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  • Articles  (31)
  • Cambridge University Press  (31)
  • Geography  (31)
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  • Articles  (31)
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  • 1
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    Climate and human influence on late Holocene fire regimes in the British Virgin Islands (2018)
    Cambridge University Press
    Details
    Publication Date: 2018
    Description: 〈div data-abstract-type="normal"〉〈p〉Global climate change poses significant threats to the Caribbean islands. Yet, little is known about the long-term disturbance regimes in island ecosystems. This research investigates 2000 yr of natural and anthropogenic fire disturbance through the analysis of a latitudinal transect of sediment records from coastal salt ponds in the British Virgin Islands (BVI). The two research objectives in this study are (1) to determine the fire regime history for the BVI over the last 2000 yr and (2) to explore ecological impacts from anthropogenic landscape modification pre- and post-European settlement. The magnitude of anthropogenic landscape modification, including the introduction of agriculture, was investigated through a multiproxy approach using sedimentary records of fossil pollen and charcoal. Our results suggest fire regimes from Belmont Pond, Thatch Island, and Skeleton Pond have been influenced by human activity, particularly during the postsettlement era, from 500 cal yr BP to modern. Our results suggest that fire regimes during the Medieval Climate Anomaly were responding to changes in climate via dominant atmospheric drivers. The presettlement fire regimes from these islands suggest that fires occurred every 90 to 120 yr. This research represents a significant data contribution to a region with little disturbance and vegetation data available.〈/p〉〈/div〉
    Print ISSN: 0033-5894
    Electronic ISSN: 1096-0287
    Topics: Geography , Geosciences
    Published by Cambridge University Press
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  • 2
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    A 7600 yr vegetation and fire history from Anthony Lake, northeastern Oregon, USA, with linkages to modern synoptic climate patterns (2019)
    Cambridge University Press
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    Publication Date: 2019
    Description: 〈div data-abstract-type="normal"〉〈p〉We used pollen and high-resolution charcoal analysis of lake sediment to reconstruct a 7600 yr vegetation and fire history from Anthony Lake, located in the Blue Mountains of northeastern Oregon. From 7300 to 6300 cal yr BP, the forest was composed primarily of 〈span〉Populus〈/span〉, and fire was common, indicating warm, dry conditions. From 6300 to 3000 cal yr BP, 〈span〉Populus〈/span〉 declined as 〈span〉Pinus〈/span〉 and 〈span〉Picea〈/span〉 increased in abundance and fire became less frequent, suggesting a shift to cooler, wetter conditions. From 3000 cal yr BP to present, modern-day forests composed of 〈span〉Pinus〈/span〉 and 〈span〉Abies〈/span〉 developed, and from 1650 cal yr BP to present, fires increased. We utilized the modern climate-analogue approach to explain the potential synoptic climatological processes associated with regional fire. The results indicate that years with high fire occurrence experience positive 500 mb height anomalies centered over the Great Basin, with anomalous southerly component of flow delivering dry air into the region and with associated sinking motions to further suppress precipitation. It is possible that such conditions became more common over the last 1650 cal yr BP, supporting an increase in fire despite the shift to more mesic conditions.〈/p〉〈/div〉
    Print ISSN: 0033-5894
    Electronic ISSN: 1096-0287
    Topics: Geography , Geosciences
    Published by Cambridge University Press
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  • 3
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    Late Quaternary lake-level and climate changes in arid central Asia inferred from sediments of Ebinur Lake, Xinjiang, northwestern China (2019)
    Cambridge University Press
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    Publication Date: 2019
    Description: 〈div data-abstract-type="normal"〉〈p〉Arid central Asia plays an important role in global climate dynamics, but large uncertainties remain in our understanding of the region's hydroclimate variability during the Late Quaternary. Here we present a new, high-resolution record of lacustrine sediment grain-size and element chemistry from Ebinur Lake, which was used to infer lake conditions and related climate changes in the study region between ca. 39.2 and 3.6 ka. End-member modeling analysis of grain-size data and PCA of elemental data show that lake level fluctuated dramatically from 39.2 to 34.0 ka. Subsequently, Ebinur Lake experienced a high stand from 34.0 to 28.0 ka, under humid climate conditions. The subsequent period, from 28.0 to 12.0 ka, was characterized by lake regression under dry climate conditions, whereas afterward (12.0–3.6 ka), considerably higher lake levels and humid conditions again prevailed. Millennial-scale abrupt climate changes, such as Heinrich events (H3 and H1) and the Younger Dryas, which are documented in the North Atlantic region, are also detected in the sediment record from Ebinur Lake. Comparisons with other sediment records from arid central Asia generally support the claim that climate change in this region was influenced mainly by variations in North Atlantic sea surface temperatures, through the westerlies.〈/p〉〈/div〉
