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

Mechanisms for emergence from diapause of Calanoides carinatus

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

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

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

Improved Surface Velocity and Trajectory Estimates in the Gulf of Mexico from Blended Satellite Altimetry and Drifter Data

Abstract This study investigates the results of blending altimetry-based surface currents in the Gulf of Mexico with available drifter observations. Here, subsets of trajectories obtained from the near-simultaneous deployment of about 300 Coastal Ocean Dynamics Experiment (CODE) surface drifters provide both input and control data. The fidelity of surface velocity fields are measured in the Lagrangian frame by a skill score that compares the separation between observed and hindcast trajectories to the observed absolute dispersion. Trajectories estimated from altimetry-based velocities provide satisfactory average results (skill score > 0.4) in large (~100 km) open-ocean structures. However, the distribution of skill score values within these structures is quite variable. In the DeSoto Canyon and on the shelf where smaller-scale structures are present, the overall altimeter skill score is typically reduced to less than 0.2. After 3 days, the dataset-averaged distance between hindcast and drifter trajectories, , is about 45 km—only slightly less than the average dispersion of the observations, km. Blending information from a subset of drifters via a variational method leads to significant improvements in all dynamical regimes. Skill scores typically increase to 0.8 with reduced to less than half of . Blending available drifter information with altimetry data restores velocity field variability at scales not directly sampled by the altimeter and introduces ageostrophic components that cannot be described by simple Ekman superposition. The proposed method provides a means to improve the fidelity of near-real-time synoptic estimates of ocean surface velocity fields by combining altimetric data with modest numbers of in situ drifter observations

Lagrangian Coherent Structures in a coastal upwelling environment

A unique spatiotemporal perspective of evolving surface currents off the northern California coast is provided with Lagrangian Coherent Structures (LCSs) determined from attracting Finite-Time Lyapunov Exponents (FTLEs). The FTLEs are calculated from hourly 2-D surface current velocities obtained with HF radars. Attracting FTLE field maxima can identify confluence and shear in flows which can be useful in mapping dynamics associated with fronts. FTLE and SST fields are compared during three time periods in 2009: late March, early September, and late September. During strong upwelling-favorable winds in late March the FTLE and SST fields were not strongly related indicating that frontal dynamics were not strongly influencing surface circulation. Exceptions to this occurred when FTLE ridges calculated from a shorter integration period captured the evolution of a cold water filament and when a FTLE ridge migrated offshore along with an upwelling front. During the two September cases an improved relationship between the FTLE and SST fields was found although occasionally they became shifted. The shifts occurred when the FTLE integration period spanned backwards in time through periods of relaxed and upwelling-favorable winds. This suggests that frontal dynamics captured by LCSs during relaxed winds can subsequently become advected after the onset of wind-forcing by a surface mixed layer decoupled from stably stratified water below the surface mixed layer. Additionally, the LCSs were found to be useful in mapping the origin and destination of surface trajectories, the confluence associated with a persistent eddy-like feature, and retention zones off coastal promontories. •Coastal circulation is mapped with HF radar-derived Lagrangian Coherent Structures.•Spatiotemporal evolution of upwelling jets, fronts, and filaments are investigated.•Eddy-like circulation, retention zones, and upwelling front speed are determined.•Mixed layer dynamics are important for identifying material boundaries associated with LCSs

Analysis of flight MH370 potential debris trajectories using ocean observations and numerical model results

