Laurie Padman: AMS Polar Meeting, 2003

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Tidal Effects on Sea Ice and Ocean-Air Interaction

• Laurence Padman
• Earth Space Research

Presented by Andrey Proshutinsky (WHOI)
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Motivation
It is evident that the (ice) pressure stands in
connection with the tidal wave. The pressure
has happened in the morning ... and afternoon,
and in between we have always lain part of the
time in open water. (10/13/1893 Northern
Laptev Sea) Nansen, Farthest North, 1898
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Mean tidal currents Ross Sea
Depth- averaged
?Tide gauges (gravity)
Cm/s
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Ice motion responds to tides
Data courtesy of M. Jeffries
(a) (b) (c)
HW (m)
Mean tidal current speed
(u,v) cm/s
Ross Sea
Utide cm/s
(a) Water depth (b) (u,v) tidal-band ice
motion (c) Measured predicted tidal speed
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Tidal divergence
Ross Sea shelf break, 12-h integration
10 km
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RMS tidal divergence from model
From Padman Kottmeier 2000 (JGR)
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Ice concentration
From Padman Kottmeier 2000 (JGR)
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Effect on ocean/atmosphere fluxes
Winter open-water flux 200 W m-2, second-year
ice (SW Weddell Sea) 5 Wm-2. So, 5 leads
(typical) gt 15 Wm-2, 10 leads (incl.
tides) gt 25 Wm-2. In the Arctic, Kowalik and
Proshutinsky 1994 estimated 10 to gt100 cm/year
tide-induced ice production over the Eurasian
shelves.
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Tide current prediction Problems

• Depends on water depth (poorly known in many
  polar regions)
• Depends on depth gradients (daily tides sometimes
  exist as topographic vorticity waves)
• Baroclinicity surface currents may be very
  different from depth-averaged currents.

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Depth-dependence of currents
South Scotia Ridge (N. Weddell Sea)
cm/s
M2
M2
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Baroclinic divergence
?(??Usurf) 3.8e-6 s-1 ?(??Ubarot)2.4e-7 s-1
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Summary

• Sea ice responds to the ocean stress on the ice
  base provided by ocean tidal currents.
• Gradients of the tidal stress field modify the
  roughness characteristics of sea ice, and lead to
  higher mean open-water fraction.
• Tidal processes can significantly increase
  ocean/atmosphere heat exchange and ice formation
  in leads. Baroclinicity is important.
• This talk is available at http//www.esr.org/antar
  ctic/confpres.html
• Contact padman_at_esr.org