Orbital control of western north america atmospheric circulation and climate over two glacial cycles

ABSTRACT The now arid Great Basin of western North America hosted expansive late Quaternary pluvial lakes, yet the climate forcings that sustained large ice age hydrologic variations remain

controversial. Here we present a 175,000 year oxygen isotope record from precisely-dated speleothems that documents a previously unrecognized and highly sensitive link between Great Basin

climate and orbital forcing. Our data match the phasing and amplitudes of 65°N summer insolation, including the classic saw-tooth pattern of global ice volume and on-time terminations.

Together with the observation of cold conditions during the marine isotope substage 5d glacial inception, our data document a strong precessional-scale Milankovitch forcing of southwestern

paleoclimate. Because the expansion of pluvial lakes was associated with cold glacial conditions, the reappearance of large lakes in the Great Basin is unlikely until _ca._ 55,000 years into

the future as climate remains in a mild non-glacial state over the next half eccentricity cycle. You have full access to this article via your institution. Download PDF SIMILAR CONTENT

BEING VIEWED BY OTHERS EARLY PLEISTOCENE EAST ANTARCTIC TEMPERATURE IN PHASE WITH LOCAL INSOLATION Article 08 December 2022 COUPLED ATMOSPHERE-ICE-OCEAN DYNAMICS DURING HEINRICH STADIAL 2

Article Open access 04 October 2022 DIRECT ASTRONOMICAL INFLUENCE ON ABRUPT CLIMATE VARIABILITY Article 01 November 2021 INTRODUCTION Paleoclimate proxy data from marine sediments, polar ice

cores and cave deposits have revealed an orbital pacing that linked global ice volume, atmospheric greenhouse gas concentrations, polar temperatures, and monsoon strength over several ice

age cycles1,2,3. In contrast, the paleoclimatic evolution of mid-latitude continental regions is less well understood because few records have sufficient dating control, duration, and

temporal resolution to compare with orbital-scale climate variations. In particular, the Devils Hole, Nevada, calcite δ18O record4 has led to interpretations that western North America (Fig.

1) responded asynchronously with Northern Hemisphere summer insolation, calling into question the applicability of Milankovitch forcing to explain paleoclimate there. Despite the poor

understanding of orbital-scale forcing on pluvial lake cycles, abundant evidence of large late Quaternary lakes attests to the sensitivity of Great Basin hydrology to ice age climate

changes5. Prominently, lakes Lahontan and Bonneville reached large extents near the end of the last ice age 25-15 ka (ka=thousands of years before present)6,7. Geomorphic evidence of

dramatic lake level changes attests to large hydrological variations occurring over millennial time scales, yet constraining climate variations from lake deposits alone is complicated by

fragmentary preservation, long periods of slow or non-deposition during non-pluvial conditions8,9, uncertain reservoir effects on carbonate 14C dating10, and the inherent limits on

radiocarbon dating to less than _ca._ 45 ka (ref. 11). The Milankovitch theory of ice ages1 posits that ice-sheet growth occurred over tens of thousands of years by the accumulation of

high-latitude snow as a result of sufficiently low Northern Hemisphere summer insolation at 65°N (hereafter ‘summer insolation’), and is supported by an orbital pacing of global ice volume2

and a large body of other paleoclimatic data12. Rapid glacial retreat is attributed to rising summer insolation, ice-sheet instability and feedbacks associated with rising sea level,

vegetation change, increased Southern Ocean upwelling and concomitant rising atmospheric CO2 concentrations13. Expanded ice sheets had widespread global impacts _via_ changes in atmospheric

circulation and temperature12, and have been linked to pluvial lake-filling episodes during glacial marine isotope stages (MIS)7,8. We use these stages here, defined by the ice volume proxy

of marine benthic δ18O values, as a convenient shorthand for contemporaneous variations in other orbital and terrestrial paleoclimate parameters. A major advance in the study of Great Basin

paleoclimate was achieved with the Devils Hole oxygen isotopic (δ18O) record14,15,16 of subaqueous calcite lining the walls of an open fault zone within the regional groundwater aquifer, and

allowed the first continuous paleoclimate record that could be radiometrically dated beyond the reach of radiocarbon (50 ka). Devils Hole thereby provided a test of the nature and timing of

previous glacials/interglacials between 500 to 4 ka (refs 4, 14). However, the Devils Hole record presented a paradox because it appeared to show deglacial warming that preceded orbital

forcing14 and global ice volume terminations2 by thousands of years. The origin of this asynchrony has been debated for several decades17,18,19,20,21,22,23. Although the Devils Hole δ18O

time series is still cited as a challenge to Milankovitch forcing24, one attempt to reconcile Devils Hole and orbital theory involved reconstructions of sea surface temperatures along the

western margin of North America associated with fluctuations in the strength of the California Current21. Here, SST increases also preceded global ice volume terminations, likely driven by

interactions between near-coastal waters and North American ice-sheet extent, thus apparently removing Devils Hole as a fundamental challenge to Milankovitch theory20,21, but it also now

leaves the question of climate forcing open. Because the existing temperature records suggested that western North America paleoclimate was asynchronous with orbital variations, major

questions remain as to the nature and timing of glacial/interglacial warmings, the duration of interglacial periods, and the relationship between orbital forcing and pluvial lake expansion

in the Great Basin. Moreover, the early warming events observed in the Devils Hole and California margin records are anomalous relative to other terrestrial paleoclimate data8,23 that

suggest Great Basin paleoclimate varied coherently with global ice ages. In particular, speleothem records from Pinnacle23 and Lehman Caves25, Nevada, indicated glacial and deglacial timings

that were consistent with Milankovitch forcing, thus calling again into question the nature of Devils Hole calcite as a record of Great Basin climate22,26. However, these stalagmite time

series were short (~5,000 years), and no other long-term Great Basin vadose zone speleothem records were previously available to corroborate their timing or that of Devils Hole. To address

the timing of paleoclimate change and its implications for Milankovitch forcing, we present a new Great Basin stalagmite δ18O record (hereafter ‘δ18O-GB’) from vadose zone (above the water

table) caves spanning the past 175,000 years. Vadose zone speleothems have a more straightforward relationship to infiltration pathways and flow times than phreatic zone calcite, making

their link to surface climate more direct. From these deposits we show evidence for a strong orbital forcing of Great Basin paleoclimate over the last 175,000 years. RESULTS AGE DATING AND

