Red Sea tectonics unveil the largest known terrestrial ice stream: New constraints on Late Ordovician ice sheet dynamics

Mega-streamlined landforms on Earth and Mars have been attributed to aeolian, glaciogenic, fluvial, and tectonic processes. Identifying the forces that shaped these landforms is paramount for understanding landscape evolution and constraining paleo-climate models and ice sheet reconstructions. In Arabia, east-northeast, kilometer-scale streamlined landforms were interpreted to have been formed by Quaternary aeolian erosion. We provide field and satellite-based evidence for a Late Ordovician glacial origin for these streamlined landforms, which were exhumed during the Red Sea–related uplift. Then we use Late Ordovician paleo-topographic data to reconstruct the Late Ordovician ice sheet using identified and previously reported glacial deposits and landforms. Our reconstruction suggests these glacial features are part of a major, topographically controlled, marine-terminating ice stream, twice the length of the largest known terrestrial ice streams. Our results support models that advocate for a single, major, and highly dynamic ice sheet and provide new morphological-based constraints for Late Ordovician climate models.

The Use of InSAR Phase Coherence Analyses for the Monitoring of Aeolian Erosion

Aeolian erosion occurring in sand deserts causes significant socio-economical threats over extensive areas through mineral dust storm generation and soil degradation. To monitor a sequence of aeolian erosion in a sand desert area, we developed an approach fusing a set of remote sensing data. Vegetation index and Interferometric Synthetic Aperture Radar (InSAR) phase coherence derived from space-borne optical/SAR remote sensing data were used. This scheme was applied to Kubuqi Desert in Inner Mongolia where the effects of activity to combat desertification could be used to verify the outcome of the approach. We first established time series phase coherence and conducted a functional operation based on principal component analysis (PCA) to remove uncorrelated noise. Then, through decomposition of vegetation effect, where a regression model together with the Enhanced Vegetation Index (EVI) was employed, we estimated surface migration caused by aeolian interaction, that is, the aeolian erosion rate (AER). AER metrics were normalized and validated by additional satellite and ground data. As a result, the spatiotemporal migration of the target environment, which certainly induced dust storm generation, was traced and analyzed based on the correlations among surface characteristics. It was revealed that the derived AER successfully monitored the surface changes that occurred before and after the activities to combat desertification in the target area. Employing the established observation scheme, we expect a better understanding of the aeolian process in sand deserts with enhanced spatio-temporal resolution. In addition, the scheme will be beneficial for the evaluation of combating desertification activities and early warning of dust storm generations.

The 38 years of the microclimate change dynamics across a cropland-windbreak-desert transition zone in the Ulan Buh Desert, northern China

<p>The windbreak system is a major component of successful agricultural systems in arid deserts throughout the world. Ulan Buh Desert is one of the eight biggest deserts in China, and the oases there offer residence and cropland for over 90% of the local residents. However, due to climate change and human disturbances, the Ulan Buh Desert continues spreading to the south, bringing more pressure on the windbreak systems there. Meanwhile, the Chinese government put much effort into greening the desert, establishing artificial shrubs to prevent dune movement and soil loss. How microclimate in the cropland-windbreak-desert system responded to human activities and climate change has rarely been studied. In this study, we investigated the microclimate change dynamics across the cropland-windbreak-desert transition zone during the past 38 years. Two 50 m climatological towers, located in the same distance inner and outside a shelterbelt, have continuously monitored climatic factors, including air temperature, soil temperature, relative humidity, precipitation, evaporation, layered wind speeds, etc., and aeolian erosion related factors, such as layered dustfall. The long-time fluctuations of the inside and outside climatic factors have been analyzed, and the global climate change data, local land-use history, as well as the record of afforestation activities implemented by government and local people, were also collected. The results revealed that both the inside and outside windbreak air temperatures and soil temperatures increased during the past 38 years, which agrees with the global warming phenomenon. The inner windbreak air temperature is consistently lower than the outer windbreak areas, and the temperature difference is biggest in summer and smallest in winter. However, the soil temperature difference between the outside and inner windbreak is unstable. In 1995, 2002, and 2004, the dune areas even had lower soil temperature than the inner cropland. The precipitation is 0.5~100.7mm higher in cropland and the evaporation is lower in cropland when comparing to outside dune areas, but their annual variations changed greatly. The wind speed and erosion rate are significantly lower in cropland than desert dune areas, and the seasonal change exhibited a bimodal curve pattern. The results suggest that the cropland-windbreak-desert transition zone responded to global climate change simultaneously. Although the shelterbelt still creates a favorable regional climatic condition for the cropland, the differences between the inner and outer windbreak areas narrowed during the past 10 years. The aeolian erosion rate reduced significantly in outside windbreak dune areas, which may largely attribute to the artificial Haloxylon ammodendron communities planted at the southeastern margin of the desert.</p>