Max Berkelhammer, a student of Lowell Stott ( a prominent and excellent researcher on ocean sediments) has been carrying out research on dO18 content of bristlecones in the White Mountains. His website shows that he has an article on this research that has been accepted for G3 and CA readers should pay attention to this article when it comes out.
His website has a number of interesting conference presentations on dO18 in bristlecone, from which today’s note is drawn. dO18 levels in White Mt bristlecones changed remarkably at the start of the 20th century.
This is entirely new and important data and their interpretation is highly interesting.
First here is a figure from Berkelhammer’s PACLIM 2007 presentation online here, showing dO18 levels from 2 different bristlecone pines – showing a remarkable change in dO18 levels of about 30 from 1700-1850 to levels of under 20 in the 20th century, with the change taking place between 1850 and 1915.
Berkelhammer and Stott PACLIM Figure 2: Measured δ18O values of Bristlecone Pine cellulose; shown in black are annual values for two cores taken from trees in the same grove. The cores have excellent correlation with an R2 value of 0.82. The red line is the mean of the two cores. The shaded region (1855-1910) is used to highlight the major transition that separates the pre-1850 values from the twentieth century values. The data has an analytical uncertainty of 0.3 (VSMOW).
They observe similar changes in dO18 levels in two other proxies, with the figure below showing the bristlecone Pine δ18O compared to Santa Barbara Basin Benthic δ13C (Holsten et al. 2004) which they note as being interpreted as an upwelling proxy – a topic that we’ve visited in connection with the Arabian Sea – and Walker Lake (Sierra Nevada) δ18O (Yuan et al. 2006), which was interpreted as a lake level proxy.
To these examples, I would also add the dO18 results from the Yukon, where Fisher et al (discussed previously) reported a substantial change in dO18 levels at Mount Logan ice core and Jellybean Lake sediments, as illustrated below. Fisher et al concluded that there had been a regime change in which atmospheric circulation had been re-oriented.
(Note that the missing Thompson Bona-Churchill ice core data can be projected to be similar to the Mount Logan results – had the dO18 levels gone up, one would have expected the results to have been available for IPCC AR4 and Al Gore’s hockey stick. As matters presently stand, if lower dO18 in Yukon ice cores are attributable to changes in atmospheric circulation, one wonders how one can confidently ascribe higher dO18 values in Himalayan ice cores to global warming as opposed to changes in atmospheric circulation.)
In any event, the change in bristlecone dO18 is not isolated – and may well be related to contemporary changes recorded in other proxies. Berkalhammer and Stott then consider how such a change in dO18 could occur. They conclude that the magnitude of the isotopic shift (over 10) could plausibly be explained only by a change in provenance of moisture:
Humidity could only account for a fraction of the isotopic variability (~1.5) Magnitude of isotopic shift exceeds shallow/deep water isotopic gradient (Tang and Feng, 2001) Data from individual storms during a winter season shows difference between North Pacific storms (~-11 ) and Pineapple Express storm (~-2.5 ) can be close to 9. Could subtropical storms have been the dominant winter storm type prior to 1850?
This mid 19th century isotopic shift is correlates with the major climate shift across the northern hemisphere that is documented in a wide-range of proxy records. Geochemical modeling of the BcP cellulosic δ18O stratigraphy indicates that the only viable explanation for a 10 enrichment during the 19th century would involve a change in the primary source of rain water to the region from one dominated by mid latitude storms during the 19th century to one dominated by more isotopically depleted, high latitude storms, during the 20th century. Measurements of the isotopic composition of individual storms during the winter of 2006 illustrate the fact that the δ18OVSMOW of rain from North Pacific storms can be 9 lower than that of their subtropical counterparts, known as the Pineapple Express. We hypothesize that the large isotopic shift in the 19th century is evidence for a change in mean storm trajectories brought about by a more southerly position of the mid-latitude jet and changes in the frequency of the Pacific Decadal Oscillation. Major changes in atmospheric circulation are noted by both ice core and marine sediment records covering this period and these findings thus offer insight onto the dramatic climatic changes that occurred at the terminus of the Little Ice Age.
Pineapple Expresses sound like a topic dear to Steve Sadlov’s heart. One nuance in this explanation that I wonder about is that it doesn’t mention precipitation coming from the north. Some of the local meteorological information on the White Mountains mentions patterns that differ from southern California.
For example, the following account associates “Tonopah lows” with snowfall in the White Mountains – incorporating White Mountain precipitation patterns more with Nevada precipitation than California precipitation (at Quelccaya in Peru, the precipitation also comes from the east):
When a surface low-pressure center forms in western Nevada accompanied by an upper trough that deepens excessively to form a cyclone over the region a weather pattern known locally as a “Tonopah low” a northeasterly to southeasterly flow often brings continental polar air or recycled maritime polar air, low clouds, and snowfall to the White-Inyo Range. When such storms involve moist Pacific air, they usually bring heavy snowfall to the region; some of the biggest snowstorms recorded in the White Mountains have occurred in such circulation patterns. Precipitation from closed cyclones over the region is most frequent in spring, resulting in a spring (April or May) precipitation maximum in much of the Great Basin, in contrast to the pronounced winter maximum in the Sierra Nevada.