OXYGEN ISOTOPIC TIME SERIES The new speleothem reconstruction (Fig. 2 and Supplementary Fig. 1) is anchored by 65 precise U-Th dates (Supplementary Table 1 and Supplementary Fig. 2) and

1,936 δ18O measurements, and is supplemented by a published Lehman Cave speleothem record25. The reconstruction is based on records from three Great Basin caves with differing drip-water

δ18O values, so the records were normalized to a common δ18O scale (see Methods). Because modern precipitation δ18O values (Supplementary Fig. 3) are strongly correlated with temperature

both temporally and spatially (Supplementary Fig. 4) and are inversely correlated to the latitude of moisture source27, we interpret δ18O-GB as a proxy for temperature and moisture source of

winter precipitation reaching the Great Basin. The δ18O values of atmospheric moisture reflect rainout history at and upwind of the precipitation site over a wide geographic area28, and

these winter precipitation δ18O variations are subsequently transmitted to caves23,29 as drip waters where they are recorded in speleothem calcite. GREAT BASIN PALEOCLIMATE LINKED TO ORBITAL

INSOLATION Our results provide strong support for a Milankovitch forcing of Great Basin paleoclimate over the past 175,000 years. Our data show strong correspondence to June 21–August 21

insolation at 65°N (Fig. 3), and exhibit a one-to-one match of peak δ18O and low ice volume that defines the classic saw-tooth pattern of ice age cycles. There is a remarkable coherency in

the timing of δ18O variability among the samples collected from three caves spread across thousands of square kilometres (Fig. 1). Most prominently, δ18O-GB variations show a remarkable fit

of relative peak and trough amplitudes to the obliquity- and eccentricity-modulated 23-kyr precession cycle of summer insolation. The interhemispheric correspondence between the δ18O-GB and

globally distributed climate records is evident in matched high δ18O-GB values and increased temperature30 and methane concentrations in the Antarctic EPICA Dome C ice core31 and shared

variations with benthic foraminifera δ18O values2, a proxy for global ice volume. These correlations support our interpretation that δ18O-GB is a proxy for past temperature and atmospheric

circulation. Interestingly, our data do not show the pronounced millennial-scale climate variations evident in other southwestern speleothem records32,33 over MIS 3, so we focus on the

orbital-scale variations. This discrepancy may indicate that the northern limit of summer moisture penetration into the Great Basin was south of our study area, or because of varying

seasonal sensitivity at our site relative to New Mexico and Arizona. TIMING AND DURATION OF GREAT BASIN INTERGLACIALS Our data further show the expected timing of glacial-interglacial

transitions associated with rising summer insolation, and that MIS 5 was characterized by a triple peak in δ18O during substages 5a, 5c and 5e (Fig. 3). We estimated the timings of Great

Basin glacial-interglacial transitions around global ice volume Terminations I and II (TI and TII) from the timing of δ18O-GB half-height increases. The TII δ18O-GB rise robustly constrains

a half-height age of 131.8 ka, which is within age uncertainties of TII (131.6 ka) in the orbitally tuned global ice volume record2 and confirms the timing estimated previously from the

short Lehman Cave record25. Because of the exceptional U-series age precision on the stalagmites LC-14 and LC-21 of better than±0.4%, the timing of the δ18O-GB half-height rise at TII is

tightly constrained. The TI half-height rise in δ18O-GB is less well constrained because of non-growth intervals in our record (see Supplementary Discussion), but was estimated to 11.9 ka by

using the 18.6 ka δ18O-GB minimum and peak Holocene warming at _ca._ 8.55 ka. This timing may be too young, and its true age is likely closer to that estimated from continuous growth

speleothems from Arizona33 and New Mexico32 at 15.0 and 14.8 ka, respectively. Low δ18O-GB values (cold conditions) during the last and penultimate glacial maxima coincide with minima in

Antarctic temperature and maximal ice volume as would be expected from Milankovitch forcing, but contrast with warm California margin alkenone-based SSTs. Our data show that the duration of

MIS 5e warmth in the Great Basin is 10.9 kyr (between 131.8 to 120.9 ka), as defined by δ18O-GB exceeding the glacial to interglacial half-height of −12.1‰, (Fig. 3). The ~11 kyr duration is

consistent with that inferred from summer insolation, global ice volume and Antarctic ice cores30,31, but is significantly shorter than the 22-kyr interglacial inferred from Devils

Hole4,34. Further, δ18O-GB shows a return to interglacial warmth during MIS 5a and 5c, similar to the triple peak interglacial observed in the Asian monsoon3 and Antarctic methane records,

as would be expected from a summer insolation forcing. The MIS 5 triple peak contrasts with relatively less pronounced MIS 5c and 5a warmings in Antarctic temperature and CO2, providing

evidence that summer insolation was a dominant control on Great Basin paleoclimate. HOLOCENE NORTH ATLANTIC IMPRINTS Our data also show similarities to Holocene climate variations in the

North Atlantic region: low δ18O values indicate cool conditions at 12.5 ka during the Younger Dryas (YD), to attainment of peak warming at 8.6 ka, similar to Greenland temperature (Fig. 4).

