Julie Brigham-Grette

Key Findings and Recommendations

Richard B. Alley et al. — Tue, 24 Jan 2012 11:53:49 PST

Paleoclimatic data provide a highly informative if incomplete history of Arctic climate. Temperature history is especially well recorded, and it commonly allows researchers to accurately reconstruct changes and rates of changes for particular seasons. Precipitation (rain or snow) and the extent of ice on land and sea are some of the many other climate variables that have also been reconstructed. The data also provide insight into the histories of many possible causes of the climate changes and feedback processes that amplify or reduce the resulting changes. Comparing climate with possible causes allows scientists to generate and test hypotheses, and those hypotheses then become the basis for projections of future changes. Arctic data show changes on numerous time scales and indicate many causes and important feedback processes. Changes in greenhouse gases appear to have been especially important in causing climate changes (Chapter 2, section 2.4; Chapter 3, sections 3.4.1 and 3.4.4; Chapter 4, sections 4.4.1 and 4.4.2). Global climate changes have been notably amplified in the Arctic (Chapter 3, section 3.5), and warmer times have melted ice on land and sea (Chapter 6). Statistically valid confidence levels often can be attached to scientific findings, but those confidence levels commonly require many independent samples from a large population. Such a standard can be applied to paleoclimatic data in only some cases, whereas in other cases the necessary archives or interpretative tools are not available. However, expert judgment can also be used to assess confidence. The key findings here cannot all be evaluated rigorously using parametric statistics, but on the basis of assessment by the authors, all of the key findings are at least “likely” as used by the Intergovernmental Panel on Climate Change (more than 66% chance of being correct); the authors believe that the most of the findings are “very likely” (more than a 90% chance of being correct).

History of Arctic Sea Ice

Leonid Polyak et al. — Tue, 24 Jan 2012 11:44:04 PST

The volume and areal extent of Arctic sea ice is rapidly declining, and to put that decline into perspective we need to know the history of Arctic sea ice in the geologic past. Sedimentary proxy records from the Arctic Ocean floor and from the surrounding coasts can provide clues. Although incomplete, existing data outline the development of Arctic sea ice during the last several million years. Some data indicate that sea ice consistently covered at least part of the Arctic Ocean for no less than 13–14 million years, and that ice was most widespread during the last approximately 2 million years in relation with Earth’s overall cooler climate. Nevertheless, episodes of considerably reduced ice cover or even a seasonally ice-free Arctic Ocean probably punctuated even this latter period. Ice diminished episodically during warmer climate events associated with changes in Earth’s orbit on the time scale of tens of thousands of years. Ice cover in the Arctic began to diminish in the late 19th century, and this shrinkage has accelerated during the last several decades. Shrinkages that were both similarly large and rapid have not been documented during at least the last few thousand years, although the paleoclimatic record is sufficiently sparse that similar events might have been missed. Orbital changes have made ice melting less likely than during the previous millennia since the end of the last ice age, making the recent changes especially anomalous. Improved reconstructions of sea-ice history would help clarify just how anomalous these recent changes are.

