Sepp Kipfstuhl

High-resolution record of Northern Hemisphere climate extending into the last interglacial period

Two deep ice cores from central Greenland, drilled in the 1990s, have played a key role in climate reconstructions of the Northern Hemisphere, but the oldest sections of the cores were disturbed in chronology owing to ice folding near the bedrock. Here we present an undisturbed climate record from a North Greenland ice core, which extends back to 123,000 years before the present, within the last interglacial period. The oxygen isotopes in the ice imply that climate was stable during the last interglacial period, with temperatures 5 °C warmer than today. We find unexpectedly large temperature differences between our new record from northern Greenland and the undisturbed sections of the cores from central Greenland, suggesting that the extent of ice in the Northern Hemisphere modulated the latitudinal temperature gradients in Greenland. This record shows a slow decline in temperatures that marked the initiation of the last glacial period. Our record reveals a hitherto unrecognized warm period initiated by an abrupt climate warming about 115,000 years ago, before glacial conditions were fully developed. This event does not appear to have an immediate Antarctic counterpart, suggesting that the climate see-saw between the hemispheres (which dominated the last glacial period) was not operating at this time.Two deep ice cores from central Greenland, drilled in the 1990s, have played a key role in climate reconstructions of the Northern Hemisphere, but the oldest sections of the cores were disturbed in chronology owing to ice folding near the bedrock. Here we present an undisturbed climate record from a North Greenland ice core, which extends back to 123,000 years before the present, within the last interglacial period. The oxygen isotopes in the ice imply that climate was stable during the last interglacial period, with temperatures 5 °C warmer than today. We find unexpectedly large temperature differences between our new record from northern Greenland and the undisturbed sections of the cores from central Greenland, suggesting that the extent of ice in the Northern Hemisphere modulated the latitudinal temperature gradients in Greenland. This record shows a slow decline in temperatures that marked the initiation of the last glacial period. Our record reveals a hitherto unrecognized warm period initiated by an abrupt climate warming about 115,000 years ago, before glacial conditions were fully developed. This event does not appear to have an immediate Antarctic counterpart, suggesting that the climate see-saw between the hemispheres (which dominated the last glacial period) was not operating at this time.

One-to-one coupling of glacial climate variability in Greenland and Antarctica.

Precise knowledge of the phase relationship between climate changes in the two hemispheres is a key for understanding the Earth’s climate dynamics. For the last glacial period, ice core studies have revealed strong coupling of the largest millennial-scale warm events in Antarctica with the longest Dansgaard–Oeschger events in Greenland through the Atlantic meridional overturning circulation. It has been unclear, however, whether the shorter Dansgaard–Oeschger events have counterparts in the shorter and less prominent Antarctic temperature variations, and whether these events are linked by the same mechanism. Here we present a glacial climate record derived from an ice core from Dronning Maud Land, Antarctica, which represents South Atlantic climate at a resolution comparable with the Greenland ice core records. After methane synchronization with an ice core from North Greenland, the oxygen isotope record from the Dronning Maud Land ice core shows a one-to-one coupling between all Antarctic warm events and Greenland Dansgaard–Oeschger events by the bipolar seesaw6. The amplitude of the Antarctic warm events is found to be linearly dependent on the duration of the concurrent stadial in the North, suggesting that they all result from a similar reduction in the meridional overturning circulation.

Timing and climate forcing of volcanic eruptions for the past 2,500 years

Volcanic eruptions contribute to climate variability, but quantifying these contributions has been limited by inconsistencies in the timing of atmospheric volcanic aerosol loading determined from ice cores and subsequent cooling from climate proxies such as tree rings. Here we resolve these inconsistencies and show that large eruptions in the tropics and high latitudes were primary drivers of interannual-to-decadal temperature variability in the Northern Hemisphere during the past 2,500 years. Our results are based on new records of atmospheric aerosol loading developed from high-resolution, multi-parameter measurements from an array of Greenland and Antarctic ice cores as well as distinctive age markers to constrain chronologies. Overall, cooling was proportional to the magnitude of volcanic forcing and persisted for up to ten years after some of the largest eruptive episodes. Our revised timescale more firmly implicates volcanic eruptions as catalysts in the major sixth-century pandemics, famines, and socioeconomic disruptions in Eurasia and Mesoamerica while allowing multi-millennium quantification of climate response to volcanic forcing.

