Chronology, Stable Isotopes, and Glaciochemistry of Perennial Ice in Strickler Cavern, Idaho, USA
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Investigation of perennial ice in Strickler Cavern, Idaho, USA Chronology, stable isotopes, and glaciochemistry of perennial ice in Strickler Cavern, Idaho, USA Jeffrey S. Munroe†, Samuel S. O’Keefe, and Andrew L. Gorin Geology Department, Middlebury College, Middlebury, Vermont 05753, USA ABSTRACT INTRODUCTION in successive layers of cave ice can provide a record of past changes in atmospheric circula- Cave ice is an understudied component The past several decades have witnessed a tion (Kern et al., 2011a). Alternating intervals of of the cryosphere that offers potentially sig- massive increase in research attention focused ice accumulation and ablation provide evidence nificant paleoclimate information for mid- on the cryosphere. Work that began in Antarc- of fluctuations in winter snowfall and summer latitude locations. This study investigated tica during the first International Geophysi- temperature over time (e.g., Luetscher et al., a recently discovered cave ice deposit in cal Year in the late 1950s (e.g., Summerhayes, 2005; Stoffel et al., 2009), and changes in cave Strickler Cavern, located in the Lost River 2008), increasingly collaborative efforts to ex- ice mass balances observed through long-term Range of Idaho, United States. Field and tract long ice cores from Antarctica (e.g., Jouzel monitoring have been linked to weather patterns laboratory analyses were combined to de- et al., 2007; Petit et al., 1999) and Greenland (Schöner et al., 2011; Colucci et al., 2016). Pol- termine the origin of the ice, to limit its age, (e.g., Grootes et al., 1993), satellite-based moni- len and other botanical evidence incorporated in to measure and interpret the stable isotope toring of glaciers (e.g., Wahr et al., 2000) and the ice can provide information about changes compositions (O and H) of the ice, and to sea-ice extent (e.g., Serreze et al., 2007), field in surface environments (Feurdean et al., 2011). investigate its glaciochemistry. Results indi- and laboratory investigations of ice-rich perma- Cave ice sequences can be dated with radiocar- cate that the ice forms through snow den- frost (e.g., Romanovsky et al., 2010; Schirrmeis- bon, tritium, dendrochronology, and other tech- sification, freezing of infiltrating water, and ter et al., 2013), and coordinated monitoring of niques (e.g., Luetscher et al., 2007; Kern et al., refreezing of meltwater. Radiocarbon dat- alpine glacier mass balances (e.g., Haeberli et 2009; Spötl et al., 2014), allowing paleoenviron- ing revealed that an ~30-m-thick deposit of al., 2000) are all examples of cryosphere-centric mental data to be studied as time series. Initial layered ice and organic matter accumulated research that have revealed tremendous infor- results from these efforts have been promising over the past several centuries. In contrast, mation about the operation of Earth’s climate (e.g., Kern et al., 2011a; Perşoiu et al., 2011), a 3.5-m-tall ice stalagmite began forming system and paleoclimatic variability during the but there is also cause for concern, because almost 2000 yr ago. Stable isotopes in the Quaternary. Despite these successes, a notable many cave ice deposits are rapidly disappearing stalagmite and in the layered ice generally drawback of this research is its uneven spatial (e.g., Fuhrmann, 2007; Kern and Perşoiu, 2013; have slopes that parallel the local winter distribution: Because most features of the mod- Pflitsch et al., 2016). This situation has added meteoric water line; however, d18O and d2H ern cryosphere are located in the polar regions new urgency to the investigation of cave ice and values are offset to the right of this line, in- or at high elevations, lower-latitude and lower- has motivated a call for increased collaborative dicating the influence of sublimation. Val- altitude areas are typically underrepresented. study of these deposits before they are lost for- ues of d18O are lower in older ice, signaling Subterranean accumulations of perennial ice ever (Veni et al., 2014). cooler temperatures during the Little Ice in caves, hereafter “cave ice,” are less-studied Caves containing perennial ice have been Age. Calcium is the most abundant element components of the cryosphere that offer a po- most intensively studied in the Alps and in in the ice, followed by Na, Mg, and K. Prin- tential solution to this problem. Caves con- eastern Europe; in contrast, cave ice has re- cipal component analyses revealed a group taining perennial ice have been reported from ceived relatively little attention in North Amer- of elements related to the local bedrock, a a wide variety of locations around the globe ica. Many sites were mentioned in a seminal second group reflecting regional transport (Kern and Perşoiu, 2013). Significantly, they work by the naturalist Edwin Balch over 100 yr