Faults, Vents, and Seeps Logbook
Leg 5, Day 10: Recap
April 4, 2012
The R/V Western Flyer is on its way to dock in La Paz today after a successful cruise. It is time to describe the overall cruise effort.
Leg 5 of the Western Flyer’s expedition and legs 1, 2, and 3 of the Zephyr’s focused on exploring the transform margin in the Gulf of California seafloor. This transform margin is where the Pacific Plate is slipping by the North American Plate along a strike-slip fault (similar to the San Andreas). Our goal was to have a coordinated program using two of MBARI’s research vessels. The Zephyr would conduct autonomous underwater vehicle (AUV) surveys to map the seafloor at specific sites where a fault or fault zone is associated with the plate margin, followed by the Western Flyer and remotely operated vehicle (ROV) video surveys to visually confirm the seafloor features seen on the AUV maps.
Luckily, the AUV team was in the process of finishing the surveys we needed as our leg of the expedition got underway. The Western Flyer rendezvoused with the Zephyr at sea and the AUV team handed over the data from AUV surveys critical for the success of the expedition. The very next morning we were able to use these data to find the best site for our ROV dive—just in time to allow us to fulfill our initial objectives. This was a testimony to the hard work of the AUV crew and MBARI’s ability to coordinate coupled AUV and ROV operations.
Data from the nine AUV surveys conducted from the Zephyr in the Gulf of California show the shape of the seafloor in unprecedented detail. Without these data we would not have known where the faults were. In retrospect, it is unlikely we could have identified them based solely on exploration with the ROV. However, the ROV diving provided the other critical information: visual observations and sampling.
Each AUV survey covered a relatively small section of seafloor, for example six square kilometers (3.7 square miles), and resulted in bathymetric maps at a one-meter (three-foot) grid resolution. In practical terms this means that the maps are an accurate rendition of the seafloor based on the average depth of each square meter within the survey area to a relative depth resolution of about 15 centimeters (six inches). Previously the best available maps made from surface vessels were made with a grid resolution no less than 10 meters (33 feet), and frequently with more than 25-meter (82-foot) grid resolution, with a depth resolution of about five meters (16.5 feet). Thus, while the general shape of the seafloor was known from previously available surface vessel maps, no one had ever seen the seafloor in these areas with the level of detail provided by these AUV surveys.
In addition to the bathymetric maps, the AUV also collected Chirp seismic reflection profiles for images of the sub-bottom structure or cross-sectional images of the seafloor. The profiles show layers within the sub-bottom sediment. Originally these layers were deposited as continuous horizontal beds. However, the layers were deformed within the fault zones, so the profiles show offsets and truncation of layers, juxtaposition of very different rock types, and folding of strata. In places these strata are exposed on the seafloor.
The AUV maps and profiles provide a detailed context that allows the ROV to sample the seafloor in a targeted fashion. The ROV dives on Leg 5 were primarily placed where the edges of up-turned strata were exposed, where material on both sides of the fault could be sampled, or where the thickness of the sediment that overlies the fault could be sampled.
The exact location where the main plate margin fault crosses the seafloor could be determined within just a few meters. In some places, it was associated with scarps that are from a few centimeters to tens of meters high. In other areas, the main fault forms a trough that is 10 or more meters (33 or more feet) deeper than the surrounding seafloor. In most areas the appearance of the seafloor and immediate subsurface was dramatically different on the two adjacent sides of the fault, which testifies to the extent of lateral movements along the fault. Occasionally, relatively distinct morphologic features were seen on both sides of the fault that appeared to have been cut apart by the fault and offset by a few kilometers (a mile or two). Much of our sampling was focused on documenting the nature of these offsets. The results of the sampling will only be known after the expedition when laboratory measurements are made.
We were also interested in investigating the nature of the movements along the fault. For instance, while we know that the movements between these two plates is on the order of eight centimeters (three inches) per year, we do not know whether this occurs as a continuous creep or in larger episodic ruptures. Making observations about this requires seeing the seafloor and being able to take samples based on the visual observations. While not yet definitively documented, we saw no evidence for continuous creep and ample evidence of previous ruptures.
One thing that surprised us was how little recent sediment cover there was in many of these survey areas. Most of the seafloor was bare of sediment and likely to be associated with slow, but ongoing erosion.
