- Email: [email protected]
Deglaciation of Cordillera Darwin, southern Chile, during the last termination
Abstracts / Quaternary International 279-280 (2012) 121–232
New glaciers were formed and existing glaciers expanded during the Little Ice Age to their largest extent since the Late Glacial Maximum around year 1900. The extension of warm-based ice again increased. The position of fossil pingos, active pingos and springs in Svalbard has been coupled to the most likely (nearest) glacier. Fossil pingos are related to glaciers that most likely disappeared or lost their accumulation zone during the Holocene Optimum, while flowing springs and pingos are related to larger glaciers, with a continuous groundwater recharge. When a groundwater flow system closed and new permafrost was formed under the glacier and in the discharge zone, it could not be reactivated during the Little Ice Age. THE PAST, CURRENT, AND FUTURE OF NORTH AMERICAN GREAT PLAINS DUNE FIELD RESEARCH: LINKING CHRONOLOGICAL DATA TO CLIMATE
185
these ages indicate that widespread activity began at the height of warming during the Medieval Climatic Anomaly (MCA). Activity continued throughout the MCA but intensified as climate shifted towards cooler conditions between 0.8 ka and 0.7 ka. At the onset of the Little Ice Age (LIA) dune activity decreased, but did not cease, and, by the end of the LIA, activity again intensified between 0.3 ka and 0.2 ka. Dune activity in the Arkansas River valley, especially that of the past 1000 years, is coeval with other Great Plains dune fields and suggests that these dunes, like others throughout the region, were highly sensitive to changes in climate. LATE-GLACIAL AND HOLOCENE ICE FLUCTUATIONS, SCORESBY SUND, EAST GREENLAND
Alan F. Halfen. University of Kansas, United States
Brenda Hall. Earth Science Department & Climate Change Institut, United States
E-mail address: [email protected]
E-mail address: [email protected]
Over the past 30 years, numerous papers have been published on the links between North American Great Plains aeolian dune activity and climate, the majority of which include either 14C- or optically-derived chronologies. Although individual dune field activation can be linked to climatic events, it has been difficult to reconcile patterns of these events across the entire region. Correlating dune activity to climate is problematic for several reasons: (1) the spatial distribution of studied dune fields, and their chronologies, is not consistent across the region, (2) 14C and first-generation optical ages may be unreliable considering recent advances in dating techniques, and (3) it is still not fully understood how climate in central North America is linked to mesoscale and global climate changes. To help overcome these problems, current research has emphasized constraining the geographical and chronological patterns of well-documented megadroughts with high spatial and temporal resolution, optical-age chronologies. In Nebraska, for example, chronologies have identified at least two periods of widespread megadrought activity. Similarly, chronologies from Kansas have been used to show that megadroughts following the MCA extended further east than previously modeled. In the future, enhanced atmospheric models may be able to better link dune activity to climate, however, aeolian research will also play an important role, especially with the release of the INQUA Quaternary Dune Atlas, an extensive geographical and chronological database of global aeolian dune fields. The true potential of this database lies in the quantitative nature of the data. Within Great Plains dune fields, new statistical relationships between aeolian activity and climate may be shown based on longitude, latitude, dune morphology, and other database attributes. This data mining should better help researchers identify past and future drivers of aeolian activity in the region.
The response of the cryosphere to past climate changes affords context for modern ice fluctuations in Greenland. Here, we present data through the late Pleistocene-Holocene transition to present for independent ice caps and outlet glaciers of the adjacent Greenland Ice Sheet in the Scoresby Sund region of East Greenland. During Late-Glacial time, both local ice caps and Greenland ice sheet outlet glaciers produced two prominent moraine sets during the Milne Land Stade. Retreat was accompanied by marine inundation. More than 150 radiocarbon dates of shells in raised beaches and deltas are the basis for two relative sea-level curves, each of which shows very high rates of relative sea-level change typical of recently deglaciated regions. The curves both indicate total uplift (including areas now drowned by rising sea level) of slightly less than 200 m. The marine limit (134 m) dates to w12,400 cal yr B.P. We suggest that this is a close minimum age for formation of the older set of moraines. The second set of Milne Land Stade moraines formed at w11,300 cal yr B.P. Our Holocene data come from landforms and sediments adjacent to mountain glaciers in the Stauning Alper and independent ice caps. Marine terraces extending to the historical (Little Ice Age) drift limit indicate that these glaciers retreated to a position similar to – or less extensive than – at present by w10,000 cal yr B.P. as a response to early Holocene warming. Analysis of glacial landforms, as well as sediments from glacially fed lakes, suggests that ice remained in this retracted state for much of the Holocene, including during the Medieval Warm Period. Our results so far indicate that the only prominent Holocene glacial advance occurred during the Little Ice Age.
