PP31E-01
Greenhouse Gas Concentration Records Extended Back to 800,000 Years From the EPICA Dome C Ice Core
The deep ice core recovered from Dome Concordia in the framework of EPICA, the European Project for Ice Coring in Antarctica, has extended the record of Antarctic climate history back to 800,000 years [Jouzel et al., 2007]. We present the current status of measurements of CO2, CH4 and N2O on air trapped in the bubbles of the Dome C ice core. CO2 is measured in two laboratories using different techniques (laser absorption spectroscopy or gas chromatography on samples of 8 and 40 g of ice which are mechanically crushed or milled, respectively). CH4 and N2O are extracted using a melt-refreeze technique and then measured by gas chromatography (in two laboratories for CH4). The greenhouse gas concentrations have now been measured on the lowest 200 m of the Dome C core, going back to Marine Isotope Stage 20 (MIS 20) as verified by a consistent gas age/ice age difference determined at termination IX [Jouzel et al., 2007]. The atmospheric CO2 concentration mostly lagged the Antarctic temperature with a rather strong correlation throughout the eight and a half glacial cycles, but with significantly lower CO2 values between 650 and 750 kyr BP. Its lowest level ever measured in ice cores (172 ppmv) is observed during MIS 16 (minimum centered at 667 kyr BP according to the EDC3 chronology) redetermining the natural span of CO2 to 172-300 ppmv. With 2245 individual measurements, the CH4 concentration is now reconstructed over 800,000 years from a single core, with an average time resolution of 380 years. Spectral analyses of the CH4 signal show an increasing contribution of precession during the last four climatic cycles compared with the four older ones, suggesting an increasing impact of low latitudes sources/sinks. Millennial scale features in this very detailed signal allows us to compare their occurrence with ice volume reconstructions and the isotopic composition of precipitation over the East Antarctic plateau. N2O is still affected by glaciological artefacts involving dust content in the ice, and its exact temporal evolution remains to be deciphered. These measurements represent the basis of the so-called "EPICA Challenge" [Wolff et al., 2005]: they will put the climate and carbon cycle modelers under the challenge of fully understanding how orbital parameters and climate system configurations could have built such tight coupling between atmospheric composition and natural climate change during the late Quaternary. Jouzel et al., Science 317, 793-796, 10 August 2007 Wolff et al., EOS 86, N°38, 341-345, 20 September 2005
PP31E-02 INVITED
Dust and climate interactions
Mineral aerosol fluctuations are correlated with climate change proxies within ice and marine paleorecords. These fluctuations are thought to be indicators of large scale changes in aridity and transport patterns. The ability of dust fluctuations at individual points to be indicators of regional climate change will be considered through model reconstructions for different time periods and scenarios. In addition to indicating climate change, dust fluctuations can drive climate change through direct forcing of the atmospheric radiative budget. Simulations from the last glacial maximum, preindustrial and current climate are used as examples showing the radiative forcing and climate feedback from dust during these different time periods.
PP31E-03
Dust Provenance in Antarctic ice During Glacial Periods: Calibrating the Dust Emission Record of Southern South America.