High-speleothem δ13C values further support the inference of dry conditions during the YD and early Holocene35,36 (Fig. 4 and Supplementary Fig. 5) because soil carbonate δ13C is inversely

correlated with rainfall amounts in the Great Basin via a soil productivity forcing37. A trend to cooler and moister late Holocene climate is evident in decreasing δ18O values and faster

stalagmite growth rates, which peak around 3–5 ka, an observation consistent with similar changes in the Southwest36 but contrasting with apparent climate stability in Greenland38 and Devils

Hole4. This transition to wetter climates and more productive soils beginning _ca._ 5 ka may have facilitated the growth of the ancient 4.9 ka bristlecone pine39 stand on the flank of

Wheeler Peak, Nevada. Further, we observe a strong inverse correspondence between δ18O-GB values and the strength of the East Asian Summer Monsoon40 (Dongge Cave, China) over the past 13

kyr, confirming that the trans-Pacific climate synchrony previously observed for the Southwest and Asia on the millennial-scale32 extends to the Great Basin on orbital time scales. PLUVIAL

LAKE EXPANSION AND GREAT BASIN PALEOCLIMATE The GB-δ18O time series sheds light on the origin of the Great Basin’s pluvial lakes. A remarkable correlation between GB-δ18O values and the

level of Lake Lahontan41 (Fig. 5) shows that lake high stands were associated with lowest speleothem δ18O values between 20 and 14 ka, and lowest lake levels with high δ18O values, for

example, around 8 ka. Maximum lake levels during cold periods thus were supplied by high-latitude moisture derived from a northerly source region. This observation is consistent with fresh

conditions and inferred high-latitude moisture filling lakes in southern California42, but not with the hypothesis of a tropical moisture source41. Low lake levels coincided with dry and

warm conditions during the early Holocene which then shifted towards slightly cooler and wetter conditions in the late Holocene associated with the Fallon Lake cycles in the Lahontan Basin7.

Given the strong inverse correlation between stalagmite δ18O and pluvial lake level over the past 25,000 years, our new 175,000 year δ18O-GB record suggests that similar pluvial lake

expansions may have occurred during other cool periods as documented for MIS 2 at Pyramid Lake43, for MIS 3 cool events in Lake Bonneville10, during the penultimate glacial maximum (MIS 6),

and perhaps during MIS 5d when δ18O values reach minimum values, consistent with correlations of deep lake cycles with glacial maxima7,8. DISCUSSION Our data document a previously

unrecognized and robust link between Great Basin climate and summer insolation. The saw-tooth character of the δ18O-GB record over the past 175 ka suggests that global ice volume and

insolation are first-order controls on western North America paleoclimate. On a finer temporal scale, the amplitudes and phasing between δ18O-GB and summer insolation provide two important

clues for Great Basin climate attribution. First, sequentially lower insolation minima (cooling) centred on 138 ka (MIS 6) and 114 ka (MIS 5d) are mimicked by correlative speleothem δ18O

(Fig. 3), but contrast with relative ice volume maxima that show a warming trend from MIS 6 to MIS 5d. The MIS 6 δ18O-GB low happens during rising obliquity and warming Northern Hemisphere

summers, which may have diminished cooling relative to MIS 5d, when obliquity and δ18O-GB were low. Further correspondence is evident in a matched triple peak of warming (high δ18O-GB) in

marine isotope substages 5a, 5c and 5e that follows summer insolation and is similar to the triple peaks of methane31 in Antarctic ice and strong monsoon intervals in Asia3, but contrasts

with increasing ice volume, and decreasing Antarctic temperature and CO2 levels. The greater similarity of δ18O-GB to precessional-scale variations in summer insolation than to global ice

volume, particularly during MIS 5, suggests a fast-response forcing on precipitation δ18O variations. A second clue is the observation that δ18O-GB minima lag insolation minima by ca. 3 kyr

(significantly exceeding age uncertainties) at the MIS 6/5 and 2/1 transitions, reaching minima at 134 and 18.6 ka, respectively, compared with insolation minima at 137 and 22 ka. The lags

suggest that summer insolation did not directly force atmospheric temperature (for example, via heating of the atmosphere by more intense summer insolation), but must have acted indirectly

by another mechanism. We argue that the fast-response forcing of δ18O-GB resulted from atmospheric circulation anomalies driven by variations in Northern Hemisphere sea ice, continental snow

cover and incipient ice-sheet growth that responded to summer insolation44. Periods of low summer insolation would have allowed persistence of summer snow (for example, during MIS 5d),

which in turn likely affected the delivery of high-latitude precipitation during cold periods, and vice versa. Changes in winter moisture source may have also resulted in temperature

anomalies from the ice-albedo feedback to produce our observed δ18O-GB record. The lags in δ18O-GB minima after insolation suggest that several millennia of snow and ice accumulation past

the insolation minimum were required before exerting a maximal influence on North Pacific storm tracks. In turn, these circulation anomalies drove the expansion and contraction of Great

