The motion and physical properties of ocean waters give rise to all manner of environmental processes, from vertical mixing driven by internal wave dynamics to subtle double-diffusive layering phenomena. From the Arctic Ocean to the Mediterranean, via the South China Sea and the Western Pacific Ocean, the ENDLab is conducting fundamental research on a wide range of topics in Physical Oceanography.
Whither the Chukchi Slope Current?
Recent measurements and modeling indicate that roughly half of the Pacific-origin water exiting the Chukchi Sea shelf through Barrow Canyon forms a westward-flowing current known as the Chukchi Slope Current (CSC), yet the trajectory and fate of this current is presently unknown. In a recent ENDLab study published in the Journal of Physical Oceanography, through the combined use of shipboard velocity data and information from five profiling floats deployed as quasi-Lagrangian particles, we delve further into the trajectory and the fate of the CSC. During the period of observation, from early September to early October 2018, the CSC progressed far to the north into the Chukchi Borderland. The northward excursion is believed to result from the current negotiating Hanna Canyon on the Chukchi slope, consistent with potential vorticity dynamics. The volume transport of the CSC, calculated using a set of shipboard transects, decreased from approximately 2 Sv to near zero over a period of 4 days. This variation can be explained by a concomitant change in the wind stress curl over the Chukchi shelf from positive to negative. After turning northward, the CSC was disrupted and four of the five floats veered offshore, with one of the floats permanently leaving the current. It is hypothesized that the observed disruption was due to an anticyclonic eddy interacting with the CSC, which has been observed previously. These results demonstrate that, at times, the CSC can get entrained into the Beaufort Gyre.
News
- ENDLab receives two new grants to study monitoring and modeling of mCDR
The ENDLab has received two new grants from the MIT Energy Initiative (MITEI) to develop state of the art approaches to underpin Monitoring, Reporting and Verification (MRV) for marine Carbon Dioxide Removal (mCDR)…. - Multi-year data sets of Arctic Ocean dynamics
Over the past six years, six Pop-up Data Shuttle (PDS) Current and Pressure-recording Inverted Echo Sounders (CPIES) have been repeatedly deployed and recovered in the abyssal Arctic Ocean, investigating deep water dynamics and ocean warming….
Publications
- Wind-Induced Quasi-Seasonal and Quasi-Monthly Variations of Near-Bottom Temperature on the Chukchi Slope of the Southwestern Canada Basin
Ku A., Jeon, C., Peacock, T., Chae, J.Y., Park, T., Cho, K.H., Park, J.H.
Journal of Geophysical Research: Oceans, 129, (7), e2023JC020490 (2024)
The time series of near-bottom temperatures collected from September 2018 until August 2020 from an array of three current- and pressure-recording inverted echo sounders showed quasi-seasonal and quasi-monthly (∼28 days) variations at a depth of ∼1,300 m near the Chukchi slope in the western Arctic Ocean. They revealed an increase of ∼0.1°C during the winter-spring period compared with the summer-fall period. These variations were observed in the data-assimilated Hybrid Coordinate Ocean Model (HYCOM) outputs near the observation site (correlation coefficient >0.7). They confirmed that variations in near-bottom temperature are related to changes in the intensity of the Atlantic Water (AW) boundary current, concurrent with the deepening of the lower AW layer by approximately 50 m. The difference in sea surface height (SSH) between the Canada Basin and the Chukchi Shelf increased because of the negative wind stress curl (WSC) and retarded the AW boundary current according to the geostrophic effect. When the near-bottom temperature increased during the winter-spring period, the SSH in the Chukchi Shelf was lower than that in the summer-fall period because of the less negative WSC. Quasi-monthly variations were related to SSH on the Chukchi Shelf owing to the negative WSC. HYCOM outputs from 1994 to 2015 showed that the AW boundary current weakened more recently than in the past due to the increased melting of sea ice. The results imply that a longer sea-ice-free season in the Arctic amplifies changes in the AW boundary current and deep ocean temperature owing to increased atmospheric forcing.
- Turbulent diapycnal fluxes as a pilot Essential Ocean Variable
Le Boyer A., Couto N., Alford M.H., Drake H.F., Bluteau C.E., Hughes, K.G. …
Frontiers in Marine Science, 10, 1241023 (2023)
We contend that ocean turbulent fluxes should be included in the list of Essential Ocean Variables (EOVs) created by the Global Ocean Observing System. This list aims to identify variables that are essential to observe to inform policy and maintain a healthy and resilient ocean. Diapycnal turbulent fluxes quantify the rates of exchange of tracers (such as temperature, salinity, density or nutrients, all of which are already EOVs) across a density layer. Measuring them is necessary to close the tracer concentration budgets of these quantities. Measuring turbulent fluxes of buoyancy (Jb), heat (Jq), salinity (JS) or any other tracer requires either synchronous microscale (a few centimeters) measurements of both the vector velocity and the scalar (e.g., temperature) to produce time series of the highly correlated perturbations of the two variables, or microscale measurements of turbulent dissipation rates of kinetic energy (ϵ) and of thermal/salinity/tracer variance (χ), from which fluxes can be derived. Unlike isopycnal turbulent fluxes, which are dominated by the mesoscale (tens of kilometers), microscale diapycnal fluxes cannot be derived as the product of existing EOVs, but rather require observations at the appropriate scales. The instrumentation, standardization of measurement practices, and data coordination of turbulence observations have advanced greatly in the past decade and are becoming increasingly robust. With more routine measurements, we can begin to unravel the relationships between physical mixing processes and ecosystem health. In addition to laying out the scientific relevance of the turbulent diapycnal fluxes, this review also compiles the current developments steering the community toward such routine measurements, strengthening the case for registering the turbulent diapycnal fluxes as an pilot Essential Ocean Variable.
- Observations of Double Diffusive Staircase Edges in the Arctic Ocean
Boury, S., Supekar, R., Fine, E.C., Musgrave, R., Mickett, J.B., Voet, G., Odier, P., Peacock, T., MacKinnon, J.A., Alford, M.H.
Journal of Geophysical Research: Oceans, 129, (11), e2022JC018906 (2022)
Recent observational studies have provided detailed descriptions of double-diffusive staircases in the Beaufort Sea, characterized by well-mixed intrusions between high-gradient interfaces. These structures result from double-diffusive convection, occurring when cooler fresh water lies atop the warmer saltier Atlantic water layer. In the present study, we investigate the spatial structure of such layers, by analyzing combined high resolution data from a subsurface mooring, a ship-towed profiling conductivity-temperature-depth/ADCP package, and a free-falling microstructure profiler. At large scale, the modular microstructure profiler data suggest a horizontal “ragged edge” of the layered water masses near the basin boundary. At smaller scales, the mooring data indicate that, in the 300–400 m depth interval, regions of layers abruptly appear. This laterally sharp (of the order of 100 m) interface is advected southwards, as shown by the shallow water integrated mapping system survey conducted nearby. Neither disruption nor formation of layers is directly observed in our data, and we thus interpret our observations as the stable and possibly recent abutment of a layered and an unlayered water masses, now globally advected southwards by a large scale flow.