Variability of a natural hydrocarbon seep and its connection to the ocean surface.

Natural hydrocarbon seeps are ubiquitous along continental margins. Despite their significance, we lack a basic understanding of the long-term temporal variability of seep dynamics, including bubble size, rise velocity, composition, and upwelling and entrainment processes. The shortcoming makes it difficult to constrain the global estimates of oil and gas entering the marine environment. Here we report on a multi-method approach based on optical, acoustic, satellite remote sensing, and simulations, to connect the characteristics of a hydrocarbon seep in the Gulf of Mexico to its footprint on the sea surface. Using an in-situ camera, bubble dynamics at the source were measured every 6 h over 153 days and the integrated total hydrocarbon release volume was estimated as 53 m3. The vertical velocity was acoustically measured at 20 m above bed (mab) and found to be approximately 40% less than the dispersed-phase at the source, indicating that the measured values are reflecting the plume continuous-phase flow. Numerical simulations predict that the oily bubbles with diameters larger than 8 mm reach the surface with a small footprint, i.e. forming an oil slick origin, deflection of which with wind and surface current leads to the formation of an oil slick on the surface. Nineteen SAR images are used to estimate the oil seepage rate from GC600 for 2017 giving an average discharge of 14.4 cm3/s.

Inorganic carbon and oxygen dynamics in a marsh-dominated estuary.

We conducted a free-water mass balance-based study to address the rate of metabolism and net carbon exchange for the tidal wetland and estuarine portion of the coastal ocean and the uncertainties associated with this approach were assessed. We measured open water diurnal O2 and dissolved inorganic carbon (DIC) dynamics seasonally in a salt marsh-estuary in Georgia, U.S.A. with a focus on the marsh-estuary linkage associated with tidal flooding. We observed that the overall estuarine system was a net source of CO2 to the atmosphere and coastal ocean and a net sink for oceanic and atmospheric O2. Rates of metabolism were extremely high, with respiration (43 mol m-2 yr-1) greatly exceeding gross primary production (28 mol m-2 yr-1), such that the overall system was net heterotrophic. Metabolism measured with DIC were higher than with O2, which we attribute to high rates of anaerobic respiration and reduced sulfur storage in salt marsh sediments, and we assume substantial levels of anoxygenic photosynthesis. We found gas exchange from a flooded marsh is substantial, accounting for about 28% of total O2 and CO2 air-water exchange. A significant percentage of the overall estuarine aquatic metabolism is attributable to metabolism of marsh organisms during inundation. Our study suggests not rely on oceanographic stoichiometry to convert from O2 to C based measurements when constructing C balances for the coastal ocean. We also suggest eddy covariance measurements of salt marsh net ecosystem exchange underestimate net ecosystem production as they do not account for lateral DIC exchange associated with marsh tidal inundation.

Treatment of prosthetic joint infections: validation of a surgical algorithm and proposal of a simplified alternative.

The Del Pozo and Patel (DPP) algorithm permits to identify suitable candidates for debridement and implant retention (DR) in prosthetic joint infections (PJI), but does not include gram-negative bacilli (GNB) as a risk factor of worst outcome. We conducted a retrospective study to validate the DPP algorithm and propose a simplified algorithm including GNB PJI. From 2002 to 2009, 73 PJI underwent surgery; 55% were chosen according to PDD algorithm. Non-adherence increased the risk of treatment failure (HR = 4.2). Performing DR in the presence of GNB PJI and performing DR in a joint prosthesis implanted for >3 months without hematogenous infection were independent risk factors. Our simplified algorithm, based on these 2 criteria, showed comparable performance to the DPP algorithm but increased eligibility for DR by a 2.4 fold.

Acoustic measurement of the Deepwater Horizon Macondo well flow rate.

On May 31, 2010, a direct acoustic measurement method was used to quantify fluid leakage rate from the Deepwater Horizon Macondo well prior to removal of its broken riser. This method utilized an acoustic imaging sonar and acoustic Doppler sonar operating onboard a remotely operated vehicle for noncontact measurement of flow cross-section and velocity from the well's two leak sites. Over 2,500 sonar cross-sections and over 85,000 Doppler velocity measurements were recorded during the acquisition process. These data were then applied to turbulent jet and plume flow models to account for entrained water and calculate a combined hydrocarbon flow rate from the two leak sites at seafloor conditions. Based on the chemical composition of end-member samples collected from within the well, this bulk volumetric rate was then normalized to account for contributions from gases and condensates at initial leak source conditions. Results from this investigation indicate that on May 31, 2010, the well's oil flow rate was approximately 0.10 ± 0.017 m(3) s(-1) at seafloor conditions, or approximately 85 ± 15 kg s(-1) (7.4 ± 1.3 Gg d(-1)), equivalent to approximately 57,000 ± 9,800 barrels of oil per day at surface conditions. End-member chemical composition indicates that this oil release rate was accompanied by approximately an additional 24 ± 4.2 kg s(-1) (2.1 ± 0.37 Gg d(-1)) of natural gas (methane through pentanes), yielding a total hydrocarbon release rate of 110 ± 19 kg s(-1) (9.5 ± 1.6 Gg d(-1)).

The relative effects of particles and turbulence on acoustic scattering from deep-sea hydrothermal vent plumes.

Acoustic methods are applied to the investigation and monitoring of a vigorous hydrothermal plume within the Main Endeavor vent field at the Endeavor segment of the Juan de Fuca Ridge. Forward propagation and scattering from suspended particulates using Rayleigh scattering theory is shown to be negligible (log-amplitude variance σ(χ) (2)~10(-7)) compared to turbulence induced by temperature fluctuations (σ(χ) (2)~0.1). The backscattering from turbulence is then quantified using the forward scattering derived turbulence level, which gives a volume backscattering strength of s(V)=6.5 × 10(-8) m(-1). The volume backscattering cross section from particulates can range from s(V)=3.3 × 10(-6) to 7.2 × 10(-10) m(-1) depending on the particle size. These results show that forward scatter acoustic methods in hydrothermal vent applications can be used to quantify turbulence and its effect on backscatter measurements, which can be a dominant factor depending on the particle size and its location within the plume.