April 21st, 2003; Leg 5, Day #1

The R/V Western Flyer left port this morning at 8:00 a.m., beginning the nearly 24-hour transit to the Guaymas Basin dive site. As the ship sailed through the day, we passed rugged, barren terrain of volcanic rocks dissected by dry valleys. Most of these volcanic rocks were formed in the Miocene, more than six million years ago. We've had calm weather, with warm breezes, and pods of dolphin have entertained us throughout the day.   

The rugged landscape, formed from banded pink and green volcanic tuffs, seen from the ship during the transit north. Volcanic tuffs are formed from the ashes ejected during large, explosive eruptions.

The objective of Leg 5A, led by geologist Charlie Paull and ocean chemist Peter Brewer, is to study the fluxes of hydrocarbon-rich gases from the ocean floor into the overlaying seawater and atmosphere. There are indications that gases like these have affected Earth's climate in profound ways in the geologic past, but few studies have been conducted to study the effects of active gas venting in modern times.  

Charlie Paull gathered the science group together this afternoon to discuss the ROV dive objectives for the next two weeks. Our first stop is north of Guaymas. The area of interest is the transform fault that extends northwest from the northeast end of the Guaymas Basin. In this area, the North American and Pacific tectonic plates are moving slowly past one another along a narrow zone. We plan to sample across this plate boundary and expect it to be only a few hundred meters in width. 

The benthic elevators on the fantail. These will be 
used to recover cores from the vibracoring system 
that is mounted on the ROV Tiburon for the first 
dives of this series.

We have targeted tomorrow's dive site because it is one of the few places known where methane-rich hydrocarbon gas plumes emanate from the seafloor and can be traced acoustically 600 meters up into the overlaying water column. This site will provide us an opportunity to study how the gas venting affects the overlying water column and how its signal is preserved in the geologic record. Our measurements here will help us to better understand geochemical signals in the rock record that are believed to record huge outgassing events that occurred in ancient times. 

The first dive transect of the morning will cross the transform fault perpendicularly and climb up the steep wall of the fault block to get to a gas-soaked ridge crest. Tomorrow's efforts will be devoted to collecting vibracores and pushcores for pore water chemical analysis in the chemistry van that is onboard.  

– Reported by Debbie Meyer with input from Charlie Paull and Bill Ussler

As part of the emergency drill procedures, 
the science party practiced putting on the immersion suits.