Coastal Trapped Waves Research Articles

A baroclinic coastal trapped wave event in the Gulf of Naples (Tyrrhenian Sea)

In this study, a baroclinic coastal trapped wave, with period ~ 4.5 days and cross-shore scale ~ 3 km, is identified in the outputs of a very-high-resolution ocean circulation model of the Campania coastal system (central Tyrrhenian Sea; including the Gulfs of Salerno, Naples, and Gaeta). The outputs are from a simulation spanning June 2003, a month in which the surface winds were always weak, except for a strong northeasterly wind event that lasted 1 day (20 June). This event is found to generate a strong upwelling along the Campania coasts, whose relaxation—virtually free, because of the weakness of the winds—produces coastal current fluctuations that propagate to the north, spanning the three gulfs. The dynamics (analyzed with a focus on the Gulf of Naples) is found to share important features with baroclinic Kelvin waves in a two-layer model, such as the sharp cross-shore decrease of the perturbation amplitude and the vertical reversal of the long-shore current velocities. The simulated phase speed, cross-shore extension, and wavelength of the perturbation are also close to those obtained using a two-layer approximation of the dynamics. Moreover, the propagation described by the models is shown to be compatible with current measurements that were made in June 2003 at the southern entrance of the Gulf of Naples. Experimental implications related to the specific oceanographic problem are finally discussed, and an experimental strategy—inspired by our modeling approach—aimed at identifying the phenomenon is proposed.

Impact of local and remote winds on the shelf circulation off the central west coast of India

A linear coastal-trapped-wave (CTW) model is used to examine the effects of large-scale winds, with time scale ranging from a few days to a few weeks, on the West India Coastal Current (WICC), particularly on the shelf off the central west coast of India. We show that unlike the seasonal cycle of WICC, which is primarily forced by the winds along the east coast of India, the high-frequency WICC is mostly driven by the west-coast winds. Nevertheless, the influence of winds as far as Sri Lanka and east coast of India cannot be neglected. Simple numerical experiments with the CTW model show that the strong current observed at Goa (15° N) compared to Bhatkal (13° N) and Jaigarh (17° N) is due to two factors: (1) the superposition of local and remote CTWs and (2) the widening of shelf width north of Goa, which decreases the amplitude of the currents poleward of Goa. If the local winds are weak, the amplitude of current decreases poleward due to friction, and the current at the south leads the north. We also note that the observed phase difference between sea level and alongshore current at Goa could be attributed to the propagation of remotely forced higher-order modes of CTWs.

Effect of coastal-trapped waves on the synoptic variations of the Yellow Sea Warm Current during winter

Significant short-term fluctuations of the Yellow Sea Warm Current (YSWC) at several days' time scale were observed in the Yellow Sea (YS) during winter of 2006–2007. Observations indicated that the synoptic fluctuations of the YSWC appear to be associated with low-frequency sea level variations. By analyzing direct current measurements, sea level elevations and results from a regional ocean model, this study characterizes the variation of the YSWC at synoptic time scale and examines its connection with propagation of coastal-trapped waves during winter. The model captures the observed short-term fluctuations of the YSWC at several days’ periods and suggests a close relation between coastal-trapped waves and the YSWC variability. The YSWC is intensified (weakened) when the westward sea level-related barotropic pressure gradient is enhanced (diminished) due to the propagation of coastal-trapped waves. Model experiments with idealized periodic surface forcing further identify the important role of the coastal-trapped waves on adjusting the strength of the YSWC. The model results also suggest that the propagation of coastal-trapped waves contribute to the intermittent northwestward intrusion of Cheju Warm Current (CWC) in the frontal region northwest of Cheju. Generation and propagation of the coastal-trapped waves give rise to the westward barotropic pressure gradient in the YS entrance, which periodically pumps the CWC water into the YS interior west of Cheju.

