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Between 2009 and 2010, two Thai ships, the MV Sun Sea and Ocean Lady, brought 568 Tamil asylum seekers to Canada’s West Coast. Border authorities seized the ships and detained their passengers as security threats. For many criticizing this anti-migrant response, the arrivals of these ships echoed that of the Komagata Maru in 1914. This steamship entered the West Coast’s Vancouver harbour, but its 376 predominantly Sikh-Punjabi passengers were denied from disembarking as British subjects entering Canada. Scholarship on these incidents often use either the Komagata Maru as a lens for attending to the MV Sun Sea or vice versa. Part of the reason is that shortly after the government had apologized for its response to the Komagata Maru, it was detaining Tamil asylum seekers and arguing for their deportation. In suggesting their link far exceeds a temporal coincidence, this paper explores what makes it possible to think of the MV Sun Sea and Komagata Maru together. It argues that they are interlinked by an economy of affirmation and forgetting in Canadian public and political discourse. Furthermore, this economy frames how these boats are remembered unequally in service of the Canadian nation-state.

Buoyancy fluxes and submarine melt rates at vertical ice‐ocean interfaces are commonly parameterized using theories derived for unbounded free plumes. A Large Eddy Simulation is used to analyze the disparate dynamics of free plumes and wall‐bounded plumes; the distinctions between the two are supported by recent theoretical and experimental results. Modifications to parameterizations consistent with these simulations are tested and compared to results from numerical and laboratory experiments of meltwater plumes. These modifications include 50% weaker entrainment and a distinct plume‐driven friction velocity in the shear boundary layer up to 8 times greater than the externally‐driven friction velocity. Using these updated plume parameter modifications leads to 40 times the ambient melt rate predicted by commonly used parameterizations at vertical glacier faces, which is consistent with observed melt rates at LeConte Glacier, Alaska. Plain Language Summary Over the past two decades, the outward flow of tidewater glaciers has accelerated, which has contributed to sea level rise. There is growing evidence that this acceleration has been triggered by melting at ice‐ocean interfaces, where the ocean comes into contact with and drives the melting of glaciers. In particular, commonly used models and theories describing the ocean turbulence and melt dynamics at vertical ice‐ocean interfaces underestimate observed melt rates by an order of magnitude. This study tests proposed changes to existing theories and uses a turbulence‐resolving ocean model to validate this alternative (plume with a wall) theory instead of commonly used (plume without a wall) theories; the first type is more appropriate and better takes into account how ocean turbulence drives the melting of a vertical ice wall. We show that these proposed changes are consistent with existing melt observations and are an important step toward understanding a critical process that may help us improve sea level rise predictions. Key Points A modified wall‐bounded plume parameterization motivated by recent numerical/lab work is proposed as an alternative to free plume theory Subglacial discharge plume simulations at a vertical ice face are consistent with entrainment/plume dynamics from wall‐bounded plume theory Melt rate estimates using updated parameters are consistent with observations at LeConte Glacier (40 times greater than standard estimates)

Diapycnal mixing plays a primary role in the thermodynamic balance of the ocean and, consequently, in oceanic heat and carbon uptake and storage. Though observed mixing rates are on average consistent with values required by inverse models, recent attention has focused on the dramatic spatial variability, spanning several orders of magnitude, of mixing rates in both the upper and deep ocean. Away from ocean boundaries, the spatiotemporal patterns of mixing are largely driven by the geography of generation, propagation, and dissipation of internal waves, which supply much of the power for turbulent mixing. Over the last 5 years and under the auspices of U.S. Climate Variability and Predictability Program (CLIVAR), a National Science Foundation (NSF)- and National Oceanic and Atmospheric Administration (NOAA)-supported Climate Process Team has been engaged in developing, implementing, and testing dynamics-based parameterizations for internal wave–driven turbulent mixing in global ocean models. The work has primarily focused on turbulence 1) near sites of internal tide generation, 2) in the upper ocean related to wind-generated near inertial motions, 3) due to internal lee waves generated by low-frequency mesoscale flows over topography, and 4) at ocean margins. Here, we review recent progress, describe the tools developed, and discuss future directions.

