Susan Ivy-Ochs

Bio: Susan Ivy-Ochs is an academic researcher from ETH Zurich. The author has contributed to research in topics: Glacier & Glacial period. The author has an hindex of 39, co-authored 193 publications receiving 4172 citations. Previous affiliations of Susan Ivy-Ochs include University of Zurich.

Surface exposure dating with cosmogenic nuclides

Abstract: . In the last decades surface exposure dating using cosmogenic nuclides has emerged as a powerful tool in Quaternary geochronology and landscape evolution studies. Cosmogenic nuclides are produced in rocks and sediment due to reactions induced by cosmic rays. Landforms ranging in age from a few hundred years to tens of millions of years can be dated (depending on rock or landform weathering rates) by measuring nuclide concentrations. In this paper the history and theory of surface exposure dating are reviewed followed by an extensive outline of the fields of application of the method. Sampling strategies as well as information on individual nuclides are discussed in detail. The power of cosmogenic nuclide methods lies in the number of nuclides available (the radionuclides 10Be, 14C, 26Al, and 36Cl and the stable noble gases 3He and 21Ne), which allows almost every mineral and hence almost every lithology to be analyzed. As a result focus can shift to the geomorphic questions. It is important that obtained exposure ages are carefully scrutinized in the framework of detailed field studies, including local terrace or moraine stratigraphy and regional morphostratigraphic relationships; as well as in light of independent age constraints.

The timing of glacier advances in the northern European Alps based on surface exposure dating with cosmogenic 10Be, 26Al, 36Cl, and 21Ne

Abstract: Exposure dating of boulder and bedrock surfaces with 10Be, 21Ne, 26Al, and 36Cl allows us to constrain periods of glacier expansion in the European Alps. The age of 155 ka from a boulder of Alpine lithology located in the Jura Mountains (Switzerland) provides a minimum age for pre-LGM (Last Glacial Maximum), more extensive Alpine glaciations. During the LGM, glaciers expanded onto the foreland after 30 ka. By 21.1 ± 0.9 ka deglaciation had begun, and the Rhône Glacier abandoned the E-mail: ivy@phys.ethz.ch. Ivy-Ochs, S., Kerschner, H., Reuther, A., Maisch, M., Sailer, R., Schaefer, J., Kubik, P.W., Synal, H., and Schlüchter, C., 2006, The timing of glacier advances in the northern European Alps based on surface exposure dating with cosmogenic Be, Al, Cl, and Ne, in Siame, L.L., Bourlès, D.L., and Brown, E.T., eds., In Situ–Produced Cosmogenic Nuclides and Quantifi cation of Geological Processes: Geological Society of America Special Paper 415, p. 43–60, doi: 10.1130/2006.2415(04). For permission to copy, contact editing@geosociety.org. © 2006 Geological Society of America. All rights reserved.

Rock avalanching into a landslide-dammed lake causing multiple dam failure in Las Conchas valley (NW Argentina) — evidence from surface exposure dating and stratigraphic analyses

Abstract: Generally landslide dams which exist for several hundreds to thousands of years are considered as stable. We show with an example from the Argentine Andes that such dams can exist for several thousands of years but still may fail catastrophically. Multiple rock avalanches impounded two lakes with surface areas of ~8 km2 and ~600 km2, respectively, in Las Conchas valley, NW Argentina. Surface exposure dating (SED) by 10Be of the rock-avalanche deposits or landslide scars indicates that these landslides occurred at 15,300±2,000 yr and 13,550±900 yr. The dams were stable during a strong earthquake, as suggested by seismites within related lake sediments and by multiple coeval landslides in this region, which occurred at ~7.5 kyr. However, when a further rock-avalanche fell into the lower, smaller lake at 4,800±500 yr the dam downriver was destroyed, presumably by the resulting tsunami wave. The resulting flood also destroyed an additional rock-fall dam which had formed at ~5,630 yr 14C cal BP 30 km downriver. The new dam formed by the second rock avalanche was eroded prior to 3,630 yr 14C cal BP. This dam erosion coincides with an important climatic shift towards more humid conditions in the Central Andes. Our results show that instead of direct effects of strong seismicity on landslide dams, (1) landsliding into a landslide-dammed lake, (2) abrupt hydrological changes, and (3) climate change towards conditions related to enhanced run-off are processes which can produce failures of “quasi-stable” natural dams.

Air pressure and cosmogenic isotope production

Abstract: The cosmic ray flux increases at higher altitude as air pressure and the shielding effect of the atmosphere decrease. Altitude-dependent scaling factors are required to compensate for this effect in calculating cosmic ray exposure ages. Scaling factors in current use assume a uniform relationship between altitude and atmospheric pressure over the Earth's surface. This masks regional differences in mean annual pressure and spatial variation in cosmogenic isotope production rates. Outside Antarctica, air pressures over land depart from the standard atmosphere by ±4.4 hPa (1σ) near sea level, corresponding to offsets of ±3–4% in isotope production rates. Greater offsets occur in regions of persistent high and low pressure such as Siberia and Iceland, where conventional scaling factors predict production rates in error by ±10%. The largest deviations occur over Antarctica where ground level pressures are 20–40 hPa lower than the standard atmosphere at all altitudes. Isotope production rates in Antarctica are therefore 25–30% higher than values calculated by scaling Northern Hemisphere production rates with conventional scaling factors. Exposure ages of old Antarctic surfaces, especially those based on cosmogenic radionuclides at levels close to saturation, may be millions of years younger than published estimates.

This is How the Discussion Started

Abstract: A copy of Guangbo jiemu bao [Broadcast Program Report] was being passed from hand to hand among a group of young people eager to be the first to read the article introducing the program "What Is Revolutionary Love?" It said: "… Young friends, you are certainly very concerned about this problem'. So, we would like you to meet the young women workers Meng Xiaoyu and Meng Yamei and the older cadre Miss Feng. They are the three leading characters in the short story ‘The Place of Love.’ Through the description of the love lives of these three, the story induces us to think deeply about two questions that merit further examination.

Paleocean circulation during the last deglaciation : a bipolar seesaw ?

Abstract: Hughen et al. [1998] have documented that during the first 200 years of Younger Dryas time the 14C content of atmospheric CO2 increased by ∼50‰ and that during the remainder of this 1200-year-duration cold event it steadily declined. The initial increase in 14C/C was likely the result of a reduction in the Atlantic's conveyor circulation. However, were the subsequent radiocarbon decline due to the rejuvenation of this potent heat pump, then it is difficult to understand why the climate conditions in the northern Atlantic basin remained cold throughout the Younger Dryas. Modeling exercises by Stocker and Wright [1996], Mikolajewicz [1998], and Schiller et al. [1998] show that if the conveyor is terminated, the transfer of radiocarbon into the deep sea shifts to the Southern Ocean, thereby stabilizing the atmospheric 14C/C ratio. Paleoclimatic evidence from the Antarctic continent suggests that this model-based scenario might have been played out in the real world. While the Younger Dryas cooling has been documented in many places around the world, including New Zealand [Denton and Hendy, 1994], Sowers and Bender [1995], using their 18O in O2-based correlation between the ice core 18O in ice records for Antarctica and Greenland, have demonstrated that in Antarctica the Younger Dryas was a time of maximum warming. The point of this paper is that the steep rise in 18O rise in Antarctic ice which commenced close to the onset of the Younger Dryas might have been caused by heat released to the atmosphere in response to an increase in deep-sea ventilation in the Southern Ocean.