Papers by Valorie Aquino
The presence of a low-to mid-latitude interhemispheric hydrologic seesaw is apparent over orbital... more The presence of a low-to mid-latitude interhemispheric hydrologic seesaw is apparent over orbital and glacial-interglacial timescales, but its existence over the most recent past remains unclear. Here we investigate, based on climate proxy reconstructions from both hemispheres, the inter-hemispherical phasing of the Intertropical Convergence Zone (ITCZ) and the low-to mid-latitude teleconnections in the Northern Hemisphere over the past 2000 years. A clear feature is a persistent southward shift of the ITCZ during the Little Ice Age until the beginning of the 19th Century. Strong covariation between our new composite ITCZ-stack and North Atlantic Oscillation (NAO) records reveals a tight coupling between these two synoptic weather and climate phenomena over decadal-to-centennial timescales. This relationship becomes most apparent when comparing two precisely dated, high-resolution paleorainfall records from Belize and Scotland, indicating that the low-to mid-latitude teleconnection was also active over annual-decadal timescales. It is likely a combination of external forcing, i.e., solar and volcanic, and internal feedbacks, that drives the synchronous ITCZ and NAO shifts via energy flux perturbations in the tropics. Hemispheric antiphasing of large-scale precipitation patterns in low-and mid-latitude regions, driven by the seasonal migration of the Intertropical Convergence Zone (ITCZ), has been described over orbital timescales, Dansgaard-Oeschger (DO), and Heinrich events 1–3. As part of the upward limb of the Hadley Cells, the ITCZ plays a crucial role in global energy redistribution. Temperature-driven meridional displacement of the tropical Hadley Cells and the ITCZ 4,5 induced synchronous shifts in higher latitude climate patterns 1 on millennial timescales. High signal-to-noise ratios of millennial-scale climate shifts during glacial periods, largely due to different boundary conditions related to the presence of extensive continental ice sheets, facilitate their detection in proxy records. Although this atmospheric reorganization has been described over glacial-interglacial timescales, the dynamics and latitudinal extent of this interhemispheric hydrologic seesaw 1 over the most recent past are still poorly understood. Additionally, chronological uncertainties, although less significant than in Pleistocene reconstructions , and low signal-to-noise ratios in Holocene paleoclimate records can hinder interpretations of rapid climate change, and this is particularly true over the last few millennia. Here we investigate the latitudinal extent of the hydrologic seesaw in the Northern Hemisphere (NH) over the past two millennia by comparing precisely dated, high-resolution paleo-rainfall records from low-and
Accurately predicting future tropical cyclone risk requires understanding the fundamental control... more Accurately predicting future tropical cyclone risk requires understanding the fundamental controls on tropical cyclone dynamics. Here we present an annually-resolved 450-year reconstruction of western Caribbean tropical cyclone activity developed using a new coupled carbon and oxygen isotope ratio technique in an exceptionally well-dated stalagmite from Belize. Western Caribbean tropical cyclone activity peaked at 1650 A.D., coincident with maximum Little Ice Age cooling, and decreased gradually until the end of the record in 1983. Considered with other reconstructions, the new record suggests that the mean track of Cape Verde tropical cyclones shifted gradually north-eastward from the western Caribbean toward the North American east coast over the last 450 years. Since ~1870 A.D., these shifts were largely driven by anthropogenic greenhouse gas and sulphate aerosol emissions. Our results strongly suggest that future emission scenarios will result in more frequent tropical cyclone impacts on the financial and population centres of the northeastern United States. Observational and modelling studies suggest that the recent multidecadal trend of rising sea surface temperatures (SST) in the North Atlantic's Main Development Region (MDR) may have increased Atlantic tropical cyclone (TC) intensity and duration 1–3 , and shifted storm tracks poleward 4,5. Some studies ascribe this oceanic warming to a multi-decadal SST periodicity known as the Atlantic Multidecadal Oscillation (AMO) 6,7 associated with the strength of thermohaline circulation 7,8 or large-scale atmospheric circulation 9,10 , while others implicate rising anthropogenic greenhouse gases (GHGs) 11,12. Deconvolving these effects is critical for predicting how GHG-induced 21 st Century warming