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Chemical changes in hot springs, as recorded by thermal waters and their deposits, provide a window into the evolution of the postglacial hydrothermal system of the Yellowstone Plateau Volcanic Field. Today, most hydrothermal travertine forms to the north and south of the ca. 631 ka Yellowstone caldera where groundwater flow through subsurface sedimentary rocks leads to calcite saturation at hot springs. In contrast, low-Ca rhyolites dominate the subsurface within the Yellowstone caldera, resulting in thermal waters that rarely deposit travertine. We investigated the timing and origin of five small travertine deposits in the Upper and Lower Geyser Basins to understand the conditions that allowed for travertine deposition. New 230Th-U dating, oxygen (δ18O), carbon (δ13C), and strontium (87Sr/86Sr) isotopic ratios, and elemental concentrations indicate that travertine deposits within the Yellowstone caldera formed during three main episodes that correspond broadly with known periods of wet climate: 13.9−13.6 ka, 12.2−9.5 ka, and 5.2−2.9 ka. Travertine deposition occurred in response to the influx of large volumes of cold meteoric water, which increased the rate of chemical weathering of surficial sediments and recharge into the hydrothermal system. The small volume of intracaldera travertine does not support a massive postglacial surge of CO2 within the Yellowstone caldera, nor was magmatic CO2 the catalyst for postglacial travertine deposition.more » « lessFree, publicly-accessible full text available February 13, 2025
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Two studies from the Patagonian forest-steppe ecotone (36–55°S; Argentina and Chile) demonstrate how interdisciplinary research combining paleoecological, archaeological, and historical methods provide information on past landscape conditions that can help prioritize conservation efforts and assess the likelihood of restoration success.more » « less
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Abstract Changes in climate and fire regime have long been recognized as drivers of the postglacial vegetation history of Yellowstone National Park, but the effects of locally dramatic hydrothermal activity are poorly known. Multi-proxy records from Goose Lake have been used to describe the history of Lower Geyser Basin where modern hydrothermal activity is widespread. From 10,300 cal yr BP to 3800 cal yr BP, thermal waters discharged into the lake, as evidenced by the deposition of arsenic-rich sediment, fluorite mud, and relatively high δ 13 C sediment values. Partially thermal conditions affected the limnobiotic composition, but prevailing climate, fire regime, and rhyolitic substrate maintained Pinus contorta forest in the basin, as found throughout the region. At 3800 cal yr BP, thermal water discharge into Goose Lake ceased, as evidenced by a shift in sediment geochemistry and limnobiota. Pollen and charcoal data indicate concurrent grassland development with limited fuel biomass and less fire activity, despite late Holocene climate conditions that were conducive to expanded forest cover. The shift in hydrothermal activity at Goose Lake and establishment of the treeless geyser basin may have been the result of a tectonic event or change in hydroclimate. This record illustrates the complex interactions of geology and climate that govern the development of an active hydrothermal geo-ecosystem.more » « less
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Researchers have long debated the degree to which Native American land use altered landscapes in the Americas prior to European colonization. Human–environment interactions in southern South America are inferred from new pollen and charcoal data from Laguna El Sosneado and their comparison with high-resolution paleoenvironmental records and archaeological/ethnohistorical information at other sites along the eastern Andes of southern Argentina and Chile (34–52°S). The records indicate that humans, by altering ignition frequency and the availability of fuels, variously muted or amplified the effects of climate on fire regimes. For example, fire activity at the northern and southern sites was low at times when the climate and vegetation were suitable for burning but lacked an ignition source. Conversely, abundant fires set by humans and infrequent lightning ignitions occurred during periods when warm, dry climate conditions coincided with ample vegetation (i.e., fuel) at midlatitude sites. Prior to European arrival, changes in Native American demography and land use influenced vegetation and fire regimes locally, but human influences were not widely evident until the 16th century, with the introduction of nonnative species (e.g., horses), and then in the late 19th century, as Euro-Americans targeted specific resources to support local and national economies. The complex interactions between past climate variability, human activities, and ecosystem dynamics at the local scale are overlooked by approaches that infer levels of land use simply from population size or that rely on regionally composited data to detect drivers of past environmental change.more » « less
