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<p>Variation in the size of the facultative symbiotic planktonic foraminifera <i>Globorotalia menardii</i> during the latest Tortonian was studied in the Potamida section (Crete Island, Eastern Mediterranean). The size analysis revealed a complete size spectrum ranging from 330 to 450&#xa0;μm, consisting of small, medium, and large specimens, as a biotic response to the environmental changes in the Mediterranean Sea during the Late Miocene. The observed size changes are attributed to the widely variable environmental conditions in this dynamic paleoceanographic setting characterized by alternating cooler-warmer and saltier-fresher seawater events just prior to the Messinian–Tortonian boundary. Following the already documented strong relationship between size and oxygen-stable isotopes for Potamida samples, additional linear correlation analyses with the key environmental parameters for the study area revealed a stronger correlation with salinity compared to temperature. Productivity seems to have only a limited effect in such an ultra-oligotrophic setting. Overall, our findings clearly point to salinity being the primary factor of <i>G. menardii</i> size variability through the study time interval. Notably, smaller apparent test sizes occurred during extremely salty, temperate (non-optimum) conditions within the lower thermocline, while larger sizes occurred during freshening and warming episodes within a well-developed shallow thermocline. Between these events, the intermediates reflect the gradual improvement of paleoceanographic conditions for <i>G. menardii</i>. The mechanism hidden behind the size alteration correlates with the differential upper water column salinities with the density of symbionts surrounding <i>G. menardii</i> specimens. This process regulates metabolism and infers changes in the biological processes controlling the foraminiferal growth.</p>

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Environmental factors determining the size variability of Globorotalia menardii prior to the Tortonian–Messinian transition: implications for the salinity effect

  • 期刊论文

  • 发表日期：

    2025年4月21日

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  • Evangelia Besiou,
  • George Kontakiotis,
  • Iuliana Vasiliev,
  • Assimina Antonarakou

摘要

Variation in the size of the facultative symbiotic planktonic foraminifera Globorotalia menardii during the latest Tortonian was studied in the Potamida section (Crete Island, Eastern Mediterranean). The size analysis revealed a complete size spectrum ranging from 330 to 450 μm, consisting of small, medium, and large specimens, as a biotic response to the environmental changes in the Mediterranean Sea during the Late Miocene. The observed size changes are attributed to the widely variable environmental conditions in this dynamic paleoceanographic setting characterized by alternating cooler-warmer and saltier-fresher seawater events just prior to the Messinian–Tortonian boundary. Following the already documented strong relationship between size and oxygen-stable isotopes for Potamida samples, additional linear correlation analyses with the key environmental parameters for the study area revealed a stronger correlation with salinity compared to temperature. Productivity seems to have only a limited effect in such an ultra-oligotrophic setting. Overall, our findings clearly point to salinity being the primary factor of G. menardii size variability through the study time interval. Notably, smaller apparent test sizes occurred during extremely salty, temperate (non-optimum) conditions within the lower thermocline, while larger sizes occurred during freshening and warming episodes within a well-developed shallow thermocline. Between these events, the intermediates reflect the gradual improvement of paleoceanographic conditions for G. menardii. The mechanism hidden behind the size alteration correlates with the differential upper water column salinities with the density of symbionts surrounding G. menardii specimens. This process regulates metabolism and infers changes in the biological processes controlling the foraminiferal growth.