate a new Holocene paleoclimate record for the less studied western part of central Mexico. Concentration of Ti, abundance of CaCO 3 , Zr/Ti ratio and TOC/Ti ratio were compared with their average values to infer variations in runoff, lake water salinity, transportation of clastic minerals by aeolian activity and total organic productivity. In general, conditions were wetter during ~ 9.6–5.7 ka (early-middle Holocene) and ~ 2.2–0.7 ka (late Holocene) compared to ~ 5.7–2.2 ka (middle-late Holocene). Transportation of above-average amounts of Zr-bearing clastic minerals from an arid watershed and deposition of the highest abundance of CaCO 3 at ~ 3.5–2.8 ka occurred within the drier interval of middle-late Holocene. Except for the interval of ~ 2.2–0.7 ka, the El Niño Southern Oscillation (ENSO) and Inter Tropical Convergence Zone (ITCZ) controlled summer precipitation forced the hydrological variations. The Etzatlán-Magdalena Basin remained wet and some sites in central Mexico were dry over a large part of ~ 2.2–0.7 ka. The activity of tropical cyclones and frontal systems may have increased in the northeastern Pacific during this interval of enhanced ENSO. Either of them, or the combination of both, possibly contributed more autumn and winter precipitation to western-central Mexico. [ABSTRACT FROM AUTHOR]

ABSTRACT Chemical composition, magnetic susceptibility and texture of sediments in a swamp from the Los Petenes Biosphere Reserve provide information about late Holocene hydrological variations on the western margin of the Yucatan Peninsula, Mexico. Periods of lower than average amounts of K-bearing clastics during 2580-2050, 1100-825 and 700-160 cal a BP represent drought intervals. Magnetic minerals were better preserved during these arid intervals, as the swamp was not perennially anoxic. Hydroclimate was unstable during 2580-2050 cal a BP, as several storm-surge events occurred within an overall arid interval. The drought of 1100-825 cal a BP was contemporary with the Terminal Classic Period and the drought of 700-160 cal a BP was characterized by the lowest erosion as well as highest abundance of authigenic carbonate. Comparison with other climate proxy records from the region suggests that droughts had different geographic coverage. We attribute the different geographic coverage of droughts to variable strengths of polar continental air masses as well as dynamics of the Caribbean Low Level Jet and tropical cyclones that brought precipitation into different parts of the peninsula. [ABSTRACT FROM AUTHOR]

Hydrological response of the Chihuahua Desert of Mexico to six different Heinrich Stadials (H6 to H1) is inferred with element ratio, carbonate abundance, and oxygen and carbon isotope compositions of lacustrine calcite in sediments collected from the Santiaguillo Basin. Overall runoff and hence precipitation remained below average during H6, H4, H2 and H1, and above average during H5 and H3. Similarly, runoff of H4 showed the least variability and it was most variable during H5. In general, dissolved HCO 3 − was dominantly sourced from atmospheric CO 2 during the intervals of less runoff. However, lacustrine productivity as well as atmospheric CO 2 influenced carbon isotope composition of dissolved HCO 3 − during the regimes of fluctuating hydrological conditions. H2 was an interval of relatively warmer water column and enhanced lacustrine productivity. Comparison with other records indicates occurrence of similar millennial-scale hydrological variability in the southwest US. However, we did not always observe concurrency in proxy records from the Chihuahua Desert of Mexico and southwest US. Similarity in tendencies of runoff into the Santiaguillo Basin and δ 18 O of speleothem from the Hulu Cave during the six different Heinrich Stadials suggests a possible hemispheric link between hydroclimate of the Chihuahua Desert of Mexico and the East Asian Monsoon. [ABSTRACT FROM AUTHOR]