On the next leg we will focus on areas where there are geomorphic features on the AUV maps of the seafloor that suggest fluid venting or seepage.
La quinta etapa de la expedición del R/V Western Flyer como las etapas 1, 2 y 3 de la expedición del R/V Zephyr estuvieron enfocadas en la exploración de los márgenes transformantes en el fondo oceánico del Golfo de California. En estos márgenes se deslizan lenta e inexorablemente las placas de Norte América y del Pacífico a lo largo de una serie de enormes fracturas de deslizamiento lateral (similares a la muy famosa falla de San Andrés que corre desde Baja California Norte a lo largo de California para hundirse de nuevo en el mar al norte de San Francisco). Desde el comienzo de esta etapa el objetivo consistió en que el R/V Zephyr realizara la batimetría de muy alta resolución utilizando un vehículo autónomo submarino (VAS, en inglés AUV) en lugares específicos donde la zona de fractura limita el borde de placa. Esta cartografía de alta resolución estaría seguida por las operaciones de reconocimiento a bordo del R/V Western Flyer desde el que se conducirían las operaciones que comprobarían la veracidad de las formas topográficas del fondo oceánico que se aprecian en los mapas producidos por el VAS.
Originalmente habíamos planeado llevar a cabo los levantamientos batimétricos un mes antes de las operaciones el R/V Western Flyer, de forma que pudiéramos estudiar las batimetrías y elegir los lugares óptimos para las inmersiones. Pero la realidad siempre es mas compleja y se atravesaron problemas con los permisos que contribuyeron a retrasar las operaciones del R/ V Zephyr hasta el punto que solo teníamos datos batimétricos de 4 de los mas de 20 lugares planificados para las inmersiones al comienzo de nuestra etapa 5. Gracias al esfuerzo y coordinación de equipo y a la suerte que nos acompañaba, pudimos encontrarnos ambos barcos en medio del Golfo donde nos pasaron la información con un arte ya olvidado, en un disco duro embolsado al final de una caña, que acababan de colectar de otros 5 lugares. Al día siguiente de haber recibido los datos que nos pasaron, estábamos explorando una de las zonas de fractura que apenas la noche anterior emergió en las pantallas del ordenador mientras procesábamos los datos que nos habían pasado esa tarde.
Los datos generados en los 9 levantamientos batimétricos del R/V Zephyr en el Golfo de California muestran la morfología del fondo oceánico con un detalle sin precedentes. Aunque cada uno de estos levantamientos cubre un área relativamente pequeña del fondo oceánico, alrededor de 6 km cuadrados, su resolución de 1 m los convierte en unos mapas extraordinariamente detallados del fondo. En términos prácticos esto significa que estos mapas son una representación exacta del piso oceánico al que divide en una rejilla de cuadrados de 1 m de lado, en el que se subdivide todo el área del levantamiento, con una resolución de profundidad de 15 cm. Para ponerlo en relación a las cartografías mas finas anteriores estas subdividen el terreno en cuadrados de hasta 10 m, aunque lo común son rejillas con resolución de 25 m con una resolución en profundidad de 5 m. De forma que aunque los patrones generales de la morfología submarina ya los conocíamos gracias a trabajos batimétricos anteriores, nadie había conseguido desvelar la topografía con el nivel de detalle que proveen estos levantamientos del VAS.
Junto con los mapas batimétricos el VAS colectó perfiles sísmicos que penetraban unos pocos de cientos de metros bajo la superficie revelando las estructuras geológicas que subyacen bajo los contornos batimétricos y que parcialmente nos revelan su historia sedimentaria y tectónica. Las capas que podemos ver en los perfiles sísmicos, que originalmente se depositaron como capas horizontales lateralmente, las podemos ver deformadas en pliegues que recuerdan trenes de olas, muchas veces fracturadas, otras truncadas, a veces la yuxtaposición de rocas muy diferentes, y cómo y donde éstas afloran en el fondo oceánico.
Estos mapas y perfiles generados por el VAS nos proveen del contexto que alimentan el muestreo y colecta del fondo oceánico para entender los procesos que los esculpieron. Las inmersiones de la etapa 5 las localizamos principalmente en las laderas sobre las que afloraban los estratos, en aquellos lugares en los que podíamos muestrear ambos lados de las fracturas, o donde el escaso espesor de sedimentos recientes nos permitían muestrear rocas más antiguas.
