Abstract It is generally assumed that regions glaciated by continental ice sheets offer little pr... more Abstract It is generally assumed that regions glaciated by continental ice sheets offer little promise for long paleoenvironmental records due to erosional processes associated with glaciation. We show that beneath portions of the northeastern Laurentide Ice Sheet, characterized by cold-based glaciation, sediment sequences representing multiple interglaciations have been preserved within extant lake basins. Radiocarbon and optically stimulated luminescence dating confirm the antiquity of the sediments, thereby extending ...
Abstract It is generally assumed that regions glaciated by continental ice sheets offer little pr... more Abstract It is generally assumed that regions glaciated by continental ice sheets offer little promise for long paleoenvironmental records due to erosional processes associated with glaciation. We show that beneath portions of the northeastern Laurentide Ice Sheet, characterized by cold-based glaciation, sediment sequences representing multiple interglaciations have been preserved within extant lake basins.
Until the ADCC was founded, data were usually made publicly accessible, at the discretion of the ... more Until the ADCC was founded, data were usually made publicly accessible, at the discretion of the investigator, through structured data centers. Published final results were available, but the raw data were not distributed as frequently. Therefore, the ADCC focused initially on collecting raw data from the then-small community of ARCSS scientists. These data were usually structured or documented in a manner easy for the principal investigator (PI) to understand and use.
Geochemical, mineralogical and biological indicators preserved in sediments are widely used to re... more Geochemical, mineralogical and biological indicators preserved in sediments are widely used to reconstruct past climate change, but proxies differ in the degree to which their utility as climate indicators has been validated via laboratory experiments, modern spatial calibrations, or down-core comparisons with instrumental climate data. Multi-proxy studies provide another means of evaluating interpretations of proxies. This paper presents a multi-proxy assessment comparing 19 sub-centennially resolved late Holocene proxy records, covering the period 300-1900 AD, from seven Icelandic marine and lacustrine core sites. We employ simple statistical comparisons between proxy reconstructions to evaluate their correlations over time and, ultimately, their utility as proxies for regional climate. Proxies examined include oxygen isotopic composition of benthic and planktonic foraminifera, abundance of the sea-ice biomarker IP 25 , allochthonous quartz in marine sediments (a proxy for drift ice around Iceland), marine carbonate abundance, total organic carbon concentration, chironomid assemblages, lacustrine biogenic silica and carbon/nitrogen ratios in lake sediments. Most of the examined proxy records, including temperature and sea-ice proxies, correlate strongly with each other over multi-centennial timescales, and thus do appear to record changes in regional climate.
Abstract Quaternary interglacial periods provide glimpses of a warmer Arctic and useful perspecti... more Abstract Quaternary interglacial periods provide glimpses of a warmer Arctic and useful perspectives on possible future conditions, but records of Arctic terrestrial conditions over multiple interglacial periods are rare. Here, we take advantage of a site in the Canadian Arctic where lacustrine sediments representing the past three interglacial periods are preserved in an extant lake. We use subfossil insects (chironomids) preserved in this exceptional sedimentary archive to derive temperature reconstructions through the ...
A continuous record of insect (Chironomidae) remains preserved in lake sediments is used to infer... more A continuous record of insect (Chironomidae) remains preserved in lake sediments is used to infer temperature changes at a small lake in Arctic Canada through the Holocene. Early Holocene summers at the study site were characterized by more thermophilous assemblages and warmer inferred temperatures than today, presumably in response to the positive anomaly in Northern Hemisphere summer insolation. Peak early Holocene warmth was interrupted by two cold reversals between 9.5 and 8 cal ka BP, during which multiple cold-stenothermous chironomid taxa appeared in the lake. The earlier reversal appears to correlate with widespread climate anomalies around 9.2 cal ka BP; the age of the younger reversal is equivocal but it may correlate with the 8.2 cal ka BP cold event documented elsewhere. Widespread, abrupt climate shifts in the early Holocene illustrate the susceptibility of the climate system to perturbations, even during periods of enhanced warmth in the Northern Hemisphere.