Subseasonal Coastal‐Trapped Wave Propagations in the Southeastern Pacific and Atlantic Oceans: 1. A New Approach to Estimate Wave Amplitude

AbstractThe Humboldt and the Benguela upwelling systems are connected to the equatorial variability through the coastal waveguide, so that a large variance of the coastal sea level and current variability can be described as an infinite sum of orthonormal free Coastal‐Trapped Wave (CTW) modes. The objective of this study is to infer the CTW mode contributions to the coastal variability in both systems at subseasonal timescales (<120 days) from regional ocean circulation model simulations. We develop and validate twin regional model configurations of the southeastern Pacific and Atlantic Oceans. Cross‐shore spatial structures of the first four free CTW modes are then derived from model mean stratification and topography along the southwestern African and South American continents. We introduce and validate a new methodology to estimate the gravest CTW mode contributions to model pressure and alongshore current. Our formulation draws on the orthonormality of the CTW modal structures, and uses a simple projection of the coastal and bottom model pressure onto each CTW structure. Results give confidence in the ability of this modal decomposition methodology to disentangle CTW mode contributions from complex nonlinear coastal processes that control the coastal subseasonal variability. In both systems, it allows to successfully extract the gravest poleward propagating CTW modes with velocities close to the theoretical values and amplitudes consistent with the solutions of a simple multimode linear CTW model. Furthermore, results show that both systems exhibit relatively different CTW dynamics and forcings which are discussed in the companion paper (Illig et al., 2018).

Cross-shelf transport induced by coastal trapped waves along the coast of East China Sea

Cross-shelf transport is important due to its role in the transport of nutrients, larvae, sediments, and pollutants. The role of coastal trapped waves (CTWs) and their contribution to the cross-shelf transport is presently unknown. The impact of wind-driven CTWs on the structure of the cross-shelf currents and transport is investigated in the East China Sea (ECS) starting from theory. The cross-shelf currents are divided into four terms: the geostrophic balance (GB) term, the second-order wave (SOW) term, the bottom friction (BF) term and Ekman (EK) term, as well as three modes: the Kelvin wave (KW) mode, the first shelf wave (SW1) mode and the second shelf wave (SW2) mode. Comparison among these decompositions shows that (1) for the four terms, the effect of the GB and EK terms is continual, while that of the BF term is confined to 60–240 km offshore, and the contribution of the SOW term can be ignored; (2) for the three modes, the KW and SW1 modes are dominant in cross-shelf transport. The results show that the total cross-shelf transport travels onshore under idealized wind stress on the order of 10-1, and it increases along the cross-shelf direction and peaks about -0.73 Sv at the continental shelf margin. With the increase of linear bottom friction coefficient, the cross-shelf transport declines with distance with the slope becoming more uniform.

Shelf Flows Forced by Deep-Ocean Anticyclonic Eddies at the Shelf Break

AbstractIsolated monopolar eddies in the ocean tend to move westward. Those shed by western boundary currents may then interact with the continental margin. This simple picture is complicated by the presence of other flow features, but satellite observations show that many western boundary continental shelves experience cross-shelfbreak exchange flows forced by mesoscale eddies translating near the shelf break. Here we extend our previous study of eddy interaction with a flat shelf to that with a sloping shelf. Using a set of primitive equation numerical simulations, we address the vertical structure of the onshore and offshore flows forced by the eddy, the origin of the exported shelf water, and the extent to which eddy water can penetrate onto the shelf. The simulations reveal an asymmetry in the vertical structure of cross-shelfbreak flows: the offshore flow is generally barotropic, whereas the onshore flow is always baroclinic. The exported shelf water is sourced from downstream of the eddy in the coastal-trapped wave direction and is supplied by a barotropic alongshore jet. This “supply jet” has a Rhines-like cross-shore length scale proportional to (eddy velocity scale/shelf topographic beta)1/2 measured from the shelf break. Eddy water is forced onto the shelf and is present up to a distance of one internal Rossby deformation radius, defined using shelf properties, from the shelf break. We rationalize these horizontal and vertical scales, connect them to existing observations, and extend our previous parameterization of eddy-forced offshore shelf-water flux to account for nonzero shelf slopes.

Wind-Driven Circulation in a Shelf Valley. Part II: Dynamics of the Along-Valley Velocity and Transport

AbstractThe dynamics controlling the along-valley (cross shelf) flow in idealized shallow shelf valleys with small to moderate Burger number are investigated, and analytical scales of the along-valley flows are derived. This paper follows Part I, which shows that along-shelf winds in the opposite direction to coastal-trapped wave propagation (upwelling regime) force a strong up-valley flow caused by the formation of a lee wave. In contrast, along-shelf winds in the other direction (downwelling regime) do not generate a lee wave and consequently force a relatively weak net down-valley flow. The valley flows in both regimes are cyclostrophic with O(1) Rossby number. A major difference between the two regimes is the along-shelf length scales of the along-valley flows Lx. In the upwelling regime Lx depends on the valley width Wc and the wavelength λlw of the coastal-trapped lee wave arrested by the along-shelf flow Us. In the downwelling regime Lx depends on the inertial length scale |Us|/f and Wc. The along-valley velocity scale in the upwelling regime, given byis based on potential vorticity (PV) conservation and lee-wave dynamics (Hs and Hc are the shelf and valley depth scales, respectively, and f is the Coriolis parameter). The velocity scale in the downwelling regime, given by is based on PV conservation. The velocity scales are validated by the numerical sensitivity simulations and can be useful for observational studies of along-valley transports. The work provides a framework for investigating cross-shelf transport induced by irregular shelf bathymetry and calls for future studies of this type under realistic environmental conditions and over a broader parameter space.

