PROPOSED SITES

North of Molokai Fracture Zone (PAT-15)
Site PAT-15D will be used primarily to define the shift in the ITCZ through the Paleogene by following the change in aeolian dust composition and flux through time. It will also help define North Equatorial Current and North Pacific subtropical gyre processes, although the probable lack of carbonate above the lower Eocene will preclude high-resolution paleoceanographic studies. Site PAT-15D will also be highly important to test whether there was significant motion of the Hawaiian hotspot with respect to the Earth's spin axis during the early Cenozoic. At 56 Ma, the backtracked location based upon a hotspot reference frame (Gripp and Gordon, 1990, for 0- to 5-Ma Pacific-hot spot rotation pole; Engebretson et al., 1985, for older poles) should be about 11°N, 117°W. At 40 Ma, the site was located at about 16°N, 121°W. If significant hotspot motion or true polar wander occurred since 57 Ma (Petronotis et al., 1994), this drill site could have been much nearer to the equator.

Between Molokai and Clarion Fracture Zones (PAT-26, PAT-13, and PAT-19)
Site PAT-26 was chosen because, based upon the seismic stratigraphy of seismic reflection data acquired on EW9709, it is near the thickest section of lower Eocene sediments along the 56-Ma transect (Moore et al., 1999). This site is relevant to understanding the processes that caused higher sediment accumulation, a sign of elevated paleoproductivity. We will be particularly interested in this drill site if the paleoequator proves to be significantly north of the position estimated by the hotspot reference frame. Site PAT-26 will also be used to define tropical circulation in the Paleogene and the shift in ITCZ in the Paleogene and Neogene.

Site PAT-13C will be drilled during Leg 200, if time becomes available, and will be used primarily to define tropical current structure and sedimentation in the early and middle Eocene, although the lack of carbonate above the lower Eocene will make it difficult to perform high resolution paleoceanographic studies. It will also help define the shift in ITCZ through the Paleogene by following the change in aeolian dust composition and flux through time. One of the important discoveries of the site survey cruise is the presence of an almost pure biogenic sediment, a middle Eocene radiolarian ooze, deposited when the site was more than 8° north of the paleoequator as defined by hotspots. This type of deposition has no analog in modern sediments and appears to be an important feature of the middle and early Eocene. Part of the objectives of drilling will be to better understand the conditions that formed the radiolarian ooze. We also want to understand whether the hotspot reference frame has moved with respect to the spin axis. At 56 Ma, the backtracked location based upon a hotspot reference frame was 8°N, 109°W. At 40 Ma, the site was located at about 10°N, 113°W.

Site PAT-19A will be important to define the North Equatorial Current/North Equatorial Countercurrent boundary and it will help define the middle and late Eocene CCD. It will also better define the extent of the middle Eocene radiolarian bloom noted at Site PAT-13 and DSDP Site 40 and will be used to define the shift in ITCZ through the Paleogene by following the change in aeolian dust composition and flux through time. At 56 Ma, the backtracked location based upon a hotspot reference frame was 5°N, 106°W. At 40 Ma, the site was located at about 8°N, 111°W. If the Hawaiian hotspot has moved significantly with respect to Earth's spin axis (Petronotis et al., 1994), this drill site would have been in a near-equatorial position.

Between Clipperton and Clarion Fracture Zones (PAT-8, PAT-17, PAT-9, PAT-10, and PAT-12)
Site PAT-8C is the only top priority drill site on the 40-Ma transect. Both it and Site PAT-9D were at the equator at 40 Ma based upon fixed hotspot backtracking. Site PAT-8C will be used to define equatorial circulation and upwelling from the middle Eocene through the Eocene/Oligocene boundary. Its primary role will be to monitor equatorial upwelling and evolution of the South Equatorial Current. It will also be used to monitor bottom waters generated in the Antarctic and changes in CCD through comparisons with Site PAT-9D. At 40 Ma, the backtracked location was 0°N, 107°W based upon a hotspot reference frame. The site passed below the CCD in the middle lower Miocene.

Site PAT-17C will be used to study equatorial ocean circulation from the late Paleocene to the late Eocene including deep-water flow and properties and will help define the CCD during the Eocene-Oligocene transition and near the Oligocene/Miocene boundary. Based on the piston core from the site survey, Site PAT-17C passed below the CCD in the lower Miocene. At 56 Ma, the backtracked location was 5°S, 107°W based upon a hotspot reference frame. At 40 Ma, the site was located at about 2°S, 113°W. Site PAT-17C crossed the equator at 29 Ma. If there has been significant southward movement of the Hawaiian hotspot relative to the Earth's spin axis in the early Cenozoic, this site will be important to determine the magnitude of that motion. PAT-17C passed below the CCD in the middle lower Miocene.

Site PAT-9D will be used to define early Eocene equatorial circulation during the early Cenozoic thermal maximum and to study the evolution of equatorial circulation as the world cooled. It will also be used to study equatorial ocean circulation in the middle and late Eocene including deep-water flow and properties and will be used to define the CCD during the Eocene-Oligocene transition. One of the high priorities of drilling will be to compare Site PAT-9D to Site PAT-8C. Both were on the equator at 40 Ma, but Site PAT-9D was about 1100 m deeper. They will best illuminate CCD changes in the middle Eocene through the Oligocene. At 56 Ma, the backtracked location was 3°S, 109°W based upon a hotspot reference frame. At 40 Ma, the site was located at about 0°N, 114°W.

Site PAT-10B will be used to define early Eocene equatorial circulation and study how ocean circulation evolved as the world cooled from maximum Cenozoic warmth. It will also be used to study equatorial ocean circulation in the middle and late Eocene, including deep-water flow and properties, as well as define the CCD during the Eocene/Oligocene transition. At 56 Ma, the backtracked location was 1°S, 110°W based upon a hotspot reference frame. At 40 Ma, the site was located at ~2°N, 115°W, and it should have crossed the equator at ~50 Ma. The site's near-equatorial position in the early Eocene will be important to define the strength of equatorial upwelling and define the evolution of the South Equatorial Current. Site PAT-10B will be important to define whether there has been significant southward movement of the hotspots with respect to the spin axis prior to 40 Ma.

Site PAT-12C will be used to define the northern boundary of the South Equatorial Current and to define the extent of upwelling at the early Eocene equator. It will also help define tropical current structure and sedimentation in the middle and late Eocene as well. Site PAT 12C will also be used to monitor bottom waters generated in the Antarctic and changes in CCD through the Paleogene. At 56 Ma, the backtracked location based upon a hotspot reference frame was 1°N, 111°W. At 40 Ma, the site was located at ~4°N, 116°W. Because of its position, Site PAT-12C will also help to monitor the position of the ITCZ in the late Eocene and perhaps early Oligocene. Finally, Site PAT-12C will be important to define whether there has been significant southward movement of the hotspots with respect to the spin axis prior to 40 Ma.