Abstract:

Our objective is to compare the impact of two marine oil well blowouts on surface sediments in the Gulf of Mexico: the recent 2010 DWH blowout in the Northern Gulf with the Ixtoc blowout in 1979/80 in the Southern Gulf. A suite of trace and minor elements (V, Cr, Mn, Fe, Co, Ni, Cu, Sr, Cd, Mo, Ba, Re, and U) some of which are sensitive to changes in sedimentary redox conditions, was analyzed in bulk surface sediments; that data is presented here. Sediment cores were collected in the SE GoM on a research cruise on the R/V Justo Sierra in August 2015. Cores were carefully extruded using a calibrated threaded rod at 2 mm or 5 mm resolution below 2 cm.

Suggested Citation:

D. W. Hastings, T. Bartlett, K. A. Quinn, B. E. Carr, D. P. Razionale, K. Husiak. 2018. Trace metals and minor elements in Southern Gulf of Mexico Sediments following the Ixtoc marine oil blow out event, 2015. Distributed by: GRIIDC, Harte Research Institute, Texas A&M University–Corpus Christi. doi:10.7266/N7DN43JM

Publications:

Hastings, D. W., Bartlett, T., Brooks, G. R., Larson, R. A., Quinn, K. A., Razionale, D., … Hollander, D. J. (2019). Changes in Redox Conditions of Surface Sediments Following the Deepwater Horizon and Ixtoc 1 Events. Deep Oil Spills, 269–284. doi:10.1007/978-3-030-11605-7_16

Purpose:

We exploit the downcore changes in the concentration of redox sensitive metals (Mn, Re, and Cd) to investigate changes in sediment redox changes following a possible pulse in organic-rich sedimentation.

Data Parameters and Units:

Sample, Depth (mm and cm), Elemental concentrations (mg/g, ppb, or ppm), Site #, Collection date (MM/DD/YYYY), Latitude (degree minutes and decimal degrees), Longitude (degree minutes and decimal degrees), Water depth (m), Length (mm)

Methods:

Subsamples (~0.2 g) were freeze dried, weighed, then digested in a Milestone Ethos EZ microwave oven in closed digestion vessels with 10mL concentrated trace metal grade HNO3 at 175°C and high pressure (~25 bar) for 15 minutes according to standard methods (US EPA method 3051a). The digest was diluted 1:10 with MQ ultrapure H2O, and filtered with 0.45 µm PVDF syringe filters. Since HF is not used during the digestion, the digest does not include refractory components such as aluminosilicates, but will include authigenic phases, crude oil, organic phases, FeMn oxides, and carbonates.

Instruments:

The samples were analyzed using an Agilent 7500cx ICP-MS with an octopole reaction cell in helium mode for V, Cr, Mn, Fe, Co, Ni, Cu, Sr, and Cd to reduce isobaric interferences and in no-gas mode for Mo, Ba, Re, and U. Prior to analysis, samples were spiked with an internal standard containing Ge, In, and Bi in order to correct for instrumental drift during analysis. Elemental concentrations were determined using a 6-point external calibration line.

Error Analysis:

Triplicate samples were typically measured for one or two depth intervals in each core with an average relative precision of ±2%, ±4%, ±4%, and ±4% (1 σ) for Mn, Re, Cd and Ba, respectively. Long-term analytical precision based on analyzing the same sample 3 times each run over 1.5 years of ICP MS analyses is ±3%, ±5%, ±5%, and ±2% (1 σ) for Mn, Re, Cd and Ba, respectively.

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