Coupled social and ecological change drove the historical extinction of the California grizzly bear ().

Large carnivores (order Carnivora) are among the world's most threatened mammals due to a confluence of ecological and social forces that have unfolded over centuries. Combining specimens from natural history collections with documents from archival records, we reconstructed the factors surrounding the extinction of the California grizzly bear (), a once-abundant brown bear subspecies last seen in 1924. Historical documents portrayed California grizzlies as massive hypercarnivores that endangered public safety.

Pre-Younger Dryas megafaunal extirpation at Rancho La Brea linked to fire-driven state shift.

The cause, or causes, of the Pleistocene megafaunal extinctions have been difficult to establish, in part because poor spatiotemporal resolution in the fossil record hinders alignment of species disappearances with archeological and environmental data. We obtained 172 new radiocarbon dates on megafauna from Rancho La Brea in California spanning 15.6 to 10.

Global reorganization of deep-sea circulation and carbon storage after the last ice age.

Using new and published marine fossil radiocarbon (C/C) measurements, a tracer uniquely sensitive to circulation and air-sea gas exchange, we establish several benchmarks for Atlantic, Southern, and Pacific deep-sea circulation and ventilation since the last ice age. We find the most C-depleted water in glacial Pacific bottom depths, rather than the mid-depths as they are today, which is best explained by a slowdown in glacial deep-sea overturning in addition to a "flipped" glacial Pacific overturning configuration. These observations cannot be produced by changes in air-sea gas exchange alone, and they underscore the major role for changes in the overturning circulation for glacial deep-sea carbon storage in the vast Pacific abyss and the concomitant drawdown of atmospheric CO.

14-Carbon demonstrates that some illegal ivory is being taken from government stockpiles.

The 14-carbon in animal tissues records the time that the tissues are formed; since the 1960s, using the "bomb curve" for C, the age of animal death can be determined accurately. Using animal tissue samples of known collection and formation dates for calibration, we determine the age of ivory samples from four ivory seizures made by law enforcement agencies between 2017 and 2019. The C measurements from these seizures show that most ivory in the illegal wildlife trade is from animals from recent poaching activities.

Response to comment on "Evidence of prehistoric human activity in the Falkland Islands".

Hamley . previously presented multiple lines of evidence that people were present in the Falkland Islands before Europeans and may have brought the now-extinct canid, . Stable isotope data reported by Clark .

Genomic basis for skin phenotype and cold adaptation in the extinct Steller's sea cow.

Steller's sea cow, an extinct sirenian and one of the largest Quaternary mammals, was described by Georg Steller in 1741 and eradicated by humans within 27 years. Here, we complement Steller's descriptions with paleogenomic data from 12 individuals. We identified convergent evolution between Steller's sea cow and cetaceans but not extant sirenians, suggesting a role of several genes in adaptation to cold aquatic (or marine) environments.

Evidence of prehistoric human activity in the Falkland Islands.

When Darwin visited the Falkland Islands in 1833, he noted the puzzling occurrence of the islands’ sole terrestrial mammal, (or “warrah”). The warrah’s origins have been debated, and prehistoric human transport was previously rejected because of a lack of evidence of pre-European human activity in the Falkland Islands. We report several lines of evidence indicating that humans were present in the Falkland Islands centuries before Europeans, including (i) an abrupt increase in fire activity, (ii) deposits of mixed marine vertebrates that predate European exploration by centuries, and (iii) a surface-find projectile point made of local quartzite.

Exceptionally preserved asphaltic coprolites expand the spatiotemporal range of a North American paleoecological proxy.

As fossilized feces, coprolites represent direct evidence of animal behavior captured in the fossil record. They encapsulate past ecological interactions between a consumer and its prey and, when they contain plant material, can also guide paleoenvironmental reconstructions. Here we describe the first coprolites from the lagerstätte Rancho La Brea (RLB) in Los Angeles, California, which also represent the first confirmed coprolites from an asphaltic ("tar pit") context globally.

Limited contribution of ancient methane to surface waters of the U.S. Beaufort Sea shelf.

In response to warming climate, methane can be released to Arctic Ocean sediment and waters from thawing subsea permafrost and decomposing methane hydrates. However, it is unknown whether methane derived from this sediment storehouse of frozen ancient carbon reaches the atmosphere. We quantified the fraction of methane derived from ancient sources in shelf waters of the U.

Bison phylogeography constrains dispersal and viability of the Ice Free Corridor in western Canada.