A sedimentary record from lake Stora Viðarvatn in northeast Iceland records environmental changes... more A sedimentary record from lake Stora Viðarvatn in northeast Iceland records environmental changes over the past 2000 years. Downcore data include chironomid (Diptera: Chironomidae) assemblage data and total organic carbon, nitrogen, and biogenic silica content. Sample scores from detrended correspondence analysis (DCA) of chironomid assemblage data are well correlated with measured temperatures at Stykkishólmur over the 170 year instrumental record, indicating that chironomid assemblages at Stora Viðarvatn have responded sensitively to past temperature changes. DCA scores appear to be useful for quantitatively inferring past temperatures at this site. In contrast, a quantitative chironomid-temperature transfer function developed for northwestern Iceland does a relatively poor job of reconstructing temperature shifts, possibly due to the lake's large size and depth relative to the calibration sites or to the limited resolution of the subfossil taxonomy. The pre-instrumental climate history inferred from chironomids and other paleolimnological proxies is supported by prior inferences from historical documents, glacier reconstructions, and paleoceanographic studies. Much of the first millennium AD was relatively warm, with temperatures comparable to warm decades of the twentieth century. Temperatures during parts of the tenth and eleventh centuries AD may have been comparably warm. Biogenic silica concentrations declined, carbon:nitrogen ratios increased, and some chironomid taxa disappeared from the lake between the thirteenth and nineteenth centuries, recording the decline of temperatures into the Little Ice Age, increasing soil erosion, and declining lake productivity. All the proxy reconstructions indicate that the most severe Little Ice Age conditions occurred during the eighteenth and nineteenth centuries, a period historically associated with maximum sea-ice and glacier extent around Iceland. This is one of fourteen papers published in a special issue dedicated to reconstructing late Holocene climate change from Arctic lake sediments. The special issue is a contribution to the International Polar Year and was edited
Multiproxy climate records from Iceland document complex changes in terrestrial climate and glaci... more Multiproxy climate records from Iceland document complex changes in terrestrial climate and glacier fluctuations through the Holocene, revealing some coherent patterns of change as well as significant spatial variability. Most studies on the Last Glacial Maximum and subsequent deglaciation reveal a dynamic Iceland Ice Sheet (IIS) that responded abruptly to changes in ocean currents and sea level. The IIS broke up catastrophically around 15 ka as the Polar Front migrated northward and sea level rose. Indications of regional advance or halt of the glaciers are seen in late Allerö d/early Younger Dryas time and again in PreBoreal time. Due to the apparent rise of relative sea level in Iceland during this time, most sites contain evidence for fluctuating, tidewater glacier termini occupying paleo fjords and bays. The time between the end of the Younger Dryas and the Preboreal was characterized by repeated jö kulhlaups that eroded glacial deposits. By 10.3 ka, the main ice sheet was in rapid retreat across the highlands of Iceland. The Holocene thermal maximum (HTM) was reached after 8 ka with land temperatures estimated to be 3 C higher than the 1961-1990 reference, and net precipitation similar to modern. Such temperatures imply largely ice-free conditions across Iceland in the early to mid-Holocene. Several marine and lacustrine sediment climate proxies record substantial summer temperature depression between 8.5 and 8 ka, but no moraines have been detected from that time. Termination of the HTM and onset of Neoglacial cooling took place sometime after 6 ka with increased glacier activity between 4.5 and 4.0 ka, intensifying between 3.0 and 2.5 ka. Although a distinct warming during the Medieval Warm Period is not dramatically apparent in Icelandic records, the interval from ca AD 0 to 1200 is commonly characterized by relative stability with slow rates of change. The literature most commonly describes Little Ice Age moraines (ca AD 1250-1900) as representing the most extensive ice margins since early Holocene deglaciation, with temperature depressions of 1-2 C compared to the AD 1961-1990 average. Steep north-south and west-east temperature gradients are reconstructed in the Holocene records of Iceland, suggesting a strong maritime influence on the terrestrial climate of Iceland.
