Leg 167-California Margin

Leg 167 will investigate the evolution of oceanogaphic conditions in the northern Pacific Ocean and will document changes in the flow of the California Current system and associated changes in coastal upwelling. These data will be used to reconstruct northern Pacific climate conditions through the Neogene, concentrating upon the time period since the advent of Northern Hemisphere glaciation (~2.5 Ma to the present). Approximately one-third of the proposed drill sites will also sample lower and middle Miocene sediments to reconstruct a Neogene history of the California Current. The results of Leg 167 drilling will also be used to better understand the links between the climates of the northern Pacific Ocean and western North America, particularly in terms of temperature change and changes in precipitation.

Thirteen proposed sites and five alternates are organized into three transects across the California Current (Baja Transect, ~30° N; Conception Transect, ~35° N; and Gorda Transect, ~40° N) and one coastal transect extending from northern Baja California to the California/Oregon border (30° to 42° N). Each of the three transects across the California Current will compare deep-water sites near the core of the California Current to coastal upwelling sites near shore. The coastal transect will examine variations in upwelling and productivity along the California margin as well as intermediate-water properties in many of the basins of the California Continental Borderland.

Leg Objectives

• To understand how a major eastern boundary current system and associated upwelling centers respond to growth of Northern Hemisphere glaciers (all sites).
• To assess feedbacks between continental and oceanic climates in the northern Pacific Ocean and North America (all sites).
• To obtain depth transects suitable for the study of variations in northern Pacific Ocean deep-water properties and carbonate deposition (North Site CA1-1033 m; Site CA2-1951 m; Site CA3-2731 m; Site CA4-3075 m; Site CA6-3316 m; Site CA5-4242 m; South Site CA15-1182 m; Site CAM2-2047 m; Site CA8-2508 m; Site CA14-3495 m; Site CA11-3873 m).
• To understand variations in the production, preservation, and burial of organic carbon in a well-studied, highly productive continental margin setting (all sites).
• To sample gas hydrates (Site CA1). Summary of Secondary Objectives
• To study tectonic development of the active continental margin of western North America (all sites).
• To investigate the deformation of the Gorda Plate (Sites CA3 and CA4).
• To test the response of continental margin sedimentation to Cordilleran uplift (all sites).
• To acquire samples of Franciscan and Gorda Plate basement where possible without compromising primary sedimentary objectives (Sites CA2, CA3, CA4, CA5, CA6, CA11, CA14, and CAM2).

Tectonic objectives, although of secondary importance, are also necessary for paleoceanographic reconstruction because many of the sites have moved hundreds of kilometers in relation to North America during the Neogene. The continental basement underneath Site CA-2, for example, is now located just south of the Mendocino Triple Junction, but it may have been separated at one time from the rest of North America as far south as northern Baja California.

Although the highest priority on Leg 167 will be given to the sampling of upper Neogene sediments (Pliocene and younger), five of the proposed drill sites will sample middle and lower Miocene sediments. The older sedimentary sections will be instrumental to understanding the Neogene paleoceanographic evolution of the northern Pacific climate.

Operations Update

A decision was reached during the PPSP meeting that SEDCO/BP 471 will not drill the Santa Barbara Basin site during Leg 167 for safety reasons.

Low transit times coupled with relatively shallow-water drilling combine to ensure that this will be a record core recovery leg. An estimated 7.2 km of core will be recovered, easily surpassing the previous record of 6730.74 m on Leg 162. As a result, during Leg 167 the ship will pull into San Diego to offload cores after the third site drilled. While in San Diego, the Mexican observer will depart the ship, and Paula Weiss will board for the remainder of the leg. It is expected that the JOIDES Resolution will clear U.S. Customs and Immigrations in San Diego harbor and will not need to clear in San Francisco.

The San Francisco port call is expected to be extremely busy with public relations activities. The cryogenic magnetometer will be replaced, microscope maintenance/training will be conducted, and possible XRF maintenance will take place during this port call.

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