MEDIEVAL CLIMATIC ANOMALY AND LITTLE ICE AGE DUNE ACTIVITY IN THE ARKANSAS RIVER VALLEY, CENTRAL GREAT PLAINS, USA
Brenda Hall. Earth Science Department & Climate Change Institut, United States
DEGLACIATION OF CORDILLERA DARWIN, SOUTHERN CHILE, DURING THE LAST TERMINATION
E-mail address: [email protected]
Alan F. Halfen. University of Kansas, United States E-mail address: [email protected]
Aeolian dunes of the Hutchinson, Arkansas Valley and Great Bend Sand Prairie Dune Fields are prominent features in the Arkansas River valley of the Central Great Plains. Collectively, these dune fields form a 10,000-km2 area that spans a 400-km east-west climatic transect of the region. Annual precipitation on the eastern margin averages 750 mm, while precipitation on the western margin averages 390 mm. This dramatic precipitation gradient, together with the geographical position of these dune fields, makes them important locales for studying the influences of past climate on dune activity in the Great Plains. We present a new chronology of dune activity from the Arkansas River valley, which is derived from previously reported ages, new AMS 14C ages, and 110 new optical ages derived over the past two years. Holocene dune sediments directly overlie a system of Pleistocene terraces deposited between 66 ka and 12 ka. Early- and middle-Holocene dune activity, however, has been difficult to reconcile because younger episodes of activity have likely overprinted those older. Nevertheless, isolated areas of the Arkansas River valley show dune activation in the middle Holocene 6-4 ka. The vast majority of activation ages from the Arkansas River valley are from the last 1000 years, and clusters of
The geographic expression and relative phasing of events during the last termination are important for isolating mechanisms behind changes in the climate system and thus for understanding how Earth emerges from an ice age. The Mystery Interval (14.5–17.5 kyr B.P.) is key for understanding the termination because of the apparently contradictory climate signals recorded by proxy records at that time. Here, we present new data from Cordillera Darwin, southernmost Chile (54-55o S, 69-70o W), that show the first evidence of rapid glacier collapse during the Mystery Interval in southern South America. This collapse was coeval with ice recession at some other Southern Hemisphere sites, with increased upwelling in the Drake Passage, with a warming of oceanic SSTs offshore of Chile, and with a rise in atmospheric CO2. Together, these data indicate a coherent response to the start of the termination in the southern middle and high latitudes. HOLOCENE ICE FLUCTUATIONS AT VENTISQUERO CORDILLERA DARWIN, SOUTHERN SOUTH AMERICA
MARINELLI,
Brenda Hall. Earth Science Department & Climate Change Institut, United States E-mail address: [email protected]
New glaciers were formed and existing glaciers expanded during the Little Ice Age to their largest extent since the Late Glacial Maximum around year 1900. The extension of warm-based ice again increased. The position of fossil pingos, active pingos and springs in Svalbard has been coupled to the most likely (nearest) glacier. Fossil pingos are related to glaciers that most likely disappeared or lost their accumulation zone during the Holocene Optimum, while flowing springs and pingos are related to larger glaciers, with a continuous groundwater recharge. When a groundwater flow system closed and new permafrost was formed under the glacier and in the discharge zone, it could not be reactivated during the Little Ice Age. THE PAST, CURRENT, AND FUTURE OF NORTH AMERICAN GREAT PLAINS DUNE FIELD RESEARCH: LINKING CHRONOLOGICAL DATA TO CLIMATE
185
these ages indicate that widespread activity began at the height of warming during the Medieval Climatic Anomaly (MCA). Activity continued throughout the MCA but intensified as climate shifted towards cooler conditions between 0.8 ka and 0.7 ka. At the onset of the Little Ice Age (LIA) dune activity decreased, but did not cease, and, by the end of the LIA, activity again intensified between 0.3 ka and 0.2 ka. Dune activity in the Arkansas River valley, especially that of the past 1000 years, is coeval with other Great Plains dune fields and suggests that these dunes, like others throughout the region, were highly sensitive to changes in climate. LATE-GLACIAL AND HOLOCENE ICE FLUCTUATIONS, SCORESBY SUND, EAST GREENLAND
Alan F. Halfen. University of Kansas, United States
Brenda Hall. Earth Science Department & Climate Change Institut, United States
E-mail address: [email protected]
E-mail address: [email protected]
Over the past 30 years, numerous papers have been published on the links between North American Great Plains aeolian dune activity and climate, the majority of which include either 14C- or optically-derived chronologies. Although individual dune field activation can be linked to climatic events, it has been difficult to reconcile patterns of these events across the entire region. Correlating dune activity to climate is problematic for several reasons: (1) the spatial distribution of studied dune fields, and their chronologies, is not consistent across the region, (2) 14C and first-generation optical ages may be unreliable considering recent advances in dating techniques, and (3) it is still not fully understood how climate in central North America is linked to mesoscale and global climate changes. To help overcome these problems, current research has emphasized constraining the geographical and chronological patterns of well-documented megadroughts with high spatial and temporal resolution, optical-age chronologies. In Nebraska, for example, chronologies have identified at least two periods of widespread megadrought activity. Similarly, chronologies from Kansas have been used to show that megadroughts following the MCA extended further east than previously modeled. In the future, enhanced atmospheric models may be able to better link dune activity to climate, however, aeolian research will also play an important role, especially with the release of the INQUA Quaternary Dune Atlas, an extensive geographical and chronological database of global aeolian dune fields. The true potential of this database lies in the quantitative nature of the data. Within Great Plains dune fields, new statistical relationships between aeolian activity and climate may be shown based on longitude, latitude, dune morphology, and other database attributes. This data mining should better help researchers identify past and future drivers of aeolian activity in the region.