Temperature and Precipitation History of the Arctic

Gifford H. Miller et al. — Tue, 24 Jan 2012 09:23:25 PST

lands that now support only polar desert and tundra. Global oceanic and atmospheric circulation was substantially different between 3 and 2.5 Ma than subsequently. The development of the first continental ice sheets over North America and Eurasia led to changes in the circulation of both the atmosphere and oceans. The onset of continental glaciation is most clearly defined by the first appearance of rock fragments in sediment cores from the central Atlantic Ocean about 2.6 Ma. These rock fragments, often referred to as ice-rafted debris (IRD), are too heavy to have blown or been washed into the central Atlantic; they must have been delivered by large icebergs emanating from continental ice sheets. The first appearance of IRD marks the onset of the Quaternary Period (2.6–0 Ma), generally equated with “ice-age” time, even though for a small fraction (about 10%) of the time the ice sheets were very likely to have been as small as or smaller than their present size. From about 2.7 to about 0.8 Ma, the ice sheets came and went about every 41 k.y., the same timing as cycles in the tilt of Earth’s axis. Ice sheets grew when Earth’s tilt was at a minimum, resulting in less seasonality (cooler summers, warmer winters), and they melted when tilt was at a maximum and seasonality was at its greatest (warmer summers and cooler winters). For the past 600 k.y., ice sheets have grown larger and ice-age times have been longer, lasting about 100 k.y.; those icy intervals have been separated by brief warm periods (interglaciations), when sea level and ice volumes were close to those at present. The duration of interglaciations ranges from about 10 k.y. to perhaps 40 k.y. The cause of the shift from 41 k.y. to 100 k.y. glacial cycles is still being debated. Most explanations center on the continued gradual planetary cooling that may have produced larger ice sheets that were more resistant to melting, or with removal of soft sedimentary cover over bedrock in glaciated regions that, once removed, increased the frictional coupling of the ice sheet to its bed, resulting in steeper ice-sheet profiles and thicker ice sheets, again more resistant to melting. The relatively warm planetary state during which human civilization developed is the most recent of the warm interglaciations, the Holocene (about 11.5–0 kiloannum (thousands of years ago (ka)). During the penultimate warm interval, about 130–120 ka, solar energy in summer in the northern high latitudes was greater than at any time in the current warm interval. As a consequence, the Arctic summer was about 5°C warmer than at present and almost all glaciers melted completely except for the Greenland Ice Sheet, and even it was reduced in size substantially from its present extent. With the increased ice melt, sea level was about 5 meters (m) higher than at present; the extra melt came from both Greenland and Antarctica as well as from small glaciers (Overpeck et al., 2006; Meier et al., 2007). Although sea ice is difficult to reconstruct, the evidence suggests that the central Arctic Ocean retained some permanent ice cover or was periodically ice free, even though the flow of warm Atlantic water into the Arctic Ocean was very likely to have been greater than during the present warm interval. The Last Glacial Maximum (LGM) peaked about 21 ka when mean annual temperatures in parts of the Arctic were as much as 20°C lower than at present. Ice recession was well underway by 16 ka, and most of the Northern Hemisphere ice sheets had melted by 7 ka. Summertime solar energy rose steadily in the Arctic from 21 ka to a maximum (10% higher than at present) about 11 ka and has been decreasing since then, primarily in response to the precession of the equinoxes causing Earth’s distance from the Sun during Northern Hemisphere summer to decrease from 21 to 11 ka and then to increase to the present. The extra energy received in early Holocene summers warmed summers throughout the Arctic about 1°–3°C above 20th century averages, enough to completely melt many small glaciers throughout the Arctic (although the Greenland Ice Sheet was only slightly smaller than present). Summer sea ice limits were substantially smaller than their 20th century average, and the flow of Atlantic water into the Arctic Ocean was substantially greater. As summer solar energy decreased in the second half of the Holocene, glaciers re-established or advanced, sea ice extended, and the flow of warm Atlantic water into the Arctic Ocean diminished. Late Holocene cooling reached its nadir during the Little Ice Age (about 1250–1850 AD), when sun-blocking volcanic eruptions and perhaps other causes added to the orbital cooling, allowing most Arctic glaciers to reach their maximum Holocene extent. During the warming of the past century and a half, glaciers have receded throughout the Arctic, terrestrial ecosystems have advanced northward, and perennial Arctic Ocean sea ice has diminished. Paleoclimate reconstructions indicate that Arctic temperature changes typically have been larger than corresponding hemispheric or globally averaged changes. This behavior is observed with conditions both warmer and colder than recently, indicating that Arctic amplification is a pervasive feature of the climate system.

