CO2 capture over steam and KOH activated biochar: Effect of relative humidity

Carbon dioxide (CO2) capture is critical for emission reduction. Biochar is a promising adsorbent for CO2 capture. In this work, the effect of relative humidity and biochar activation with steam or KOH treatment on CO2 capture was investigated. The results demonstrate that the biochar sample activated by KOH has a high CO2 capture capacity (50.73 mg g−1). In addition, the biochar after 1.0 h of steam treatment showed a carbon capture capacity of 38.84 mg g−1. The results also show that the capture ability of biochar decreased as CO2 concentration decreased from 100% to 15%. The relative humidity had a negative impact on CO2 capture over biochar. The CO2 capture capability of biochar materials treated by steam decreased by a range of 31.38%–62.89% as the relative humidity rose from 8.8% to 87.9%. Furthermore, the lifetime of biochar samples at various relative humidity shows that increased relative humidity had a negative impact on CO2 adsorption due to water molecules occupying active sites

Late Quaternary terrigenous sediment supply in the Drake Passage in response to Patagonian and Antarctic ice dynamics

The Drake Passage, as the narrowest passage around Antarctica, exerts significant influences on the physical, chemical, and biological interactions between the Pacific and Atlantic Ocean. Here, we identify terrigenous sediment sources and transport pathways in the Drake Passage region over the past 140 ka BP (thousand years before present), based on grain size, clay mineral assemblages, geochemistry and mass-specific magnetic susceptibility records. Terrigenous sediment supply in the Drake Passage is mainly derived from the southeast Pacific, southern South America and the Antarctic Peninsula. Our results provide robust evidence that the Antarctic Circumpolar Current (ACC) has served as the key driver for sediment dispersal in the Drake Passage. High glacial mass accumulation rates indicate enhanced detrital input, which was closely linked to a large expansion of ice sheets in southern South America and on the Antarctic Peninsula during the glacial maximum, as significantly advanced glaciers eroded more glaciogenic sediments from the continental hinterlands into the Drake Passage. Moreover, lower glacial sea levels exposed large continental shelves, which together with weakened ACC strength likely amplified the efficiency of sediment supply and deposition in the deep ocean. In contrast, significant glaciers' shrinkage during interglacials, together with higher sea-level conditions and storage of sediment in nearby fjords reduced terrigenous sediment inputs. Furthermore, a stronger ACC may have induced winnowing effects and further lowered the mass accumulation rates. Evolution of ice sheets, sea level changes and climate related ACC dynamic have thus exerted critical influences on the terrigenous sediment supply and deposition in the Drake Passage region over the last glacial-interglacial cycle

Potassium-promoted limestone for preferential direct hydrogenation of carbonates in integrated CO 2 capture and utilization

Integrated CO2 capture and utilization (ICCU) via the reverse water–gas shift (RWGS) reaction offers a particularly promising route for converting diluted CO2 into CO using renewable H2. Current ICCU-RWGS processes typically involve a gas–gas catalytic reaction whose efficiency is inherently limited by the Le Chatelier principle and side reactions. Here, we show a highly efficient ICCU process based on gas–solid carbonate hydrogenation using K promoted CaO (K-CaO) as a dual functional sorbent and catalyst. Importantly, this material allows ∼100% CO2 capture efficiency during carbonation and bypasses the thermodynamic limitations of conventional gas-phase catalytic processes in hydrogenation of ICCU, achieving >95% CO2-to-CO conversion with ∼100% selectivity. We showed that the excellent functionalities of the K-CaO materials arose from the formation of K2Ca­(CO3)2 bicarbonates with septal K2CO3 and CaCO3 layers, which preferentially undergo a direct gas–solid phase carbonates hydrogenation leading to the formation of CO, K2CO3 CaO and H2O. This work highlights the immediate potential of K-CaO as a class of dual-functional material for highly efficient ICCU and provides a new rationale for designing functional materials that could benefit the real-life application of ICCU processes

Holocene sediment source analysis and paleoclimatic significance of core KZK01 from the eastern part of the Beibu Gulf