A new bipolar ice core record of volcanism from WAIS Divide and NEEM and implications for climate forcing of the last 2000 years

Volcanism is a natural climate forcing causing short-term variations in temperatures. Histories of volcanic eruptions are needed to quantify their role in climate variability and assess human impacts. We present two new seasonally resolved, annually dated non-sea-salt sulfur records from polar ice cores - WAIS Divide (WDC06A) from West Antarctica spanning 408 B.C.E. to 2003 C.E. and NEEM (NEEM-2011-S1) from Greenland spanning 78 to 1997 C.E. - both analyzed using high-resolution continuous flow analysis coupled to two mass spectrometers. The high dating accuracy allowed placing the large bi-hemispheric deposition event ascribed to the eruption of Kuwae in Vanuatu (previously thought to be 1452/1453 C.E. and used as a tie-point in ice core dating) into the year 1458/1459 C.E. This new age is consistent with an independent ice core timescale from Law Dome and explains an apparent delayed response in tree rings to this volcanic event. A second volcanic event is detected in 1453 C.E. in both ice cores. We show for the first time ice core signals in Greenland and Antarctica from the strong eruption of Taupo in New Zealand in 232 C.E. In total, 133 volcanic events were extracted from WDC06A and 138 from NEEM-2011-S1, with 50 ice core signals - predominantly from tropical source volcanoes - identified simultaneously in both records. We assess the effect of large bipolar events on temperature-sensitive tree ring proxies. These two new volcanic records, synchronized with available ice core records to account for spatial variability in sulfate deposition, provide a basis for improving existing time series of volcanic forcing.

Ice core evidence for a very tight link between North Atlantic and east Asian glacial climate

[1] Corresponding millennial-scale climate changes have been reported from the North Atlantic region and from east Asia for the last glacial period on independent timescales only. To assess their degree of synchrony we suggest interpreting Greenland ice core dust parameters as proxies for the east Asian monsoon systems. This allows comparing North Atlantic and east Asian climate on the same timescale in high resolution ice core data without relative dating uncertainties. We find that during Dansgaard-Oeschger events North Atlantic region temperature and east Asian storminess were tightly coupled and changed synchronously within 5–10 years with no systematic lead or lag, thus providing instantaneous climatic feedback. The tight link between North Atlantic and east Asian glacial climate could have amplified changes in the northern polar cell to larger scales. We further find evidence for an early onset of a Younger Dryas-like event in continental Asia, which gives

Revision of the EPICA Dome C CO2 record from 800 to 600 kyr before present

The European Project for Ice Coring in Antarctica Dome ice core from Dome C (EDC) has allowed for the reconstruction of atmospheric CO2 concentrations for the last 800,000 years. Here we revisit the oldest part of the EDC CO2 record using different air extraction methods and sections of the core. For our established cracker system, we found an analytical artifact, which increases over the deepest 200 m and reaches 10.1 ± 2.4 ppm in the oldest/deepest part. The governing mechanism is not yet fully understood, but it is related to insufficient gas extraction in combination with ice relaxation during storage and ice structure. The corrected record presented here resolves partly - but not completely - the issue with a different correlation between CO2 and Antarctic temperatures found in this oldest part of the records. In addition, we provide here an update of 800,000 years atmospheric CO2 history including recent studies covering the last glacial cycle.