    Print ISSN: 0033-5894
    Electronic ISSN: 1096-0287
    Topics: Geography , Geosciences
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  • 4
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    Drainage networks, lakes and water fluxes beneath the Antarctic ice sheet (2016)
    Cambridge University Press
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    Publication Date: 2016-07-01
    Description: Antarctica Bedmap2 datasets are used to calculate subglacial hydraulic potential and the area, depth and volume of hydraulic potential sinks. There are over 32 000 contiguous sinks, which can be thought of as predicted lakes. Patterns of subglacial melt are modelled with a balanced ice flux flow model, and water fluxes are cumulated along predicted flow pathways to quantify steady-state fluxes from the main basin outlets and from known subglacial lakes. The total flux from the continent is similar to 21 km(3) a(-1). Byrd Glacier has the greatest basin flux of similar to 2.7 km(3) a(-1). Fluxes from subglacial lakes range from similar to 1 x 10(-4) to similar to 1.5 km(3) a(-1). Lake turnover times are calculated from their volumes and fluxes, and have median values of similar to 100 a for known 'active' lakes and similar to 500 a for other lakes. Recurrence intervals of a 0.25 km(3) flood range from similar to 2 months to similar to 2000 a (median approximate to 130 a) for known 'active' lakes and from similar to 2 to similar to 2400 a (median approximate to 360 a) for other lakes. Thus, several lakes that have recently been observed to fill and drain may not do so again for many centuries; and several lakes that have not, so far, been observed to fill and drain have the potential to do so, even at annual to decadal timescales.
    Print ISSN: 0260-3055
    Electronic ISSN: 1727-5644
    Topics: Geography , Geosciences
    Published by Cambridge University Press on behalf of International Glaciological Society.
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  • 5
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    Growth and longevity of the Antarctic scallop Adamussium colbecki under annual and multiannual sea ice (2020)
    Cambridge University Press
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    Publication Date: 2020-06-18
    Description: Ecosystem engineers such as the Antarctic scallop (Adamussium colbecki) shape marine communities. Thus, changes to their lifespan and growth could have far-reaching effects on other organisms. Sea ice is critical to polar marine ecosystem function, attenuating light and thereby affecting nutrient availability. Sea ice could therefore impact longevity and growth in polar bivalves unless temperature is the overriding factor. Here, we compare the longevity and growth of A. colbecki from two Antarctic sites: Explorers Cove and Bay of Sails, which differ by sea-ice cover, but share similar seawater temperatures, the coldest on Earth (-1.97°C). We hypothesize that scallops from the multiannual sea-ice site will have slower growth and greater longevity. We found maximum ages to be similar at both sites (18–19 years). Growth was slower, with higher inter-individual variability, under multiannual sea ice than under annual sea ice, which we attribute to patchier nutrient availability under multiannual sea ice. Contrary to expectations, A. colbecki growth, but not longevity, is affected by sea-ice duration when temperatures are comparable. Recent dramatic reductions in Antarctic sea ice and predicted temperature increases may irrevocably alter the life histories of this ecosystem engineer and other polar organisms.
    Print ISSN: 0954-1020
    Electronic ISSN: 1365-2079
    Topics: Biology , Geography , Geosciences
    Published by Cambridge University Press
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  • 6
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    A 7600 yr vegetation and fire history from Anthony Lake, northeastern Oregon, USA, with linkages to modern synoptic climate patterns (2019)
    Cambridge University Press
    Details
    Publication Date: 2019-01-10
    Print ISSN: 0033-5894
    Electronic ISSN: 1096-0287
    Topics: Geography , Geosciences
    Published by Cambridge University Press
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  • 7
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    OSL chronology and possible forcing mechanisms of dune evolution in the Horqin dunefield in northern China since the Last Glacial Maximum (2012)
    Cambridge University Press
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    Publication Date: 2012-06-17
    Description: The evolution processes and forcing mechanisms of the Horqin dunefield in northern China are poorly understood. In this study, systematic OSL dating of multiple sites is used together with pollen analysis of a representative section in order to reconstruct the evolution of the dunefield since the Last Glacial Maximum (LGM). Our results show that there was extensive dune mobilization 25–10 ka, transition to stabilization 10–8 ka, considerable dune stabilization 8–3 ka, and multiple episodes of stabilization and mobilization after 3 ka. Comparison of dune evolution of the dunefields in northern China during the Holocene showed that Asian monsoon and resultant effective moisture have played an important role in the evolution of dunefields at the millennial time scale. Further analysis indicated that the dune evolution in the Horqin dunefield before 3 ka was synchronous with climatic changes. However, increasing human activity has impacted dune evolution during the last 3 ka.