may impact future TC activity 13 , however the observational record's brevity complicates assessing the relative influence of natural versus anthropogenic climate forcings on past North Atlantic TC activity. Additionally, multi-model ensemble studies predict that overall TC frequency will decrease through the 21 st Century while the frequency and intensity of the largest storms will increase 14. Although global TC activity and strength predictions are reasonably well constrained, projections for individual basins have considerably more uncertainty 15. Consequently, understanding the drivers of TC strength, frequency, and track for individual basins is critical. Well-dated, high resolution proxy records of total TC activity (including weaker tropical storms) from multiple individual locations are required 16 to identify and characterise long-term trends
Climate of the Past, 2012
Reliable age models are fundamental for any palaeoclimate reconstruction. Available interpolation... more Reliable age models are fundamental for any palaeoclimate reconstruction. Available interpolation procedures between age control points are often inadequately reported, and very few translate age uncertainties to proxy uncertainties. Most available modeling algorithms do not allow incorporation of layer counted intervals to improve the confidence limits of the age model in question.
Speleothem Paleoclimatic Reconstruction in Southern Belize
The goal of the speleothem (stalagmite) paleoclimate component of this project is to generate a p... more The goal of the speleothem (stalagmite) paleoclimate component of this project is to generate a precisely dated decadally resolved precipitation record for southern Belize for much of the late Holocene (~ 3500 to present). During the past year we have been forced to reconfigure the research team working on this part of the project because Dr. Kevin Cannariato has left the University of Southern California (USC) and is taking a leave from active research. He may not return. Dr. Douglas Kennett from the University of Oregon is ...
Nature Geoscience, Feb 9, 2015
The position of the intertropical convergence zone is an important control on the distribution of... more The position of the intertropical convergence zone is an important control on the distribution of low-latitude precipitation. Its position is largely controlled by hemisphere temperature contrasts1, 2. The release of aerosols by human activities may have resulted in a southward shift of the intertropical convergence zone since the early 1900s (refs 1, 3, 4, 5, 6) by muting the warming of the Northern Hemisphere relative to the Southern Hemisphere over this interval1, 7, 8, but this proposed shift remains equivocal. Here we reconstruct monthly rainfall over Belize for the past 456 years from variations in the carbon isotope composition of a well-dated, monthly resolved speleothem. We identify an unprecedented drying trend since AD 1850 that indicates a southward displacement of the intertropical convergence zone. This drying coincides with increasing aerosol emissions in the Northern Hemisphere and also marks a breakdown in the relationship between Northern Hemisphere temperatures and the position of the intertropical convergence zone observed earlier in the record. We also identify nine short-lived drying events since AD 1550 each following a large volcanic eruption in the Northern Hemisphere. We conclude that anthropogenic aerosol emissions have led to a reduction of rainfall in the northern tropics during the twentieth century, and suggest that geographic changes in aerosol emissions should be considered when assessing potential future rainfall shifts in the tropics.
Research Reports in Belizean Archaeology Vol. 10, 2013
Mexico traveled to the School of Advanced Research (SAR) and the Indian Arts Research Center to t... more Mexico traveled to the School of Advanced Research (SAR) and the Indian Arts Research Center to test a number of ethnographic materials for the presence of toxins using Portable Energy Dispersive X-Ray fluorescence (XRF). XRF operates through the emission of characteristic "secondary" (or fluorescent) X-rays from a material that has been excited by bombarding it with high-energy X-rays or gamma rays that are mechanically generated by a rhodium (Rh) tube. The technique is widely used for elemental and chemical analysis and is considered an excellent means to detect non-organic compounds commonly used to treat ethnographic materials. Portable XRF is a handheld device that can be easily transported to collections. It rapidly determines if the objects contain toxic metals. The process is entirely non-destructive to the artifacts tested. The instrument used was a Bruker AXS Tracer 3-V Analyzer.
