Large closed-basin lakes sustainably supplied phosphate during the origins of life

American Association for the Advancement of Science (AAAS) | February 19th, 2025

The origin of life on Earth required a supply of phosphorus (P) for the synthesis of universal biomolecules. Closed lakes may have accumulated high P concentrations on ea

The origin of life on Earth required a supply of phosphorus (P) for the synthesis of universal biomolecules. Closed lakes may have accumulated high P concentrations on early Earth. However, it is not clear whether prebiotic P uptake in such settings would then have been sustainable. We show that large closed-basin lakes can combine high P concentrations at steady state with extremely high rates of biological productivity. Our case study is Mono Lake in California, which has close to 1 millimolar dissolved P at steady state despite extremely high rates of biological productivity, in contrast to smaller closed basins where life is scarce. Hence, large closed-basin lakes offer an environment where high rates of prebiotic P productivity can plausibly coexist with high steady-state P concentrations. Such lakes should have readily formed on the heavily cratered and volcanically active surface of early Earth.

Late Cenozoic Tectonism of the Sacramento Valley, California

U.S. Geological Survey (USGS) | July 15th, 1987

Late Holocene Lacustrine Chronology and Archaeology of Ancient Lake Cahuilla, California

Quaternary Research (Elsevier) | May 1st, 1983

Freshwater lakes existed intermittently in the Salton Trough of southern California during the late Holocene. The lakes formed north of the subaerial Colorado River Delta

Freshwater lakes existed intermittently in the Salton Trough of southern California during the late Holocene. The lakes formed north of the subaerial Colorado River Delta whenever the Colorado River flowed west into the trough instead of south to the Gulf of California. Water filled the trough to a maximum altitude of 12 m. Stratigraphy, radiocarbon dates, and supplementary evidence document four lacustral intervals of Lake Cahuilla between A.D. 700 and 1580. Archaeological sites are associated with the 12-m shoreline and their occupation correlates with these lacustral intervals.

Late Pleistocene exploration and settlement of the Americas by modern humans

American Association for the Advancement of Science (AAAS) | June 12th, 2019

North and South America were the last continents to be explored and settled by modern humans at the end of the Pleistocene. Genetic data, derived from contemporary popul

North and South America were the last continents to be explored and settled by modern humans at the end of the Pleistocene. Genetic data, derived from contemporary populations and ancient individuals, show that the first Americans originated from Asia and after several population splits moved south of the continental ice sheets that covered Canada sometime between ~17.5 and ~14.6 thousand years (ka) ago. Archaeological evidence shows that geographically dispersed populations lived successfully, using biface, blade, and osseous technologies, in multiple places in North and South America between ~15.5 and ~14 ka ago. Regional archaeological complexes emerged by at least ~13 ka ago in North America and ~12.9 ka ago in South America. Current genetic and archaeological data do not support an earlier (pre–17.5 ka ago) occupation of the Americas.

Levee Failures in the Sacramento-San Joaquin River Delta: Characteristics and Perspectives

Texas A&M University | December 15th, 2011

Between 1850 and 1922, agriculturalists built 1,700 kilometers of levees to convert 250,000 hectares of tidal marsh to farmland where the San Joaquin and Sacramento River

Between 1850 and 1922, agriculturalists built 1,700 kilometers of levees to convert 250,000 hectares of tidal marsh to farmland where the San Joaquin and Sacramento Rivers enter the San Francisco Bay (the Delta). Drained, farmed and isolated from the water channels, the organic soils behind the levees subsided to elevations as low as 8 meters below sea level, turning "levees" into "dams" that hold back water constantly. Engineers built water transfer projects in the mid-20th century, transferring water from the south Delta to 25 million Californians who now rely on the "dams" accidentally converted into supply channels. In 1972, however, a levee failure caused a salt-water intrusion into the Delta, raising the prominence of the polemic Peripheral Canal which, if built would replace the levees in the trans-Delta water transport role. Levee failures in 2004 (the Delta) and 2005 (New Orleans) have re-ignited the debate, fueled by comments made by public officials who warned that the Delta levees posed more risk of failure than did the pre-Katina Louisiana levees. This background motivates two research questions: What are the social perspectives regarding levee failures of the experts managing the Delta; and what is the history of levee failures that might support their perspectives? The research employed Q-Method to identify and describe four social perspectives: Delta Sustainers, Abandon the Levees, Levee Pragmatists, and Multi-Purpose Levee Advocates. A critical element underlying differences among the perspectives revolved around the perceived history of failures of Delta levees. This dissertation employed semi-structured interviews, archival record searches, and historic map and aerial photograph comparisons to compile a history of 265 levee failures since 1868, many of which are referenced to location, segment, and levee type. In addition, the dissertation compiled a list of emergency repairs and successful flood-fights. The history of failures indicates that important levees of the Delta have performed significantly better than previously identified. Sharing these social perspectives and research results among the key actors addressing Delta issues may lead to improved consensus decisions.

