IMAGES V, 1999 – Short introductionary Report

Introduction

During summer 1999, the French Institute for Polar Research and Technology (IFRTP) conducted the 5th giant sediment coring cruise for the IMAGES program (International Marine Global Change Study, which is a subprogram of the IGBP (International Global Change Program) PAGES (Past Global Change Program).

How can we distinguish natural climate change from that which is caused by human activities? How will climatic change affect environment and world economy in the next decades end century? Why are climatic changes often rapid and dramatic? What is the role of the ocean in climate change, and how will they be affected in the future? These are pressing questions in the current discussions on climate change and climate politics. The ocean is a key element in these questions, as a possible releaser, amplifier or moderator of climatic changes. Studies on the present variability of the oceanic system are necessary. But the time scales covered by the instrumental records are much too short to sample and understand adequately the changes that may affect the future of the ocean system. Only by studies of the climatic signals embedded in the sediments buried on the ocean floor is it possible to obtain the long records of how oceans and climates have developed over long enough periods, and to understand the causes of changes in ocean circulation and its effects on climate change. This is a prerequisite for placement of changes occurring today or forecasted for the future into a framework of how much and how fast and with what consequences past changes took place. It is also a prerequisite for many attempts to understand why climates change and what effects the increasing greenhouse effect will have on the climate system.

The requirements of this type of research is to provide these records at a temporal scale which approaches that of the instrumental record, which at best only goes 100 years back into the past. Hence we must look for sedimentary archives which can contribute the optimal temporal resolution whilst retaining the ability to use paleoclimatic proxy methods to record and quantify the changes of the past.

The IMAGES program has been initiated to respond to the challenge of understanding the mechanisms and consequences of climatic changes at time scales of decades to millennia using oceanic sedimentary records.

Climatic mechanisms must be studied at global scale using sophisticated models based on high quality data that represent the variability of surface and deep ocean physical and chemical characteristics during key periods of recent earth history. The overriding IMAGES science issue is to quantify climate and chemical variability of the ocean on time scales of oceanic and cryospheric processes; to determine its sensitivity to identified internal and external forcing, and to determine its role in controlling atmospheric CO2. In order to achieve these scientific objectives, IMAGES co-ordinates a global program to collect and study marine sediment records to address three fundamental questions:

• How have changes in surface ocean properties controlled the evolution of global heat transfer through the deep and surface ocean and thereby modified climate?
• How have changes in ocean circulation, ocean chemistry, and biological activity interacted to generate the observed record of atmospheric pCO2 over the past 300 Ky.?
• How closely has continental climate linked to ocean surface and deep-water properties?

Individual research is no longer sufficient to resolve these problems because the acquisition of the required large number of long sediment cores in high sedimentation rate areas is expensive, and the proper study of such cores demands the use of multiple tools and large numbers of measurements. IMAGES was established to obtain the necessary information from giant sediment cores and develop the required international cooperation and integration of data. It now includes 26 member countries: Australia, Canada, China, Denmark, France, Germany, Iceland, India, Indonesia, Japan, Mexico, Netherlands, New Zealand, Norway, Portugal, Turkey, Russia, South Africa, Spain, Sweden, Switzerland, Taiwan cons, Tunisia, UK, USA. Since 1995, a major IMAGES cruise has been organized each year on the French Research Vessel Marion-Dufresne under responsibility of the IFRTP. Each cruise was supported in a large part by the French Ministère de la Recherche, additional shared funding from the main participating countries, with invited scientists from other member countries of IMAGES.

R/V Marion-Dufresne is the only oceanographic ship in the world able to take the long sediment cores (several tens of meters) which are necessary to reach the IMAGES scientific objectives. The giant corer (named "Calypso") operates much faster and for a smaller cost than drilling ships. Past IMAGES cruises of the Marion-Dufresne have focused on the North Atlantic (1995), South Africa (1996), South Indian Ocean and SouthWestern Pacific (1997), Western Pacific and Indonesia (1998). The results of these campaigns show that ocean sediments do record numerous large amplitude climatic changes, even within the last several hundred years. They are associated with large-scale changes in the surface ocean hydrology and circulation. Since this cruise, other cruises have been realized in the NorthEast Indian Ocean, Indonesia and the North-west Pacific Ocean (WEPAMA 2001). Mona-Page along the North and Central Americas Pacific, Caribbean and Gulf of Mexico coasts should occur in summer 2002. The main focus for these cruises is to better understand the role of low latitudes in climate changes (variability of the warm pools, ITCZ, monsoons and role for the atmospheric transport of water and oceanic transport of salt to high latitudes).