Malaysian Airlines flight MH370 disappeared in March 2014. Potential sites of where the plane entered the water are considered within a vast region of the Indian Ocean. We present a methodology to assess the potential crash site based on where airplane debris was found, with an emphasis on the first debris discovery on Reunion Island. This methodology uses the historical dataset of surface drifters and numerical modeling results. Marine debris, depending on its buoyancy, is exposed to varying amounts of wind, and we conducted tests for a suite of different scenarios. The methodology proposed here enables us to generate fields of particle density probability to assess debris trajectories and, therefore, hypothesize on the potential crash site. We provide an estimate of the most likely windage affecting floating debris on its way to Reunion Island by assuming the plane entered the sea in the defined search area. Our results indicate that areas within the Indian Ocean subtropical gyre, including the search area, could be a source of the debris found on Reunion Island. We also identify zones that can be excluded as potential crash sites and provide estimated travel times and probable ashore positions of plane debris through an analysis of the historical surface drifter dataset. Recent discoveries of new debris linked to flight MH370 in Mozambique, South Africa, Mauritius, and Tanzania are consistent with our results and confirm the general westward drift and travel time of debris from the search area

Relative risk assessment of cruise ships biosolids disposal alternatives

► We examine biosolids disposal alternatives for cruise ships in the Caribbean Sea. ► For land disposal, human health risk is higher than those for deep ocean disposal. ► For land disposal, ecological risk is higher than those for incineration. ► For incineration, ecological impacts were lower relative to deep ocean disposal. A relative risk assessment of biosolids disposal alternatives for cruise ships is presented in this paper. The area of study encompasses islands and marine waters of the Caribbean Sea. The objective was to evaluate relative human health and ecological risks of (a) dewatering/incineration, (b) landing the solids for disposal, considering that in some countries land-disposed solids might be discharged in the near-shore environment untreated, and (c) deep ocean disposal. Input to the Bayesian assessment consisted of professional judgment based on available literature and modeling information, data on constituent concentrations in cruise ship biosolids, and simulations of constituent concentrations in Caribbean waters assuming ocean disposal. Results indicate that human health and ecological risks associated with land disposal and shallow ocean disposal are higher than those of the deep ocean disposal and incineration. For incineration, predicted ecological impacts were lower relative to deep ocean disposal before considering potential impacts of carbon emissions

Modeling Ocean Ecosystems: The PARADIGM Program

The role of the oceans in Earth systems ecology, and the effects of climate variability on the ocean and its ecosystems, can be understood only by observing, describing, and ultimately predicting the state of the ocean as a physically forced ecological and biogeochemical system. This is a daunting but exciting challenge, because the ocean-atmosphere system is dynamically linked, and oceanic habitats are both diverse and complex, providing tremendous variety in environmental conditions and associated life forms. And paradoxically, as we learn more and more about ocean life, for example, through the genomics revolution (Doney et al., 2004), the number of unanswered questions increases.National Oceanographic Partnership Program (U.S.) (NSF/ONR/NOPP grant N000140210370

Research Overview of the Consortium for Advanced Research on Transport of Hydrocarbon in the Environment (CARTHE)

CARTHE (http://carthe.org/) is a Gulf of Mexico Research Initiative (GoMRI) consortium established through a competitive peer-reviewed selection process. CARTHE comprises 26 principal investigators from 14 universities and research institutions distributed across four Gulf of Mexico states and other four states. It fuses into one group investigators with unique scientific and technical knowledge and extensive publications related to oil fate/transport processes, oceanic and atmospheric turbulence, air-sea interactions, tropical cyclones and winter storms, and coastal and nearshore modeling and observations. Our primary goal is to accurately predict the fate of hydrocarbons released into the environment. Achieving this goal is particularly challenging since petroleum releases into the environment interact with natural processes across six orders of magnitude of time and space scales. We are developing a multi-scale modeling tool by incorporating state-of-the-art hydrophysical models, each applicable for a restricted range of scales, into a single, interconnected modeling system to predict the physical dispersal of hydrocarbons across scales ranging from the microscale at the wellhead to oceanic and atmospheric mesoscales. CARTHE is also conducting novel in-situ observations and laboratory experiments specifically designed for quantifying submesoscale dispersion as well as for both model validation and parameterization. Finally, we are providing a robust set of uncertainty metrics and analysis tools to assess model performance and quantify predictive uncertainty