Circulation Off Research Articles

Observed water-mass characteristics and circulation off Prydz Bay, East Antarctica

Observed water-mass characteristics and circulation off Prydz Bay, East Antarctica

Implementation of additional spectral wave field exchanges in a three-dimensional wave–current coupled WAVEWATCH-III (version 6.07) and CROCO (version 1.2) configuration: assessment of their implications for macro-tidal coastal hydrodynamics

Abstract. An advanced coupling between a three-dimensional ocean circulation model (CROCO) and a spectral wave model (WAVEWATCH-III) is presented to better represent the interactions of macro-tidal currents with winds and waves. In the previous implementation of the coupled interface between these two models, some of the wave-induced terms in the ocean dynamic equations were computed from their monochromatic approximations (e.g. Stokes drift, Bernoulli head, near-bottom wave orbital velocity, wave-to-ocean energy flux). In the present study, the exchanges of these fields computed from the spectral wave model are implemented and evaluated. A set of numerical experiments for a coastal configuration of the macro-tidal circulation off the Bay of Somme (France) is designed. The impact of the spectral versus monochromatic computation of wave-induced terms has a notable effect on the macro-tidal hydrodynamics, particularly in scenarios involving storm waves and opposing winds to tidal flows. This effect manifests as a reduction in the wave-induced deceleration of the vertical profile of tidal currents. The new implementation provides current magnitudes closer to measurements than those predicted using monochromatic formulations, particularly at the free surface. The spectral-surface Stokes drift and the near-bottom wave orbital velocity are found to be the spectral fields with the most impact, respectively increasing advection towards the free surface and shifting the profile close to the seabed. In the particular case of the Bay of Somme, the approximation of these spectral terms with their monochromatic counterparts ultimately results in an underestimation of ocean surface currents. Our model developments thus provide a better description of the competing effects of tides, winds, and waves on the circulation off macro-tidal bays, with implications for the study of air–sea interactions and sediment transport processes.

A comparative study of ocean surface interannual variability in Northern Tanzania and the Northern Kenya Bank

The livelihoods of most residents of Tanga (Northern Tanzania) and Malindi (Northern Kenya), rely strongly on fishing activities in the East African shelf region. Thus, understanding variations in sea surface temperature (SST) and its related parameters such as thermocline depths and upper ocean circulation are crucial. This study applies a regional model to understand interannual spatial relationships between ocean circulation and SST off Northern Tanzania and on the Northern Kenya Bank. The results indicate slight differences in variations off the Northern Tanzanian shelf region and the Northern Kenya Bank. Such small variations might have local impacts on the human population through influencing primary productivity and fisheries. The coastal waters off Malindi indicate stronger variations, particularly in 1997 (cold SST) and 1998 (warm SST), than those off Tanga region. The SST anomalies seem to be associated with thermocline and sea surface height (SSH) off Malindi, while off Tanga they relate only to SSH. This information provides further understanding of parameters that may affect fishing activities in these regions and can be used for planning and management processes.

Near-surface western boundary circulation off Northeast Brazil

In the tropical Atlantic Ocean, the North Brazil Undercurrent (NBUC) and the North Brazil Current (NBC) play important roles as near-surface northward paths for the Atlantic meridional overturning circulation. To investigate the meridional evolution of the near-surface western boundary circulation in that region, two surveys were carried out off Northeast Brazil during austral spring 2015 and fall 2017, periods that we show to be representative of typical conditions for the spring and fall seasons. Using conductivity temperature depth oxygen probe and ship-mounted acoustic Doppler current profiler measurements, altimetry data, and numerical reanalysis products, we examine the spatiotemporal variability of the NBUC, providing a comprehensive view of the circulation, including NBUC-NBC transition and the potential impact of mesoscale eddies. The NBUC originating south of 10°S flows equatorward over the continental slope. NBUC mean velocity, transport and vertical extent of the velocity core were higher in spring 2015 (0.81 m s−1, 15.6 Sv, and >400 m) than in fall 2017 (0.65 m s−1, 11.0 Sv, and ~300 m). The upper limit of the NBUC velocity core rose slightly from 160 m at 9°S to 105 m depth at 6°S. This pattern is associated with a northward increase in current velocity from 0.7 m s−1 at 9°S to 1 m s−1 at 5°S. The orographic effect shifts the flow from northeastward south of 7.5°S to northwestward north of 7.5°S, following the shoreline. Besides, altimetry data show that this flow can be locally influenced by mesoscale activity. Farther north, at ~4.8°S, data obtained in fall 2017 show that the central branch of the South Equatorial Current (cSEC) enters into the western boundary system where it coalesces with the NBUC to form the NBC, flowing toward the Caribbean Sea. Finally, in fall, the NBUC retroflection does not feed the South Equatorial Undercurrent (SEUC), which, instead originates from retroflections of the cSEC and the equatorial branch of the South Equatorial Current (eSEC).