The response of the cryosphere to past climate changes affords context for modern ice fluctuations in Greenland. Here, we present data through the late Pleistocene-Holocene transition to present for independent ice caps and outlet glaciers of the adjacent Greenland Ice Sheet in the Scoresby Sund region of East Greenland. During Late-Glacial time, both local ice caps and Greenland ice sheet outlet glaciers produced two prominent moraine sets during the Milne Land Stade. Retreat was accompanied by marine inundation. More than 150 radiocarbon dates of shells in raised beaches and deltas are the basis for two relative sea-level curves, each of which shows very high rates of relative sea-level change typical of recently deglaciated regions. The curves both indicate total uplift (including areas now drowned by rising sea level) of slightly less than 200 m. The marine limit (134 m) dates to w12,400 cal yr B.P. We suggest that this is a close minimum age for formation of the older set of moraines. The second set of Milne Land Stade moraines formed at w11,300 cal yr B.P. Our Holocene data come from landforms and sediments adjacent to mountain glaciers in the Stauning Alper and independent ice caps. Marine terraces extending to the historical (Little Ice Age) drift limit indicate that these glaciers retreated to a position similar to – or less extensive than – at present by w10,000 cal yr B.P. as a response to early Holocene warming. Analysis of glacial landforms, as well as sediments from glacially fed lakes, suggests that ice remained in this retracted state for much of the Holocene, including during the Medieval Warm Period. Our results so far indicate that the only prominent Holocene glacial advance occurred during the Little Ice Age.
MEDIEVAL CLIMATIC ANOMALY AND LITTLE ICE AGE DUNE ACTIVITY IN THE ARKANSAS RIVER VALLEY, CENTRAL GREAT PLAINS, USA
Brenda Hall. Earth Science Department & Climate Change Institut, United States
DEGLACIATION OF CORDILLERA DARWIN, SOUTHERN CHILE, DURING THE LAST TERMINATION
E-mail address: [email protected]
Alan F. Halfen. University of Kansas, United States E-mail address: [email protected]
Aeolian dunes of the Hutchinson, Arkansas Valley and Great Bend Sand Prairie Dune Fields are prominent features in the Arkansas River valley of the Central Great Plains. Collectively, these dune fields form a 10,000-km2 area that spans a 400-km east-west climatic transect of the region. Annual precipitation on the eastern margin averages 750 mm, while precipitation on the western margin averages 390 mm. This dramatic precipitation gradient, together with the geographical position of these dune fields, makes them important locales for studying the influences of past climate on dune activity in the Great Plains. We present a new chronology of dune activity from the Arkansas River valley, which is derived from previously reported ages, new AMS 14C ages, and 110 new optical ages derived over the past two years. Holocene dune sediments directly overlie a system of Pleistocene terraces deposited between 66 ka and 12 ka. Early- and middle-Holocene dune activity, however, has been difficult to reconcile because younger episodes of activity have likely overprinted those older. Nevertheless, isolated areas of the Arkansas River valley show dune activation in the middle Holocene 6-4 ka. The vast majority of activation ages from the Arkansas River valley are from the last 1000 years, and clusters of
The geographic expression and relative phasing of events during the last termination are important for isolating mechanisms behind changes in the climate system and thus for understanding how Earth emerges from an ice age. The Mystery Interval (14.5–17.5 kyr B.P.) is key for understanding the termination because of the apparently contradictory climate signals recorded by proxy records at that time. Here, we present new data from Cordillera Darwin, southernmost Chile (54-55o S, 69-70o W), that show the first evidence of rapid glacier collapse during the Mystery Interval in southern South America. This collapse was coeval with ice recession at some other Southern Hemisphere sites, with increased upwelling in the Drake Passage, with a warming of oceanic SSTs offshore of Chile, and with a rise in atmospheric CO2. Together, these data indicate a coherent response to the start of the termination in the southern middle and high latitudes. HOLOCENE ICE FLUCTUATIONS AT VENTISQUERO CORDILLERA DARWIN, SOUTHERN SOUTH AMERICA
MARINELLI,
Brenda Hall. Earth Science Department & Climate Change Institut, United States E-mail address: [email protected]