Paleoclimate Concepts

Richared B. Alley et al. — Tue, 24 Jan 2012 09:09:57 PST

Interpretation of paleoclimate records requires an understanding of Earth’s climate system, the causes (forcings) of climate changes, and the processes that amplify (positive feedback) or damp (negative feedback) these changes. Paleoclimatologists reconstruct the history of climate from proxies, which are those characteristics of sedimentary deposits that preserve paleoclimate information. A great range of physical, chemical, isotopic, and biological characteristics of lake and ocean sediments, ice cores, cave formations, tree rings, the land surface itself, and more are used to reconstruct past climate. Ages of climate events are obtained by counting annual layers, measuring effects of the decay of radioactive atoms, assessing other changes that accumulate through time at rates that can be assessed accurately, and using time-markers to correlate sediments with others that have had their ages measured more accurately. Not all questions about the history of Earth’s climate can be answered through paleoclimatology: in some cases the necessary sediments are not preserved, or the climatic variable of interest is not recorded in the sediments. Nonetheless, many questions can be answered from the available information. An overview of the history of Arctic climate during the past 65 million years (m.y.) shows a long-term irregular cooling for tens of millions of years. As ice became established in the Arctic, it grew and shrank for tens of thousands of years in regular cycles. During at least the most recent of these cycles, shorter lived, large, and rapid fluctuations occurred, especially around the North Atlantic Ocean. The last 11,000 years or so have remained generally warm and relatively stable, but with small climate changes of varying spacing and size. Assessment of the causes of climate changes, and the records of those causes, shows that reduction in atmospheric carbon-dioxide concentration and changes in continental positions were important in the cooling trend throughout tens of millions of years. The cycling in ice extent was paced by features of Earth’s orbit and amplified by the effects of the ice itself, changes in carbon dioxide and other greenhouse gases, and additional feedbacks. Abrupt climate changes were linked to changes in the circulation of the ocean and the extent of sea ice. Changes in the Sun’s output and in Earth’s orbit, volcanic eruptions, and other factors have contributed to the natural climate changes since the end of the last ice age.

Preface—Why and How to Use This Synthesis and Assessment Report

Joan Fitzpatrick et al. — Tue, 24 Jan 2012 09:00:07 PST

The U.S. Climate Change Science Program (CCSP), a consortium of Federal agencies that investigates climate, has established a Synthesis and Assessment Program as part of its Strategic Plan. A primary objective of the CCSP is to provide the best science-based knowledge possible to support public discussion and government- and private-sector decisions about the risks and opportunities associated with changes in climate and in related environmental systems (U.S. Climate Change Science Program, 2007). The CCSP has identified an initial set of 21 Synthesis and Assessment Products (SAPs) that address the highest-priority research, observation, and information needed to support decisions about issues related to climate change. This assessment, SAP 1.2, focuses on the evidence for and record of past climate change in the Arctic. This SAP is one of three reports that addresses the climate-variability-and-change research element and Goal 1 of the CCSP Strategic Plan to improve knowledge of Earth’s past and present climate and environment, including its natural variability, and improve understanding of the causes of observed variability and change. The development of an improved understanding of natural, long-term cycles in climate is one of the primary goals of the climate research element and Goal 1 of the CCSP (U.S. Climate Change Science Program, 2007). The Arctic region of Earth, by virtue of its sensitivity to the effects of climate change through strong climate feedback mechanisms, has a particularly informative paleoclimate record. Because mechanisms operating in the Arctic and at high northern latitudes are also linked to global climate mechanisms, an examination of how Arctic climate has changed in the past is also globally informative.

