Mar 8, 2008: New U/Th ages from Petralona speleothems
Xianfeng Wang at the University of Minnesota has provided us with the ages of two more stalagmite samples from the Petralona cave in northern Greece. Sample P2 spans approximately 330-500 ka, while P3 spans 235-245 ka. We hope to analyze stable isotopes in these samples shortly, at which point we could re-date them with higher precision.
Jan 14, 2008: CSI News features article on New York drought reconstructions from Palisades trees
"CSI students find keys to history and future drought areas in Palisades trees" [more]
Tree-ring research in Palisades Park
Dec 15-17, 2007: Field expedition to Sequoia National Forest for tree-ring sampling
Following AGU in San Francisco, I organized a mini expedition to the northern district of Sequoia National Forest near Hume Lake (webcam), close to the boundary with Kings Canyon National Park. I spent three days in this area coring trees and collecting samples for an initial assessment of the dendroclimatologic potential of three conifer species: white fir (Abies concolor), incense cedar (Calocedrus decurrens), and Jeffrey pine (Pinus jeffreyi). Fortunately the weather cooperated (it can be very unpredictable this time of year) and I managed to collect several samples from a few sites at 6000-6500 feet. This forest is truly beautiful as was part-frozen Hume Lake, with low lake levels (probably due to ongoing drought in the western US) having exposed submerged rooted stumps from the time the lake was a meadow; it was dammed to form the lake in 1909 to facilitate logging. A few massive giant sequoia logs remain stranded on the lake bottom or have fully emerged with the drop in lake level. An update of the results from these samples will be posted when they've been analyzed (1-2 months). Permission to sample in this area was obtained with the help of Dr. Steve Hanna and Larry Burd of the USDA Forest Service who are gratefully acknowledged. As an aside, staying at the John Muir Lodge in Grant Grove at KCNP, was a treat. The Lodge has a beautiful cathedral-ceiling lobby with wood-burning fireplace, perfect for drying one's feet after an extended hike in the snow (not to mention the sore muscles and aching lungs after a day of increment boring at 6,000 ft!). Click here for fieldwork pictures.
Dec 10-14, 2007: Fall Meeting of the American Geophysical Union (AGU) in San Francisco
As every year this Fall AGU featured many stimulating talks and posters. Here's my personal and highly subjective list of highlights:
(a) Alan Mix showed in his talk that measurement of foraminiferal calcite Mg/Ca ratios (a paleotemperature proxy) with the Klinkhammer flow-through technique can dramatically change the character of temperature reconstructions compared with a standard "bulk cleaning" approach;
(b) Gabriel Vecchi discussed whether 20th century climate changes in the Pacific amount to El Nino- or La Nina-like patterns; he showed that different observational datasets give different answers (!), and suggested that paleoclimate data (e.g. from corals) may be better suited to settle this than actual instrumental observations (the speaker seemed unaware of the many problems and uncertainties associated with these archives);
(c) Case in point: in his talk Aldo Shemesh showed many experiments with corals where standard isotopic and trace metal approaches completely failed to record the 1997-98 El Nino event in the Pacific. In one example a coral grown in culture shut down its growth for 2-3 years and then resumed growing, leaving no trace of a hiatus in its skeleton. These and other examples tempered my enthusiasm for corals as paleoceanographic archives despite their clear advantage in resolution;
(d) David Lea gave an outstanding Emiliani Lecture on recent Mg/Ca insights into tropical climate changes during ice ages and their relationship to high latitudes;
(e) Peter deMenocal gave a provocative talk, showing that core-top Mg/Ca values from the Mid-Atlantic Ridge spanning the salinity gradient between the subtropical gyres and the equator, appear to indicate a large salinity influence on foraminiferal Mg/Ca incorporation, with troubling implications for reconstructing ocean temperatures;
(f) A very interesting session on the "divergence problem" between tree rings and temperature in northern forests, addressing a very thorny and complicated issue that truly seems to require a return to basics and reevaluation of fundamental understanding of tree growth (I thought the session was an excellent example of
self-examination by the tree-ring community, something we don't do as
well in the paleoceanographic field). At the end of the session I was not optimistic that this problem is close to being sorted out, and that makes one wonder how much confidence we can have on tree-ring based climate reconstructions, which dominate paleoclimate records of the last 1,000 years. Fortunately this problem appears to be limited in northern high latitudes today, but if it exists there today it may have existed elsewhere in the past.
(g) Finally, a brief mention of my own invited talk on Wednesday afternoon, where I showed that we can reconstruct El Nino variability with individual foraminifera from ocean sediments, and that in the mid-Holocene our calculations and data (in progress) support a complete absence of ENSO.
Nov 6, 2007: Students participate in the 2007 National Collegiate Honors Council (NCHC) conference in Denver, Colorado
Jessica Mulligan, Ray Pfaff, and Samantha Balestriere, CUNY Macaulay Honors College students, just returned from the NCHC conference where they presented results from their dendrochronology research project on tree-ring drought reconstructions in the lower Hudson River Valley (PDF of poster).
Nov 4, 2007: Oldest yet white oak from Palisades Park cored
We have just obtained our oldest yet core sample from a white oak growing in Palisades Park just south of the Alpine Lookout. The core contains at least 220 visible rings - possibly more, making this the oldest living oak we have so far identified in this park, and the first to extend back to the 18th century! More when the sample is measured... Nov 26, 2007: The earliest ring on this sample dates to 1771 - a remarkably old tree indeed (click here for a chart of the data).
View of the George Washington bridge and New York City across the Hudson River from Palisades Park, NJ.
Oct 26, 2007: Stable isotope data from Petralona speleothem acquired
Our first set of 30 paired oxygen and carbon isotope data from the P1 stalagmite just came off the mass spectrometer. The 30-cm long stalagmite has been dated between 400-450 ky BP, and was sampled every 1 cm for these initial data. The good news is that oxygen isotope values are consistent with modern day winter precipitation values of -7 to -11 per mil for d18O. The bad news is that d18O and d13C are strongly correlated, and this raises suspicion that the sample has suffered diagenetic alteration. We continue our investigation with dating and stable isotope work on two more stalagmites from the Petralona Cave.