Turbulent mixing in the seasonally-stratified western Irish Sea: a Thorpe Scale perspective
K. L. Stansfield1, M. R. Palmer2, T. P. Rippeth3, and J. H. Simpson31School of Ocean and Earth Science, National Oceanography Centre, European Way, Southampton, SO14 3ZH, UK 2National Oceanography Centre, Joseph Proudman Building, 6 Brownlow Street, Liverpool, L3 5DA, UK 3School of Ocean Sciences, Bangor University, Menai Bridge, Anglesey, LL59 5AB, UK
Received: 11 Oct 2013 – Accepted for review: 23 Oct 2013 – Discussion started: 19 Nov 2013
Abstract. The seasonal thermocline in shelf-seas represents an important biogeophysical barrier to the vertical flux of nutrients into the photic zone. Episodic weakening of this barrier plays an important role in sustaining the sub-surface chlorophyll maximum in summer and hence impacts the carbon draw-down in the seasonally-stratified zones of the shelf seas. Here we present estimates of the rate of turbulent kinetic energy dissipation inferred from microstructure shear probes and compare them with dissipation rates inferred from a standard conductivity-temperature-depth instrument and from a fast thermistor (Thorpe Scale methodology) at a site in the seasonally-stratified Irish Sea. All methods show strong dissipation rates in response to tidal stresses near the bed (order 10−2 Wm−3) with qualitatively similar temporal and spatial patterns. In the interior of the water column, however, only the microstructure shear probe estimates resolve the mixing in the region of the thermocline.
Stansfield, K. L., Palmer, M. R., Rippeth, T. P., and Simpson, J. H.: Turbulent mixing in the seasonally-stratified western Irish Sea: a Thorpe Scale perspective, Ocean Sci. Discuss., 10, 2141-2155, doi:10.5194/osd-10-2141-2013, 2013.