Seasonal variability of phytoplankton fluorescence in relation to the Straits of Messina (Sicily) tidal upwelling

[摘要] In the Straits of Messina, large gradients of tidal displacements, as wellas the topographic constrictions, determine the upwelling of deeper watersin the surface layer. This work describes the seasonal variability in thesurface distribution of phytoplankton biomass depending on the upwellingphenomena. Temperature, salinity, nitrates and phytoplankton fluorescencewere measured in 1994 and 1995 by continuous underway surface real-timemeasurements onboard dedicated research boats. Each survey was performedfollowing the dynamic phases of flooding and ebbing tides. Tidal currentsare essentially southward during high tide and northward during low tide.

During the low water slack tide, large spatial gradients ofphysical-chemical and biological parameters were found, while at the highwater slack tide, a diffused phytoplankton fluorescence was observed only inautumn due to a seasonal thermocline. Salinity, nitrate and chlorophyll-afluorescence data revealed a significant positive intercorrelation, whereasthey were inversely correlated with temperature. Generally, the upwellingdistribution was limited to narrow zones during winter, while in summer itwas found in the middle of the Straits and in the southern zones. Duringspring in the southern zone of the Straits, the maximum chlorophyll-afluorescence was detected (May 1995, 0.32 μg-Chla l⁻¹); in summer,when back and forth tidal movements between the Tyrrhenian and the Ionianseas intensify, decreased values were observed throughout the study area.

The data set obtained through continuous and repeatable samplings hasallowed the study of different time-space scales in the Straits of Messina,a very strong and dynamic environment.

The Straits system could be compared to an "intermittent pump" which, duringthe different seasons, initially enriches itself and subsequently providesnutrients to the surrounding basins.

[学科分类] 海洋学与技术