Juan Pablo Bernal

A 2400 yr Mesoamerican rainfall reconstruction links climate and cultural change

Droughts are a recurring feature of Mexican climate, but few high-resolution data are available to test for climate-change forcing of Mesoamerican civilizations. We present a quantitative 2400 yr rainfall reconstruction for the Basin of Mexico, from a precisely dated and highly resolved speleothem, that documents highly variable rainfall over the past 2400 yr. Dry conditions peaked during a 150-yr-long late Classic (ca. 600–900 CE) (Common Era) mega drought that culminated at 770 CE which followed centuries of climatic drying that spanned the fall of the city of Teotihuacan ca. 550 CE. The wettest conditions in the 1450s CE were associated with fl ooding in the Basin of Mexico. Our data suggest that rainfall variability was likely forced by the El Nino–Southern Oscillation, and impacts on spring-fed irrigation agriculture may have been a stressor on Mesoamerican civilizations.

Timing and structure of Mega‐SACZ events during Heinrich Stadial 1

A substantial strengthening of the South American monsoon system (SAMS) during Heinrich Stadials (HS) points toward decreased cross-equatorial heat transport as the main driver of monsoonal hydroclimate variability at millennial time scales. In order to better constrain the exact timing and internal structure of HS1 over tropical South America, we assessed two precisely dated speleothem records from central-eastern and northeastern Brazil in combination with two marine records of terrestrial organic and inorganic matter input into the western equatorial Atlantic. During HS1, we recognize at least two events of widespread intensification of the SAMS across the entire region influenced by the South Atlantic Convergence Zone (SACZ) at 16.11–14.69 kyr B.P. and 18.1–16.66 kyr B.P. (labeled as HS1a and HS1c, respectively), separated by a dry excursion from 16.66 to 16.11 kyr B.P. (HS1b). In view of the spatial structure of precipitation anomalies, the widespread increase of monsoon precipitation over the SACZ domain was termed “Mega-SACZ.”

Orbital pacing and ocean circulation-induced collapses of the Mesoamerican monsoon over the past 22,000 y

The dominant controls on global paleomonsoon strength include summer insolation driven by precession cycles, ocean circulation through its influence on atmospheric circulation, and sea-surface temperatures. However, few records from the summer North American Monsoon system are available to test for a synchronous response with other global monsoons to shared forcings. In particular, the monsoon response to widespread atmospheric reorganizations associated with disruptions of the Atlantic Meridional Overturning Circulation (AMOC) during the deglacial period remains unconstrained. Here, we present a high-resolution and radiometrically dated monsoon rainfall reconstruction over the past 22,000 y from speleothems of tropical southwestern Mexico. The data document an active Last Glacial Maximum (18–24 cal ka B.P.) monsoon with similar δ18O values to the modern, and that the monsoon collapsed during periods of weakened AMOC during Heinrich stadial 1 (ca. 17 ka) and the Younger Dryas (12.9–11.5 ka). The Holocene was marked by a trend to a weaker monsoon that was paced by orbital insolation. We conclude that the Mesoamerican monsoon responded in concert with other global monsoon regions, and that monsoon strength was driven by variations in the strength and latitudinal position of the Intertropical Convergence Zone, which was forced by AMOC variations in the North Atlantic Ocean. The surprising observation of an active Last Glacial Maximum monsoon is attributed to an active but shallow AMOC and proximity to the Intertropical Convergence Zone. The emergence of agriculture in southwestern Mexico was likely only possible after monsoon strengthening in the Early Holocene at ca. 11 ka.

Stratigraphy, geochronology, and geochemistry of the Laramide magmatic arc in north-central Sonora, Mexico

