Leg 5: March 27, 2012
Day 2: Wallowing in the fault
You might think looking at mud all day could be kind of boring. But today was an exciting day of sampling. We were able to do chemical, thermal, and lithological (the physical characteristics of a rock formation) measurements across a transform fault. What was even more exciting was sitting smack dab in the middle of a fault trough while sampling. The sonar images combined with the maps from the autonomous underwater vehicle (AUV), D. Allan B., helped us to visualize the topography of the bottom, and to find the fault scarp, a big wall that was covered with anemones and seastars.
This large scarp is interesting because it indicates recent movement along the fault zone. The thermal measurements we took are used to help understand whether warm water is moving upwards along the fault. The temperature probe is inserted into the bottom for 15 minutes and takes incredibly precise measurements every second. It is so sensitive that the friction of inserting the probe into the seafloor affects the initial measurements. Thus, measurements are made over a 15-minute time period. We made these measurements at six sites on a transect across the fault.
Chemical measurements of the water surrounding the remotely operated vehicle (ROV) are also being taken with the in situ ultraviolet spectrophotometer (ISUS). With this piece of equipment, Ken Johnson is looking for dissolved hydrogen sulfide, which is important because it is present in geologically active seepage areas and can support chemosynthetic biologic communities.
We also took six vibracores across the fault. These are super-sized push cores that go up to 170 centimeters (five and a half feet) deep in the mud and are used to study sedimentation, and to reconstruct environmental conditions and tectonic motions over historical time. The vibracores we are taking here in the Gulf of California will enable the geologists to look back thousands of years. The Pacific and the North American Plates meet in the Gulf of California, which is a geologically active tectonic region and also biologically productive. With these attributes combined, we are able to unearth fascinating and important mysteries with respect to how environmental conditions change over time.
In addition to vibracores, we took old-fashioned push cores. These tubes go much shallower in the mud than the vibracores. We use these to collect mud and benthic foraminiferans. Mary McGann and Juan Carlos Herguera are studying these important, tiny detrital feeders. Foraminiferans, or “forams,” are wonderful proxies for changing environmental conditions, and, besides bacteria, they are one of the most ubiquitous creatures in the world. Scientists can differentiate climactic conditions based on the presence, abundance, and composition of the different species. Forams have a hard “test,” or shell, which enables them to be easily fossilized, and these fossils can then be collected in cores and studied. We are also working to preserve living forams in order to extract DNA to create a catalog of the species found in the Gulf of California, and to look at how the species vary as we head north, farther into the gulf.
One of the most exciting parts of our day was the “technology transfer” from the R/V Zephyr to the R/V Western Flyer! The Zephyr team is busy making maps with the AUV D. Allan B., and we use those maps to decide where we should dive next. In fact, as I type this log, Charlie Paull and Eve Lundsten are processing the data and looking for sites that have interesting geological structures, and inferring the evolution of the seafloor caused by sedimentation, deposition, and tectonics. However, these files are HUGE and you can’t easily transfer these data without a big fat network cable, or, say a net! So the Zephyr met us in the middle of the gulf and we traded them some warm food and treats for some tofu, garlic, and DATA!!! Thanks Zephyr crew! We are still wondering why the tofu and garlic…
All in all it was a very successful day! Lots of mud, rocks, faults, and fun!