Monica B. Heintz

Propane Respiration Jump-Starts Microbial Response to a Deep Oil Spill

Diving into Deep Water The Deepwater Horizon oil spill in the Gulf of Mexico was one of the largest oil spills on record. Its setting at the bottom of the sea floor posed an unanticipated risk as substantial amounts of hydrocarbons leaked into the deepwater column. Three separate cruises identified and sampled deep underwater hydrocarbon plumes that existed in May and June, 2010—before the well head was ultimately sealed. Camilli et al. (p. 201; published online 19 August) used an automated underwater vehicle to assess the dimensions of a stabilized, diffuse underwater plume of oil that was 22 miles long and estimated the daily quantity of oil released from the well, based on the concentration and dimensions of the plume. Hazen et al. (p. 204; published online 26 August) also observed an underwater plume at the same depth and found that hydrocarbon-degrading bacteria were enriched in the plume and were breaking down some parts of the oil. Finally, Valentine et al. (p. 208; published online 16 September) found that natural gas, including propane and ethane, were also present in hydrocarbon plumes. These gases were broken down quickly by bacteria, but primed the system for biodegradation of larger hydrocarbons, including those comprising the leaking crude oil. Differences were observed in dissolved oxygen levels in the plumes (a proxy for bacterial respiration), which may reflect differences in the location of sampling or the aging of the plumes. Hydrocarbon gases were the first compounds that bacteria degraded in deep underwater petroleum plumes. The Deepwater Horizon event resulted in suspension of oil in the Gulf of Mexico water column because the leakage occurred at great depth. The distribution and fate of other abundant hydrocarbon constituents, such as natural gases, are also important in determining the impact of the leakage but are not yet well understood. From 11 to 21 June 2010, we investigated dissolved hydrocarbon gases at depth using chemical and isotopic surveys and on-site biodegradation studies. Propane and ethane were the primary drivers of microbial respiration, accounting for up to 70% of the observed oxygen depletion in fresh plumes. Propane and ethane trapped in the deep water may therefore promote rapid hydrocarbon respiration by low-diversity bacterial blooms, priming bacterial populations for degradation of other hydrocarbons in the aging plume.

Methane oxidation in the eastern tropical North Pacific Ocean water column

©2015. American Geophysical Union. We report methane (CH 4 ) concentration and methane oxidation (MO x ) rate measurements from the eastern tropical north Pacific (ETNP) water column. This region comprises low-CH 4 waters and a depth interval (~200-760m) of CH 4 supersaturation that is located within a regional oxygen minimum zone (OMZ). MO x rate measurements were made in parallel using tracer-based methods with low-level 14C-CH 4 (LL 14C) and 3H-CH 4 (3H). The two tracers showed similar trends in MO x rate with water depth, but consistent with previous work, the LL 14C rates (range: 0.034-15×10-3nmol CH 4 L-1d-1) were systematically slower than the parallel 3H rates (range: 0.098-4000×10-3nmol CH 4 L-1d-1). Priming and background effects associated with the 3H-CH 4 tracer and LL 14C filtering effects are implicated as the cause of the systematic difference. The MO x rates reported here include some of the slowest rates measured in the ocean to date, are the first rates for the ETNP region, and show zones of slow CH 4 turnover within the OMZ that may permit CH 4 derived from coastal sediments to travel great lateral distances. The MO x rate constants correlate with both CH 4 and oxygen concentrations, suggesting that their combined availability regulates MO x rates in the region. Depth-integrated MO x rates provide an upper limit on the magnitude of regional CH 4 sources and demonstrate the importance of water column MO x , even at slow rates, as a sink for CH 4 that limits the ocean-atmosphere CH 4 flux in the ETNP region.