The Laramide magmatic arc in the Arizpe-Mazocahui quadrangle of north-central Sonora, Mexico, is composed of volcanic rocks assigned to the Tarahumara Formation and several granitic plutons that intrude it. The arc was built over juxtaposed crustal basements of the Caborca and Mazatzal provinces. A basal conglomerate of the >4-km-thick Tarahumara Formation overlies deformed Proterozoic igneous rocks and Neoproterozoic to Early Cretaceous strata, thus constraining the age of a contractional tectonic event that occurred between Cenomanian and early Campanian time. The lower part of the Tarahumara Formation is composed of rhyolitic ignimbrite and ash-fall tuffs, andesite flows, and interbedded volcaniclastic strata, and its upper part consists of rhyolitic to dacitic ignimbrites, ash-fall tuffs, and volcaniclastic rocks. The Tarahumara Formation shows marked lateral facies change within the study area, and further to the north it grades into the coeval fluvial and lacustrine Cabullona Group. The age of the Tarahumara Formation is between ca. 79 and 59 Ma; the monzonitic to granitic plutons have ages of ca. 71–50 Ma. The informally named El Babizo and Huepac granites, La Aurora and La Alamedita tonalities, and the Puerta del Sol granodiorite compose the El Jaralito batholith in the southern part of the area. Major and trace element composition of the Laramide igneous rocks shows calc-alkaline differentiation trends typical of continental magmatic arcs, and the isotope geochemistry indicates strong contribution from a mature continental crust. Initial 87Sr/86Sr values range from 0.70589 to 0.71369, and eNd values range from –6.2 to –13.6, except for the El Gueriguito quartz monzonite value, –0.5. The Nd, Sr, and Pb isotopic values of the studied Laramide rocks permit comparison with the previously defined Laramide isotopic provinces of Sonora and Arizona. The El Gueriguito pluton and Bella Esperanza granodiorite in the northeastern part of the study area along with plutons and mineralization of neighboring northern Sonora have isotopic values that correspond with those of the southeastern Arizona province formed over the Mazatzal basement ([Lang and Titley, 1998][1]; [Bouse et al., 1999][2]). Isotopic values of the other Laramide rocks throughout the study area are similar to values of provinces A and B of Sonora ([Housh and McDowell, 2005][3]) and to those of the Laramide Pb boundary zone of western Arizona, while the Rancho Vaqueria and La Cubana plutons in the northernmost part of the area have the isotopic composition of the Proterozoic Mojave province of the southwestern United States. These data permit us to infer that a covered crustal boundary, between the Caborca block with a basement of the Mojave or boundary zone and the Mazatzal province, crosses through the northeastern part of the area. The boundary may be placed between outcrops of the El Gueriguito and Rancho Vaqueria plutons, probably following a reactivated Cretaceous thrust fault located north of the hypothesized Mojave-Sonora megashear, proposed to cross through the central part of the area. [1]: #ref-53 [2]: #ref-13 [3]: #ref-50

Pharmacokinetics and hematotoxicity of a novel copper-based anticancer agent: casiopeina III-Ea, after a single intravenous dose in rats.

Casiopeina III‐Ea is a mixed chelate copper (II) complex that has shown cytotoxic and antitumor activity in vitro and in vivo. The aim of this study was to investigate the pharmacokinetics of total copper derived from casiopeina III‐Ea administered by intravenous bolus injection to Wistar rats. Other objective was to evaluate the hematotoxicity produced by this compound in those animals. Wistar rats received a single intravenous dose of 4 mg/kg of casiopeina III‐Ea. Blood samples were taken and pharmacokinetics evaluated. Furthermore, erythrocyte copper levels were determined to identify a potential target and Zn levels were analyzed to determine a possible change. For the evaluation of hematotoxicity, both blood and urine samples were collected for hematological and biochemical analyses; moreover, Fe determination was performed. Blood copper and zinc levels, red blood cell copper levels as well as copper, zinc, and iron amounts excreted into urine were analyzed by ICP‐MS. The blood concentration–time profile of copper derived from casiopeina III‐Ea was fitted to a two‐compartment model with a zero‐order input. Cumulative amounts of Cu, Zn, and Fe excreted into rat urine after administration of casiopeina III‐Ea were different with respect to control. Hematological and biochemical data indicated a hemolytic toxicity. Pharmacokinetic analysis of total copper derived from casiopeina III‐Ea provided a general knowledge about distribution and elimination process of this compound. Additionally, the systemic exposure of the copper derived from casiopeina III‐Ea accounts for the hematotoxicity of this complex at test dose.

