Multibeam bathymetry and sub-bottom profiler data acquired in 2011 from R/V Marcus Langseth in a b... more Multibeam bathymetry and sub-bottom profiler data acquired in 2011 from R/V Marcus Langseth in a broad grid over the Chukchi Sea margin reveal multiple glacigenic features on the top and slopes of the outer Chukchi Shelf/Rise and adjacent Borderland. Glacial lineations record a complex pattern of erosion likely formed by both local glaciation and far-traveled ice shelves/streams sourced from the Laurentide, and possibly East Siberian ice sheets. Multiple till units and stacked debris flows indicate recurrent glacial grounding events. Composite till wedges of several hundred meters thick extend the shelf edge by 10-20 km in places. Distribution of ice-marginal features on the Chukchi Rise suggests stepwise deglacial retreat towards the shelf, backing up the broad bathymetric trough at the eastern side of the Rise. Glacigenic features other than extensive iceberg scouring cannot be identified above 350-m depth, and no glacigenic bedforms are present on the current-swept shallow shelf. Despite the resulting uncertainty with the southern extent of the glaciation, the data suggest a widespread grounded-ice presence on the northern Chukchi Shelf, which makes it an important, previously underestimated component of the Arctic paleo-glacial system.
Sediment cores from the Northwind Ridge, western Arctic Ocean, including uniquely preserved calca... more Sediment cores from the Northwind Ridge, western Arctic Ocean, including uniquely preserved calca- reous microfossils, provide the first continuous proxy record of sea ice in the Arctic Ocean encompassing more than half of the Quaternary. The cores were investigated for foraminiferal assemblages along with coarse grain size and bulk chemical composition. By combination of glacial cycles and unique events reflected in the stratigraphy, the age of the foraminiferal record was estimated as ca 1.5 Ma. Foraminiferal abundances, diversity, and composition of benthic assemblages, especially phytodetritus and polar species, were used as proxies for sea-ice conditions. Foraminiferal Assemblage Zone 2 in the Lower Pleistocene indicates diminished, mostly seasonal sea ice, probably facilitated by enhanced inflow of Pacific waters. A gradual decrease in ice-free season with episodes of abrupt ice expansion is interpreted for the Mid-Pleistocene Transition, consistent with climatic cooling and ice-sheet growth in the Northern Hemisphere. A principal faunal and sedimentary turnover occurred near the EarlyeMiddle Pleistocene boundary ca 0.75 Ma, with mostly perennial sea ice indicated by the overlying Assemblage Zone 1. Two steps of further increase in sea-ice coverage are inferred from foraminiferal assemblage changes in the “Glacial” Pleistocene by ca 0.4 and 0.24 Ma, possibly related to hemispheric (Mid-Brunhes Event) and Laurentide ice sheet growth, respectively. These results suggest that year-round ice in the western Arctic was a norm for the last several 100 ka, in contrast to rapidly disappearing summer ice today.
Sparker and shallow drilling data indicate that the Quaternary deposits in the Central Deep of th... more Sparker and shallow drilling data indicate that the Quaternary deposits in the Central Deep of the Barents Sea are mainly composed of glacigenic sediments. They comprise basal till and proximal and distal glaciomarine sediments deposited during the last glacial cycle. Apparent glaciotectonic features imply strong glacial erosion of Mesozoic bedrock. The general ice movement is assumed to have been from off Novaya Zemlya and it is concluded that the whole eastern Barents Sea was covered by the Late Weichselian ice-sheet.
Arctic sea-ice extent and volume are declining rapidly. Several studies project that the Arctic O... more Arctic sea-ice extent and volume are declining rapidly. Several studies project that the Arctic Ocean may become seasonally ice-free by the year 2040 or even earlier. Putting this into perspective requires information on the history of Arctic sea-ice conditions through the geologic past. This information can be provided by proxy records from the Arctic Ocean floor and from the surrounding coasts. Although existing records are far from complete, they indicate that sea ice became a feature of the Arctic by 47 Ma, following a pronounced decline in atmospheric pCO2 after the Paleocene–Eocene Thermal Optimum, and consistently covered at least part of the Arctic Ocean for no less than the last 13–14 million years. Ice was apparently most widespread during the last 2–3 million years, in accordance with Earth's overall cooler climate. Nevertheless, episodes of considerably reduced sea ice or even seasonally ice-free conditions occurred during warmer periods linked to orbital variations. The last low-ice event related to orbital forcing (high insolation) was in the early Holocene, after which the northern high latitudes cooled overall, with some superimposed shorter-term (multidecadal to millennial-scale) and lower-magnitude variability. The current reduction in Arctic ice cover started in the late 19th century, consistent with the rapidly warming climate, and became very pronounced over the last three decades. This ice loss appears to be unmatched over at least the last few thousand years and unexplainable by any of the known natural variabilities.
