Grain-Size Record of Ocean Current Winnowing in Oligocene to Pleistocene Ooze, Broken Ridge, Southeastern Indian Ocean

Abstract

At Ocean Drilling Program Sites 752 and 754, located on Broken Ridge in the eastern Indian Ocean, we recovered a sequence of shallow-water pelagic sediments that span the past 90 m.y. The Oligocene to Pleistocene portion of these sediments are unconsolidated carbonate oozes that display a coherent variation in bulk grain size. We believe these sediments to be winnowed, and suggest that their grain size is a measure of that winnowing energy. The largest increase in grain size, interpreted to represent an enhancement in the energy of ocean currents, occurs in the earliest late Miocene. This increase occurs about 20 m upcore from the oxygen isotope indication of ice-volume increase about 13 Ma, and is about 3 m.y. younger. If this distinct temporal separation between proxy indicators of ice volume and of current intensity observed in the Broken Ridge cores is correct, the general impression of paleoclimatologists that the planetary temperature gradient and therefore atmospheric and oceanic circulation intensity varies directly with ice volume needs to be reconsidered.

Late Miocene Onset of Tasman Leakage and Southern Hemisphere Supergyre Ushers in Near‐Modern Circulation

“…Gaps in sedimentation in the GAB sites occur at the depth of TL ODP Leg 182 Site 1126, 784 m; Site 1134, 701 m; Site 1130, 488 m (Feary et al, 2004) and act as secondary evidence for enhanced circulation along the TL pathway south of Australia. Grain size data from the Broken Ridge indicates current 10.1029/2021GL095036 7 of 11 winnowing associated with TL onset at 7 Ma (Figure 2; House et al, 1992). In addition, the alignment of Broken Ridge winnowing (House et al, 1992) with evidence for a southerly shift in westerlies (Groeneveld et al, 2017) provides additional support for an atmospheric enhancement to the TL pathway.…”

“…Oxygen Minimum Zone (OMZ) data from Dickens and Owen (1994). Winnowing data from House et al (1992). SAF position from Groeneveld et al (2017).…”

Textural variations in Neogene pelagic carbonate ooze at DSDP Site 593, southern Tasman Sea, and their paleoceanographic implications

“…An increase in the >63 µm fraction at c. 10 Ma is evident in the sediments from Broken Ridge in the southern Indian Ocean and is attributed to an increase in winnowing energy associated with invigorated SCIW (House et al 1991). These authors make the suggestion that the oxygen isotope evidence for an increase in ice volume at 13 Ma (i.e., glacial events Mi3 and Mi4; Flower & Kennett 1994, 1995 is manifested in the textural record at Broken Ridge some 3 m.y.…”

“…Studies of the grain-size distribution of carbonatedominated pelagic sediments have been few in number (e.g., Oser 1972;van Andel 1973;Gardner et al 1986a;House et al 1991). This study investigates the nature and possible controls on sediment textural changes in the carbonate-dominated ooze through the earliest Miocene-Holocene interval (c. 19-0 Ma, or most of the Neogene) of core from the midlatitude, intermediate water depth, Deep Sea Drilling Site (DSDP) 593 in southern Tasman Sea (Fig.…”

Current and sea-level signals in periplatform ooze (Neogene, Maldives, Indian Ocean)

“…Although there is growing evidence for the occurrence of bottom currents affecting periplatform areas (Isern et al, 2004;Betzler et al, 2009;Bergmann et al, 2010;Eberli et al, 2010), such currents or fluctuations of the bottom-current regime were not identified as a major agent controlling the deposition of periplatform carbonate ooze. Bottom currents, however, are known to winnow carbonate ooze, and grain-size variations of such sediments are used as an index of bottom current variations elsewhere (Gardner et al, 1986;House et al, 1991;Kastanja and Henrich, 2007). Based on planktonic foraminiferal associations, Lidz and McNeill (1995) showed the admixture of fresh and reworked periplatform ooze at the Bahamas.…”