The Arctic has a disproportionately large response to changes in radiative forcing of climate, an... more The Arctic has a disproportionately large response to changes in radiative forcing of climate, and arctic lacustrine ecosystems respond sensitively to these changes. The goal of this research is to generate high-resolution climate records for the past two millennia using multiple proxies in order to place 20th and 21st century climate and environmental change into a long-term context. We use a 14 C-and 210 Pb-dated surface core from Lake CF8 on northeastern Baffin Island, Arctic Canada to generate a high-resolution multiproxy reconstruction of climate and environmental change. Throughout the late Holocene, primary productivity in Lake CF8 was low, but increased almost 20-fold in the past 200 years. Insect (Chironomidae) assemblages also show dramatic changes since 1950 AD, with cold stenothermous chironomid taxa disappearing from the record altogether. These changes in productivity and chironomid assemblages are unprecedented in the past 5,000 years. The dramatic ecological shifts that occurred at Lake CF8 have also been observed elsewhere in the Arctic, and will likely continue at ever-increasing rates as anthropogenic inputs of green house gases continue to cause climate warming and enhanced lacustrine primary production.
The Holocene temperature history of Iceland is not well known, despite Iceland's climatically str... more The Holocene temperature history of Iceland is not well known, despite Iceland's climatically strategic location at the intersection of major surface currents in the high-latitude North Atlantic. Existing terrestrial records reveal spatially heterogeneous changes in Iceland's glacier extent, vegetation cover, and climate over the Holocene, but these records are temporally discontinuous and mostly qualitative. This paper presents the first quantitative estimates of temperatures throughout the entire Holocene on Iceland. Mean July temperatures are inferred based upon subfossil midge (Chironomidae) assemblages from three coastal lakes in northern Iceland. Midge data from each of the three lakes indicate broadly similar temperature trends, and suggest that the North Icelandic coast experienced relatively cool early Holocene summers and gradual warming throughout the Holocene until after 3 ka. This contrasts with many sites on Iceland and around the high-latitude Northern Hemisphere that experienced an early to mid-Holocene ''thermal maximum'' in response to enhanced summer insolation forcing. Our results suggest a heightened temperature gradient across Iceland in the early Holocene, with suppressed terrestrial temperatures along the northern coastal fringe, possibly as a result of sea surface conditions on the North Iceland shelf. r
Reconstructions of past environmental changes are critical for understanding the natural variabil... more Reconstructions of past environmental changes are critical for understanding the natural variability of Earth's climate system and for providing a context for present and future global change. Radiocarbon-dated lake sediments from Lake CF3, northeastern Baffin Island, Arctic Canada, are used to reconstruct past environmental conditions over the last 11,200 years. Numerous proxies, including chironomidinferred July air temperatures, diatom-inferred lakewater pH, and sediment organic matter, reveal a pronounced Holocene thermal maximum as much as 5-C warmer than historic summer temperatures from¨10,000 to 8500 cal yr B.P. Following rapid cooling¨8500 cal yr B.P., Lake CF3 proxies indicate cooling through the late Holocene. At many sites in northeastern Canada, the Holocene thermal maximum occurred later than at Lake CF3; this late onset of Holocene warmth is generally attributed to the impacts of the decaying Laurentide Ice Sheet on early Holocene temperatures in northeastern Canada. However, the lacustrine proxies in Lake CF3 apparently responded to insolation-driven warmth, despite the proximity of Lake CF3 to the Laurentide Ice Sheet and its meltwater. The magnitude and timing of the Holocene thermal maximum at Lake CF3 indicate that temperatures and environmental conditions at this site are highly sensitive to changes in radiative forcing.
UMI, ProQuest ® Dissertations & Theses. The world's most... more UMI, ProQuest ® Dissertations & Theses. The world's most comprehensive collection of dissertations and theses. Learn more... ProQuest, Interglacial temperature variability in the high-latitude North Atlantic region inferred from ...
