- Email: [email protected]
Permafrost records from the easternmost edge of Beringia (Yukon Coast, Canada)
152
Abstracts / Quaternary International 279-280 (2012) 121–232
discuss implications of these findings for current models of Holocene ice retreat in the region.
RELICT ICE AND THERMOKARST DURING PAST INTERGLACIATIONS IN EASTERN BERINGIA
PERMAFROST RECORDS FROM THE EASTERNMOST EDGE OF BERINGIA (YUKON COAST, CANADA)
Duane G. Froese. University of Alberta, Canada
Michael Fritz. Alfred Wegener Insitute for Polar and Marine Resea, Germany
Relict permafrost is a widespread feature of the non-glaciated western Arctic and Subarctic of North America, having survived past intervals of climate as warm or warmer than present in the early Holocene (ca. 11,500 yr BP), the last interglaciation (ca. 120,000 yr BP) and earlier interglaciations of the Middle Pleistocene. In the western Arctic of North America these intervals show conditions similar to modern or modest warming on the scale of 1-3 degrees C, near analogous to projected warming this century. In the case of the early Holocene, these conditions persisted over centuries to a few thousand years, while warmer conditions during the last interglaciation persisted for several millennia, with a surface vegetation cover similar to present. In each of these warmer intervals, there is evidence for widespread thawing of shallow permafrost, including development of thermokarst lakes, active layer deepening and initiation of retrogressive thaw slumps. The local response depends strongly on site conditions, but where independent geochronology is available thaw appears synchronous. The widespread thaw of shallow permafrost is contrasted at several sites by the preservation of relict ice wedges locally exceeding several hundred thousand years in age. Regional persistence of relict ground ice suggests both an antiquity and resilience of discontinuous permafrost. The message from these paleo studies appears to be that even modest warming can lead to widespread and severe shallow thaw, and that deeper permafrost, that more than several metres in depth, is likely a persistent, ancient feature of the western Arctic cryosphere.
E-mail address: [email protected]
The Yukon Coastal Plain facing the Southern Beaufort Sea was only partly glaciated during the last glacial maximum (LGM). Large areas remained ice-free and became part of the vast unglaciated land mass ? Beringia ? and are therefore an excellent study site to reconstruct paleoenvironmental dynamics where records since the Late Pleistocene are still sparse. Multiproxy analyses on sediments and stable isotope analyses on ground ice (ice wedges, pore ice) have been performed to unravel periglacial processes towards sedimentary history, permafrost aggradation and degradation through time as well as to link these processes to distinct periods of climatic change. Stratigraphic appraisals within the glacial limit are generally difficult due to the deformed nature of the morainic ridge sediments. Beyond the glacial limit, radiocarbon dated peat and ice wedge cast fillings suggest that until 11.4 cal ka BP bioproductivity was inhibited due to continuous harsh climate conditions. During the Holocene Thermal Maximum (HTM) thaw lakes developed as a result of extensive thermokarst and a rapid accumulation of peat followed on polygonal ground. An active layer thickening is recorded by a widespread thaw unconformity along the Yukon coast at depths between 1.2 to 2.0 m below surface. The oxygen isotopic signature of Holocene ice wedges and recent ice veins varies between w24 to w20 &, which is in good agreement with recent temperatures that are supposed to produce d18O values of about w20 & in the study area. In contrast, relict ice wedges below a distinctive thaw unconformity revealed d18O values from w30 to w27 &. The combination of sedimentary and ground ice records leads to the conclusion that the study area holds environmental records of at least three episodes of ice wedge growth and active thermokarst, i.e. Late Pleistocene cold period Early Holocene warm interval - Mid-Holocene climate deterioration. LATE HOLOCENE CLIMATE CHANGES IN THE EURASIAN ARCTIC RECORDED IN THE AKADEMII NAUK ICE CORE (SEVERNAYA ZEMLYA) Diedrich Fritzsche. Alfred Wegener Institute for Polar and Marine Rese, Germany E-mail address: [email protected]
