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Paleodust:
Varves are lake mud deposits consisting of alternating annual layers of sediments. The white band indicates spring deposition, whereas the dark bands indicate fall deposition. Similar to counting tree rings on a tree, we can determine a timeline of accumulation and ask important questions.
These questions include the following:
What does the varve record tell us about dust accumulation? When is there more dust accumulation: during droughts, pluvials, or normal years?
How can the varve record be used to reveal climate cycles and land disturbances?
Why is learning about the varve record important?
How can the varve record and tree ring data inform human disturbances, such as colonization of the Southwest, the Dust Bowl of the 1930s, and the 1950s Drought?
What about megadroughts and megapluvials (epic pluvials)?
How can the varve record inform modern dust accumulation?
What is the story of dust in the American Southwest? Why is there an excursion of dust fluctuation in the 1600s and then increased uncertainty thereafter? Perhaps, it has to do with the Doctrine of Discovery to exploit and dispossess the Indigenous peoples of their lands. In 1680, Tewa leader Po'pay successfully organized the first decolonization campaign, the so-called Pueblo Revolt. However, in 1692, the Spanish sent Diego Vargas and other Franciscan fathers to negotiate a truce/reconquest with the Pueblo Peoples. By the time Jesuit Father Eusebio Francisco Kino arrived to southern Arizona in the 1690s, there were already at least 100,000 cattle, and he added about 4,200 cattle and furthered unsustainable agriculture to the peoples of the Southwest (Officer, 1993).
We speculate that the introduction of those first livestock was more responsible for the land degradation and enhanced dust emissions than the millions of cattle and sheep in the 20th century. In the 20th century, we speculate that there is a direct connection between drought and dust and they are negatively correlated; the lack of soil moisture leads to higher dust emissions.
The United States Department of Agriculture census records focus on the 20th century because southwestern territories did not gain statehood until the 20th century. We believe that land disturbance was the main culprit in the dust fluctuation excursion, however, we need more evidence.
For example, what is the carrying capacity of livestock on a fresh arid to semi-arid landscape? How can we model the cattle numbers that devastate a landscape and produce dust emissions detectable by lake catchment records?
Additionally, how can traditional and local knowledge help better piece together the story of dust in the last 300 years and how can archaeology serve as a tool to understand pre-contact conditions?
The varve record of this study comes from Columbine Lake, Colorado, situated in the alpine region of the southern Rockies.
The varve record extends back to more than 3000 years. This record covers a maximum of 1358 BCE to 2016 CE.
Wupatki National Monument, north of Flagstaff, Arizona. Haboob can be seen towards the north (Navajo Nation). Photo taken August 31, 2024.
Other questions to ponder: Can this varve record show wildfire events and the eruption of Sunset Crater Volcano in 1084-1085 CE?
Methods
Methods
Point counts of dust in the varve record were made in the first phase of this project at the century scale (Arcusa et al., 2022).
Based on these counts, an algorithm in R was developed to determine dust flux and sedimentation rates. The code is run with 900 ensemble determinations.
PDSI data was obtained from the North American Drought Atlas and GridMET.
Results (so far)
Results (so far)
What you are seeing are the last 2000 years for PDSI (state of Arizona) and dust accumulations (dust fluxes) for Columbine Lake varves. PDSI for Arizona was selected because most of the dust accumulated in this alpine lake derives from upwind sources, in this case, Arizona. The PDSI data was obtained from the North American Drought Atlas and gridMET.
PDSI is the Palmer Drought Severity Index and it is derived from tree ring chronologies and proxy for soil moisture. JJA = June, July, August.
xEns: X and X.1 are two random ensemble members from the 900 runs in counting dust in the varve record .
Historical records (Oñate, Peralta, Kino, Culbert, Love, etc) 1540-1900 and United States Department of Agriculture livestock inventory records,
1900-2020.
Upwind/adjacent states = Arizona, New Mexico, Utah.
1540s: Francisco Vasquez de Coronado brings 150 cattle and 5000 sheep to the Southwest
1598: Governor Juan de Oñate brings 1600 cattle, 3400 sheep, other animals, and exotic plants to the colony of San Juan de Los Caballeros/San Gabriel del Yunque-Ouingue, Nuevo Mexico
1690s-1700: 100,000 cattle in the Southwest and Eusebio Francisco Kino brings over 4000 cattle to Pimería Alta (modern day Arizona)
XIX century: Mexican independence (1821), U.S. Manifest Destiny (Homestead Act of 1863)
XX century: Taylor Grazing Act of 1934
XXI century: Further development of the U.S. Southwest
Historical records (Oñate, Peralta, Kino, Culbert, Love, etc) 1540-1900 and United States Department of Agriculture livestock inventory records,
1860-2017.
Upwind/adjacent states = Arizona, New Mexico, Utah.
Please note that these livestock numbers only reflect what was recorded by primary and secondary U.S. sources. In order to find more precise numbers, more research is required in the archives of official Spanish and Mexican sources from the XVII-XIX centuries.
Why past dust matters?
Why past dust matters?
Droughts and pluvials impact dust flux emissions
pluvial of the early 20th century and subsequent droughts later in the same century
Colonialism, industrialization, land management (land use), and policies have caused more dust sources and emissions
e.g., Doctrines of Discovery of 1452-1537, Coronado Expedition of 1539-1542, New Mexico Colonization beginning 1598, Homestead Act of 1863, Taylor Grazing Act of 1934
Dust reduces albedo on snow causing flooding and water shortages on the watersheds downstream
The past informs current air quality and identifies actions that can be taken to mitigate air and land degradation.
The journal of Father Escalante of the journey of 1776 describes the meeting of various Indigenous groups in New Mexico, Colorado, Arizona, and Utah: https://issuu.com/utah10/docs/volume_11_1943/s/68476
As this journal describes, the West was not devoid of people ("terra nullius"), but instead was occupied by the Indigenous caretakers of the landscape. Yes, these areas were devoid of European settlements. However, it underscores the importance of what the initial European settlements in New Mexico had on the ecological impacts and geomorphic responses on the landscape.
Conclusion
Conclusion
Based on the evidence from the dust records of lake deposits in the San Juan Mountains, in particular the Columbine Lake varves, we conclude that Spanish colonization initiated landscapes degradation, only to be exerbated by Manifest Destiny and industrialization of the West. Therefore, the Orbis GSSP is the best option for the golden spike for the onset of the Anthropocene epoch. Since the mid-1990s, the amount of dust accumulation is unprecedented in the archives, something not seen in 11,000 years.
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