Basin pluvial lakes during cold and warm conditions, respectively, thus allowing for correlation and future projection of high-lake level stands to low insolation. Additional tests of the

climate/lake level correlation, such as during MIS two and three10 await further high-resolution lake level dating and continuous speleothem data over this time interval. Our data provide

additional evidence for the importance of MIS 5d for glacial inception44 over North America during an interval of low obliquity (Fig. 2). The MIS 5d orbital configuration has been

hypothesized to be a key forcing of the initiation of Northern Hemisphere glaciations, and would have driven the expansion of Arctic sea ice and perennial snow cover. Initial ice build up

during MIS 5d was volumetrically small with a concomitant minor change in benthic δ18O, but an areally-extensive snow cover could have strongly impacted circulation patterns via atmospheric

and land-surface albedo feedbacks44. Climate simulations set to 115 ka obliquity values found that when perihelion occurs during the northern winter, reduced summer insolation allows snow to

persist through the summer44, resulting in a stronger Aleutian Low45 and strengthened storm tracks46 over the eastern North Pacific, supported by δ18O-GB minima during MIS 5d. Consistent

with observations of the development of atmospheric circulation anomalies following ice-sheet growth47, we suggest that the low δ18O values around MIS 5d may be related to the development of

a stationary wave that resulted in transmission of low-δ18O moisture to the study area. Our data provide evidence that the last glacial inception may have been partly triggered by cold

atmospheric conditions during MIS 5d in western North America, and provide a challenge to test whether climate models are capable of reproducing our observations of rapid precessional-scale

climate variability at times of low ice volume. Despite several decades of controversy on the forcings of Great Basin paleoclimate, our new data show that atmospheric circulation over the

northeastern Pacific Ocean and Great Basin was indeed paced by Milankovitch forcing. Our new data support previous interpretations that the Devils Hole δ18O record may have been influenced

by changing latitudes of infiltration of ground water into the regional carbonate aquifer reaching Devils Hole23. Variable proportions of higher latitude and altitude (_ca._ 38°N) waters

with low δ18O values and lower latitude (_ca._ 36°N) higher δ18O waters could have influenced the shape of the Devils Hole δ18O curve. If the proportion of low-latitude ground waters

reaching Devils Hole varied significantly ~10 kyr before global ice volume terminations, it would have produced a δ18O increase that mimicked an early deglacial warming. Although this

mechanism is speculative, it could be tested by additional work on fluid inclusions of both the Devils Hole phreatic calcite and our vadose zone speleothems, and more high-resolution dating

of the Devils Hole phreatic calcite. Our data demonstrate that Great Basin stalagmite δ18O variations closely match the shape and amplitudes of 65°N summer insolation, documenting a strong

Milankovitch forcing on southwestern paleoclimate. We have shown that this orbital control is linked to the expansion of pluvial lakes during full glacial periods. Because the ongoing

interglacial appears most analogous to the very long ‘super interglacial’48 of MIS 11 (424–374 ka), and because modern warming (increasing δ18O-GB) appears to have already begun despite

decreasing summer insolation, we hypothesize that future climate variations will also follow summer insolation. Rising insolation and an added anthropogenic climate control is likely to keep

Great Basin climate mostly mild49 and dry50 over the next half eccentricity cycle until insolation reaches a new minimum ~55,000 years in the future (Fig. 6). METHODS STUDY AREA The three

caves in our study area are located in the central Great Basin: Leviathan Cave is located in the Worthington Mountains (37.89°N, 115.58°W, 2,400 m) of Nevada, in the northern part of the

Death Valley regional ground water flow system that also feeds Devils Hole. Stalagmite LC-1 was collected from this cave and covers the YD to modern and portions of MIS 3 and MIS 5. The

sampling site has constant temperature (8.32±0.06 °C) and 100% relative humidity, based on 23 months of continuous data logging (27-May-2011 to 28-April-2013). Stalagmite LC-1 was collected

beneath an active drip and is 551 mm tall. Stalagmite PC-1 was collected from Pinnacle Cave (35.97°N, 115.50°W, 1,792 m), on the flank of Mount Potosi in the Spring Mountains of southern

Nevada. The entrance to Pinnacle Cave is restricted and requires a long vertical drop, ensuring the cave has a stable cave climate and high-relative humidity. Pinnacle Cave is located in the

Spring Mountain recharge zone for Devils Hole; details on Pinnacle Cave and stalagmite PC-1 were previously reported23. Lehman Cave is located in Great Basin National Park (39.0°N,

−114.2°W, 2,080 m). Stalagmites LMC-14 and LMC-21 were collected down and broken from deep within Lehman Cave. Additionally, we used the recently-published data for stalagmite LC-2 from

Lehman Cave25. The LC-2 stalagmite represents a key time interval of Termination II and connects a temporal gap between our LMC-14 and -21 stalagmites, and we confirm that it records climate

variations in the Great Basin over the penultimate termination25. The hydrology of the alpine cave sites is straightforward, as they each receive water from infiltration of precipitation

through overlying bedrock and are not connected to regional aquifers. Each of the caves is overlain by only a few tens of metres of overlying carbonate bedrock, and because of their

ridge-top locations, they receive water infiltration only from directly above the drip sites. Because of these characteristics, the selected cave drip hydrology can be considered a more

robust proxy for δ18O of precipitation than groundwater-fed vein calcite, which integrates isotope signals over large areal and latitudinal extents. ISOTOPIC ANALYSES U-series ages were

determined at the Radiogenic Isotope Laboratory, University of New Mexico, by dissolving subsample powders (50–200 mg) in nitric acid and spiking them with a mixed 229Th-233U-236U spike. The

U and Th isotopic measurements were made on a Thermo Neptune Plus multi-collector inductively coupled plasma mass spectrometer. Analytical uncertainties are 2σ of the mean; age

uncertainties include analytical errors and uncertainties in the initial 230Th/232Th ratios, which is set equal to 4.4 p.p.m. by assuming a bulk earth 232Th/238U value of 3.8. U-series ages

(Supplementary Table 1; Supplementary Fig. 2) are in correct stratigraphic order (except for one closely-spaced age pair at 60 and 64 mm in LMC-14, which have identical ages within

uncertainty), and have high precisions, in most cases better than ±1%. The stalagmite age models in years before 2,000 CE (year B2k) were determined from linear interpolation between dates;

for the minor (within uncertainty) age inversion in LMC-14, the 60-mm subsample was omitted from the linear age model. δ18O subsamples were drilled or milled from the growth axis at

intervals ranging from 0.1 to 1.0 mm, resulting in an average sub-decadal to centennial-scale time resolution. δ18O values were analyzed at the Las Vegas Isotope Science Lab, University of

