The unprecedented nature of the Deepwater Horizon oil spill required the application of research methods to estimate the rate at which oil was escaping from the well in the deep sea, its disposition after it entered the ocean, and total reservoir depletion. Here, we review what advances were made in scientific understanding of quantification of flow rates during deep sea oil well blowouts. We assess the degree to which a consensus was reached on the flow rate of the well by comparing in situ observations of the leaking well with a time-dependent flow rate model derived from pressure readings taken after the Macondo well was shut in for the well integrity test. Model simulations also proved valuable for predicting the effect of partial deployment of the blowout preventer rams on flow rate. Taken together, the scientific analyses support flow rates in the range of ∼50,000-70,000 barrels/d, perhaps modestly decreasing over the duration of the oil spill, for a total release of ∼5.0 million barrels of oil, not accounting for BP's collection effort. By quantifying the amount of oil at different locations (wellhead, ocean surface, and atmosphere), we conclude that just over 2 million barrels of oil (after accounting for containment) and all of the released methane remained in the deep sea. By better understanding the fate of the hydrocarbons, the total discharge can be partitioned into separate components that pose threats to deep sea vs. coastal ecosystems, allowing responders in future events to scale their actions accordingly.oil budget | particle image velocimetry | manual feature tracking

To fully understand the environmental and ecological impacts of the Deepwater Horizon disaster, an accurate estimate of the total oil released is required. We used optical plume velocimetry to estimate the velocity of fluids issuing from the damaged well both before and after the collapsed riser pipe was removed. We then calculated the volumetric flow rate under a range of assumptions. With a liquid oil fraction of 0.4, we estimated that the average flow rate from 22 April 2010 to 3 June 2010 was 5.6 × 10(4) ± 21% barrels/day (1.0 × 10(-1) meter(3)/second), excluding secondary leaks. After the riser was removed, the flow was 6.8 × 10(4) ± 19% barrels/day (1.2 × 10(-1) meters(3)/second). Taking into account the oil collected at the seafloor, this suggests that 4.4 × 10(6) ± 20% barrels of oil (7.0 × 10(5) meters(3)) was released into the ocean.

[1] Tidal signals are observed in numerous time-series measurements obtained from mid-ocean ridge hydrothermal systems. In some instances these tidal signals are clearly the result of ocean currents, but in other instances it appears that the signals may originate in the subseafloor formation. In order to explore the effect of ocean tidal loading on mid-ocean ridge hydrothermal systems, we apply a one-dimensional analytical model of tidal loading on a poroelastic half-space and develop a two-dimensional numerical model of tidal loading on a poroelastic convection cell. The one-dimensional models show that for a reasonable range of fluid, elastic, and hydrological properties, the loading efficiency may vary from near zero to near unity and the diffusive penetration depth for tidal pressure signals may vary from tens of meters to kilometers. The two-dimensional models demonstrate that tides may generate significant vertical and horizontal pressure gradients in mid-ocean ridge hydrothermal systems as a result of spatial variations in fluid temperatures and the elastic and hydrological properties of the crust. These continuum models predict that outflow temperature perturbations will be very small (<10 À4°C), but in real systems where the continuum hypothesis does not always apply, the perturbations may be on the order of $0.1°C. The models predict relatively large perturbations to fluid velocity at the seafloor. For high-temperature vents the outflow perturbations normalized to the mean flow velocity increase as the permeability decreases. Flow reversals at the seafloor are predicted in some regions of net low-temperature outflow and net inflow during the tidal cycle. In the subseafloor, tidally induced flow perturbations are likely to significantly enhance mixing and fluid exchange below the seafloor in regions of slow flow and in regions where there are strong gradients in temperature or in the mechanical and hydrological properties of the crust. Tidally enhanced mixing and fluid exchange may significantly influence the extent and character of microbial production in the subseafloor.

[1] The R/V Marcus G. Langseth is the first 3-D seismic vessel operated by the U.S. academic community. With up to a four-string, 36-element source and four 6-km-long solid state hydrophone arrays, this vessel promises significant new insights into Earth science processes. The potential impact of anthropogenic sound sources on marine life is an important topic to the marine seismic community. To ensure that operations fully comply with existing and future marine mammal permitting requirements, a calibration experiment was conducted in the Gulf of Mexico in [2007][2008]. Results are presented from deep (1.6 km) and shallow (50 m) water sites, obtained using the full 36-element (6600 cubic inches) seismic source. This array configuration will require the largest safety radii, and the deep and shallow sites provide two contrasting operational environments. Results show that safety radii and the offset between root-meansquare and sound exposure level measurements were highly dependent on water depth.

