March 2012 Archives

Ancient hazards, modern problems

Our readings next week will be real fire-and-brimestone stuff. We'll start with a classic study by Tom Swetnam and Julio Betancourt that first identified the role that ENSO plays in synchronizing wildfire across the southwestern United States. Then we'll move up the coast to look at geomorphic evidence left behind by ancient earthquakes. Finally, we'll read a more recent paper from Nature that uses sedimentary sequences to chart the course of Atlantic hurricanes over five millennia.

Atwater and Yamaguchi, Sudden, probably coseismic submergence of Holocene trees and grass in coastal Washington state

Swetnam and Betancourt, Fire-southern oscillation relations in the southwestern United States

Donnely and Woodruff, Intense hurricane activity over the past 5,000 years controlled by El Nin ̃o and the West African monsoon

REMINDER We are only three weeks away from your second in-class presentation, with this set focused on climatic and environmental change in your study region during the Holocene. As before, I'll ask each of you to submit a list of 10 references in advance. Those lists will be due in class on April 11.


Next week, we'll discuss one of the main ways that paleoenvironmental data is applied to real-world problems in the field of resource management. I've selected three papers that deal with the subject of 'megadroughts', past droughts that were either more severe or more prolonged than the droughts that occurred during the last century. These studies use different proxies to explore drought history in three separate regions but the underlying message is the same: the modern period does not reflect the full range of variability exhibited by critical aspects of North American hydrology.

Meko et al., Medieval drought in the upper Colorado River basin

Laird et al., Lake sediments record large-scale shifts in moisture regimes across the northern prairies of North America during the past two millennia

Stine, Extreme and persistent drought in California and Patagonia during mediaeval time

Conroy poster 2012.jpg
Also this week, my lab and Department of Geography are hosting a lecture by Dr. Jessica Conroy (Georgia Tech), who'll be discussing her paleolimnological work on dust flux and climate change in Tibet. Jess is a fine young scientist who gives a great talk, so please attend if you'd like!

Friday. March 23 2012
Blegen 445
Coffee & Cookies 3:15 pm, Talk 3:30 pm

"Shaking out the dust: Understanding long-term dust variations and their link to climate in the Himalayas and southern Tibetan Plateau"
Dr. Jessica Conroy, School and Earth and Atmospheric Sciences, Georgia Tech

Dust over the southern Tibetan Plateau and the Himalayas has important feedbacks on glacial melting and the Asian monsoon, but little is know about dust variability over the last millennium. Some paleorecords reveal an increase in 20th century dust hypothesized to be due to human land-use changes, but other studies suggest links between dust variability and large-scale climate modes. In this study we present a 1000-year proxy record of dust from a lake in southwestern Tibet. Our inferred dust record covaries strongly with dust content in Dasuopu ice core, located over 400km to the east of our site. Although the 20th century increase in dust content in Dasuopu is attributed to human activity, our analysis indicates increased dust content covaries with both instrumental and reconstructed summer Arctic Oscillation (AO) index values from AD 1650 to present, with increased dust deposition occurring during more positive AO summers. As the AO is projected to remain in its positive phase in coming decades, we may expect a dusty future in southern Tibet and the Himalayas, with implications for receding Himalayan glaciers and Asian monsoon precipitation.

Reminder: Presentations this week

I hope everyone is enjoying break week. This Wednesday we're back at it with presentations on the modern climate history of our study regions. Each of you will have 15 minutes to introduce us to your study region, explain the major features of its climate and describe how its climate has varied during the modern period. Because this topic is still very broad, you'll have to make choices about what topics are critical for your presentation and which ones can be left to your final paper.

Possible questions (based on our discussion in class) you might address
What is the seasonality of your region's climate? How is regional climate influenced by major climate modes like ENSO or the PDO? What are the most important climate events (for example, droughts or pluvials) that occurred in the modern period? How is climate variability in your location similar or dissimilar to conditions elsewhere?

If you would like to use presentation software, please bring your own laptop or save your graphics on a flash drive.

See you Wednesday!


Next week we'll slip into a lower gear and discuss how the climate system changes over longer timescales (decades to several decades). We'll start with a paper introducing us to the Pacific Decadal Oscillation, which is similar to ENSO in many ways but has its own distinctive flavor. We'll then read a short (but technical) paper on the physical dynamics of the PDO, along with a proxy-based estimate of this system during the last thousand years.

If I recall correctly, Max and Eric will lead our discussion while the rest of us will be responsible for contribution our own questions and comments about this set of articles.

As a reminder, your responses to Assignment #1 (the NCEP/NCAR Reanalysis) are due at the beginning of class. I'd also like you to give me your set of 10 articles related to the modern climate of your study area. I'll return comments on your article list as soon as I can, so you can have feedback before Spring Break.

Mantua and Hare, 2002, The Pacific Decadal Oscillation

Newman et al., 2003, ENSO-forced variability of the Pacific Decadal Oscillation

MacDonald and Case, 2005, Variations in the Pacific Decadal Oscillation over the past millennium

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