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.
benthic elevators on the fantail. These will be
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.
part of the emergency drill procedures,