Interannual variation of landfast ice condition in Lützow-Holmbukta, Antarctica, derived from navigation log of icebreaker Shirase

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1 180 Scientific Note +,,, + Interannual variation of landfast ice condition in Lützow-Holmbukta, Antarctica, derived from navigation log of icebreaker Shirase Shuki Ushio +, Shotaro Uto,, Koh Izumiyama,, Haruhito Shimoda, and Masaru Ayukawa +,**. / 1 ;,**. 2,- Abstract: Characteristics of sea-ice conditions in Lützow-Holmbukta, Antarctica, have been investigated using the ice navigation log from the icebreaker Shirase, which has made a voyage almost at the same season and in the same sailing route every year since The vessel is considered as a suitable monitoring platform for sea ice. Not onlybasic information such as ice thickness and snow depth, but also ramming icebreaking data have been analyzed. In particular, the penetrating distances by ramming reflect di$cultyin ice navigation and show distinctlyinterannual variations from +32- to,**,. The periods with longer distances are consistent with those when breakup of landfast ice occurred frequentlyin the bay. The penetrating distances have shown a tendencyto increase since the end of the +33*s, when ice breakup has been pronounced. : +32-,**, +33* +33*,**, +. + National Institute of Polar Research, Research Organization of Information and Systems, Kaga +-chome, Itabashi-ku, Tokyo +1-2/+/., National Maritime Research Institute, Shinkawa, Mitaka-shi, Tokyo +2+ ***.., Vol..2, No.-, +2* +3*,,**. Nankyoku Shiryô (Antarctic Record), Vol..2, No.-, +2* +3*,,**.,**. National Institute of Polar Research

2 *,**-,3 -, -3.+./ +331;,**.,***.,,** , Wakatsuchi, +32,; Takizawa et al., +33,; / +32.,*,. +, ,/,**, ,,

3 ,**,,/.. Fig. +. The outward-voyage tracks of the icebreaker Shirase in Lützow-Holmbukta. Each symbol indicates the location at noon on a certain day. All the year tracks have been superimposed for operations from +32- to,**,. Straight lines connecting locations which cross land have been eliminated.

4 183, a b c / Fig.,. Interannual variations of (a) sea-ice thickness, (b) snow depth and (c) maximum ice thickness plus snow depth. Plotted data are maximum values for each day. No data were recorded in +32. or +32/.

5 , / +33*,***,c + +33* RADARSAT +33* -.,. +./ m - knots ramming 0 +, knots charging, Schultz et al., +33.,* * +32.,0 +32/,1 +321,3 +32*

6 185 - : ; : knot Fig. -. Interannual variations of number of rams and average speed in the fast ice region en route to Syowa Station. A bar chart shows the number of rams and closed circles show average speed (knot) in the fast ice region. +33* ,*** , * *** *./ knot -. +

7 /

8 187. / * +32* +33*,**. +33* -,,***.,,**-././,***,c 0,**-. a b c Fig... Relation between penetration distance and (a) maximum ice thickness and (b) snow depth. The distances are indicated as daily mean value per one ramming action. Each solid line is an exponential approximation.

9 188 / Fig. /. Maximum values for snow depth versus ice thickness during the period of icebreaking. The solid line is a linear regression. 0 : + ; : ; : Fig. 0. Interannual variation of penetration distance by ramming icebreaking. In +33-, the icebreaker did not come alongside Syowa Station because of tremendously heavy ice condition in the Lützow-Holmbukta. Open circles: daily mean value of penetration distance per ramming; closed triangles: maximum increase of snow depth at Kita-no-ura Cove o# Syowa Station. The shaded periods indicate occurrence of ice breakup in Lützow-Holmbukta.

10 189 Nathaniel B. Palmer Schultz et al., ,* Kawamura et al / C +//+**+/

11 190 Kawamura, T., Ohshima, K.I., Takizawa, T. and Ushio, S. (+331): Physical, structural, and isotopic characteristics and growth processes of fast sea ice in Lützow-Holm Bay, Antarctica. J. Geophys. Res., +*,, --./ --// :.+ -3/.+.. Schultz, L.A., Middleton, R.W. and Dai, R.Y.T. (+33.): Operation performance of the RV Nathaniel B. Palmer. ICETECH 3., The Soc. Naval Arch. Marine Eng., T+,/ :.+ -// -0/. Takizawa, T., Ushio, S., Kawamura, T., Ohshima, K.I., Ono, N. and Kawaguchi, S. (+33,): Preliminary results of hydrography under fast ice in Lützow-Holm Bay, Antarctica in +33*. Proc. NIPR Symp. Polar Meteorol. Glaciol., 0, +*0 +,/.,**- : +32*,** ,**. :.2 +0/ +13. Wakatsuchi, M. (+32,): Seasonal variations in water structure under fast ice near Syowa Station, Antarctica, in Nankyoku Shiryô (Antarct. Rec.), 1., 2/ +*2. +32/ : ,..

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National Institute of Polar Research, Research Organization of Information and Systems, Kaga +-chome, Itabashi-ku, Tokyo +1-2/+/.

National Institute of Polar Research, Research Organization of Information and Systems, Kaga +-chome, Itabashi-ku, Tokyo +1-2/+/. 165 Scientific Note + + +, -,. / Characteristics of sea ice thickness and snow depth distributions of the land-fast ice during summer in Lützow-Holmbukta, Antarctica, revealed from ship-based observations