Sediment transport processes at the head of Halibut Canyon, Eastern Canada margin: An interplay between internal tides and dense shelf water cascading

European Geosciences Union General Assembly 2013, 7-12 April, Vienna, Austria.-- 1 pageTo investigate the processes by which sediment is transported through a submarine canyon incised in a glaciated margin, the bottom boundary layer quadrapod RALPH was deployed at 276-m depth in the West Halibut Canyon (off Newfoundland) during winter 2008–2009. Two main sediment transport processes were identified throughout the deployment. Firstly, periodic increases of near-bottom suspended-sediment concentrations (SSC) were recorded associated with the up-canyon propagation of the semidiurnal internal tidal bore along the canyon axis, carrying fine sediment particles resuspended from deeper canyon regions. The recorded SSC peaks, lasting less than 1 h, were observed sporadically and were linked to bottom intensified up-canyon flows (~ 40 cm s− 1) concomitant with sharp drops in temperature. Secondly, sediment transport was also observed during events of intensified down-canyon current velocities that occurred during periods of sustained heat loss from surface waters, but were not associated with large storm waves. High-resolution velocity profiles throughout the water column during these events revealed that the highest current speeds (~ 1 m s− 1) were centered several meters above the sea floor and corresponded to the region of maximum velocities of a gravity flow. Such flows had associated low SSC and cold water temperatures and are interpreted as dense shelf water cascading events channelized along the canyon axis. Sediment transport during these events was largely restricted to bedload and saltation, producing winnowing of sands and fine sediments around larger gravel particles. Analysis of historical hydrographic data suggests that such gravity flows are not related to the formation of coastal dense waters advected towards the outer shelf that reached the canyon head. Rather, the dense shelf waters appear to be generated around the outer shelf, where convection during winter is able to reach the sea floor and generate a pool of near-bottom dense water that cascades into the canyon during one or two tidal cycles. A similar transport mechanism is likely to occur in other submarine canyons along the eastern Canadian margin, as well in other canyoned margins where winter convection can reach the shelf-edgePeer Reviewe

Stirring by small-scale vortices caused by patchy mixing

Author Posting. © American Meteorological Society, 2005. This article is posted here by permission of American Meteorological Society for personal use, not for redistribution. The definitive version was published in Journal of Physical Oceanography 35 (2005): 1245-1262, doi:10.1175/JPO2713.1.Evidence is presented that lateral dispersion on scales of 1–10 km in the stratified waters of the continental shelf may be significantly enhanced by stirring by small-scale geostrophic motions caused by patches of mixed fluid adjusting in the aftermath of diapycnal mixing events. Dye-release experiments conducted during the recent Coastal Mixing and Optics (CMO) experiment provide estimates of diapycnal and lateral dispersion. Microstructure observations made during these experiments showed patchy turbulence on vertical scales of 1–10 m and horizontal scales of a few hundred meters to a few kilometers. Momentum scaling and a simple random walk formulation were used to estimate the effective lateral dispersion caused by motions resulting from lateral adjustment following episodic mixing events. It is predicted that lateral dispersion is largest when the scale of mixed patches is on the order of the internal Rossby radius of deformation, which seems to have been the case for CMO. For parameter values relevant to CMO, lower-bound estimates of the effective lateral diffusivity by this mechanism ranged from 0.1 to 1 m2s−1. Revised estimates after accounting for the possibility of long-lived motions were an order of magnitude larger and ranged from 1 to 10 m2s−1. The predicted dispersion is large enough to explain the observed lateral dispersion in all four CMO dye-release experiments examined.The Coastal Mixing and Optics dye studies were funded by the Office of Naval Research under Grants N00014-95-1-0633 (tracer experiments) and N00014-95-1-1063 (AASERT fellowship). Additional analysis was also performed under ONR Grant N00014-01-1-0984

Overturning in the Subpolar North Atlantic Program: A New International Ocean Observing System

