Paleoclimate evolution of the North Pacific Ocean during the late Quaternary: Progress and challenges

High- and low-latitude climatic processes in the North Pacific Ocean are important components of the global climate system. For example, the interplay among North Pacific atmospheric circulation, ocean circulation, and biological productivity affects atmospheric carbon dioxide levels and marine oxygen concentrations. Here we review recent research on the North Pacific paleoclimatic and paleoceanographic evolution during the late Quaternary and its response to external forcings such as orbital insolation, ice-sheet extent, and greenhouse gas concentrations. First, we summarize the principles and application of relative paleointensity as a critical chronological tool in North Pacific paleoclimate research. Second, we illustrate the latest discoveries on the interaction between North Pacific Intermediate Water formation and high-to-low latitude teleconnection processes. Third, recent progress in linking dust fluxes and marine productivity and their global significance for the carbon cycle are presented. Finally, several key scientific problems are highlighted for future research on ocean-atmosphere-climate interactions in the North Pacific, pointing to the importance of combining paleo-records and modeling simulations. Overall, this review also aims to provide a broad insight into possible future changes of ocean-atmosphere circulation in the North Pacific region under a rapidly warming climate

Orbital Controls on North Pacific Dust Flux During the Late Quaternary

Airborne mineral dust is sensitive to climatic changes, but its response to orbital forcing is still not fully understood. Here, we present a reconstruction of dust input to the Subarctic Pacific Ocean covering the past 190 kyr. The dust composition record is indicative of source moisture conditions, which were dominated by precessional variations. In contrast, the dust flux record is dominated by obliquity variations and displays an out-of-phase relationship with a dust record from the mid-latitude North Pacific Ocean. Climate model simulations suggest precession likely drove changes in the aridity and extent of dust source regions. Additionally, the obliquity variations in dust flux can be explained by meridional shifts in the North Pacific westerly jet, driven by changes in the meridional atmospheric temperature gradient. Overall, our findings suggest that North Pacific dust input was primarily modulated by orbital-controlled source aridity and the strength and position of the westerly winds

Orbital Controls on North Pacific Dust Flux During the Late Quaternary

Abstract Airborne mineral dust is sensitive to climatic changes, but its response to orbital forcing is still not fully understood. Here, we present a reconstruction of dust input to the Subarctic Pacific Ocean covering the past 190 kyr. The dust composition record is indicative of source moisture conditions, which were dominated by precessional variations. In contrast, the dust flux record is dominated by obliquity variations and displays an out‐of‐phase relationship with a dust record from the mid‐latitude North Pacific Ocean. Climate model simulations suggest precession likely drove changes in the aridity and extent of dust source regions. Additionally, the obliquity variations in dust flux can be explained by meridional shifts in the North Pacific westerly jet, driven by changes in the meridional atmospheric temperature gradient. Overall, our findings suggest that North Pacific dust input was primarily modulated by orbital‐controlled source aridity and the strength and position of the westerly winds

Simulation Analysis on Flow Field of Paint Mist Recovery with Single Nozzle for Ship Outer Panel Spraying Robot

In this paper, we design a kind of negative pressure vacuum recovery hood, arranged at the front of the spray gun nozzle by CFD simulation; this addresses the paint mist pollution problem of the robot spraying on the outer plate of the ship, and the nozzle is arranged at the center of the recovery hood. Three vacuum recovery hood schemes are designed as follows: Scheme A, a hemispherical recovery hood with a diameter of 1.2 m; Scheme B, with a diameter of 1.6 m; Scheme C, with a diameter of 2.0 m. The recovery vacuum suction holes of the three recovery hoods are arranged differently. Firstly, a mathematical model of the spraying jet for the case of 0.48 mm diameter nozzle was established, and the established nozzle jet flow field model was verified to be feasible through case simulation analysis and experimental comparison. Secondly, a detailed discussion and analysis of the simulation process was conducted focusing on Scheme A. During the simulation of Scheme A, it was found that: the air velocity at the inlet surface and the kinetic energy of the paint mist had a large impact on the simulation effect, so it is necessary to try to further improve the structure of the recovery hood. Finally, the further simulation analysis of Scheme B and Scheme C shows that Scheme C > Scheme B > Scheme A in terms of the paint mist recovery effect. It can be seen that the use of Scheme C as a shipyard robotic spray paint mist recovery shows better results, which provides a theoretical scheme for shipyards to achieve paint mist anti-fouling as soon as possible

