How ubiquitous, variable or persistent are nepheloid layers? What is the main process generating these “clouds at the bottom of the sea”? Gardner and co-workers (2017, see reference below) explore these two critical questions, with a focus on the western North Atlantic for which numerous time series and survey data exist. They piece together a detailed review of the mechanisms and provide important new insights into the creation, persistence, and decay of nepheloid layers, a major issue for the geochemistry of particle-reactive elements. Their main results are: Deep western boundary currents are too weak to create benthic storms and therefore to generate intense nepheloid layers; benthic storms are created primarily by deep cyclones beneath Gulf Stream meanders; benthic storms erode the seafloor and maintain the benthic nepheloid layer; and finally, benthic nepheloid layers are weak to non-existent in areas of low eddy kinetic energy.
Figure 1: Contours of integrated benthic particle load (red lines, in μg cm− 2) and abyssal eddy kinetic energy (EKE, dashed green lines, in cm2 s− 2). Numbers by stars and triangles are related to the mean time-series particle concentration and standard deviation of particle concentration (in parentheses). Click here to view the figure larger.
Figure 2: Map of surface EKE based on satellite observations during 2002–2006 (Dixon et al., 2011). Time-series stations are indicated. Click here to view the figure larger.
Gardner, W. D., Tucholke, B. E., Richardson, M. J., & Biscaye, P. E. (2017). Benthic storms, nepheloid layers, and linkage with upper ocean dynamics in the western North Atlantic. Marine Geology. DOI:10.1016/j.margeo.2016.12.012 Open Access
K.W. Dixon, T.L. Delworth, A.J. Rosati, W. Anderson, A. Adcroft, V. Balaji, R. Benson, S.M. Griffies, H.-C. Lee, R.C. Pacanowski, G.A. Vecchi, A.T. Wittenberg, F. Zeng, R. Zhang Ocean circulation features of the GFDL CM2.6 & CM2.5 high-resolution global coupled climate models. WCRP Open Science Conference, October 2011, Denver, Colorado (2011)