Ralph Schneider Prof. Ralph Schneider Institute for Geosciences Christian Albrechts University Germany If you would like to interview this scientist, please contact Leah Christen. > biographical information > abstract > paper

Biographical Information:

After studying Geology, Paleontology, and Geophysics, I graduated in 1988, reconstructing Neogene oxygen minimum conditions in the Peruvian upwelling system. My PhD, obtained from Bremen University (Germany) combined with a research visit at LDEO, Palisades, USA, investigated changes in African monsoonal climate and river discharge. Since then, I have studied Quaternary variations in Atlantic and Indian Ocean surface circulation and productivity, as well as ocean-continent climate interactions. For this purpose, I have participated in 15 sea-going expeditions around South America and Africa with American, French, and German research vessels. More recently, I initiated two projects aiming for global syntheses of surface ocean temperature conditions during the Holocene and the Last Ice Age. In 2003, I was appointed Professor for Paleoclimatology and Paleoceanography at Bordeaux University, France. Now I am back at Kiel University, heading the Marine Paleoclimate Research Unit. I serve the PAGES community as the Executive Director of the IMAGES program.

Abstract:

From Milankovitch to rapid climate change – IMAGES research

IMAGES (International Marine Global Change Study) is a core program of Past Global Changes (PAGES) and is affiliated with SCOR. IMAGES was initiated about 10 years ago to respond to the challenge of understanding the mechanisms and consequences of climate change using ocean sediments as a the main archive. The overriding IMAGES goals are to quantify physical and chemical variability of the ocean on time scales of oceanic and cryospheric processes, e.g. from Milankovitch to decadal time scales; to determine its sensitivity to identified internal and external forcing, and to determine its role in controlling atmospheric carbon dioxide. In order to achieve these scientific objectives, IMAGES coordinates a global program to collect and study marine sediment records to address three fundamental questions:

1. How have changes in surface ocean properties controlled the evolution of global heat transfer through the surface and deep ocean circulation?

2. How have changes in ocean circulation, ocean chemistry, and biological activity interacted to generate the observed record of atmospheric pCO₂ over the past 400 kyr?

3. How closely has continental climate been linked to ocean surface and deep-water properties?

Paper:

From Long-term to Rapid Climate Change, IMAGES Research

What is the role of the ocean for future climate change?
The ongoing, very controversial debate about future climate change always concentrates on two major questions: 1) Will the emission of carbon dioxide and other trace gases into the atmosphere through the use of fossil fuels lead to global warming, and 2) what would be the climatic consequences of this for different regions in the world. For the first question, a scientific consensus seems to be slowly emerging now, accepting that humans will drive the planet into a different climatic state. However, the magnitude and speed of such anticipated warming is not clear, as is the question whether all world regions will heat up or if certain areas will cool down first. In this context, many of us immediately look at the ocean, which covers nearly 70% of the Earth’s surface. The ocean has a tremendous capacity to store heat and gaseous carbon dioxide. On the other hand, with this huge reservoir for both heat and carbon dioxide, the ocean is a very active player in controlling overall climate conditions because the surface ocean either releases heat and carbon dioxide or takes it up from the atmosphere. Therefore, future changes in ocean circulation and in the activity of marine plankton that live at the surface consuming large amounts of carbon dioxide, as well as in the chemical state of the entire ocean will define whether the ocean will reduce or enhance the effects of global warming. This is exactly what we want to know better!

How to better understand the ocean as a climate engine?
If we want to define the role of the ocean for future climate change, we only can hypothesize or try to simulate the physical, chemical and biological conditions that will occur at the surface and in the deep interior. Furthermore, we can be sure that future climate change induced by humankind will have an, as yet undefined, impact on the ocean. The only approach to overcoming part of these two problems is to look into the past and try to find out how the former ocean behaved when climate change on Earth was a purely natural phenomenon. For this purpose, paleoclimate researchers have developed tools to reconstruct past environmental conditions in the ocean, in the atmosphere and on the continents by looking at so-called “archives” of climate change. These archives allow us to read the history, e.g., past temperatures, rainfall, composition of the atmosphere, and ocean and atmosphere circulation, as well as changes in vegetation on land and in marine life. In the marine realm, soft chalky, clayey, or sandy muds, which are continuously deposited at the sea floor, serve as the major archive of climate change. These sediments contain a great deal of important information about the physical, chemical and biological conditions in the past ocean. By assembling and assessing this information on regional and global scales, it is possible to reconstruct the response and the driving mechanisms of the ocean within the climate system on Earth on time scales of millions, hundred of thousands, or even thousands of years. In some cases, we can read a very detailed history at intervals of only centuries or decades. This is our main tool to learn about the role of the ocean in natural climate change.

The risk of very rapid climate change
From our paleoclimate investigations we know that the ocean has cooled by about 10°C over the last 50 million years, that over the last one million years, ice-ages have alternated with warm climate periods every 100,000 years—the latter very similar to our modern world—and that regular oscillations in ocean circulation and biological activity have occurred at periods of tens of thousands to thousands of years. The most astonishing result has been the finding of very rapid climate changes in ice cores from Greenland, where regional temperatures have risen or dropped by about 5 to 10°C within decades. IMAGES research has provided many examples that such rapid changes have also occurred in the ocean and over adjacent continents. Very surprisingly, not only the cold regions but also the tropics, where climate variability is mainly expressed as precipitation changes, have experienced such rapid oscillations. It is now evident that dry and wet phases over Africa, Asia, Australia and South America are intimately connected to tropical ocean temperature changes, which in turn relate to atmosphere and ocean circulation changes, closely coupled to the rapid polar climate oscillations. However, the drivers behind these teleconnections are yet not well understood. This lack of understanding makes it very difficult to forecast the probability of similar rapid changes for the cold and warm climates of the world, particularly under the expectation of global warming. Therefore, IMAGES will continue to reconstruct natural climate variability from marine sediments with special emphasis on rapid climate oscillations under more general warm or cold conditions, and will try to acquire a more coherent picture on a global scale.


Figure 1. Pictures from an IMAGES Cruise (MONA cruise, see IMAGES website: www.images-pages.org) showing a 40-m-long sediment core on deck of the RV Marion Dusfresne. The sediment cores, containing the climate archive, are carefully treated, cut in 1.5-m-long sections, registered, and released for use in paleoclimate reconstructions.