Abstract
Abstract. Foraminiferal communities are not static, but change in response to environmental perturbations. Given sufficient time, the change will be recorded in the total (live+dead) seafloor assemblage, from which valuable information regarding environmental trends can be obtained by re-sampling assemblages at the decadal scale.The seafloor assemblage in the 5 km × 6 km Ibis Field, off southeast Trinidad, first surveyed in 1953, was re-examined in 2005. The fauna had changed markedly between the surveys. Overall increases in the proportional abundances of Uvigerina subperegrina, Ammonia pauciloculata/Rolhausenia rolhauseni and Pseudononion atlanticum indicate an increase in nutrient supply that apparently killed off Cibicidoides pseudoungerianus and Miliolinella subrotunda, and reduced the relative abundance of Hanzawaia concentrica, but did not affect the relative abundance of Cancris sagrai. As shown by similar 1953 and 2005 planktonic/benthonic foraminiferal ratios, the increased nutrient supply impacted on both surface and bottom waters.Of the six most abundant species in 2005, five showed the same general biogeographical distributions within the field in 1953 and 2005. However, whereas the proportional abundance of Uvigerina subperegrina in 1953 increased southwards, in 2005 it increased northwards.Trinidad cannot be the source for the nutrient enrichment: the island lies down-current from the Ibis Field. Sources must therefore be sought up-current and to the southeast, in the Amazon, Essequibo and Orinoco river basins, or along the South American shoreline. It is speculated that the nutrient enrichment may be a consequence of increased phytoplankton primary production associated with nitrogen-rich run-off from South American sugarcane plantations, or from flushing of organic carbon from poorly regulated sewage systems or shrimp farms in South America.
Highlights
Micropalaeontologists have been surveying contemporary foraminiferal seafloor assemblages for well over a century, and repeated examinations of some areas have formed datasets that can be used to determine environmental trends
Differences in assemblages in the two surveys indicate an increase in nutrient supply over time
Trinidad cannot be the source for the nutrient enrichment; the current flowing over the Ibis Field trends towards Trinidad, not away from it
Summary
Micropalaeontologists have been surveying contemporary foraminiferal seafloor assemblages for well over a century, and repeated examinations of some areas have formed datasets that can be used to determine environmental trends. Contemporary and older data are used to determine changes in foraminiferal seafloor assemblages over the last fifty years in a small area off Trinidad, southeast Caribbean. The earliest studies documenting foraminiferal distributions gave only semi-quantitative records of abundance, using qualifiers such as Rare, Common or Abundant Such qualifiers are of relatively limited use in determining environmental trends, they continue to be used
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
