An alternative explanation for the precipitation changes over North America during the mid-Holocene is changes in the tropical Pacific.
I don't fully get why these two things are mutually exclusive, as they note I think this kinda fits.
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Similarly, patterns of change in rainfall-sensitive proxies across western North America are in better agreement with simulated win-ter precipitation in simulations with prescribed vegetation and the PDO-like SST pattern (using the Gwet’s AC and Cohen’s Kappa metrics; Fig. 3, Extended Data Fig. 7, Supplementary Table 4 and Supplemen-tary Discussion). Both proxies and winter precipitation anomalies display a tripole pattern, with widespread drying over the Southwest United States, wetter conditions over the Pacific Northwest and dry-ing along the coast of Alaska (Fig. 3b), a pattern that is similar to the response seen in instrumental data during the negative phase of the PDO33 when the Aleutian Low is also anomalously weak (Extended Data Fig. 5)
This I very much buy and think is cool
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This is evident in a distinct pattern of SST changes over the North Pacific, with intense surface warming extending across the mid- to high-latitude western Pacific surrounded by a ‘horseshoe’ pattern of minimal surface warming or cooling to the east and a weak La Niña-like pattern in the tropical Pacific (Fig. 3b).
2 things about this: (1) To me, this doesn't really look that much like the PDO. They say they get a significant correlation between it and the historical PDO so OK, sure, but I'm guessing there's a few different ways to do the test. (2) Fig 3B looks more like the positive phase of the PDO than the negative phase to me? We can pull up another image. The weird thing is that they do have a La Niña response at the veeeeery bottom margin (which would be associated with PDO-) but it's hard to tell. I think I'd need to talk to someone about what this figure is actually showing.
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Winter precipitation tends to have stable isotope values that are significantly more negative
Is it somehow a convention in these short format papers to not discuss the chain lengths in the body of the text? They say in methods it's 28-30 cause they want terrestrial. If you were a reviewer would it be fair to ask them to include more of this in the body? I guess they're pretty explicitly not writing for a leaf wax crowd if they're ok avoiding this discussion
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coherent shifts in winter precipitation
Woah why did we all of a sudden jump to decreases in winter precip?
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seasonal distributions of modern precipitation isotopes to estimate the range of possible winter and summer precipitation contributions consistent with the leaf-wax isotope records (
It's been interesting to discuss mixing models in here and realize all the ways they can be applied in sketchy/problematic ways. Maybe it'd be helpful to discuss what some of the most common sins against good mixing model practice are here and we can see if this use case clears the bar?
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However, the magnitudes of past and current precipitation deficits associated with this North Pacific response are systematically underestimated in models,
As we get better at proxy system modeling and we start comparing our paleo data more directly to model output this finding seems like it's getting reproduced in many different contexts
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