Executive Summary

Richard B. Alley et al. — Tue, 24 Jan 2012 08:24:52 PST

Paleoclimate records play a key role in our understanding of Earth’s past and present climate system and in our confidence in predicting future climate changes. Paleoclimate data help to elucidate past and present active mechanisms of climate change by placing the short instrumental record into a longer term context and by permitting models to be tested beyond the limited time that instrumental measurements have been available. Recent observations in the Arctic have identified large ongoing changes and important climate feedback mechanisms that multiply the effects of global-scale climate changes. Ice is especially important in these “Arctic amplification” processes, which also involve the ocean, the atmosphere, and the land surface (vegetation, soils, and water). As discussed in this report, paleoclimate data show that land and sea ice have grown with cooling temperatures and have shrunk with warming ones, amplifying temperature changes while causing and responding to ecosystem shifts and sea-level changes.

Climate Dynamics and Global Environments: A community vision for the next decade in ICDP

Julie Brigham_Grette et al. — Tue, 24 Jan 2012 07:33:48 PST

Today's provocative transformation of the Earth's climate system provides timely scientific impetus to an array of paleolimnological studies aimed at understaning natural climate variability vs. anthropogenic-induced change on global and regional scales. Continental drilling to acquire long paleoclimate records from a strategic network of sites is essential to documenting regional hydrologic and climatic responses to atmospheric change, providing a record that is key to resolving climate dynamics at fine spatial scales relevant to both climate modeling and societal impacts of climate change. An in-depth scientific assessment of natural climate variability based on lake drilling will also allow us to close huge gaps in our knowledge on the impact of climate change on the continental landscape and its ecosystems, vegetation and other biota, and ultimately the human environment. The scientific returns from lake drilling include, e.g., data needed to assess the environmental context of early human evolution, knowledge of paleoseismicity, natural hazard frequency, paleohydrology, and drought. Core scanning technology and other emerging proxy developments continue to propel international standards for initial core processing and storage ensuring the maximum investment return on studies of past continental and environmental change.

Elemental and Isotopic Constraints on the Late Glacial-Holocene Transgression and Paleoceanography of the Chukchi Sea

Zachery J. Lundeen et al. — Tue, 24 Jan 2012 07:05:46 PST

Results obtained from analyses of three sediment cores collected from the Chukchi Shelf at 55m, 80m, and 107m water depths show changes in the composition and quantity of sedimentary organic matter delivered to the core locations from the Late-glacial up to near modern times. Two of the cores (80m, and 107m) show an abrupt and substantial increase in the total organic content and a shift in stable carbon and nitrogen isotopic composition of the organic matter at 8000-9000 years BP. We interpret this shift to be indicative of increased marine primary productivity that subsequently led to the onset of denitrification, as observed today in modern Chukchi Shelf sediments. The shift coincides with the probable re-advance of sea ice coverage at 8500 14C yrs BP, as well as a shift in the Trans Polar Drift. Together, these occurrences suggest a major reorganization of Arctic paleoceanography at 8-9ka that has more or less persisted through the Holocene. A small increase in productivity is also observed at ~11ka in the 80m core that could coincide with the first onset of Bering Strait through-flow following the LGM. Additional studies are underway to help constrain sea ice conditions at various times during the Holocene in the Bering and Chukchi Seas in order to elucidate the relationship between former ice coverage regimes and primary production.

Last Glacial Maximum to Holocene sea surface conditions at Umnak Plateau, Bering Sea, as inferred from diatom, alkenone, and stable isotope records