Scientific Objectives of the IMAGES-V Cruise

A special motivation and element of the IMAGES cruise V has been to identify and core deposits where high sedimentation rate sediments are available, thereby bringing the Marion Dufresne and its coring system to coastal and offshore areas with excess or focussed sedimentation. A new research priority in the cruise is therefore the emphasis on the highly detailed records of recent climatic changes that are embedded in the coastal sediments of estuaries and fjords. It has been a bold attempt to strive for the ultimate in terms of temporal resolution in sediment basins that have not before been tapped and used for standard paleoceanographic/ paleoclimatic purposes. In this respect this has been a unique effort, which brought a new focus into the IMAGES program.

The main objective has been to understand the changes in the circulation and hydrology of the Gulf Stream, which transports heat from the low latitudes to Europe, and salt to the Northern Atlantic and beyond, in relation to the evolution of the Northern ice sheets and the hydrology of the Arctic seas. Several additional objectives were sought: -changes in surface and deep water ocean hydrology and dynamic, using high accumulation rate sediments from drift deposits along deep contour currents; -study of deep coral deposits along the North European margin; -study of past changes in geostrophic deformation of the thermocline along the Gulf Stream and its links to meridional transport.

The French Institute for Polar Research and Technology (IFRTP) conducted in the summer of 1999 this 5th giant sediment coring cruise for the IMAGES program. The cruise was divided into five legs, with different chief scientists and, in part, specific objectives, covering the whole range of environments from the tropics of the Caribbean to the Arctic regions of Spitsbergen and Greenland. In short it follows the flow of the Gulf Stream waters on their transit from their sources to their destiny in the north.

• Leg 1 (Fort de France to Quebec) had as main focus the study of the climatic changes in the tropics and how these interact with rapid changes in the higher latitudes. Specific targets covered the post-glacial environmental and hydrological changes along the western margin of the North Atlantic and at shallow depth in the Eastern Us-Chesapeake Bay.
• Leg 2, 3 and 4 were aimed at studying the variability of climate and ocean system at high Northern latitudes for both glacial/interglacial time scales and for the last few thousand years, at decadal to centennial time scales. The evolution of the ice sheets surrounding the North Atlantic and Arctic Sea has been studied in parallel, as they may have played a major role in the climatic evolution in the past. Specific targets from Leg 2 (Quebec to Reykjavik) covered several fjords from the St Laurence basin and the Labrador coast, and deeper cores around Greenland. Leg 3 (Reykjavik to Tromso) and Leg 4 (Tromso to Brest) focused on the evolution of the Arctic seas (Greenland and Norwegian seas) and their relationship with the North Atlantic, both at surface and at depth.
• Leg 5 (Brest to Marseilles) focused on the evolution of the sub-polar to subtropical areas of the North Eastern Atlantic, Western Europe and Western Mediterranean Sea, and the exchanges between Atlantic and Mediterranean waters.

The co-chief scientists of IMAGES-V cruise are Professor Laurent Labeyrie (University Paris Sud-Orsay and LSCE), Elsa Cortijo (LSCE) who was responsible for most of the cruise preparation and Professor Eystein Jansen (University of Bergen, Norway). Eight countries shared the cost of the cruise with France: Norway, USA, Canada and Germany as main contributors and United Kingdom, Iceland, Denmark and Spain as smaller contributors. Scientists on board from Portugal, Taiwan, Sweden and Netherlands participate as IMAGES members. France, which contributes to about 2/3 of the coast of the cruise is represented by scientific groups from 7 Universities and Laboratories from the Centre National de la Recherche scientifique (LSCE-Gif/Yvette, CNRS et CEA; DGO Bordeaux (CNRS and Université Bordeaux 1; Laboratoire de Géochimie Université Paris Sud Orsay and CNRS; Laboratoire de Géologie Université de Lille et CNRS; CEREGE Université Aix-Marseille et CNRS, Laboratoire de Géologie Université de Chambéry, Laboratoire de Sédimentologie Université Paris VI et CNRS). As a whole, more than 300 scientists participated in the cruise.