Diurnal tidal currents attributed to free baroclinic coastal-trapped waves on the Pacific shelf off the southeastern coast of Hokkaido, Japan

To understand the properties of tides and tidal currents on the Pacific shelf off the southeastern coast of Hokkaido, Japan, we analyzed time series of 9 current meters that were moored on the shelf for 1 month to 2 years. Diurnal tidal currents such as the K1 and O1 constituents were more dominant than semi-diurnal ones by an order of magnitude. The diurnal tidal currents clearly propagated westward along the coast with a typical phase velocity of 2 m s–1 and wavelength of 200 km. Moreover, the shape and phase of the diurnal currents measured by a bottom-mounted ADCP were vertically homogeneous, except in the vicinity of the bottom boundary layer. These features were very consistent with theoretically estimated properties of free baroclinic coastal-trapped waves of the first mode. An annual (semi-annual) variation was apparent for the phase (amplitude) of the O1 tidal current, which was correlated with density stratification (intensity of an along-shelf current called the Coastal Oyashio). These possible causes are discussed in terms of the propagation and generation of coastal-trapped waves.

Seasonal and annual variability of coastal sulphur plumes in the northern Benguela upwelling system.

We investigated the seasonal and annual variability of surface sulphur plumes in the northern Benguela upwelling system off Namibia because of their significant impacts on the marine ecosystem, fishing industry, aquaculture farming and tourism due to their toxic properties. We identified the sulphur plumes in ocean colour satellite data of the medium resolution imaging spectrometer (MERIS) for the 2002–2012 time period using the differences in the spectral properties of Namibian Benguela optical water types. The sulphur events have a strong seasonal cycle with pronounced main and off-seasons forced by local and remote-driven processes. The main peak season is in late austral summer and early austral autumn at the beginning of the annual upwelling cycle caused by increasing equatorwards alongshore winds. The sulphur plume activity is high between February and April during the seasonal oxygen minimum associated with the seasonal reduction of cross-shore ventilation of the bottom waters, the seasonal southernmost position of the Angola Benguela Frontal Zone, the seasonal maximum of water mass fractions of South Atlantic and Angola Gyre Central Waters as well as the seasonal arrival of the downwelling coastal trapped waves. The off-season is in austral spring and early austral summer during increased upwelling intensity and enhanced oxygen supply. The annual variability of sulphur events is characterized by very high activities in years 2004, 2005 and 2010 interrupted by periods of lower activity in years 2002 to 2003, 2006 to 2009 and 2011 to 2012. This result can be explained by the relative contributions or adding effects of local and remote-driven forces (from the equatorial area). The probability for the occurrence of sulphur plumes is enhanced in years with a lower annual mean of upwelling intensity, decreased oxygen supply associated with decreased lateral ventilation of bottom waters, more southern position of the Angola Benguela Frontal Zone, increased mass fraction of South Atlantic Central Water and stronger downwelling coastal trapped waves. Understanding of the variability and forcing processes of the toxic sulphur events will help in the future to monitor and forecast them as well as to manage their social and economic consequences in the northern Benguela upwelling system off Namibia.

Generation and propagation processes of near-inertial internal waves and coastal-trapped waves in and around Toyama Bay, Japan, calculated by high-resolution nesting ocean model

Generation and propagation processes of near-inertial internal waves and coastal-trapped waves in and around Toyama Bay, Japan, calculated by high-resolution nesting ocean model

Impact of tropical cyclones on the evolution of the monsoon-driven upwelling system in the coastal waters of the northern South China Sea

