In spring 1983 work on the ice shelves of northern Ellesmere Island was continued. A total of 55 m of 7.6 cm diameter ice core was obtained from 10 locations. The longest core of 31.79 m is composed of ice-firn and basement ice and can be divided into three distinct strata according to ice salinity. Oscillating strains in Ward Hunt Ice Shelf were measured with a wire strainmeter. It is suggested that the periodic calving of ice from Ward Hunt Ice Shelf might be related to the effects of high frequency oscillation of 35 s to 40 s. Ice conditions along 150 km of coastline continue to change. Continued monitoring of the ice is believed to be necessary in view of the offshore development in the Beaufort Sea.Key words: Ward Hunt Ice Shelf, Milne Ice Shelf, ice cores, strainmeter, coastal ice conditionsMots cl&eacute;s: plateau de glace Ward Hunt, plateau de glace Milne, carottes glaciales, glace saline, jauge extensiom&eacute;trique, conditions glaciales des c&ocirc;te

Jeffries, Martin O.

English

University of Calgary Journal Hosting

ARCTIC 1~ VOL. 38, NO. 3 (SEPTEMBER 1985) P. 174.177 Ice Shelf Studies off Northern Ellesmere Island, Spring 1983 MARTIN O .  JEFFRIES' ~ , ABSTRACT. ln spring 1983 work on the ice shelves of northern Ellesmere lsland was continued. A total of 55 m of 7.6 cm diameter ice core was ob- ~ tained  from 10 locations. The  longest core of 31.79 m is  composed  of  iced-firn  and  basement  ice  and  can be divided  into three distinct strata accord- ing to  ice salinity. Oscillating strains in  Ward  Hunt  Ice  Shelf  were  measured  with a wire strainmeter. It  is  suggested  that  the periodic calving  of ice ~ from Ward  Hunt Ice  Shelf  might  be  related to the effects of  the  high  frequency  oscillation  of 35s to 40s. Ice conditions along 150 km of  coastline con- i tinue  to change. Continued  monitoring  of  the  ice  shelves and landfast ice is believed  to be necessary in view  of  the offshore development in  the ~ Beaufort Sea. Key words:  Ward  Hunt  Ice Shelf, Milne  Ice Shelf, ice cores, saline ice, strainmeter, coastal  ice  conditions ICE  SHELVES OF NORTHERN  ELLESMERE ISLAND 175 FIG. 2. MaD of the  north coast of Ellesmere Island  and  the  area of study: Ward  Hunt Ice  Shelf  to  Milne  Ice Shelf, with  the  location of  ice cores and snow pits. Ice cores WH/Ol to WH/07 were drilled in spring 1982 (Jeffries, 1982): TABLE 1. Depth and  location of ice  cores Core  Location  Depth (m) WH/08 Ridge, 20 km E. of base camp, Ward Hunt Ice  Shelf 31.79 WH/09 Trough, 20 km E. of base camp, Ward Hunt Ice  Shelf 2.16 WH/10  Ridge,  base camp 5.00 WH/ 11 Milne  Ice  Shelf reentrant 1.55 WH/12  Milne  Ice  Shelf  re-entrant 2.05 WH113 Trough,  outer  nit of Milne  Ice  Sh lf 1 .OO WH114 Ridge,  central unit of Milne  Ice  Shelf 2.00 WH/15  Ridge, inner  u it of Milne  Ice Shelf  1.90 WH/16  Basement ice, Ward  Hunt Ice  Shelf 2.06 Disraeli  Fiord 2.19 Total 55.00 of 55 m of 7.6 cm diameter ice core, to complement the cores taken  in 1982, was obtained  from ten different locations along the northern coast  of Ellesmere Island (Table  1; Fig. 2).  