High resolution paleo-environmental changes during the Sapropel 1 in the North Ionian Sea, central Mediterranean

Abstract

High-resolution paleoceanographic reconstruction of surface water properties during the most recent Sapropel event (S1) has been carried out by means of quantitative analyses of planktonic foraminiferal assemblages, planktonic foraminiferal oxygen isotopes (δ18O) and XRF elemental data from a 655 m depth core recovered in the North Ionian Sea. The results show that the S1 interval presents two distinctive warm phases (S1a and S1b), separated by a cold interruption event (S1i). High resolution faunal and geochemical analyses allow to identify two sub-phases within S1a interval, the oldest one has similar characteristics to S1b interval while the youngest sub-phase has less stratified surface waters with relatively lower nutrient content. The high abundance of Globigerinoides ruber white variety opposite to the low percentages of Neogloboquadrina pachyderma during the pre-S1 phase suggests that the onset of surface waters stratification occurred prior to the beginning of Sapropel deposition, acting as a pre-conditioning phase. Paleo-productivity proxies indicate that the deposition of S1 initiated after an increase in nutrient content, potentially related to increased fluvial inputs. Based on the integrated ecological interpretation of our records we argue that S1a and S1b are characterized as warm, stratified and nutrient rich surface waters in the Ionian Sea, while proxies related to oxygen content indicate dysoxic deep waters linked to a combination of the high nutrient content and stratified water column. The S1 interruption phase is characterized by the entrance of colder waters that caused mixing of the stratified water column and re-ventilation of the deep dysoxic waters.

Eastern Mediterranean water outflow during the Younger Dryas was twice that of the present day

“…The maximum reduction of the E-Med intermediate/deep water convection was reached during the early Holocene, with the deposition of an organic-rich sediment layer known as the last Sapropel (S1) 8,10,13,18,[28][29][30][31][32] . General consensus is that the S1 occurred between 10.8 and 6.1 kyr BP 31 , although several authors have proposed that the end of S1 was asynchronous in the water column, with intermediate depths in the E-Med being "re-ventilated" between 7.7 and 7 kyr BP [33][34][35] . The S1 formation is attributed to the sum of 1) strong surface ocean stratification resulting from increased influx of fresh-water by river systems, that led to the establishment deep-basin anoxic conditions and 2) increased export productivity resulted in enhanced organic matter fluxes to the deep sea floor 8,17,[31][32][33][34][35][36][37][38] .…”

Holocene hydroclimate changes in continental Croatia recorded in speleothem δ13C and δ18O from Nova Grgosova Cave

“…Based on the combined planktonic and benthic stable oxygen and carbon isotopes from South Adriatic marine core MD 90–917, two main mid-Holocene sea surface temperature (SST) coolings were reported at 8.2 ka and within post-sapropel S1b phase between 7.3 and 6.3 ka (Siani et al, 2013) (Figure 7). These cooling episodes are related to long-term (multi-decadal) periods of strong winter inflow of cold and dry air from eastern Europe, causing severe northeast winds ( bora ) along the eastern Adriatic coast (Rohling et al, 2002; Siani et al, 2013) which is also the principal mechanism for cool Adriatic deep water (ADW) forming (Checa et al, 2020).…”

Globorotalia truncatulinoides in the Mediterranean Basin during the Middle–Late Holocene: Bio-Chronological and Oceanographic Indicator

“…In the central-western Mediterranean Sea, several studies have highlighted that l.c. G. truncatulinoides temporarily disappears just before the base of Sapropel S1 [99,108].…”

“…In the Mediterranean Sea, the Middle-Late Holocene transition is characterized by significant paleoclimatic and paleoceanographic changes corresponding to the end of Sapropel S1 layer (c.a. 6 ka BP) [79,108] and to the end of the African Humid climatic period (c.a. 5 ka BP) [109].…”