An upwelling system exists in the coastal waters of the northern South China Sea (NSCS), a region that is frequently affected by tropical cyclones in summer. This study investigates the evolution of the NSCS monsoon-driven upwelling system and the effects of the Talim and Doksuri tropical cyclones on the system using in situ observational data obtained at three mooring stations, one land-based meteorological station, and concurrent satellite remote sensing data for the NSCS coastal waters from May to July 2012. The results show that the occurrence and evolution of the upwelling system were mainly controlled by the Asian southwest monsoon, while the eastward current also made important contributions to the upwelling intensity. A decrease in the bottom water temperature and shifts in the along-shore and cross-shore currents were direct evidence of the establishment, existence, and recovery of this upwelling. Tropical cyclones have significant impacts on hydrodynamics and can thus influence the evolution of the NSCS upwelling system by changing the local wind and current fields. Variations in water level and local current systems impeded the development of upwelling during tropical cyclones Talim and Doksuri in the study area, which have low-frequency fluctuations of approximately 2–10 days. These variations were the results of the coupled interactions between local wind fields, coastal trapped waves, and other factors. The hydrodynamic environment of the marine water (including coastal upwelling system) rapidly recovered to normal sea conditions after each cyclone passed due to the relatively short duration of the impact of a tropical cyclone on the dynamic environment of the waters.

A Study of Low-Frequency, Wind-Driven, Coastal-Trapped Waves along the Southeast Coast of Australia

AbstractCoastal-trapped waves (CTWs) along the southeast coast of Australia were investigated based on a frictional, wind-driven long-wave theory. It was found that low-frequency sea level anomalies (SLAs) were continuously propagating from the south coast up along the east coast as CTWs, mainly forced by the alongshore wind stress. Three main subinertial peaks existed in the spectral characteristics of the SLAs, with periods of 14.2, 10.2, and 7.8 days, respectively. Power spectral density distributions of the peaks showed that the CTW amplitudes varied significantly along the southeast coast. For idealized linear and exponential shelves, a theoretical analysis indicated that the fundamental factor influencing the eigenvector of mode 1, and therefore the CTW amplitude, was the offshore water depth. This theoretical work was well supported by eight sensitivity cases. Four additional cases were conducted, and time-averaged energy fluxes were calculated to identify the energy source of the CTWs in the Australian Coastal Experiment (ACE) region. It was shown that both the local wind stress and the wind stress in Bass Strait contributed to the CTWs in the ACE region, with the latter playing a more important role. The remaining CTW energy came from remote forcing farther west of Bass Strait. The energy flux calculation also showed that the CTW energy flux was almost constant along the investigated coast because of the balance between frictional dissipation and the energy gain from the alongshore wind stress; the significant variations in the power spectral density (PSD) of the subinertial peaks were mainly due to the variations in the modal eigenvectors caused by the shelf geometry.

Wind-Driven Circulation in a Shelf Valley. Part I: Mechanism of the Asymmetrical Response to Along-Shelf Winds in Opposite Directions

AbstractMotivated by observations in Hudson shelf valley showing stronger onshore than offshore flows, this study investigates wind-driven flows in idealized shallow shelf valleys. This first part of a two-part sequence focuses on the mechanism of the asymmetrical flow response in a valley to along-shelf winds of opposite directions. Model simulations show that (i) when the wind is in the opposite direction to coastal-trapped wave (CTW) phase propagation, the shelf flow turns onshore in the valley and generates strong up-valley transport and a standing meander on the upstream side (in the sense of CTW phase propagation) of the valley, and (ii) when the wind is in the same direction as CTW phase propagation, the flow forms a symmetric onshore detour pattern over the valley with negligible down-valley transport. Comparison of the modeled upstream meanders in the first scenario with CTW characteristics confirms that the up-valley flow results from CTWs being arrested by the wind-driven shelf flow establishing lee waves. The valley bathymetry generates an initial excessive onshore pressure gradient force that drives the up-valley flow and induces CTW lee waves that sustain the up-valley flow. When the wind-driven shelf flow aligns with CTW phase propagation, the initial disturbance generated in the valley propagates away, allowing the valley flow to adjust to roughly follow isobaths. Because of the similarity in the physical setup, this mechanism of arrested CTWs generating stronger onshore than offshore flow is expected to be applicable to the flow response in slope canyons to along-isobath background flows of opposite directions.

