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1. Regional and Local Stratigraphic Markers in Three Hudson River Cores Taken Near Peekskill, New York: Core LWB 4-5

   Abdul, B.; Adeghe, S.; Diallo, M. B.; McCann, B.; Abbott, D. H.; Bostick, B. C.; Chang, C.; Block, K. A. (December 2018, American Geophysical Union, Fall Meeting 2018, abstract #B53I-2167)

   We have been studying the stratigraphy of core LWB 4-5 taken in 2001 in the Hudson River 1.5 km north of the transit of the Peekskill meteorite in October 1992. We measured magnetic susceptibility and elemental composition at 1 cm intervals down to 50 cm and then at 5 cm intervals down to 108 cm. Magnetic susceptibilities are unusually high (above 20 cgs units) from 12-19 cm and again at 31 cm. The level at 31 cm contains mm-sized fragments of Fe oxide. X-Ray Fluorescence spectroscopy revealed high Ni/Cr levels concentrated from 9-11 cm and again below 97 cm. We found tektite-like spheroids, dumbbells and teardrops from 8-15 cm depth. They are glasses and they contain appreciable K, consistent with an origin as true tektites but we have not identified the source. Overall, we interpret the high susceptibility, high Ni/Cr and possibly tektite bearing layer as a resulting from the fall of one of the bodies postulated to have fallen with the Peekskill meteorite in 1992. A 1992 age for the top of the Peekskill layer at 8-9 cm depth is consistent with a uniform sedimentation rate in the core and the occurrence of the base of modern Pb at 97 cm depth. From previous work on cores from Central Park Lake, the base of modern Pb represents the year 1880 A.D. We also found other prominent horizons whose ages fit a linear sedimentation rate model. We found a step change in As/Pb ratio whose inferred age matches 1988, the year when Pb and Cu arsenide were banned as pesticides. Our core exhibits peaks in Ca and Sr content and a minor susceptibility peak at 17.5 depth that may represent the 1980 "Great Catskill Toilet Flush" Hudson River flood event. The Catskills contain abundant marine limestone that could serve as a source for Ca and Sr. A prominent susceptibility peak at 37.5 cm could represent a flood in 1955. We also found a peak in Pb at 50 cm depth whose inferred age matches that of the cessation of incinerator burning in 1938. 137Cs and 210Pb ages are in progress and may be available by the time of the meeting. The high Pb and As levels in parts of LWB 4-5 are supported by examination of the coarse fraction. We found two bright orange grains, both with carbon rich coatings. One grain analyses on the X-ray analyzer of an SEM as 8%C, 70% Pb, 17%As and 2% Cu. The second grain analyzes as 10% C, 43% Pb, 1% Ca, 2% P, 27% As, 4% Fe, 2% Ni, 1% Si, and 6% Zn. All analyses are in wt.% on an oxygen free basis. 

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2. Can We See Dust from the 1992 Fall of the Peekskill Meteorite in Hudson River Sediments and Can We Use It as a Stratigraphic Marker?(Regional and Local Stratigraphic Markers in Three Hudson River Cores Taken Near Peekskill, New York: LWB4-1)

   Diallo, M. B.; McCann, B.; Abdul, B.; Adeghe, S.; Abbott, D. H.; Bostick, B. C.; Chang, C.; Block, K. A. (December 2018, American Geophysical Union, Fall Meeting 2018, abstract #B53I-2168)

   We have been studying the stratigraphy of core LWB4-1 taken in 2001 in the Hudson River about 100 meters north of the calculated transit path of the Peekskill meteorite in October 1992. We measured magnetic susceptibility at 1cm intervals from 0 -70 cm depth and found a layer with a magnetic susceptibility of 11 cgs units at 6 cm depth. This is the highest susceptibility in the top 40 cm of the core. Scanning X-Ray Fluorescence spectroscopy revealed the high susceptibility layer at 6 cm depth is part of a 3 cm interval with a high Ni/Cr ratio, but the depth of the peak in the Ni/Cr ratio is poorly resolved due to measurement error. We plan to dry and homogenize discreet samples for analysis on bench top XRF to reduce Ni and Cr error. Based on our identification of the base of modern Pb at 68 cm depth, the top 40 cm of the core covers the time interval from 2001 to 1930. From previous work on Central Park Lake, the base of modern Pb represents the year 1880 A.D. A uniform sedimentation rate model is supported a peak in Pb and As at 8 cm depth. The peak might represent the 1988 ban on the use of Pb arsenide and the start of use of DDT as a pesticide. We found a second peak in Pb at 37.5cm potentially from 1938, the date at which incineration was banned in New York City. We found a third peak in Pb at 50.5cm that might be from World War I around 1914. We found two deeper susceptibility peaks of 12 cgs at 43 cm and 8 cgs at 59 cm. These peaks could represent major Hudson River floods in 1927 and 1903. 137Cs and 210Pb 210 dating are in progress and will help us to determine if our age model is correct. Also, our core exhibits a distinct increase in Ca content starting at 18-25 cm depth and increasing towards the top of the core. This increase could be due to increased erosion, anthropogenic inputs or increased dissolution of CaCO3 rich rocks. We are measuring CaCO3 in the core to better determine the origin of this increase of Ca. 

