Ice sheet model dependency of the simulated Greenland Ice Sheet in the mid-Pliocene
Summary: The paper assess the Greenland Ice Sheet’s sensitivity to a warm period in the past, a time when atmospheric CO2 concentrations were comparable to current levels. We quantify ice sheet volume and locations in Greenland and find that the ice sheets are less sensitive to differences in ice sheet model configurations than to changes in imposed climate forcing. We conclude that Pliocene ice was most likely to be limited to highest elevations in eastern and southern Greenland.
S. J. Koenig, A. M. Dolan, B. de Boer, E. J. Stone, D. J. Hill, R. M. DeConto, A. Abe-Ouchi, D. J. Lunt, D. Pollard, A. Quiquet, F. Saito, J. Savage, and R. van de Wal Clim. Past, 11, 369-381, doi:10.5194/cp-11-369-2015, 2015 AbstractFinal Revised Paper (PDF, 4021 KB)Discussion Paper (CPD)
05 Mar 2015
Comparing past accumulation rate reconstructions in East Antarctic ice cores using 10Be, water isotopes and CMIP5-PMIP3 models
Summary: We present a new 10Be record at EDC between 269 and 355ka. Our 10Be-based accumulation rate is in good agreement with the one associated with the EDC3 timescale except for the warm MIS 9.3 optimum. This suggests that temperature reconstruction from water isotopes may be underestimated by 2.4K for the difference between the MIS 9.3 and present day. The CMIP5-PMIP3 models do not quantitatively reproduce changes in precipitation vs. temperature increase during glacial–interglacial transitions.
A. Cauquoin, A. Landais, G. M. Raisbeck, J. Jouzel, L. Bazin, M. Kageyama, J.-Y. Peterschmitt, M. Werner, E. Bard, and ASTER Team Clim. Past, 11, 355-367, doi:10.5194/cp-11-355-2015, 2015 AbstractFinal Revised Paper (PDF, 290 KB)Supplement (142 KB)Discussion Paper (CPD)
05 Mar 2015
East Asian Monsoon controls on the inter-annual variability in precipitation isotope ratio in Japan
Summary: This study demonstrates that the intensity of the East Asian summer and winter monsoon is the primary driver of variations of summer and winter precipitation isotopes in central Japan. Japan lies in the northeast limits of the East Asian monsoon region. Understanding the past monsoon changes in Japan is important for determining whether the isotopic variability recorded in Chinese stalagmite reflects the East Asian summer monsoon intensity or rainfall variability in the Indian summer monsoon.
Two distinct decadal and centennial cyclicities forced marine upwelling intensity and precipitation during the late Early Miocene in central Europe
Summary: High-resolution analyses of paleoecological and geochemical proxies give insight into environmental processes and climate variations in the past on a timescale that is relevant for humans. This study, as the first of its kind, aims to resolve cyclic variations of nannofossil assemblages on a decadal to centennial scale in a highly sensitive Early Miocene (~17Ma) shallow marine setting. Our results indicate that solar variation played a major role in shaping short-term climate variability.
Changes in East Asian summer monsoon precipitation during the Holocene deduced from a freshwater flux reconstruction of the Changjiang (Yangtze River) based on the oxygen isotope mass balance in the northern East China Sea
A comparison of model simulations of Asian mega-droughts during the past millennium with proxy reconstructions
Summary: Our results show that state-of-the-art climate model simulations are able to capture historically recorded Asian monsoon failures during the past millennium at the right time and with a comparable spatial distribution. During the Little Ice Age, both model and proxy reconstructions point to fewer monsoon failures. The results suggest an influential impact of volcanic eruptions on the atmosphere-ocean interactions throughout the past millennium.
Reconstruction of recent climate change in Alaska from the Aurora Peak ice core, central Alaska
Summary: A 180.17-m ice core was drilled at Aurora Peak in the central part of the Alaska Range, Alaska, in 2008. The ice core age was determined by annual counts of δD and seasonal cycles of Na+. Here, we show that the chronology of the Aurora Peak ice core from 95.61 m to the top corresponds to the period from 1900 to the summer season of 2008, with a dating error of ±3 years. Our results suggest that temporal variations in δD and annual accumulation rates are strongly related to shifts in PDO Index.
