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High-resolution oxygen and carbon isotope stratigraphy is presented for Miocene to early Pliocene sequences at three DSDP sites from the Lord Howe Rise, southwest Pacific, at water depths ranging from 1,300 to 2,000 m. Site 588 is located in the warm subtropics (~ 26°S), whereas Sites 590 and 591 are positioned in transitional (northern temperate) water masses (~ 31°S). Benthic foraminiferal oxygen and carbon isotope analyses were conducted on all sites; planktonic foraminiferal isotope data were generated for Site 590 only. Sample resolution in these sequences is on the order of 50,000 yr. or better. The chronological framework employed in this study is based largely upon ages assigned to Neogene calcareous nannoplankton boundaries. The benthic oxygen isotope record exhibits several major features during the Neogene. During most of the early Miocene, δ 1 8 θ values were relatively low, reaching minimum values in the late early Miocene (19.5 to 16.5 Ma), and recording the climax of Neogene warmth. This was followed by a major increase in benthic δ 1 8 θ values between ~ 16.5 and 13.5 Ma, which is interpreted as representing major, permanent accumulation of the East Antarctic ice sheet and cooling of bottom waters. During the 3 m.y. 1 O enrichment, surface waters at these middle latitudes warmed between 16 and 14.5 Ma. During the remainder of the middle and late Miocene, benthic δ 1 8 θ values exhibit distinct fluctuations, but the average value remained unchanged. The isotopic data show two distinct episodes of climatic cooling close to the middle/late Miocene boundary. The earliest of these events occurred between 12.5 and 11.5 Ma in the latest middle Miocene. The second cooling event occurred from 11 to 9 Ma, and is marked by some of the highest δ 1 8 θ values of the entire Miocene. This was followed by relative warmth during the middle part of the late Miocene. The latest Miocene and earliest Pliocene (6.2 to 4.5 Ma) were marked by relatively high δ 1 8 θ values, indicating increased cooling and glaciation. During the middle Pliocene, at about 3.4 Ma, a 0.4‰ increase in benthic δ 1 8 θ documents a net increase in average global ice volume and cooling of bottom waters. During this interval of increased glaciation, surface waters warmed by 2-3°C in southern middle-latitude regions. During the late Pliocene, between 2.6 and 2.4 Ma, a further increase in δ 1 8 θ occurred; this has been interpreted by previous workers as heralding the onset of Northern Hemisphere glaciation. Surface-water warming in the middle latitudes occurred in association with major high-latitude glacial increases in the early middle Miocene (16-14 Ma), middle Pliocene (-3.5 Ma), and late Pliocene (~2.4 Ma). These intervals were also marked by increases in the vertical temperature gradient in the open ocean. Intersite correlation is enhanced by using carbon isotope stratigraphy. The great similarity of the δ C time-series records within and between ocean basins and with water depth clearly indicates that changes in oceanwide average δ 1 C of HCOJ in seawater dominated the records, rather than local effects. Broad changes in the Neogene δ 1 C record were caused largely by transfer of organic carbon between continental and oceanic reservoirs. These transfers were caused by marine transgressions and regressions on the continental margins. The dominant feature of Neogene δ 1 C stratigraphy is a broad late early to early middle Miocene increase of about l‰ between ~ 19 and 14.5 Ma. This trend occurred contemporaneously with a period of maximum coastal onlap (transgression) and maximum Neogene climatic warmth. The δ 1 C trend terminated during the expansion of the Antarctic ice sheet and associated marine regression. The latest Miocene carbon isotope shift (of up to O.75‰) at 6.2 Ma is clearly recorded in all sites examined and was followed by relatively low values during the remainder of the Neogene. This shift was caused by a glacioeustatic sealevel lowering that exposed continental margins via regression and ultimately increased the flux of organic carbon to the deep sea. An increase in δ 1 C values during the early Pliocene (~ 5 to 4 Ma) resulted from marine transgression during a time of global warmth.

Miocene to Early Pliocene Oxygen and Carbon Isotope Stratigraphy in the Southwest Pacific, Deep Sea Drilling Project Leg 90