Time-Dependent Linear Theory for the Generation of Poleward Undercurrents on Eastern Boundaries

AbstractA time-dependent, inviscid, linear theory for the generation of poleward undercurrent flow under upwelling conditions along midlatitude ocean eastern boundaries is proposed. The theory relies on a conceptual separation of time scales between the rapid, coastal-trapped wave response to upwelling winds and the subsequent slow, interior, quasigeostrophic evolution. Solutions are obtained under idealized conditions in which the coastal boundary and the continental-slope topography are uniform alongshore, and the time-dependent wind-stress forcing is applied over a limited meridional range, uniform cross-shore, and directed alongshore. A time-dependent coastal boundary condition on the slow-time-scale interior flow, consisting of the low-frequency, geostrophically balanced sea surface height disturbance over the outer shelf, is obtained from consideration of the fast-time-scale, coastal-trapped response. A quasigeostrophic potential vorticity equation is then solved to determine the interior response to this time-dependent boundary condition. Under upwelling conditions, the results show the formation of a localized region of subsurface poleward flow over the upper continental slope that is qualitatively consistent in amplitude, location, and timing with observations of poleward undercurrents on eastern boundaries. Despite its origin as a sea surface height anomaly, the coastal-boundary condition drives a baroclinic planetary wave response, in which the poleward subsurface flow evolves in planetary vorticity balance with induced subsurface upwelling.

Model-simulated coastal trapped waves stimulated by typhoon in northwestern South China Sea

In this paper, we apply an unstructured grid coastal ocean model to simulate variations in the sea level and currents forced by two typhoons in the northwestern South China Sea (SCS). The model simulations show distinct differences for the two cases in which the typhoon paths were north and south of the Qiongzhou (QZ) Strait. In both cases, coastal trapped waves (CTWs) are stimulated but their propagation behaviors differ. Model sensitivity simulations suggest the dominant role played by alongshore wind in the eastern SCS (near Shanwei) and southeast of Hainan Island. We also examine the influence of the Leizhou Peninsula by changing the coastline in simulation experiments. Based on our results, we can draw the following conclusions: 1) The CTWs stimulated by the northern typhoon are stronger than the southern CTW. 2) In the two cases, the directions of the current structures of the QZ cross-transect are reversed. The strongest flow cores are both located in the middle-upper area of the strait and the results of our empirical orthogonal function analysis show that the vertical structure is highly barotropic. 3) The simulated CTWs divide into two branches in the QZ Strait for the northern typhoon, and an island trapped wave (ITW) around Hainan Island for the southern typhoon. 4) The Leizhou Peninsula plays a significant role in the distribution of the kinetic energy flux between the two CTW branches. In the presence of the Leizhou Peninsula, the QZ branch has only 39.7 percent of the total energy, whereas that ratio increases to 72.2 percent in its absence.

Transition of the Tsushima Warm Current Path Observed over Toyama Trough, Japan

AbstractMooring, CTD, and ADCP observations were made in 2012 in and around the Toyama Trough (TT) cutting across a continental shelf along the Japanese coast of the Japan Sea between Noto Peninsula (NP) and Sado Island (SI) to investigate spatiotemporal characteristics of path transition of the coastal branch of the Tsushima Warm Current (CBTWC). Around SI, downstream of the TT boundary, a wavelike alongshore current perturbation, accompanied by sea level rise, was observed. This perturbation occurred after the seasonal amplification of the CBTWC around the NP on the upstream boundary of the TT. This process was delineated by the results of numerical experiments performed with a two-layer model using idealized topography. The model showed that a current path of the CBTWC shifted from alongshore mode to offshore mode bridged over the TT in association with the lee eddy development behind the NP toward the SI over the TT. This lee eddy is generated by positive vorticity induced over topographic discontinuity between the continental shelf off the northern coast of the NP and deeper region of the TT. The model indicated the period of eddy formation is 60–90 days if the volume transport is 1 Sv (1 Sv ≡ 106 m3 s−1), whereas the observations showed the formation period was only 47 days at 1.2 Sv of volume transport. To explain this discrepancy, temporal variation of the CBTWC, vortex supply from preexisting eddies, or eddies caused by the scattering of coastal-trapped waves were suggested as new processes that accelerate the growth rate of the lee eddy.

Large-Scale Structure in Wind Forcing over the California Current System in Summer

The wind that drives oceanic eastern boundary upwelling systems is highly variable. In many locations, the standard deviation of wind velocity on time scales of days to weeks is larger than the mean. In the ~1600-km-long California Current System (CCS), the spatial decorrelation scale of the wind fluctuations is ~400–800 km, suggesting wind fluctuations in the north and south ends of the system are not related. Yet, there is also the suggestion in the literature of a larger-scale structure in the fluctuations. Here, empirical orthogonal function (EOF) analysis of buoy and satellite wind velocities confirms the existence of that structure. This analysis covers a larger spatial domain than previous EOF studies in the CCS and, to allow for propagation of the wind fluctuations, includes an approach for calculating Hilbert EOFs from time series with gaps. The large-scale structure in the wind fluctuations is a quasi-dipole pattern spanning the coastline from Washington through California. It accounts for ~60% of the wind velocity variance on time scales of days to weeks. The time-mean wind velocity, showing a continuous zone of intensified wind along the coast, is deceptive. When the northern half of the CCS is in a relaxation state, the southern half often experiences intensified winds, and vice versa. There should be a resulting out-of-phase structure in oceanic upwelling. The out-of-phase wind fluctuations in the north and south parts of the CCS may affect the forcing of oceanic coastal-trapped waves, mesoscale eddy generation at capes, and offshore export of carbon.