Internal oceanic waves are subsurface gravity waves that can be enormous and travel thousands of kilometres before breaking but they are difficult to study; here observations of such waves in the South China Sea reveal their formation mechanism, extreme turbulence, relationship to the Kuroshio Current and energy budget. IWISE catches internal waves mid-ocean Internal waves are the underwater version of more familiar surface waves. They can be enormous and travel thousands of kilometres before breaking. The South China Sea is known to be home to the largest internal waves in the world's oceans, but their size, generation mechanisms and role in the regional energy budget are unknown. Matthew Alford and colleagues now present the results from the IWISE observational campaign and reveal that internal waves more than 200 metres high break in the South China Sea and create turbulence that is orders of magnitude larger than in the open ocean, and that wave formation is influenced by the Kuroshio current. These results now allow for a complete energy budget of the South China Sea, and for a more accurate incorporation of internal waves into climate models. Internal gravity waves, the subsurface analogue of the familiar surface gravity waves that break on beaches, are ubiquitous in the ocean. Because of their strong vertical and horizontal currents, and the turbulent mixing caused by their breaking, they affect a panoply of ocean processes, such as the supply of nutrients for photosynthesis 1 , sediment and pollutant transport 2 and acoustic transmission 3 ; they also pose hazards for man-made structures in the ocean 4 . Generated primarily by the wind and the tides, internal waves can travel thousands of kilometres from their sources before breaking 5 , making it challenging to observe them and to include them in numerical climate models, which are sensitive to their effects 6 , 7 . For over a decade, studies 8 , 9 , 10 , 11 have targeted the South China Sea, where the oceans’ most powerful known internal waves are generated in the Luzon Strait and steepen dramatically as they propagate west. Confusion has persisted regarding their mechanism of generation, variability and energy budget, however, owing to the lack of in situ data from the Luzon Strait, where extreme flow conditions make measurements difficult. Here we use new observations and numerical models to (1) show that the waves begin as sinusoidal disturbances rather than arising from sharp hydraulic phenomena, (2) reveal the existence of >200-metre-high breaking internal waves in the region of generation that give rise to turbulence levels >10,000 times that in the open ocean, (3) determine that the Kuroshio western boundary current noticeably refracts the internal wave field emanating from the Luzon Strait, and (4) demonstrate a factor-of-two agreement between modelled and observed energy fluxes, which allows us to produce an observationally supported energy budget of the region. Together, these findings give a cradle-to-grave picture of internal waves on a basin scale, which will support further improvements of their representation in numerical climate predictions.

Over the Texas-Louisiana Shelf in the Northern Gulf of Mexico, the eutrophic, fresh Mississippi/Atchafalaya river plume isolates saltier waters below, supporting the formation of bottom hypoxia in summer. The plume also generates strong density fronts, features of the circulation that are known pathways for the exchange of water between the ocean surface and the deep. Using high-resolution ocean observations and numerical simulations, we demonstrate how the summer land-sea breeze generates rapid vertical exchange at the plume fronts. We show that the interaction between the land-sea breeze and the fronts leads to convergence/divergence in the surface mixed layer, which further facilitates a slantwise circulation that subducts surface water along isopycnals into the interior and upwells bottom waters to the surface. This process causes significant vertical displacements of water parcels and creates a ventilation pathway for the bottom water in the northern Gulf. The ventilation of bottom water can bypass the stratification barrier associated with the Mississippi/Atchafalaya river plume and might impact the dynamics of the region’s dead zone. Vertical exchange in the ocean is an important conduit connecting the surface to the deep and influences the distributions of gases, nutrients, pollutants, and other tracers. Here the authors using high-resolution observations and numerical simulations of the ocean fronts in the Northern Gulf of Mexico reveal that the interaction between the fronts and land-sea breeze creates slantwise pathways for water parcels and induces significant subduction of surface water and upwelling of bottom water.

In the tropics, a strong seasonal cycle in sea surface temperature exists despite comparatively constant radiation inputs; turbulent mixing from below is now shown to control the cooling phase of the seasonal cycle in the equatorial Pacific ‘cold tongue’ at 140° W. Seasonal cycles in the equatorial Pacific In much of the non-tropical ocean, the seasonal cycle is dominated by seasonal variations in solar radiation. Yet in the tropics, there is a strong seasonal cycle in sea surface temperature despite comparatively constant radiation inputs. James Moum and colleagues present multi-year observations that show that turbulent mixing from below accounts for much of the magnitude of the seasonal cycle of sea surface temperature in the equatorial Pacific cold tongue at 140° W. These findings should contribute to improved understanding of the El Niño/Southern Oscillation cycle and to more accuracy in many coupled ocean–atmosphere climate models. Sea surface temperature (SST) is a critical control on the atmosphere 1 , and numerical models of atmosphere–ocean circulation emphasize its accurate prediction. Yet many models demonstrate large, systematic biases in simulated SST in the equatorial ‘cold tongues’ (expansive regions of net heat uptake from the atmosphere) of the Atlantic 2 and Pacific 3 oceans, particularly with regard to a central but little-understood feature of tropical oceans: a strong seasonal cycle. The biases may be related to the inability of models to constrain turbulent mixing realistically 4 , given that turbulent mixing, combined with seasonal variations in atmospheric heating, determines SST. In temperate oceans, the seasonal SST cycle is clearly related to varying solar heating 5 ; in the tropics, however, SSTs vary seasonally in the absence of similar variations in solar inputs 6 . Turbulent mixing has long been a likely explanation, but firm, long-term observational evidence has been absent. Here we show the existence of a distinctive seasonal cycle of subsurface cooling via mixing in the equatorial Pacific cold tongue, using multi-year measurements of turbulence in the ocean. In boreal spring, SST rises by 2 kelvin when heating of the upper ocean by the atmosphere exceeds cooling by mixing from below. In boreal summer, SST decreases because cooling from below exceeds heating from above. When the effects of lateral advection are considered, the magnitude of summer cooling via mixing (4 kelvin per month) is equivalent to that required to counter the heating terms. These results provide quantitative assessment of how mixing varies on timescales longer than a few weeks, clearly showing its controlling influence on seasonal cooling of SST in a critical oceanic regime.

Feedbacks between ice melt, glacier flow and ocean circulation can rapidly accelerate ice loss at tidewater glaciers and alter projections of sea-level rise. At the core of these projections is a model for ice melt that neglects the fact that glacier ice contains pressurized bubbles of air due to its formation from compressed snow. Current model estimates can underpredict glacier melt at termini outside the region influenced by the subglacial discharge plume by a factor of 10–100 compared with observations. Here we use laboratory-scale experiments and theoretical arguments to show that the bursting of pressurized bubbles from glacier ice could be a source of this discrepancy. These bubbles eject air into the seawater, delivering additional buoyancy and impulses of turbulent kinetic energy to the boundary layer, accelerating ice melt. We show that real glacier ice melts 2.25 times faster than clear bubble-free ice when driven by natural convection in a laboratory setting. We extend these results to the geophysical scale to show how bubble dynamics contribute to ice melt from tidewater glaciers. Consequently, these results could increase the accuracy of modelled predictions of ice loss to better constrain sea-level rise projections globally.Laboratory experiments suggest that bursting bubbles enhance ice melt from tidewater glaciers, and consequently, glacier-ice structure needs to be accounted for in projections of ice loss and sea-level rise.