Beth E. Cassie et al. — Tue, 24 Jan 2012 06:53:31 PST

The Bering Sea gateway between the Pacific and Arctic oceans impacts global climate when glacial-interglacial shifts in shore line position and ice coverage change regional albedo. Previous work has shown that during the last glacial termination and into the Holocene, sea level rises and sea ice coverage diminishes from perennial to absent. Yet, existing work has not quantified sea ice duration or sea surface temperatures (SST) during this transition. Here we combine diatom assemblages with the first alkenone record from the Bering Sea to provide a semiquantitative record of sea ice duration, SST, and productivity change since the Last Glacial Maximum (LGM). During the LGM, diatom assemblages indicate that sea ice covered the southeastern Bering Sea perennially. At 15.1 cal ka B.P., the diatom assemblage shifts to one more characteristic of seasonal sea ice and alkenones occur in the sediments in low concentrations. Deglaciation is characterized by laminated intervals with highly productive and diverse diatom assemblages and inferred high coccolithophorid production. At 11.3 cal ka B.P. the diatom assemblage shifts from one dominated by sea ice species to one dominated by a warmer water, North Pacific species. Simultaneously, the SST increases by 3°C and the southeastern Bering Sea becomes ice-free year-round. Productivity and temperature proxies are positively correlated with independently dated records from elsewhere in the Bering Sea, the Sea of Okhotsk, and the North Pacific, indicating that productivity and SST changes are coeval across the region.

New evidence for high discharge to the Chukchi shelf since the Last Glacial Maximum

Jenna C. Hill et al. — Tue, 24 Jan 2012 06:40:36 PST

Using CHIRP subbottom profiling across the Chukchi shelf, offshore NW Alaska, we observed a large incised valley that measures tens of kilometers in width. The valley appears to have been repeatedly excavated during sea level lowering; however, the two most recent incisions appear to have been downcut during the last sea level rise, suggesting an increase in the volume of discharge. Modern drainage from the northwestern Alaskan margin is dominated by small, low-discharge rivers that do not appear to be large enough to have carved the offshore drainage. The renewed downcutting and incision during the deglaciation and consequent base level rise implies there must have been an additional source of discharge. Paleoprecipitation during deglaciation is predicted to be at least 10% less than modern precipitation and thus cannot account for the higher discharge to the shelf. Glacial meltwater is the most likely source for the increased discharge.

Rapid sea-level rise and Holocene climate in the Chukchi Sea

Lloyd D. Keigwin et al. — Mon, 23 Jan 2012 12:54:54 PST

Three new sediment cores from the Chukchi Sea preserve a record of local paleoenvironment, sedimentation, and flooding of the Chukchi Shelf (50 m) by glacial-eustatic sea-level rise. Radiocarbon dates on foraminifera provide the first marine evidence that the sea invaded Hope Valley (southern Chukchi Sea, 53 m) as early as 12 ka. The lack of significant sediment accumulation since ca. 7 ka in Hope Valley, southeastern Chukchi Shelf, is consistent with decreased sediment supply and fluvial discharge to the shelf as deglaciation of Alaska concluded. Abundant benthic foraminifera from a site west of Barrow Canyon indicate that surface waters were more productive 4–6 ka, and this productivity varied on centennial time scales. An offshore companion to this core contains a 20 m record of the Holocene. These results show that carefully selected core sites from the western Arctic Ocean can have a temporal resolution equal to the best cores from other regions, and that these sites can be exploited for high-resolution studies of the paleoenvironment.

Paloenvironmental Conditions in Western Beringia before and during the Last Glacial Maximum

Julie Brigham_Grette et al. — Mon, 23 Jan 2012 12:44:27 PST

Lake El’gygytgyn’s emerging IPY record of Pliocene to recent Arctic change

Julie Brigham_Grette et al. — Fri, 02 Dec 2011 11:34:40 PST

Lacustrine sediments representing the last 3 glacial cycles from NE Russia chronicle the magnitude and dynamics of millennial-scale change across the western Arctic. Logistics are now underway in a multi-national effort to collect the complete paleoclimate archive from this region back to 3.6 Myr ago.

