Quaternay deep-water exchange between the
South Atlantic / Southern Ocean and Indian Ocean

 

Dipl. Geol. S. Krüger
Dr. D. C. Leuschner

Prof. Dr. W. Ehrmann
PD Dr. G. Schmiedl


Cooperation:
PD Dr. A. Mackensen, Dr. H. Grobe, Dr. G. Kuhn, Dr. F. Niessen
Alfred-Wegener-Institut für Polar- und Meeresforschung, Bremerhaven
PD Dr. B. Diekmann
Alfred-Wegener-Institut für Polar- und Meeresforschung, Potsdam



Funding: Deutsche Forschungsgemeinschaft (DFG)

 

Scientific Background

The project aims to describe the exchange of deep and bottom water masses between the South Atlantic / Southern Ocean and the Indian Ocean during the Pliocene to late Quaternary. This project is a multi-proxy study with sedimentological, geochemical, sediment physical and micropaleontological investigations along a NW-SE core transect between the South African continental margin and the Conrad Rise (Polarstern cruise ANT XI/4). Main target is to evaluate the significance and timing of the oceanic transmission of Antarctic and Northern hemisphere climate signals into the Indian Ocean at Milankovitch and millennial time scales. 


 

Fig.1: Bathymetric map of the Atlantic and Indian sectors of the Southern Ocean with locations of selected sediment cores. Positions of major oceanic fronts and pathways of deep and bottom water masses are indicated. Shaded areas mark water depths below 4000 m. The general flow pattern of southern deep water masses (mainly Lower Circumpolar Deep Water) and North Atlantic Deep Water  is indicated.


 
Aims of the study

1) How did the deep and bottom water circulation at the transition zone between the Atlantic and Indian oceans evolve since the Pliocene? Is the advection of North Atlantic Deep Water into the Indian Ocean coherent with the onset and intensification of northern hemisphere glaciation and how did the contribution of southern deep water masses change during this time?

2) How did the proportion of northern-derived deep water (NADW) and southern-derived deep water (LCDW, AABW) change at lower bathyal to abyssal depth of the ACC during the last glacial-to-interglacial cycle? Emphasis will be laid on different glacial (stages 2, 4), interglacial (stages 5.5, Holocene), and transitional (stage 3) boundary conditions. Assessment of the importance of polar deep water signals at low latitudes of the Indian Ocean by comparison of the new data sets with existing data sets from the Arabian Sea and adjacent areas.

3) Are the short-term changes in deep-water convection coherent with atmospheric changes recorded in polar ice cores adjacent to the main deep-water formation sites? Is the asynchrony of Antarctic and Greenland climate change during the last glacial period, observed in ice cores, also reflected in the advection of northern versus southern deep water masses?

4) Is the deep-water signal masked by regional environmental signals independent from the deep-water advection? Assessment of the contribution of wind-transported sediment material and reconstruction of regional changes in productivity.


Fig. 2: a) Generalized hydrography of the investigation area along a section between 35°S, 20°E and 55°S, 50°E. Location of Polarstern cores selected for the proposed study is indicated. b) Distribution of Recent benthic foraminiferal faunas along the same section as shown above. The faunal pattern is based on the investigation of surface samples during Polarstern cruise ANTXI/4 (G. Schmiedl, unpublished data).