Response of the barrier island coastal region of southwestern Nigeria to climate and non-climate forcing

Despite threats emanating from the influence of climate and non-climate forcing on the barrier island coastal region of southwestern Nigeria, the extent of the coastal erosion is poorly understood. We report evidence of coastal erosion and sediment accumulation in the region over a 34-year period (1973–2017), using Landsat imagery at intervals of approximately six years. Landsat image corrections and various water-extraction algorithms were used to systematically delineate coastal erosion and accumulation in the area. The region was subdivided into western and eastern subregions separated by Lagos Harbour. In the west, erosion took place during the periods 1973–1979, 1979–1984, 1990–1999 and 2005–2011, whereas in the east, erosion occurred during 1973–1979, 1990–1999 and 1999–2005. Coastal sediment accumulation occurred in the east during 1979–1984, 1984–1990, 2005–2011 and 2011–2017, whereas gains in the west occurred during 1984–1990, 1999–2005 and 2011–2017. The study revealed substantial net erosion of 1 228.1 ha in the region as a whole, over the full period. Sediment accumulation accompanying the coastal erosion appears to be linked to longshore drift. Erosion between 1973 and 2011 was probably attributable to climate change (storms and tidal conditions), longshore drift, the inflow and outflow of water at Lagos Harbour, coastal morphology and, possibly, human impacts. However, the coastal changes between 2011 and 2017 were more obviously associated with human activities, such as development of the Eko Atlantic construction project. Coastal surveillance, together with the use of environmentally sensitive protective measures, could possibly help to reduce coastal erosion in the region. Careful coastal management practices, including artificial nourishing and the installation of resilient structures (e.g. seawalls), should be undertaken to protect human settlements that are already at risk from sea-level rise.     

Late- and postglacial history of the Great Belt, Denmark

On the basis of shallow seismic records, vibrocoring, macrofossil analyses and AMS radiocarbon-dating, five stratigraphical units have been distinguished from the deepest parts of the central Great Belt (Storebælt) in southern Scandinavia. Widespread glacial deposits are followed by two lateglacial units confined to deeply incised channels and separated by an erosional boundary. Lateglacial Unit I dates from the time interval from the last deglaciation to the Allerød; lateglacial Unit II is of Younger Dryas age. Early Holocene deposits show a development from river deposits and lake-shore deposits to large lake deposits, corresponding to a rising shore level. Lake deposits are found up to 20 m below the sea floor, and the lake extended over some 200–300 km2. The early Holocene freshwater deposits are dated to the time interval c. 10900 to c. 8800 cal. yr BP and the oldest shells of marine molluscs from the Great Belt are dated to c. 8100 cal. yr BP.     

Studies on flow till in Denmark

Profiles with till and stratified meltwater sediments have been examined. Structural and morphological conditions indicate a deposition of till in the same environment as the stratified sediments. The till is interpreted as flow till which originated from considerable amounts of supraglacial material.     

Norwegian corals: radiocarbon and stable isotopes in Lophelia pertusa

The ahermatypic coral Lophelia pertusa which produces aragonitic skeletons is widely distributed along the Norwegian coast. Specimens from a number of localities have been analyzed for oxygen and stable carbon isotope composition and ¹⁴C age. Stable isotope ratios of recent corals provide information on growth rate and seasonality of oceanographic conditions. Lophelia can be useful in paleoenvironmental reconstructions. ¹⁴C dates of fossil Lophelia from Drøak in the Oslofjord, collected from 20 m ahove and 40 m below present day sea-level, indicate regional extinction between 8700 and 7800 years ago. We suggest that the extinction resulted from the cut-off of deep waters by a rising sill in connection with the postglacial shoreline displacement. Radiocarbon dating of coral bushes suggests a fairly rapid growth rate as older and younger parts of recent corals do not reveal any difference in activity despite the short time scale of the history of bomb-produced ¹⁴C in the oceans.     

