Icelandic Low and Azores High Migrations Impact Florida Current Transport in Winter

Previous work to find an association between variations of annually averaged Florida Current transport and the North Atlantic Oscillation (NAO) have yielded negative results (Meinen et al. 2010). Here we show that Florida current in winter is impacted by displacements in the positions of the Azores High and the Icelandic Low, the constituent pressure centers of the NAO. As a one-dimensional representation of North Atlantic atmospheric circulation, the NAO index does not distinguish displacements of the pressure centers from fluctuations in their intensity. Florida Current transport is significantly correlated with Icelandic Low longitude with a lag of less than one season. We carried out perturbation experiments in the ECCOv4 model to investigate these correlations. These experiments reveal that east-west shifts of the Icelandic Low perturb the wind stress in mid-latitudes adjacent to the American coast, driving downwelling (through longshore winds) and offshore sea level anomalies (through wind stress curl) which travel to the Florida Straits within the same season. Florida Current transport is also correlated with the latitude variations of both the Icelandic Low and the Azores High with a lag of four years. Regression analysis shows that latitude variations of the Icelandic Low and the Azores High are associated with positive wind stress curl anomalies over extended regions in the ocean east of Florida. Rossby wave propagation from this region to the Florida Straits has been suggested as a mechanism for perturbing FCT transport in several previous studies (DiNezio et al. 2009; Czeschel et al. 2012; Frajka-Williams et al. 2013; Domingues et al. 2016, 2019).

Submesoscale Instability in the Straits of Florida

The Florida Current (FC) flows in the Straits of Florida (SoF) and connects the Loop Current in the Gulf of Mexico to the Gulf Stream (GS) in the Western Atlantic Ocean. Its journey through the SoF is at time characterized by the formation and presence of mesoscale but mostly submesoscale frontal eddies on the cyclonic side of the current. The formation of those frontal eddies was investigated in a very high resolution two-way nested simulation using the Regional Oceanic Modeling System (ROMS). Frontal eddies were either locally formed or originated from outside the SoF. The northern front of the incoming eddies was susceptible to superinertial shear instability over the shelf slope when the eddies were pushed up against the slope by the FC. Otherwise, incoming eddies could be advected relatively unaffected by the current, when in the southern part of the straits. In absence of incoming eddies, submesoscale eddies were locally formed by the roll-up of superinertial barotropically unstable vorticity filaments when the FC was pushed up against the shelf slope. The vorticity filaments were intensified by the friction-induced bottom layer vorticity flux as previously demonstrated by Gula et al. (2015b) in the GS. When the FC retreated further south, negative vorticity West Florida Shelf waters overflowed into the SOF and led to the formation of submesocale eddies by baroclinic instability. The instability regimes, hence, the submesoscale frontal eddies formation appear to be controlled by the lateral ‘sloshing’ of the FC in the SoF.

Raffaelea lauricola (Laurel wilt).

Laurel wilt is responsible for the death of hundreds of millions of redbay (Persea borbonia sensu lato) trees throughout the southeastern USA, and the disease is also having significant effects on other species such as sassafras (Sassafras albidum) in natural ecosystems and avocado (Persea americana) in commercial production areas of south Florida. Laurel wilt is caused by the pathogen Raffaelea lauricola, a fungal symbiont of the redbay ambrosia beetle, Xyleborus glabratus. Thus far, the disease is confined to members of the Lauraceae that are native to the USA, or native to such places as the Caribbean, Central America and Europe and grown in the USA. The beetle and fungus are native to Asia and were likely introduced with untreated solid wood packing material at Port Wentworth, Georgia in the early 2000s. Since that time laurel wilt has spread rapidly in the coastal plains of the southeastern USA, spreading north into central North Carolina, as far west as Texas, and reaching the southernmost counties of Florida. Current models suggest that X. glabratus can tolerate temperature conditions that occur throughout much of the eastern USA, and so the disease threatens sassafras throughout much of this region. The disease poses a threat to lauraceous species indigenous to other areas of the Americas as well as Europe and Africa.

From the deep ocean to the coasts and estuaries through the shelf: linking coastal response to a deep blow-out

ABSTRACT # 685087 As a marginal sea connected to neighboring basins through straits, the Gulf of Mexico (GoM) is dynamically and topographically complex. Physical processes are strongly influenced by the interaction of circulation in the GoM deep basin interior and in the surrounding shelf areas of diverse morphologies that include deltas, estuaries, barrier islands and marshes. This was particularly evident during the 2010 Deepwater Horizon (DwH) incident, a deep blow-out close to the Northern GoM shelves, over an area strongly affected by the brackish river plume originated from the Mississippi River Delta. The specific physical conditions are revisited, to illustrate the synergy between the evolution of the Loop Current – Florida Current system and the rapidly changing shelf and coastal currents under the influence of river runoff and winds. Each of these physical factors had been studied prior to the DwH incident, but their combined effects on hydrocarbon pathways were not known. Examples are given on what has been learned through research under the Gulf of Mexico Research Initiative (GoMRI) in the last 10 years. The focus is on transport processes in the GoM along the ocean continuum from the deep basin interior to the coastal and wetland areas, and their relevance for oil transport and fate. Post-DwH studies have advanced regarding methodologies and tools. These include multi-platform observations and data analyses, in tandem with high-resolution, data assimilative models for past simulations and predictions. Important new findings include the connectivity between remote coastal regions, as deep oceanic currents can facilitate the cross-marginal transport of materials not only locally, but regionally. This creates a broader and more challenging view for the management of coastal marine resources that should be integrated for preparedness and response. Two examples are presented on connectivity processes. First, advances in the understanding of transport rates and pathways from the Mississippi Delta to the Florida Keys. Second, new findings on how coastal circulation near Cuba influences the evolution of the Loop Current system and the oil fate from a potential oil spill in Cuban waters. The synthesis of the above findings aims to demonstrate how knowledge acquired during GoMRI can advise future planning of scientific research to aid preparedness and response not only for the GoM, but for many offshore areas of oil exploration. The goal is to advance the understanding and predictability of oil slick trajectories over pathways from the deep to the coastal environment and vice versa.

