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 AE 0.017 m 3 s −1 at seafloor conditions, or approximately 85AE 15 kg s −1 (7.4 AE 1.3 Gg d −1 ), equivalent to approximately 57,000AE 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 AE 4.2 kg s −1 (2.1AE 0.37 Gg d −1 ) of natural gas (methane through pentanes), yielding a total hydrocarbon release rate of 110 AE 19 kg s −1 (9.5 AE 1.6 Gg d −1 ).Gulf of Mexico | oil spill | buoyant plume | buoyant jet | subsurface A ccurate assessment of the hydrocarbon fluid release rate from well blowouts such as that of the Deepwater Horizon Macondo well provides fundamental information for evaluating intervention options to regain well control, properly scaling oil collection and containment operations, estimating the total spill volume, assessing environmental damage, and investigating well casing or blowout preventer (BOP) failure modes. On May 31, 2010, a direct acoustic technique was used to measure the volumetric flow rate of fluids (liquid and gas) emitted from the Deepwater Horizon Macondo well. This method, which adapts acoustic techniques previously developed for deep-sea hydrothermal vent research (1), enabled observation from a remotely operated vehicle (ROV) (Fig. S1) at horizontal standoff distances of between 2 and 7 m, providing a noncontact method of measurement wherein the sensors did not disturb the flow or become fouled with oil or gas hydrate accretions. Despite the optical opacity of the fluid, this acoustic technique enabled quantitatively detailed measurement of the leaks' cross-sectional areas and velocity profiles. This acoustic flow rate assessment was conducted on a "not to interfere basis" due to the well containment operations being carried out from late April through mid-July. Data were thus collected on an opportunistic basis during short time intervals between containment procedures.Acoustic measurement commenced immediately following the unsuccessful "...

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Export of terrigenous dissolved organic matter (DOM) from rivers to the ocean plays an important role in the carbon cycle. Observations from six research cruises in 2014 were used to characterize the seasonal evolution of terrigenous DOM in the shallow and broad South Atlantic Bight (SAB) shelf. While DOM with a strong terrigenous molecular, optical and isotopic signature was restricted to a coastal band early in the year, a plume with terrigenous DOM extended further to the shelf break in late spring. The offshore transport of this terrigenous DOM was consistent with wind‐driven advection in a surface Ekman layer. On time scales spanning about 1 month, the traceable riverine DOM compounds were mostly resistant to bio‐ and photo‐degradation, and the decrease in their relative abundance over the shelf following peak river discharge during spring was consistent with dilution of the river plume due to entrainment of oceanic water associated with wind‐driven mixing. Comparisons between optical absorbance measurements and ultrahigh resolution mass spectrometry data revealed that the fraction of the DOM pool with a riverine signature in the SAB can be estimated using the spectral slope coefficient of chromophoric DOM in the 275–295 nm range. This finding opens up the possibility of observing the distribution of riverine DOM on the SAB shelf in high spatial resolution and by using remote sensing methods, a crucial step for quantifying shelf‐slope exchange and the fate of terrigenous DOM in shelf seas.

[1] The acoustic scintillation method is applied to the investigation and monitoring of a vigorous hydrothermal plume from Dante within the Main Endeavour vent field (MEF) in the Endeavour Ridge segment. A 40 day time series of the plume's vertical velocity and temperature fluctuations provides a unique opportunity to study deep sea plume dynamics in a tidally varying horizontal cross flow. An integral plume model that takes into account ambient stratification and horizontal cross flows is established from the conservation equations of mass, momentum and density deficit. Using a linear additive entrainment velocity in the model (E = aU m + bU ? ) that is a function of both the plume relative axial velocity (U m ) and the relative ambient flow perpendicular to the plume (U ? ) gives consistent results to the experimental data, suggesting entrainment coefficients a = 0.1 and b = 0.6. Also from the integral model, the plume height in a horizontal cross flow (U a ) is shown to scale as 1.8B 1/3 U a À1/3 N À2/3 for 0.01 ≤ U a ≤ 0.1 m/s where B is the initial buoyancy transport and N is the ambient stratification, both of which are assumed constant.

[1] A turbulent convection model for a hydrothermal fluid discharging into a tidally modulated, stratified cross flow is used to investigate time-variable conditions in plumes, such as the one rising from Dante, a sulfide mound at $2175 m depth on the Endeavour segment of the Juan de Fuca Ridge. That plume is the consequence of the coalescence of 10 or more small, individual plumes from chimneys discharging hot, salt-diminished fluid into the near-bottom ocean. At Dante, the discharge encounters ambient horizontal currents with speeds oscillating from near zero to a maximum of $7 cm s 21 , speeds which can bend a plume more than 45 from the vertical. Model results are compatible with field measurements of the plume footprint size and vertical velocity both 20 m above the source when earlier estimates for Dante's heat flux of $50 MW drive the convection. The smallscale short period variability of velocities and properties distributions observed in the field is mimicked in model results. Plumes pool above a source during periods of weak cross flows but stream away from the source, with more diluted concentrations and lower rise heights, at other times. Plume distributions, at identical cross-flow speeds, differ whether the flow is accelerating or decelerating. Small changes in background hydrographic profiles create differences in rise heights comparable to those caused by large changes in source buoyancy flux. If put into an entrainment context, results suggest an entrainment coefficient (a EFF ) that varies from $0.11 to $0.025 with increasing height (2-76 m) above the source.