Environmental controls on marine productivity near Cape St. Francis, South Africa

This study considers ocean–atmosphere influences on marine productivity over the shelf near Cape St. Francis, South Africa. Multiday estimates of chlorophyll fluorescence in the period 2006–2017 with an area outlined by 34.5–33.75∘ S and 24–26.5∘ E provide the basis for evaluation using data from high-resolution reanalyses. Correlations with the mean annual cycle of chlorophyll fluorescence were significant for salinity, linking marine productivity and the coastal hydrology. A strengthened Agulhas Current induces cyclonic shear that lifts water at the shelf edge. Composite high-chlorophyll-fluorescence events were dominated by a large-scale midlatitude atmospheric ridge of high pressure. The resultant easterly winds caused offshore transport and the upwelling of cool nutrient-rich water in multiday events at the beginning and end of austral summer. Environmental controls on interannual fluctuations of the commercial fishery were also explored. Southwestward currents and diminished heat fluxes favored the squid catch, while anchovy and sardine catches were linked with upper northerly wind, consistent with large-scale weather patterns that underpin coastal upwelling and river discharge. Productivity lags a few days behind cyclonic wind and current shear and the upstream coastal hydrology, which shares a common atmospheric driver.

Environmental controls on marine productivity near Cape St Francis, South Africa

This study considers ocean-atmosphere influences on marine productivity over the shelf near Cape St Francis, South Africa. Multi-day estimates of chlorophyll fluorescence in the period 2006–2017 with an area: 34.5–33.75S, 24–26.5E, provide the basis for evaluation using data from high resolution reanalysis. Correlations with the mean annual cycle of chlorophyll fluorescence were significant for salinity, linking marine productivity and the coastal hydrology. A strengthened Agulhas Current induces cyclonic shear that lifts water at the shelf edge. Composite high chlorophyll fluorescence events were dominated by a large-scale mid-latitude atmospheric ridge of high pressure. The resultant easterly winds caused offshore transport and the upwelling of cool nutrient-rich water, in multi-day events at the beginning and end of austral summer. Environmental controls on inter-annual fluctuations of the commercial fishery were also explored. Southwestward currents and diminished heat fluxes favoured squid catch, while anchovy and sardine were linked with upper northerly wind, consistent with large-scale weather patterns that underpin coastal upwelling and river discharge. Productivity lags a few days behind cyclonic wind and current shear and the upstream coastal hydrology, which shares a common atmospheric driver.

TIDAL PATTERNS AND RESOURCE USE IN THE MUSI-BANYUASIN COASTAL ZONE OF SUMATRA

Tidal influence extends 100 km upriver in the coastal swamplands of Sumatra and Kalimantan. In planning development or resource use, description of local tidal variation is important since tides interact with river flow to zone the land and waters into a series of distinctive environments. The coastal swamps are being opened for rice cultivation with tidally-influenced irrigation and drainage canals. There are also forestry and fishery activities plus major shipping activities in these delta areas. The tidal patterns arc studied in the South Sumatra coastal portion of the Musi and Banyuasin River basins. The tides are mixed, predominantly diurnal with a maximum range of 3.5 m near the coast. Significant differences in tidal amplitude and phase exist between rivers separated by deltas often less than 10 km in width. Differences in river water flow atributed to season or basin characteristics influence tidal patterns. On the Musi river the relationship between tidally-influenced resource uses and distance from the sea suggests the greatest variety of activities occurs within the zone of maximum tidal range 0 to 30 km from the delta fronts. This zone should therefore be considered a region of special ecological concern. A mechanism is needed for coordinated planning of infrastructure changes likely to influence hydrology or resource uses. Predictive models should be developed for measuring the likely impact of such development on coastal hydrology.

Mid-Holocene coastal hydrology and salinity changes in the east Taihu area of the lower Yangtze wetlands, China

During the mid-Holocene the eastern Taihu area, on China's Yangtze delta plain, was populated by advanced late Neolithic cultures supported by intensive domesticated rice cultivation. This agricultural system collapsed around 4200 cal yr BP, with severe population decline, the end of the Liangzhu culture, and about half a millennium of very low-scale human activity in the area before the re-establishment of agricultural production. Microfossil analyses from six sedimentary sequences, supported by AMS 14C dating, has allowed reconstruction of mid-Holocene hydrological conditions and salinity changes which would have had a major influence on agricultural viability and cultural history in the coastal wetlands. These data, allied to existing stratigraphic and sea-level records, show that chenier ridges that developed after ca. 7000 cal yr BP in the east of the area sheltered it from marine inundation and although still connected to the sea through tidal creeks, low-salinity conditions persisted throughout the Neolithic period. There is no evidence that marine flooding caused the collapse of Liangzhu culture. Marine influence was stable and evolved slowly. Social and cultural causes may also have been important, but if environmental change triggered the collapse of Neolithic agricultural society here, other natural forces must be sought to explain this event.