    Print ISSN: 0033-5894
    Electronic ISSN: 1096-0287
    Topics: Geography , Geosciences
    Published by Cambridge University Press
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  • 8
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    Fire and Vegetation History from the Coastal Rain Forest of the Western Oregon Coast Range (2002)
    Cambridge University Press
    Details
    Publication Date: 2002-11-01
    Description: High-resolution charcoal and pollen analyses were used to reconstruct a 4600-yr-long history of fire and vegetation near Taylor Lake in the wettest forests of coastal Oregon. Today, fires in these forests are rare because the season of ignition does not coincide with months of dry fuels. From ca. 4600 to 2700 cal yr B.P. fire episodes occurred at intervals of 140±30 yr while forest vegetation was dominated by disturbance-adapted taxa such as Alnus rubra. From ca. 2700 cal yr B.P. to the present, fire episodes have become less common, occurring at intervals of 240±30 yr, and fire-sensitive forest taxa, such as Tsuga heterophylla and Picea sitchensis, have become more prominent. Fire occurrence during the mid-Holocene was similar to that of the more xeric forests in the eastern Coast Range and suggests that summer drought was widespread. After ca. 2700 cal yr B.P., a decrease in fire episode frequency suggests that cooler conditions and possibly increased summer fog allowed the establishment of present-day Picea sitchensis forests within the watershed. These results provide evidence that fire has been an important disturbance agent in the Coast Range of Oregon, and variations in fire frequency and climate have led to the establishment of present-day forests.
    Print ISSN: 0033-5894
    Electronic ISSN: 1096-0287
    Topics: Geography , Geosciences
    Published by Cambridge University Press
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  • 9
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    Paleofire severity and vegetation change in the Cascade Range, Oregon, USA (2016)
    Cambridge University Press
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    Publication Date: 2016-03-01
    Description: Paleoecological research has expanded our knowledge of the relationships between climate, fire and vegetation. Fire can be a significant driver of forest composition and structure change, but identifying and quantifying fire regimes has been elusive. Using high-resolution charcoal analysis and pollen analysis we reconstructed a 13,200-year-old fire and vegetation history from Breitenbush Lake, Oregon, located in the central Cascade Range, USA. Our objective was to examine if fire occurrence and severity may have been a driver of Holocene forest-composition change. The data from this study suggests that while fire can create opportunities for successional process to occur, fire events were not significant catalysts for forest change. Instead, most major transitions at Breitenbush Lake occurred during prolonged fire-free intervals. Our results reinforce the view that climate is the major control of vegetation composition change in the Cascade Range.
    Print ISSN: 0033-5894
    Electronic ISSN: 1096-0287
    Topics: Geography , Geosciences
    Published by Cambridge University Press
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  • 10
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    Quantifying the periodicity of Heinrich and Dansgaard–Oeschger events during Marine Oxygen Isotope Stage 3 (2013)
    Cambridge University Press
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    Publication Date: 2013-05-01
    Description: Data from multiple ice and sediment cores in the North Atlantic show that Marine Oxygen Isotope Stage 3 (MIS 3) was characterized by recurring millennial-scale variations in climate, but the periodic behavior of the well-known millennial-scale variations, Heinrich events and Dansgaard–Oeschger events, is uncertain. We use oxygen isotope values from the Greenland Ice Sheet Project 2 (GISP2) and North Greenland Ice Core Project (NGRIP) ice cores and estimated sea-surface temperature derived from a Bermuda Rise marine sediment core as climate proxies to assess the periodic behavior of Heinrich events and Dansgaard–Oeschger events using Lomb–Scargle spectral decomposition and continuous time autoregressive models. We find that continuous time autoregressive models produce less variable estimates of periodicity for Heinrich events than Lomb–Scargle methods. Heinrich events during MIS 3 are periodic with an estimated periodicity of 6.29–6.49 ka in the GISP 2 ice core, 6.71–6.76 ka in the marine sediment core, and 7.89–8.23 ka in the NGRIP core. There is insufficient evidence from these data to conclude that Dansgaard–Oeschger events exhibit a single periodicity during MIS 3. We also find that the periodic behavior of millennial-scale variations depends on the observational time frame.
    Print ISSN: 0033-5894
    Electronic ISSN: 1096-0287
    Topics: Geography , Geosciences
    Published by Cambridge University Press
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