The 724 m deep ice core drilled recently on the relatively low-altitude Akademii Nauk (AN) ice cap (Severnaya Zemlya, 80.52 N, 94.82 E, about 750 m a.s.l.) is shown to provide high-resolution climate proxy data from the Western Eurasian Arctic, although the ice cap is affected by melt water infiltration. We present stable water isotope data (d18O and deuterium excess) for approximately the last two millennia in annual to decadal resolution. The core chronology is based on volcanic reference layers and annual layer counting (stable isotopes). The multi-annual AN d18O data are highly correlated to instrumental temperature data from the Western Eurasian Arctic (e.g. r ¼ 0.76 for Vardø/Northern Norway, 1840-1998) and thus provide a valuable near-surface temperature proxy for this region. AN d18O data reveal major temperature changes in the last two millennia, e.g. the absolute minimum around 1800 and the exceptional warming to the double-peaked early 20th century maximum, which represents the warmest temperatures in the Late Holocene. A long-term decrease of AN d18O data does not solely reflect climate cooling but probably also the growth of AN ice cap. Neither a pronounced Medieval Warm Period nor a Little Ice Age could be identified. However, AN proxy records show evidence for several rapid climate changes, e.g. strong warming and cooling events in the 15th and 16th centuries. They indicate considerable shifts in the internal dynamics of the Arctic climate system comprising changes in the atmospheric circulation patterns and accompanied sea ice extent changes. AN d18O values coincide good with that of the Austfonna ice core (Svalbard), underlining the regional significance of AN ice core data. Variations in the deuterium excess data indicate changes in moisture generation and transport, probably related to changes in the atmospheric circulation patterns and/or sea ice dynamics.
E-mail address: [email protected]
LATE QUATERNARY PALAEOCLIMATE OF THE SOUTHERN LEVANT FROM STROMATOLITES AND SPELEOTHEMS OF THE DEAD SEA REGION Amos Frumkin. The Hebrew University, Israel E-mail address: [email protected]
Calcite speleothems are a hitherto hardly documented occurrence in the nowadays arid to hyper-arid rain-shadow Dead Sea area of eastern Israel. Speleothem ages (U-Th) from two caves on the Dead Sea Fault Escarpment and two caves from arid rain-shadow areas surrounding the Dead Sea, span the last three glacial cycles from ca. 354 to 12 ka and suggest episodic wet local palaeoclimate mainly during the glacial periods of Marine Isotopic Stages (MIS) 6 and 4 to 2. U-Th ages of stromatolites deposited in the Late Pleistocene Lake Lisan and preserved in caves of the Dead Sea Fault Escarpment, suggest that regional relatively wet climate affected the lake catchment area during the late part of (relatively warm) MIS-3 lasting until middle (cold) MIS-2, as well as at the MIS-5 to 4 (interglacialglacial) transition. Speleothem deposition periods spanning the 38.4 0.5 to 16.4 0.3 ka time interval, i.e. late MIS-3 to early MIS-2, representing moist periods in the lake area, are coeval to regional wet conditions inferred by the stromatolite record. A direct connection is thus implied between local and regional climate at the latest Pleistocene based on correlation between two independent data sets. This connection implies that glacial climate has generally been moister than interglacial climate during the last glacial-interglacial cycle at both local and regional scales around the Dead Sea and its predecessors. This suggests southward migration of the northern hemisphere climatic belts during glacial periods. This migration did not invade the Sahsra arid belt which remained dry during the last glacial period. THE TEMPORAL AND SPATIAL QUANTIFICATION OF HOLOCENE SEDIMENT DYNAMICS IN A MESO-SCALE CATCHMENT IN NORTHERN BAVARIA / GERMANY Markus Fuchs. Universität Bayreuth, Germany E-mail address: [email protected]
The Aufsess River catchment (97 km2) in northern Bavaria, Germany, is studied to establish a Holocene sediment budget and to investigate the sediment dynamics since the early times of farming in the 3rd millennium
Abstracts / Quaternary International 279-280 (2012) 121–232
discuss implications of these findings for current models of Holocene ice retreat in the region.