Sedimentary geochemistry of core PG1351 from Lake El’gygytgyn—a sensitive record of climate variability in the East Siberian Arctic during the past three glacial–interglacial cycles

Martin Melles et al. — Fri, 02 Dec 2011 11:21:33 PST

Abstract The ca. 13 m long sediment core PG1351, recovered in 1998 from the central part of Lake El’gygytgyn, NE Siberia, was investigated for lithostratigraphy, water content, dry bulk density (DBD), total organic carbon (TOC), total nitrogen (TN), total sulphur (TS) and biogenic silica (opal) contents, and for TOC stable isotope ratios (d13CTOC). The event stratigraphy recorded in major differences in sediment composition match variations in regional summer insolation, thus confirming a new age model for this core, which suggests that it spans the last 250 ka BP. Four depositional units of contrasting lithological and biogeochemical composition have been distinguished, reflecting past environmental conditions associated with relatively warm, peak warm, cold and dry, and cold but more moist climate modes. A relatively warm climate, resulting in complete summer melt of the lake ice cover and seasonal mixing of the water column, prevailed during the Holocene and Marine Isotope Stages (MIS) 3, 5.1, 5.3, 6.1, 6.3, 6.5, 7.1–7.3, 7.5, 8.1 and 8.3. MIS 5.5 (Eemian) was characterized by significantly enhanced aquatic primary production and organic matter supply from the catchment, indicating peak warm conditions. During MIS 2, 5.2, 5.4, 6.2 and 6.4 the climate was cold and dry, leading to perennial lake ice cover, little regional snowfall, and a stagnant water body. A cold but more moist climate during MIS 4, 6.6, 7.4, 8.2 and 8.4 is thought to have produced more snow cover on the perennial ice, strongly reducing light penetration and biogenic primary production in the lake. While the cold–warm pattern during the past three glacial–interglacial cycles is probably controlled by changes in regional summer insolation, differences in the intensity of the warm phases and in the degree of aridity (changing snowfall) during cold phases likely were due to changes in atmospheric circulation patterns.

Diatom stratigraphy of the last 250 ka at Lake El’gygytgyn, northeast Siberia

Marina V. Cherapanova et al. — Fri, 02 Dec 2011 09:38:48 PST

Diatom species counts were conducted on 171 sediment samples from the 13-m-long core PG1351 from Lake El’gygytgyn, northeast Siberia. The planktonic Cyclotella ocellata-complex dominates the diatom assemblage through most of the core record, persisting through a variety of climate conditions. Periphytic diatoms, although less abundant, have greater diversity and greater down-core assemblage variation. During warm climate modes, longer summer ice-free conditions may have allowed more complex diatom communities to develop in shallow-water habitats, and enhanced circulation may have increased transport of these diatoms to deeper parts of the lake. Zones of low overall diatom abundance further support inferred intervals of low lake productivity during times of extended lake ice and snow cover. More data on the modern spatial and temporal distribution of diatom species in the Lake El’gygytgyn system will improve inferences from core records.

Inorganic geochemistry of El’gygytgyn Lake sediments (northeastern Russia) as an indicator of paleoclimatic change for the last 250 kyr

Pavel S. Minyuk et al. — Fri, 02 Dec 2011 09:29:34 PST

The inorganic geochemistry of sediments from El’gygytgyn Lake shift in phase with interpreted paleoclimatic fluctuations seen in the record over the past 250 ka. Warm periods, when the lake was seasonally ice free and fully mixed, are characterized by increased concentrations of SiO2, CaO, Na2O, K2O, and Rb, by decreased contents of TiO2, Fe2O3, Al2O3, and MgO, and by a lower chemical index of alteration (CIA). Increased levels of SiO2 reflect increases in limnic productivity whereas many of the other elements and the CIA likely reflect increased hydrological activity coincident with an increase in coarser sand and silt content and a decrease in clay mineral content. For cold/cooler periods when perennial lake ice cover lead to a stratifed water column and anoxic bottom waters, the opposite is generally observed suggesting a decrease in hydrological activity and an increase in postdepositional chemical alteration. Peaks in P2O3 and MnO, coincident with an increased abundance of vivianite, suggest possible linkages to the paleoproductivity of local fish fauna regardless of climate change across the region surrounding Lake El’gygytgyn. Strontium is high in concentration during warmer intervals and may also be linked to paleoproductivity. Enrichment of the post-Eemian portion of the sediment record in niobium, and yttrium appears independent of glacial–interglacial change; rather it may reflect a gradual shift in the geomorphology of the catchment, particularly the hydrology of large alluvial fans along the western side of the lake. In contrast to some lake records, changes in Zr concentration over time suggests only a weak, if any, increase in eolian sediment supply during colder periods.