Near 5-Day Nonisostatic Response to Atmospheric Surface Pressure and Coastal-Trapped Waves Observed in the Northern South China Sea

AbstractOceanic, nonisostatic responses to near 5-day Rossby–Haurwitz atmospheric pressure waves have been observed in open oceans; however, such responses based on observations in marginal seas such as the South China Sea have not been reported, owing to the limited ocean bottom pressure Pbot records. The Pbot measurements from pressure recording inverted echo sounders (PIESs) at sites in the northern South China Sea revealed a nonisostatic-like response near 5 days, although the coastal-trapped waves (CTWs) appeared to obscure it because their broadband periods include the near 5-day band. Cross-spectral analysis revealed that the PIES Pbot records and the sea level (SL) records of Hong Kong all correlate strongly with the atmospheric pressure and winds over the East China Sea. This is indicative of remotely forced CTWs. The PIES Pbot records showed higher coherence near 5 days with the zonal low-pass wavelength filters applied to the atmospheric pressure, and the phase analysis results strongly suggest nonisostatic oceanic responses to the westward-propagating Rossby–Haurwitz waves. Effective separation of CTWs and the nonisostatic responses from the Pbot records at the near 5-day period was achieved. The oceanic responses to the Rossby–Haurwitz waves in the northern South China Sea were nonisostatic; a 1-mbar change in air pressure resulted in a 1.58-mbar change in Pbot with a phase lag of 14.8°. The mean phase speed of CTWs from Hong Kong to station P3 was estimated to be 9.9 m s−1.

Episodic surface intrusions in the Yellow Sea during relaxation of northerly winds

AbstractThe surface currents over the Yellow and East China Seas are mapped from the Geostationary Ocean Color Imager (GOCI). Based on a composite of six intrusion events in January–April, the strong northward surface current in the Yellow Sea is shown to be concentrated along the deep trough, accompanied by a broad northward surface current over the East China Sea. From the corresponding surface winds, the episodic northward surface flow bursts appear to be associated with abrupt changes from the strong northerly winds to weak southerly winds during cold front passages. A three‐dimensional model driven with observed surface winds is used to simulate the observed shelf‐wide response to northerly winds. There is an outstanding agreement between the simulated and observed surface currents. The surface intrusion in the Yellow Sea is shown to be driven primarily by a barotropic longitudinal surface slope, while the strong northward current in the East China Sea is associated with a coastal trapped wave. Moreover, the surface intrusion is associated with a large volume transport, suggesting that the transient intrusions could be important in the northward heat transport. The unprecedented capability of GOCI satellite in providing a regional circulation pattern, in conjunction with complementary model simulations, could contribute greatly to understanding of the dynamics of the Yellow and East China Seas.

Localized rapid warming of West Antarctic subsurface waters by remote winds

The highest rates of Antarctic glacial ice mass loss are occurring to the west of the Antarctica Peninsula in regions where warming of subsurface continental shelf waters is also largest. However, the physical mechanisms responsible for this warming remain unknown. Here we show how localized changes in coastal winds off East Antarctica can produce significant subsurface temperature anomalies (>2 °C) around much of the continent. We demonstrate how coastal-trapped barotropic Kelvin waves communicate the wind disturbance around the Antarctic coastline. The warming is focused on the western flank of the Antarctic Peninsula because the circulation induced by the coastal-trapped waves is intensified by the steep continental slope there, and because of the presence of pre-existing warm subsurface water offshore. The adjustment to the coastal-trapped waves shoals the subsurface isotherms and brings warm deep water upwards onto the continental shelf and closer to the coast. This result demonstrates the vulnerability of the West Antarctic region to a changing climate. The subsurface waters west of the Antarctic Peninsula are warming rapidly. This study shows that changes in coastal winds in East Antarctica are remotely impacting this region and drive the upwelling of warm deep water.