RELICT ICE AND THERMOKARST DURING PAST INTERGLACIATIONS IN EASTERN BERINGIA
PERMAFROST RECORDS FROM THE EASTERNMOST EDGE OF BERINGIA (YUKON COAST, CANADA)
Duane G. Froese. University of Alberta, Canada
Michael Fritz. Alfred Wegener Insitute for Polar and Marine Resea, Germany
Relict permafrost is a widespread feature of the non-glaciated western Arctic and Subarctic of North America, having survived past intervals of climate as warm or warmer than present in the early Holocene (ca. 11,500 yr BP), the last interglaciation (ca. 120,000 yr BP) and earlier interglaciations of the Middle Pleistocene. In the western Arctic of North America these intervals show conditions similar to modern or modest warming on the scale of 1-3 degrees C, near analogous to projected warming this century. In the case of the early Holocene, these conditions persisted over centuries to a few thousand years, while warmer conditions during the last interglaciation persisted for several millennia, with a surface vegetation cover similar to present. In each of these warmer intervals, there is evidence for widespread thawing of shallow permafrost, including development of thermokarst lakes, active layer deepening and initiation of retrogressive thaw slumps. The local response depends strongly on site conditions, but where independent geochronology is available thaw appears synchronous. The widespread thaw of shallow permafrost is contrasted at several sites by the preservation of relict ice wedges locally exceeding several hundred thousand years in age. Regional persistence of relict ground ice suggests both an antiquity and resilience of discontinuous permafrost. The message from these paleo studies appears to be that even modest warming can lead to widespread and severe shallow thaw, and that deeper permafrost, that more than several metres in depth, is likely a persistent, ancient feature of the western Arctic cryosphere.
E-mail address: [email protected]
The Yukon Coastal Plain facing the Southern Beaufort Sea was only partly glaciated during the last glacial maximum (LGM). Large areas remained ice-free and became part of the vast unglaciated land mass ? Beringia ? and are therefore an excellent study site to reconstruct paleoenvironmental dynamics where records since the Late Pleistocene are still sparse. Multiproxy analyses on sediments and stable isotope analyses on ground ice (ice wedges, pore ice) have been performed to unravel periglacial processes towards sedimentary history, permafrost aggradation and degradation through time as well as to link these processes to distinct periods of climatic change. Stratigraphic appraisals within the glacial limit are generally difficult due to the deformed nature of the morainic ridge sediments. Beyond the glacial limit, radiocarbon dated peat and ice wedge cast fillings suggest that until 11.4 cal ka BP bioproductivity was inhibited due to continuous harsh climate conditions. During the Holocene Thermal Maximum (HTM) thaw lakes developed as a result of extensive thermokarst and a rapid accumulation of peat followed on polygonal ground. An active layer thickening is recorded by a widespread thaw unconformity along the Yukon coast at depths between 1.2 to 2.0 m below surface. The oxygen isotopic signature of Holocene ice wedges and recent ice veins varies between w24 to w20 &, which is in good agreement with recent temperatures that are supposed to produce d18O values of about w20 & in the study area. In contrast, relict ice wedges below a distinctive thaw unconformity revealed d18O values from w30 to w27 &. The combination of sedimentary and ground ice records leads to the conclusion that the study area holds environmental records of at least three episodes of ice wedge growth and active thermokarst, i.e. Late Pleistocene cold period Early Holocene warm interval - Mid-Holocene climate deterioration. LATE HOLOCENE CLIMATE CHANGES IN THE EURASIAN ARCTIC RECORDED IN THE AKADEMII NAUK ICE CORE (SEVERNAYA ZEMLYA) Diedrich Fritzsche. Alfred Wegener Institute for Polar and Marine Rese, Germany E-mail address: [email protected]