Methane oxidation rates by AMS

Goldschmidt Conference Abstracts 2009 Spring residence times: Role in weathering rates F.A.L. P ACHECO 1 AND C.H. V AN DER W EIJDEN 2 Department of Geology and Centre for Chemistry, UTAD, Vila Real, Portugal (fpacheco@utad.pt) Utrecht University, The Netherlands (chvdw@geo.uu.nl) Estimation of plagioclase (Pl) weathering rates (W Pl = ([Pl]/t)×(Q/A Pl )) at the watershed scale of springs requires the prior evaluation of a number of parameters which include the mole fractions of Pl ([Pl]) and their fracture surface areas (A Pl ), the residence times of springs (t) and their annual discharge (Q). An atempt to relate the weathering of plagioclase to mixtures rich in halloysite and to quantify the W Pl for a number of very small spring watersheds from the Vila Pouca de Aguiar region (VPA, North of Portugal) is documented in [1]. In this paper we take a step further by focusing our attention on adjusting the previously used advective flow equation and introducing hydraulic turnovers for the assessment of t. Now, the advective flow equation (t = (n e /K)(F 2 /D h )) replaces the average watershed depth (D) by the average depth of the saturated aquifer (D h ), whereas hydraulic turnovers assign t = V h n e /Q. V h is the saturated volume of the aquifer characterized by an effective porosity n e and a hydraulic conductivity K, and F is the average lateral path from the recharge area to the spring site. The evaluation of n e , K, F and Q has been addressed by [1]. The D h of the VPA springs could be related to their isotopic composition ( 87 Sr/ 86 Sr) and to annual precipitation (P): D h = [( 87 Sr/ 86 Sr) spring – ( 87 Sr/ 86 Sr) rain ] / (5.62×10 –7 P – 4.66×10 –4 ). The corresponding V h ’s were determined from the total watershed volumes (V) as calculated by a terrain modeling software: V h = V×(D h /D). The plagioclase log rates (Figure 1) are: –12.4±1.8 (adjusted flow equation) and –13.5±1.1 (turnover times). Relative to the former results, there is a decrease in the average log rates, by 0.2 in the first case and 1.4 in se second case. Number of cases Methane oxidation rates by AMS M. P ACK 1 *, M. H EINTZ 2 , W.S. R EEBUR G H 1 , S.E. T RUMBORE 1 , D.L. V ALENTINE 2 AND X. X U 1 University of California Irvine, Irvine, CA 92697 (*correspondence: mpack@uci.edu) University of California Santa Barbara, Santa Barbara, CA 93106 (mbheintz@umail.ucsb.edu, valentine@geol.ucsb.edu) In the marine environment methane (CH 4 ) oxidation consumes up to 84% of the CH 4 produced and mitigates the release of CH 4 , a potent green house gas, to the atmosphere [1]. The microbialy mediated process is an important sink in the global CH 4 budget, yet it remains poorly quantified because only a small number of direct oxidation rate measurements are available. Traditional oxidation rate measurements use regulated levels of radiotracers ( 14 C- and 3 H-CH 4 ) in conjunction with scintillation counting and come with certain limitations: safety and contamination factors restrict the measurements to isotope vans, and radioisotope use may not be permitted in foreign venues and may complicate shipping. We have developed a rate measurement that utilizes non- regulated levels of 14 C-CH 4 tracer (<50nCi/g) [2] in conjunction with accelerator mass spectrometry (AMS). The high sensitivity of AMS allows for a 10 3 reduction in tracer activity which relaxes complications with tracer shipping, handling and waste disposal. Together with ease of performance, this method could provide a larger sample throughput and therefore a better quantification of the marine CH 4 oxidation sink. Further, it allows for easy quantification of the fraction of CH 4 taken up in microbial biomass as well as the fraction oxidized, thereby providing important information about the activity of methanotrophs in the ocean. Our rate measurements compared to 3 H-CH 4 rate measurements on water from the same Niskin bottles are generally consistent. The two measurements are similar when ambient rates are high, but diverge when rates are low. [1] Reeburgh (2007) Chem. Rev. 107, 486-513. [2] Vogel (2000) Nucl. Instrum. Methods Phys. Res. B 172, 885-891. Turnover times Flow equation Times A983 Log (W Pl ) Figure 1: Log rates of plagioclase. [1] Pacheco F.A.L., Van der Weijden C.H. (2008). Geochimica et Cosmochimica Acta, v. 72, no. 17, Page A715.