Much of the researches dedicated to study the provenance of sediments in Antarctica ice cores and sediment cores in the ocean promoted not-too-convincing conclusions in some of their interpretations, mainly due to unawareness on the actual composition of sediments derived from Patagonia and important source areas of southern South America (SSA). Most of the latest works [e.g. EPICA community members, 2006; Fischer et al., 2007] that attempted to model and understand the increase of dust deposition in Antarctic ice during last glacial periods used Patagonia as the most obvious provenance area. However, it was indicated recently that Patagonia could only explain the composition of a few Antarctic dust samples [Gaiero et al., 2007a], which implied that other dust sources should be taken into account in order to improve atmospheric circulation models and to better understand the changes in source areas during glacial periods. This work mainly focuses on the origin of those Antarctic dust samples that do not have a Patagonian signature. This is made by using isotopic composition of sediments from different southern latitude environments; i.e., exploring the role played by the Argentinean shelf and the Argentinean loess as possible direct sources of this non-Patagonian signature [Gaiero, 2007b]. The study concludes that both areas should not be considered as significant dust sources during glacial times highlighting, however, the importance of the Argentinean loess to understand the sources that contributed to its accumulation and hence, to understand the long-range dust transport in the Southern Hemisphere. Based on isotopic data and on environmental characteristics it is demonstrated that along Patagonia, the Puna-Altiplano plateau (10S-26S) should be an extra important subtropical dust source. EPICA Community Membres (2006), One-to-one coupling of glacial climate variability in Greenland and Antarctica. Nature, 444, 195-198. Fischer H., et al. (2007), Reconstruction of millennial changes in dust emission, transport and regional sea ice coverage using the deep EPICA ice cores from tha Atlantic and Indian Ocean sector of Antarctica, Earth and Planet. Sci. Lett., 260, 340-354. Gaiero, D.M., et al. (2007a), A uniform isotopic and chemical signature of dust exported from Patagonia: Rock sources and occurrence in southern environments, Chem. Geol. 238, 107-120. Gaiero, D.M. (2007b), Dust Provenance In Antarctic Ice During Glacial Periods: from where in the Southern Hemisphere? Geophys. Res. Lett. (doi 10.10292007GL030520).
PP31E-04
Atmospheric CO2 and climate change on millennial time scales during the last glacial period
How atmospheric CO2 varies and is controlled on millennial time scale is an important question for understanding how the carbon cycle and climate change are linked. Common time scales for climate proxies and atmospheric CO2 are needed to answer this question. Here we provide atmospheric CO2 records from ~90 to 20 ka BP (thousand years before 1950) from the Byrd ice core, on a chronology synchronized with Greenland ice core records, allowing direct comparison of CO2 with Greenlandic and Antarctic temperature proxies, Heinrich events and atmospheric CH4. Atmospheric CO2 rose several thousand years before abrupt warming in Greenland associated with Dansgaard- Oeschger events, 2, 4, 8, 12, 14, 17, 19, 20, and 21, and the start of CO2 increases predates massive ice discharge events (H events 2, 3, 4, 5, 5a, 6) by 0 to 3 ka. The CO2 increase rate was rapidly reduced at the Greenland warming (which also corresponds to a maximum in Antarctic temperature) for each of these events, implying a global mechanism that can simultaneously affect atmospheric CO2 and temperature in both hemispheres. The CO2 decrease following Antarctic temperature maxima/abrupt Greenland warming event lagged those features by several centuries. CO2 variations during millennial events of the last ice age have features in common with the CO2 rise during the last glacial termination, including tight correlation with Antarctic warming, a several thousand year lead relative to Greenland warming, and possibly small jumps in CO2 at the time of abrupt Greenland warming.
PP31E-05
The Influence of Sea-Level Rise on Atmospheric CO2 Concentration Over the Last Deglacial Transition
Although shelf seas account for only 7% of the oceanic surface area, they play a key role in the global carbon cycle, linking the terrestrial, atmospheric and oceanic carbon pools. Recent observations suggest that whilst tropical shelf seas act as major sources of atmospheric CO2, temperate and polar shelf seas are significant sinks. Here we provide the first global assessment of the impact of the flooding of the continental shelves by rising sea level on atmospheric pCO2. We combine reconstructions of shelf palaeogeography, bathymetry and tides, with contemporary estimates of seasonally averaged shelf sea – atmosphere CO2 exchange to demonstrate the role of the expanding shelf seas in regulating atmospheric CO2 over the past 21,000 years. This period covers the last deglacial transition following the Last Glacial Maximum (LGM). We show that the relative growth of these different regimes provides a mechanism which can explain the direction, rate and timing of a number of previously unexplained transitions in the atmospheric pCO2 record derived from ice-core measurements. The results demonstrate the influence of rising sea level on atmospheric pCO2 and the important role of the contemporary shelf seas within the global carbon cycle.
