Paleoclimatic Record of the Pliocene at Deep Sea Drilling Project Sites 519, 521, 522, and 523 (Central South Atlantic)

Abstract

We established a composite oxygen-and carbon-isotope stratigraphy for the Pliocene in the central South Atlantic. Monospecific samples of benthic and planktonic foraminifers from pelagic sediments from DSDP Sites 519, 521, 522, and 523 were analyzed isotopically. The resulting benthic oxygen-isotope stratigraphy allowed three paleoclimatic periods in the Pliocene to be distinguished. During the early Pliocene (5.2-3.3 Ma), low-amplitude climatic changes prevailed in a world that was less glaciated than during the Pleistocene. A net increase in global ice volume is documented in a 0.5% 0 positive shift in the average 18 O composition of the benthic foraminifers at 3.2 Ma. The middle Pliocene (3.3-2.5 Ma) is not only characterized by a more widespread glaciation of the Southern and Northern hemispheres but also by more drastic isotopic differences between glacial and interglacial times. A minor shift in the average 18 O composition of the benthic foraminifers marks the beginning of the late Pliocene-early Pleistocene climatic period (2.5-1.1 Ma). Alternating cold and warm climate is documented in both the oxygen-isotope record and in the pelagic sediments. During cold periods, sediments with a lower CaCO 3 content indicate more corrosive bottom-water conditions. More negative 13 C signals in the benthic foraminifers from these sediments suggest that the Antarctic Bottom Water current was intensified in glacial times. The oxygen-isotope composition of the measured planktonic foraminifers suggests that the surface water in this part of the South Atlantic remained relatively warm during the growth of the Pliocene glaciers.

Southwest Pacific Cenozoic Paleoceanography

“…Between 3.6 and 2.2 Ma at Site 590, a positive shift of 0.4‰ in benthic δ 18 θ generally coincided with a negative shift of about 0.4‰ in planktonic δ 18 θ (Elmstrom and Kennett, this volume). This is interpreted by Kennett (this volume) to represent a surface-water warming of at least 2°C at these latitudes, in concurrence with the observation of Weissert et al (1984) at similar latitudes (~30°S) in the South Atlantic. This warming occurred when high-latitude glaciers were growing.…”

“…5), documenting a net increase in average global ice volume and cooling of bottom waters (Elmstrom and Kennett; Kennett; both this volume). A similar oxygen isotope shift has been reported from the equatorial Pacific (Shackleton and Opdyke, 1977;Prell, 1984), the South Atlantic (Weissert et al, 1984), the North Atlantic (Shackleton and Cita, 1979), and the Mediterranean (Keigwin and Thunell, 1980). This shift almost certainly documents a cooling of intermediate waters (Prell, 1984), but possibly also some additional growth of Antarctic ice (Weissert et al, 1984).…”

“…A similar oxygen isotope shift has been reported from the equatorial Pacific (Shackleton and Opdyke, 1977;Prell, 1984), the South Atlantic (Weissert et al, 1984), the North Atlantic (Shackleton and Cita, 1979), and the Mediterranean (Keigwin and Thunell, 1980). This shift almost certainly documents a cooling of intermediate waters (Prell, 1984), but possibly also some additional growth of Antarctic ice (Weissert et al, 1984). Increased glaciation of Antarctica at about 3.5 Ma created a northward shift in the deposition of circum-Antarctic glacial marine sediments (Ciesielski and Weaver, 1974).…”

Pliocene Stable Isotope and Carbonate Stratigraphy (Holes 572C and 573A): Paleoceanographic Data Bearing on the Question of Pliocene Glaciation

“…Hence, the magnetic data are apparently disturbed and the isotopic record may also be affected. In this connection, a large number of benthic records do show an enrichment at about 3.2 Ma (e.g., Keigwin, 1982b;Hodell et al, 1983;Weissert et al, 1984;Shackleton and Cita, 1979). Hence, the Hole 552A record may be not definitive for this interval.…”

Mesozoic climates and oceans – a tribute to Hugh Jenkyns and Helmut Weissert

“…During the 1970s and early 1980s, the field of Mesozoic palaeoceanography was just emerging, fostered by the integration of geological observations with the novel discoveries from ocean drilling. During his early career, Helmi Weissert took part in DSDP Leg 73 to the South Atlantic Ocean, encountering new palaeoceanographic concepts and ideas, and developing research on Pliocene climates and oceanography (Weissert et al ., ; Weissert & Oberhänsli, ). Although the Mesozoic remained a primary stratigraphic focus, Helmi Weissert's work on Neogene palaeoceanography certainly influenced his later work on deep‐time sedimentary systems.…”