Earth Sciences

The variation of sea level at 11 stations distributed along the Suez Canal was studied during the period from 1980 to 1986. The ranges of variation in daily mean sea level at Port Said and Port Tawfik are about 60 and 120cm, respectively. The minimum range of daily variation is at Kantara (47cm).The fluctuations of the monthly mean sea level

The variation of sea level at 11 stations distributed along the Suez Canal was studied during the period from 1980 to 1986. The ranges of variation in daily mean sea level at Port Said and Port Tawfik are about 60 and 120cm, respectively. The minimum range of daily variation is at Kantara (47cm).The fluctuations of the monthly mean sea level

For the last three decades, space science remote sensing technologies have been providing enormous amounts of useful data and information in broadening our understanding of the solar system including our home planet. This research, as it has expanded our learning process, has generated additional questions. This has further resulted in establishing new science requirements, which have culminated in defining and pushing the state-of-the-art technology needs. NASAs Earth Science exploration has deployed about 18 highly complex satellites so far and is in a process of defining and launching multiple observing systems in the next decade. Due to the heightened security alert of our Nation, researchers and technologists are paying serious attention to make use of these science driven technologies for dual use. In other words, how such sophisticated observing and measuring systems can be used in detecting multiple types of security concerns with substantial lead time so that the appropriate law enforcement agencies and decision makers can take adequate steps to defuse any potential risks and protect society. This paper examines numerous NASA technologies such as laser/lidar systems, microwave and millimeter wave technologies, optical observing systems, high performance computational techniques for rapid analyses, and imaging products that can have a tremendous pay off for security applications.

ABSTRACT During the African Humid Period (AHP, 15–5 ka BP) an almost 300 m deep paleo-lake covering 2200 km2 developed in the Suguta Valley, in the Northern Kenya Rift. Data from lacustrine sediments and paleo-shorelines indicate that a large paleo-lake already existed by 13.9 ka BP, and record rapid water level fluctuations of up to 100 m within periods of 100 years or less, and a final lowstand at the end of the AHP (5 ka BP). We used a hydro-balance model to assess the abruptness of these water level fluctuations and identify their causes. We observed that fluctuations within the AHP were caused by abrupt changes in precipitation of 26–40%. Despite the absence of continuous lacustrine data documenting the onset of the AHP in the Suguta Valley, we conclude from the hydro-balance model that only an abrupt onset to the AHP, prior to 14.8 ka BP, could have led to high water levels recorded. The modeling results suggest that the sudden increase in rainfall was the direct consequence of an eastward migration of the Congo Air Boundary (CAB), caused by an enhanced atmospheric pressure gradient between East Africa and southern Asia during a northern hemisphere (NH) summer insolation maximum. In contrast, the end of the AHP must have been gradual despite an abrupt change in the source of precipitation when a decreasing pressure gradient between Asia and Africa prevented the CAB from reaching the study area. This abruptness was probably buffered by a contemporaneous change in precession producing an insolation maximum at the equator during September–October. This change would have meant that the only rain source was the Intertropical Convergence Zone (ITCZ), which would have carried a greater amount of moisture during the short rainy season thus slowing the fall in water level over a period of about 1000 years in association with the reduction in insolation. The results of this study provide an indication of the amount of time available for humans in north-eastern Africa to adapt in response to a changing climate, from hunting and gathering to farming and herding.

ABSTRACT Debate about the impact of climate-driven environmental change on prehistoric human populations suffers from the rarity of continuous paleoenvironmental records in the vicinity of archaeological sites. Here we compare the last 20 ka of a continuous paleoclimatic record from the Chew Bahir basin, southwest Ethiopia, with the available archaeological record of human presence in the region. The paleoclimatic record suggests a complex nonlinear response of the environment to orbitally-driven insolation variations, reflected in several long-term and short-term transitions of only several years between wet and dry conditions, interpreted as favorable and unfavorable human living conditions, respectively. Correlating the patchy archaeological record in the surrounding region, postulated to include montane and lake-marginal refugia for human populations, with our record of climate change suggests a complex interplay between humans and their environment during the last 20 ka. The result may be an indication of how a dynamic environment may have impacted the adaptation and dispersal of early humans in eastern Africa.

... such as the abrupt onset and termination of the AHP, which have been generally attributed to strong biogeophysical feedbacks ([Claussen et al ... part of the East African Rift System (EARS) in order to differentiate between the effects of local and regional climate change and local ...

ABSTRACT During the African Humid Period (AHP, 15–5 ka BP) an almost 300 m deep paleo-lake covering 2200 km2 developed in the Suguta Valley, in the Northern Kenya Rift. Data from lacustrine sediments and paleo-shorelines indicate that a large paleo-lake already existed by 13.9 ka BP, and record rapid water level fluctuations of up to 100 m within periods of 100 years or less, and a final lowstand at the end of the AHP (5 ka BP). We used a hydro-balance model to assess the abruptness of these water level fluctuations and identify their causes. We observed that fluctuations within the AHP were caused by abrupt changes in precipitation of 26–40%. Despite the absence of continuous lacustrine data documenting the onset of the AHP in the Suguta Valley, we conclude from the hydro-balance model that only an abrupt onset to the AHP, prior to 14.8 ka BP, could have led to high water levels recorded. The modeling results suggest that the sudden increase in rainfall was the direct consequence of an eastward migration of the Congo Air Boundary (CAB), caused by an enhanced atmospheric pressure gradient between East Africa and southern Asia during a northern hemisphere (NH) summer insolation maximum. In contrast, the end of the AHP must have been gradual despite an abrupt change in the source of precipitation when a decreasing pressure gradient between Asia and Africa prevented the CAB from reaching the study area. This abruptness was probably buffered by a contemporaneous change in precession producing an insolation maximum at the equator during September–October. This change would have meant that the only rain source was the Intertropical Convergence Zone (ITCZ), which would have carried a greater amount of moisture during the short rainy season thus slowing the fall in water level over a period of about 1000 years in association with the reduction in insolation. The results of this study provide an indication of the amount of time available for humans in north-eastern Africa to adapt in response to a changing climate, from hunting and gathering to farming and herding.

ABSTRACT Existing models of coastal occupation, in one form or another, embrace the assumption that changes in mean sea level were the prime driver for shifts in coastal resource productivity of consequence to coastal foragers. Focusing on the North West Shelf of Australia, this paper considers the role of physical sedimentary processes in understanding both past coastal resource productivity and the archaeology of drowned coastal landscapes. From a review of up-to-date literature on sea-level related coastal formation process related to the North West Shelf, we describe the complex interplay of sea-level change and sedimentary processes in determining (i) coastal resource availability, and (ii) archaeological site preservation potential through time. We argue that human behavioral models that have been linked solely to changes in sea level change from ca. 45 ka onward along the Australia continental shelf have inadequately accounted for local sedimentary regimes. It is not past sea-level per se, which is of relevance to coastal productivity and human behavioral ecology models but changes in tidal regimes, coastal configurations and sedimentation. We conclude that our understanding of maritime adaptations for Sahul (Greater Australia) remain incomplete without investigating former coastlines and archaeological information that now lies submerged offshore.

... The waves typically are 3–20 m high and have wavelengths of 300–6000 m. Limited data suggest that sediment waves are commonly linear to slightly sinuous and oblique to channel orientation ( Migeon; McHugh and Wynn), so that they may result either from local levee ...

... The waves typically are 3–20 m high and have wavelengths of 300–6000 m. Limited data suggest that sediment waves are commonly linear to slightly sinuous and oblique to channel orientation ( Migeon; McHugh and Wynn), so that they may result either from local levee ...