For decades oceanographers have understood the Atlantic meridional overturning circulation (AMOC) to be primarily driven by changes in the production of deep-water formation in the subpolar and subarctic North Atlantic. Indeed, current Intergovernmental Panel on Climate Change (IPCC) projections of an AMOC slowdown in the twenty-first century based on climate models are attributed to the inhibition of deep convection in the North Atlantic. However, observational evidence for this linkage has been elusive: there has been no clear demonstration of AMOC variability in response to changes in deep-water formation. The motivation for understanding this linkage is compelling, since the overturning circulation has been shown to sequester heat and anthropogenic carbon in the deep ocean. Furthermore, AMOC variability is expected to impact this sequestration as well as have consequences for regional and global climates through its effect on the poleward transport of warm water. Motivated by the need for a mechanistic understanding of the AMOC, an international community has assembled an observing system, Overturning in the Subpolar North Atlantic Program (OSNAP), to provide a continuous record of the transbasin fluxes of heat, mass, and freshwater, and to link that record to convective activity and water mass transformation at high latitudes. OSNAP, in conjunction with the Rapid Climate Change–Meridional Overturning Circulation and Heatflux Array (RAPID–MOCHA) at 26°N and other observational elements, will provide a comprehensive measure of the three-dimensional AMOC and an understanding of what drives its variability. The OSNAP observing system was fully deployed in the summer of 2014, and the first OSNAP data products are expected in the fall of 2017

Argo data 1999-2019: two million temperature-salinity profiles and subsurface velocity observations from a global array of profiling floats.

© The Author(s), 2020. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Wong, A. P. S., Wijffels, S. E., Riser, S. C., Pouliquen, S., Hosoda, S., Roemmich, D., Gilson, J., Johnson, G. C., Martini, K., Murphy, D. J., Scanderbeg, M., Bhaskar, T. V. S. U., Buck, J. J. H., Merceur, F., Carval, T., Maze, G., Cabanes, C., Andre, X., Poffa, N., Yashayaev, I., Barker, P. M., Guinehut, S., Belbeoch, M., Ignaszewski, M., Baringer, M. O., Schmid, C., Lyman, J. M., McTaggart, K. E., Purkey, S. G., Zilberman, N., Alkire, M. B., Swift, D., Owens, W. B., Jayne, S. R., Hersh, C., Robbins, P., West-Mack, D., Bahr, F., Yoshida, S., Sutton, P. J. H., Cancouet, R., Coatanoan, C., Dobbler, D., Juan, A. G., Gourrion, J., Kolodziejczyk, N., Bernard, V., Bourles, B., Claustre, H., D'Ortenzio, F., Le Reste, S., Le Traon, P., Rannou, J., Saout-Grit, C., Speich, S., Thierry, V., Verbrugge, N., Angel-Benavides, I. M., Klein, B., Notarstefano, G., Poulain, P., Velez-Belchi, P., Suga, T., Ando, K., Iwasaska, N., Kobayashi, T., Masuda, S., Oka, E., Sato, K., Nakamura, T., Sato, K., Takatsuki, Y., Yoshida, T., Cowley, R., Lovell, J. L., Oke, P. R., van Wijk, E. M., Carse, F., Donnelly, M., Gould, W. J., Gowers, K., King, B. A., Loch, S. G., Mowat, M., Turton, J., Rama Rao, E. P., Ravichandran, M., Freeland, H. J., Gaboury, I., Gilbert, D., Greenan, B. J. W., Ouellet, M., Ross, T., Tran, A., Dong, M., Liu, Z., Xu, J., Kang, K., Jo, H., Kim, S., & Park, H. Argo data 1999-2019: two million temperature-salinity profiles and subsurface velocity observations from a global array of profiling floats. Frontiers in Marine Science, 7, (2020): 700, doi:10.3389/fmars.2020.00700.In the past two decades, the Argo Program has collected, processed, and distributed over two million vertical profiles of temperature and salinity from the upper two kilometers of the global ocean. A similar number of subsurface velocity observations near 1,000 dbar have also been collected. This paper recounts the history of the global Argo Program, from its aspiration arising out of the World Ocean Circulation Experiment, to the development and implementation of its instrumentation and telecommunication systems, and the various technical problems encountered. We describe the Argo data system and its quality control procedures, and the gradual changes in the vertical resolution and spatial coverage of Argo data from 1999 to 2019. The accuracies of the float data have been assessed by comparison with high-quality shipboard measurements, and are concluded to be 0.002°C for temperature, 2.4 dbar for pressure, and 0.01 PSS-78 for salinity, after delayed-mode adjustments. Finally, the challenges faced by the vision of an expanding Argo Program beyond 2020 are discussed.AW, SR, and other scientists at the University of Washington (UW) were supported by the US Argo Program through the NOAA Grant NA15OAR4320063 to the Joint Institute for the Study of the Atmosphere and Ocean (JISAO) at the UW. SW and other scientists at the Woods Hole Oceanographic Institution (WHOI) were supported by the US Argo Program through the NOAA Grant NA19OAR4320074 (CINAR/WHOI Argo). The Scripps Institution of Oceanography's role in Argo was supported by the US Argo Program through the NOAA Grant NA15OAR4320071 (CIMEC). Euro-Argo scientists were supported by the Monitoring the Oceans and Climate Change with Argo (MOCCA) project, under the Grant Agreement EASME/EMFF/2015/1.2.1.1/SI2.709624 for the European Commission

Taking the Ocean’s Pulse: A Vision for the Canadian Biogeochemical Argo Program

The international Argo Program, described in the NYTimes as one of the scientific triumphs of our time (Gillis, J., 12 August 2014, In the Ocean, Clues to Change, New York Times, D3), has fundamentally transformed our ability to measure interior properties of the ocean. Argo is a global array of almost 4,000 autonomous profilers measuring temperature and salinity of the upper 2,000 m. These observations are relayed by satellite and available within hours of collection. While traditional sampling from research vessels is important, it is too infrequent and geographically limited to observe the dynamic and rapidly changing ocean adequately. Satellites provide broad-scale views, but are limited to the surface and in terms of the properties they can observe. Over the past two decades, Argo floats have collected over a million profiles of temperature and salinity, twice the number obtained by research vessels during all of the 20th century. These unprecedented views of the ocean’s interior physical properties have enabled quantification of ocean warming due to climate change, and resulted in significant improvements in ocean and weather forecasting. The ocean’s biogeochemical properties are also changing rapidly, with profound impacts on ecosystems and climate, but to date, our ability to observe these changes is limited. The proposed biogeochemical extension of the Argo network (BGC-Argo) would revolutionize our ability to observe the ocean’s changing biogeochemical state by enabling us to observe seasonal to decadal-scale variability in biological productivity, ocean acidification, and ocean deoxygenation, as well as allowing quantification of the ocean’s uptake of CO2. In 2016, the Science Plan for BGC-Argo was formulated by an international group of experts; the plan calls for an additional 1000 biogeochemical floats that would measure pH, oxygen, nitrate, chlorophyll, suspended particles and light. The biogeochemical extension of Argo has been specifically mentioned by the G7 Science Ministers in their Tsukuba Communiqué in May 2016, which calls for an enhanced and sustained global observing system that integrates new chemical and biological observations, while sustaining critical ongoing observations. In January 2017, a group of scientists from the Canadian federal government and universities gathered to discuss opportunities for Canada that arise from the international BGC-Argo initiative. Their recommendations are summarized in this document. It is clear that Canada is well positioned to play a leadership role in an expanded global ocean measurement program, and that the nation would derive significant scientific and technological benefits from it. In addition to addressing fundamental questions about our changing ocean—questions that have significant societal implications—the program holds economic opportunities for Canada’s vibrant and thriving ocean economy sector. Specific recommendations for Canada are: 1) Actively strive to maintain and enhance our position as an international leader in ocean observation through strong participation in the global BGC-Argo program. 2) Enhance Canadian scientific capacity in biogeochemical modelling and prediction, in order to capitalize fully on the potential of BGC-Argo. 3) For Canada to reap maximum scientific and societal benefit from BGC-Argo, ample training opportunities for young scientists should be provided, which would also help to ensure that “eyes are on the data” at all times. 4) Ensure free and near real-time access to the emerging data streams through properly resourcing data management. 5) Form a national BGC-Argo steering committee to facilitate communication within the Canadian user community