On infrequent occasions, usually several years apart (e.g., January 1937, January 1949, December 1972, February 1989, and December 1990), a long northerly fetch of air may bring an invasion of true Arctic air from interior Alaska or the Yukon. These episodes bring record cold temperatures to the White-Inyo Range and adjacent valleys; at such times minimum temperatures may dip to -25°F (-31°C) or below.
Most winters include one or two episodes of “warm storms,” periods of a few to several days in which very moist tropical air reaches California from the vicinity of Hawaii. In these events the freezing level may be above 10,000 ft (3,000 m), and the heavy rainfall may result in widespread flooding in much of California. It is during such storms that heavy rime icing may form on trees, structures, and power lines on high mountain ridges. This is caused by the combined effect of strong winds and supercooled clouds (composed of water droplets at air temperatures below freezing). The cloud droplets freeze on contact, building great formations of ice that grow into the direction of the wind.
Conversely, “cold storms” bring snow to low elevations, including the floor of Owen Valley and desert areas to the south and east of the White-Inyo Range. Major westerly storms that last for two or three days bring heavy accumulations of snow a foot (30 cm) or more in the valleys, and two or three times as much at the highest elevations. Very cold storms from the northwest contain less water vapor, are of shorter duration, and usually bring only a few inches (several centimeters) of snow.
As discussed previously, precipitation in the White Mountain area results primarily from the passage of cyclones with associated fronts during fall, winter, and spring; from closed cyclones in late winter and spring; and from the flow of moist tropical air from the southeast to the southwest quadrant in the summer. Annual amounts vary from 56 in (125150 mm) on the valley floors to 20 in (508 mm) or a little more at the highest elevations. Totals appear to increase right up to the crest of the range. The rate of increase averages about 1.5 to 2.5 in per 1,000 ft (120205 mm per km) rise. However, this average is difficult to apply to any one portion of the range, and the increase is not linear, being higher at upper elevations. Table 1.3 gives average monthly and annual precipitation amounts for stations within the region.
Empirical observation also indicates that the buildup of cumulonimbus clouds in summer thunderstorms is more likely to occur over specific portions of the summit upland than at random. Topographic influence on air moving into the area from characteristic directions is the probable cause. This could add a checkerboard pattern of precipitation distribution independent of more general patterns, such as the increase with elevation and from south to north. Four areas of cloud concentration are noticeable. From south to north, these are Sheep Mountain-Piute (or Paiute) Mountain, the plateau just south of White Mountain Peak, Chiatovich Flats and the area just north of the Cabin Creek-Birch Creek saddle, and the northern portion of Pellisier Flats at the head of Chiatovich Creek. Common features of the four areas are rises in elevation from south to north and broad lateral extent from west to east. Cumulonimbus clouds may form over any part of the range on any summer day, and during extensive storms all or most of the higher elevations may be cloud-covered, but initial formation and greater subsequent development more commonly occur over these four areas.
Another account of Nevada meteorology says:
it is the driest of the fifty states Passing frontal systems will typically cause a temperature fall and winds will shift to northwesterly, northerly, or even northeasterly. These frontal passages may produce gusty winds and scattered to broken mid-level cloudiness. But they will generally produce only light precipitation, if any.
Cold fronts approaching Fallon from the north during the Winter months produce some of the most intense weather observed. If the wind flow preceding the front has a northerly component, snow usually results, if it has a southerly component, rain will occur.
I think that Berkelhammer and Stott’s association of the change in bristlecone dO18 with a change in precipitation provenance is quite plausible – whether the change is from Pineapple Express to North Pacific or whether it involves some aspect of Tonopah Lows is a small nuance that isn’t material to their main point, but may be worth attending to for people with an interest in bristlecones.
I’ve corresponded with Stott about this in very cordial terms and he’s offered to analyze one of our Colorado cores when the crossdating is completed and I plan to take him up on this offer.
M. Berkelhammer and L.D. Stott. An extreme turn-of-the-century hydrologic event recorded in d18O from Bristlecone Pine tree-ring cellulose. Pacific Climate Conference. Pacific Grove, California. May 14, 2007. pdf
Jennifer Holsten, Lowell Stott and Will Berelson, 2004. Reconstructing benthic carbon oxidation rates using δ13C of benthic foraminifers Marine Micropaleontology 53, 2004, 117-132 url
Yuan, F., B. K. Linsley, S. P. Lund, and J. P. McGeehin (2004), A 1200 year record of hydrologic variability in the Sierra
Nevada from sediments in Walker Lake, Nevada, Geochem. Geophys. Geosyst., 5, Q03007, doi:10.1029/2003GC000652.