Key Environmental Factors Controlling Planktonic Foraminiferal and Pteropod Community’s Response to Late Quaternary Hydroclimate Changes in the South Aegean Sea (Eastern Mediterranean)

Abstract

A multidisciplinary study was conducted in order to investigate the environmental factors affecting the planktonic foraminiferal and pteropod communities of the south Aegean Sea. Aspects of the Late Quaternary paleoceanographic evolution were revealed by means of quantitative analyses of planktonic foraminiferal and pteropod assemblages (including multivariate statistical approach; principal component analysis (PCA)), the oxygen (δ18O) and carbon (δ13C) isotopic composition of planktonic foraminifera and related paleoceanographic (planktonic paleoclimatic curve (PPC), productivity (E-index), stratification (S-index), seasonality) indices, extracted by the gravity core KIM-2A derived from the submarine area between Kimolos and Sifnos islands. Focusing on the last ~21 calibrated thousands of years before present (ka BP), cold and eutrophicated conditions were identified during the Late Glacial period (21.1–15.7 ka BP) and were followed by warmer and wetter conditions during the deglaciation phase. The beginning of the Holocene was marked by a climatic amelioration and increased seasonality. The more pronounced environmental changes were identified during the deposition of the sapropel sublayers S1a (9.4–7.7 ka BP) and S1b (6.9–6.4 ka BP), with extremely warm and stratified conditions. Pteropod fauna during the sapropel deposition were recorded for the first time in the south Aegean Sea, suggesting arid conditions towards the end of S1a. Besides sea surface temperature (SST), which shows the highest explanatory power for the distribution of the analyzed fauna, water column stratification, primary productivity, and seasonality also control their communities during the Late Quaternary.

Ecological Constraints of Plankton Bio-Indicators for Water Column Stratification and Productivity: A Case Study of the Holocene North Aegean Sedimentary Record

“…In contrast, the pteropod distribution pattern does not respond in the same way as planktonic foraminifera to changes in productivity. It is known that nutrient concentration is not a limited factor for their distribution [99], though our data suggest that fluctuations in nutrients and salinity due to the increased freshwater inputs, especially during the sapropel S1 deposition, favor the flourishment of the species B. chierchiae [29]. The stratification factor, on the contrary, affects the pteropod fauna (38%) more than the planktonic foraminifera (16%) (Tables 1 and 2).…”

“…The stratification factor, on the contrary, affects the pteropod fauna (38%) more than the planktonic foraminifera (16%) (Tables 1 and 2). Our data suggest that the pteropod distribution pattern is controlled primarily by the oxygen concentration of the water column and, thus, the extent and intensity of the OMZ [29,56], which is related to the stratification of the entire water column. OMZ alterations are climatically controlled, with humid and milder climates favoring a strong and well developed OMZ, whereas cooler and/or arid periods are characterized by a more aerated OMZ [93,100].…”

“…The second factor (PCA2) explains the 27.66% of the total variance (Table 2). Its positive pole is represented mainly by the mesopelagic oligotrophic H. inflatus and the negative pole by the epipelagic B. chierchiae, which proliferates in nutrient-enriched waters (Table 4) [29,57]. Therefore, PCA2 is interpreted as a productivity factor (Figure 4e).…”

“…The presence of low salinity surface waters, as inferred from the planktonic foraminifera, is also enhanced by the high relative abundance of the epipelagic pteropod B. chierchiae. This species is known to proliferate in low, as well as high, salinity shallow waters [29,91,92]. Thus, both plankton assemblages (T. quinqueloba and H. inflatus) that correspond to the sapropel S1 represent a biotope with a strongly stratified water column characterized by intense OMZ, with low salinity and high fertility of the surficial waters.…”

Climate Change and Marine Geological Dynamics

“…The book Climate Change and Marine Geological Dynamics includes nine contributions [1][2][3][4][5][6][7][8][9] to this Special Issue published during 2020-2021. Overall, the aim of this Special Issue is to collect studies that provide new views on marginal and open marine geological phenomena and processes by using different methodologies and approaches.…”