Late Quaternary dinoflagellate cysts from the Black, Marmara and Aegean seas: variations in assemblages, morphology and paleosalinity

Abstract

The link between sea surface salinity (SSS) and dinoflagellate cyst morphology was studied quantitatively in cores of Late Quaternary mud from the Black, Marmara and Aegean seas, where oxygen isotopic and planktonic foraminiferal data show salinities of about 5–19, 15–22 and 36–39 ppt, respectively. In the Black Sea, late glacial muds contain low-diversity assemblages of the cruciform species Spiniferites cruciformis and Pyxidinopsis psilata, with most S. cruciformis cysts having expanded septal membranes (form 1: circular outline, form 2: irregular). The assemblage is associated with surface salinities of <7 ppt. Overlying sapropelic muds have salinity estimates of ∼14–18 ppt and contain Lingulodinium machaerophorum– Spiniferites– Cymatiosphaera assemblages, with many L. machaerophorum cysts having short processes and S. cruciformis with reduced septa (forms 3, 4 and 5). The late Holocene coccolith-rich sediments, with salinity of ∼18–20 ppt, have diverse assemblages of Brigantedinium, Peridinium ponticum and other protoperidinioids, together with normal cysts of L. machaerophorum and Operculodinium centrocarpum (sensu Wall and Dale (1966), Nature 211, 1025–1026) that bear long processes. In the northeast Aegean core, stenohaline species and morphotypes are rare, occurring only as low percentages of S. cruciformis forms 3 and 4, and O. centrocarpum var. ‘ truncatum’ in a mid-Holocene sapropel that was deposited during a period of high runoff and Black Sea water outflow. Marmara Sea cores record surface salinities of 14–18 ppt during late glacial sapropel deposition and 20–22 ppt for the overlying marine sediments. The sapropel is dominated by S. cruciformis forms 1 and 2 and by P. psilata, with common L. machaerophorum (clavate and normal forms). In surface sediments, L. machaerophorum is co-dominant with O. centrocarpum (normal and truncate forms), Brigantedinium and Spiniferites spp. Percentages of S. cruciformis (five forms) and L. machaerophorum (two forms) plotted against proxy-salinity data, however, show no clear correlation, indicating that morphological variation is not a simple function of salinity.