Tom Ager (Former Employee)
Science and Products
Map of glacial limits and possible refugia in the southern Alexander Archipelago, Alaska, during the late Wisconsin glaciation
During the late Wisconsin glaciation (circa 26,000-13,000 carbon-14 yr BP) the Cordilleran glacier complex formed vast ice fields and large glaciers along the crest of the Coast Mountains. As these glaciers flowed west to the Pacific Ocean, they were joined by local glaciers originating on the higher reaches of the Alexander Archipelago (Mann and Hamiltion, 1995). This extensive volume of
Filter Total Items: 17
Late Quaternary vegetation development following deglaciation of northwestern Alexander Archipelago, Alaska
The Cordilleran Ice sheet covered most of southeastern Alaska during the Last Glacial Interval (LGI: Marine Isotope Stage 2). Ice began to recede from western Alexander Archipelago ~17,000 + 700 yr BP. In this study pollen analysis and radiocarbon dating of three sediment cores were used to reconstruct, for the first time, the postglacial development of vegetation of the northwestern Alexander Ar
Authors
Thomas A. Ager
Holocene evolution of diatom and silicoflagellate paleoceanography in Slocum Arm, a fjord in southeastern Alaska
Diatom and silicoflagellate assemblages in cores EW0408-47JC, -47TC, -46MC (57° 34.5278′ N, 136° 3.7764′ W, 114 m water depth) taken from the outer portion of Slocum Arm, a post-glacial fjord in southeastern Alaska, reveal the paleoclimatic and paleoceanographic evolution of the eastern margin of the Gulf of Alaska (GoA) during the past 10,000 years. Between ~ 10 and 6.8 cal ka, periods of low sal
Authors
John A. Barron, David Bukry, Jason A. Addison, Thomas A. Ager
A high-elevation, multi-proxy biotic and environmental record of MIS 6-4 from the Ziegler Reservoir fossil site, Snowmass Village, Colorado, USA
In North America, terrestrial records of biodiversity and climate change that span Marine Oxygen Isotope Stage (MIS) 5 are rare. Where found, they provide insight into how the coupling of the ocean–atmosphere system is manifested in biotic and environmental records and how the biosphere responds to climate change. In 2010–2011, construction at Ziegler Reservoir near Snowmass Village, Colorado (USA
Authors
Ian M. Miller, Jeffrey S. Pigati, R. Scott Anderson, Kirk R. Johnson, Shannon Mahan, Thomas A. Ager, Richard G. Baker, Maarten Blaauw, Jordon Bright, Peter M. Brown, Bruce Bryant, Zachary T. Calamari, Paul E. Carrara, Cherney Michael D., John R. Demboski, Scott A. Elias, Daniel C. Fisher, Harrison J. Gray, Danielle R. Haskett, Jeffrey S. Honke, Stephen T. Jackson, Gonzalo Jiménez-Moreno, Douglas Kline, Eric M. Leonard, Nathaniel A. Lifton, Carol Lucking, H. Gregory McDonald, Dane M. Miller, Daniel R. Muhs, Stephen E. Nash, Cody Newton, James B. Paces, Lesley Petrie, Mitchell A. Plummer, David F. Porinchu, Adam N. Rountrey, Eric Scott, Joseph J. W. Sertich, Saxon E. Sharpe, Gary L. Skipp, Laura E. Strickland, Richard K. Stucky, Robert S. Thompson, Jim Wilson
Identification of last interglacial deposits in eastern Beringia: a cautionary note from the Palisades, interior Alaska
Last interglacial sediments in unglaciated Alaska and Yukon (eastern Beringia) are commonly identified by palaeoecological indicators and stratigraphic position ~2-5m above the regionally prominent Old Crow tephra (124 + or - 10ka). We demonstrate that this approach can yield erroneous age assignments using data from a new exposure at the Palisades, a site in interior Alaska with numerous exposure