Assessment of sample preparation methods for the analysis of trace elements in airborne particulate matter

The determination of trace element composition of airborne particles usually requires dissolution in acidic media followed by Inductively Coupled Plasma Mass Spectrometry (ICP-MS) analysis. Analytical methods are usually validated on NIST SRM 1648 and 1648a, but without any further discussion regarding their application to real atmospheric samples. Here, we present an assessment of 5 digestion methods (over a hot plate and using a microwave system) for SRM 1648a and atmospheric particles based on the analysis of 30 elements by ICP-MS. Recoveries of NIST-certified elements for SRM 1648a confirm that a digestion method using HNO3–HF on a hot-plate yields acceptable recoveries for most of the NIST-certified elements (with the exception of Cr). By conducting the elemental analysis in triplicate samples of particles collected on PTFE filters, we determined that the analytical method is reproducible within 9% for real PM samples. Heterogeneity of the reference material and atmospheric samples, as well as differences in chemical composition and particle size between both, suggests that uncertainties related to the dissolution of trace elements using acidic mixtures are not well characterized.

Direct analysis of lanthanides by ICPMS in calcium-rich water samples using a modular high-efficiency sample introduction system–membrane desolvator

Lanthanoids (also known as rare-earth elements – REE) are well-known tracers of water–rock interaction processes due to their behavior being coherent with their atomic radii, and the capability of Ce and Eu to reflect redox conditions. However, analysis of REE in natural waters is hampered by their relatively low concentration (sub-pg g−1), and the concentration of dissolved solids ranging in the hundreds of μg g−1, imposing important matrix effects to the analysis. Because of this, different analytical techniques have been developed to analyze them by Q-ICPMS and SF-ICPMS, which usually involve matrix removal and analyte pre-concentration. Analysis of REE in karstic waters, those naturally saturated in CaCO3, presents an additional challenge due to the presence of high Ba concentrations (several ng g−1) which can bias the analysis due to the formation of BaO+ and BaOH+ ions during ionization, interfering with the mass range of 148–155 m/z+, including both Eu isotopes, and significantly hampering the direct analysis of such samples. Here, using a modular high-efficiency sample introduction system and desolvator we eliminate the formation of BaO+, and significantly reduce BaOH+, allowing us to analyze small samples (1–2 ml) with Ba/Eu ratios as high as 8 × 104 (mol/mol), and up to 600 μg g−1 of Ca, without any sample pretreatment. Our methodology was validated by analyzing VIDAC18 and SERMIN1 reference materials, and permits the quantification of all REE with detection limits ranging between 500 and 30 fg g−1 and with RSD ∼ 10% for 1 pg g−1, controlled by counting statistics.

Retrograde Accretion of a Caribbean Fringing Reef Controlled by Hurricanes and Sea-level Rise

Predicting the impact of sea-level (SL) rise on coral reefs requires reliable models of reef accretion. Most assume that accretion results from vertical growth of coralgal framework, but recent studies show that reefs exposed to hurricanes consist of layers of coral gravel rather than in-place corals. New models are therefore needed to account for hurricane impact on reef accretion over geological timescales. To investigate this geological impact, we report the configuration and development of a 4-km-long fringing reef at Punta Maroma along the northeast Yucatan Peninsula. Satellite-derived bathymetry shows the crest is set-back a uniform distance of 315 ±15 m from a mid-shelf slope break, and the reef-front decreases 50% in width and depth along its length. A 12-core drill transect constrained by multiple 230Th ages shows the reef is composed of an ~ 2-m thick layer of coral clasts that has retrograded 100 m over its back-reef during the last 5.5 ka. These findings are consistent with a hurricane-control model of reef development where large waves trip and break over the mid-shelf slope break, triggering rapid energy dissipation and thus limiting how far upslope individual waves can fragment corals and redistribute clasts. As SL rises and water depth increases, energy dissipation during wave-breaking is reduced, extending the clast-transport limit, thus leading to reef retrogradation. This hurricane model may be applicable to a large sub-set of fringing reefs in the tropical Western-Atlantic necessitating a reappraisal of their accretion rates and response to future SL rise.

Timing of speleogenesis of Las Karmidas Cave (Mexico): first description of pseudokarst developed in ignimbrite

*jpbernal@unam.mx Citation: