Extracting quasi-steady Lagrangian transport patterns from the ocean circulation: An application to the Gulf of Mexico

We construct a climatology of Lagrangian coherent structures (LCSs), the concealed skeleton that shapes transport, with a twelve-year-long data-assimilative simulation of the sea-surface circulation in the Gulf of Mexico (GoM). Computed as time-mean Cauchy-Green strain tensorlines of the climatological velocity, the climatological LCSs (cLCSs) unveil recurrent Lagrangian circulation patterns. cLCSs strongly constrain the ensemble-mean Lagrangian circulation of the instantaneous model velocity, thus we show that a climatological velocity may preserve meaningful transport information. Also, the climatological transport patterns we report agree well with GoM kinematics and dynamics, as described in several previous observational and numerical studies. For example, cLCSs identify regions of persistent isolation, and suggest that coastal regions previously identified as high-risk for pollution impact, are regions of maximal attraction. Also, we show examples where cLCSs are remarkably similar to transport patterns observed during the Deepwater Horizon and Ixtoc oil spills, and during the Grand LAgrangian Deployment (GLAD) experiment. Thus, it is shown that cLCSs are an efficient way of synthesizing vast amounts of Lagrangian information. The cLCS method confirms previous GoM studies, and contributes to our understanding by revealing the persistent nature of the dynamics and kinematics treated therein.Comment: To be submitte

Submesoscale dispersion in the vicinity of the Deepwater Horizon spill

Reliable forecasts for the dispersion of oceanic contamination are important for coastal ecosystems, society and the economy as evidenced by the Deepwater Horizon oil spill in the Gulf of Mexico in 2010 and the Fukushima nuclear plant incident in the Pacific Ocean in 2011. Accurate prediction of pollutant pathways and concentrations at the ocean surface requires understanding ocean dynamics over a broad range of spatial scales. Fundamental questions concerning the structure of the velocity field at the submesoscales (100 meters to tens of kilometers, hours to days) remain unresolved due to a lack of synoptic measurements at these scales. \textcolor{black} {Using high-frequency position data provided by the near-simultaneous release of hundreds of accurately tracked surface drifters, we study the structure of submesoscale surface velocity fluctuations in the Northern Gulf Mexico. Observed two-point statistics confirm the accuracy of classic turbulence scaling laws at 200m$-$50km scales and clearly indicate that dispersion at the submesoscales is \textit{local}, driven predominantly by energetic submesoscale fluctuations.} The results demonstrate the feasibility and utility of deploying large clusters of drifting instruments to provide synoptic observations of spatial variability of the ocean surface velocity field. Our findings allow quantification of the submesoscale-driven dispersion missing in current operational circulation models and satellite altimeter-derived velocity fields.Comment: 9 pages, 6 figure

Over what area did the oil and gas spread during the 2010 Deepwater Horizon oil spill?

Author Posting. © The Oceanography Society, 2016. This article is posted here by permission of The Oceanography Society for personal use, not for redistribution. The definitive version was published in Oceanography 29, no. 3 (2016): 96–107, doi:10.5670/oceanog.2016.74.The 2010 Deepwater Horizon (DWH) oil spill in the Gulf of Mexico resulted in the collection of a vast amount of situ and remotely sensed data that can be used to determine the spatiotemporal extent of the oil spill and test advances in oil spill models, verifying their utility for future operational use. This article summarizes observations of hydrocarbon dispersion collected at the surface and at depth and our current understanding of the factors that affect the dispersion, as well as our improved ability to model and predict oil and gas transport. As a direct result of studying the area where oil and gas spread during the DWH oil spill, our forecasting capabilities have been greatly enhanced. State-of-the-art oil spill models now include the ability to simulate the rise of a buoyant plume of oil from sources at the seabed to the surface. A number of efforts have focused on improving our understanding of the influences of the near-surface oceanic layer and the atmospheric boundary layer on oil spill dispersion, including the effects of waves. In the future, oil spill modeling routines will likely be included in Earth system modeling environments, which will link physical models (hydrodynamic, surface wave, and atmospheric) with marine sediment and biogeochemical components.This research was made possible by a grant from BP/The Gulf of Mexico Research Initiative to the CARTHE and Deep-C Consortia, and by contract M12PC00003 from the Bureau of Ocean Energy Management (BOEM)

Influence of Caribbean eddies on the Loop current system evolution

The Loop Current (LC) system dynamics are an essential component of the processes influencing circulation and transport in the Gulf of Mexico (GoM). The LC evolution is influenced by various factors, including the rich eddy field of the region and the flow exchange through the Yucatan Strait with the neighboring Caribbean Sea. These factors contribute to the complexity of the LC and, as a result, to the limitations in the predictability of the system. The focus of this study is to further elucidate the evolution of the LC, by quantifying the influence of coherent eddy fluxes originating in the Caribbean Sea. This is achieved by employing the Lagrangian-Averaged Vorticity Deviation (LAVD) method, an objective metric to evaluate eddy coherence in the Caribbean Sea that allows, for the first time, to quantify at different depths the evolution of coherent Caribbean eddies through the Yucatan Channel towards the GoM. The physical connectivity between the Caribbean Sea and the GoM is addressed using Lagrangian techniques to analyze processes that take place south of the Yucatan Channel and help quantify their strong relationship with the GoM eddy field. Coherent anticyclonic vorticity fluxes, as well as the net coherent anticyclonic volume transport between the Caribbean Sea and the GoM are associated with Loop Current Eddy (LCE) detachments through direct connectivity between the coherent Caribbean anticyclones and the forming LCE. The findings have important implications for understanding and predicting the LC system and the physical connectivity processes between the GoM and the Caribbean Sea

