www.noc.ac.uk
Effects of tides on water masses and mixing in the Arctic Ocean
Maria Luneva, Yevgeny Aksenov ,
James Harle, Jason Holt
NEMO-shelf pan-Arctic model (NOC Liverpool)
• NEMOv3.2 with shelf processes included coupled with
LIM2-evp V3.6-CICE +MEDUSA
• ¼ resolution based on ORCA-025 tripolar grid (7-15km)-
3.5km regular grid
• Terrain following s-levels on the shelf, resolving BBL + z
levels below (50 levels s-z 75)
• Tides: geopotential 15 harmonics + boundary conditions
from OTPS-7 .2 (1/4) inverse model
• BC and IC – from global ORCA025-LIM2 ORCA0083
• gls vertical mixing : k-eps with Kantha Clayson94 closure
Canuto 2015 closure ( double diffusion included)
• Vppm- vertical piecewise parabolic advection with small
numerical diffusivity
• Smagorinsky horizontal mixing
• Model runs: 1978-2007 (1990-2014) with/without tides
Forcing: DFS5.1
Effect of tides on sea ice.
•Simulations with tides (solid lines)
demonstrate stronger reduction in ice
volume (~15%) and extent (~5%) in
comparison with simulation without
tides (dashed lines); predicts right trends
in comparison with PIOMAS.
Tidal effects decrease ice thickness
mostly everywhere from 10cm to 1m
in Central Arctic, and up to 2m in the
Canadian Archipelago
Luneva et al., 2015 JGR
Effects of tides on the sea surface salinity and river runoff pathways
On a multi-decadal scale
tides significantly affect
the water mass and
freshwater pathways of
river runoff with net
surface salinity increase
by 1-2 PSU, improving
the prediction of heat
content and surface
salinity
Figure: SSS in simulations (NT)
without and (T) with tides and their
differences (T-NT)
Upper panel: winter: March-April
Lowe panel: summer , September
Effects of tides on sea-ice—atmosphere exchange:
Opening and closing of leads due to
tide
Winter: increase heat loss to
atmosphere and ice formation:
Summer: change the albedo and
radiation flux to water
Ocean to ice heat flux differences (T-
NT) and changes in non-solar flux to
atmosphere mostly identical, except
late December.
But: there are strong changes in
downward solar radiation:
opening –closing of ice leads decrease
the albedo and increase heat flux to
water.
Effects of tides on the mixing:
•Tides increase the mixed layer depth
in the polar regions resulting in the
stronger entrainment of warm Atlantic
waters to the surface layer and melting
of ice.
•Tides increase the shear stresses in the
halocline resulting in a burst of
turbulence and mixing.
Figure 1: Difference in ice thickness in
simulations with and without tides after a
year of integration
Figure 2: Difference in the mixed layer depth
Figure 3. Ratio of vertical diffusivities in
simulations with and without tides: 2 orders
higher in Fram Strait (transect shown in
Figure 1.
Figure 1 Figure 2
Figure 3
Greenland Fram St. Svalbard Barents Sea
Tidal shear
Tides induce a strong shear stresses with maximum located below the
surface and over bottom topography anomalies.
As M2 and S2 frequencies are very close to inertial, potential depth of
Ekman layer can be very deep: he~u*/|f-w | or ( he~(Av/|f-w |)1/2 )
Tides induce quasi-steady ageostrophic circulations with strong vertical motions.
Due to nonlinear effects and vertical shear of tidal
velocity tides induce quasi –steady ageostrophic
overturning circulations across jet currents, effecting
•vertical mixing;
•water mass transformations;
• nutrient supply form the deep waters to surface layers.
Figure3: Streamfunction and vertical velocity reconstructed from
nonlinear tidal forcing using phases and amplitudes of tidal velocities
from model output:
Figure1. Monthly mean vertical
velocity and temperature,
simulations with tides
Figure2.simulations without tides