Nevada Las Vegas, by phosphoric acid reaction at 70 °C in a Kiel IV automated carbonate preparation device coupled to a ThermoElectron Delta V Plus mass spectrometer, and corrected with

internal and external standards. δ18O and δ13C precisions are better than 0.08‰. δ18O and δ13C are defined as δ=(_R_sample−_R_standard)÷_R_standard × 1,000, where _R_ is the ratio of 18O/16O

and 13C/12C in per mil (‰) variations of the sample relative to the Vienna Pee Dee Belemnite (VPDB) standard (_δ_=0‰ for both oxygen and carbon). Stable isotopic data will be deposited at

the NOAA Palaeoclimatology data repository at http://www.ncdc.noaa.gov/paleo/paleo.html. COMPOSITE TIME SERIES A composite δ18O time series was constructed by interpolating the measured δ18O

time series (Supplementary Fig. S1) at a 50 year resolution and splicing into a single time series by choosing the record of highest temporal resolution, best dating or most continuous

coverage (‘Measured’ time series in Supplementary Fig. S1). Then, the composite time series was corrected for changes in the δ18O value of the ocean51 (‘Sea-water corrected’). Lastly,

because the three cave sites span 340 km of latitude and have site-water (precipitation) δ18O values that decrease by ca. 3‰ with increasing latitude, the δ18O data were normalized by the

different site-water δ18O values to plot on the same δ18O scale as LC-1. This normalization was realized via multiple regression, using winter precipitation-amount weighted δ18O values from

the central Great Basin52, supplemented with stable isotopic data of creeks and springs near Lehman Cave in Great Basin National Park53,54. The multiple regression model contained two

significant (_P_-value <0.05) variables: latitude (in decimal degrees) and altitude (in metres) to yield the equation δ18O=(latitude × −0.593718666)+(altitude × −0.001075451)+9.773431178

(_r__2_=0.65; RMSE=0.93; _P_-value =0.00022). The model has a median δ18O residual of ±0.62‰, indicating high-predictive power. The model resulted in δ18O values, relative to Leviathan Cave,

of -0.36‰ at Lehman Cave, and +1.73‰ at Pinnacle Cave, and the δ18O time series for Lehman and Pinnacle Caves were thus adjusted by these offset amounts (‘Sea and site-water corrected’ time

series in Supplementary Fig. 1). This offset correction allows for the direct comparison of the δ18O values between the sites. The resulting time series spans 174,100 years, with gaps

between 13,350 and 15,650, 20,050 and 32,300, 60,150 and 69,650 and 103,800 and 105,700 years before 2,000 CE (year B2k). year B2k, respectively. The age models (Supplementary Fig. S2) are

expressed in yr B2k. ASSESSMENT OF ISOTOPIC EQUILIBRIUM Stalagmite LC-1, the only stalagmite that was actively growing when collected, is in apparent isotopic equilibrium with cave drip

water. Using the equation of (ref. 55), a temperature of 8.3 °C, and average δ18O value of calcite deposited over the last 200 years of −11.56‰ VPDB, the drip-water δ18O value with which the

calcite is in isotopic equilibrium is −14.24‰ Vienna standard mean ocean water (VSMOW), which is identical to measured drip-water δ18O value of -14.23‰ VSMOW. The Leviathan, Pinnacle and

Lehman Cave drip water and spring isotope values plot directly on the southern Nevada winter meteoric water line (Supplementary Fig. S3), indicating they are unaffected by evaporation. The

low-drip-water δ18O values of between -12 and -14‰ VSMOW indicate a winter precipitation source, consistent with mountain recharge in the Great Basin23,29. STABLE-ISOTOPE VALUES IN MODERN

PRECIPITATION Winter precipitation, falling mostly as snow, is the dominant source of groundwater recharge in the Great Basin29. To determine the correlation between winter precipitation

δ18O and climate variables, we extracted a sub-set of 18 stations with winter δ18O values from the Friedman _et al._ analysis52, supplemented by data for Great Basin National Park. We

determined the Pearson correlation coefficients and significance levels in Microsoft Excel between precipitation-weighted winter δ18O values at each site to average winter temperature and

precipitation over the months of December–April extracted from the WorldClim database56 for each site location. The average winter temperatures were calculated as the median values of the

average-minimum and -maximum temperatures. These data (Supplementary Fig. 4) show a statistically-significant and strong correlation between winter δ18O and median temperature (δ18O=0.31 ×

Temp(DJFMA)−15.78, _r_=0.82, _P_<0.000005, _n_=19), but no significant correlation to precipitation amount (_r_=−0.35, _P_=0.14). This spatial correlation shows that temperature is a

strong and dominant control on the δ18O values of mean winter precipitation. This spatial δ18O temperature effect has a temporal corollary whereby winter precipitation δ18O values are

inversely related to the origination latitude of source moisture, with low δ18O values associated with a northerly (cold) moisture source in the Gulf of Alaska, and highest values with a

subtropical (warm) Pacific source27. Further, a detailed analysis of regional event-based δ18O of precipitation demonstrated that the lowest at-a-site δ18O values had moisture sources around