Abstract It is generally assumed that regions glaciated by continental ice sheets offer little pr... more Abstract It is generally assumed that regions glaciated by continental ice sheets offer little promise for long paleoenvironmental records due to erosional processes associated with glaciation. We show that beneath portions of the northeastern Laurentide Ice Sheet, characterized by cold-based glaciation, sediment sequences representing multiple interglaciations have been preserved within extant lake basins. Radiocarbon and optically stimulated luminescence dating confirm the antiquity of the sediments, thereby extending ...
Abstract It is generally assumed that regions glaciated by continental ice sheets offer little pr... more Abstract It is generally assumed that regions glaciated by continental ice sheets offer little promise for long paleoenvironmental records due to erosional processes associated with glaciation. We show that beneath portions of the northeastern Laurentide Ice Sheet, characterized by cold-based glaciation, sediment sequences representing multiple interglaciations have been preserved within extant lake basins.
Until the ADCC was founded, data were usually made publicly accessible, at the discretion of the ... more Until the ADCC was founded, data were usually made publicly accessible, at the discretion of the investigator, through structured data centers. Published final results were available, but the raw data were not distributed as frequently. Therefore, the ADCC focused initially on collecting raw data from the then-small community of ARCSS scientists. These data were usually structured or documented in a manner easy for the principal investigator (PI) to understand and use.
Geochemical, mineralogical and biological indicators preserved in sediments are widely used to re... more Geochemical, mineralogical and biological indicators preserved in sediments are widely used to reconstruct past climate change, but proxies differ in the degree to which their utility as climate indicators has been validated via laboratory experiments, modern spatial calibrations, or down-core comparisons with instrumental climate data. Multi-proxy studies provide another means of evaluating interpretations of proxies. This paper presents a multi-proxy assessment comparing 19 sub-centennially resolved late Holocene proxy records, covering the period 300-1900 AD, from seven Icelandic marine and lacustrine core sites. We employ simple statistical comparisons between proxy reconstructions to evaluate their correlations over time and, ultimately, their utility as proxies for regional climate. Proxies examined include oxygen isotopic composition of benthic and planktonic foraminifera, abundance of the sea-ice biomarker IP 25 , allochthonous quartz in marine sediments (a proxy for drift ice around Iceland), marine carbonate abundance, total organic carbon concentration, chironomid assemblages, lacustrine biogenic silica and carbon/nitrogen ratios in lake sediments. Most of the examined proxy records, including temperature and sea-ice proxies, correlate strongly with each other over multi-centennial timescales, and thus do appear to record changes in regional climate.
Abstract Quaternary interglacial periods provide glimpses of a warmer Arctic and useful perspecti... more Abstract Quaternary interglacial periods provide glimpses of a warmer Arctic and useful perspectives on possible future conditions, but records of Arctic terrestrial conditions over multiple interglacial periods are rare. Here, we take advantage of a site in the Canadian Arctic where lacustrine sediments representing the past three interglacial periods are preserved in an extant lake. We use subfossil insects (chironomids) preserved in this exceptional sedimentary archive to derive temperature reconstructions through the ...
A continuous record of insect (Chironomidae) remains preserved in lake sediments is used to infer... more A continuous record of insect (Chironomidae) remains preserved in lake sediments is used to infer temperature changes at a small lake in Arctic Canada through the Holocene. Early Holocene summers at the study site were characterized by more thermophilous assemblages and warmer inferred temperatures than today, presumably in response to the positive anomaly in Northern Hemisphere summer insolation. Peak early Holocene warmth was interrupted by two cold reversals between 9.5 and 8 cal ka BP, during which multiple cold-stenothermous chironomid taxa appeared in the lake. The earlier reversal appears to correlate with widespread climate anomalies around 9.2 cal ka BP; the age of the younger reversal is equivocal but it may correlate with the 8.2 cal ka BP cold event documented elsewhere. Widespread, abrupt climate shifts in the early Holocene illustrate the susceptibility of the climate system to perturbations, even during periods of enhanced warmth in the Northern Hemisphere.