Authors
Alberto V. Reyes, Grant D. Zazula, Svetlana Kuzmina, Thomas A. Ager, Duane G. Froese
Marine tephrochronology of the Mt. Edgecumbe volcanic field, southeast Alaska, USA
The Mt. Edgecumbe Volcanic Field (MEVF), located on Kruzof Island near Sitka Sound in southeast Alaska, experienced a large multiple-stage eruption during the last glacial maximum (LGM)-Holocene transition that generated a regionally extensive series of compositionally similar rhyolite tephra horizons and a single well-dated dacite (MEd) tephra. Marine sediment cores collected from adjacent basins
Authors
Jason A. Addison, James E. Beget, Thomas A. Ager, Bruce P. Finney
Late Quaternary paleoclimate of western Alaska inferred from fossil chironomids and its relation to vegetation histories
Fossil Chironomidae assemblages (with a few Chaoboridae and Ceratopogonidae) from Zagoskin and Burial Lakes in western Alaska provide quantitative reconstructions of mean July air temperatures for periods of the late-middle Wisconsin (~39,000-34,000 cal yr B.P.) to the present. Inferred temperatures are compared with previously analyzed pollen data from each site summarized here by indirect ordina
Authors
Joshua Kurek, Les C. Cwynar, Thomas A. Ager, Mark B. Abbott, Mary E. Edwards
Pollen-based biome reconstructions for Latin America at 0, 6000 and 18 000 radiocarbon years ago
The biomisation method is used to reconstruct Latin American vegetation at 6000±500 and 18 000±1000 radiocarbon years before present (14C yr BP) from pollen data. Tests using modern pollen data from 381 samples derived from 287 locations broadly reproduce potential natural vegetation. The strong temperature gradient associated with the Andes is recorded by a transition from high altitude cool gras
Authors
R. Marchant, A. Cleef, S. P. Harrison, H. Hooghiemstra, Vera Markgraf, J. Van Boxel, T. Ager, L. Almeida, R. Anderson, C. Baied, H. Behling, J. C. Berrio, R. Burbridge, S. Bjorck, R. Byrne, M. Bush, J. Duivenvoorden, J. Flenley, P. De Oliveira, B. Van Gee, K. Graf, W. D. Gosling, S. Harbele, T. Van Der Hammen, B. Hansen, S. Horn, P. Kuhry, M.-P. Ledru, F. Mayle, B. Leyden, S. Lozano-Garcia, A. M. Melief, P. Moreno, N. T. Moar, A. Prieto, G. Van Reenen, F. Schabitz, M. Salgado-Labouriau, E. J. Schreve-Brinkman, M. Wille
Late Glacial-Holocene Pollen-Based Vegetation History from Pass Lake, Prince of Wales Island, Southeastern Alaska
A radiocarbon-dated history of vegetation development since late Wisconsin deglaciation has been reconstructed from pollen evidence preserved in a sediment core from Pass Lake on Prince of Wales Island, southeastern Alaska. The shallow lake is in the south-central part of the island and occupies a low pass that was filled by glacial ice of local origin during the late Wisconsin glaciation. The old
Authors
Thomas A. Ager, Joseph G. Rosenbaum
Vegetation response to climate change in Alaska: examples from the fossil record
Preface:
This report was presented as an invited paper at the Fish & Wildlife Service Climate Forum held in Anchorage, Alaska on February 21-23, 2007. The purpose of the talk was to provide some examples of past climate changes that appear to have caused significant responses in Alaskan vegetation. These examples are based on interpretations of dated fossil assemblages (pollen, spores and plant m
Authors
Thomas A. Ager
Environments of northwestern North America before the last glacial maximum
No abstract available.
