The Antarctic ice masses flow outwards to form floating ice shelves which give rise to the large tabular icebergs, or grounded glaciers which forms

Transcription

1 Oceanographic and glacier information from observations of Antarctic icebergs Olav Orheim, NPI & GRID-Arendal* Norsk Geofysisk Forening, Solstrand 21 October 2015 * With collaborators Barry Giles & Jo Jacka, Australian Antarctic Division, Hobart, and Are Bjørdal, Stein Tronstad & Jan-Gunnar Winther, Norwegian Polar Institute, Tromsø

2 The Antarctic ice masses flow outwards to form floating ice shelves which give rise to the large tabular icebergs, or grounded glaciers which forms smaller icebergs. The tabular bergs may reach 100 x 50 km². Annual Antarctic iceberg production is around 2000 km³. At any time there are more than icebergs floating in the Southern Ocean

3 1977: HRH Prince Mohamed Al-Faisal Al-Saud established Iceberg Transport International & Icebergs For the Future (IFF). IFF contact Olav Orheim about getting field iceberg data. OO involves Arne Foldvik, UnivB they study icebergs on NARE 1978/ : OO establishes, through SCAR, International Iceberg Observing Programme, the so-called «Blue forms». Since then 223 ship cruises have made observations of altogether Antarctic bergs, of which have been classified by size. The t

4 Blue forms were sent to all institutions with research vessels going to Antarctica. The instruction was to record icebergs every six hours, classified into five size classses. An observation is typically of what is seen within a 12 nm (22 km) radius, i.e. within 500 km². % size distribution of bergs: Observed size classes (m) > ,2% 33,1% 18% 7,3% 2,5%

5 Geographic distribution of the observations: Density of observations mirror ship tracks to the coastal research stations. The number of observations are particularly large around the northern part of the Antarctic Peninsula, which has the highest density of stations. Number of observations are given for each «box» of 1 latitude x 5 longitude. A box is white when there are no observations. Total area of observations is approx. 14x10⁶km

6 Concentration of icebergs (defined as total no. of bergs in box/no. observations). Distribution reflect both variations in sources, and the currents around Antarctica. Note exit routes for the bergs.

7 The currents around Antarctica Yellow line marks Antarctic Convergence Dashed line is the Antarctic Divergence. This divides the clockwise and anticlockwise currents near the continent

8 Zero iceberg observations. i.e. observations of no icebergs in a box. At 60 S the area of a box of 1x5 is km² (9000 nm²).

9 Frequency of zero iceberg observations (zero berg observed /no. obs.). Obviously the frequency will increase with distance from the continent, but there are also other patterns: * high at the Divergence * high in the Ross Sea

10 High frequency of zero berg observations north of Dronning Maud Land coincide with the Antarctic Divergence which divides east and westward trending currents (dashed line).

11 The bathymetry of the Southern Ocean is one factor in the distribution of the currents. The deep ocean exchange with the underside of the ice shelves is another.

12 Satellite interferometry shows the regions of major mass loss from the Perimiter of Antarctica.

13 Number of icebergs > 1000m

14 Concentration of bergs >1000m (Number bergs > 1000m/ number of observations in each box)

15 Some observations, which still needs statistical testing Large year-to year variations reflecting variations in calving rates? i.e: 1986/87: 17 bergs /observation (1400) All other years around 12 bergs/obs, most years obs. Minimum in 1992/93 with 7 bergs/obs (1600) Very large regional variations: Sector out from Pine Island Bay largest density: > 17 bergs/obs. Out of Ross Sea has lowest density, < 7/obs, but largest proportion of largest icebergs size, with 5% > 1000m. Smaller seasonal variations than expected, but winter data are few. Large icebergs drift in a different route from smaller tabular bergs. Why? More affected by Coriolis, also by larger base area giving more sheear forces (all tabular bergs have similar draughts).

16 This is work in progress and like these penguins we are riding a course with no clear end in sight. Thank you for your attention!

