Yan Liu, Catherine Kissel, Alain Mazaud, Yongxin Pan, Jinhua Li.
The Southern Ocean (SO) plays a critical role in global climate due to the presence of the intense eastward-flowing Antarctic Circumpolar Current (ACC), one of the most important ocean current systems on Earth. The configuration of the frontal systems of the ACC is controlled by the orbital- and millennial-scale variations of the Southern Hemisphere Westerly Winds (SHWW) and of the SO upwelling, a key part of the meridional overturning circulation of the ocean. However, the reconstruction of paleoclimate and paleocurrent in the Southern Hemisphere remains controversial possibly because of the complex interpretation of paleo-proxies and the local regional variations.
Here, we present results from rock magnetic and electron microscopic investigations on a marine core (MD11-3353), located in the Polar Front Zone, west of the Kerguelen Plateau. Our dataset covers the past 150 kyrs and shows climate-controlled variations of both detrital and biogenic magnetic minerals. The biogenic fraction corresponds to fossil remains of magnetotactic bacteria (MTB) with a single domain nature and distinctive crystal morphologies (Fig. 1).
During the glacial periods (MIS 6, MIS 4-2, and T1), the SHWW stress and the ACC intensity increases, the sea level drops, and both the current erosion and eolian dust induce an increase in detrital input mainly made of inorganic titanomagnetites with minor contribution of hematite. The cold substages within MIS 5 (MIS 5b and 5d) also show the same characteristics (Fig. 2).
In contrast, during the interglacial periods (MIS 5 and the Holocene) with reduced detrital input due to a reduced ACC intensity, the increased SO upwelling strength, resulting from the southward migration of the APF, delivered organic matter and other nutrients to the region southwest of the Kerguelen Plateau, stimulating blooming of magnetotactic bacteria and subsequent magnetofossil preservation (Fig. 2).
Therefore, our results suggest that the detrital magnetic minerals in core MD11-3353 record the time variations of the ACC intensity and the SHWW stress over the last climatic cycle, while the occurrence magnetofossils testifies for the latitudinal variations of the Antarctic polar front and of the strength of the SO upwelling in the southern Indian Ocean during interglacials.
Journal of Geophysical Research: Solid Earth, 128, e2023JB027741.https://doi.org/10.1029/2023JB027741