200 YEAR INTERRUPTION OF HOLOCENE SAPROPEL FORMATION IN THE ADRIATIC SEA

An interruption of Holocene sapropel S-1 is found in cores from variou s subbasins of the eastern Mediterranean. In core IN68-9 from the Adri atic Sea, sapropel S-1 is dated between 8300 and 6340 BP, interrupted between 7100 and 6900 BP (C-14 years uncorrected for reservoir age). L ithology and variations in the foraminiferal faunas suggest that the i ntermption is genuine, and not the result of resedimentation. The resu lts indicate that S-1 was deposited within a period of enhanced levels of productivity (resulting from increased seasonal contrasts) which s tarted around 9300 BP and ended around 5200 BP. The onset, interruptio n, and final ending of S-1 deposition in the Adriatic Sea, however, ap pear to have been triggered by changes in ventilation of the basin rel ated to changes in sea surface temperature (SST). Although the rough e stimates of SST change are relatively small (< 2 degrees C), they stil l are significant when compared with the relative SST changes consider ed necessary to upset convection in the Adriatic. Moreover, recent stu dies show that the influence of the inferred temperature changes shoul d be viewed in combination with that of reduced salinities due to (1) the deglaciation, and (2) increased humidity in the eastern Mediterran ean area during the deposition of S-1. The lithological and benthic fo raminiferal evidence that sapropel formation in the Adriatic Sea ended around 6340 BP contrasts with the conclusion from a recent geochemica l study that sapropel formation in the open eastern Mediterranean woul d have ended as late as 5000 BP. More significantly, the results of th e present study combined with other reports on sapropel interruptions suggest that the process of sapropel formation is not a very stable mo de in the basin, but that it may be relatively easily interrupted in r esponse to subtle rearrangements in the balance between productivity a nd, especially, deep water ventilation.