Planktonic foraminifera as proxies of the Holocene climatic variability (Tyrrhenian, Mediterranean Sea)

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Abstract

Introduction. The focus of this study is the paleoclimatic reconstruction of the southern Tyrrhenianbetween ~9.2 and 2.9 ka, through the study of planktonic foraminiferal assemblages and stableisotopes, and comparing data with other coeval intervals. Several authors have studied the climaticsensitivity of Holocene planktonic foraminifera in different parts of the Mediterranean. Planktonicforaminifera produce good records of Holocene climatic variability, especially as regards the suborbitalevents such as Bond events (Bond et al., 1997) and other cooling/warming oscillations.Therefore, the obtained eco-biostratigraphy has allowed us to analyze how climatic forcing influencedsea surface temperature (SST) and water column structure during the Holocene in this sectorof the southern Tyrrhenian Sea.Methodology. A sedimentary core (196 cm long) was collected in the Gulf of Palermo at the baseof the upper continental slope (990 m bsl) and sub-sampled every 2 cm. Micropaleontological andgeochemical analyses were performed on 98 samples, and three AMS 14C dates were determined.Micropaleontological analyses consisted of qualitative and quantitative characterization of theplanktonic foraminiferal assemblages, in the size fraction greater than 125 μm. Geochemical analyseswere performed on 8–10 specimens of Globigerina bulloides.Results. The calibrated AMS 14C ages, together with planktonic foraminiferal fluctuations and G.bulloides oxygen isotope records, were used to develop an age model of the studied interval. In orderto obtain additional age control points, the studied records were also tuned to the NGRIP δ18O(GICC05) (Svensson et al., 2008) and GISP2 ice core temperature (Alley, 2000) records.Twenty species and eco-morphotypes were recognized in the planktonic foraminiferal assemblageand grouped depending upon their climatic and feeding affinity. The warm-water species, minusthe typical cold-water species, were used to obtain the paleoclimatic curve, whilst the herbivorous/carnivorous ratio has permitted us to reconstruct the trophism of the southern Tyrrhenian. Inparticular, between ~8 and 6.4 ka, an important warming phase was recognized, clearly indicatedby the increase of Globigerinoides gr. ruber and G. gr. quadrilobatus. This interval corresponds tothe deposition of Sapropel S1b-equivalent stage (Sprovieri et al., 2003; Lirer et al., 2013; Siani etal., 2013), when high SSTs and oligotrophy characterized the entire Mediterranean region, especiallyduring the summer seasons. Between ~5.9 and 4.2 ka, another warming phase occurred in theGulf of Palermo, differing from the previous one due to the enhanced winter mixing of the watercolumn, testified by the high abundance of deep dweller species, such as Globorotalia truncatulinoidesand Globorotalia inflata left coilings. The last important warming phase corresponds to theMinoan Warm Period, briefly interrupted by a rapid cooling event (at ~3.5 ka).Among these warm climatic phases, several rapid cold-cool events were recognized. In particular,Neogloboquadrina pachyderma and Turborotalita quinqueloba represent the best cold-water indicators, increasing in abundance during the Bond events (B2, B3, B4, B5, B6) and other rapid coolingevents that characterized the western (M3, M4, M5, M6, M7) (Frigola et al., 2007) and centralMediterranean (TC2, TC3, TC4) (Cacho et al., 2001) during the 9.2–2.9 ka interval.Conclusions. Planktonic foraminifera and oxygen isotope variations highlight the climatic oscillationsof the relatively stable Holocene stage. These oscillations are
Lingua originaleEnglish
Numero di pagine3
Stato di pubblicazionePublished - 2017

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