The Ice Free Corridor has been invoked as a route for Pleistocene human and animal dispersals between eastern Beringia and more southerly areas of North America. Despite the significance of the corridor, there are limited data for when and how this corridor was used. Hypothetical uses of the corridor include: the first expansion of humans from Beringia into the Americas, northward postglacial expansions of fluted point technologies into Beringia, and continued use of the corridor as a contact route between the north and south.

Widespread collapse of the Ross Ice Shelf during the late Holocene.

The stability of modern ice shelves is threatened by atmospheric and oceanic warming. The geologic record of formerly glaciated continental shelves provides a window into the past of how ice shelves responded to a warming climate. Fields of deep (-560 m), linear iceberg furrows on the outer, western Ross Sea continental shelf record an early post-Last Glacial Maximum episode of ice-shelf collapse that was followed by continuous retreat of the grounding line for ∼200 km.

Angel's share combats wine fraud: (14)C dating of wine without opening the bottle.

The problem of fraud continues to plague the wine industry, and detecting cases where the original bottle has been refilled with an inferior vintage is especially difficult. A novel noninvasive procedure presented here relies on radiocarbon dating the so-called angel's share: the trace amounts of ethanol and other gases that diffuse into and through the cork as bottled wine ages and matures. These are collected by applying a vacuum to the top of the bottle and cryo-trapping the extracted gas, leaving the liquid contents untouched.

American mastodon extirpation in the Arctic and Subarctic predates human colonization and terminal Pleistocene climate change.

Existing radiocarbon ((14)C) dates on American mastodon (Mammut americanum) fossils from eastern Beringia (Alaska and Yukon) have been interpreted as evidence they inhabited the Arctic and Subarctic during Pleistocene full-glacial times (∼ 18,000 (14)C years B.P.).

Abrupt pre-Bølling-Allerød warming and circulation changes in the deep ocean.

Several large and rapid changes in atmospheric temperature and the partial pressure of carbon dioxide in the atmosphere--probably linked to changes in deep ocean circulation--occurred during the last deglaciation. The abrupt temperature rise in the Northern Hemisphere and the restart of the Atlantic meridional overturning circulation at the start of the Bølling-Allerød interstadial, 14,700 years ago, are among the most dramatic deglacial events, but their underlying physical causes are not known. Here we show that the release of heat from warm waters in the deep North Atlantic Ocean probably triggered the Bølling-Allerød warming and reinvigoration of the Atlantic meridional overturning circulation.

Millennial-scale isotope records from a wide-ranging predator show evidence of recent human impact to oceanic food webs.

Human exploitation of marine ecosystems is more recent in oceanic than near shore regions, yet our understanding of human impacts on oceanic food webs is comparatively poor. Few records of species that live beyond the continental shelves date back more than 60 y, and the sheer size of oceanic regions makes their food webs difficult to study, even in modern times. Here, we use stable carbon and nitrogen isotopes to study the foraging history of a generalist, oceanic predator, the Hawaiian petrel (Pterodroma sandwichensis), which ranges broadly in the Pacific from the equator to near the Aleutian Islands.

Carbon dioxide release from the North Pacific abyss during the last deglaciation.

Atmospheric carbon dioxide concentrations were significantly lower during glacial periods than during intervening interglacial periods, but the mechanisms responsible for this difference remain uncertain. Many recent explanations call on greater carbon storage in a poorly ventilated deep ocean during glacial periods, but direct evidence regarding the ventilation and respired carbon content of the glacial deep ocean is sparse and often equivocal. Here we present sedimentary geochemical records from sites spanning the deep subarctic Pacific that--together with previously published results--show that a poorly ventilated water mass containing a high concentration of respired carbon dioxide occupied the North Pacific abyss during the Last Glacial Maximum.

Use of tritium accelerator mass spectrometry for tree ring analysis.

Public concerns over the health effects associated with low-level and long-term exposure to tritium released from industrial point sources have generated the demand for better methods to evaluate historical tritium exposure levels for these communities. The cellulose of trees accurately reflects the tritium concentration in the source water and may contain the only historical record of tritium exposure. The tritium activity in the annual rings of a tree was measured using accelerator mass spectrometry to reconstruct historical annual averages of tritium exposure.

Long-living lotus: germination and soil {gamma}-irradiation of centuries-old fruits, and cultivation, growth, and phenotypic abnormalities of offspring.

Sacred lotus (Nelumbo nucifera) has been cultivated as a crop in Asia for thousands of years. An ∼1300-yr-old lotus fruit, recovered from an originally cultivated but now dry lakebed in northeastern China, is the oldest germinated and directly (14)C-dated fruit known. In 1996, we traveled to the dry lake at Xipaozi Village, China, the source of the old viable fruits.