Thar Desert is a rainfall deficient (~500-100 mm/year) region in the northwestern India. Previously published information on sediment facies, mineralogy, and radiocarbon chronology helped to reconstruct orbital-scale lake stands and variations in water column salinity of five different lacustrine basins in the desert. We evaluated the hydrological conditions with respect to strength (i.e., amount and geographic coverage) of the southwest summer monsoon since the last glacial maximum (LGM). Between LGM and c.15 cal. ka BP, the eastern basins hosted saline and hypersaline playa lakes and the western part had an intermittent variable lake. A shift from saline-hypersaline playa lakes to perennial deep lakes occurred in the eastern margin at c.15 cal. ka BP as more summer insolation increased sea surface temperature (SST) of the Indian Ocean and strengthened the southwest summer monsoon. During the Pleistocene-Holocene transition, the highest summer insolation as well as warmer SST of the Indian Ocean increased the amount of summer precipitation and expanded the southwest monsoon over the entire desert. However, more winter precipitation and minimal summer rainfall maintained perennial lakes across the desert during the early and middle Holocene. Over the middle-late Holocene, the regional arid conditions were contemporary to intervals of reduced summer insolation, southerly located Inter-Tropical Convergence Zone and frequent El-Niño Southern Oscillation. [ABSTRACT FROM AUTHOR]

Proxy records generated from chemical composition and radiocarbon dating of a sediment sequence collected from the El Potosi Basin provide information about variable hydroclimate of the subtropical northeastern Mexico since the last glacial maximum (LGM). Minimal amounts of runoff and more carbonate deposition during >19 ka represent the LGM. The deglaciation was wetter compared to the LGM and enhanced runoff during ∼ 19 – 12 ka transported more Ti-bearing clastics from a relatively humid watershed. Over the deglaciation, the basin received more runoff during the Bølling-Allerød compared to the Heinrich Stadial 1 and Younger Dryas. Reduction in the amount of runoff during ∼ 10 – 1 ka and deposition of unweathered Si-bearing clastics during ∼ 4 – 1 ka suggest that the Holocene was drier compared to the deglaciation. Hydroclimates of the northeastern Mexico and southern US were synchronous during the LGM as well as deglaciation. Change from the drier LGM to wetter Bølling-Allerød occurred as the Gulf of Mexico became warmer and the region received more summer precipitation. However, the dissimilarities observed in regional hydroclimates of the Holocene need further evaluation. [ABSTRACT FROM AUTHOR]

Stratigraphy, geochemistry and radiocarbon dating of a succession of sediment in the Santiaguillo Basin (central-northern Mexico) help reconstruct the millennial-scale dynamics of hydrological variability that occurred in the southern part of western subtropical North America since the late last glacial. Runoff was generally above average during the late last glacial from ~ 27 to 18 ka. Following this interval, runoff decreased and deposition of authigenic carbonate and aeolian transported sediment increased until ~ 4 ka. Heinrich 1 and 2, and Younger Dryas were intervals of reduced runoff and increased aeolian activity. The wetter climate of central-northern Mexico and arid conditions in north–northwestern Mexico during the late last glacial were probably related to formation of tropical cyclones in the eastern North Pacific during the autumn with restricted rainfall swaths and an absent/weaker North American Monsoon. Enhanced North American Monsoon and tropical cyclones with expanded rainfall swaths brought more summer and autumn precipitation to a broader region extending from the central-northern Mexico to the continental interiors of southwestern US during the early Holocene. [ABSTRACT FROM AUTHOR]

We inferred millennial-scale climate variations and paleohydrological conditions in the northern sector of the American tropics for 30.3–5.5 cal ka BP using geochemical characteristics of sediments from Lake Chalco in central Mexico. The sediment sequence is chronologically constrained with three tephra and nine radiocarbon dates. Temporal variations in titanium, total inorganic carbon, total organic carbon/titanium ratio, carbon/nitrogen ratio, and silica/titanium ratio indicate changes in runoff, salinity, productivity, and sources. Higher concentrations of Ti indicate more runoff during latest Marine Isotope Stage (MIS) 3 (30.3–28.6 cal ka BP). Runoff was lower during the last glacial maximum (LGM; 23–19 cal ka BP) than during the Heinrich 2 event (26–24 cal ka BP). The interval of reduced runoff continued up to 17.5 cal ka BP but increased during the Bølling/Allerød. Trends of decreasing runoff and increasing salinity are observed throughout MIS 1. Lake Chalco received less runoff during the LGM compared to deglaciation, opposite the trend of other North American tropical records. Different amounts of rainfall at different sites are possibly due to shifts in the position of the Intertropical Convergence Zone, changes in the size of the Altlantic warm pool, and varying sea-surface temperatures of the Atlantic and Pacific oceans. [ABSTRACT FROM AUTHOR]