Structure of the Subpolar Gyre in the Australian‐Antarctic Basin Derived From Argo Floats

AbstractThe climatological structure of the subpolar cyclonic circulation off East Antarctica is delineated with Argo float data from the past decade. Up to 40% of the float profiles in the seasonal ice zone have been without satellite positioning. We refined their position data as following the bathymetry to get appropriate positions in the continental margin. The error of the terrain‐following interpolation was estimated by using positioned data to be 23 ± 27 (78 ± 70) km for 90 (390) day period. Profiles with the under‐ice period shorter than 360 days are adopted. The float trajectories reveal the extent of the subpolar gyre adjoined to the westward Antarctic Slope Current to its south and the southernmost eastward jet of the Antarctic Circumpolar Current along 4,000 m isobath to its north. The subpolar circulation in the Australian‐Antarctic Basin comprises of a series of quasi‐barotropic subgyre circulations, which are bounded by bathymetric spurs in the continental slope. The temperature field reveals shoreward excursions of Circumpolar Deep Water associated with the subgyres, effectively supplying heat to the continental shelves. An along‐slope temperature variation up to 1°C in 27.7–27.8 kg/m3 σθ indicates an active cross‐slope exchange within the layer. Provided the velocity field and the water mass structure, the subsurface water mass exchange is likely accomplished by a combination of topographically controlled mean flow and the eddy transports. Our findings suggest that the bathymetry primarily determines the structure of the subpolar gyre.

Water Circulation Off the Northeastern Coast of Sakhalin during the Passage of Three Types of Deep Cyclones over the Sea of Okhotsk

Based on the numerical simulation of water circulation in the Sea of Okhotsk in 1986 to 2015, the impact of deep cyclones on the circulation off the northeastern coast of Sakhalin is studied. The circulation in the Sea of Okhotsk is simulated with the COSMO-Ru-INMOM-CICE model configuration, where the COSMO-Ru and INMOM resolve explicitly the mesoscale atmosphere and ocean dynamics and the CICE resolves the ice cover evolution. The extreme atmospheric events associated with the intensive cyclone activity over the Sea of Okhotsk during the cold season are classified. It is found that high velocity is typical of the cyclones coming to the sea from Sakhalin, and wind speed on the periphery is higher for the cyclones coming to the Sea of Okhotsk from the south and southwest. The analysis of water circulation response off the northeastern coast of Sakhalin demonstrates that the meridional current velocity on the shelf increased by several times from the sea surface to the bottom for all types of cyclones. On the edge of the shelf, southern currents intensified in the surface and bottom layers during the passage of cyclones and at the intermediate depths during the passage of fronts. On the continental slope, southern currents intensified in the surface, intermediate, and bottom layers depending on the type of extreme events.

Strengthening of the Indian Ocean Dipole With Increasing Seasonal Cycle in the Mid‐Holocene

AbstractThis study presents modeling evidence that the Indian Ocean Dipole (IOD) is enhanced in its frequency and amplitude under mid‐Holocene (8‐ka) conditions. This enhancement is identified in a global climate model simulation driven by the 8‐ka insolation, in which negative sea surface temperature anomalies grow more than the present‐day simulation in the eastern Indian Ocean. The mechanism of IOD amplification is explained in terms of a positive feedback among sea surface temperature, precipitation, and wind speeds over the eastern Indian Ocean. A series of idealized experiments in which the present‐day insolation seasonal cycle over the tropics is systematically perturbed in the model demonstrates that the IOD frequency and amplitude are proportional to the seasonal cycle strength of the atmospheric circulation off Sumatra‐Java, consistent with proxy records in the mid‐Holocene. Greater surface warming over Eurasia due to increased insolation in boreal summer is not critical to the amplification of the IOD.

Sensitivity of the Near‐Shore Oceanic Circulation Off Central Chile to Coastal Wind Profiles Characteristics

AbstractIn Eastern Boundary Upwelling Systems (EBUS), the upwelling favorable wind speeds decrease toward the coast in the so‐called wind drop‐off coastal strip, which has been shown to be influential on the coastal upwelling dynamics, particularly in terms of the relative contributions of Ekman drift and Ekman suction to coastal upwelling. Currently, the wind drop‐off length scale is not properly resolved by the atmospheric forcing of regional ocean models in EBUS, featuring a smoother cross‐shore wind profile that results in stronger near‐shore speeds that could partly explain the coastal cold bias often found in those model simulations. Here, as a case study for the upwelling system off Central Chile, the sensitivity of upwelling dynamics to the coastal wind reduction is investigated using a Regional Ocean Modeling System (ROMS). Coastal wind profiles at different resolutions are first generated using a regional atmospheric model, validated from altimeter data, and then used to correct the coarse atmospheric wind forcing used for sensitivity experiments with ROMS. It is shown that the wind drop‐off correction induces a reduction in the oceanic coastal jet intensity, a stronger poleward undercurrent and a coherent offshore Ekman drift. It also yields a significant reduction of the cold bias along the coast compared to the simulation with “uncorrected” winds. Such reduction cannot be solely explained by the reduced Ekman transport only partially compensated by increase in Ekman suction. The analysis of the surface heat budget reveals in fact that an important contributor to the cooling reduction along the coast in the presence of coastal wind drop‐off is the heat flux term mediated by the reduction in the mixed‐layer depth. Overall, our results illustrate the nonlinear response of the upwelling dynamics to the coastal wind profiles in this region.

Women's views, adherence and experience with postnatal thromboprophylaxis

IntroductionBased on current guidelines, many women qualify for postnatal thromboprophylaxis following childbirth, however, little information exists on how adherent women are and their experiences to both pharmacological and mechanical forms of thromboprophylaxis. Materials and methodsWomen requiring postnatal thromboprophylaxis were given questionnaire packs exploring their beliefs about enoxaparin, anti-embolic stockings (AES) and intermittent pneumatic compression devices (IPCD). Women were also asked to complete a diary recording when doses of enoxaparin were injected, along with an estimation of the number of hours the AES were worn each day, if at all. Results were entered onto SPSS and analysed. ResultsSixty-seven women completed the questionnaire packs. Adherence to enoxaparin therapy was relatively high (82.4%). Women self-reported sub-optimal adherence levels to the AES, with 24% stating they never wore them once home. Reasons for this included being mobile, feeling hot and feeling as if they were cutting circulation off in the legs. Women reported a high level of acceptance of IPCD post caesarean section and would be happy for IPCD to be applied again in future deliveries, if required. ConclusionsAlthough many women are adherent to postnatal TP, our findings suggest that adherence to AES is sub-optimal following discharge from hospital and therefore their usefulness is questionable. Front-line clinical staff should discuss the importance of adherence to postnatal TP, in order to avert preventable venous thromboembolic events.

Variability and Long‐Term Trends in the Shelf Circulation Off Eastern Tasmania

AbstractThis study investigates trends and interannual variability of the marine climate across the continental shelf off eastern Tasmania for 1993–2016. This region is a hotspot for global warming and biodiversity. Eastern Tasmania lies at the boundary between two ocean currents (the East Australian Current Extension, or EAC Extension, and the Zeehan Current, ZC) leading to the local marine climate exhibiting trends and variability from both boundary currents. A numerical ocean model is used to provide high‐resolution (∼2 km) estimates of the temperature, salinity, and circulation for the region. Results indicate significant positive trends in temperature, salinity, and southward flow over the shelf, consistent with an increasing EAC Extension. These trends are particularly strong in autumn, indicating a lengthening of the warm season. The interannual variability in the EAC Extension and ZC was quantified by a simple index, based on a modal analysis of surface circulation, indicating the relative dominance of each current. Strong EAC years were related to significantly more summertime marine heat wave days. Large‐scale remote drivers of variability were considered, and we found weak but significant links with El Niño–Southern Oscillation and Tasman Sea Blocking. El Niño–Southern Oscillation was found to modulate the EAC Extension in summer with a El Niño leading to enhanced southward flow and warming over the shelf. Tasman Sea Blocking was found to drive enhanced southward surface flow, particularly in winter. Nonetheless, large‐scale forcing modes explain less than 25% of the total variability in the EAC‐ZC system indicating that most of the variability is internally generated.

Role of Equatorial Basin-Mode Resonance for the Seasonal Variability of the Angola Current at 11°S

AbstractMultiyear moored velocity observations of the Angola Current near 11°S reveal a weak southward mean flow superimposed by substantial intraseasonal to seasonal variability, including annual and semiannual cycles with distinct baroclinic structures. In the equatorial Atlantic these oscillations are associated with basin-mode resonances of the fourth and second baroclinic modes, respectively. Here, the role of basin-mode resonance and local forcing for the Angola Current seasonality is investigated. A suite of linear shallow-water models for the tropical Atlantic is employed, each model representing a single baroclinic mode forced at a specific period. The annually and semiannually oscillating forcing is given by 1) an idealized zonally uniform zonal forcing restricted to the equatorial band corresponding to a remote equatorial forcing or 2) realistic, spatially varying Fourier components of wind stress data that include local forcing off Angola, particularly alongshore winds. Model-computed modal amplitudes are scaled to match moored velocity observations from the equatorial Atlantic. The observed annual cycle of alongshore velocity at 11°S is well reproduced by the remote equatorial forcing. Including local forcing slightly improves the agreement between observed and simulated semiannual oscillations at 11°S compared to the purely equatorial forcing. However, the model-computed semiannual cycle lacks amplitude at middepth. This could be the result of either underestimating the strength of the second equatorial basin mode of the fourth baroclinic mode or other processes not accounted for in the shallow-water models. Overall, the findings underline the importance of large-scale linear equatorial wave dynamics for the seasonal variability of the boundary circulation off Angola.

Modulation of currents near Durban

The modulation of near-surface currents off Durban (29.9S, 31E) is studied using monthly and daily ocean and atmosphere reanalysis products. Poleward flow on the shelf-edge exhibits long-lived 2–3 yr and 50–150 day fluctuations, whereas cyclonic circulations inshore exhibit short-lived ∼6 day pulsing by coastal winds. Monthly meridional currents near Durban 1979–2015 relate to lower air pressure over the SW Indian Ocean (∼37S, 40E) that slows the offshore anticyclonic gyre and shelf-edge Agulhas Current. Daily meridional currents near Durban 2009–2015 relate to a pattern of offshore positive / inshore negative sea surface temperatures that propagate poleward at ∼7 km/day.The upper ocean structure and circulation off KwaZulu-Natal is analyzed using daily 8 km resolution fields over the area 28–31.5S, 30–33E. The shelf oceanography of a cyclonic shear event on 25–26 October 2010 corresponds with a transient low pressure cell, 12 m/s southwest winds and 5 m swells. A coastal wind jet near Durban deepens the mixed layer >50 m during a cold air outbreak with latent heat flux >250 W/m2.While the regional atmosphere modulates longshore winds and inshore currents at high frequency, the offshore anticyclonic gyre pulses the shelf-edge Agulhas Current at low frequency in association with poleward moving eddies. As these advance down the coast, water draws off the shelf contributing to upwelling and productivity.

First Detailed Study of Circulation off Angola

New data give scientists insight into the eastern boundary current off Angola, helping them to evaluate and assess why simulations create sea surface temperature biases in the region.

Flow variability within the A laska C oastal C urrent in winter

Coastal circulation off Kayak Island in the northern Gulf of Alaska was explored in wintertime (October 2012-March 2013) by deploying nine moorings within the Alaska Coastal Current (ACC). Hydrographic, bottom pressure, and velocity observations depicted well the winter variability of the ACC. Atmospheric observations showed a net loss of heat, 30 W m−2 or more, from the ocean to the atmosphere and indicated that storms with downwelling-favorable winds over 10 m s−1 frequently passed over the area. Due to vigorous mixing during storms, the waters were well-mixed or weakly stratified whereas bottom-pressure anomalies were mainly related to surface-elevation fluctuations and indicated that there was also a cross-shelf surface-elevation gradient. Current observations showed along-shelf nearly-barotropic subtidal flow of 40 cm s−1 or more throughout the water column. They also indicated that along-shelf flow was primarily driven by the cross-shelf pressure gradient resulting from the cross-shelf surface-elevation gradient and not by wind stress. Analyses suggested that flow dynamics within the ACC in winter were well-described by vertically-averaged momentum equations and showed a dominance of the cross-shelf pressure gradient that was mainly balanced by the Coriolis term. Observations also showed that when winds relaxed, cold low-salinity waters moved offshore and stratification was reestablished. Consequently, near-shore waters were less dense, i.e., cooler and fresher than offshore waters resulting in the cross-shelf density gradient that may have contributed to the along-shelf flow by generating near-surface currents of ∼ 20 cm s−1. This article is protected by copyright. All rights reserved.

Modelling the shelf circulation off eastern Tasmania

The marine waters across Tasmanian's eastern continental shelf are biologically productive and home to economically important fisheries and aquaculture industries. However, the marine climate there is poorly understood. We use a high-resolution (∼2km in the horizontal), three-dimensional ocean model for eastern Tasmania (ETAS) to examine the simulated mean state and seasonal cycle of temperature, salinity and three-dimensional flow field, and the evaluation of daily model outputs against in situ and remote observations for the 1993–2014 period. We also use the model to examine the roles of river input and tidal forcing. The model is evaluated against remotely-sensed sea surface temperature and in-situ observations of sea level and subsurface temperature, salinity, and currents. The mean state demonstrates the influence of two well-known boundary currents (the East Australian Current, EAC, and the Zeehan Current, ZC) as well as the effects of local freshwater input from river runoff. The EAC is dominant in summer and the ZC in winter; the influence of the EAC also increases northwards and in the offshore direction. In addition, the model indicates the presence of a semi-permanent subsurface (50–100m depth) northward flow trapped near the coast. Cool freshwater runoff from the Derwent and Huon Rivers directly impacts the temperature and salinity in their estuaries but has little influence further across the shelf. Tidal forcing impacts the mean state through tide-river interactions which flush Frederick Henry Bay and Norfolk Bay with freshwater. Tidal forcing also impacts the variability of temperature all along the coastline, most likely due to changes in the turbulent mixing near to the coast. The ETAS model output data are available as a high-resolution representation of the mean state, seasonal variations, and interannual variability of Tasmania's eastern continental shelf marine climate.

The Mexican Coastal Current: A subsurface seasonal bridge that connects the tropical and subtropical Northeastern Pacific

We used a three-dimensional numerical model to analyze the seasonal variability of the coastal circulation off SW Mexico. In agreement with previous research, our model reproduced a Mexican Coastal Current (MCC) that dominates the regional poleward circulation. The modeled dynamics evidenced an energetic semiannual component that governed the subsurface seasonal variability of this poleward flow. Below the thermocline the MCC was stronger during spring and fall, when it reached subsurface seasonal-averaged velocities of ∼10cms−1 and flowed continuously from the Gulf of Tehuantepec to the entrance of the Gulf of California. There, the subsurface MCC bifurcated in one branch that continued along the coast of mainland Mexico and a second branch that crossed the gulf and joined the California Undercurrent. Instead of the local wind, the semiannual MCC variability was induced by the transit of equatorial Kelvin waves whose upwelling (downwelling) phase propagation strengthen (weakened) the subsurface poleward circulation along the Tropical Pacific off Mexico. The MCC dynamics reported in this study accounts for the, previously reported, semiannual variability of the alongshore transport and salinity content in the southern Gulf of California. Moreover, the subsurface bridge between the MCC and the California Current System represents an external source of momentum that helps to explain the intensification of the California Undercurrent during spring and fall.

Interpretation of coastal wind transfer functions with momentum balances derived from idealized numerical model simulations

The local wind-driven circulation off southern San Diego is addressed with two complementary statistical and dynamical frameworks based on observations and idealized numerical model simulations. The observations including surface currents from high-frequency radars, subsurface currents from a nearshore mooring, and wind records at a local wind station are analyzed with the idealized ocean model (MITgcm) simulations using realistic bottom topography and spatially uniform wind stress forcing. Statistically estimated anisotropic local wind transfer functions characterize the observed oceanic spectral response to wind stress separately in the x (east-west) and y (north-south) directions. We delineate the coastal circulation at three primary frequencies [low (σ L=0.0767 cycles per day (cpd)), diurnal (σ D=1 cpd), and inertial (σ f=1.07 cpd) frequencies] with the momentum budget equations and transfer functions. At low frequency, the magnitudes of transfer functions are enhanced near the coast, attributed to geostrophic balance between wind-driven pressure gradients and the Coriolis force on currents. The response diminishes away from the coast, returning to the balance between frictional and Coriolis terms, as in the classic Ekman model. On the contrary, transfer functions in the near-inertial frequency band show reduced magnitudes near the coast primarily due to friction, but exhibits the enhanced seaward response as a result of the inertial resonance. The idealized model simulations forced by local wind stress can identify the influences of remote wind stress and the biases in the data-derived transfer functions.

Statistical clustering of drifting buoy trajectories to identify Lagrangian circulation features around Japan and off Fukushima

Abstract A simple statistical clustering method is demonstrated to aid the identification of spatially repeating or persistent Lagrangian circulation patterns inherent in ensembles of drifting buoy trajectories. The technique is applied to the regional oceanic circulation about Japan and to the mesoscale circulation off Fukushima on Japan’s east coast. The drifter trajectories form a highly irregular data set in both space and time, with very different locations, configurations, cumulative travel distances (tens of metres to thousands of km), travel times (hours to years), and start and end positions. The interpolation technique of Kim, Kim, Ho, and Chu, Journal of Climate 24 (2) (2011), is found suitable to transform the spatially complex buoy data into a form suitable for statistical clustering. To resolve and give context to the very different spatial scales encountered in oceanic circulations the methods are applied in a hierarchical fashion to progressively smaller areas (120–180°E, 20–50°N; 140–160°E, 32–44°N; 140–145°E, 35–40°N). A winding number method is devised to identify and distinguish between clockwise and anti-clockwise sense of circulation. The analysis techniques provide what can be regarded as a spatial decomposition of Lagrangian flow fields. The methods do not require curve fitting or modelling, feature analysis, curve alignment, or spatial gridding, binning, and averaging, and are not dependent on density of observations. The methodology forms a useful data exploration technique for examination of trajectory data in general.

Numerical modeling of the coastal circulation off northern Baja California and southern California

A numerical study of the coastal circulation off northern Baja California and Southern California is presented. A series of numerical experiments was designed with the objective of understanding the main mechanisms that maintain and control the variability of the California Surface Current (CSC) and the California Undercurrent (CUC) off the northern Baja California coast. The coastal circulation variability in the area reflects the seasonal and mesoscale evolution of the CSC and the CUC. These currents are formed outside the model domain and are included in the open boundary conditions, which were obtained from SODA model (Simple Ocean Data Assimilation). The seasonal evolution of these currents is mainly due to wind forcing. The spring–summer intensification of the CSC is the result of density fronts caused by coastal upwelling. Upwelling produces, in spring, a strong and deep (>50m) density gradient due to an Ekman transport up to 100m3s−1×100m of coastline. The wind stress curl is strong in spring and summer, but it is more effective in strengthening the CUC during summer because during spring its effect on the CUC is inhibited due to a stronger and deeper CSC at this time. The coastal heads, especially Point Loma, enhance positive vertical relative vorticity in the near-coast part of the CSC, causing flow separation. The mesoscale variability of the currents is associated with the presence of cyclonic eddies, which interact with the seasonal currents, migrate west, and merge with each other. The high variability found in the CSC and the CUC, the low values of the baroclinic time scale parameter, and the change of sign of the potential vorticity gradient suggest that both currents are barotropically and baroclinically unstable.

Dynamics of the summer shelf circulation and transient upwelling off Ningaloo Reef, Western Australia

The shelf circulation off Ningaloo Reef near the North West Cape of Western Australia is driven by complex interactions between the southward flowing Leeuwin Current and wind‐driven currents that episodically reverse the coastal flow toward the north. The presence of these northward (equatorward) wind‐driven currents is thought to make this section of coast one of the few locations along Western Australia to experience periodic coastal upwelling. We used a combination of field observations and numerical modeling to investigate the summer circulation and upwelling dynamics along Ningaloo Reef. We analyzed current and temperature profiles from moorings at four sites across the shelf and used two Regional Ocean Modeling System (ROMS) sub‐models: (1) a coarser model of northwestern Australia forced by a global ocean model and (2) a nested fine‐scale model of the Ningaloo region. This nesting significantly improved model skill as it included the offshore mesoscale dynamics that strongly influenced the shelf circulation off Ningaloo. The field observations revealed several northward flow reversals, accompanied by cooling of the coastal waters adjacent to Ningaloo, which were associated with strong northward wind events. Analysis of the coastal heat budget revealed that cooling events were primarily driven by upwelling, whereas warming of coastal waters during relaxation events resulted mostly from along‐shelf advection of warm water from the north. Due to the combined effects of its relatively steep (~1/50 slope) shelf and strong summer stratification, upwelled water was sourced from the interior of the water column, likely influencing the sources and fluxes of nutrients to Ningaloo Reef.