JOVR•TALOF GEOPHYSXCALRESEARCH ¾OLV•fE 65, NO. 12 DaCEUSER1960 Oxygen-IsotopeRatios in the Blue Glacier,Olympic Mountains, Washington, U.S.A. i•OBERTP. SHARP,SAMUEL EPSTEIN, AND IRENE VIDZIUNAS Cal#ornia Institute ot Technology Pasadena, Calitornia Abstract. The mean per mil deviation from a standard (average ocean water) in the O•]O •e ratio of 291 specimensof ice, tim, snow, and rain from the Blue Glacier is --12A; extremes are --8.6 and --192. This is consistentwith the moist temperate climatological en- vironment. The 0•/0 •øratio of snowdecreases with declining temperature of precipitation, and it also decreaseswith increasingaltitude at 0.5/100 meters. Analysesof the three principal types of ice, coarse-bubbly,coarse-clear, and fine, composing lower Blue Glacier, show that ratios for coarse-clearice are generally lower and for fine ice they are mostly higher than the ratios for coarse-bubblyice. This indicates that the fine ice representsmasses of firn and snow recently incorporatedinto the glacier by filling of crevasses or by infolding in areas of severedeformation. Coarse-clearice massesmay representfragments of coarse-bubblyice within a brecciaformed in the icefall. Becauseof unfavorable orientation, these fragments could have undergone exceptional recrystallization with reduction in air bubblesand, possibly,a relative decreasein 0 TM. A longitudinal septurn in the lower Blue Glacier is characterized by higher than normal O•8]0•ø ratios. These valuesare consistentwith an origin for this feature involving incorporation of much surficial snow and firn near the base of the icefall. Samples from longitudinal profiles on the ice tongue suggestthat ice closeto the snout comesfrom high parts of the accumulation area. Analyses from the light and dark bands of ogives are compatible with the concept that the dark bands represent greatly modified insets of tim-ice breccia filling icefall crevasses. The range in ratios of materialsis much'greater in the accumulationarea than in the ice tongue. This is attributed to homogenization,much of which takes place during the conversion of snow to glacier ice. This is supported by comparative analyses of snow layers when first depositedand months later after alteration. Refreezing of rain and meltwater percolatinginto underlying cold snow is an important mechanismas shownby analysesof ice layers and lenses in the firn formed in this manner. Introduction. Somepotential uses of oxygen- area of a glacier acquirespatterns in the dis- isotopedata in glaciologicalresearch have been tribution of 018/010ratios which can be used as illustrated by analysesof samples from the natural tracers. Although the ratios are modi- Saskatchewanand Malaspina glaciers [Epstein fied duringconversion of snowto ice and during and Sharp, 1959]. 'Otheruses will be demon- subsequentflow within the glacier,this doesnot strated by analysesof materials from Green- destroytheir value as tracers.Among the modi- land [Benson,1960; IGY Bull., 1959,pp. 82-83] fying influencesare freezingof meltwater and and Antarctica, to be publishedshortly. The rain, captureof snowin crevasses,and homoge- usefulnessof the stable isotopesof oxygenand nization by other unidentifiedprocesses. Thus hydrogenin glaciologicalresearch rests on the the 0•8/0 •øratios tell somethingabout the origi- fact that their range of abundancein snow is nal conditions of accumulation and reflect the relatively large, far exceedinganalytical errors influenceof modifyingprocesses during a subse- of +--0.1in the ratio values.The value and range quent history. of 0•/0 •ø ratios in glaciersdepend principally Oxygen-isotopestudies of glaciersare still in upon meteorologicalconditions, especially upon a formativestage. The usefulnessof this ap- the temperatureat the time of snowfall.Thus proachvaries with the nature of a glacier,its the ratio varies with the storm, the season,the environment,and the problemschosen for study. elevation,and other factors.The accumulation For example,the 0•/0 'ø ratios in snow on the • Contribution No. 967, Division of Geological Greenlandice sheetdisplay simple relationships Sciences. usefulin stratigraphiccorrelation. In contrast,it 4043 4044 SHARP, EPSTEIN, AND VIDZIUNAS I 47o49 ' Mercury • PortAngeles ø •:;.•.'• •, Eo Eo ' I .'r,.-..q-.•$,•0 5•'" I00 150km • ...... -'• ' ''.' ' "Apollo • .'..' .' .. • • Do ;,.;'.;...-'•,.:.::....:.........'i :.'. '.;..... ß, • • ..:5. '"' .:.:..:.' , ,• .• :... ......... , •. ..y... , ß • ::L::'.': '. ß •. '-.• ,;•.'.'..ß . ß. ,, \ ,9'e • '-'.'..•...:: ....... ß . /i • ...."::":" ' ' ' ' ' ' ' ' ' .. \ P•tA (hrn) '•,• \ \ N Btizzordoss .".-.'.:- :'.' ß o . \ \ \ -. ß ß ß .. ß . ß ßß'.'i '.::.;. •- ":':"::""?%L so,, "/,?• •/• ..• • Pit C(firn) •?:e .' ß.v/:•4::• % •.. No,thSosin •?:•:•L .'