Moored observations and a realistic, tidally forced 3D model are presented of flow and internal-tide-driven turbulence over a supercritical 3D fan in southeastern Luzon Strait. Two stacked moored profilers, an acoustic Doppler current profiler, and a thermistor string measured horizontal velocity, density, and salinity over nearly the entire water column every 1.5 h for 50 days. Observed dissipation rate computed from Thorpe scales decays away from the bottom and shows a strong spring–neap cycle; observed depth-integrated dissipation rate scales as where U BT is the barotropic velocity. Vertical velocities are strong enough to be comparable at times to the vertical profiling speed of the moored profilers, requiring careful treatment to quantify bias in dissipation rate estimates. Observations and the model are in reasonable agreement for velocity, internal wave displacement and depth-integrated dissipation rate, allowing the model to be used to understand the 3D flow. Turbulence is maximum following the transition from up-fan to down-fan flow, consistent with breaking lee waves advected past the mooring as seen previously at the Hawaiian Ridge, but asymmetric flow arises because of the 3D topography. Observed turbulence varies by a factor of 2 over the four observed spring tides as low-frequency near-bottom flow changes, but the exact means for inclusion of such low-frequency effects is not clear. Our results suggest that for the extremely energetic turbulence associated with breaking lee waves, dissipation rates may be quantitatively predicted to within a factor of 2 or so using numerical models and simple scalings.

Fjord-scale circulation forced by rising turbulent plumes of subglacial meltwater has been identified as one possible mechanism of oceanic heat transfer to marine-terminating outlet glaciers. This study uses buoyant plume theory and a nonhydrostatic, three-dimensional ocean–ice model of a typical outlet glacier fjord in west Greenland to investigate the sensitivity of meltwater plume dynamics and fjord-scale circulation to subglacial discharge rates, ambient stratification, turbulent diffusivity, and subglacial conduit geometry. The terminal level of a rising plume depends on the cumulative turbulent entrainment and ambient stratification. Plumes with large vertical velocities penetrate to the free surface near the ice face; however, midcolumn stratification maxima create a barrier that can trap plumes at depth as they flow downstream. Subglacial discharge is varied from 1–750 m 3 s −1 ; large discharges result in plumes with positive temperature and salinity anomalies in the upper water column. For these flows, turbulent entrainment along the ice face acts as a mechanism to vertically transport heat and salt. These results suggest that plumes intruding into stratified outlet glacier fjords do not always retain the cold, fresh signature of meltwater but may appear as warm, salty anomalies. Fjord-scale circulation is sensitive to subglacial conduit geometry; multiple point source and line plumes result in stronger return flows of warm water toward the glacier. Classic plume theory provides a useful estimate of the plume’s outflow depth; however, more complex models are needed to resolve the fjord-scale circulation and melt rates at the ice face.

Time‐dependent buoyant plumes form at the outflow of tidally dominated estuaries. When estuary discharge velocity exceeds plume internal wave speed c, a sharp front forms at the plume's leading edge that expands from the time‐dependent source. Using observations of the Columbia River tidal plume from multiple tidal cycles we characterize time‐evolving plume structure and quantify front speed Uf, plume internal wave speed c, front curvature, and ultimate extent. We identify three distinct stages of propagation: (1) Initially, the plume is strongly influenced by shallow bathymetry near the river mouth. (2) As the front advances offshore the plume detaches from the bottom and expands as a freely propagating gravity current with relatively constant Uf, c and frontal Froude number F = Uf/c. Ambient currents explain intracycle variability in Uf and winds alter front shape. Variability in ambient stratification associated with previous cycles' plume remnants leads to complex fronts and internal waves. (3) Finally, the plume decelerates, adjusts toward geostrophy, and may radiate additional internal waves. Using a simple kinematic model, we suggest that constant frontal propagation speed, Uf = 0.9 ± 0.1 m/s, during stage 2 is primarily controlled by linearly increasing volume flux from the Columbia River mouth. As this discharge rate subsides, the plume expands as a fixed volume with decreasing front speed (stage 3). The plume's final extent is controlled by the Rossby radius, which scales with a length based on the total volume discharged. This provides an integral description of plume front evolution based on the time‐dependent estuary discharge.