The 724 m deep ice core drilled recently on the relatively low-altitude Akademii Nauk (AN) ice cap (Severnaya Zemlya, 80.52 N, 94.82 E, about 750 m a.s.l.) is shown to provide high-resolution climate proxy data from the Western Eurasian Arctic, although the ice cap is affected by melt water infiltration. We present stable water isotope data (d18O and deuterium excess) for approximately the last two millennia in annual to decadal resolution. The core chronology is based on volcanic reference layers and annual layer counting (stable isotopes). The multi-annual AN d18O data are highly correlated to instrumental temperature data from the Western Eurasian Arctic (e.g. r ¼ 0.76 for Vardø/Northern Norway, 1840-1998) and thus provide a valuable near-surface temperature proxy for this region. AN d18O data reveal major temperature changes in the last two millennia, e.g. the absolute minimum around 1800 and the exceptional warming to the double-peaked early 20th century maximum, which represents the warmest temperatures in the Late Holocene. A long-term decrease of AN d18O data does not solely reflect climate cooling but probably also the growth of AN ice cap. Neither a pronounced Medieval Warm Period nor a Little Ice Age could be identified. However, AN proxy records show evidence for several rapid climate changes, e.g. strong warming and cooling events in the 15th and 16th centuries. They indicate considerable shifts in the internal dynamics of the Arctic climate system comprising changes in the atmospheric circulation patterns and accompanied sea ice extent changes. AN d18O values coincide good with that of the Austfonna ice core (Svalbard), underlining the regional significance of AN ice core data. Variations in the deuterium excess data indicate changes in moisture generation and transport, probably related to changes in the atmospheric circulation patterns and/or sea ice dynamics.
E-mail address: [email protected]
LATE QUATERNARY PALAEOCLIMATE OF THE SOUTHERN LEVANT FROM STROMATOLITES AND SPELEOTHEMS OF THE DEAD SEA REGION Amos Frumkin. The Hebrew University, Israel E-mail address: [email protected]
Calcite speleothems are a hitherto hardly documented occurrence in the nowadays arid to hyper-arid rain-shadow Dead Sea area of eastern Israel. Speleothem ages (U-Th) from two caves on the Dead Sea Fault Escarpment and two caves from arid rain-shadow areas surrounding the Dead Sea, span the last three glacial cycles from ca. 354 to 12 ka and suggest episodic wet local palaeoclimate mainly during the glacial periods of Marine Isotopic Stages (MIS) 6 and 4 to 2. U-Th ages of stromatolites deposited in the Late Pleistocene Lake Lisan and preserved in caves of the Dead Sea Fault Escarpment, suggest that regional relatively wet climate affected the lake catchment area during the late part of (relatively warm) MIS-3 lasting until middle (cold) MIS-2, as well as at the MIS-5 to 4 (interglacialglacial) transition. Speleothem deposition periods spanning the 38.4 0.5 to 16.4 0.3 ka time interval, i.e. late MIS-3 to early MIS-2, representing moist periods in the lake area, are coeval to regional wet conditions inferred by the stromatolite record. A direct connection is thus implied between local and regional climate at the latest Pleistocene based on correlation between two independent data sets. This connection implies that glacial climate has generally been moister than interglacial climate during the last glacial-interglacial cycle at both local and regional scales around the Dead Sea and its predecessors. This suggests southward migration of the northern hemisphere climatic belts during glacial periods. This migration did not invade the Sahsra arid belt which remained dry during the last glacial period. THE TEMPORAL AND SPATIAL QUANTIFICATION OF HOLOCENE SEDIMENT DYNAMICS IN A MESO-SCALE CATCHMENT IN NORTHERN BAVARIA / GERMANY Markus Fuchs. Universität Bayreuth, Germany E-mail address: [email protected]
The Aufsess River catchment (97 km2) in northern Bavaria, Germany, is studied to establish a Holocene sediment budget and to investigate the sediment dynamics since the early times of farming in the 3rd millennium