Multibeam bathymetry and sub-bottom profiler data acquired in 2011 from R/V Marcus Langseth in a b... more Multibeam bathymetry and sub-bottom profiler data acquired in 2011 from R/V Marcus Langseth in a broad grid over the Chukchi Sea margin reveal multiple glacigenic features on the top and slopes of the outer Chukchi Shelf/Rise and adjacent Borderland. Glacial lineations record a complex pattern of erosion likely formed by both local glaciation and far-traveled ice shelves/streams sourced from the Laurentide, and possibly East Siberian ice sheets. Multiple till units and stacked debris flows indicate recurrent glacial grounding events. Composite till wedges of several hundred meters thick extend the shelf edge by 10-20 km in places. Distribution of ice-marginal features on the Chukchi Rise suggests stepwise deglacial retreat towards the shelf, backing up the broad bathymetric trough at the eastern side of the Rise. Glacigenic features other than extensive iceberg scouring cannot be identified above 350-m depth, and no glacigenic bedforms are present on the current-swept shallow shelf. Despite the resulting uncertainty with the southern extent of the glaciation, the data suggest a widespread grounded-ice presence on the northern Chukchi Shelf, which makes it an important, previously underestimated component of the Arctic paleo-glacial system.
Sediment cores from the Northwind Ridge, western Arctic Ocean, including uniquely preserved calca... more Sediment cores from the Northwind Ridge, western Arctic Ocean, including uniquely preserved calca- reous microfossils, provide the first continuous proxy record of sea ice in the Arctic Ocean encompassing more than half of the Quaternary. The cores were investigated for foraminiferal assemblages along with coarse grain size and bulk chemical composition. By combination of glacial cycles and unique events reflected in the stratigraphy, the age of the foraminiferal record was estimated as ca 1.5 Ma. Foraminiferal abundances, diversity, and composition of benthic assemblages, especially phytodetritus and polar species, were used as proxies for sea-ice conditions. Foraminiferal Assemblage Zone 2 in the Lower Pleistocene indicates diminished, mostly seasonal sea ice, probably facilitated by enhanced inflow of Pacific waters. A gradual decrease in ice-free season with episodes of abrupt ice expansion is interpreted for the Mid-Pleistocene Transition, consistent with climatic cooling and ice-sheet growth in the Northern Hemisphere. A principal faunal and sedimentary turnover occurred near the EarlyeMiddle Pleistocene boundary ca 0.75 Ma, with mostly perennial sea ice indicated by the overlying Assemblage Zone 1. Two steps of further increase in sea-ice coverage are inferred from foraminiferal assemblage changes in the “Glacial” Pleistocene by ca 0.4 and 0.24 Ma, possibly related to hemispheric (Mid-Brunhes Event) and Laurentide ice sheet growth, respectively. These results suggest that year-round ice in the western Arctic was a norm for the last several 100 ka, in contrast to rapidly disappearing summer ice today.
Sparker and shallow drilling data indicate that the Quaternary deposits in the Central Deep of th... more Sparker and shallow drilling data indicate that the Quaternary deposits in the Central Deep of the Barents Sea are mainly composed of glacigenic sediments. They comprise basal till and proximal and distal glaciomarine sediments deposited during the last glacial cycle. Apparent glaciotectonic features imply strong glacial erosion of Mesozoic bedrock. The general ice movement is assumed to have been from off Novaya Zemlya and it is concluded that the whole eastern Barents Sea was covered by the Late Weichselian ice-sheet.