Late Holocene depositional environments of the Lake Coatetelco, with a volcaniclastic watershed, were evaluated with respect to cultural transitions in the nearby archeological site at Xochicalco in order to explore the relationship between hydroclimate and evolution of one of the important Mesoamerican cultures in central-southern Mexico. Several high-energy runoff events between ca. 2576 and 2232 cal yr BP (627–283 BCE) represented unstable watershed in an overall humid hydroclimate during the Pre-Classic Period. More silt and clay of ca. 1258–1006 cal yr BP (665–944 CE) were contemporary with flourishing of religious and political center on the Xochicalco Hills during the Epiclassic Period. Anthropogenic perturbations over this interval led to depositional hiatus and caused alterations in sediment composition and chronology. Deposition of authigenic calcite between ca. 1006 and 854 cal yr BP (944–1096 CE) suggested droughts over earlier part of the Post-Classic Period, and aeolian activity of this interval possibly transported fine sand into the lake. Our observation of dry conditions, coeval with abandonment at Xochicalco, contributes additional data during the demise of a vital pre-Columbian center in Mesoamerica. This arid hydroclimate occurred simultaneously as the ENSO became stronger, and the conditions improved post ca. 854 cal yr BP (>1096 CE) with an unstable paleohydrology during the latter part of the Post-Classic Period. • Late Holocene hydrological regimes of central-southern Mexico. • Comparison between depositional environments and Mesoamerican culture. • Anthropogenic perturbation during the Epiclassic. • Drought-like conditions during demise at the Xochicalco. [ABSTRACT FROM AUTHOR]

An evaporite enriched sediment archive from the dry Sandia Basin located in the water-stressed western foothills of the Sierra Madre Oriental Mountains (northeast Mexico) was studied to reconstruct depositional histories of vegetation and rainfall intensity in orbital to millennial-scales over the last ~32.5 cal ka. Surrounding vegetation had more C 3 plants during the late last glacial and deglaciation and the expansion of more drought tolerant C 4 plants occurred only after ~5 cal ka BP. Clastic minerals were sourced from different lithologies within the watershed and their abundances helped to infer runoff dynamics and hence the rainfall intensities. Deposition of more mixed-layer clay represented wetter intervals over the late last glacial and deglaciation. Transportation of clastics from the nearby lithology during these wetter intervals suggested that high-intensity rainfall events were less frequent. Response to the Heinrich stadials (H3, H2 and early H1) was mainly similar (drier) and erosion in the watershed remained less-than-average. Transportation of more quartz-rich sediments from distal lithologies during the late Bølling-Allerød (B/A) interstadial and between ~6.2 and 4 cal ka BP with a depositional hiatus between ~12.7 and 6.2 cal ka BP represented the intervals of more frequent high-intensity rainfall events, possibly related to short-lived storms. We hypothesize that the Gulf of Mexico sea surface temperature was a principal forcing. Total annual precipitation in this region decreased but the frequency of short-lived storms increased during the warmer Atlantic Multidecadal Oscillation (AMO) states. Warmer conditions also led to deposition of more gypsum. Our observation, however, needs further evaluation under the modern-day greenhouse warming scenario. • Late Quaternary vegetation and rainfall records from semi-arid north-east Mexico. • Forcing of Atlantic Multidecadal Oscillation state on high intensity precipitation events. • Less frequent high-intensity rainfall events during cooler late last glacial. • More frequent short-lived storms since the B/A interstadial. • Expansion of drought tolerant C 4 plants after 5,000 cal years BP. [ABSTRACT FROM AUTHOR]