Authors
John J. Clague, Rolf Mathewes, Thomas A. Ager
Palynology of Eocene strata in the Sagavanirktok and Canning Formations on the North Slope of Alaska
This paper describes, illustrates, and interprets Eocene palynomorph assemblages from the North Slope of Alaska, mainly from 31 outcrop samples from seven stratigraphic sections at Franklin Bluffs on the Sagavanirktok River. The top of the Sagwon Member of the Sagavanirktok Formation is shown to be a thin, coaly, apparently nonmarine sequence almost certainly of early Eocene age; the remainder of
Authors
Norman O. Frederiksen, Lucy E. Edwards, Thomas A. Ager, Thomas P. Sheehan
An evaluation of methods for identifying and interpreting buried soils in late Quaternary loess in Alaska: A section in Geologic studies in Alaska by the U.S. Geological Survey, 1998
The presence of buried soils in Alaskan loess is controversial, and therefore criteria for identifying buried soils in these deposits need to be evaluated. In this paper, morphologic and chemical criteria for identifying buried soils are evaluated by studying modern soils developed mostly in Holocene loess under tundra, boreal forest, and transitional coastal-boreal forest vegetation in different
Authors
Daniel R. Muhs, Thomas A. Ager, Josh M. Been, Joseph G. Rosenbaum, Richard J. Reynolds
Science and Products
Map of glacial limits and possible refugia in the southern Alexander Archipelago, Alaska, during the late Wisconsin glaciation
During the late Wisconsin glaciation (circa 26,000-13,000 carbon-14 yr BP) the Cordilleran glacier complex formed vast ice fields and large glaciers along the crest of the Coast Mountains. As these glaciers flowed west to the Pacific Ocean, they were joined by local glaciers originating on the higher reaches of the Alexander Archipelago (Mann and Hamiltion, 1995). This extensive volume of
Filter Total Items: 17
Late Quaternary vegetation development following deglaciation of northwestern Alexander Archipelago, Alaska
The Cordilleran Ice sheet covered most of southeastern Alaska during the Last Glacial Interval (LGI: Marine Isotope Stage 2). Ice began to recede from western Alexander Archipelago ~17,000 + 700 yr BP. In this study pollen analysis and radiocarbon dating of three sediment cores were used to reconstruct, for the first time, the postglacial development of vegetation of the northwestern Alexander Ar
Authors
Thomas A. Ager
Holocene evolution of diatom and silicoflagellate paleoceanography in Slocum Arm, a fjord in southeastern Alaska
Diatom and silicoflagellate assemblages in cores EW0408-47JC, -47TC, -46MC (57° 34.5278′ N, 136° 3.7764′ W, 114 m water depth) taken from the outer portion of Slocum Arm, a post-glacial fjord in southeastern Alaska, reveal the paleoclimatic and paleoceanographic evolution of the eastern margin of the Gulf of Alaska (GoA) during the past 10,000 years. Between ~ 10 and 6.8 cal ka, periods of low sal
Authors
John A. Barron, David Bukry, Jason A. Addison, Thomas A. Ager
A high-elevation, multi-proxy biotic and environmental record of MIS 6-4 from the Ziegler Reservoir fossil site, Snowmass Village, Colorado, USA
In North America, terrestrial records of biodiversity and climate change that span Marine Oxygen Isotope Stage (MIS) 5 are rare. Where found, they provide insight into how the coupling of the ocean–atmosphere system is manifested in biotic and environmental records and how the biosphere responds to climate change. In 2010–2011, construction at Ziegler Reservoir near Snowmass Village, Colorado (USA
Authors
Ian M. Miller, Jeffrey S. Pigati, R. Scott Anderson, Kirk R. Johnson, Shannon Mahan, Thomas A. Ager, Richard G. Baker, Maarten Blaauw, Jordon Bright, Peter M. Brown, Bruce Bryant, Zachary T. Calamari, Paul E. Carrara, Cherney Michael D., John R. Demboski, Scott A. Elias, Daniel C. Fisher, Harrison J. Gray, Danielle R. Haskett, Jeffrey S. Honke, Stephen T. Jackson, Gonzalo Jiménez-Moreno, Douglas Kline, Eric M. Leonard, Nathaniel A. Lifton, Carol Lucking, H. Gregory McDonald, Dane M. Miller, Daniel R. Muhs, Stephen E. Nash, Cody Newton, James B. Paces, Lesley Petrie, Mitchell A. Plummer, David F. Porinchu, Adam N. Rountrey, Eric Scott, Joseph J. W. Sertich, Saxon E. Sharpe, Gary L. Skipp, Laura E. Strickland, Richard K. Stucky, Robert S. Thompson, Jim Wilson
Identification of last interglacial deposits in eastern Beringia: a cautionary note from the Palisades, interior Alaska
Last interglacial sediments in unglaciated Alaska and Yukon (eastern Beringia) are commonly identified by palaeoecological indicators and stratigraphic position ~2-5m above the regionally prominent Old Crow tephra (124 + or - 10ka). We demonstrate that this approach can yield erroneous age assignments using data from a new exposure at the Palisades, a site in interior Alaska with numerous exposure
