More Like this

1. Subregional variability in the response of New England vegetation to postglacial climate change

   https://doi.org/10.1111/jbi.13407  

   Oswald, W. Wyatt ; Foster, David R. ; Shuman, Bryan N. ; Doughty, Elaine D. ; Faison, Edward K. ; Hall, Brian R. ; Hansen, Barbara C. S. ; Lindbladh, Matts ; Marroquin, Adriana ; Truebe, Sarah A. ( September 2018 , Journal of Biogeography)

   We analysed a dataset composed of multiple palaeoclimate and lake‐sediment pollen records from New England to explore how postglacial changes in the composition and spatial patterns of vegetation were controlled by regional‐scale climate change, a subregional environmental gradient, and landscape‐scale variations in soil characteristics.

   The 120,000‐km²study area includes parts of Vermont and New Hampshire in the north, where sites are 150–200 km from the Atlantic Ocean, and spans the coastline from southeastern New York to Cape Cod and the adjacent islands, including Block Island, the Elizabeth Islands, Nantucket, and Martha's Vineyard.

   We analysed pollen records from 29 study sites, using multivariate cluster analysis to visualize changes in the composition and spatial patterns of vegetation during the last 14,000 years. The pollen data were compared with temperature and precipitation reconstructions.

   Boreal forest featuringPiceaandPinus banksianawas present across the region when conditions were cool and dry 14,000–12,000 calibrated¹⁴C years before present (ybp).Pinus strobusbecame regionally dominant as temperatures increased between 12,000 and 10,000 ybp. The composition of forests in inland and coastal areas diverged in response to further warming after 10,000 ybp, whenQuercusandPinus rigidaexpanded across southern New England, whereas conditions remained cool enough in inland areas to maintainPinus strobus. Increasing precipitation allowedTsuga canadensis,Fagus grandifolia, andBetulato replacePinus strobusin inland areas during 9,000–8,000 ybp, and also led to the expansion ofCaryaacross the coastal part of the region beginning at 7,000–6,000 ybp. Abrupt cooling at 5,500–5,000 ybp caused sharp declines inTsugain inland areas andQuercusat some coastal sites, and the populations of those taxa remained low until they recovered around 3,000 ybp in response to rising precipitation. Throughout most of the Holocene, sites underlain by sandy glacial deposits were occupied byPinus rigidaandQuercus.

   Postglacial changes in the composition and spatial pattern of New England forests were controlled by long‐term trends and abrupt shifts in temperature and precipitation, as well as by the environmental gradient between coastal and inland parts of the region. Substrate and soil moisture shaped landscape‐scale variations in forest composition.

    

   more » « less
2. A stable isotope record of late Quaternary hydrologic change in the northwestern Brooks Range, Alaska (eastern Beringia)

   https://doi.org/10.1002/jqs.3368  

   King, Amanda L. ; Anderson, Lesleigh ; Abbott, Mark ; Edwards, Mary ; Finkenbinder, Matthew S. ; Finney, Bruce ; Wooller, Matthew J. ( September 2021 , Journal of Quaternary Science)

   A submillennial‐resolution record of lake water oxygen isotope composition (δ¹⁸O) from chironomid head capsules is presented from Burial Lake, northwest Alaska. The record spans the Last Glacial Maximum (LGM; ~20–16k cal abp) to the present and shows a series of large lake δ¹⁸O shifts (~5‰). Relatively low δ¹⁸O values occurred during a period covering the LGM, when the lake was a shallow, closed‐basin pond. Higher values characterize deglaciation (~16–11.5k cal abp) when the lake was still closed but lake levels were higher. A rapid decline between ~11 and 10.5k cal abpindicates that lake levels rose to overflowing. Lake δ¹⁸O values are interpreted to reflect the combined effects of changes in lake hydrology, growing season temperature and meteoric source water as well as large‐scale environmental changes impacting this site, including opening of the Bering Strait and shifts in atmospheric circulation patterns related to ice‐sheet dynamics. The results indicate significant shifts in precipitation minus evaporation across the late Pleistocene to early Holocene transition, which are consistent with temporal patterns of vegetation change and paludification. This study provides new perspectives on the paleohydrology of eastern Beringia concomitant with human migration and major turnover in megafaunal assemblages.