PP31E-06
Spatial complexity in the climatic response to solar forcing at 2800 cal. BP
A number of studies have proposed that a major climatic change to wetter/cooler conditions at 2800 cal. BP was triggered by a sudden decline of solar activity, inferred from an anomaly in the 14C record. It has been hypothesised that this climate shift, at the time of the subboreal-subatlantic transition, was global in nature. However, proxy climate records from peatlands in Northern Ireland reveal that a major shift to wetter/cooler climatic conditions post-dated the rapid decrease in solar activity at 2800 cal. BP by ~100 years. These findings are based on multiproxy palaeoecological data (testate amoebae, plant macrofossils and peat humification) and are precisely constrained using tephrochronology and 14C wiggle match dating. These replicated data may indicate marked spatial complexity in the climatic response to solar forcing, which has major implications for understanding how the Sun alters global climate.
PP31E-07
Impact of Big Tambora Eruption on ENSO, Ocean Heat Uptake, and Sea Level
Strong explosive volcanic eruptions could produce global stratospheric aerosol clouds that last for 2-3 years reflecting solar radiation and cooling the earth's surface. The climate response to volcanic impact forms as a result of interaction of associated thermal and dynamic perturbations with the major modes of climate variability. The paleo proxy data even suggest that strong tropical eruptions could increase the likelihood of El Niño. E.g., the strongest explosive events of 19th and 20th centuries, Tambora eruption in 1815 and the Mt. Pinatubo eruption in 1991, occurred in El Niño years. After volcanic impacts surface air temperature relaxes typically for 7 years but cooling accumulated in the ocean can be seen for about a century in the sub-thermocline waters. Decrease of deep ocean temperature is associated with negative anomalies of sea level. This provides a mechanism of how short-term volcanic radiative impacts could produce perturbations in climate system that last for centuries producing a cumulative cooling effect. In this study we have employed a coupled climate model (GFDL CM2.1) for calculating impacts of the Big Tambora, and Pinatubo eruptions. The aerosol cloud of Tambora eruption was about 3 times of that from the Pinatubo eruption therefore it produced much stronger climate effect. Here we consider Tambora climate effect in context of a well observed Pinatubo impact because this adds in confidence of simulation results. To synchronize volcanic eruptions and ENSO we have chosen initial conditions from those years of a control run that exhibited, specific ENSO phase and conducted ten 20-year ensemble runs with El Niño, La Niña, and Neutral initial conditions, for each volcano. We found that maximum cooling for El Niño cases tends to shift to the second year after an eruption therefore notorious Tambora's year without a summer was simulated in 1816 as observed. In La Niña cases maximum cooling appears in the year when eruption occurred. In the runs with El Nino initial conditions volcanic cooling decreases amplitude of El Nino but causes dynamic warming of the equatorial SST in the year following an El Nino event. In the runs with the neutral initial conditions volcanic impact tends to produce El Nino-like response in the second year after volcanic eruption that might explain Volcano-El Nino statistical relation, observed in the paleo-data analysis. This robust warming effect gets stronger in the runs with weaker El Nino and with increase of volcanic forcing. Simulated ocean cooling caused by Tambora eruption decreased the mean sea level by about 14 mm versus 5 mm after the Pinatubo eruption. The later figure agrees well with Church et al. (2005). Because of extremely long relaxation time of ocean subsurface temperature the perturbations caused by Tambora eruption could affect climate state in the mid 19th century used to initiate IPCC AR4 simulations. The sea level decrease forced by Tambora eruption might have to be accounted for estimating the sea level trends caused by Global Warming.
PP31E-08
The late Pliocene-early Pleistocene 100-kyr problem
The forcing mechanisms for the dominant 100-kyr ice volume cycles over the last one Myr have been extensively studied. Little is known, however, about the 100-kyr ice volume and other climatic cycles immediately before 1 Ma except that they are coherent with the 100-kyr eccentricity cycles. Here we show that the amplitude of the 100-kyr cycles in the intensity of East Asian summer monsoon and ice volume between 3-1 Ma does not follow that of eccentricity, but follows that of benthic carbon isotopes, suggesting that, even in the Pliocene, the link between eccentricity and climate is complicated.