Microstructure and Wear Property of ZrO2-Added NiCrAlY Prepared by Ultrasonic-Assisted Direct Laser Deposition

For improving the wear properties of NiCrAlY, the 10 wt %, 20 wt % and 30 wt % ZrO2-added NiCrAlY samples were prepared by ultrasonic-assisted direct laser deposition, respectively. The results showed that the ultrasonic-assisted direct laser deposition can realize the ZrO2-added NiCrAlY preparation. Furthermore, due to the cavitation effect and agitation of the ultrasound in the molten pool, ultrasonic-assisted could make the upper surface of the samples smoother and flatter, and it also improved the microstructural homogeneity. The microstructure was mainly composed of columnar dendrites, and most of ZrO2 particles were located in the intergranular regions. The principal phase constituents were found to contain γ-Ni and t-NiZr2, and the amorphous (Ni, Zr) intermetallic phase generated, because of more rapid solidification after ultrasound assisted. The microhardness was improved slightly with the increase of ZrO2 contents, rising from 407.9 HV (10% ZrO2) to 420.4 HV (30% ZrO2). Correspondingly, wear mass loss was decreased with the maximum drop 22.7% of 30% ZrO2 compared to that of 10% ZrO2, and wear mechanisms were mainly abrasive wear with slightly adhesive wear. After applying ultrasound, the oxide islands in samples disappeared, and more ceramic particles were retained. Thus, the hardness and wear performance of the samples were improved

Sea surface temperature and surface seawater oxygen isotope composition reconstructions for sediment core I106

We present sea surface temperature and oxygen isotopes in a sediment core I106 (6°14′49.76″N, 90°00′1.04″E; 2,910 m water depth) from the tropical East Indian Ocean, which provide new insights into the variability of tropical precipitation belt in Asian Monsoon region during the last deglaciation. The age model for the core is constrained by 17 AMS radiocarbon ages based on mixed planktonic foraminiferal samples. Mg/Ca derived sea surface temperature reconstructions based on Globigerinoides ruber (s. s., white) increased rapidly at about 19.5 ka, which is consisted with Mg/Ca-SST records in other cores in the tropical East Indian Ocean. Ice-volume corrected d18O seawater (d18Osw) exhibited a remarkable decline during the early Heinrich Stadial 1 (about 18.3-16.3 ka), and an increase during the late Heinrich Stadial 1 (16.3-14.7) ka. We attribute the decline of d18Osw in north of Equator from Asian Monsoon region to a contracted tropical precipitation belt during the early Heinrich Stadial 1

3D printing concrete containing thermal responsive gelatin: Towards cold environment applications

Construction with cementitious materials via 3D printing requires a highly thixotropic behavior, which is a challenge for construction industry. In this work a facile and low-cost gelatin-modified thermal responsive smart cement paste formulation was developed for extrusion-based 3D printing in cold environments The paste's temperature-dependent rheological properties were characterised, and the underlying mechanism was explored. At room temperature, the modified paste presents similar rheological properties as the reference cement paste. After resting for 10 min at 5 °C, the modified cement paste has a yield stress of 1900 Pa which is 10 times that of the reference paste. Moreover, the mechanical properties of the modified paste are comparable to or higher than that of the reference paste at later age. Our approach may inspire a facile manipulation of paste rheology through temperature, which facilitates smartly controlled 3D concrete printings

A contracting Intertropical Convergence Zone during the Early Heinrich Stadial 1

Despite the fact that the response of tropical hydroclimate to North Atlantic cooling events during the Heinrich Stadial 1 (HS1) has been extensively studied in African, South American and Indonesia, the nature of such responses remains debated. Here we investigate the tropical hydroclimate pattern over the Indo-Asian-Australian monsoon region during the HS1 by integrating hydroclimatic records, and examining a δ18Oseawater record from Globigerinoides ruber (white) in the tropical Indian Ocean. Our findings indicate that tropical hydrological conditions were synchronously arid in both hemispheres during the early HS1 (~18.3-16.3 ka) in the Indo-Asian-Australian monsoon region, except for a narrow, wet hydrological belt in northern low latitudes, suggesting the existence of a contracted tropical precipitation belt at that time. This study reveals that the meltwater discharge and resulting changes in global temperatures and El Niño exerted a profound influence on the tropical hydroclimate in the Indo-Asian-Australian monsoon region during the early HS1