A search in north Greenland for a new ice-core drill site

A new deep ice-core drilling site has been identified in north Greenland at 75.12°N, 42.30°W, 316 km north-northwest (NNW) of the GRIP drill site on the summit of the ice sheet. The ice thickness here is 3085 m; the surface elevation is 2919 m. The North GRIP (NGRIP) site is identified so that ice of Eemian age (115-130 ka BP, calendar years before present) is located as far above bedrock as possible and so the thickness of the Eemian layer is as great as possible. An ice-flow model, similar to the one used to date the GRIP ice core, is used to simulate the flow along the NNW-trending ice ridge. Surface and bedrock elevations, surface accumulation-rate distribution and ratio-echo sounding along the ridge have been used as model input. The surface accumulation rate drops from 0.23 m ice equivalent year -1 at GRIP to 0.19 m ice equivalent year -1 50 km from GRIP. Over the following 300 km the accumulation is relatively constant, before is starts decreasing again further north. Ice thickness up to 3250 m bring the temperature of the basal ice up to the pressure-melting point 100-250 km from GRIP. The NGRIP site is located 316 km from GRIP in a region where the bedrock is smooth and the accumulation rate is 0.19 m ice equivalent year -1 . The modeled basal ice here has always been a few degrees below the pressure-melting point. Internal radio-echo sounding horizons can be traced between the GRIP and NGRIP sites, allowing us to date the ice down to 2300 m depth (52 ka BP). An ice-flow model predicts that the Eemian-age ice will be located in the depth range 2710-2800 m, which is 285 m above the bedrock. This is 120 m further above the bedrock, and the thickness of the Eemian layer of ice is 20 m thicker, than at the GRIP ice-core site.

Visual stratigraphy of the North Greenland Ice Core Project (NorthGRIP) ice core during the last glacial period

[1] A continuous high-resolution record of digital images has been obtained from the North Greenland Ice Core Project (NorthGRIP) ice core (75.1� N, 42.3� W) in the depth interval from 1330 m to the bedrock at 3085 m. The ice core stratigraphy is clearly visible throughout the glacial period with the most frequent and brightest visible layers appearing during the coldest events. Down to a depth of 2600 m the horizontal layering is very regular; below this depth, small irregularities in the layering start to appear, and below 2800 m the visual stratigraphy becomes more uncertain, perhaps because of penetration into climatically warmer ice. Comparison of the visual stratigraphy with high-resolution continuous records of chemical impurities and dust reveals a high degree of correlation, which indicates that the visible layers are caused by these impurities. A new approach is used to automatically determine annual layer thicknesses from the visual stratigraphy record by carrying out a frequency analysis of the most prominent visible layers in the profile. The result gives strong support for the NorthGRIP timescale model.

Recent Greenland Accumulation Estimated from Regional Climate Model Simulations and Ice Core Analysis

Abstract The accumulation defined as “precipitation minus evaporation” over Greenland has been simulated with the high-resolution limited-area regional climate model HIRHAM4 applied over an Arctic integration domain. This simulation is compared with a revised estimate of annual accumulation rate distribution over Greenland taking into account information from a new set of ice core analyses, based on surface sample collections from the North Greenland Traverse. The region with accumulation rates below 150 mm yr−1 in central-northwest Greenland is much larger than previously assumed and extends about 500 km farther to the south. It is demonstrated that good agreement between modeled and observed regional precipitation and accumulation patterns exists, particularly concerning the location and the values of very low accumulation in the middle of Greenland. The accumulation rates in the northern part of Greenland are reduced in comparison to previous estimates. These minima are connected with a prevailing bloc...

Antarctic-wide array of high-resolution ice core records reveals pervasive lead pollution began in 1889 and persists today

Interior Antarctica is among the most remote places on Earth and was thought to be beyond the reach of human impacts when Amundsen and Scott raced to the South Pole in 1911. Here we show detailed measurements from an extensive array of 16 ice cores quantifying substantial toxic heavy metal lead pollution at South Pole and throughout Antarctica by 1889 – beating polar explorers by more than 22 years. Unlike the Arctic where lead pollution peaked in the 1970s, lead pollution in Antarctica was as high in the early 20th century as at any time since industrialization. The similar timing and magnitude of changes in lead deposition across Antarctica, as well as the characteristic isotopic signature of Broken Hill lead found throughout the continent, suggest that this single emission source in southern Australia was responsible for the introduction of lead pollution into Antarctica at the end of the 19th century and remains a significant source today. An estimated 660 t of industrial lead have been deposited over Antarctica during the past 130 years as a result of mid-latitude industrial emissions, with regional-to-global scale circulation likely modulating aerosol concentrations. Despite abatement efforts, significant lead pollution in Antarctica persists into the 21st century.