Abstract
The South American Summer Monsoon (SASM) system governs the annual hydrologic cycle in the Amazon Basin and central Andes. It varies strongly on an annual cycle, but recent paleoclimatic records indicate that it may vary on centennial to multimillennial cycles. Speleothem deposits record isotopic variation over both short and long timescales, and have proven to track Dansgaard-Oeschger (D/O) events, which are defined as abrupt warming periods in the Northern Hemisphere. D/O events are represented in Southern Hemisphere proxies, as they impact SASM strength in the Southern Hemisphere tropics. Huagapo Cave is located in Palcamayo, Peru (11.27ËšS; 75.79ËšW; 3,850 meters above sea level) and is 2800 meters in length. Twelve speleothem deposits were collected in May of 2019. Samples were dated using the Uranium-Thorium disequilibrium dating technique, and results indicate the time range covered spans from 2,000 years BP to 440,000 years BP. Time frames not covered in the composite record from all speleothems collected include 2,500-25,000 years BP, 227,000-312,000 years BP, and 320,000-370,000 years BP. One sample, spanning from 25,021 (±53) to 63,799 (±119) years BP, was analyzed for stable oxygen (δ18O) and carbon (δ13C) isotopes with the purpose of better constraining climatic variability in the region and confirm the reproducibility of speleothem records with well-constrained D/O events within South America. Preliminary data suggest that the δ18O and δ13C results follow the amount effect variations, with strong SASM conditions indicated by decreased δ18O and decreased δ13C that reflect rainfall isotopic concentrations and the respiration of organic matter in surface soil horizons. Published speleothem data from a nearby cave was correlated with data from this study, as well as Greenland ice core data (NGRIP) and a 700,000-year sediment core from Lake JunÃn, showing the D/O events in the Southern Hemisphere tropics region aligning with increased temperatures well-constrained in NGRIP. Data from previously published work confirms that the anti-phase relationship between the Northern Hemisphere and Southern Hemisphere climate fluctuations is caused by meridional shifts in the mean position of the Intertropical Convergence Zone (ITCZ), which changes location based on warming in different hemispheres. The increased warming in the Northern Hemisphere during D/O events caused a likely northward shift of the ITCZ, and a corresponding decrease in strength of the SASM in South America.
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VideoObject
Rights Statement
In Copyright - Educational Use PermittedAbstract
The South American Summer Monsoon (SASM) system governs the annual hydrologic cycle in the Amazon Basin. It varies on an annual cycle, but recent paleoclimatic records indicate that it may also vary on centennial to multimillennial cycles. Speleothem deposits record isotopic variation over both short and long timescales, and have proven to track Dansgaard-Oeschger (D/O) events, which are defined as abrupt warming periods in the Northern Hemisphere. D/O events are represented in Southern Hemisphere proxies, as they impact SASM strength in the Southern Hemisphere. Huagapo Cave is located in Palcamayo, Peru (11.27˚S; 75.79˚W; 3,850 meters above sea level) and is 2800 meters in length. Twelve speleothem deposits were collected in May of 2019. Samples were dated using the Uranium-Thorium dating technique, and results indicate the time range covered is 2,000 years BP to 440,000 years BP. Time frames not covered include 2,500-25,000 years BP and 227,000-312,000 years BP. One sample, spanning from 63,799 (±119) to 25,021 (±53) years BP, was analyzed for stable oxygen (δ<sup>18</sup>O) and carbon (δ<sup>13</sup>C) isotopes to better constrain climatic variability and confirm the reproducibility of one published speleothem record that documents the impact of D/O events in the Peruvian Andes. Preliminary data suggest that the δ<sup>18</sup>O and δ<sup>13</sup>C reflect amount effect variations, with strong SASM conditions indicated by decreased δ<sup>18</sup>O and decreased δ<sup>13</sup>C that reflect rainfall isotopic concentrations and the respiration of organic matter in surface soil horizons, respectfully. Data from this study shows that the anti-phase relationship between the Northern Hemisphere and Southern Hemisphere climate fluctuations is caused by meridional shifts in the mean position of the Intertropical Convergence Zone (ITCZ), which changes location based on warming in different hemispheres. The increased warming in the Northern Hemisphere during D/O events caused a likely northward shift of the ITCZ, and a corresponding decrease in strength of the SASM in South America.
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Thesis
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In Copyright - Educational Use PermittedAbstract
Peruvian speleothems have been shown to be excellent recorders of paleoclimate by tracking changes in rainfall amount through oxygen isotopes in calcite. Measured changes in rainfall amount have been attributed to changes in the intensity of the South American Seasonal Monsoon (SASM). High insolation in the Southern Hemisphere and low insolation in the Northern Hemisphere is believed to increase the meridional SST gradient, leading to a southerly migration of the mean position of the Inter-Tropical Convergence Zone (ITCZ) and strengthening of the SASM intensity. Conversely, a decrease in Southern Hemisphere insolation and an increase in Northern Hemisphere insolation is believed to have led the ITCZ to a more northerly mean position and weakening of SASM intensity. I present a record from speleothem 19-11, which grew in Pacupahuain Cave between 167,068 yrs B.P. and 135,165 yrs B.P., also known as the penultimate glacial period or Marine Isotope Stage 6 (MIS 6). The ?<sup>18</sup>O record from 19-11 shows exceptional agreement with overlapping speleothem records from nearby Huagapo Cave (HC). All of these records are anti-phased with 11°S January insolation, supporting the idea that shifts in the mean position of the ITCZ modulate SASM intensity. From 165 ka to 150 ka an increase in ?<sup>18</sup>O occurs contemporaneously with a decrease in 11°S Jan insolation. This period of time reflects a broad decrease in SASM intensity, a hypothesis corroborated by decreased sediment input into regional lake records. ?<sup>18</sup>O values are lower at the beginning and end of the 19-11 record, coinciding with 11°S Jan insolation highs. Within long-term insolation driven changes in ?<sup>18</sup>O, the 19-11 record has rapid oscillations that are also seen in the HC records. Previous researchers have attributed these rapid fluctuations to high-latitude Northern Hemisphere forcing. Increased temperature in the Northern Atlantic and ice sheet melt coincides with apparent weakening of the SASM. This relationship is explained by a weakening of SST gradient and northern migration of the ITCZ. The true cause of this ice melt and increase in Northern Hemisphere temperatures is not fully understood, however, they show remarkable similarity to events recorded in other proxies during MIS 2. When compared to Chinese and Mediterranean speleothem records it is clear that some of these short-term fluctuations, namely the 161-159 ka event, have profound global significance. The cause and regional effects of short-term oscillations is an important topic for future work.