The cores taken from  troughs  (WH/09 and WH/13) represent re- frozen  meltwater or lake water  that accumulates in surface de- pressions during the ablation season. Cores  WH/1 l and WH/12 represent re-entrant ice from the NW part of Milne Ice Shelf. Jeffries (1982)  described this area as “FLAT  ICE” and unlike the remainder of the ice shelf; it is believed to be an area of  ice regeneration after an ice  island calving. The  cores from ridges represent surface accumulation  of iced-firn (WH/10), glacier ice (WH/14), and fiord ice (WH/15). The latter is similar to the present-day ice cover on Disraeli Fiord. Ice core  WH/16 is  of  basement ice. The greatest effort was  devoted to core  WH/08. A total  of 31.79  m of 7.6 cm diameter ice core was  removed before drill- ing was discontinued; not  only were  cores being lost despite modifications to the core barrel, but there was the added possibility of losing the equipment in a brine-soaked hole. Salinity measurements  undertaken in  the  field  with an  Endeco refracting salinometer (accuracy +O. 1 %,) revealed  the stratified nature of the  ice  shelf  at  this location. It  is  noted  that brine drainage  from the ice  might  result  in  an  underestimation of salinity values. Saline ice  was first detected  at a little over 14 m  (4%, at 14.56  m); a maximum ice salinity of 16.9%, occurred at 29.42  m; brine-soaked  ice chips from the  bottom of the borehole had a salinity of 50°/,,. A plot  of  salinity ver- sus depth (Fig. 3) shows three quite distinct layers evident in the  ice shelf; 0-10  m, negligible salinity; 10-26  m, mean salinity of 2.30°/,,; 26-31.79 m, mean salinity of 9.30%,. Theupper 10 m is an  accumulation of iced-firn while  the saline ice  is  probably  both  basement  ice  and  ice grown from  bottom freezing. The very  high salinities are probably due to  soaking by underlying seawater. Stable isotope (oxygen- 18) measurements are being  made  on all the ice types in  an  attempt to characterize each according to its  isotope signature and  to further elucidate processes of for- mation (Jeffries, 1983). In the case of the accumulation of snow  and firn at  the  ice  shelf surface the oxygen- 18 variations can be altered considerably from the original precipitation values due to processes  described by Koerner et al. (1973) for Meighen Ice Cap. In order to determine the stable isotope variations in present-day precipitation and to compare these with variations in the iced-firn, 10 snow pits were dug and snow samples  obtained  from locations along  the  coast (Fig. 2). ICE SHELF DYNAMICS The massive calving of ice from Ward Hunt Ice Shelf in 1961-62 (Hattersley-Smith, 1963)  has  been  discussed  in terms of the occurrence of a seismic  event and  unusually  high tides, which  might  have created  a critical condition  in the ice  shelf NEOLIQIBLE SALINITY - e MEAN SALINITY.2.34%o * e  -4b SALINITY.S.3OQ. ICE CHIPS MEAN  BRINE-SOAKED 0 10 20 30 40 50 SALINITY(%o) FIG. 3. Plot of salinity versus depth for ice  core WH/08. (Holdsworth, 197 1). Although these events possibly contri- buted  to  the loss of almost 600  km2 of  ice shelf, it is  suggested that they do not wholly explain the calving mechanism. A floating  ice  mass acts as a filter of ocean wave energy. When a dominant frequency occurring in the incident wave spectrum coincides with one of the  natural frequencies of  the ice, then a resonant  motion  will occur. At relatively high  modes  of oscillation (vibration) sustained stresses may  lead to crack pro- pagation  and  fatigue failure in the  ice (Holdsworth and Glynn, 1981). These  authors  propose such a vibration  mechanism for the calving of tabular icebergs (ice islands) from ice shelves and glacier tongues. The vibrations, or oscillating strains, can be  measured  using wire strainmeters. A new instrument described by Moore and  Wadhams (1981) was  loaned by the Scott  Polar  Research lnstitute (Cambridge, U . K . )  for a preliminary examination of oscillating strains in Ward Hunt Ice Shelf. The strainmeter, installed at the west end of the ice shelf, registered three approximate cycles. The first was a 35s-40s period similar to that reported for ice  island T-3 (e.g., Holdsworth and Traetteberg, 1974). This cycle is related to the  ocean swell and  is  probably  enhanced by the natural modes in the ice shelf (V. Squire, pers. comm.).  The  second, much longer period, was one of about 20  minutes. Keys (1978) notes a similar period for internal waves in Disraeli Fiord (Fig. 2). Since the  main  connection  between Disraeli Fiord  and  the Arc- tic Ocean is believed to lie to the west of Ward Hunt Island (Crary, 1960), these tide-driven internal waves are expected to M.O.JEFFRlES induce  ice  shelf  movement also. Keys  (1978) also recorded  a 5.5-6 minute period in Disraeli Fiord that was noted on the strainmeter records and also on tiltmeter records for Ward Hunt Shelf in 1983 (Holdsworth, pers. comm.). There  appear to be three common oscillating strains in Ward Hunt  Ice Shelf, one of which  (35s-40s)  might  lead to calving and disintegration of the ice. Further consideration of these vibrations might  explain the cyclic pattern of calving. It  is  sug- gested  that  the  tidal  and seismic  events of  1962 served to  in- crease and accelerate the effects of the normal vibrations leading to the massive calving of five ice islands. COASTAL ICE CONDITIONS The coastal ice  between  Ward  Hunt Ice Shelf  and  Yelverton Bay (Fig.  2) consists mainly  of  shelf  ice  and multiyear landfast ice  and  is  subject to considerable  change  due to calving  and/or growth of ice. Beyond this coastal ice fringe lies the  pack  ice of the Arctic Ocean. The most recent changes have occurred at Ward Hunt Ice Shelf (Fig.  2). Jeffries (1982)  described the loss and/or grounding of  35-40 km2 of  ice  at  the  west  end  of  the  ice shelf. At some time  during the summer  or early fall  of 1982, a fur- ther 40 k m 2  of  ice  calved from the east end  of  the  ice  shelf  (Jef- fries and Serson, 1983). In spring 1982 there were  con- siderable areas of multiyear ice attached to the western front of Ward Hunt Ice Shelf. In spring 1983 there were no signs of this ice, which  most  likely sheared off during  summer 1982. The mouth  of M’Clintock Inlet consists of a mass  of  multi- year landfast  ice together with  pieces of old  shelf  ice (recognized by numerous rocks and rock mounds on the ice surface). In 1983  the pressure ridge at  the  ice front was  up  to 5 km south  of  its  1982 position, suggesting  a  change  here. At the west  end of the  mouth  of M’Clintock Inlet there was a group of small (up to 0.05 km2) ice  shelf fragments most  likely derived from the  most  recent  Ward  Hunt calving. Recent changes at  the front of  Ayles  and Milne Ice shelves are to be  described  elsewhere in greater detail. However the following observations are noteworthy. The ice front across the mouth of Ayles Fiord is 2-5 km beyond that mapped in 1959. The fiord no longer contains a complete ice shelf; rather, part of the  ice  shelf  has  moved  some distance out of the fiord, allowing  the escape of another piece of ice  shelf together with some icebergs created by the disintegration of an ice tongue.  