Authors
Alberto V. Reyes, Grant D. Zazula, Svetlana Kuzmina, Thomas A. Ager, Duane G. Froese
Marine tephrochronology of the Mt. Edgecumbe volcanic field, southeast Alaska, USA
The Mt. Edgecumbe Volcanic Field (MEVF), located on Kruzof Island near Sitka Sound in southeast Alaska, experienced a large multiple-stage eruption during the last glacial maximum (LGM)-Holocene transition that generated a regionally extensive series of compositionally similar rhyolite tephra horizons and a single well-dated dacite (MEd) tephra. Marine sediment cores collected from adjacent basins
Authors
Jason A. Addison, James E. Beget, Thomas A. Ager, Bruce P. Finney
Late Quaternary paleoclimate of western Alaska inferred from fossil chironomids and its relation to vegetation histories
Fossil Chironomidae assemblages (with a few Chaoboridae and Ceratopogonidae) from Zagoskin and Burial Lakes in western Alaska provide quantitative reconstructions of mean July air temperatures for periods of the late-middle Wisconsin (~39,000-34,000 cal yr B.P.) to the present. Inferred temperatures are compared with previously analyzed pollen data from each site summarized here by indirect ordina
Authors
Joshua Kurek, Les C. Cwynar, Thomas A. Ager, Mark B. Abbott, Mary E. Edwards
Pollen-based biome reconstructions for Latin America at 0, 6000 and 18 000 radiocarbon years ago
The biomisation method is used to reconstruct Latin American vegetation at 6000±500 and 18 000±1000 radiocarbon years before present (14C yr BP) from pollen data. Tests using modern pollen data from 381 samples derived from 287 locations broadly reproduce potential natural vegetation. The strong temperature gradient associated with the Andes is recorded by a transition from high altitude cool gras
Authors
R. Marchant, A. Cleef, S. P. Harrison, H. Hooghiemstra, Vera Markgraf, J. Van Boxel, T. Ager, L. Almeida, R. Anderson, C. Baied, H. Behling, J. C. Berrio, R. Burbridge, S. Bjorck, R. Byrne, M. Bush, J. Duivenvoorden, J. Flenley, P. De Oliveira, B. Van Gee, K. Graf, W. D. Gosling, S. Harbele, T. Van Der Hammen, B. Hansen, S. Horn, P. Kuhry, M.-P. Ledru, F. Mayle, B. Leyden, S. Lozano-Garcia, A. M. Melief, P. Moreno, N. T. Moar, A. Prieto, G. Van Reenen, F. Schabitz, M. Salgado-Labouriau, E. J. Schreve-Brinkman, M. Wille
Late Glacial-Holocene Pollen-Based Vegetation History from Pass Lake, Prince of Wales Island, Southeastern Alaska
A radiocarbon-dated history of vegetation development since late Wisconsin deglaciation has been reconstructed from pollen evidence preserved in a sediment core from Pass Lake on Prince of Wales Island, southeastern Alaska. The shallow lake is in the south-central part of the island and occupies a low pass that was filled by glacial ice of local origin during the late Wisconsin glaciation. The old
Authors
Thomas A. Ager, Joseph G. Rosenbaum
Vegetation response to climate change in Alaska: examples from the fossil record
Preface:
This report was presented as an invited paper at the Fish & Wildlife Service Climate Forum held in Anchorage, Alaska on February 21-23, 2007. The purpose of the talk was to provide some examples of past climate changes that appear to have caused significant responses in Alaskan vegetation. These examples are based on interpretations of dated fossil assemblages (pollen, spores and plant m
Authors
Thomas A. Ager
Environments of northwestern North America before the last glacial maximum
No abstract available.
Authors
John J. Clague, Rolf Mathewes, Thomas A. Ager
Palynology of Eocene strata in the Sagavanirktok and Canning Formations on the North Slope of Alaska
This paper describes, illustrates, and interprets Eocene palynomorph assemblages from the North Slope of Alaska, mainly from 31 outcrop samples from seven stratigraphic sections at Franklin Bluffs on the Sagavanirktok River. The top of the Sagwon Member of the Sagavanirktok Formation is shown to be a thin, coaly, apparently nonmarine sequence almost certainly of early Eocene age; the remainder of
Authors
Norman O. Frederiksen, Lucy E. Edwards, Thomas A. Ager, Thomas P. Sheehan
An evaluation of methods for identifying and interpreting buried soils in late Quaternary loess in Alaska: A section in Geologic studies in Alaska by the U.S. Geological Survey, 1998
The presence of buried soils in Alaskan loess is controversial, and therefore criteria for identifying buried soils in these deposits need to be evaluated. In this paper, morphologic and chemical criteria for identifying buried soils are evaluated by studying modern soils developed mostly in Holocene loess under tundra, boreal forest, and transitional coastal-boreal forest vegetation in different
Authors
Daniel R. Muhs, Thomas A. Ager, Josh M. Been, Joseph G. Rosenbaum, Richard J. Reynolds