Pudimos determinar con un error de unos pocos metros la localización exacta donde las principales zonas de fractura de los márgenes de placa cruzan el fondo oceánico. En algunos lugares estaban a asociadas a escarpes de unos pocos centímetros a decenas de metros de altura. En otras áreas la fractura principal forma una depresión de unos 10 metros de profundidad que aparecían como largos y estrechos corredores encajonados por abruptas paredes cubiertas por un fino velo de sedimentos. Gran parte de nuestro muestreo estuvo enfocado a documentar la naturaleza de las discontinuidades a ambos lados de las zonas de fractura. En la mayoría de los lugares la apariencia del piso oceánico o de los materiales que los cubrían eran dramáticamente diferentes a ambos lados de la fractura. Ocasionalmente observamos cómo algunos rasgos morfológicos distintivos a ambos lados de la zona de fractura parecían haber sido cortados por la falla y desplazados unos pocos km en la horizontal. Observaciones que nos proveen de importantes pistas sobre el alcance de los movimientos laterales a lo largo de la zona de la falla.
Otro tema de interés en nuestra investigación tiene que ver con la naturaleza de los movimientos a lo largo de la falla. Sabemos que los movimientos entre ambas placas es del orden de 8 cm por año, pero desconocemos como se produce este desplazamiento, si éste es debido a un arrastre continuo o a rupturas episódicas. Aunque aún no podemos documentar esto último de una forma definitiva, podemos afirmar que no vimos evidencias de arrastre contínuo.
Otra de las sorpresas con la que nos encontramos es la escasa cobertera sedimentaria reciente en las zonas que visitamos. Gran parte del fondo oceánico no tenía sedimentos recientes y posiblemente esté asociado a procesos activos de erosión lenta.
En la próxima etapa nos vamos a enfocar en áreas cuyos rasgos geomorfológicos sugieren la existencia de flujos subsuperficiales de fluidos ricos en elementos reducidos y/o fugas de gases que alimentan una fauna muy especial en el fondo del océano que se alimenta o sustenta de procesos quimiosintéticos, que es otra estrategia ancestral para obtener la energía necesaria que tienen algunos los seres vivos en nuestro planeta.
R/V Western Flyer
The R/V Western Flyer is a small water-plane area twin hull (SWATH) oceanographic research vessel measuring 35.6 meters long and 16.2 meters wide. It was designed and constructed for MBARI to serve as the support vessel for ROV operations. Her missions include the Monterey Bay as well as extended cruises to Hawaii, Gulf of California and the Pacific Northwest.
ROV Doc Ricketts is MBARI's next generation ROV. The system breaks new ground in providing an integrated unmanned submersible research platform, with many powerful features providing efficient, reliable and precise sampling and data collection in a wide range of missions.
MBARI's heat-flow probe is mounted on the side of the ROV Doc Ricketts inside the vertical stainless steel box. This both protects the delicate probe and provide the track so that the probe can be inserted into the sediment along a totally straight path. The probe contains five high precision platinum sensors which are used to measure the vertical temperature gradient in the sediments. This gradient along with some knowledge of the heat capacity of the sediment allows scientists to calculate the rate of heat loss from the sediments into the ocean.In situ gas sampler
These are devices that are used to collect and sample gaseous gases bubbling out of seafloor vents. The way they work is by having small pressure vials (like tiny scuba tanks) from which the air is pumped out with a vacuum pump on the surface and sealed with the valve. On the bottom gases are captured underneath an overturned funnel so that a large gas headspace is developed. Then the value on the pressure vial is opened, gas is sucked into the vial, and the vial's value is re-closed. This way a sample of the gas at the high seafloor pressures is recovered.In situ ultraviolet spectrophotometer (ISUS)
The ISUS is a sensor used to measure concentrations of dissolved chemicals directly from their Ultraviolet Absorption Spectrum. A variety of chemicals absorb light in the UV and each of these chemicals has a unique absorption spectrum. We can determine the concentration of these chemicals directly, with no chemical manipulation, by measuring the absorption spectrum of seawater in the UV and then deconvolving the spectra to yield the concentration of each component. ISUS has been used to determine nitrate concentrations while deployed on CTD/Rosette profilers, undulating towed vehicles such as a SeaSoar or SeaSciences Acrobat, and on deep-sea moorings. It has also been used to measure sulfide flux from cold seeps in Monterey Bay while deployed on the ROV Ventana.
