Oceanographic and glacier information from observations of 330 000 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
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 200 000 icebergs floating in the Southern Ocean
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 1978/79. 1981: OO establishes, through SCAR, International Iceberg Observing Programme, the so-called «Blue forms». Since then 223 ship cruises have made 28 100 observations of altogether 338 800 Antarctic bergs, of which 271 500 have been classified by size. The t
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 271 599 bergs: Observed size classes (m) 10-50 50-200 200-500 500-1000 >1000 39,2% 33,1% 18% 7,3% 2,5%
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
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.
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
Zero iceberg observations. i.e. observations of no icebergs in a box. At 60 S the area of a box of 1x5 is 30 000 km² (9000 nm²).
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
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).
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.
Satellite interferometry shows the regions of major mass loss from the Perimiter of Antarctica.
Number of icebergs > 1000m
Concentration of bergs >1000m (Number bergs > 1000m/ number of observations in each box)
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 1982-89 around 12 bergs/obs, most years 1500 + 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).
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!
April 1844 16222 8,8 3936 4165 2454 888 315 11758 33,5 35,4 20,9 7,6 2,7 May 401 3215 8,0 917 987 643 200 76 2823 32,5 35,0 22,8 7,1 2,7 June 156 818 5,2 239 444 63 3 2 751 31,8 59,1 8,4 0,4 0,3 July 182 427 2,3 245 156 17 1 1 420 58,3 37,1 4,0 0,2 0,2 August 92 103 1,1 38 61 3 0 0 102 37,3 58,8 2,9 0,0 0,0 September 139 429 3,1 72 71 105 7 5 260 27,7 27,3 40,4 2,7 1,9 October 466 3459 7,4 1369 709 539 246 103 2966 46,2 23,9 18,2 8,3 3,5 May-Sept 970 4994 5,1 1511 1719 831 211 84 4356 34,7 39,5 19,1 4,8 1,9 nter, April-Oct 3295 24706 7,5 6805 6576 3849 1346 500 19076 35,7 34,5 20,2 7,1 2,6 Summer 24815 314094 12,7 99562 83220 44914 18474 6238 252408 39,4 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. 10-50 50-200 200-500 500-1000 >1000 classified 10-50 50-200 200-500 500-1000 >1000 Comments 2011/12 Puerto Deseado 1 13 112 8,7 23 45 28 14 2 112 20,5 40,2 25,0 12,5 1,8 summer 2009/10 Shackleton 1 176 628 3,6 209 316 13 1 1 540 38,7 58,5 2,4 0,2 0,2 summer 2007/08 Shackleton 1 198 1642 8,3 1243 217 72 15 5 1552 80,1 14,0 4,6 1,0 0,3 summer 2006/07 Polarstern 1 853 14566 17,1 6822 4364 1867 565 112 13730 49,7 31,8 13,6 4,1 0,8 year, April-March 2005/06 Pstern Tangaroa 2 423 9019 21,3 5412 1987 846 212 80 8537 63,4 23,3 9,9 2,5 0,9 summer 2004/05 P.stern Agulhas 2 454 4053 8,9 748 696 442 338 65 2289 32,7 30,4 19,3 14,8 2,8 summer 2003/04 Shack, Agul Pstern Italica Tangaroa 5 944 6264 6,6 3096 1549 401 200 108 5354 57,8 28,9 7,5 3,7 2,0 summer + Aug, May 2002/03 Agul Pstern Shack, Explora Rongel 5 828 10659 12,9 4769 3360 1223 293 55 9700 49,2 34,6 12,6 3,0 0,6 summer+june, July 2001/02 Shack Pstern Agulhas Rongel Italica 5 688 7676 11,2 677 1480 547 315 187 3206 21,1 46,2 17,1 9,8 5,8 summer, incl. May 2000/01 Irizar Pstern Agulhas Rongel Italica Hesper 7 956 15241 15,9 5627 3808 2363 938 268 13004 43,3 29,3 18,2 7,2 2,1 summer, incl. May 1999/2000Pstern JCR Shack Shirase Italica Gorruchaga 7 847 6325 7,5 1682 1259 597 277 66 3881 43,3 32,4 15,4 7,1 1,7 summer 1998/99 Palmer Pstyern Irizar JCR Rongel Italica Pu 8 1143 9606 8,4 2756 2862 1549 739 402 8308 33,2 34,4 18,6 8,9 4,8 summer+may-july 1997/98 Palmer Pstern Irizar Bransfield Rongel End 11 1631 19027 11,7 6788 5376 2651 1146 633 16594 40,9 32,4 16,0 6,9 3,8 