The variation in basal channels and basal melt rates of Pine Island Ice Shelf

In recent years,there has been a significant acceleration in the thinning,calving and retreat of the Pine Island Ice Shelf(PIIS).The basal channels,results of enhanced basal melting,have the potential to significantly impact the stability of the PIIS.In this study,we used a variety of remote sensing data,including Landsat,REMA DEM,ICESat-1 and ICESat-2 satellite altimetry observations,and Ice Bridge airborne measurements,to study the spatiotemporal changes in the basal channels from 2003 to 2020 and basal melt rate from 2010 to 2017 of the PIIS under the Eulerian framework.We found that the basal channels are highly developed in the PIIS,with a total length exceeding 450 km.Most of the basal channels are ocean-sourced or groundingline-sourced basal channels,caused by the rapid melting under the ice shelf or near the groundingline.A raised seabed prevented warm water intrusion into the eastern branch of the PIIS,resulting in a lower basal melt rate in that area.In contrast,a deepsea trough facilitates warm seawater into the mainstream and the western branch of the PIIS,resulting in a higher basal melt rate in the main-stream,and the surface elevation changes above the basal channels of the mainstream and western branch are more significant.The El Ni?o event in 2015–2016 possibly slowed down the basal melting of the PIIS by modulating wind field,surface sea temperature and depth seawater temperature.Ocean and atmospheric changes were driven by El Ni?o,which can further explain and confirm the changes in the basal melting of the PIIS.

The morphological changes of basal channels based on multisource remote sensing data at the Pine Island Ice Shelf

The basal channel is a detailed morphological feature of the ice shelf caused by uneven basal melting.This kind of specifically morphology is widely distributed in polar ice shelves.It is an important research object of sea-ice interaction and plays a vital role in studying the relationship between the ice sheet/ice shelf and global warming.In this paper,high-resolution remote sensing image and ice penetration data were combined to extract the basal channel of the Pine Island Ice Shelf.The depth variation of Pine Island Ice Shelf in the recent 20 years was analyzed and discussed by using ICESat-1,ICESat-2,and IceBridge data.Combined with relevant marine meteorological elements(sea surface temperature,surface melting days,circumpolar deep water and wind)to analyze the basal channel changes,the redistribution of ocean heat is considered to be the most important factor affecting the evolution and development of the basal channel.

Greenhouse gas emission analysis and measurement for urban rail transit: A review of research progress and prospects

Rail transit plays a key role in mitigating transportation system carbon emissions.Accurate measurement of urban rail transit carbon emission can help quantify the contribution of urban rail transit towards urban transportation carbon emission reduction.Since the whole life cycle of urban rail transit carbon emission measurement involves a wide range of aspects,a systematic framework model is required for analysis.This research reviews the existing studies on carbon emission of urban rail transit.First,the characteristics of urban rail transit carbon emission were determined and the complexity of carbon emission measurement was analyzed.Then,the urban rail transit carbon emission measurement models were compared and analyzed in terms of the selection of research boundaries,the types of greenhouse gas(GHG)emissions calculation,and the accuracy of the measurement.Following that,an intelligent station was introduced to analyze the practical application of digital collaboration technology and energy-saving and carbon-reducing system platforms for rail transit.Finally,the urgent problems and future research directions at this stage were discussed.This research presents the necessity of establishing a dynamic carbon emission factor library and the important development trend of system integration of carbon emission measurement and digital system technology.

Temporal and spatial changes of the basal channel of the Getz Ice Shelf in Antarctica derived from multi-source data

Basal melting is an important factor affecting the stability of the ice shelf.The basal channel is formed from uneven melting,which also has an important impact on the stability of the ice shelf.Therefore,it has important scientific value to study the basal channel changes.This study combined datasets of Mosaics of Antarctica,Reference Elevation Model of Antarctica(REMA) and Operation Ice Bridge to study the temporal and spatial changes of basal channels at the Getz Ice Shelf in Antarctica.The relationships between the cross-sectional area and width of basal channel and those of its corresponding surface depression were statistically analyzed.Then,the changes of the basal channels of Getz Ice Shelf were derived from the ICESat observations and REMA digital elevation models(DEMs).After a detailed analysis of the factors affecting the basal channel changes,we found that the basal channels of Getz Ice Shelf were mainly concentrated in the eastern of the ice shelf,and most of them belonged to the ocean-sourced basal channel.From 2009 to 2016,the total length of the basal channel has increased by approximately 60 km.Affected by the warm Circumpolar Deep Water(CDW),significant changes in the basal channel occurred in the middle reaches of the Getz Ice Shelf.The change of the basal channels at the edge of the Getz Ice Shelf is significantly weaker than that in its middle and upper reaches.Especially in 2005–2012,the eastward wind on the ocean wind field and the westward wind around the continental shelf caused the invasion and upwelling of CDW.Meanwhile,the continuous warming of deep seawater also caused the deepening of the basal channel.During from 2012 to 2020,the fluctuations of the basal channels seem to be caused by the changes in temperature of CDW.