Sodium and strontium in mollusc shells: preservation,palaeosalinity and palaeotemperature of the Middle Pleistocene of eastern England

This paper revisits the utility of sodium (Na) content in aragonite and calcite mollusc shells as an indicator of palaeosalinity. The data come mainly from a related suite of Middle Pleistocene marine and freshwater fossils that have been subject to broadly similar diagenetic histories. Environmental salinity is re-affirmed as the primary factor in determining the sodium content of modern and ancient mollusc shells: values <2000 ppm Na are generally indicative of non-marine environments while values >2000 Na ppm are typically from marine shells. There is a positive relationship between Na (salinity) and Sr which is a helpful discriminator of palaeosalinity in the fossil data set. The Na and Sr data give confidence that the fossil shells have not suffered pervasive diagenetic alteration and that the marine fossils lived in fully marine conditions. Oxygen isotope values in the best-preserved, fully marine fossil shells, suggest Middle Pleistocene ‘eastern England’ seawater temperatures were broadly similar to those of the modern North Sea.     

Observational aspects of the low-level cross-equatorial jet stream of the western Indian Ocean

Summary Studies of all available upper wind data up to 3 km over eastern Africa and the western Indian Ocean reveal a major low-level air current circulating at about 1.5 km in the western periphery of the monsoon regime. The current originates in the southern hemisphere and penetrates progressively further north in spring until it reaches its maximum development in July. The major current is composed of systems of low-level jet streams which can be located on a daily basis, always in the same geographical areas, with speeds reaching 25–50 ms^–1 at heights of only 1–1.5 km. Because the current is topographically-locked over eastern Africa the massive flow of air from one hemisphere to the other can be monitored and some relationships with the rainfall of parts of western India can be deduced.This paper is only a brief review of the observational and analytical studies which have been carried out and reference should be made to original papers for details of the structure and development of the current.