A REVIEW OF LICHEN GROWTH AND APPLIED LICHENOMETRY IN SOUTHWEST AND SOUTHEAST GREENLAND

This paper presents a critical review of previous lichenometric and lichen growth studies in southern parts of West and East Greenland. These studies include classic work from around Søndre Strømfjord, Sukkertoppen, Sermilik and Angmagssalik. Particular emphasis is placed on those studies examining the role played by climatic continentality on the growth rate of crustose lichens in Greenland. The latter part of the paper presents new data on lichen growth rates from Sermilik, between 2001 and 2006, in 22 different lichen species. Measurements show that different species grow at different rates and growth rates vary from site to site. In this study Rhizocarpon geographicum generally grows slowly (<0.2 mm a⁻¹) while other species such as Pseudephebe minuscula grow more rapidly (1.0 mm a⁻¹) in the same environment. Comparison with other studies shows that taxa-specific growth rates are slightly greater in West than in East Greenland – probably as a result of the slightly more favourable climate and higher precipitation levels. It is suggested that recent climate change, most marked in southern Greenland, will probably result in changed growth curves (over time) for species such as Rhizocarpon geographicum . However, only more precise growth curves and lichenometric dating curves can demonstrate such a phenomenon.     

The Trachybasaltic Suite of Jan Mayen

The alkalic suite of Jan Mayen is of the trachybasaltic typewith a K₂O/Na₂O ratio of about 1·64. The suite includesall intermediate types of lavas between ankaramite and trachyte,with ankaramites being particularly prevalent. The major andtrace element trends are well defined. A new method allows distinctionbetween fractionated and accumulative ankaramites, and it isshown that the most primitive ankaramite contains 13–14per cent MgO. Experimentally determined P-T phase relationsof this composition suggest that it might be a primary composition,formed by partial melting of a spinel lherzolitic source at19·5kb and 1415°C. The fractionation from ankaramiteto trachybasalt occurred at low pressure, and was controlledby delayed gravitative settling of phenocrysts, while the fractionationfrom trachybasalt to trachyte is explained by crystallizationon the walls of the magma chambers.     

Supposed area-wasting of the Weichselian ice sheet in Denmark

The deglaciation at the end of the Weichselian in the Danish area has previously been considered to occur as a frontal wastage. Since the glacier ice was assumed to be debris-free, the wasting should be characterized by outwash plains and successions of end-moraines. The almost complete lack of sandur plains in the eastern part of the area and indications from recent investigations of widespread occurrence of flow till justify a re-evaluation of the mentioned deglaciation model.
Two morphological features have a general occurrence: the plains and the 'tunnel' valleys. The plains appear stepwise in the landscapes, and are frequently limited by steep slopes. Topmost is a subcircular kame-like hill. Sedimentologically, the plains mainly consist of melt water deposits, and the scattered occurrences of till are interpreted as flow till. The plains continue from the open landscape into the 'tunnel' valleys where they appear as terraces.
These features are considered to have been formed during the deglaciation. The almost horizontal surface of the ice sheet over large areas caused a sensitivity to changes in the climate. The wasting of the ice may therefore be expected to affect large areas almost simultaneously. On the assumption that the ice contained debris, an increasing amount of clastic matter was released on the ice surface. This material was concentrated in the depressions. If such a depression perforated the ice, the content of sediments settled on the substratum and a plain was established. During continued wasting the thickness of the ice decreased and the depressions were enlarged. They assumed the character of sandur plains. As still larger areas of these supraglacial sandurs rested on the basement the successive lower situated plains were formed. The latest ice was preserved where the 'tunnel' valleys are situated to-day.     

An observational study of the structure of the nocturnal boundary layer

In an effort to describe the basic vertical structure of the nocturnal boundary layer, observations from four experiments are analyzed. During the night, the depth of significant cooling appears to increase with time while the depth of the turbulence and height of the low level wind maximum tend to remain constant or decrease with time. Since the inversion layer extends above the low level wind maximum and shear is small in the region of the low level jet, the Richardson number reaches a maximum at the jet level and then decreases again with height. As a result, turbulence is observed to be a minimum at the height of the low level wind maximum and then increases again above this height.The National Center for Atmospheric Research is sponsored by the National Science Foundation.Part of this work was performed while a visiting scientist at Oregon State University.     

Distinguishing between lodgement till and flow till in Weichselian deposits

Lodgement till and flow till are depositcd in quite different environments. In Weichselian depmits, they can be distinguishcd by the setting of the sediments, the fabric, geotechnical characters, and the morphological appearance. These indications support each other. Of the outlined methods, the morphological is the most convenient in practice. Since flow till normally exists together with meltwater sediments it is suggested that systematic morphological mapping will be time-saving and most profitable for the prospecting of economically important clay, sand, and gravel deposits.