!The processes and instabilities occurring at the ocean surface in the northern Gulf of Mexico are investigated with a regional model at submesoscale-permitting horizontal grid resolution (i.e., HR with dx = 1.6 km) over a three-year period, from January 2010 to December 2012. A mesoscale-resolving, lower resolution run (LR, with dx = 5 km) is also considered for comparison. The HR run is obtained through two-way nesting within the LR run. In HR quantities such local Rossby number, horizontal divergence, vertical velocity, and strain rate are amplified in winter, when the mixed layer is deepest, as found in other basins. In the model configuration considered this amplification occurs in surface waters over the continental slope and off-shore but not over the shelf. Submesoscale structures consist of a mixture of fronts and eddies generated by frontogenesis and mixed layer instabilities, with elevated conversion rates of available potential energy (APE) into eddy kinetic energy (EKE). In all quantities a secondary maximum emerges during the summer season, when the mixed layer depth is shallowest, barely 15-20 m. The secondary peak extends to the coast and is due to the intense lateral density gradients created by the fresh water inflow from the Mississippi River system. Submesoscale structures in summer consist predominately of fronts, as observed in the aftermath of the 2010 Deepwater Horizon oil spill, and their secondary circulations are impeded due to the limited depth of the mixed layer. Freshwater river input is key to the submesoscale activity in summer but modulates it also in winter, as shown with a sensitivity run in which the riverine inflow is absent. Implications for transport studies in regions characterized by intense freshwater fluxes and for submesoscale parameterizations are discussed.

9The predictability of the mesoscale circulation in the Gulf of Mexico is evaluated using an 10 ensemble of four integrations for the period 2000-2008 using the Regional Ocean Modeling 11 System (ROMS). In all four runs ROMS is forced by identical, monthly varying, heat and 12 momentum fluxes. We explore the role of initial conditions, boundary conditions, atmospheric 13 forcing, and resolution in the Mississippi plume area, on the potential predictability of the Gulf 14 circulation at scales of 20 km or greater. The potential for predictability varies regionally and 15 seasonally. The modeled circulation is mainly atmospherically forced in the coastal areas and 16 dominated by chaotic mesoscale activity in the central portion of the basin. The mesoscale 17 circulation in the top 1000 m of the water column does not correlate with the one below it except 18 for a limited number of small areas. The potential for predicting the circulation at depths deeper 19 than 1000 m is limited by the intrinsic variability of the eddy field and by the unavailability of a 20 continuous monitoring system that extends below the surface. 21 Key words 22 Gulf of Mexico, predictability, deep circulation, mesoscale. 23 © 2014. This manuscript version is made available under the Elsevier user license http://www.elsevier.com/open-access/userlicense/1.0/ 2 1. Introduction 24 The Gulf of Mexico circulation has been measured extensively, in particular over the last few 25 years. Continuous observational records, however, are limited to the surface, via satellite 26 measurements, and to the coastal and shelf areas, and only sporadic in waters deeper than ~ 800 27 m (see http://data.gcoos.org/). Predicting the Gulf of Mexico circulation is still challenging not 28 only at the submesoscales (10 km or less) but also at scales greater than 10-20 km, as evidenced 29 in the aftermath of the Deepwater Horizon spill in 2010, when different data assimilative models, 30 run in both hindcast and forecast mode at resolutions reaching 0.04 o , diverged in their predictions 31 of surface oil trajectories, and more generally of current behaviors (Liu et al., 2011). The 32 evaluation of those divergent solutions, and improvements in the representation of oil behavior in 33 sea water, have allowed modelers to obtain more realistic representations of the observed oil 34 trajectories in subsequent works (e.g. Adcroft et al., 2010; Chan et al., 2011; Klemas, 2010; Paris 35 et al., 2012). With the discovery of deep oil plumes (Camilli et al., 2010; Joye et al., 2011), 36 however, it became apparent that during the Deepwater Horizon emergency response a reliable 37 prediction of the deep circulation in the Gulf would have been as important as modeling the 38 drifting of oil at the surface. 39 In this paper we focus on the predictability of the mesoscale circulation in the Gulf of Mexico. 40 More specifically, we pose two questions: Is the deep (> 1000 m) mesoscale circulation of the 41 Gulf of Mexico predictable, and if so on which time scale? Are surface meso...