    

   more » « less
3. Holocene geo-ecological evolution of Lower Geyser Basin, Yellowstone National Park (USA)

   https://doi.org/10.1017/qua.2021.42  

   Schiller, Christopher M. ; Whitlock, Cathy ; Brown, Sabrina R. ( January 2022 , Quaternary Research)

   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
4. Terrestrial ecosystem transformations in response to rapid climate change during the last deglaciation around Mono Lake, California, USA

   https://doi.org/10.1017/qua.2022.70  

   Benfield, Adam J. ; Ivory, Sarah J. ; Hodelka, Bailee N. ; Zimmerman, Susan R.H. ; McGlue, Michael M. ( May 2023 , Quaternary Research)

   We examine major reorganizations of the terrestrial ecosystem around Mono Lake, California during the last deglacial period from 16,000–9,000 cal yr BP using pollen, microcharcoal, and coprophilous fungal spores (Sporormiella) from a deep-water sediment core. The pollen results record the assemblage, decline, and replacement of a mixed wooded community of Sierran and Great Basin taxa with Alkali Sink and Sagebrush Steppe biomes around Mono Lake. In particular, the enigmatic presence ofSequoiadendron-type pollen and its extirpation during the early Holocene hint at substantial biogeographic reorganizations on the Sierran-Great Basin ecotone during deglaciation. Rapid regional hydroclimate changes produced structural alterations in pine–juniper woodlands facilitated by increases in wildfires at 14,800 cal yr BP, 13,900 cal yr BP, and 12,800 cal yr BP. The rapid canopy changes altered the availability of herbaceous understory plants, likely putting pressure on megafauna populations, which declined in a stepwise fashion at 15,000 cal yr BP and 12,700 cal yr BP before final extirpation from Mono Basin at 11,500 cal yr BP. However, wooded vegetation communities overall remained resistant to abrupt hydroclimate changes during the late Pleistocene; instead, they gradually declined and were replaced by Alkali Sink communities in the lowlands as temperature increased into the Early Holocene, and Mono Lake regressed.

    

   more » « less
5. Late Holocene environmental change in Celestun Lagoon, Yucatan, Mexico

   https://doi.org/10.1007/s10933-021-00227-4  

   Hardage, Kyle ; Street, Joseph ; Herrera-Silveira, Jorge A. ; Oberle, Ferdinand K. J. ; Paytan, Adina ( December 2021 , Journal of Paleolimnology)

   Epikarst estuary response to hydroclimate change remains poorly understood, despite the well-studied link between climate and karst groundwater aquifers. The influence of sea-level rise and coastal geomorphic change on these estuaries obscures climate signals, thus requiring careful development of paleoenvironmental histories to interpret the paleoclimate archives. We used foraminifera assemblages, carbon stable isotope ratios (δ¹³C) and carbon:nitrogen (C:N) mass ratios of organic matter in sediment cores to infer environmental changes over the past 5300 years in Celestun Lagoon, Yucatan, Mexico. Specimens (> 125 µm) from modern core top sediments revealed three assemblages: (1) a brackish mangrove assemblage of agglutinatedMiliamminaandAmmotiumtaxa and hyalineHaynesina(2) an inner-shelf marine assemblage ofBolivina,Hanzawaia, andRosalina,and (3) a brackish assemblage dominated byAmmoniaandElphidium. Assemblages changed along the lagoon channel in response to changes in salinity and vegetation, i.e. seagrass and mangrove. In addition to these three foraminifera assemblages, lagoon sediments deposited since 5300 cal yr BP are comprised of two more assemblages, defined byArchaiasandLaevipeneroplis,which indicate marineThalassiaseagrasses, andTrichohyalus,which indicates restricted inland mangrove ponds. Our data suggest that Celestun Lagoon displayed four phases of development: (1) an inland mangrove pond (5300 BP) (2) a shallow unprotected coastline with marine seagrass and barrier island initiation (4900 BP) (3) a protected brackish lagoon (3000 BP), and (4) a protected lagoon surrounded by mangroves (1700 BP). Stratigraphic (temporal) changes in core assemblages resemble spatial differences in communities across the modern lagoon, from the southern marine sector to the northern brackish region. Similar temporal patterns have been reported from other Yucatan Peninsula lagoons and fromcenotes(Nichupte, Aktun Ha), suggesting a regional coastal response to sea level rise and climate change, including geomorphic controls (longshore drift) on lagoon salinity, as observed today. Holocene barrier island development progressively protected the northwest Yucatan Peninsula coastline, reducing mixing between seawater and rain-fed submarine groundwater discharge. Superimposed on this geomorphic signal, assemblage changes that are observed reflect the most severe regional wet and dry climate episodes, which coincide with paleoclimate records from lowland lake archives (Chichancanab, Salpeten). Our results emphasize the need to consider coastal geomorphic evolution when using epikarst estuary and lagoon sediment archives for paleoclimate reconstruction and provide evidence of hydroclimate changes on the Yucatan Peninsula.

    

   more » « less