A push-core looks like a clear plastic tube with a rubber handle on one end. Just as its name implies, the push core is pushed down into loose sediment using the ROV's manipulator arm. As the sediment fills up the core, water exits out the top through one-way valves. When the core is pulled up again, these valves close, which (most of the time) keeps the sediment from sliding out of the core tube. When we bring these cores back to the surface, we typically look for living animals and organic material in the sediments.
Vibracoring is a common technique used to obtain samples from water-saturated sediment. These corers work by attaching a motor that induces high frequency vibrations in the core liner that in turn liquefies the sediment directly around the core cutter, enabling it to pass through the sediment with little resistance.Gravity corer
Device lowered off the ship to the seafloor on a wire which consists of a long tube that extends below a moderately heavy weight. When the device encounters the bottom, the weight forces the tube into the sediments. When it is pulled out of the bottom the tube will contain a sediment sample (i.e., core) of the upper layers of the ocean floor.
R/V Western Flyer
ROV Doc Ricketts
Leg 5 Research Team
Charlie Paull has been a marine geologist and geochemical stratigrapher at MBARI since January 1999. The central theme of Charlie's work involves investigating the fluxes of fluids and gases through continental margins. Over the past decade his primary focus has been gas hydrate research on the Blake Ridge gas hydrate field on the continental rise off of southeastern North America. Assessing the global distribution of gas hydrate and interstitial gas is a continuing interest as well as the development of new techniques to detect the presence of gas hydrate in marine sediments. Charlie's other ongoing work is focused on the geology associated with seafloor seepage sites, including investigating the deposits associated with chemosynthetic communities, determining the processes that occur at the methane-sulfate boundary, and understanding the origin of pockmarks and other potential seafloor fluid venting sites.
Ken's research interests are focused on the development of new analytical methods for chemicals in seawater and application of these tools to studies of chemical cycling throughout the ocean. Over the past 15 years, Ken's Chemical Sensor Program at MBARI has developed a variety of sensors and analyzers that operate in situ to depths of 4,000 meters. These instruments have been used to study processes ranging from the distribution of sulfide in deep-sea hydrothermal vent systems, to nitrate in coastal ponds surrounded by intensive agricultural activities.
Krystle Anderson is a research technician working for Charlie Paull in the Continental Margins Lab. Krystle's background is primarily in the acquisition and processing of seafloor mapping data. She came from the California State University, Monterey Bay Seafloor Mapping Lab where she obtained her data processing and Geographic Information System (GIS) skills. Krystle spends a majority of her time processing and creating high-resolution maps of multibeam data collected from the mapping AUV. The high-resolution maps Krystle helps create will then be used to aid navigation for the ROV to explore particular areas of interest. On this expedition Krystle will assist with running the GIS system, and processing and cataloguing sediment samples and vibracores. This is Krystle's second research expedition with MBARI and she is very excited to be involved in this expedition.
Roberto is a geochemist by training. His interests lie at the intersection of marine geology and sediment and water chemistry. During cruises Roberto operates a custom-built, portable chemistry lab that includes a complete set of analytical platforms for measurements of fluids and gases. On this expedition, Roberto will be responsible for analytical measurements of pore water chemistry on samples taken from sediment cores. He will also be in charge of collecting gas samples emanating from fluid vents and performing hydrocarbon analyses on dissolved gases collected from pore waters, from gas vents and from seawater.
Eve Lundsten works with Charlie Paull in the Continental Margins Lab. Eve's background is in hydrology but she uses her technical and mapping skills to help understand the processes that create the morphology we see on the seafloor. The Continental Margins Lab uses high-resolution, AUV-collected bathymetric maps to help direct research to the precise location of interest on the seafloor where samples can be collected for further analysis. Eve's responsibilities on this cruise include running the GIS mapping system, assisting with the processing of vibracores, and push cores collected on ROV dives, and documentation of the many samples collected during this leg of the cruise. Eve is very excited to participate in this cruise and is looking forward to many exciting discoveries.