50°N, whereas the highest δ18O values had a moisture source at around 20°N in the tropical Pacific Ocean57, demonstrating that the temporal variations in δ18O at individual locations varies

strongly as a function of moisture source. Additional discussion is included in22,26. Although the modern Δδ18O/ ΔT gradient is well constrained both spatially (Δδ18O/ΔT=0.31‰ / °C) and

temporally (Δδ18O/ΔT=0.96‰ / °C), we do not quantitatively interpret the δ18O time series in terms of temperature, because (1) it is unclear which of the two Δδ18O/ΔT gradients is more

relevant, and (2) the Δδ18O/ΔT gradients may have changed over time under different climatic boundary conditions, as has been demonstrated at other sites58. However, the strong correlation

between δ18O and temperature reflects the fundamental processes of Rayleigh distillation and moisture source origination, such that colder moisture sources (for example, Gulf of Alaska) and

colder atmospheric temperatures result in lower δ18O values, and our data is highly correlated to summer insolation in a sense expected by the temperature effect. As such, we favour a

semi-quantitative interpretation of speleothem δ18O values as a paleotemperature and moisture source proxy. ADDITIONAL INFORMATION HOW TO CITE THIS ARTICLE: Lachniet, M. S. _et al._ Orbital

control of Western North America atmospheric circulation and climate over two glacial cycles. _Nat. Commun._ 5:3805 doi: 10.1038/ncomms4805 (2014). REFERENCES * Hays, J. D., Imbrie, J. &

Shackleton, N. J. Variations in earths orbit—pacemaker of ice ages. _Science_ 194, 1121–1132 (1976). Article  ADS  CAS  PubMed  Google Scholar  * Lisiecki, L. E. & Raymo, M. E. A

Pliocene-Pleistocene stack of 57 globally distributed benthic δ18O records. _Paleoceanography_ 20, 1–17 (2005). Google Scholar  * Cheng, H. et al. Ice age terminations. _Science_ 326,

248–252 (2009). Article  ADS  CAS  PubMed  Google Scholar  * Winograd, I. J. et al. Devils Hole, Nevada, δ18O record extended to the mid-Holocene. _Quat. Res._ 66, 202–212 (2006). Article 

CAS  Google Scholar  * Grayson, D. K. _The Great Basin: a Natural Prehistory_ University of California Press (2011). * Benson, L. in_The Quaternary Period in the United States_ eds Gillespie

A. R., Porter S. C., Atwater B. F. 185–204Elsevier (2004). * Morrison, R. B. in_The Geology of North America_ VOL. K-2, ed. Morrison R. B. Ch. 10,283–320Geol. Soc. Am. (1991). Google

Scholar  * Oviatt, C. G., Thompson, R. S., Kaufman, D. S., Bright, J. & Forester, R. M. Reinterpretation of the Burmester Core, Bonneville Basin, Utah. _Quat. Res._ 52, 180–184 (1999).

Article  Google Scholar  * Oviatt, C. G. & McCoy, W. Early Wisconsin lakes and glaciers in the Great Basin, U.S.A. _Geological Society of America Special Paper_ 270, 279–287 (1992).

Article  Google Scholar  * Nishizawa, S., Currey, D. R., Brunelle, A. & Sack, D. Bonneville basin shoreline records of large lake intervals during Marine Isotope Stage 3 and the Last

Glacial Maximum. _Palaeogeogr. Palaeoclimatol. Palaeoecol._ 386, 374–391 (2013). Article  Google Scholar  * Reimer, P. J. et al. Intcal09 and Marine09 Radiocarbon Age Calibration Curves,

0-50,000 Years Cal Bp. _Radiocarbon_ 51, 1111–1150 (2009). Article  CAS  Google Scholar  * Clark, P. U. et al. The last glacial maximum. _Science_ 325, 710–714 (2009). Article  ADS  CAS 

PubMed  Google Scholar  * Denton, G. H. et al. The last glacial termination. _Science_ 328, 1652–1656 (2010). Article  ADS  CAS  PubMed  Google Scholar  * Winograd, I. J. et al. Continuous

500,000-year climate record from vein calcite in Devils Hole, Nevada. _Science_ 258, 255–260 (1992). Article  ADS  CAS  PubMed  Google Scholar  * Winograd, I. J., Szabo, B. J., Coplen, T. B.

& Riggs, A. C. A 250,000-year climatic record from Great Basin vein calcite; implications for Milankovitch theory. _Science_ 242, 1275–1280 (1988). Article  ADS  CAS  PubMed  Google

Scholar  * Edwards, R. L. et al. Dating of the Devils Hole calcite vein; discussion and reply. _Science_ 259, 1626–1627 (1993). Article  ADS  CAS  PubMed  Google Scholar  * Herbert, T. D. et

al. Response: the California Current, Devils Hole, and Pleistocene climate. _Science_ 296, 7a (2002). Article  Google Scholar  * Johnson, R. G., Wright, H. E. Jr, Winograd, I. J. &

Coplen, T. B. Great Basin calcite vein and the Pleistocene time scale; discussion and reply. _Science_ 246, 262–263 (1989). Article  ADS  CAS  PubMed  Google Scholar  * Shackleton, N. J. et

al. Last interglacial in Devils Hole; discussion and reply. _Nature (London)_ 362, 596 (1993). Article  ADS  Google Scholar  * Winograd, I. J. The California Current, Devils Hole, and

Pleistocene climate. _Science_ 296, 7a (2002). Article  Google Scholar  * Herbert, T. D. et al. Collapse of the California Current during glacial maxima linked to climate change on land.