A sedimentary record from lake Stora Viðarvatn in northeast Iceland records environmental changes... more A sedimentary record from lake Stora Viðarvatn in northeast Iceland records environmental changes over the past 2000 years. Downcore data include chironomid (Diptera: Chironomidae) assemblage data and total organic carbon, nitrogen, and biogenic silica content. Sample scores from detrended correspondence analysis (DCA) of chironomid assemblage data are well correlated with measured temperatures at Stykkishólmur over the 170 year instrumental record, indicating that chironomid assemblages at Stora Viðarvatn have responded sensitively to past temperature changes. DCA scores appear to be useful for quantitatively inferring past temperatures at this site. In contrast, a quantitative chironomid-temperature transfer function developed for northwestern Iceland does a relatively poor job of reconstructing temperature shifts, possibly due to the lake's large size and depth relative to the calibration sites or to the limited resolution of the subfossil taxonomy. The pre-instrumental climate history inferred from chironomids and other paleolimnological proxies is supported by prior inferences from historical documents, glacier reconstructions, and paleoceanographic studies. Much of the first millennium AD was relatively warm, with temperatures comparable to warm decades of the twentieth century. Temperatures during parts of the tenth and eleventh centuries AD may have been comparably warm. Biogenic silica concentrations declined, carbon:nitrogen ratios increased, and some chironomid taxa disappeared from the lake between the thirteenth and nineteenth centuries, recording the decline of temperatures into the Little Ice Age, increasing soil erosion, and declining lake productivity. All the proxy reconstructions indicate that the most severe Little Ice Age conditions occurred during the eighteenth and nineteenth centuries, a period historically associated with maximum sea-ice and glacier extent around Iceland. This is one of fourteen papers published in a special issue dedicated to reconstructing late Holocene climate change from Arctic lake sediments. The special issue is a contribution to the International Polar Year and was edited
Multiproxy climate records from Iceland document complex changes in terrestrial climate and glaci... more Multiproxy climate records from Iceland document complex changes in terrestrial climate and glacier fluctuations through the Holocene, revealing some coherent patterns of change as well as significant spatial variability. Most studies on the Last Glacial Maximum and subsequent deglaciation reveal a dynamic Iceland Ice Sheet (IIS) that responded abruptly to changes in ocean currents and sea level. The IIS broke up catastrophically around 15 ka as the Polar Front migrated northward and sea level rose. Indications of regional advance or halt of the glaciers are seen in late Allerö d/early Younger Dryas time and again in PreBoreal time. Due to the apparent rise of relative sea level in Iceland during this time, most sites contain evidence for fluctuating, tidewater glacier termini occupying paleo fjords and bays. The time between the end of the Younger Dryas and the Preboreal was characterized by repeated jö kulhlaups that eroded glacial deposits. By 10.3 ka, the main ice sheet was in rapid retreat across the highlands of Iceland. The Holocene thermal maximum (HTM) was reached after 8 ka with land temperatures estimated to be 3 C higher than the 1961-1990 reference, and net precipitation similar to modern. Such temperatures imply largely ice-free conditions across Iceland in the early to mid-Holocene. Several marine and lacustrine sediment climate proxies record substantial summer temperature depression between 8.5 and 8 ka, but no moraines have been detected from that time. Termination of the HTM and onset of Neoglacial cooling took place sometime after 6 ka with increased glacier activity between 4.5 and 4.0 ka, intensifying between 3.0 and 2.5 ka. Although a distinct warming during the Medieval Warm Period is not dramatically apparent in Icelandic records, the interval from ca AD 0 to 1200 is commonly characterized by relative stability with slow rates of change. The literature most commonly describes Little Ice Age moraines (ca AD 1250-1900) as representing the most extensive ice margins since early Holocene deglaciation, with temperature depressions of 1-2 C compared to the AD 1961-1990 average. Steep north-south and west-east temperature gradients are reconstructed in the Holocene records of Iceland, suggesting a strong maritime influence on the terrestrial climate of Iceland.
