Observed and modeled meridional overturning circulation related flow into the Caribbean

A major pathway of the Atlantic meridional overturning circulation (MOC) is the warm inflow into the Caribbean Sea. The transport and the contribution of water from the South Atlantic is calculated from observations (ADCP data and hydrography) and compared to the results of the equation image° FLAME model. The model and the observations show high consistency in the strength of the mean total inflow and its range of variability as well as in the general distribution of water from South Atlantic origin. The measurements give an annual mean South Atlantic Water (SAW) transport into the Caribbean of 9.3 Sv with high variability. This estimate has to be regarded as a lower bound since the present method (using temperature and salinity data) cannot identify the SAW included in the North Equatorial Current (NEC), which recirculated and was transformed in the interior tropical Atlantic. The model transport reproduces the observational values rather closely, with an annual mean inflow of 8.6 Sv and similar high variability. Closer inspection of the SAW pathways in the model suggest that the additional contribution by the NEC‐pathway is only about 2 Sv. The model results confirm the relative importance of the MOC pathways suggested by observations: the Caribbean inflow seems to be the main pathway (63%) for the warm and central water (σθ < 27.1 kg m−3), whereas for the intermediate water a larger fraction (59%) is transported northward at the eastern side of the Lesser Antilles

On the propagation and decay of North Brazil Current rings

Near the western boundary of the tropical North Atlantic, where the North Brazil Current (NBC) retroflects into the North Equatorial Countercurrent, large anticyclonic rings are shed. After separating from the retroflection region, the so-called NBC rings travel northwestward along the Brazilian coast, until they reach the island chain of the Lesser Antilles and disintegrate. These rings contribute substantially to the upper limb return flow of the Atlantic Meridional Overturning Circulation by carrying South Atlantic Water into the northern subtropical gyre. Their relevance for the northward transport of South Atlantic Water depends on the frequency of their generation as well as on their horizontal and vertical structure. The ring shedding and propagation and the complex interaction of the rings with the Lesser Antilles are investigated in the inline equation Family of Linked Atlantic Model Experiments (FLAME) model. The ring properties simulated in FLAME reach the upper limit of the observed rings in diameter and agree with recent observations on seasonal variability, which indicates a maximum shedding during the first half of the year. When the rings reach the shallow topography of the Lesser Antilles, they are trapped by the island triangle of St. Lucia, Barbados and Tobago and interact with the island chain. The model provides a resolution that is capable of resolving the complex topographic conditions at the islands and illuminates various possible fates for the water contained in the rings. It also reproduces laboratory experiments that indicate that both cyclones and anticyclones are formed after a ring passes through a topographic gap. Trajectories of artificial floats, which were inserted into the modeled velocity field, are used to investigate the pathways of the ring cores and their fate after they encounter the Lesser Antilles. The majority of the floats entered the Caribbean, while the northward Atlantic pathway was found to be of minor importance. No prominent pathway was found east of Barbados, where a ring could avoid the interaction with the islands and migrate toward the northern Lesser Antilles undisturbed

On the spreading of South Atlantic water into the northern Hemisphere

The upper branch of the meridional overturning circulation in the North Atlantic is fed by cross‐equatorial transport of various water masses from the Southern Hemisphere. Here, we study the large‐scale spreading of South Atlantic Water (SAW) into the western tropical North Atlantic from the equator to 25°N. The fractions of SAW in the upper ocean water masses are quantified using a water mass analysis applied on a data set of conductivity‐temperature‐depth data from the Hydrobase project and the Argo float program. To fill gaps in the data coverage and to gain insight into the mechanisms involved, the observations are complemented with results from the high‐resolution Family of Linked Atlantic Model Experiments model (equation image°), which has been shown to realistically simulate the inflow of SAW into the Caribbean. The analysis reveals the mean SAW propagation pathways in the North Atlantic and identifies the regions of largest variability. High SAW fractions in the thermocline and central water layers are limited to the region south of 10°N, where the water body consists of 80%–90% SAW. Thus, the zonal currents in the equatorial gyre are mainly formed of SAW. The weaker currents in the intermediate layer combined with a northward excursion of the North Equatorial Current allow the SAW in this layer to intrude farther north compared to the layers above. The transition into North Atlantic Water occurs gradually from 12°N to 20°N in the intermediate layer

Establishing Consensus on Essential Resources for Musculoskeletal Trauma Care Worldwide: A Modified Delphi Study