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In Copyright - Educational Use PermittedAbstract
This abstract volume contains the program and extended abstracts for 39 presentations at the Annual Mohawk Watershed Symposium. The focus this year is on water quality.This is the 9th annual Mohawk Watershed Symposium and over the years the meeting has taken on an important role in unifying and galvanizing stakeholders in the Basin. Building and sustaining a coalition of concerned and invested stakeholders allow us to be informed about important issues that affect water quality, recreation opportunities, and other developments in the basin. This was a big year in the Watershed with a number of exciting and interesting developments. The NYS Canal System was designated a National Historic Landmark and this designation places the currently operating canal system among the premier historic sites in the United States. In addition, this year we celebrate the 200th anniversary of the Canal, it is important to think about how the canal has affected NY State and the watershed. Earlier in 2016, the Erie Canal, which is a big part of the State Canal Corp, was taken over by the NY Power Authority (NYPA). Since 1992 it was under the Thruway Authority, and this new transfer is certainly an interesting development as the Canal struggles with costs, some of which are a hangover from Irene in 2011. This last summer was a pretty dry, and drought and near drought conditions affected much of the basin. In the early part of summer 2016, the Canal Corporation directed the NYPA to reduce releases from Hinckley Reservoir according to the 2012 Operating Diagram. The newly completed Mohawk Valley Gateway Overlook Bridge in Amsterdam was funded through the 2005 Rebuild and Renew New York Transportation Bond, and this development is part of an effort to look to the River for economic and cultural transformation in river-lining cities on the Mohawk. Water contamination, brownfields, and water quality are intricately intertwined. PCBs, PFOS and PFOA, Pb, microplastics, and other toxins in our environment and our drinking water dominated this past year's headlines. Locally we are making progress: Schenectady had one of the more contaminated brownfields in the basin, and the important remediation effort allowed this river-lining property to be developed into the new Rivers Casino, which opened in February of 2017. This is an important lesson in cleaning brownfields, and development of urban areas in communities that are along the River. Our infrastructure needs attention because its failure is affecting water quality. One of the sad stories of the past year is the sewage leak in Amsterdam where millions of gallons of raw sewage has dumped into the Mohawk. Discovered in July 2016, the spill continues (March 2017), and this has become symbolic of the struggle to fix our aging infrastructure and its impact on water quality in the Basin. Amsterdam will receive millions from the state Water Infrastructure Improvement Act and loans from the Clean Water State Revolving Fund. Some positive news from the upper part of the watershed as money and work has gone into improving the sewage system in Utica / Oneida county. Once done, the project will reduce the amount of sewage that flows into the Mohawk River by reducing the reliance on Combined Sanitary and Sewer outfalls. There is hope that our aging infrastructure, and thus water quality, is being addressed at the State and Federal level. The Water Infrastructure Improvements act passed the U.S. House of Representatives and was subsequently signed by President Obama. The bill included Representative Tonko's AQUA Act and legislation updating the Safe Drinking Water Act. There has been considerable activity in the State, one highlight was the recent introduction of the Safe Water Infrastructure Action Program (SWAP) bill (S.3292/A.3907) introduced by Senator Tedisco and Assemblyman Steck in February 2017, which is designed to fund and maintain our local infrastructure including water, sewer, and storm water. We are making progress in the Mohawk Watershed, and the Symposium will highlight much of the new and exciting work that has happened over the last year. We are seeing money flow in the basin to address watershed science and education, and some of that money has gone directly to water quality studies. The NY Department of Environmental Conservation (NYSDEC) awarded more than $155,000 in Mohawk River Basin Program grants for four projects in the Mohawk River Basin Watershed. Results from these four projects will be presented this year as part of the invited presentations at the 2017 Symposium. We are indebted to our sponsors NYSDEC for their continued support, which helps to make each Symposium a success. We appreciate support from Cornell and from the Union College Geology Department. This year we have 39 presentations to shape the discussion and dialog. Some of these presentations are a direct result of funding from the new grants program at the NYSDEC that is aimed at fostering the five items on the Mohawk Basin Action agenda. We continue to see new ideas, many of them presented by students from a number of different educational institutions, this growth in student participation is both exciting, and a welcome sign of continued progress. By the end of the day, the Mohawk Watershed Symposium series will have been the forum for 281 talks, posters, and special presentations since inception in 2009.
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