Identifying the sources of sediments is of great significance in reconstructing Holocene paleoclimate evolution in the Beibu Gulf and in understanding the characteristics of regional responses to changes in global climate. The Holocene paleoclimatic evolutionary history of the Beibu Gulf was investigated by chronological, geochemical, and mineralogical means using the sediments of Core KZK01 from the eastern part of the Beibu Gulf. The rare earth element (REE) distribution curves, (Gd/Yb)N and (La/Yb)N discriminant diagram, and (Gd/Lu)N and ∑LREE/∑HREE discriminant diagram indicated that the detrital materials in the eastern part of the Beibu Gulf primarily originated from Hainan Island and its proximal sources, with considerable contributions from Taiwan and Pearl River materials. Source analysis of clay minerals showed that Luzon Island was the main source of smectite, followed by Hainan Island. Rivers in Taiwan were the main sources of illite in the study area, followed by the Red River. The Red River was the main contributor of chlorite, followed by the Pearl River. Kaolinite mainly originated from Hainan Island and Guangxi. Coastal currents, surface currents, and warm currents were the main drivers of material transport. Paleoclimatic variations since the Holocene in the Beibu Gulf were divided into three stages: 12–9 cal kyr BP, 9–1.3 cal kyr BP, and 1.3 cal kyr BP to the present. During different stages of climatic evolution, drought was often accompanied by cold and humidity coexisted with warmth, and cold-dry-warm-humid alternation is characterized by significant phases. The illite crystallinity clearly recorded the extreme cold events, such as Bond Events (except Bond6) and the Younger Dryas, and the change trend was essentially consistent with the regional climate record, reflecting the control of global climate change on the process of land–sea interaction in the tropical region. Furthermore, it highlights the great potential of illite crystallinity as a proxy indicator for reconstructing the surface chemical weathering processes of the region

Atmosphere-ocean changes in the Pacific Southern Ocean over the past 1 Million years and implications for global climate

Atmosphere-ocean interactions play an important role for understanding processes and feedbacks in the Southern Ocean (SO) and are relevant for changes in Antarctic ice-sheets and atmospheric CO2 concentrations. The most important atmospheric forcing at high and mid-latitudes of the Southern Hemisphere is the westerly wind belt (SWW), which strongly affects the strength and extension of the Antarctic Circumpolar Current (ACC), upwelling of deep-water masses, and controls the back-flow of intermediate waters to the tropics. In order to address orbital and millennial-scale changes of the SWW and the ACC, we present sediment proxy records from the Pacific SO including the Chilean Margin and the Drake Passage. The Drake Passage (DP) represents the most important oceanic gateway along the ACC. Based on grain-size and geochemical properties of sediment records from the southernmost continental margin of South America, we reconstruct changes in DP throughflow dynamics over the past 65,000 years. In combination with published sediment records from the Scotia Sea and preliminary sediment records from the central Drake Passage (Polarstern cruise PS97, 2016), we argue for a considerable total reduction of DP transport and reveal an up to ~40% decrease in flow speed along the northernmost ACC pathway entering the DP during glacial times. Superimposed on this long-term decrease are high-amplitude millennial-scale variations, which parallel Southern Ocean and Antarctic temperature patterns. The glacial intervals of strong weakening of the ACC entering the DP imply a reduced Pacific-Atlantic exchange via the DP (“cold-water route”). The reduced Drake Passage glacial throughflow was accompanied by a pronounced northward extension of the Antarctic cold-water sphere in the Southeast Pacific sector and stronger export of northern ACC water into the South Pacific gyre. These oceanographic changes are consistent with reduced SWW within the modern maximum wind strength zone over the subantarctic ACC and reduced wind forcing due to extended sea-ice further south. Despite this reduction in winds in the core of the westerlies, we observe 3-fold higher dust deposition during glacial periods in Past Antarctic Ice Sheet Dynamics (PAIS) Conference September 10-15th 2017, Trieste - Italy the Pacific Southern Ocean (SO). This observation may be explained by a combination of factors including more expanded arid dust source areas in Australia and a northward extent or enhancement of the SWW over Southeast Australia during glacials that would plausibly increase the dust uptake and export into the Pacific SO. Such scenario would imply stronger SWW at the present northernmost margin of the wind belt coeval with weaker core westerlies in the south and reduced ACC strength, including Drake Passage throughflow during glacials. We conclude that changes in DP throughflow play a critical role for the global meridional overturning circulation and interbasin exchange in the Southern Ocean, most likely regulated by variations in the westerly wind field and changes in Antarctic sea-ice extent. Keywords: Pelagic Southern Ocean, Antarctic Circumpolar Current, Southern Westerlies, Teleconnections