Sediment fabric, clay mineralogy, and grainsize as indicators of climate change since 65 ka at El’gygytgyn Crater Lake, Northeast Siberia

Celeste A. Asikainen et al. — Fri, 02 Dec 2011 09:14:24 PST

Abstract El’gygytgyn Crater Lake, NE Siberia was investigated for sedimentological proxies for regional climate change with a focus on the past 65 ka. Sedimentological parameters assessed relative to magnetic susceptibility include stratigraphy, grain size, clay mineralogy and crystallinity. Earlier work suggests that intervals of high susceptibility in these sediments are coincident with warmer (interglacial- like) conditions and well-mixed oxygenated bottom waters. In contrast, low susceptibility intervals correlate with cold (glacial-like) conditions when perennial ice-cover resulted in anoxia and the dissolution of magnetic carrier minerals. The core stratigraphy contains both well-laminated to non-laminated sequences. Reduced oxygen and lack of water column mixing preserved laminated sequences in the core. A bioturbation index based upon these laminated and nonlaminated sequences co-varies with total organic carbon (TOC) and magnetic susceptibility. Clay mineral assemblages include illite, highly inter-stratified illite/smectite, and chlorite. Under warm or hydrolyzing conditions on the landscape around the lake, chlorite weathers easily and illite/ smectite abundance increase, which produces an inverse relationship in the relative abundance of these clays. Trends in relative abundance show distinct down-core changes that correlate with shifts in susceptibility. The mean grain-size (6.92 lm) is in the silt-size fraction, with few grains larger than 65 lm. Terrigenous input to the lake comes from over 50 streams that are filtered through storm berms, which limits clastic deposition into the lake system. The sedimentation rate and terrigenous input grain-size is reduced during glacial intervals. Measurements of particle-size distribution indicate that the magnetic susceptibility fluctuations are not related to grain size. Lake El’gygytgyn’s magnetic susceptibility and clay mineralogy preserves regional shifts in climate including many globally recognized events like the Younger Dryas and Bolling/Allerod. The sedimentary deposits reflect the climatic transitions starting with MIS4 through the Holocene transition. This work represents the first extensive sedimentological study of limnic sediment proxies of this age from Chukotka (Fig. 1).

Overview and significance of a 250 ka paleoclimate record from El’gygytgyn Crater Lake, NE Russia

Julie Brigham_Grette et al. — Fri, 02 Dec 2011 08:58:21 PST

Abstract Sediment piston cores from Lake El’gygytgyn (67N, 172E), a 3.6 million year old meteorite impact crater in northeastern Siberia, have been analyzed to extract a multi-proxy millennial- scale climate record extending to nearly 250 ka, with distinct fluctuations in sedimentological, physical, biochemical, and paleoecological parameters. Five major themes emerge from this research. First the pilot cores and seismic data show that El’gygytygn Crater Lake contains what is expected to be the longest, most continuous terrestrial record of past climate change in the entire Arctic back to the time of impact. Second, processes operating in the El’gygytygn basin lead to changes in the limnogeology and the biogeochemistry that reflect robust changes in the regional climate and paleoecology over a large part of the western Arctic. Third, the magnetic susceptibility and other proxies record numerous rapid change events. The recovered lake sediment contains both the best-resolved record of the last interglacial and the longest terrestrial record of millennial scale climate change in the Arctic, yielding a high fidelity multi-proxy record extending nearly 150,000 years beyond what has been obtained from the Greenland Ice Sheet. Fourth, the potential for evaluating teleconnections under different mean climate states is high. Despite the heterogeneous nature of recent Arctic climate change, millennial scale climate events in the North Atlantic/Greenland region are recorded in the most distal regions of the Arctic under variable boundary conditions. Finally, deep drilling of the complete depositional record in Lake El’gygytgyn will offer new insights and, perhaps, surprises into the late Cenozoic evolution of Arctic climate.