Shannon is a molecular ecologist. This means she uses genetics to solve mysteries about how invertebrates like worms, snails, mussels and clams, who live at hydrothermal vents, cold seeps, wood, and whale falls move around in the deep sea. These environments act like islands in the ocean because most of the animals that inhabit these environments depend on chemosynthetic bacteria for food. The reducing environments provide mineral-rich water that feed the bacteria, creating an abundance of life. On the cruise, Shannon will be responsible for collecting, identifying, and dissecting invertebrates as well as filtering water to study their larvae.
Susan von Thun
Susan works in the video lab at MBARI, where she is a senior research technician. Her primary role at MBARI is to help manage and annotate the remotely operated vehicle (ROV) video archive. Observations about the biology, geology, and equipment in ROV videos are logged using software designed by MBARI engineers called the Video Annotation and Reference System (VARS). On this expedition, Susan will use VARS to annotate and document video coming back to the ship from ROV Doc Ricketts. As one of the few biologists on this leg of the expedition, Susan will be busy identifying and processing biological samples.
Teresa has worked as a Logistics Specialist in the Division of Marine Operations at MBARI for 12 years. She has spent much of the past year planning and preparing for this expedition, including obtaining scientific permits from the Mexican government, scheduling the science missions and port stops, arranging for services during port stops, and arranging visas for the scientists. During this expedition Teresa will help process samples collected with the ROV, assist in the ROV control room with video tapes and frame grabs, and other science tasks. Teresa is very excited to sail as a member of the science team and will no doubt learn a lot from both marine operations and science perspectives.
Brian specializes in sedimentary processes and stratigraphy, integrating insights gleaned from seafloor rock and sediment samples with information from remote-mapping products, such as close-up photographs of the seafloor, high-resolution bathymetric maps, and seismic-reflection profiles. His recent studies have focused on how sediment moves from the land to the deep sea, processes controlling submarine landslides, saltwater intrusion into coastal aquifer systems, marine pollution, seafloor habitats, and the Cenozoic history of the Arctic Ocean.
Juan Carlos Herguera
Juan Carlos is interested in the history of past oceans, how changes in climate and ocean circulation contribute to the ecology and biogeochemical cycling sustained by coastal environments in the California Current and the Gulf of California regions. During this cruise he will be involved in sampling benthic foraminifera to help characterize their genomic information, and, through their stable isotopic and metal compositions, to understand how these geochemical markers reflect their ambient conditions. He will further use planktonic foraminifera for dating the deep-sea cores with radiocarbon techniques, which hold important clues on the tectonic rupturing rhythm along the boundary between the North American and Pacific plates. He is fascinated by these new observation windows opened up by the ROV deployed from the Western Flyer, making possible the discovery of new vent environments along these fractured boundaries and the chemosynthetic oasis sustained by these leaky enclaves that connect the deep ocean with the lower crust and mantle dynamics.
Mary's interests focus on using microbiota (primarily foraminifera but also pollen) to investigate marine sediment transport, geohazards (faulting, landslides and paleotsunamis), climate change, and the pathways and impact of invasive species introductions using sediment records and molecular analysis techniques. She also uses foraminifera in biomonitoring marine pollution sites and carbon-14 chronostratigraphy—the study of the age of rock layers in relation to time.
Luis Arturo Terán Ortega
As a member of the Mexican Geological Survey (SGM), Luis has conducted extensive geological research and prospective surveying mining studies focused on detecting resources with potential economic value. In 2007, the Mexican government commissioned the Mexican Geological Survey to conduct prospective efforts over the entire Mexican territory and adjacent sea to identify potential energy resources such as gas, coal, uranium, and other strategic minerals. Luis is the Manager of Regional Exploration of SGM and his prospective studies encompass Sonora, the Gulf of California, the Baja California peninsula, and the territorial Sea in the Pacific Ocean. This is his first experience on a research cruise and he hopes to gain a better understanding of the richness of the Gulf of California environment from a geologic, biologic, and mineral resources perspective. Luis is very eager to learn from and collaborate with his peers from MBARI.