BACKGROUND: Despite evidence that formalized trauma systems enhance patient functional outcomes and decrease mortality rates, there remains a lack of such systems globally. Critical to trauma systems are the equipment, materials, and supplies needed to support care, which vary in availability regionally. The purpose of the present study was to identify essential resources for musculoskeletal trauma care across diverse resource settings worldwide. METHODS: The modified Delphi method was utilized, with 3 rounds of electronic surveys. Respondents consisted of 1 surgeon with expertise in musculoskeletal trauma per country. Participants were identified with use of the AO Trauma, AO Alliance, Orthopaedic Trauma Association, and European Society for Trauma and Emergency Surgery networks. Respondents rated resources on a Likert scale from 1 (most important) to 9 (least important). The "most essential" resources were classified as those rated ≤2 by ≥75% of the sampled group. RESULTS: One hundred and three of 111 invited surgeons completed the first survey and were included throughout the subsequent rounds (representing a 93% response rate). Most participants were fellowship-trained (78%) trauma and orthopaedic surgeons (90%) practicing in an academic setting (62%), and 46% had >20 years of experience. Respondents represented low-income and lower-middle-income countries (LMICs; 35%), upper-middle income countries (UMICs; 30%), and high-income countries (HICs; 35%). The initial survey identified 308 unique resources for pre-hospital, in-hospital, and post-hospital phases of care, of which 71 resources achieved consensus as the most essential. There was a significant difference (p < 0.0167) in ratings between income groups for 16 resources, all of which were related to general trauma care rather than musculoskeletal injury management. CONCLUSIONS: There was agreement on a core list of essential musculoskeletal trauma care resources by respondents from LMICs, UMICs, and HICs. All significant differences in resource ratings were related to general trauma management. This study represents a first step toward establishing international consensus and underscores the need to prioritize resources that are locally available. The information can be used to develop effective guidelines and policies, create best-practice treatment standards, and advocate for necessary resources worldwide. CLINICAL RELEVANCE: This study utilized the Delphi method representing expert opinion; however, this work did not examine patient management and therefore does not have a clinical Level of Evidence

Pathways and variability of the off-equatorial undercurrents in the Atlantic Ocean

The cold upwelling waters of the eastern tropical oceans not only interact with the atmospheric circulation via changing the sea surface temperatures but also influence the biological activity via affecting the nutrient and oxygen contents of the upwelling waters. While the sources of the equatorial upwelling associated with the Equatorial Undercurrent (EUC) have been studied extensively, the relevance of the northern and southern off-equatorial undercurrents (NEUC, SEUC) for the off-equatorial upwelling regions has remained unclear. In this study we use output from a high-resolution, 1/12° model (FLAME) to investigate the mean pathways and variability of the off-equatorial undercurrents (OEUCs) in the Atlantic. In particular, a calculation of Lagrangian trajectories helps to gain insight into the source waters of the OEUCs and their connection to the upwelling regions in the eastern tropical Atlantic. In the model solution the sources of both OEUCs belong almost exclusively to the Southern Hemisphere. The pathways of the source waters are found to be governed by strong recirculations between the different eastward and westward zonal currents because of intense eddy motions associated with the tropical instability wave activity. Whereas the SEUC is predominantly fed through the recirculation in the ocean interior, the NEUC is also fed by a weak inflow from the western boundary current. Investigation of the fate of the NEUC shows only a weak direct supply to the upwelling in the Guinea Dome and along the African coast but a significant contribution to the equatorial upwelling

Mechanisms of decadal variability in the shallow subtropical-tropical circulation of the Atlantic Ocean: a model study

A suite of basin-scale models of the thermohaline and wind-driven circulation in the Atlantic Ocean is used to study the mechanisms of decadal variability in the shallow subtropical-tropical cells (STCs). The emphasis is on the spatial patterns of the transport anomalies in the tropical thermocline, particularly their manifestation in the equatorial current system and on the relative role of changes in the deep meridional overturning cell (MOC) associated with variations in the formation of Labrador Sea Water (LSW) in the subpolar North Atlantic. Using wind stress and heat flux variations based on NCEP/NCAR-reanalysis products, the variability of the zonally integrated STC transports is similar to that obtained in a recent regional model study, corroborating the role of both the southern and northern STC in supporting wind-driven transport anomalies of O(2 Sv) near the equator. Sensitivity experiments indicate that changes in subarctic MOC transports associated with the strong variability in LSW formation during the last decades contributed a signal of O(0.3 Sv) to the upper-layer equatorial transports. Whereas the local wind-driven variability clearly dominates on interannual-decadal timescales and is confined to depths down to 150 m, the weak MOC-related signal is primarily reflected in an interdecadal modulation of the STC transports. While a strong part in the STC's transport anomalies is associated with the western boundary current (NBC), there is an important contribution also by weaker, interior ocean flow anomalies which tend to counteract the variability of the NBC