_Science_ 293, 71–75 (2001). Article  ADS  CAS  PubMed  Google Scholar  * Winograd, I. J. Discussion of "Deglacial paleoclimate in the southwestern United States: an abrupt 18.6 cold

event and evidence for a North Atlantic forcing of Termination I" by M.S. Lachniet, Y. Asmerom, and V. Polyak. _Quat. Sci. Rev._ 45, 126–128 (2012). Article  ADS  Google Scholar  *

Lachniet, M. S., Asmerom, Y. & Polyak, V. Deglacial paleoclimate in the southwestern United States: an abrupt 18.6 ka cold event and evidence for a North Atlantic forcing of Termination

I. _Quat. Sci. Rev._ 30, 3803–3811 (2011). Article  ADS  Google Scholar  * Müller, U. C., Fletcher, W. J., Milner, A. M. & Scheiter, S. Interhemispheric anti-phasing of orbitally driven

monsoon intensity: implications for ice-volume forcing in the high latitudes. _Earth Planet. Sci. Lett._ 377, 34–42 (2013). Article  ADS  Google Scholar  * Shakun, J. D., Burns, S. J.,

Clark, P. U., Cheng, H. & Edwards, R. L. Milankovitch-paced Termination II in a Nevada speleothem. _Geophys. Res. Lett._ 38 (2011). * Lachniet, M. S., Asmerom, Y. & Polyak, V.

Discussion of "Deglacial paleoclimate in the southwestern United States: an abrupt 18.6 cold event and evidence for a North Atlantic forcing of Termination I" by M.S. Lachniet, Y.

Asmerom and V. Polyak Response. _Quat. Sci. Rev._ 45, 129–133 (2012). Article  ADS  Google Scholar  * Friedman, I., Harris, J. M., Smith, G. I. & Johnson, C. A. Stable isotope

composition of waters in the Great Basin, United States; 1, Air-mass trajectories. _J. Geophys. Res._ 107, 1–14 (2002a). Google Scholar  * Lachniet, M. S. Climatic and environmental controls

on speleothem oxygen isotope values. _Quat. Sci. Rev._ 28, 412–432 (2009). Article  ADS  Google Scholar  * Winograd, I. J., Riggs, A. C. & Coplen, T. B. The relative contributions of

summer and cool-season precipitation to groundwater recharge, Spring Mountains, Nevada, USA. _Hydrogeol. J._ 6, 77–93 (1998). Article  ADS  Google Scholar  * Jouzel, J. et al. Orbital and

millennial Antarctic climate variability over the past 800,000 years. _Science_ 317, 793–796 (2007). Article  ADS  CAS  PubMed  Google Scholar  * Loulergue, L. et al. Orbital and

millennial-scale features of atmospheric CH4 over the past 800,000 years. _Nature_ 453, 383–386 (2008). Article  ADS  CAS  PubMed  Google Scholar  * Asmerom, Y., Polyak, V. J. & Burns,

S. J. Variable winter moisture in the southwestern United States linked to rapid glacial climate shifts. _Nat. Geosci._ 3, 114–117 (2010). Article  ADS  CAS  Google Scholar  * Wagner, J. D.

M. et al. Moisture variability in the southwestern United Sates linked to abrupt glacial climate change. _Nat. Geosci._ 3, 110–113 (2010). Article  ADS  CAS  Google Scholar  * Winograd, I.

J., Landwehr, J. M., Ludwig, K. R., Coplen, T. B. & Riggs, A. C. Duration and structure of the past four interglaciations. _Quat. Res._ 48, 141–154 (1997). Article  Google Scholar  *

Polyak, V., Asmerom, Y., Burns, S. & Lachniet, M. S. Climatic backdrop to the terminal Pleistocene extinction of North American mammals. _Geology_ 40, 1023–1026 (2012). Article  ADS 

Google Scholar  * Asmerom, Y., Polyak, V., Burns, S. & Rassmussen, J. Solar forcing of Holocene climate; new insights from a speleothem record, Southwestern United States. _Geology

(Boulder)_ 35, 1–4 (2007). Article  ADS  CAS  Google Scholar  * Quade, J., Cerling, T. E. & Bowman, J. R. Systematic variations in the carbon and oxygen isotopic composition of pedogenic

carbonate along elevation transects in the southern Great Basin, United States; with Suppl. Data 89-10. _Geol. Soc. Am. Bull._ 101, 464–475 (1989). Article  ADS  CAS  Google Scholar  *

Svensson, A. et al. The Greenland Ice Core Chronology 2005, 15-42 ka. Part 2: comparison to other records. _Quat. Sci. Rev._ 25, 3258–3267 (2006). Article  ADS  Google Scholar  * Currey, D.

R. An ancient bristlecone pine stand in Eastern Nevada. _Ecology_ 46, 564–566 (1965). Article  Google Scholar  * Dykoski, C. A. et al. A high-resolution, absolute-dated Holocene and

deglacial Asian monsoon record from Dongge Cave, China. _Earth Planet. Sci. Lett._ 233, 71–86 (2005). Article  ADS  CAS  Google Scholar  * Lyle, M. et al. Out of the tropics: The Pacific,

Great Basin Lakes, and Late Pleistocene Water Cycle in the Western United States. _Science_ 337, 1629–1633 (2012). Article  ADS  CAS  PubMed  Google Scholar  * Kirby, M. E., Feakins, S. J.,

Bonuso, N., Fantozzi, J. M. & Hiner, C. A. Latest Pleistocene to Holocene hydroclimates from Lake Elsinore, California. _Quat. Sci. Rev._ 76, 1–15 (2013). Article  ADS  Google Scholar  *

Benson, L. V. et al. Insights from a synthesis of old and new climate-proxy data from the Pyramid and Winnemucca lake basins for the period 48 to 11.5 cal ka. _Quat. Int._ 310, 62–82

(2013). Article  Google Scholar  * Khodri, M. et al. Simulating the amplification of orbital forcing by ocean feedbacks in the last glaciation. _Nature_ 410, 570–574 (2001). Article  ADS 

CAS  PubMed  Google Scholar  * Francis, J. A., Chan, W. H., Leathers, D. J., Miller, J. R. & Veron, D. E. Winter Northern Hemisphere weather patterns remember summer Arctic sea-ice

extent. _Geophys. Res. Lett._ 36, 1–5 (2009). Article  Google Scholar  * Walland, D. J. & Simmonds, I. Modelled atmospheric response to changes in Northern Hemisphere snow cover. _Clim.