Antarctic Circumpolar Current dynamics, and terrigenous sediment provenance variations in the Drake Passage during the last 140,000 years

The Antarctic Circumpolar Current (ACC) is the largest ocean current system on Earth. Through promoting deep water upwelling and new water masses formation, the ACC plays a crucial role on global ocean circulation and climate changes. The Drake Passage is the narrowest constriction for the ACC and exerts a strong control on the physical, chemical, and biological exchange between the Pacific and Atlantic Ocean. Resolving changes in the ACC through this specific channel is, therefore, important for elevating our knowledge of the Southern Ocean’s role in global ocean circulation and climate variability. However, previous studies showed a significant disagreement of the ACC flow speed changes and its potential impacts on ocean circulation and climate variability remain elusive. In Wu et al., (2019), we identified southern Patagonia and the Antarctic Peninsula as the main sources for terrigenous sediments in the modern Drake Passage region, based on a comprehensive set of surface sediment samples. We found the variability of the ACC shows a clear bottom current speed pattern in the Drake Passage responding to the dynamics of ocean fronts, in agreement with modern observation. Understanding present-day sediment provenance and transport processes is crucial for studies about the dynamics of ocean circulation, as well as for paleoclimate reconstructions in the Drake Passage. Further, we reconstruct changes in the ACC strength in the central Drake Passage over the past 140,000 years. We found substantial reductions in ACC bottom flow speeds during the glacial periods and increased bottom currents during interglacials. The amplitude was larger during Termination II compared to Termination I. Superimposed on these long-term changes, we found strong millennial-scale fluctuations in ACC intensity, increasing in amplitude toward the Last Glacial Maximum (LGM). We hypothesize that the central ACC reacts highly sensitive to the Southern Hemisphere millennial-scale climate oscillations, likely related to westerly’s wind stress, oceanic fronts and Antarctic sea ice extent during the LGM. This strong variation of ACC regulates Pacific-Atlantic water mass exchange via the “cold water route” and could significantly affect the Atlantic Meridional Overturning Circulation (AMOC). In a third study, the mineralogical, magnetic and geochemical properties of terrigenous sediments reveal that the fine-grained materials mainly derived from western Patagonia and the Antarctic Peninsula over the last 140 ka. The ACC might have severed as a major driver for the sediment transport in the Drake Passage region. Expansion of ice sheets in Patagonia and on the Antarctic Peninsula together with relative sea-level lowstands enhanced the efficiency of terrigenous input during glacial maxima. Our high-resolution records reflect the waxing and waning of glaciers in southern Patagonia and on the Antarctic Peninsula. In the last study, authigenic Nd and Pb isotopic records from the central Drake Passage deciphered past water mass mixing in the Southern Ocean during the last 140,000 years. We found enhanced Pacific-derived deep waters into the deep Southern Ocean at the expense of the North Atlantic-derived waters during glacial times. A pronounced gradient between mid-depth and deep waters suggests a stratified deep ocean during glacial periods. Enhanced stratification together with a stronger biological pump would support an enhanced storage of CO2 in the deep Southern Ocean during glacial maxima. Finally, this thesis improves our understanding of terrigenous sediment sources, changes in the ACC dynamics and ocean circulation in the Pacific sector of the Southern Ocean over orbital to millennial time-scales. The studies provide new insights into the evolution of the ACC dynamic changes in the central Drake Passage and its potential influences on global thermohaline circulation over the past 140,000 years. Future sedimentological and palaeoceanographic work should reconstruct Quaternary changes of the ACC across a meridional transect in the Drake Passage to better quantify the ACC and throughflow transport and velocities