Ice core records show a tight correlation between changes in atmospheric CO 2 65 where k = 0.59 ± 0.01 (1used throughout) ( Supplementary Fig. 1, 2 Fig. 9-10 Atlantic (>~3 km) from MIS 5a to 4 (Fig. 3a-c in the deep Atlantic across the MIS 5a-4 transition ( Supplementary Fig. 11-12 25±13 mol/kg calculated based on [CO 3 2-] reconstructions for the 10 studied cores (Fig. 3a-c ~8,000 years after a weakening or shutdown of NADW ( Supplementary Fig. 15, 19) which is ~38% smaller than the observed DIC change (Fig. 1c). The difference is caused by a 177 ~40 mol/kg ALK increase from NADW to AABW (Fig. 1d) ratio of -0.37 been applied, which empirically includes the ALK changes (Fig. 3c), then our 179 calculated deep Atlantic carbon storage increase would be amplified by a factor of 1.6, and the 180 quantity of carbon sequestration in the deep Atlantic would be comparable within uncertainty to 181 the entire atmospheric CO 2 decline from MIS 5a to MIS 4. Additionally, consideration of larger 182  B/Ca in the western Atlantic, which is currently under sampled (Fig. 3a), would potentially raise (Fig. 4b) 34 , which was previously used to infer global carbon budget 199 change leading an AMOC reorganization 3 , might be caused by air-sea isotopic exchange effects

Surface monolayers assembled on a liquid sub-phase represent a class of systems that is of great interest for studies of phase transitions in quasi-2D systems, chemical self-assembly, surfactant behavior, and biologically relevant monolayers and membranes. X-ray scattering is ideal for studying structural, dynamic, and mechanical properties of these surface monolayers at nanoscale due to the penetrating ability and short wavelength of x-rays. We show here that grazing incidence x-ray off-specular scattering (GIXOS) provides rapid access to in-plane and out-of-plane nanoscale structure, surface fluctuating modes, and potentially bending stiffness. We show that analysis of GIXOS data is highly sensitive to resolution effects. We further present detailed analysis of GIXOS from phospholipid 1,2-dipalmitoyl-phosphatidyl-choline C40H80NO8P (DPPC) and obtain quantitative, angstrom-resolution details of electron density profile normal to the surface that is comparable to those that are obtained from specular x-ray reflectivity measurements. We compare these GIXOS results to x-ray reflectivity measurements performed on the same samples. While electron density and main structural characteristics (such as monolayer thickness) obtained by GIXOS agree with x-ray reflectivity results, the interfaces of GIXOS-derived density profiles are found to be systematically sharper than those obtained with x-ray reflectivity. The possible reasons for these differences are discussed.

Interfacial nanostructures represent a class of systems that are highly relevant to studies of quasi-2D phases, chemical self-assembly, surfactant behavior, and biologically relevant membranes. Previous studies have shown that under lateral compression a Langmuir film of gold (Au) nanoparticles assembled at the liquid-air interface exhibits rich mechanical behavior: it undergoes a rapid structural and morphological evolution from a monolayer to a trilayer via an intermediate hash-like phase. We report the results of studying this structural evolution using grazing incidence X-ray off-specular scattering (GIXOS). We utilize GIXOS to obtain a quantitative mapping of electron density profile normal to the liquid surface with a subnanometer resolution and follow the structural evolution of the Au nanoparticle film under lateral compression with a subminute temporal resolution. As the surface pressure is increased, the self-assembled nanoparticle monolayer first crinkles into a double-layer phase before forming a trilayer. This study reveals the existence of a transient bilayer phase and provides a microscopic picture of the particle-level crinkling phenomena of ultrathin films. These studies were previously impossible due to the relatively short time scales involved in crinkling formation of these transient phases and their intrinsically inhomogeneous nature.

The mechanical properties of self-assembled silver nanoparticle (Ag-NP) films at the air-liquid interface are studied using both visible light optics and x-ray scattering techniques. The response of such films to compression is compared with results from previously studied gold nanoparticle (Au-NP) films, showing many similarities, along with significant differences. Possible factors governing the stress response of nanoparticle films are discussed.

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 .