Conference Presentations by Valorie Aquino
Aquino would like to thank Brendan Culleton and Chris Jazwa (University of Oregon) for their pati... more Aquino would like to thank Brendan Culleton and Chris Jazwa (University of Oregon) for their patient training on carbon chemical preparation and the software program OxCal, as well as the Mopan Maya who assisted greatly with field excavations. Additional thanks to Jacob Bartruff, Ethan Kalosky, and Claire Ebert for producing maps. This work was generously funded by the Alphawood Foundation.
Highly integrated socioeconomic and political systems marked by administrative hierarchies and ru... more Highly integrated socioeconomic and political systems marked by administrative hierarchies and rulers developed in multiple locations around the world during the last 8000 years. The process was episodic and marked by frequent economic failure and political disintegration, in some instances in the context of abrupt climate change. The dynamic socioecological processes guiding economic and political evolution are multivariate and poorly understood. Analysis requires a computational modeling approach, guided by appropriate theory, paleoenvironmental, archaeological and ethnographic research for ground truthing, and testing. Our primary objective is to model dynamic human behavioral responses to environmental transformation, abrupt or gradual, linking these processes to patterns of settlement, resource exploitation, agricultural intensification, competition, and polity stability. To accomplish this we apply a theoretical framework drawn from behavioral ecology that integrates key variables: population density and distribution, environmental suitability as a function of economic intensification and endogenous environmental change, and political exploitation. A secondary goal is to test this model at Uxbenká, a Maya polity that formed in southern Belize between 4000-1500 BP. Archaeological work in the region suggests that increasingly integrated socioeconomic systems formed in the context of demographic expansion, political fissioning, agricultural intensification, and environmental degradation. The available paleoclimatic data also suggest that an abrupt decrease in rainfall played a role in the disintegration of certain polities between 2100-1800 BP that was followed by the reintegration and proliferation of higher order socioeconomic systems after 1800 BP. Many of these systems collapsed completely at 1000 BP, again within the context of abrupt climate change. Extant data from a century of research in this region, complemented with strategic paleoenvironmental, archaeological, and ethnographic work in southern Belize, will guide our statistical evaluation of functional relationships, choice of model parameters and help test model outcomes. In this poster we update our progress after a year of inter-disciplinary collaborative research.
We thank Stewart Bishop and the sta of the Laboratory of Ion Physics for help in the lab. We ackn... more We thank Stewart Bishop and the sta of the Laboratory of Ion Physics for help in the lab. We acknowledge nancial support from the ERC grant "Hurricane".
Chan Chich Reports by Valorie Aquino
Journal Articles by Valorie Aquino
In 2016, the Chan Chich Archaeological Project (CCAP) and Belize Estates Archaeological Survey Te... more In 2016, the Chan Chich Archaeological Project (CCAP) and Belize Estates Archaeological Survey Team (BEAST) pursued multiple research agendas within the 144,000-acre permit area in Northwestern Belize. At Chan Chich, excavations in the Upper Plaza began a 3-year initiative to build a high-resolution chronology of the plaza's and associated structures' construction history. This multi-season effort will investigate the relationship between divine kingship and the architectural evolution of the Upper Plaza. Additionally, CCAP renewed excavations at Norman's Temple complex, a hilltop group west of the Main Plaza, documenting ancient Maya graffiti and discovering a dense terminal artifact deposit. Under the auspices of BEAST, a drone survey mapped cleared pasturelands of Gallon Jug and a large lagoon know as Laguna Seca, and the project completed its second and final season of investigations at Kaxil Uinic, an historic period San Pedro Maya village. This paper summarizes the results of the 2016 investigations.
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Papers by Valorie Aquino
Conference Presentations by Valorie Aquino
Chan Chich Reports by Valorie Aquino
Journal Articles by Valorie Aquino