The Arctic has a disproportionately large response to changes in radiative forcing of climate, an... more The Arctic has a disproportionately large response to changes in radiative forcing of climate, and arctic lacustrine ecosystems respond sensitively to these changes. The goal of this research is to generate high-resolution climate records for the past two millennia using multiple proxies in order to place 20th and 21st century climate and environmental change into a long-term context. We use a 14 C-and 210 Pb-dated surface core from Lake CF8 on northeastern Baffin Island, Arctic Canada to generate a high-resolution multiproxy reconstruction of climate and environmental change. Throughout the late Holocene, primary productivity in Lake CF8 was low, but increased almost 20-fold in the past 200 years. Insect (Chironomidae) assemblages also show dramatic changes since 1950 AD, with cold stenothermous chironomid taxa disappearing from the record altogether. These changes in productivity and chironomid assemblages are unprecedented in the past 5,000 years. The dramatic ecological shifts that occurred at Lake CF8 have also been observed elsewhere in the Arctic, and will likely continue at ever-increasing rates as anthropogenic inputs of green house gases continue to cause climate warming and enhanced lacustrine primary production.
The Holocene temperature history of Iceland is not well known, despite Iceland's climatically str... more The Holocene temperature history of Iceland is not well known, despite Iceland's climatically strategic location at the intersection of major surface currents in the high-latitude North Atlantic. Existing terrestrial records reveal spatially heterogeneous changes in Iceland's glacier extent, vegetation cover, and climate over the Holocene, but these records are temporally discontinuous and mostly qualitative. This paper presents the first quantitative estimates of temperatures throughout the entire Holocene on Iceland. Mean July temperatures are inferred based upon subfossil midge (Chironomidae) assemblages from three coastal lakes in northern Iceland. Midge data from each of the three lakes indicate broadly similar temperature trends, and suggest that the North Icelandic coast experienced relatively cool early Holocene summers and gradual warming throughout the Holocene until after 3 ka. This contrasts with many sites on Iceland and around the high-latitude Northern Hemisphere that experienced an early to mid-Holocene ''thermal maximum'' in response to enhanced summer insolation forcing. Our results suggest a heightened temperature gradient across Iceland in the early Holocene, with suppressed terrestrial temperatures along the northern coastal fringe, possibly as a result of sea surface conditions on the North Iceland shelf. r
Reconstructions of past environmental changes are critical for understanding the natural variabil... more Reconstructions of past environmental changes are critical for understanding the natural variability of Earth's climate system and for providing a context for present and future global change. Radiocarbon-dated lake sediments from Lake CF3, northeastern Baffin Island, Arctic Canada, are used to reconstruct past environmental conditions over the last 11,200 years. Numerous proxies, including chironomidinferred July air temperatures, diatom-inferred lakewater pH, and sediment organic matter, reveal a pronounced Holocene thermal maximum as much as 5-C warmer than historic summer temperatures from¨10,000 to 8500 cal yr B.P. Following rapid cooling¨8500 cal yr B.P., Lake CF3 proxies indicate cooling through the late Holocene. At many sites in northeastern Canada, the Holocene thermal maximum occurred later than at Lake CF3; this late onset of Holocene warmth is generally attributed to the impacts of the decaying Laurentide Ice Sheet on early Holocene temperatures in northeastern Canada. However, the lacustrine proxies in Lake CF3 apparently responded to insolation-driven warmth, despite the proximity of Lake CF3 to the Laurentide Ice Sheet and its meltwater. The magnitude and timing of the Holocene thermal maximum at Lake CF3 indicate that temperatures and environmental conditions at this site are highly sensitive to changes in radiative forcing.
UMI, ProQuest ® Dissertations & Theses. The world's most... more UMI, ProQuest ® Dissertations & Theses. The world's most comprehensive collection of dissertations and theses. Learn more... ProQuest, Interglacial temperature variability in the high-latitude North Atlantic region inferred from ...
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