Clustering on the surface ocean

Non UBCUnreviewedAuthor affiliation: University of MiamiFacult

Mechanisms for emergence from diapause of Calanoides carinatus in the Somali current

We studied mechanisms that might control the emergence of the last juvenile stage of Calanoides carinatus from diapause in the Arabian Sea. Diapaused copepods are modeled as Lagrangian particles that include a simplified means for lipid catabolism during diapause. The advective field for the particles, which are released at intermediate and deep layers off the Somali shelf, is determined by a regional version of the Miami isopycnic coordinate model (MICOM). Dormant copepods emerge from diapause in response to either onshore advection (physical upwelling) or depletion of lipid reserves to an assumed critical level (internal biological clock). The majority of the diapaused copepods that successfully complete their life cycle are those retained within the coastal upwelling zone and emerge as a consequence of depletion of the lipid reserves. Calanoid copepods, with life history strategies that include arrested development (diapause) in late juvenile stages, are observed to drift for a period of time in deep ocean currents. It is generally believed that the mechanism controlling dia-pause is a combination of internal cues in the form of a timing mechanism, such as endocrine titer levels or critica

Influence of Caribbean eddies on the Loop current system evolution

The Loop Current (LC) system dynamics are an essential component of the processes influencing circulation and transport in the Gulf of Mexico (GoM). The LC evolution is influenced by various factors, including the rich eddy field of the region and the flow exchange through the Yucatan Strait with the neighboring Caribbean Sea. These factors contribute to the complexity of the LC and, as a result, to the limitations in the predictability of the system. The focus of this study is to further elucidate the evolution of the LC, by quantifying the influence of coherent eddy fluxes originating in the Caribbean Sea. This is achieved by employing the Lagrangian-Averaged Vorticity Deviation (LAVD) method, an objective metric to evaluate eddy coherence in the Caribbean Sea that allows, for the first time, to quantify at different depths the evolution of coherent Caribbean eddies through the Yucatan Channel towards the GoM. The physical connectivity between the Caribbean Sea and the GoM is addressed using Lagrangian techniques to analyze processes that take place south of the Yucatan Channel and help quantify their strong relationship with the GoM eddy field. Coherent anticyclonic vorticity fluxes, as well as the net coherent anticyclonic volume transport between the Caribbean Sea and the GoM are associated with Loop Current Eddy (LCE) detachments through direct connectivity between the coherent Caribbean anticyclones and the forming LCE. The findings have important implications for understanding and predicting the LC system and the physical connectivity processes between the GoM and the Caribbean Sea

The perfect storm: Match-mismatch of bio-physical events drives larval reef fish connectivity between Pulley Ridge mesophotic reef and the Florida Keys

Mesophotic coral reef ecosystems are remote from coastal stressors, but are still vulnerable to over-exploitation, and remain mostly unprotected. They may be the key to coral reefs resilience, yet little is known about the pattern of larval subsidies from deeper to shallower coral reef habitats. Here we use a biophysical modeling approach to test the hypothesis that fishes from mesophotic coral reef ecosystems may replenish shallow reef populations. We aim at identifying the spatio-temporal patterns and underlying mechanisms of larval connections between Pulley Ridge, a mesophotic reef in the Gulf of Mexico hosting of a variety of shallow-water tropical fishes, and the Florida Keys reefs. A new three-dimensional (3D) polygon habitat module is developed for the open-source Connectivity Modeling System to simulate larval movement behavior of the bicolor damselfish, Stegastes partitus, in a realistic 3D representation of the coral reef habitat. Biological traits such as spawning periodicity, mortality, and vertical migration are also incorporated in the model. Virtual damselfish larvae are released daily from the Pulley Ridge at 80m depth over 60 lunar spawning cycles and tracked until settlement within a fine resolution (~900m) hydrodynamic model of the region. Such probabilistic simulations reveal mesophotic-shallow connections with large, yet sporadic pulses of larvae settling in the Florida Keys. Modal and spectral analyses on the spawning time of successful larvae, and on the position of the Florida Current front with respect to Pulley Ridge, demonstrate that specific physical-biological interactions modulate these “perfect storm” events. Indeed, the co-occurrence of (1) peak spawning with frontal features, and (2) cyclonic eddies with ontogenetic vertical migration, contribute to high settlement in the Florida Keys. This study demonstrates that mesophotic coral reef ecosystems can also serve as refugia for coral reef fish and suggests that they have a critical role in the resilience of shallow reef communities. •Mesophotic reefs can act as refugia for coral reef fish•Deep-shallow connections are modulated by physical mechanisms•Pulley Ridge mesophotic reef and Florida Keys shallow reefs are sporadically connected•Physical-Biological interactions influence deep-shallow connection