Raffaelea lauricola (laurel wilt).

Laurel wilt is responsible for the death of hundreds of millions of redbay (Persea borbonia sensu lato) trees throughout the southeastern USA, and the disease is also having significant effects on other species such as sassafras (Sassafras albidum) in natural ecosystems and avocado (Persea americana) in commercial production areas of south Florida. Laurel wilt is caused by the pathogen Raffaelea lauricola, a fungal symbiont of the redbay ambrosia beetle, Xyleborus glabratus. Thus far, the disease is confined to members of the Lauraceae that are native to the USA, or native to such places as the Caribbean, Central America and Europe and grown in the USA. The beetle and fungus are native to Asia and were likely introduced with untreated solid wood packing material at Port Wentworth, Georgia in the early 2000s. Since that time laurel wilt has spread rapidly in the coastal plains of the southeastern USA, spreading north into central North Carolina, as far west as Texas, and reaching the southernmost counties of Florida. Current models suggest that X. glabratus can tolerate temperature conditions that occur throughout much of the eastern USA, and so the disease threatens sassafras throughout much of this region. The disease poses a threat to lauraceous species indigenous to other areas of the Americas as well as Europe and Africa.

Pathways connecting the North Brazil Current and the RAPID line

<p>The North Brazil Current is considered a bottleneck in the South Atlantic, responsible for funneling upper-ocean waters into the North Atlantic. This work explores the surface and subsurface pathways that connect the North Brazil Current to the RAPID line. To that extent, observational trajectories from surface drifters and Argo floats are used in conjunction with Markov chain theory and tools from dynamical systems analysis to compute probable pathways. More specifically, these pathways are computed as ensembles of paths transitioning directly between the North Brazil Current and the RAPID line. In addition, simulated trajectories will be used (1) to assess how representative the two-dimensional observational trajectories are of the three-dimensional circulation, and (2) to compute the associated volume transport of different pathways. Preliminary results suggest that two dominant pathways connect the North Brazil Current and the RAPID line. First, is the traditional pathway through the Caribbean Sea and Gulf of Mexico, which carries waters to the Florida Current, and second is a more direct route east of the Caribbean that supplies waters to the Antilles Current and the basin interior.  </p>

The Antilles Current and wind-driven gyre circulation at 26oN

<p>The Antilles Current is a narrow, northward flowing boundary current in the western Atlantic just east of the Bahamas. Its role in the larger scale circulation has been debated: alternately thought to be part of the western boundary closure of the gyre circulation or the northward flowing limb of the meridional overturning circulation (MOC). From 19 years of moored current meter observations (1987--1991, 2004--2018), we define the strength of the Antilles Current by the net transport between the Bahamas and 76.5°W (spanning about 45 km zonally) and in the thermocline (0–1000 m). We find a mean northward transport of 3.5 Sv, substantial interannual variability, and no discernable trend since 1987. The interannual variability of the AC transport is independent of the variability of the Florida Current (the Gulf Stream through the Florida Straits). Instead, the Antilles Current contributes to the interannual variability of the MOC at 26°N, while the trend in the strength of the gyre circulation (defined as the transbasin thermocline transport minus the AC) is responsible for the trend in the MOC. In particular, the 2009/10 slowdown of the MOC resulted from a weaker northward AC transport, rather than an intensified gyre transport. Using the recent 14 years of in situ transport records, we compare the interannual variability of the gyre circulation to that of wind stress curl forcing via a Sverdrup transport calculation, identifying a potential role for wind stress curl (WSC) forcing at 26°N with a ~2 year lag until 2016.<span>  </span>From 2016, the predicted gyre circulation using WSC diverges from the measured gyre strength.</p>

The Role of Mesoscale Dynamics over Northwestern Cuba in the Loop Current Evolution in 2010, during the Deepwater Horizon Incident

The Loop Current (LC) system controls the connectivity between the northern Gulf of Mexico (GoM) region and the Straits of Florida. The evolution of the LC and the shedding sequence of the LC anticyclonic ring (Eddy Franklin) were crucial for the fate of the hydrocarbons released during the Deepwater Horizon (DwH) oil spill in 2010. In a previous study, we identified LC-related anticyclonic eddies in the southern GoM, named “Cuba anticyclones” (“CubANs”). Here, we investigate the relation between these eddies and LC evolution in 2010, focusing on the DwH period. We use high-resolution model results in tandem with observational data to describe the connection between the LC system evolution within the GoM (LC extensions, Eddy Franklin and LC Frontal Eddies—LCFEs) and the mesoscale dynamics within the Straits of Florida where CubANs propagate. Five periods of CubAN eddy activity were identified during the oil spill period, featuring different formation processes under a combination of local and regional conditions. Most of these cases are related to the retracted LC phases, when the major LC anticyclone (Eddy Franklin in 2010) is detached from the main body and CubAN eddy activity is most likely. However, two cases of CubAN eddy presence during elongated LC were detected, which led to the attenuation of the eastward flows of warm waters through the Straits (Florida Current; outflow), allowing the stronger supply of Caribbean waters through the Yucatan Channel into the Gulf (inflow), which contributed to short-term LC northward extensions. Oceanographic (LCFEs) and meteorological (wind-induced upwelling) conditions contributed to the release of CubANs from the main LC body, which, in tandem with other processes, contributed to the LC evolution during the DwH oil spill incident.