Influence of Mississippi River induced circulation on the Deepwater Horizon oil spill transport

Abstract

[1] The 2010 Deepwater Horizon oil rig explosion caused $7 Â 10 5 m 3 of oil gushing from the Northern Gulf of Mexico bottom. The close proximity of the rig to the Mississippi Delta raised early questions from disaster managers about possible influence of river induced circulation on oil patch evolution. In particular, it was hypothesized that the high Mississippi River (MR) discharge in May 2010 might have helped to initially keep oil from reaching coastal marshes. We have explored this intriguing hypothesis, quantifying similar and connecting patterns in the evolution of riverine and oil covered waters. We used numerical simulations, satellite and in situ data to show the unique influence of a large river plume on a surface oil patch resulting from a deep oil release. The MR induced circulation, modified by shelf and slope flows, was found to substantially influence the near surface transport of oil. The MR plume buoyancy-driven effects on oil transport had different aspects east and west of the Mississippi Delta. Anticyclonic circulation within the upstream plume region (east of the Delta, extending over the Mississippi-Alabama-Florida shelf) created a front that restrained onshore transport. Conversely, the shoreward tendency within the downstream plume region (west of the Delta, dominated by the westward, buoyancydriven narrow coastal current) guided oil transport along the Louisiana-Texas shelf. Periods of low discharge reduced the dominance of buoyancy-driven effects, but an interval of sustained downwelling-favorable winds, combined with river induced stratification, resulted in a strong westward current and surface oil patch extension along the Louisiana coast.

How Did the Deepwater Horizon Oil Spill Affect Coastal and Continental Shelf Ecosystems of the Gulf of Mexico?

“…During the DWH oil spill, freshwater diversions along the lower Mississippi River were opened between mid-May and October with the intent to minimize the impact of the oil spill on estuaries and wetlands (Bianchi et al, 2011). In addition to wind forcing, Mississippi River-induced circulation significantly influenced near-surface oil transport (Kourafalou and Androulidakis, 2013). Three storm events during the oil spill led to changes in surface oil extent and deep mixing and likely nutrient injection into surface waters (Goni et al, 2015).…”

Can Continental Shelf River Plumes in the Northern and Southern Gulf of Mexico Promote Ecological Resilience in a Time of Climate Change?

“…This designation has been reinforced by Taylor et al [43], and most recently by Fuentes-Franco et al [44] based on a CMIP5 based RCM (RegCM4 CORDEX). Future discharge regimes for the UGCPR are inferred from runoff forecasts through the 2090s by Imbach et al [45] No fishery-independent data on shrimp populations exist for the Bay of Campeche [29], but such information from the northern GoM [32] indicates that penaid stocks are more affected by short-term changes in fishing effort (Figure 3) than by a 3800 km 2 (20%) loss of MAR delta wetlands since 1956 [12], the expansion of hypoxia on the LATEX shelf since the 1980s [13][14][15], the 2010 Deepwater Horizon oil spill [17] or climate change. The 75% reduction in fishing pressure since the late 1990s in areas influenced by the MAR plume reflects competition with low-cost farmed shrimp imported mainly from Asian countries [33].…”

“…The Ixtoc I blowout released 3 million barrels into the Bay of Campeche about 100 km offshore of the Usamacinta River mouth over 10 months in 1979 and 1980, while the Deepwater Horizon well gushed 5 million barrels about 60 km offshore of the Mississippi River birdsfoot over 3 months in 2010 [16,17]. Long-term influences of climate change on weather systems and sea-level rise can be expected to synergistically interact with these anthropogenic stressors to collectively challenge resiliency of GoM deltas.…”

Functioning of Coastal River-Dominated Ecosystems and Implications for Oil Spill Response: From Observations to Mechanisms and Models

“…The unprecedented magnitude of this 87-day spill eventually led to oil washing up along the northern Gulf of Mexico (nGOM) coast from Louisiana to Florida, producing substantial environmental damage (Michel et al, 2013;Murawski et al, 2016). Wind-driven circulation interacting with complex freshwater flows derived from numerous river inputs influenced the trajectory of oil on the shelf (Kourafalou and Androulidakis, 2013;Özgökmen et al, 2016) and made predictions of oil transport and impacts difficult (Joye et al, 2016;Özgökmen et al, 2016). The ability to forecast the movement of the oil was further complicated by river diversions that augmented river discharge in an attempt to keep oil from coming ashore in certain areas (O'Connor et al, 2016).…”