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ABSTRACT Accelerator mass spectrometry (AMS) dating of pollen concentrates is often used in lake sediment records where large, terrestrial plant remains are unavailable. Ages produced from chemically concentrated pollen as well as manually picked Pinaceae grains in Yellowstone Lake (Wyoming) sediments were consistently 1700–4300 cal years older than ages established by terrestrial plant remains, tephrochronology, and the age of the sediment-water interface. Previous studies have successfully utilized the same laboratory space and methods, suggesting the source of old-carbon contamination is specific to these samples. Manually picking pollen grains precludes admixture of non-pollen materials. Furthermore, no clear source of old pollen grains occurs on the deglaciated landscape, making reworking of old pollen grains unlikely. High volumes of CO 2 are degassed in the Yellowstone Caldera, potentially introducing old carbon to pollen. While uptake of old CO 2 through photosynthesis is minor (F 14 C approximately 0.99), old-carbon contamination may still take place in the water column or in surficial lake sediments. It remains unclear, however, what mechanism allows for the erroneous ages of highly refractory pollen grains while terrestrial plant remains were unaffected. In the absence of a satisfactory explanation for erroneously old radiocarbon ages from pollen concentrates, we propose steps for further study.more » « less
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Abstract Aim Although it is established that climate and fire have greatly influenced the long‐term ecosystem dynamics of Patagonia south of 40°S, the environmental history from northernmost Patagonia (37–40°S), where endemic and endangered monkey puzzle tree (
Araucaria araucana ) occurs, is poorly known. Here we ask: (a) What is the Holocene vegetation and fire history at the north‐eastern extent ofA. araucana forest? (b) How have climate and humans influenced the past distribution ofA. araucana ?Location Northernmost Patagonia, Argentina and Chile (37–40°S).
Taxa Araucaria araucana ,Nothofagus , Poaceae.Methods Sedimentary pollen and charcoal from Laguna Portezuelo (37.9°S, 71.0°W; 1,730 m; 11,100 BP) were evaluated using statistical methods and compared with other palaeoecological, independent palaeoclimate, and historical records to assess how changes in climate and land use influenced local‐to‐regional environmental history.
Results An open forest‐steppe landscape persisted at L. Portezuelo throughout the Holocene with generally low‐to‐moderate fire activity. Increased
Nothofagus pollen after ~6,590 BP suggests increases in shrubland and moisture in association with cooler conditions and greater seasonality and ENSO activity.Araucaria pollen appeared at L. Portezuelo at ~6,380 BP, but was low in abundance until ~370 BP, when it rose with charcoal levels. This increase inAraucaria and fire coincided with a regional influx of Mapuche American Indians.Nothofagus deforestation andPinus silviculture marked Euro‐American settlement beginning in the 19–20th century.Main conclusions (a) Rapid postglacial warming and drying limited the distribution of
Araucaria in the central valley of Chile. In the middle and late Holocene, decreased temperatures and greater seasonality and ENSO activity increased precipitation variability allowingAraucaria expansion at its north‐eastern limit. (b) Greater abundance ofAraucaria and heightened fire activity at L. Portezuelo after 370 BP coincided with increased Mapuche‐Pehuenche American Indian land use, suggesting thatAraucaria may have been managed in a human‐altered landscape. -
ABSTRACT Mountain ecosystems are characterized by their complex vegetation responses to past climate variability because of the interplay between large‐scale climate changes and local‐scale biotic and abiotic conditions. This study reconstructs the early postglacial expansion of conifer populations in the northern Greater Yellowstone Ecosystem (GYE). The objective is to examine how climate change and non‐climatic factors, including species characteristics, edaphic conditions and disturbance, governed postglacial vegetation changes. Spruce populations expanded first at 13 300 cal a
BP , concurrent with soil development and warming summers. Subalpine fir populations expanded after 12 300 cal aBP and probably lagged spruce expansion due to differences in climatic tolerances and/or its poorer seed dispersing capacity. Pine species expanded nearly synchronously after 11 300 cal aBP in response to elevated summer temperatures and increased fire activity. Douglas‐fir populations expanded last after 10 200 cal aBP during the early Holocene summer insolation maximum and cooler winters. The sequence and timing of conifer expansions in the northern GYE are consistent with the regional conifer history, indicating strong vegetation responses to millennial‐scale climate change associated with the seasonal cycle of insolation across spatial scales. Nonetheless, non‐climatic factors, including landscape stabilization and subsequent soil development, seed dispersing characteristics and fire, still shaped local‐scale patterns of conifer expansion.