Using simulations of the last millennium to understand climate variability seen in palaeo-observations: similar variation of Iceland–Scotland overflow strength and Atlantic Multidecadal Oscillation
Summary: We use model simulations to investigate mechanisms of similar Iceland--Scotland overflow (outflow from the Nordic seas) and North Atlantic sea surface temperature variability, suggested from palaeo-reconstructions (Mjell et al., 2015). Our results indicate the influence of Nordic Seas surface temperature on the pressure gradient across the Iceland--Scotland ridge, not a large-scale link through the meridional overturning circulation, is responsible for the (simulated) co-variability.
K. Lohmann, J. Mignot, H. R. Langehaug, J. H. Jungclaus, D. Matei, O. H. Otterå, Y. Q. Gao, T. L. Mjell, U. S. Ninnemann, and H. F. Kleiven Clim. Past, 11, 203-216, doi:10.5194/cp-11-203-2015, 2015 AbstractFinal Revised Paper (PDF, 1364 KB)Discussion Paper (CPD)
10 Feb 2015
Nutrient utilisation and weathering inputs in the Peruvian upwelling region since the Little Ice Age
North African vegetation–precipitation feedback in early and mid-Holocene climate simulations with CCSM3-DGVM
Summary: The role of vegetation-precipitation feedbacks in modifying the North African rainfall response to enhanced early to mid-Holocene summer insolation is analysed using the climate-vegetation model CCSM3-DGVM. Dynamic vegetation amplifies the positive early to mid-Holocene summer precipitation anomaly by ca. 20% in the Sahara-Sahel region. The primary vegetation feedback operates through surface latent heat flux anomalies by canopy evapotranspiration and their effect on the African easterly jet.
The WAIS Divide deep ice core WD2014 chronology – Part 1: Methane synchronization (68–31 ka BP) and the gas age–ice age difference
C. Buizert, K. M. Cuffey, J. P. Severinghaus, D. Baggenstos, T. J. Fudge, E. J. Steig, B. R. Markle, M. Winstrup, R. H. Rhodes, E. J. Brook, T. A. Sowers, G. D. Clow, H. Cheng, R. L. Edwards, M. Sigl, J. R. McConnell, and K. C. Taylor Clim. Past, 11, 153-173, doi:10.5194/cp-11-153-2015, 2015 AbstractFinal Revised Paper (PDF, 1670 KB)Supplement (6644 KB)Discussion Paper (CPD)
05 Feb 2015
Early deglacial Atlantic overturning decline and its role in atmospheric CO2 rise inferred from carbon isotopes (δ13C)
Summary: Model simulations of carbon isotope changes as a result of a reduction in the Atlantic Meridional Overturning Circulation (AMOC) agree well with sediment data from the early last deglaciation, supporting the idea that the AMOC was substantially reduced during that time period of global warming. We hypothesize, and present supporting evidence, that changes in the AMOC may have caused the coeval rise in atmospheric CO2, owing to a reduction in the efficiency of the ocean's biological pump.
Simulating ice core 10Be on the glacial–interglacial timescale
C. Elsässer, D. Wagenbach, I. Levin, A. Stanzick, M. Christl, A. Wallner, S. Kipfstuhl, I. K. Seierstad, H. Wershofen, and J. Dibb Clim. Past, 11, 115-133, doi:10.5194/cp-11-115-2015, 2015 AbstractFinal Revised Paper (PDF, 2597 KB)Supplement (3586 KB)Discussion Paper (CPD)
03 Feb 2015
Tree ring effects and ice core acidities clarify the volcanic record of the first millennium
Summary: Ice core acidities agree with historical volcanic eruptions and tree ring effects in recent centuries, but in the 1st millennium, ice acid dates appear offset from tree ring evidence. This offset appears real between AD 1000 and 50 BC. If correct, then current identification of Vesuvius tephra at AD 79 is erroneous, and geophysicists are working with a false volcanic record especially regarding multiple eruptions in AD 536 and 540-541, highlighting a major global hazard in proximate eruptions.
Drilling disturbance and constraints on the onset of the Paleocene–Eocene boundary carbon isotope excursion in New Jersey
Summary: The Paleocene-to-Eocene thermal maximum was a period of extreme global warming caused by perturbation to the global carbon cycle 56Mya. Evidence from marine sediment cores has been used to suggest that the onset of the event was very rapid, over just 11 years of annually resolved sedimentation. However, we argue that the supposed annual layers are an artifact caused by drilling disturbance, and that the microfossil content of the cores shows the onset took in the order of thousands of years.