Arctic sea-ice extent and volume are declining rapidly. Several studies project that the Arctic O... more Arctic sea-ice extent and volume are declining rapidly. Several studies project that the Arctic Ocean may become seasonally ice-free by the year 2040 or even earlier. Putting this into perspective requires information on the history of Arctic sea-ice conditions through the geologic past. This information can be provided by proxy records from the Arctic Ocean floor and from the surrounding coasts. Although existing records are far from complete, they indicate that sea ice became a feature of the Arctic by 47 Ma, following a pronounced decline in atmospheric pCO2 after the Paleocene–Eocene Thermal Optimum, and consistently covered at least part of the Arctic Ocean for no less than the last 13–14 million years. Ice was apparently most widespread during the last 2–3 million years, in accordance with Earth's overall cooler climate. Nevertheless, episodes of considerably reduced sea ice or even seasonally ice-free conditions occurred during warmer periods linked to orbital variations. The last low-ice event related to orbital forcing (high insolation) was in the early Holocene, after which the northern high latitudes cooled overall, with some superimposed shorter-term (multidecadal to millennial-scale) and lower-magnitude variability. The current reduction in Arctic ice cover started in the late 19th century, consistent with the rapidly warming climate, and became very pronounced over the last three decades. This ice loss appears to be unmatched over at least the last few thousand years and unexplainable by any of the known natural variabilities.
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Papers by Leonid Polyak
reous microfossils, provide the first continuous proxy record of sea ice in the Arctic Ocean encompassing
more than half of the Quaternary. The cores were investigated for foraminiferal assemblages along with
coarse grain size and bulk chemical composition. By combination of glacial cycles and unique events
reflected in the stratigraphy, the age of the foraminiferal record was estimated as ca 1.5 Ma. Foraminiferal
abundances, diversity, and composition of benthic assemblages, especially phytodetritus and polar
species, were used as proxies for sea-ice conditions. Foraminiferal Assemblage Zone 2 in the Lower
Pleistocene indicates diminished, mostly seasonal sea ice, probably facilitated by enhanced inflow of
Pacific waters. A gradual decrease in ice-free season with episodes of abrupt ice expansion is interpreted
for the Mid-Pleistocene Transition, consistent with climatic cooling and ice-sheet growth in the Northern
Hemisphere. A principal faunal and sedimentary turnover occurred near the EarlyeMiddle Pleistocene
boundary ca 0.75 Ma, with mostly perennial sea ice indicated by the overlying Assemblage Zone 1. Two
steps of further increase in sea-ice coverage are inferred from foraminiferal assemblage changes in the
“Glacial” Pleistocene by ca 0.4 and 0.24 Ma, possibly related to hemispheric (Mid-Brunhes Event) and
Laurentide ice sheet growth, respectively. These results suggest that year-round ice in the western Arctic
was a norm for the last several 100 ka, in contrast to rapidly disappearing summer ice today.
reous microfossils, provide the first continuous proxy record of sea ice in the Arctic Ocean encompassing
more than half of the Quaternary. The cores were investigated for foraminiferal assemblages along with
coarse grain size and bulk chemical composition. By combination of glacial cycles and unique events
reflected in the stratigraphy, the age of the foraminiferal record was estimated as ca 1.5 Ma. Foraminiferal
abundances, diversity, and composition of benthic assemblages, especially phytodetritus and polar
species, were used as proxies for sea-ice conditions. Foraminiferal Assemblage Zone 2 in the Lower
Pleistocene indicates diminished, mostly seasonal sea ice, probably facilitated by enhanced inflow of
Pacific waters. A gradual decrease in ice-free season with episodes of abrupt ice expansion is interpreted
for the Mid-Pleistocene Transition, consistent with climatic cooling and ice-sheet growth in the Northern
Hemisphere. A principal faunal and sedimentary turnover occurred near the EarlyeMiddle Pleistocene
boundary ca 0.75 Ma, with mostly perennial sea ice indicated by the overlying Assemblage Zone 1. Two
steps of further increase in sea-ice coverage are inferred from foraminiferal assemblage changes in the
“Glacial” Pleistocene by ca 0.4 and 0.24 Ma, possibly related to hemispheric (Mid-Brunhes Event) and
Laurentide ice sheet growth, respectively. These results suggest that year-round ice in the western Arctic
was a norm for the last several 100 ka, in contrast to rapidly disappearing summer ice today.