The black coral Leiopathes glaberrima is a foundation species of deep-sea benthic communities but little is known of the longevity of its larvae and the timing of spawning because it inhabits environments deeper than 50 m that are logistically challenging to observe. Here, the potential connectivity of L. glaberrima in the northern Gulf of Mexico was investigated using a genetic and a physical dispersal model. The genetic analysis focused on data collected at four sites distributed to the east and west of Mississippi Canyon, provided information integrated over many (~10,000) generations and revealed low but detectable realized connectivity. The physical dispersal model simulated the circulation in the northern Gulf at a 1km horizontal resolution with transport-tracking capabilities; virtual larvae were deployed 12 times over the course of 3 years and followed over intervals of 40 days. Connectivity between sites to the east and west of the canyon was hampered by the complex bathymetry, by differences in mean circulation to the east and west of the Mississippi Canyon, and by flow instabilities at scales of a few kilometers. Further, the interannual variability of the flow field surpassed seasonal changes. Together, these results suggest that a) dispersal among sites is limited, b) any recovery in the event of a large perturbation will depend on local larvae produced by surviving individuals, and c) a competency period longer than a month is required for the simulated potential connectivity to match the connectivity from multi-locus genetic data under the hypothesis that connectivity has not changed significantly over the past 10,000 generations.

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The distribution of surface nutrients along the salinity gradient in the Mississippi-Atchafalaya River outflow region was examined during four cruises, including two simultaneous cruises, conducted in the northern Gulf during the summer of 2010 and 2011, and in late spring of 2012. The new, extensive data set covers the salinity gradient from 11 to 37 psu (practical salinity unit) in a year of extraordinarily high river discharge (2011), with few samples from a year of average (2010) and below average (2012) river outflow. The overall surface concentrations of nitrate + nitrite, orthophosphate and silicate are compared to those recorded in cruises spanning the 1985-2009 interval. Using Monte Carlo simulations to test the statistical significance, we found that surface orthophosphate and nitrate+nitrite concentrations are approximately three and two fold smaller, respectively, in the 2010-2012 period compared to the previous years. Changes in silicate concentrations were, in most cases, not significant, and their assessment complicated by different measurement techniques and potential preservation artifacts. The weighted river loading of these nutrients was, on the other hand, very high in the latest period when samples mostly covered 2011 during which the discharge was particularly high. The well-known negative correlation between nutrient concentrations and salinity at the ocean surface is confirmed in the most recent data. The area surrounding the Mississippi River mouth is characterized by inorganic N:P ratios greater than 30:1 that decrease to values typically less than 10:1 at about 100 km from of the mouth. Overall our analysis suggests that surface nutrient concentrations in the northern Gulf of Mexico cannot be described with any good accuracy by a linear model based on river discharge alone.

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Las Comunicaciones Nacionales sobre Cambio Climático (CNCC) son un mecanismo para que los países informen sus avances en mitigación y adaptación, y constituyen uno de los elementos de base para la política sobre cambio climático a escala nacional. Colombia ha emitido tres CNCC. La tercera plantea un escenario que considera las proyecciones de diversos modelos incluidos en la quinta fase del Proyecto de Comparación de Modelos Acoplados (Coupled Model Intercomparison Project, CMIP), el cual se estima como el promedio de las proyecciones correspondientes a las cuatro trayectorias de concentración representativa (Representative Concentration Pathways,RCP) presentadas en el quinto reporte de evaluación del Panel Intergubernamental sobre Cambio Climático. Cada una de estas RCP representa una trayectoria de concentración de gases de efecto invernadero (GEI) para un escenario particular de crecimiento poblacional, económico y tecnológico que conduce a una posible trayectoria de evolución del sistema climático. En este estudio se comparan las proyecciones presentadas en la Tercera CNCC con las obtenidas directamente de los modelos empleados. Nuestros resultados demuestran que al utilizarse un promedio de RCP se pierden escenarios alternos que podrían ser importantes a la hora de considerar posibles futuros diferentes y anulan la utilidad de plantear diversas trayectorias de emisiones de GEI. Más aun, una comparación entre la Segunda y la Tercera CNCC muestra proyecciones de precipitación opuestas para diferentes regiones del país, lo cual es de particular importancia, pues el escenario de cambio climático planteado en la Tercera CNCC sirve de referencia para la toma de decisiones en materia de cambio climático a nivel nacional.