AN INTEGRATED VIEW OF INORGANIC AND ORGANIC BIOGEOCHEMICAL INDICATORSOF PALAEOPRODUCTIVITY CHANGES IN A COASTAL UPWELLING AREA

In order to evaluate the role of the continental margin areas in the c hanges of atmospheric CO? during past climatic cycles, it is crucial t o reconstruct reliably export palaeoproductivity changes in such areas . This paper examines and discusses the specific relationships between various productivity-dependent geochemical signals recorded in a sing le sediment core from the northwestern Africa continental slope, inclu ding both major and trace parameters of inorganic and organic origin. This paper clearly shows that the export productivity flux, as well as its composition (e.g. the relative contribution of calcareous, silice ous and mineral-free producers) have changed. These changes have subse quently modified benthic conditions, which can have had, in turn, a re troaction on major biogenic element contents. This effect seems, howev er, to be only minor compared to that one directly induced by changes in biogenic fluxes. These results indicate that direct palaeoproductiv ity transfer functions, which are based on present-day statistical cal ibrations of one single parameter and which are valid to some extent f or sediments from abyssal open ocean, cannot be properly applied in ma rginal areas which are much more complex and, in particular, highly af fected by sea level changes. In such areas, quantitative palaeoproduct ivity reconstructions should be only considered at a regional scale in cluding off-shoreward, on-shoreward and latitudinal migration or exten sion of the productive areas, as well as the palaeoproductivity intens ity and composition. Copyright (C) 1996 Elsevier Science Ltd