(Table S1, S4) Campanian-Maastrichtian benthic foraminifera from ODP Hole 113-690C

During the latest Cretaceous cooling phase, a positive shift in benthic foraminiferal d18O values lasting about 1.5 Myr (71.5-70 Ma) can be observed at a global scale (Campanian-Maastrichtian Boundary Event, CMBE). This d18O excursion is interpreted as being influenced by a change in intermediate- to deep-water circulation or by temporal build-up of Antarctic ice sheets. Here we test whether benthic foraminiferal assemblages from a southern high-latitudinal site near Antarctica (ODP Site 690) are influenced by the CMBE. If the d18O transition reflects a change in intermediate- to deep-water circulation from low-latitude to high-latitude water masses, then this change would result in cooler temperatures, higher oxygen concentration, and possibly lower organic-matter flux at the seafloor, resulting in a major benthic foraminiferal assemblage change. If, however, the d18O transition was mainly triggered by ice formation, no considerable compositional difference in benthic foraminiferal assemblages would be expected. Our data show a separation of the studied succession into two parts with distinctly different benthic foraminiferal assemblages. Species dominating the older part (73.0-70.5 Ma) tolerate less bottom water oxygenation and are typical components of low-latitude assemblages. In contrast, the younger part (70.0-68.0 Ma) is characterized by species that indicate well-oxygenated bottom waters and species common in high-latitude assemblages. We interpret the observed change in benthic foraminiferal assemblages toward a well-oxygenated environment to reflect the onset of a shift from low-latitude toward high-latitude dominated intermediate- to deep-water sources. This implies that a change in oceanic circulation was at least a major component of the CMBE.

Stable oxygen and carbon isotope data for planktic and benthic foraminifera from southern Atlantic of DSDP Hole 74-525A and ODP Hole 113-690C

Published stable isotope records in marine carbonate are characterized by a positive d18O excursion associated with a negative d13C shift during the early Maastrichtian. However, the cause and even the precise timing of these excursions remain uncertain. We have generated high-resolution foraminiferal stable isotope and gray-scale records for the latest Campanian to early Maastrichtian (73-68 Ma) at two Ocean Drilling Program sites, 525 (Walvis Ridge) and 690 (Weddell Sea). We demonstrate that the negative d13C excursion is decoupled from the d18O increase with a lag of about 600 ka. Our d13C records (both planktic and benthic) show an amplitude for the negative excursion of 0.7 per mill that falls between about 72.1 and 70.7 Ma. Our planktic d18O records indicate an overall increase of 1.2 per mill from 73 to 68 Ma at Site 690, whereas at Site 525 they record a slightly smaller increase (1 per mill) that peaks around 70.1 Ma with decreasing values thereafter. Our benthic d18O data indicate an increase of 1.5 per mill at Site 525 and 0.7 per mill at Site 690 between about 71.4 and 69.9 Ma. Benthic d18O values show different baseline values at the two sites before and after the excursion, but the larger increase at Site 525 means that the values attained at the peak of the excursion are similar at the two sites. We interpret this observation in terms of water mass changes. The excursion is interpreted to reflect a cooling of bottom waters in response to the strengthening contribution of intermediate- to deep-water production in the high southern latitudes rather than increased ice volume. The associated carbon cycle perturbations that we observe are interpreted to reflect a weakening of surface water stratification and increased productivity, as supported by our gray value data.

(Fig. 1) Stable carbon and oxygen isotope ratios of foraminifera of ODP Hole 113-690B

A remarkable oxygen and carbon isotope excursion occurred in Antarctic waters near the end of the Palaeocene (~57.33 Myr ago), indicating rapid global warming and oceanographic changes that caused one of the largest deep-sea benthic extinctions of the past 90 million years. In contrast, the oceanic plankton were largely unaffected, implying a decoupling of the deep and shallow ecosystems. The data suggest that for a few thousand years, ocean circulation underwent fundamental changes producing a transient state that, although brief, had long-term effects on environmental and biotic evolution.

Paleomagnetic age assigments of ODP Site 113-697 (Table 1)

At Site 697 a 320 m thick Pleistocene and Pliocene section was recovered, consisting of hemipelagic terrigenous mud with varying amounts of diatoms, thin altered ash layers, and ice-rafted debris (IRD). Sedimentation rates range from 41 m/m.y. (upper Pleistocene) to 150 m/m.y. (lower Pliocene). Diatom percentage and sediment grain-size have been measured for the whole section with approximately one sample per 5,000 yr. IRD is most abundant in the lower Pliocene (sediments older than 4.5 Ma) following the first major West Antarctic glaciation. A decrease in IRD to near-zero above 3.2 Ma may record a transition from valley glaciers to a grounded ice-sheet on West Antarctica. Bottom current flow, recorded in sediments as the proportion of silt, was at a maximum around 3.0-3.3 Ma then gradually decreased until 0.5 Ma. In the upper Pleistocene, maxima in diatom percentage are assumed to occur during interglacials, implying reduced sea-ice cover; maxima in silt percentage correspond to diatom maxima, implying stronger bottom water flow during interglacials.

Benthic foraminifera and phytodetritus species in sediments from DSDP Leg 85, and ODP Legs 113 and 143

From late middle Eocene through earliest Oligocene, high-latitude regions cooled, and by the end of the period, continental ice sheets existed in Antarctica. Diversity of planktonic microorganisms declined, and modern groups of terrestrial vertebrates originated. Coeval faunal changes in deep-sea benthic foraminifers have been related to cooling of deep waters and increased oxygenation. Cooling, however, occurred globally, whereas species richness declined at high latitudes and not in the tropics. The late Eocene and younger lower-diversity, high-latitude faunas typically contain common Epistominella exigua and Alabaminella weddellensis, opportunistic phytodetritus-exploiting species that indicate a seasonally fluctuating input of organic matter to the sea floor. We speculate that the species-richness gradient and increase in abundance of phytodetritus-exploiting species resulted largely from the onset of a more unpredictable and seasonally fluctuating food supply, especially at high latitudes.