Stable carbon and oxygen isotope ratios of bulk sediment, planktonic and benthic foraminifera of the Cenomanian/Turonian section of DSDP Hole 80-551 in the Northeast Atlantic (Table 1)

Stable isotopes of bulk sediment and well preserved tests of planktonic and benthic foraminifera from midlatitude NE Atlantic DSDP Site 551 (Goban Spur) provide the first estimates of carbon isotope gradients within the water column at a lower bathyal site during the Cenomanian/Turonian boundary interval (CTBI). The CTBI carbon isotope excursion is prominent (up to 2‰ shift in delta13C) in the bulk (coccolith) signal, but less pronounced (approximately 0.5‰ shift in delta13C) in planktonic and benthic foraminifera. This difference indicates a very steep 13C gradient in the upper water column and a very efficient biological pump during the CTBI carbon isotope excursion. We suggest significantly increased seasonal primary production in the uppermost water column with an enhanced shallow water chlorophyll maximum as a cause for this steep carbon isotope gradient. Deep-water and surface-water temperature changes during the CTBI are estimated using benthic and planktonic foraminiferal oxygen isotopes. Warm deep-water masses (13-16°C) and a low temperature gradient within the water column prevailed in the late Cenomanian. Additional warming (approximately 2°C for both surface and deep water) occurred in the latest Cenomanian prior to CTBI black shale deposition. This pattern of CTBI black shale deposition during a temperature maximum is also evident at two low latitude locations (ODP Site 1050, Blake Nose and Tarfaya, southern Morocco).