The mouth  of the fiord is  now  blocked by both  shelf ice and re-entrant ice, behind which lies 5 m thick fiord ice into which are locked scattered icebergs and small pieces of shelf ice. While the ice  front  of Milne Ice Shelf  remains  the same as in 1982, it is  now  believed  that  about 35 k m 2  of shelf  ice  calved from  the  northwest area of Milne Ice  Shelf  some  time  between 1959 and 1974. Since that time re-entrant ice has grown in place  of  the former ice shelf. This  9  m thick  ice (J. Thorleifs- son, pers. comm.) is considered to be a part of the  ice shelf, not  of the Arctic Ocean. The bay to the south  of Milne re-entrant, where snow  pit 8 ICE  SHELVES  OF  NORTHERN  ELLESMERE  ISLAND  177 was dug  (Fig.  2), remains filled with an ice  shelf  beyond PetroCanada;  Supply  and  Services  Canada,  Contract  No. 065B, which there a 5 ‘km wide  expanse  of  multiyear landfast ice 97708-1-0993 ( t h h g h  the Arctic  Acoustics  Section,  Defence that broadens farther across the mouth  of  Yelverton  Bay. Research  Establishment  Pacific);  Polar  Continental  Shelf  Project;  The Arctic  Institute of  North  America  and  The University of  Calgarv. MY SUMMARY  AND  CONCLUSION thanks to Dr. S.A. Harris for reading the origina<manusc& and also to  Claudette  Reed  Upton  and  “anonymous”  refesees  for  their  ad- During the period 23  April to 5 June 1983 a successful pro- son for his assistance and companionship in the field. vice  and  suggestions  for  improvements.  Special  thanks  to  Harold Ser- gram of ice shelf studies was completed on  the north coast of Ellesmere Island. As in 1982, the emphasis was  on ice coring; a total  of 55 m of 7.6 cm diameter ice core  obtained by SIPRE hand corer will  be the subject of chemical, isotopic  and cry- composed of ice-firn/superimposed ice to a depth of 10 m, below  which the salinity values show  the  ice to be  old  sea ice. mere  Island.  Canadian  Geographer  12:32-34. Shelf (Hattersley-Smith, 1963) has been discussed in terms of Journal  of  Glaciology  4:415-424. REFERENCES stallographic investigations. The longest core, 3 1.79  m, was CRARY, A.P. 1960. Arctic ice islands and ice shelf studies. Part 11. Arctic HATTERSLEY-SMITH, G .  1958. Glaciological research in northern Elles- The ImSt nxent massive  calving  of ice from Ward Hunt Ice -. 1963. The Ward Hunt Ice Shelf recent changes of the ice front. 13:32-50. the  near coincidence of  tidal  and seismic  events creating condi- tions in the ice shelf leading to fracture (Holdsworth, 1971). Undoubtedly  this  influenced the calving not  only at Ward  Hunt Ice  Shelf  but also at Milne and  Ayles fiords. The  calving might also have been related to vibrations within  the ice. Strainmeter measurements revealed vibrations or oscillating strains with 35- to 40-second cycles, 5- to 6-minute cycles and  20-minute cycles. All these oscillations will exist in  the water adjacent to and  beneath  the  ice shelf. Whereas Ward  Hunt Ice Shelf has  grown  through a combi- nation  of  sea  ice thickening, surface accumulation and  bottom freezing (Crary, 1960;  Hattersley-Smith,  1958;  Marshall, 1955), Milne Ice Shelf is believed to have a more complex structure and growth history. While the outer unit  is  probably similar in origin to Ward  Hunt Ice Shelf, the central unit, con- stituting one-third of  the  total  ice  shelf area and covered with many moraines, is undoubtedly of glacier origin. The inner unit  of the ice  shelf  is  not  well  understood  but the ice  is similar to  that  on  the surface of Disraeli Fiord. The Mihe re-entrant offers an  opportunity to study the growth of multiyear sea  ice that  might resemble the original thick  sea  ice  basement from which  most  of  the  ice shelves were essentially created. Changes to the  ice along the  north  coast of Ellesmere Island continue. If the coastal ice conditions remain subject to sudden changes, closer