Physical oceanography of Seahorse profiler and CARIOCA buoy at station HL2 at the Scotain Shelf in 2007 and 2014

The understanding of the seasonal variability of carbon cycling on the Scotian Shelf in the NW Atlantic Ocean has improved in recent years; however, very little information is available regarding its short-term variability. In order to shed light on this aspect of carbon cycling on the Scotian Shelf we investigate the effects of Hurricane Arthur, which passed the region on 5 July 2014. The hurricane caused a substantial decline in the surface water partial pressure of CO2 (pCO2), even though the Scotian Shelf possesses CO2-rich deep waters. High-temporal-resolution data of moored autonomous instruments demonstrate that there is a distinct layer of relatively cold water with low dissolved inorganic carbon (DIC) slightly above the thermocline, presumably due to a sustained population of phytoplankton. Strong storm-related wind mixing caused this cold intermediate layer with high phytoplankton biomass to be entrained into the surface mixed layer. At the surface, phytoplankton begin to grow more rapidly due to increased light. The combination of growth and the mixing of low DIC water led to a short-term reduction in the partial pressure of CO2 until wind speeds relaxed and allowed for the restratification of the upper water column. These hurricane-related processes caused a (net) CO2 uptake by the Scotian Shelf region that is comparable to the spring bloom, thus exerting a major impact on the annual CO2 flux budget

Layered mixing on the New England Shelf in summer

The article of record as published may be located at http://dx.doi.org/10.1002/2014JC009947The layered structure of stratification and mixing on the New England Shelf (NES) in summer is examined by analyzing a comprehensive set of observations of hydrography, currents and turbulence. A clear distinction in mixing characteristics between the midcolumn water (consisting of subsurface stratification, middepth weak stratification and lower-layer stratification) and a well-mixed bottom boundary layer (BBL) is revealed. The combination of subtidal Ekman onshore bottom transport and cross-shore density gradient created a lower-layer stratification that inhibited the upward extension of the BBL turbulence. The BBL mixing was related to strong shear generated by bottom stress, and the magnitude and periodic variation of BBL mixing was determined by both the tidal and subtidal flows. Mixing in the midcolumn water occurred under stably stratified conditions and showed correspondence with the occurrence of near-inertial and semidiurnal internal waves. Positive correlations between buoyancy frequency squared (N2) and shear variance (S2), S2 and dissipation rate (e), N2 and e are established in the midcolumn, but not in the BBL. The midcolumn e was reasonably described by a slightly modified MacKinnon-Gregg (MG) model.The field component of this program was jointly supported by the US Office of Naval Research (grants N00014-95-1-1030, N00014-95-1-0373, and N00014-96-1- 0953) and Fisheries and Oceans of Canada

A prospective framework to support climate-adaptive fisheries in Canada

Climate change affects virtually all marine life and is increasingly a dominant concern for fisheries, reinforcing the need to incorporate climate variability and change when managing fish stocks. Canada is expected to experience widespread climate-driven impacts on its fisheries but does not yet have a clear adaptation strategy. Here, we provide an overview of a project we are developing, the Climate Adaptation Framework for Fisheries, to address this need and support climate adaptation in Canadian marine fisheries. The framework seeks to quantitatively and flexibly evaluate species, fishing infrastructure, and the management and operation of fisheries to assess climate vulnerability comprehensively and provide outputs that can support climate adaptation planning across different sectors, agencies, and stakeholders. This new framework should allow future climate scenarios to be evaluated and identify actionable climate vulnerabilities related to the management of fisheries, creating a systematic approach to supporting climate adaptation in Canada’s fisheries