A Geobiological Approach to Understanding Dolomite Formation at Deep Springs Lake, CA
What: This Keck project is an interdisciplinary investigation of biologically mediated precipitation of dolomite and other carbonate minerals in Deep Springs Lake, CA. Elucidating the mechanisms of modern dolomite precipitation is a fundamental and longstanding problem in sedimentology and Earth history. Students and faculty will develop an integrated suite of field and laboratory data utilizing techniques in microbiology, aqueous geochemistry, sedimentology, mineralogy, and isotope geochemistry. During the project, participants will have the opportunity to perform cutting-edge geobiological research, including one week of fieldwork in a modern alkaline playa lake and three weeks of lab research at the sponsoring institutions.
When: June 15-July 13 and during the 2013-2014 academic year.
Where: The project will start with fieldwork at Deep Springs Lake, California for approximately one week (6/15 – 6/22) followed by three weeks in Amherst, MA conducting laboratory-based research at four colleges in the area (i.e. Amherst, Smith, Mount Holyoke, and Hampshire Colleges).
Who: Six students with David S. Jones (Amherst College), Jason M. Tor (Hampshire College), M. Darby Dyar (Mount Holyoke College), Anna M. Martini (Amherst College), and Sarah B. Pruss (Smith College).
Project Overview and Goals
In order to decipher the history of Earth’s early surface environments, it is critical to develop an understanding of potential modern analog environments. In particular, many modern carbonate-forming environments may be analogs for certain Precambrian depositional systems. Strata deposited in these ancient environments host many of the records used to reconstruct the early history of our planet, potentially providing insight into the geological, chemical, and biological processes occurring at the time of their formation. Understanding interactions among these processes, particularly microbiological contributions, is essential for determining the signatures of early life and environments on Earth, and may provide new ways to detect biological activity on Mars and other planets.
In both field observations and laboratory experiments, microorganisms play a role in the formation of many carbonate minerals, possibly by reducing the thermodynamic barriers to mineral precipitation. The discovery of such microbe-mineral interactions provides fresh insights into the origin of these minerals. For example, the metabolic activity of sulfate-reducing bacteria involved in the anaerobic respiration of organic matter was shown to result in an elevated pH and a concentration of ions (e.g., Ca2+, Mg2+, HCO3-), leading to the nucleation of carbonate crystals. This process was also shown to stimulate dolomite precipitation, and may be a major contributor to the global carbonate sedimentary budget (Warthmann et al., 2000; van Lith et al., 2002). Dolomite occurs extensively in the geological record, despite its scarcity in contemporary settings (Land, 1998). This disparity, along with an inability to experimentally form dolomite in a laboratory setting at temperatures and pressures closest to those found in environments where formation has occurred, is often referred to as the “dolomite problem.” In particular, microorganisms with a broad range of metabolisms (including sulfur-oxidizers, methanogens, methanotrophs, and phototrophs) have been implicated in dolomite formation. We hypothesize that microbial metabolic activity creates conditions favorable for dolomite formation at Deep Springs Lake, and that these microbe-mineral interactions exert primary controls on elemental cycling in this environment.
The research goals for this study are to: 1) cultivate and identify the bacteria potentially responsible for the formation of dolomite; 2) assess the geochemical conditions and biochemical mechanisms that contribute to microbially-mediated dolomite formation; 3) characterize early mineral precipitates, both microbially-mediated and inorganic; 4) characterize the sedimentology and microstratigraphy of the lake deposits; and 5) elucidate the differences in the microbial communities of Deep Springs Lake, based on location within the water column and sediment.
Deep Springs Lake is an ephemeral saline lake whose sediments include approximately fifteen different carbonate minerals (Jones, 1965). Of all these, dolomite is the most abundant. A biogenic origin of dolomite formation was recently proposed for low temperature environments involving sulfate-reducing bacteria (Vasconcelos et al., 1995; Vasconcelos et al., 1997; Warthmann et al., 2000; Wright, 2000). This hypothesis proposes that sulfate-reducing bacteria may help overcome three major kinetic constraints that otherwise inhibit dolomite formation: 1) they lower sulfate concentrations, which inhibits dolomite formation at high concentration; 2) they increase the availability of magnesium, since sulfate is often associated in seawater with magnesium; and 3) they increase the pH and carbonate alkalinity through respiration (van Lith et al., 2003b; Wright and Wacey, 2005).
While a significant amount of evidence both in vitro and in situ exists to link sulfate-reducing bacteria with dolomite precipitation, this model is based on observations from only three very similar locations, Lagoa Vermelha and Brejo do Espinho in Brazil, and the Coorong region of Southern Australia (van Lith et al., 2003a). These sites share a great deal in common by being large, alkaline, hypersaline lagoons that are located at sea level and are very close to oceans. In contrast, Deep Springs Lake is an ephemeral lake 1,500 m above sea level in an arid region fed in part by springs of meteoric water, thus subject to vastly different biogeochemical conditions and variation.
Potential Student Research Projects
Microbe-mineral interactions are beyond the scope of a single discipline, and this project will provide students with an opportunity to conduct interdisciplinary research into the role of contemporary microorganisms in formation of carbonates at Deep Springs Lake. Our interdisciplinary research approach will provide students with a clear vision for this project, through effective communication and team-building skills. This will serve as a catalyst for accelerating scientific discovery and will prepare students to work more effectively in advancing their studies and solving problems.