Sedimentary geochemistry of a pilot core from Lake El’gygytgyn – a sensitive record of climate variability in the East Siberian Arctic durng the past three climate cycles

Martin Melles et al. — Wed, 30 Nov 2011 13:05:45 PST

The ca. 13 m long sediment core PG1351, recovered in 1998 from the central part of Lake El’gygytgyn, NE Siberia, was investigated for lithostratigraphy, water content, dry bulk density (DBD), total organic carbon (TOC), total nitrogen (TN), total sulphur (TS) and biogenic silica (opal) contents, and for TOC stable isotope ratios (δ13CTOC). The event stratigraphy recorded in major differences in sediment composition match variations in regional summer insolation, thus confirming a new age model for this core, which suggests that it spans the last 250 ka BP. Four depositional units of contrasting lithological and biogeochemical composition have been distinguished, reflecting past environmental conditions associated with relatively warm, peak warm, cold and dry, and cold but more moist climate modes. A relatively warm climate, resulting in complete summer melt of the lake ice cover and seasonal mixing of the water column, prevailed during the Holocene and Marine Isotope Stages (MIS) 3, 5.1, 5.3, 6.1, 6.3, 6.5, 7.1–7.3, 7.5, 8.1 and 8.3. MIS 5.5 (Eemian) was characterized by significantly enhanced aquatic primary production and organic matter supply from the catchment, indicating peak warm conditions. During MIS 2, 5.2, 5.4, 6.2 and 6.4 the climate was cold and dry, leading to perennial lake ice cover, little regional snowfall, and a stagnant water body. A cold but more moist climate during MIS 4, 6.6, 7.4, 8.2 and 8.4 is thought to have produced more snow cover on␣the perennial ice, strongly reducing light penetration and biogenic primary production in␣the lake. While the cold–warm pattern during␣the past three glacial–interglacial cycles is probably controlled by changes in regional summer insolation, differences in the intensity of the warm phases and in the degree of aridity (changing snowfall) during cold phases likely were due to changes in atmospheric circulation patterns.

Luminescence geochronology for sediments from Lake El’gygytgyn, northeast Siberia, Russia: constraining the timeing of paleoenvirommental events for the past 200ka

Steven L. Forman et al. — Wed, 30 Nov 2011 12:12:34 PST

This study focused on the luminescence dating of sediments from Lake El’gygytgyn, a meteorite impact crater 100 km north of the Arctic Circle in northeast Siberia, formed 3.58 Ma ago. The sediment is principally eolian deposited in to a lake with nearly permanently ice. The fine-grained polymineral and quartz extracts taken from nine distinct levels from the upper 12.3 m of sediment core PG1351 were dated by infrared stimulated (IRSL) and green stimulated luminescence (GSL) using multiple aliquot additive dose procedures. The veracity of these ages is evaluated by comparing to an age model for the core derived from magnetic excursions and from correlation of variations of the magnetic susceptibility record to similar magnitude variations in δ 18O in the Greenland Ice core record. The IRSL ages from the upper 9 m of core correspond well with the independent age control for the past ca. 200 ka. However, sediments deeper in the core at 12.3 m with an inferred age of ca. 250 ka age yield a saturated IRSL response and therefore a non-finite OSL age. The youngest sediment dated from 0.70 m depth yielded the IRSL age of ca. 11.5 ka, older than the corresponding age of 9.3–8.8 ka, indicating a discrepancy in dating the youngest sediments in the upper 1 m of core. This study confirms the utility of IRSL by the multiple aliquot additive dose method to date sediments <200 ka old from eastern>Siberia.