•.4:::.:•;'•'' ß ß ' ":•f•:•.• %'. •;.:•::•L •:•'::'•ß• ß . .,'.?,...... • .. ..:.:::?•.•' • ' ß' ".'::•.. : .......:.•::::':??j') ;'::.).'0- .. :.. :L• .-... Fig. 1. Location, setting, shape and principal componentsof Blue Glacier. appears that icefalls and temperate conditions to determinethe usefulnessof the oxygen-iso- with copiousmeltwater and rapid exchangeof tope methodon a small temperateglacier with material lead to complicationsdifficult to in- a largematerial budget [LaChapelle, 1959, pp. terpret. In investigationsto date, the applica- 443-446]. bility of oxygen-isotopestudies to all types of The Blue Glacier was selected because it is glaciershas not been satisfactorilydefined. The relativelysmall, geometrically simple, and easily present investigationwas made in an attempt accessible;its constitution and structure are OXYGEN-ISOTOPE RATIOS IN THE BLUE GLACIER 4045 known [Allen, Kamb, Meier, and Sharp, 1960], upglacier from the edge of the tim, separates and associatedglaciological and meteorological lower Blue Glacier from its principalaccumula- studiescontribute to an understandingof oxy- tion basins,termed 'upper Blue Glacier.' The gen-isotoperelationships. The principal items Blue Glacier,supposedly temperate, has a high investigatedare (1) the range and mean value rate of massexchange owing to heavy accumu- of 0•8/0 •6 ratios as related to general environ- lation and strong ablation [LaChapelle, 1959, mental conditionsand to the theory of oxygen- p. 445]. isotopefractionation; (2) the influenceof alti- The climatologicalenvironment is strongly tude and temperature on 0•8/0 •6 ratios; (3) maritime, that is, relatively warm and moist. changesin isotoperatios within firn layers dur- Records from the Snowdome station at 2070 m ing alteration; (4) differencesin isotoperatios on upper Blue Glacier [LaChapelle, 1958, p. 12] of the three principaltypes of ice,coarse-bubbly, for the period August 1, 1957,to July 31, 1958, coarse-clear,and fine, composingthis glacier show a mean annual temperature of 1.6øC and their beating on the origin and history of (34.9øF), a meanfor the coldestmonth (March) these types of ice; (5) differencesin isotope of --6.1øC (q-21.1øF), and a mean minimum ratios of ice coming from various accumulation for March of --8.9øC (16.1øF). The lowesttem- areas; (6) variations in isotope ratios along perature recordedwas -15øC (5øF) and the longitudinal profiles on the surface of the ice highest21.7øC (71øF). Total precipitationwas tonguebelow the firn edgeand their relation to 378 cm (148.9 inches)of water, of which 305 cm flow lines within the glacier; (7) differencesin (119.7 inches), or 80 per cent, fell as snow.This isotoperatios of the materials composingogive period of observationwas unusuallywarm and bands as an aid in understandingthe origin of dry, judging from recordsat other meteorologi- this structure; and (8) changesin oxygen-iso- cal stations in northwesternWashington, and tope ratios,if any, producedby recrystallization, the abovefigures are not representativeof long- changesof state, and other processesrelated to range means. In an average year the mean an- solid flow. nual precipitation on Snowdomemay exceed A general program of glaciologicalresearch 500 cm (200 inches) of water. was begun on Blue Glacier in the summer of Lower Blue Glacier consistsof two major and 1957; it has extendedthrough 1960 and will be three minor ice streams, each originating in continued,with the permissionof the National separateaccumulation areas (Fig. 1). Only ma- Park Service.It was precededby Park Service jor streamsA and B extendto the snout; minor observationsin the 1940'sand early 1950'sand streams C, D, and E terminate along the east glaciologicaland glacio-meteorologicalwork dur- margin. Ice stream B consistsof two currents ing 1955 and 1956 [Hubley, 1957], and it has below the icefall separated by an intensely been accompaniedby glacio-meteorologicalre- foliated, structurally complex zone, the longi- searchon upper Blue Glacierfrom 1957to 1959 tudinal septurn,which is unusually rich in fine [LaChapelle, 1958, 1959]. Samplesfor oxygen- ice and coarse-clearice. This septurnseparates isotopeanalyses were collectedduring the win- two arc-shapedfoliation patterns displayedby ter of 1957-19-58 and in the summers of 1958 compositeice streamsA q- B• and B2 q- C and 1959. (Fig. 1). Ice stream A also displaysa seriesof Physical setting and constitutiono/ the Blue weak ogives of the internal variety. Details of Glacier. The Blue Glacier is a small ice stream these and other structuresare given elsewhere that rises high on the northeasternslope of [Allen, Kamb, Meier, and Sharp, 1960]. Mount Olympus (2413 m) in the heart of the Samplingand analysis. The methodof analy- Olympic Mountains of