monitoring of the ice ought to be considered. With continued  offshore exploration and development in the Beaufort Sea and elsewhere the creation of new ice islands should  be documented. Note added in proof The salinity  and oxygen- 18 profiles of  ice core WH/O8 have now been analyzed and described in greater detail (Jeffries, 1985; Jeffries and Krouse, in press). Four distinct layers are now recognized in Ward Hunt Ice Shelf at the location of WH/08 with a freshwater, frazil ice-derived stratum at 18.90 m to 19.72 m. This ice layer is  sandwiched  between layers of old sea ice. HOLDSWORTH, G. 1971. Calving from Ward Hunt Ice Shelf, 1961-1962. Canadian  Journal  of  Earth  Sciences 8299-305. -and GLYNN, J.E. 1981.  A  mechanism  for  the  formation of large  ice- bergs.  Journal of  Geophysical  Research  86:3210-3222. HOLDSWORTH, G., and TRAETTEBERG, A. 1974. Deformation of an Arctic  ice  island.  Proceedings  of  the  2nd  International  Conference  on  Port and  Ocean  Engineering  under  Arctic  Conditions,  Iceland.  419-440. JEFFRIES,  M.  1982.  The  Ward Hunt  Ice  Shelf,  Spring  1982.  Arctic ~. 1983.  Preliminary  isotope  studies  on  Ward  Hunt  Ice  Shelf.  Defence Research  Establishment  Pacific,  Contractor’s  Report  Series,  83-26.  56  p. -. 1985. Physical, chemical and isotopic investigations of Ward Hunt Ice  Shelf  and  Milne  Ice  Shelf,  Ellesmere  Island,  NWT.  Ph.D.  thesis.  The University  of  Calgary.  310  p. JEFFRIES, M.O., and SERSON, H. 1983. Recent changes at the front of Ward Hunt Ice Shelf, Ellesmere Island, NWT. Arctic 36289-290. JEFFRIES, M.O., and KROUSE, H.R. In press. Arctic ice shelf growth, fiord  oceanography  and  climate.  Zeitschrift  fur  Gletscherkunde  and  Gla- zialgeologie 21 (1985). KEYS, J.E. 1978.  Water  regime of Disraeli  Fiord,  Ellesmere  Island.  Defence Research Establishment Ottawa, Report No. 792. 58 p. KOERNER, R.M., PATERSON, W.S.B., and KROUSE, H.R. 1973. 6180 profile in ice formed between the equilibrium and firn lines. Nature LYONS, J.B., and  LEAVITT, F.G. 1961.  Structural and Stratigraphic Studies  on  the  Ward  Hunt  Ice  Shelf.  Bedford,  Massachusetts,  Geophysics Research  Directorate,  U.S. Air Force,  Cambridge  Research  Laboratories. Final  Report  on  Contract  AF19  (604)-6188.  37  p. LYONS, J.B., SAVIN, S.M., and TAMBURI, A.J. 1971. Basement ice, Ward Hunt Ice Shelf, Ellesmere Island, Canada. Journal of Glaciology MARSHALL,  E.W.  1955.  Structural  and  stratigraphic  studies of the  northern Ellesmere  Ice  Shelf.  Arctic 8: 109-1 14. MOORE, S.C., and  WADHAMS, P. 1981. Recent  developments in strainmeter  design. Scott  Polar  Research Institute, Sea Ice Group  Report 81-2.  A  paper  presented  to  the  Workshop  on  Sea  Ice  Field  Movement, St. John’s, Newfoundland, April 29-May 1, 1980. 25 p. RAGLE, R.H., BLAIR, R.G., and  PERSSON, L.E. 1964.  Ice  core  studies  of Ward  Hunt  Ice  Shelf,  1960.  Journal  of  Glaciology  5:39-59. TRETTIN, H.P., and FRISCH, T.O. 1981. Preliminary geological map and notes,  Yelverton  Inlet  map-area,  District  of  Franklin  (NTS  340F,  540G). Geological  Survey  of  Canada. Open File  758. 35:542-544. 245:137-140. 10:93-100. ACKNOWLEDGMENTS This  work  was  made possible by  the  generous  financial  and logistic support of the following:  Dome  Petroleum  Ltd.; Gulf Canada Ltd.; 

Ice Shelf Studies off Northern Ellesmere Island, Spring 1983

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Ice Shelf Studies off Northern Ellesmere Island, Spring 1983

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