Little Ice Age flood events recorded in sag pond sediments in the Carrizo Plains National Monument, California

Nature Portfolio (Springer Nature) | March 8th, 2024

In California, severe precipitation events (SPEs) are often associated with winter season atmospheric rivers. These SPEs can generate hurricane-scale precipitation, creat

In California, severe precipitation events (SPEs) are often associated with winter season atmospheric rivers. These SPEs can generate hurricane-scale precipitation, creating a variety of natural hazards such as floods and landslides. For California, the most complete SPE-flood record yet generated is a 9000-year paleoflood reconstruction from the Santa Barbara Basin (Du et al. in Mar Geol 397:29–42, 2018). Finding terrestrial counterparts to compare to the Santa Barbara Basin is a challenge in Southern California where lake basins are rare and the terrestrial spatiotemporal signature of SPE floods remains largely unconstrained. Here, we present five 1–2 m sediment cores from a sag pond along the San Andreas Fault in the southern Carrizo Plain. The most complete record (core CLPC21-4) was selected for a variety of chronological, sedimentological, and biological analyses. Principal Component Analysis on these data reveals two end member sediment unit types: event versus ambient sedimentation. We focus on the two thickest sediment units likely generated by SPEs. These two units (EU 1 and EU 2) are especially distinct within CLPC21-4, characterized by erosive bases, above average sand content, normal grading, low magnetic susceptibility, and low total organic matter. Moreover, they are visually apparent across all five cores within the sag pond and thin from source to sink. Age control for the two units is constrained by AMS 14C dates on discrete organic materials and supported by the identification of Erodium’s first appearance ca. 1750–1765 CE in the Santa Barbara region. Using these age constraints, we infer the maximum limiting age range for Event Unit 1 from 1470 to 1640 CE and Event Unit 2 from 1740 to 1800 CE. Within the limits of dating, site-specific proxy sensitivities, and inherent meteorological heterogeneity, we propose a probable correlation to Santa Barbara Basin flood events at 1525 CE and 1760 CE. Our results suggest that sag ponds may represent a viable and untapped paleoclimatic archive for California. Future work will focus on a latitudinal series of sag ponds to determine the spatiotemporal sequence and correlativity of SPEs in the sediment record.

Megapluvials in Southwestern North America

American Geophysical Union (AGU) | March 25th, 2025

Droughts over the last century in Southwestern North America (SWNA) have had severe consequences for people and ecosystems across the region, most recently during the ear

Droughts over the last century in Southwestern North America (SWNA) have had severe consequences for people and ecosystems across the region, most recently during the early 21st-century megadrought (2000–2022). The 20thcentury, however, was bracketed by two extended pluvials that also had significant impacts in the region. We use a 1,224 years (800–2023 CE) record of observed and reconstructed soil moisture, in concert with a paleoclimate reanalysis product, to place the 20th-century pluvials in a longer-term context and investigate the occurrence and dynamics of similar events in the Common Era.

Memorialization and Memory of Southern California's St. Francis Dam Disaster of 1928

California State University, Northridge (CSUN) | August 1st, 2014

The commemoration of disasters is a product of social, cultural, economic, and  political forces in human society. Southern California's largely unheard-of St. Francis D

The commemoration of disasters is a product of social, cultural, economic, and  political forces in human society. Southern California's largely unheard-of St. Francis Dam Disaster of 1928 provides an excellent opportunity to study this complex process of commemoration, engaging memory within difference frames of reference. In particular, evaluating how and why this man-made dam disaster has been forgotten on a state and national level, but tenuously remembered within the flood-zone, allows for consideration of the diversity of commemorative processes in the construction of memory and heritage related to major catastrophes.

Mission Bay Historical Ecology Reconnaissance Study: Data Collection Summary (Technical Report)

San Francisco Estuary Institute (SFEI) | February 1st, 2016

The goals of the Mission Bay Historical Ecology Reconnaissance Study were to collect and compile high-priority historical data about the Mission Bay landscape, identify

The goals of the Mission Bay Historical Ecology Reconnaissance Study were to collect and compile high-priority historical data about the Mission Bay landscape, identify sources that could help to develop a deeper understanding of early ecological conditions, and to identify future possible research directions based on the available data. This technical memorandum is intended to document the archives consulted during the reconnaissance study, summarize the collected and compiled data, and to identify potential next steps. A separate technical presentation to project staff and advisors will summarize the preliminary findings and questions generated from a review of the historical dataset. Ultimately, this research is intended to support the San Diego Audubon Society’s Mission Bay Wetlands Conceptual Restoration Plan (CRP) and the ReWild Mission Bay project. Also on this topic: Mission Bay Historical Ecology Reconnaissance Study: Data CollectionSummary and Initial Findings (Presentation)

Natural Curiosities of California

Scientific American | April 12th, 1862