Although critical for global climate and the carbon cycle, the nature of past ocean circulation changes remains elusive. Based on deep-water carbonate ion ([CO3 2-]) reconstructions for wide locations, we discover a low-[CO3 2-] water mass in the South Atlantic at ~3-4 km (extending northward up to ~20°S) during the Last Glacial Maximum. Multiple proxies suggest that this low-[CO3 2-] signal likely reflects an extensive expansion of carbon-rich Pacific deep waters, revealing an ocean circulation scheme different from the long-held view for the glacial deep Atlantic. Comparison of high-resolution [CO3 2-] records from different water depths in the South Atlantic indicates that this expansion occurred between ~38 and ~28 thousand years ago. We infer that the associated carbon sequestration might have contributed critically to the contemporary ~20 ppm atmospheric CO2 decline and thereby helped pushing the global climate to the glacial maximum. Ocean circulation and the carbon cycle are intricately linked, and ocean circulation reconstructions can therefore provide important insights into mechanisms for past atmospheric CO2 changes. Ocean circulation in the deep Atlantic Ocean (>~2.5 km) during the Last Glacial Maximum (LGM; 18-22 ka) is traditionally viewed to follow a mixing model between northernand southern-sourced deep waters produced in the polar Atlantic, without much need to involve waters from other oceans 1-4. Using this long-held ocean circulation model, however, it is difficult to explain the observed older radiocarbon ages (14 C ages) and more radiogenic neodymium isotopic (Nd) signatures at ~3.8 km than at ~5 km in the LGM South Atlantic 5,6 (Fig. 1). Burke et al. 7 showed that sluggish recirculation of southern-sourced waters combined with reduced mixing with 14 C-rich northern-sourced waters can contribute to the old 14 C ages at ~3.

During the Last Glacial Maximum (LGM; ~20,000 years ago), the global ocean sequestered a large amount of carbon lost from the atmosphere and terrestrial biosphere. Suppressed CO 2 outgassing from the Southern Ocean is the prevailing explanation for this carbon sequestration. By contrast, the North Atlantic Ocean—a major conduit for atmospheric CO 2 transport to the ocean interior via the overturning circulation—has received much less attention. Here we demonstrate that North Atlantic carbon pump efficiency during the LGM was almost doubled relative to the Holocene. This is based on a novel proxy approach to estimate air–sea CO 2 exchange signals using combined carbonate ion and nutrient reconstructions for multiple sediment cores from the North Atlantic. Our data indicate that in tandem with Southern Ocean processes, enhanced North Atlantic CO 2 absorption contributed to lowering ice-age atmospheric CO 2 .

The manipulation of spin degree of freedom have been demonstrated in spin polarized electron plasma in a heterostructure by using exchange-interaction induced dynamic spin splitting rather than the Rashba and Dresselhaus types, as revealed by time resolved Kerr rotation. The measured spin splitting increases from 0.256meV to 0.559meV as the bias varies from -0.3V to -0.6V. Both the sign switch of Kerr signal and the phase reversal of Larmor precessions have been observed with biases, which all fit into the framework of exchange-interaction-induced spin splitting. The electrical control of it may provide a new effective scheme for manipulating spin-selected transport in spin FET-like devices.