Morphometry of Coccolithus pelagicus s.l. (Coccolithophore, Haptophyta) from offshore Portugal, during the last 200 kyr.

摘要

A morphometric study of Coccolithus pelagicus s. l. coccoliths was performed on 98 samples from a long sediment core recovered off the Portuguese margin (MD95-2040) and 29 more surface samples from an extensive area of the North Atlantic. The core allowed following in detail morphometric changes of this species through the last two glacial cycles while surface samples were used to analyse biogeographic distribution of the morphotypes. The main purpose of the present work is to identify and characterize the existence of distinct morphotypes of the species Coccolithus pelagicus s.l. and test the presence of its two extant subspecies (C. pelagicus pelagicus and C. pelagicus braarudii) in the studied area. For each sample maximum placolith diameters of one hundred randomly selected specimens were tabulated into 1μm morphons. The behaviour of these morphons, characterized by R-mode Factor Analysis, allows defining morphotypes as groups of highly correlated morphons. Surface sample data set showed the existence of three morphotypes; a small (7-10μm), an intermediate (1 l-13μm), and a large morphotype (15-16μm). The factor scores distribution shows that at present day, the smallest morphotype mainly occurs above 60°N, the intermediate is predominant in the West coast of Iberia, whereas the largest one tends to occur in areas surrounding the Azores region. Data from MD95-2040 also allowed the identification of three morphotypes: a small (6-9μm), an intermediate (10-13μm) and a large (14-15μm) morphotype. The small morphotype shows significant similarities to the records of the two independent proxies for the periodic influence of cold waters off Iberia, the abundances of left-coiling N. pachyderma and ice-rafted detritus (IRD). These confirm its positive response to subpolar influxes off western Iberia, its direct relationship to C. pelagicus pelagicus and thus its future use as a proxy for cold waters. The intermediate morphotype is related to C. pelagicus braarudii and to the upwelling conditions off Iberia while the predominance of a larger morphotype (here described as C. pelagicus azorinus) in the Azores region may allow its future use as a proxy of the influence of the Azores current in Eastern North Atlantic.