Students will gain experience in planning and conducting field work, documenting field observations, critiquing primary research literature, developing research questions, sampling in the field, and performing geomicrobiological laboratory techniques and data analysis, while enhancing their written and oral communication. The project will devote one quarter of the time to fieldwork and the remainder to laboratory research.
- Sedimentology and mineralogy (1-2 students). This project will analyze the sedimentology and mineralogy of sediment cores taken from various locations around the lake. Scanning electron microscopy and x-ray diffraction will complement field observations and sediment core analysis. This project should yield important data on dolomite abundance and early diagenetic processes in the lake sediment.
- Geomicrobiology (2-3 students). This project will identify the microbial community in the lake water and sediment using novel enrichment and isolation techniques as well as cultivation-independent genetic analysis. Assessing the community of organisms should provide insight into their effect on the lake geochemistry and possibly identify species contributing to dolomite formation. Some isolates will be incubated directly in the lake to assess their ability to form carbonates in situ.
- Lake geochemistry (2-3 students). This project will analyze the major chemical components of the lake water, particularly the cation, anion, and organic carbon concentrations. In addition, isotopic analysis of magnesium and sulfur metabolites will enable us to characterize the sulfur metabolizing microbial community, provide insights into the modern microbe-mineral interactions, and provide a framework for interpreting sulfur isotopes in ancient dolomite rocks.
Logistics and Field Conditions
The project will begin and end in Amherst, MA with the group members meeting on June 15 for introductions and to organize our field gear. We will depart for the field on the next day. The group will fly to Las Vegas, NV and drive to Bishop, CA, with stops in Death Valley National Park and the eastern Sierra Mountains to gain an understanding of the geology and microbiology in the region. Over the following days students and faculty will work in groups to conduct the fieldwork and develop research projects. Lodging during fieldwork will be at a motel in Bishop, CA (approximately 36 miles from Deep Springs Lake). We will be preparing most of our own meals.
Deep Springs Lake is a relatively safe research environment but as in all arid environments, dehydration and heat exhaustion are possible. Therefore students should bring refillable water bottles, sunblock, and light-weight clothing (e.g. long-sleeve shirts, loose pants, durable shoes, a wide-brim hat, and sunglasses). Other natural hazards include the possibility of encountering toxic insects and animals. Students should be prepared for the potential of strenuous hiking on steep terrain and extended periods of the day in the hot sun without shade.
Upon finishing the fieldwork, we will return to the Pioneer Valley (Amherst/Northampton/South Hadley) to begin processing the samples, pool data and notes, and conduct laboratory-based research. We will introduce all students to the operation and safety requirements of all the laboratories before the students begin focused work on their project. Students will work in the labs at Hampshire, Amherst, Smith, and Mount Holyoke and will meet regularly as a large group to discuss their projects and share data. Lodging for students during lab work will be in dormitories on the campuses of Amherst, Hampshire, and Mount Holyoke colleges. Close-toed shoes and pants are typically required in the laboratories.
Recommended Courses and Prerequisites
This is an interdisciplinary research project, so students with a background and interest in a range fields are desirable, including but not limited to mineralogy, geochemistry, sedimentology, microbiology, and molecular biology. Some laboratory experience is preferred. Students should be well-organized, detail-orientated, and safety-minded.
- Jones BF (1965) The hydrology and mineralogy of Deep Springs Lake, Inyo County, California. U.S. Geological Survey Professional Paper 502-A, 56.
- Land LS (1998) Failure to precipitate dolomite at 25°C from dilute solution despite 1000-fold oversaturation after 32 years. Aquatic Geochem. 4:361-368.
- van Lith Y, Vasconcelos C, Warthmann R, Martins JCF, McKenzie JA (2002) Bacterial sulfate reduction and salinity: two controls on dolomite precipitation in Lagoa Vermelha and Brejo do Espinho (Brazil). Hydrobiologia 485:35-49.
- van Lith Y, Warthmann R, Vasconcelos C, McKenzie JA (2003a) Sulphate-reducing bacteria induce low-temperature Ca-dolomite and high Mg-calcite formation. Geobiology 1:71-79.
- van Lith Y, Warthmann R, Vasconcelos C, McKenzie JA (2003b) Microbial fossilization in carbonate sediments: a result of the bacterial surface involvement in dolomite precipitation. Sedimentology 50:237-245.
- Vasconcelos C, McKenzie JA (1997) Microbial mediation of modern dolomite precipitation and diagenesis under anoxic conditions (Lagoa Vermelha, Rio de Janeiro, Brazil). J. Sed. Res. 67:378-390.
- Vasconcelos C, McKenzie JA, Berrnasconi S, Grujic D, Tien AJ (1995) Microbial mediation as a possible mechanism for natural dolomite formation at low temperatures. Nature 377:220-222.
- Warthmann R, van Lith Y, Vasconcelos C, McKenzie JA, Karpoff AM (2000) Bacterially induced dolomite precipitation in anoxic culture experiments. Geology 28:1091-1094.
- Warthmann R, Vasconcelos C, Sass H, McKenzie JA (2005) Desulfovibrio brasiliensis sp. nov. a moderate halophilic sulfate-reducing bacterium from Lagoa Vermelha (Brazil) mediating dolomite formation. Extremophiles 9:255-261.
- Wright DT (2000) Benthic microbial communities and dolomite formation in marine and lacustrine environments: a new dolomite model. SEPM Special Publications 66:7-20.
- Wright DT, Wacey D (2005) Precipitation of dolomite using sulphate-reducing bacteria from the Coorong region, South Australia: significance and implications. Sedimentology 52:987-1008.