Project

climate dynamics; stable isotopes; paleoclimate reconstruction; greenhouse gases

Lead
By the unique combination of physciallly based modelling, high-resolution analytics on polar ice cores, and the measurement of environmental tracers (stable and unstable isotopes), progress in the understanding of the Earth System was made.
Lay summary
Understanding past, present and future climate change requires both highest quality paleoclimatic data and climate simulation capabilities. A hierarchy of physical-biogeochemical climate models has been used, ranging from simplified models to state-of-the-art comprehensive models. Direct simulation of paleoceanographic tracers and ensemble simulations has been performed over many 100,000 years. The models were also used to perform simulations over the last millennium, the 20th, and 21st centuries to investigate the effect of climate change on the global carbon cycle. Climate reconstruction is based on polar ice cores from Greenland and Antarctica on which greenhouse gas concentrations were measured including their isotopic composition, and chemical components in high-resolution. The research covers the last glacial maximum (ca 20,000 years before present), the sequence of abrupt events during the last ice age, and, generally, previous glacials during the past 800,000 years. A better quantification of environmental processes using a palette of natural radionuclides (14C, 37Ar, 39Ar, 81Kr, 85Kr) was achieved. This permits dating of groundwater and by extending these studies to the stable isotopes of water, information on past humidity conditions was obtained.

Direct link to Lay Summary

Last update: 21.05.2013

Number	Title	Start	Funding scheme

Climate and Earth System modelling at our division is organized in two streams. First, the climate model of reduced complexity, referred to as the Bern3D model, is developed in our division and includes a 3-dimensional dynamical component of the ocean circulation and tracer transport and a 2-dimensional atmospheric moisture and energy balance. In addition, modules of the global marine and terrestrial carbon cycle, including isotopes are coupled. We use this cost-efficent model to investigate the physical and biogeochemical dynamics of large-scale climate reorganizations such as glacial terminations, sequences of abrupt climate change and long-term climate evolution over the past 800,000 years. Direct simulation of paleoceanographic tracers and ensemble simulations will be performed. We propose to extend this time scale to the last 2 million years in order to prepare and extend the process understanding for the climate transition of 40,000-yr to 100,000-yr glaciation cycles. Variations of noble gas concentrations will be simulated, and uncertainties in reconstructing global ocean temperature changes based on this proxy will be estimated. The second modeling stream uses the comprehensive community system model CESM1.0, developed by the National Center for Atmospheric Research (USA). It will be used to perform simulations over the 20th and 21st centuries to investigate the sensitivity of the global carbon cycle on forced and natural climate change. We will focus on ocean acidification and decreasing oxygen trends. As part of the community development, we plan to implement carbon cycle isotope modules into the CESM1.0 both for the ocean and the terrestrial components. Climate reconstruction from a range of polar ice cores will focus on three streams: (i) reconstruction of greenhouse gas concentrations, (ii) reconstruction of isotopic compositions of the greenhouse gases, and (iii) high-resolution chemical records of the atmosphere. First, of particular interest will be high-resolution greenhouse gas measurements on various ice cores in order to determine phases between these gases and their isotopic composition. This information will be compared to physical-biogeochemical model simulations performed in our division. The interhemispheric difference, jointly with the complete isotope signal of CH4, carries a wealth of information which we would like to harvest in the next two years. Second, the isotopic signatures of various gases will now be routinely measured and a number of records over selected time windows will be established. The last glacial maximum, the sequence of abrupt events during MIS3, and with the availability of the new ice core from NEEM Station (Greenland), the penultimate interglacial, are windows of primary interest. However, also previous glacials MIS10, MIS12, and MIS16, and their transitions into interglacials, as recorded in Antarctic cores, will be analysed for isotopes in greenhouse gases. Third, in-field measurements using Continuous Flow Analysis have provided, for the first time, an uninterrupted record of chemical changes in Greenland snow over the past 125,000 years. These data will be analysed and interpreted in the coming two years with a focus on aerosol components. In addition to the three streams, we would like to start an effort in expanding our research infrastructure in ice core science including a rapid dry extraction device, a borehole sonar, and a planning phase for a fast access drill for ice sheet exploration.Isotopes yield indispensable information on environmental processes such as characteristic exchange fluxes between reservoirs and fingerprints of specific changes. In the coming two years, we will extract climate information form various aquifers in international collaborations. Our contribution is the dating of these old waters using a palette of natural radionuclides (14C, 81Kr, 85Kr, 37Ar, 39Ar, 14C). By extending these measurements to the stable isotopes of water, information on past humidity conditions may be obtained. Isotopic composition of the major air components (N2 and O2) and the elemental ratios (O2/N2, Ar/N2, etc.) will be measured on air entrapped in polar ice cores, as well as in modern air to constrain changes in local temperature, and also mean ocean temperature, during abrupt climate change and large climate reorganizations.