of mineral dust, and a third group sugges- are often found in midlatitudes at elevations ago, which described ice caves all over the tive of eolian transport from a mining dust below alpine glaciers and in locations where world and speculated on their origins (Balch, source. Future work should build upon this ice-rich permafrost or other cryospheric ar- 1900). More recently published North Ameri- foundation to further exploit the significant chives are absent (Perşoiu and Onac, 2012). In can work includes long-term monitoring of ice paleoenvironmental information archived light of this potential, researchers have begun to in Candelaria Cave, New Mexico (Dickfoss et in Strickler Cavern. focus on cave ice as a source of paleoclimate al., 1997), in Merrill Cave on the California- information (Laursen, 2010). Cave ice formed Oregon border (Fuhrmann, 2007), at Lava Beds from precipitation that infiltrates the ground National Monument in California (Kern and carries a paleoenvironmental signal in stable Thomas, 2014), and in a lava tube on the Big Is- isotopes of hydrogen and oxygen (Yonge and land of Hawaii (Pflitsch et al., 2016). Ice caves †[email protected] MacDonald, 1999). Geochemical variability have also been studied at a number of locations GSA Bulletin; January/February 2018; v. 130; no. 1/2; p. 175–192; https://doi.org/10.1130/B31776.1; 12 figures; 4 tables; published online 29 August 2017. For permission to copy, contact [email protected] Geological Society of America Bulletin, v. 130, no. 1/2 175 © 2017 Geological Society of America Munroe et al. in the northern Rocky Mountains (Marshall and not available for the cave site; however, data year-round maintenance of subzero cave tem- Brown, 1974; Lauriol and Clark, 1993; Mac- collected since 1978 at the Mill Creek Sum- peratures despite a mean annual air temperature Donald, 1994; Yonge and MacDonald, 1999; mit SNOTEL (Snowpack Telemetry) station >0 °C at the surface. Yonge, 2014). These projects have reinforced at a slightly higher elevation (2680 m) in the The entrance to Strickler Cavern is a collapse the notion that cave ice is a significant paleo- Salmon River Mountains NW of the Lost River doline, ~5 m in diameter, that descends ~8 m to climate archive, but that potential remains pro- Range are likely similar. The mean annual air the top of a steep-sided cone of snow, firn, and foundly underdeveloped. temperature at the Mill Creek Summit SNOTEL ice ~5 m tall (Fig. 2). This “snow cone” rises Here, we report on our study of a recently is 1.1 °C. December through February tempera- from a relatively flat floor of ice that forms the discovered cave ice deposit at a moderate el- tures average −7.1 °C, whereas June through Upper Level of the cave (Fig. 1). During July evation (~2500 m) in midlatitude (~44°N) in August temperatures average 10.7 °C. Mean of 2015, a shallow (<10 cm) meltwater pond Idaho, United States. Previous reconnaissance annual precipitation is 730 mm, with less than covering ~25 m2 was located on the floor of work and mapping indicated that the ice deposit 20% of the precipitation falling during the sum- the Upper Level to the north of the snow cone. is in excess of 30 m thick and possibly several mer months. December and January have the From the Upper Level, a nearly vertical slope hundred years old (Cecil et al., 2004). These greatest precipitation (>12% of the annual total of ice leads down into a large chamber known characteristics, coupled with the dearth of cave in each month), and 64% of the annual precipi- as the Big Room (Fig. 1). This room, with a ice studies from this region, the absence of gla- tation falls during months with subzero average ceiling height locally in excess of 15 m, fea- ciers from this part of the Rocky Mountains, air temperatures (November through April). tures a floor of ice that grades laterally into a and concerns about the stability of cave ice un- Strickler Cavern can be classified as a “static slope of breakdown derived from the cave roof. der a warming climate, motivated a field- and cave with congelation ice and firn” (Luetscher Packrat middens, wood, and other organic de- laboratory-based investigation in pursuit of the and Jeannin, 2004, Fig. 1, p. 64). The air circula- bris are scattered across this slope, and an inac- following objectives: tion within the cave is likely static because the cessible dome extends upward in the center of (1) to investigate the origin of the ice present only entrance is at the top, and cold air that en- the ceiling. A large stalagmite of ice occupies in the cave; ters through density settling in winter is trapped the center of the Big Room floor, and a smaller (2) to determine the age of the ice; in the cave during the summer. This permits the stalagmite is located on the breakdown slope. (3) to evaluate the potential paleoclimate significance of stable isotope variations in the ice; and (4) to analyze and interpret the glaciochem- istry of the ice.