summer+may-july 1996/97 Bransfield Explora Pstern Italica JCR 5 370 4892 13,2 1402 892 421 322 128 3165 44,3 28,2 13,3 10,2 4,0 summer 1995/96 JCR Bransfield Irizar Aviso Castillo Puerto D 7 537 13817 11,3 6865 3934 1256 434 110 12599 54,5 31,2 10,0 3,4 0,9 summer 1994/95 Irizar Somov Bransfield JCR Explora Italica 6 916 10340 11,3 2320 2889 2173 1154 390 8926 26,0 32,4 24,3 12,9 4,4 summer, incl. May 1993/94 Pstern Agulhas Irizar Africana Hesperides I 7 654 10398 15,9 1765 1705 994 399 106 4969 35,5 34,3 20,0 8,0 2,1 summer 1992/93 A. Australis Bfield Icebird Agulhas Polarbjø 8 1638 12310 7,5 2578 3496 2129 659 217 9079 28,4 38,5 23,4 7,3 2,4 summer 1991/92 Bfield JCR de Teffe Irizar Gondwana Agulh 7 771 8110 10,5 2443 2642 1537 662 164 7448 32,8 35,5 20,6 8,9 2,2 summer 1990/91 Gondwana Irizar Explora Bfield Pstern de T 11 992 8431 8,5 2392 2760 1612 686 294 7744 30,9 35,6 20,8 8,9 3,8 summer 1989/90 Bfield Irizar Thuleland Andenes VII Brazil A 9 781 9961 12,8 3540 3455 1613 583 194 9385 37,7 36,8 17,2 6,2 2,1 summer 1988/89 Somov Bfield Icebird Irizar de Teffe Shiras 12 1643 17059 10,4 3060 4432 3131 1082 367 12072 25,3 36,7 25,9 9,0 3,0summer, incl. Oct. May 1987/88 Somov Viese Bfield Zubov Icebird Shirase 17 2046 26514 13,0 8172 7143 3689 1559 403 20966 39,0 34,1 17,6 7,4 1,9 summer 1986/87 Somov Bfield Viese Irizar Pstern Glacier Ba 10 1391 24161 17,4 8642 7596 4062 1646 505 22451 38,5 33,8 18,1 7,3 2,2 summer 1985/86 Pstern Agulhas Zubov Glacier Bfield Endur 10 1197 13533 11,3 4424 3657 2157 813 298 11349 39,0 32,2 19,0 7,2 2,6 summer 1984/85 Capt. Myshevskij Endurance Discovery Iceb 15 2009 22848 11,4 5687 5708 3235 1069 233 15932 35,7 35,8 20,3 6,7 1,5 summer, some Oct. 1983/84 Somov Agulhas Bfield Viese Endurance My 16 2294 31520 13,7 8486 7544 5090 2604 887 24611 34,5 30,7 20,7 10,6 3,6 summer 1982/83 Somov Bfield Nanok Viese Zubov Polar Cir 13 806 11837 14,7 2566 2815 2224 848 339 8792 29,2 32,0 25,3 9,6 3,9 summer, some Oct. 1981/82 Bfield Bahia Paraiso Polar Queen Fuji Agul 7 489 3974 8,1 1203 1181 662 146 45 3237 37,2 36,5 20,4 4,5 1,4 summer 1980/81 John Biscoe 1 33 40 0 0 0 3 37 40 0,0 0,0 0,0 7,5 92,5 summer 1979/80 Bransfield 1 22 22 0 0 0 3 19 22 0,0 0,0 0,0 13,6 86,4 summer 1978/79 Bransfield Agulhas Polarsirkel Yelco 4 208 2342 11,3 970 628 179 95 18 1890 51,3 33,2 9,5 5,0 1,0 summer 1976/77 Polarsirkel 1 159 1873 11,8 0 0 0 0 0 0 summer Total sums 223 28110 338800 12,1 106367 89796 48763 19820 6738 271484 39,2 33,1 18,0 7,3 2,5
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. 10-50 50-200 200-500 500-1000 >1000 classified 10-50 50-200 200-500 500-1000 >1000-44⁰ 59 W 9694 115322 11,9 38940 32253 16591 6753 2420 96957 40,2 33,3 17,1 14,4 2,5 ⁰ - 89⁰ 59W 7334 117168 16,0 45492 30111 15145 5580 1612 97940 46,4 30,7 15,5 5,7 1,6 ⁰ - 134⁰ 59W 471 8397 17,8 1503 2157 1294 469 164 5587 26,9 38,6 23,2 8,4 2,9 5⁰ - 180⁰ W 963 10951 11,4 2424 3288 1698 724 302 8436 28,7 39,0 20,1 8,6 3,5 0⁰ - 135⁰E 1661 10381 6,2 2499 2369 1695 996 501 8060 31,0 29,4 21,0 12,4 6,2 4⁰ 59-90⁰E 1585 25686 16,2 4532 5638 3892 2088 795 16945 26,7 33,3 23,0 12,3 4,7 ⁰ 59-45⁰E 2564 32310 12,6 5577 7955 5676 2150 706 22064 25,3 36,1 25,7 9,7 3,2 ⁰ 59-0⁰E 3838 18828 4,9 5400 6025 2682 1060 238 15405 35,1 39,1 17,4 6,9 1,5 tals 28110 339043 12,1 106367 89796 48673 19820 6738 271394 39,2 33,1 17,9 7,3 2,5-74 59W 10680 154202 14,4 58703 40378 20441 7770 2328 129620 45,3 31,2 15,8 6,0 1,8-159 59W 1110 19083 17,2 3575 4497 2691 1025 392 12180 29,4 36,9 22,1 8,4 3,2 0W-160E 1944 13090 6,7 3580 3488 2129 1026 534 10757 33,2 32,4 19,8 9,5 5,0 9 59E - 30E 4693 60354 12,9 10459 14213 10120 4576 1602 40970 25,5 34,7 24,7 11,1 3,9 59E - 29 59W 9683 92071 9,5 30250 27220 13382 5423 1882 78157 38,7 34,8 17,1 6,9 2,4 ntrol 271684 0-135W 390 7397 19,0 1266 1980 1144 471 150 5011 25,3 39,5 22,9 9,4 3,0