[1] Although there is indirect evidence for strong connections between tectonic processes and mid-ocean ridge hydrothermal flow, there are no direct observations of these links, primarily because measuring flow in these systems is difficult. Here we use an optical analysis technique to obtain a 44 day record of flow rate changes in a black smoker vent in the Main Endeavour field of the Juan de Fuca Ridge. We show that variations in the flow rate coincide with an earthquake swarm observed using an ocean bottom seismometer array. These observations indicate that connections between tectonics and flow are indeed strong, that hydraulic connections within this hydrothermal system are long ranging, and that enhanced tidal pumping of fluids may be initiated by earthquake activity. Because the effects of the swarm cross over an intervening vent field, we infer that the upflow zones feeding this field are narrow. Using the time lag between the swarm onset and the flow rate changes we estimate that the bulk permeability of the crust on the Endeavour segment ranges from 3.0 × 10 −13 m 2 to 6.0 × 10 −12 m 2 .

Hydrothermal fluid circulation at mid‐ocean ridges facilitates the exchange of heat and chemicals between the oceans and the solid Earth, and supports chemosynthetic microbial and macro‐faunal communities. The structure and evolution of newly formed oceanic crust plays a dominant role in controlling the character and longevity of hydrothermal systems; however, direct measurements of subsurface processes remain technologically challenging to obtain. Previous studies have shown that tidally‐induced stresses within the subseafloor modulate both fluid flow and microearthquake origin times. In this study, we observe systematic along‐axis variations between peak microearthquake activity and maximum predicted tidal extension beneath the hydrothermal vent site at 9°50′N East Pacific Rise. We interpret this systematic triggering to result from pore‐pressure perturbations propagating laterally through the hydrothermal system. Based on our observations and a one‐dimensional pore pressure perturbation model, we estimate bulk permeability at ∼10−13 to 10−12 m2 within layer 2B over a calculated diffusive lengthscale of 2.0 km.

Permeability is a primary control on fluid flow within mid‐ocean ridge hydrothermal systems and strongly influences the transfer of energy and mass between the ocean and the lithosphere. Little is known about how this parameter might vary in zero‐age crust even though such variations may determine the locations and areal extents of upflow and downflow zones. Typically, estimates of permeability in seafloor environments are given as a single value (or range of values) for entire systems. Here we model crustal stresses inferred from poroelastically triggered earthquake patterns to estimate the two‐dimensional permeability structure within a hydrothermal system on the East Pacific Rise at 9°50′N. We show that permeability in young ocean crust may vary by several orders of magnitude over horizontal scales of hundreds of meters with values ranging from 10−13.4 to 10−9.4 m2. Such values are consistent with other estimates of permeability in ocean crust. These variations may prescribe the geometry of hydrothermal convection and should be considered in future models of these systems.

Long‐lived hydrothermal circulation is now well documented along slow and ultraslow spreading mid‐ocean ridges, even though these settings only receive a moderate and intermittent supply of magma. This challenges the notion that hydrothermal convection must be sustained by a continuously replenished magma body. Here we investigate the possibility of sustaining hydrothermal circulation by infrequent magmatic intrusions separated by episodes of downward propagation of small cracks enabling fluids to tap heat from deep hot rocks. We focus on cracks nucleating from grain boundary flaws in response to the buildup of cooling stresses at the base of the convection system. We develop an analytical model describing the stable propagation of a percolation front and the associated heat transfer through hydrothermal circulation. Convection ceases when thermoelastic stresses can no longer overcome lithostatic pressure and hydrothermal circulation can no longer mine heat from underlying units. For lithospheric permeabilities greater than ∼10−15 m2 and over a wide range of grain and flaw sizes, this occurs within ∼100 kyr to ∼1 Myr from the onset of cracking, after the cracking front has moved by a few kilometers. We validate this analytical prediction by developing two‐dimensional numerical models of porous convection subjected to a lower boundary condition representing the dynamics of the cracking front. These models suggest that moderate‐ to low‐temperature hydrothermal venting in off‐axis, ultramafic‐hosted sites does not require an underlying magma sill at all times, but instead repeated sill intrusions every ∼10–100 kyr, which periodically reinvigorate hydrothermal convection without building a continuous crustal section.