Dyn._ 13, 25–34 (1996). Article  Google Scholar  * Beghin, P. et al. Interdependence of the growth of the Northern Hemisphere ice sheets during the last glaciation: the role of atmospheric

circulation. _Clim. Past_ 10, 345–358 (2014). Article  Google Scholar  * Droxler, A. W., Poore, R. Z. & Burckle, L. H. in_Geophysical Monograph_ 137, 240American Geophysical Union

(2003). * Berger, A. & Loutre, M. F. An exceptionally long interglacial ahead? _Science_ 297, 1287–1288 (2002). Article  CAS  PubMed  Google Scholar  * Seager, R. et al. Model

projections of an imminent transition to a more arid climate in Southwestern North America. _Science_ 316, 1181–1184 (2007). Article  ADS  CAS  PubMed  Google Scholar  * Waelbroeck, C. et

al. Sea-level and deep water temperature changes derived from benthic foraminifera isotopic records. _Quat. Sci. Rev._ 21, 295–305 (2002). Article  ADS  Google Scholar  * Friedman, I.,

Smith, G. I., Johnson, C. A. & Moscati, R. J. Stable isotope compositions of waters in the Great Basin, United States; 2, Modern precipitation. _J. Geophys. Res._ 107, 21 (2002b).

Article  Google Scholar  * Acheampong, S. Y. _Isotope hydrology of Lehman and Baker Creeks Drainages, Great Basin National Park, Nevada M.S. thesis_ University of Nevada: Las Vegas, (1992).

* Prudic, D. E. & Glancy, P. A. _Geochemical Investigation of Source Water to Cave Springs, Great Basin National Park, White Pine County, Nevada_ 40U.S. Geological Survey (2009). *

Coplen, T. B. Calibration of the calcite-water oxygen-isotope geothermometer at Devils Hole, Nevada, a natural laboratory. _Geochim. Cosmochim. Acta_ 71, 3948–3957 (2007). Article  ADS  CAS

  Google Scholar  * Hijmans, R. J., Cameron, S. E., Parra, J. L., Jones, P. G. & Jarvis, A. Very high resolution interpolated climate surfaces for global land areas. _Int. J. Climatol._

25, 1965–1978 (2005). Article  Google Scholar  * Berkelhammer, M., Stott, L., Yoshimura, K., Johnson, K. & Sinha, A. Synoptic and mesoscale controls on the isotopic composition of

precipitation in the western United States. _Clim. Dyn._ 38, 433–454 (2012). Article  Google Scholar  * Charles, C. D., Rind, D., Jouzel, J., Koster, R. D. & Fairbanks, R. G.

Glacial-interglacial changes in moisture sources for Greenland—Influences on the ice core record of climate. _Science_ 263, 508–511 (1994). Article  ADS  CAS  PubMed  Google Scholar 

Download references ACKNOWLEDGEMENTS P. Pribyl, D. Haber, S. Deveny, R. Bowersox, T. Madsen, W. Christy and D. Jacobsen provided field and lab support. Site selection supported by NSF EPSCoR

0814372 subaward; analyses supported by EAR 0521196 to UNLV and EAR 0326902 and ATM 0703353 to UNM. Sampling permission from permits # 8560 NVL0200 and GRBA-99-12. AUTHOR INFORMATION

AUTHORS AND AFFILIATIONS * Department of Geoscience, University of Nevada Las Vegas, 4505 Maryland Parkway, Las Vegas, 89154, Nevada, USA Matthew S. Lachniet * Department of Geology, Cornell

College, 600 First Street West, Mount Vernon, 52314, Iowa, USA Rhawn F. Denniston * Department of Earth and Planetary Science, University of New Mexico, 221 Yale Boulevard NE, Albuquerque,

87131, New Mexico, USA Yemane Asmerom & Victor J. Polyak Authors * Matthew S. Lachniet View author publications You can also search for this author inPubMed Google Scholar * Rhawn F.

Denniston View author publications You can also search for this author inPubMed Google Scholar * Yemane Asmerom View author publications You can also search for this author inPubMed Google

Scholar * Victor J. Polyak View author publications You can also search for this author inPubMed Google Scholar CONTRIBUTIONS M.S.L. and R.F.D. realized the experimental and field strategy;

M.S.L. completed all stable-isotope analyses and Y.A. and V.J.P. completed age dating; M.S.L., R.F.D., Y.A. and V.J.P., participated in site selection; M.S.L. wrote the manuscript with

contributions from R.D., Y.A. and V.J.P. All authors contributed to finalizing and approving the manuscript. CORRESPONDING AUTHOR Correspondence to Matthew S. Lachniet. ETHICS DECLARATIONS

COMPETING INTERESTS The authors declare no competing financial interests. SUPPLEMENTARY INFORMATION SUPPLEMENTARY INFORMATION Supplementary Figures 1-5, Supplementary Table 1, Supplementary

Discussion and Supplementary References (PDF 646 kb) RIGHTS AND PERMISSIONS Reprints and permissions ABOUT THIS ARTICLE CITE THIS ARTICLE Lachniet, M., Denniston, R., Asmerom, Y. _et al._

Orbital control of western North America atmospheric circulation and climate over two glacial cycles. _Nat Commun_ 5, 3805 (2014). https://doi.org/10.1038/ncomms4805 Download citation *

Received: 09 December 2013 * Accepted: 04 April 2014 * Published: 02 May 2014 * DOI: https://doi.org/10.1038/ncomms4805 SHARE THIS ARTICLE Anyone you share the following link with will be

able to read this content: Get shareable link Sorry, a shareable link is not currently available for this article. Copy to clipboard Provided by the Springer Nature SharedIt content-sharing

initiative