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19 April , ,5 35,4 20,9 7,6 2,7 May , ,5 35,0 22,8 7,1 2,7 June , ,8 59,1 8,4 0,4 0,3 July , ,3 37,1 4,0 0,2 0,2 August , ,3 58,8 2,9 0,0 0,0 September , ,7 27,3 40,4 2,7 1,9 October , ,2 23,9 18,2 8,3 3,5 May-Sept , ,7 39,5 19,1 4,8 1,9 nter, April-Oct , ,7 34,5 20,2 7,1 2,6 Summer , ,4 33,0 17,8 7,3 2,5 PI final database (30 Jan 2015) No. Number Total Bergs Observed numbers of each size class total % for each size class Season Vessel names ships observat bergs /obs >1000 classified >1000 Comments 2011/12 Puerto Deseado , ,5 40,2 25,0 12,5 1,8 summer 2009/10 Shackleton , ,7 58,5 2,4 0,2 0,2 summer 2007/08 Shackleton , ,1 14,0 4,6 1,0 0,3 summer 2006/07 Polarstern , ,7 31,8 13,6 4,1 0,8 year, April-March 2005/06 Pstern Tangaroa , ,4 23,3 9,9 2,5 0,9 summer 2004/05 P.stern Agulhas , ,7 30,4 19,3 14,8 2,8 summer 2003/04 Shack, Agul Pstern Italica Tangaroa , ,8 28,9 7,5 3,7 2,0 summer + Aug, May 2002/03 Agul Pstern Shack, Explora Rongel , ,2 34,6 12,6 3,0 0,6 summer+june, July 2001/02 Shack Pstern Agulhas Rongel Italica , ,1 46,2 17,1 9,8 5,8 summer, incl. May 2000/01 Irizar Pstern Agulhas Rongel Italica Hesper , ,3 29,3 18,2 7,2 2,1 summer, incl. May 1999/2000Pstern JCR Shack Shirase Italica Gorruchaga , ,3 32,4 15,4 7,1 1,7 summer 1998/99 Palmer Pstyern Irizar JCR Rongel Italica Pu , ,2 34,4 18,6 8,9 4,8 summer+may-july 1997/98 Palmer Pstern Irizar Bransfield Rongel End , ,9 32,4 16,0 6,9 3,8 summer+may-july 1996/97 Bransfield Explora Pstern Italica JCR , ,3 28,2 13,3 10,2 4,0 summer 1995/96 JCR Bransfield Irizar Aviso Castillo Puerto D , ,5 31,2 10,0 3,4 0,9 summer 1994/95 Irizar Somov Bransfield JCR Explora Italica , ,0 32,4 24,3 12,9 4,4 summer, incl. May 1993/94 Pstern Agulhas Irizar Africana Hesperides I , ,5 34,3 20,0 8,0 2,1 summer 1992/93 A. Australis Bfield Icebird Agulhas Polarbjø , ,4 38,5 23,4 7,3 2,4 summer 1991/92 Bfield JCR de Teffe Irizar Gondwana Agulh , ,8 35,5 20,6 8,9 2,2 summer 1990/91 Gondwana Irizar Explora Bfield Pstern de T , ,9 35,6 20,8 8,9 3,8 summer 1989/90 Bfield Irizar Thuleland Andenes VII Brazil A , ,7 36,8 17,2 6,2 2,1 summer 1988/89 Somov Bfield Icebird Irizar de Teffe Shiras , ,3 36,7 25,9 9,0 3,0summer, incl. Oct. May 1987/88 Somov Viese Bfield Zubov Icebird Shirase , ,0 34,1 17,6 7,4 1,9 summer 1986/87 Somov Bfield Viese Irizar Pstern Glacier Ba , ,5 33,8 18,1 7,3 2,2 summer 1985/86 Pstern Agulhas Zubov Glacier Bfield Endur , ,0 32,2 19,0 7,2 2,6 summer 1984/85 Capt. Myshevskij Endurance Discovery Iceb , ,7 35,8 20,3 6,7 1,5 summer, some Oct. 1983/84 Somov Agulhas Bfield Viese Endurance My , ,5 30,7 20,7 10,6 3,6 summer 1982/83 Somov Bfield Nanok Viese Zubov Polar Cir , ,2 32,0 25,3 9,6 3,9 summer, some Oct. 1981/82 Bfield Bahia Paraiso Polar Queen Fuji Agul , ,2 36,5 20,4 4,5 1,4 summer 1980/81 John Biscoe ,0 0,0 0,0 7,5 92,5 summer 1979/80 Bransfield ,0 0,0 0,0 13,6 86,4 summer 1978/79 Bransfield Agulhas Polarsirkel Yelco , ,3 33,2 9,5 5,0 1,0 summer 1976/77 Polarsirkel , summer Total sums , ,2 33,1 18,0 7,3 2,5

20 eberg statistics on NPI final database (3 July 2015) Number Total Bergs Observed numbers of each size class total % for each size class Sector observ bergs /obs >1000 classified > ⁰ 59 W , ,2 33,3 17,1 14,4 2,5 ⁰ - 89⁰ 59W , ,4 30,7 15,5 5,7 1,6 ⁰ - 134⁰ 59W , ,9 38,6 23,2 8,4 2,9 5⁰ - 180⁰ W , ,7 39,0 20,1 8,6 3,5 0⁰ - 135⁰E , ,0 29,4 21,0 12,4 6,2 4⁰ 59-90⁰E , ,7 33,3 23,0 12,3 4,7 ⁰ 59-45⁰E , ,3 36,1 25,7 9,7 3,2 ⁰ 59-0⁰E , ,1 39,1 17,4 6,9 1,5 tals , ,2 33,1 17,9 7,3 2, W , ,3 31,2 15,8 6,0 1, W , ,4 36,9 22,1 8,4 3,2 0W-160E , ,2 32,4 19,8 9,5 5,0 9 59E - 30E , ,5 34,7 24,7 11,1 3,9 59E W , ,7 34,8 17,1 6,9 2,4 ntrol W , ,3 39,5 22,9 9,4 3,0

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