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3. The Paleogeography of Laurentia in Its Early Years: New Constraints From the Paleoproterozoic East‐Central Minnesota Batholith

   https://doi.org/10.1029/2021TC006751  

   Swanson‐Hysell, Nicholas L.; Avery, Margaret S.; Zhang, Yiming; Hodgin, Eben B.; Sherwood, Robert J.; Apen, Francisco E.; Boerboom, Terrence J.; Keller, C. Brenhin; Cottle, John M. (May 2021, Tectonics)

   Abstract Theca. 1.83 Ga Trans‐Hudson orogeny resulted from collision of an upper plate consisting of the Hearne, Rae, and Slave provinces with a lower plate consisting of the Superior province. While the geologic record ofca. 1.83 Ga peak metamorphism within the orogen suggests that these provinces were a single amalgamated craton from this time onward, a lack of paleomagnetic poles from the Superior province following Trans‐Hudson orogenesis has made this coherency difficult to test. We develop a high‐quality paleomagnetic pole for northeast‐trending diabase dikes of the post‐Penokean orogen East‐Central Minnesota Batholith (pole longitude: 265.8°; pole latitude: 20.4°; A₉₅: 4.5°; K: 45.6 N: 23) whose age we constrain to be 1,779.1 ± 2.3 Ma (95% CI) with new U‐Pb dates. Demagnetization and low‐temperature magnetometry experiments establish dike remanence be held by low‐Ti titanomagnetite. Thermochronology data constrain the intrusions to have cooled below magnetite blocking temperatures upon initial emplacement with a mild subsequent thermal history within the stable craton. The similarity of this new Superior province pole with poles from the Slave and Rae provinces establishes the coherency of Laurentia following Trans‐Hudson orogenesis. This consistency supports interpretations that older discrepant 2.22–1.87 Ga pole positions between the provinces are the result of differential motion through mobile‐lid plate tectonics. The new pole supports the northern Europe and North America connection between the Laurentia and Fennoscandia cratons. The pole can be used to jointly reconstruct these cratonsca. 1,780 Ma strengthening the paleogeographic position of these major constituents of the hypothesized late Paleoproterozoic supercontinent Nuna. 

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4. Can We Use Unusual Events to Date Local Sediments and to Develop a Longer Pollution and Volcanic Ash History for the Hudson River?

   Noble, Josephine; Abbott, Dallas (December 2024, American Geophysical Union)

   We sought to develop a longer and more robust history of pollution in the Hudson River by studying LWB1-8, a high sedimentation rate core (~1 cm/yr) retrieved near Yonkers, NY. The sediment has been affected both by industrial pollution and natural disasters such as distant volcanic eruptions. In order to study this core, we analyzed its elemental composition in a variety of ways. Previous data from ITRAX scanning of the core years ago was lined up with new elemental analyses done with an XRF machine in order to pick which layers may be the most likely to contain volcanic ash. If ash particles were deemed likely in these layers, samples were run through a Franz, or magnetic materials were separated out using a Nb magnet. Then, particles of potential ash were picked out by hand. These ash candidates were then run through an SEM machine to provide a more in-depth elemental analysis of the particles as well as obtain high-resolution photos of them. Peaks in uncalibrated Ni, Ti, and SI (peaks in counts) from the ITRAK can be used to locate the depths of prospective volcanic ash layers. Ni peaks were especially good at identifying which layers may contain volcanic ash. .We found at least four layers containing volcanic ash , but there is still uncertainty about their source volcanoes. Many of the volcanic ash particles have very high Fe and very low K contents. These likely come from explosive Icelandic eruptions like those of Hekla. Other ashes have very low Fe, higher K and higher Si. These ashes likely come from volcanic arcs located at high latitudes, such as the Cascade and Aleutian arcs. This experiment has shown that it is possible to find volcanic ash in Hudson River cores. However, the number of ash particles we have retrieved so far is very small, from one to nine per age horizon. We do best at finding ash below 100 cm, where there is little industrial pollution. In future, we need to refine our methods of segregating ash from industrial debris. We must also analyze our ash particles on a microprobe and an ICPMS to determine their source volcanoes. Only then can we convert our measurements of metals versus depth into a pollution history. 

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5. Species invasions shift microbial phenology in a two-decade freshwater time series

   https://doi.org/10.1073/pnas.2211796120  

   Rohwer, Robin R.; Hale, Riley J.; Vander Zanden, M. Jake; Miller, Todd R.; McMahon, Katherine D. (March 2023, Proceedings of the National Academy of Sciences)

   Invasive species impart abrupt changes on ecosystems, but their impacts on microbial communities are often overlooked. We paired a 20 y freshwater microbial community time series with zooplankton and phytoplankton counts, rich environmental data, and a 6 y cyanotoxin time series. We observed strong microbial phenological patterns that were disrupted by the invasions of spiny water flea ( Bythotrephes cederströmii ) and zebra mussels ( Dreissena polymorpha ). First, we detected shifts in Cyanobacteria phenology. After the spiny water flea invasion, Cyanobacteria dominance crept earlier into clearwater; and after the zebra mussel invasion, Cyanobacteria abundance crept even earlier into the diatom-dominated spring. During summer, the spiny water flea invasion sparked a cascade of shifting diversity where zooplankton diversity decreased and Cyanobacteria diversity increased. Second, we detected shifts in cyanotoxin phenology. After the zebra mussel invasion, microcystin increased in early summer and the duration of toxin production increased by over a month. Third, we observed shifts in heterotrophic bacteria phenology. The Bacteroidota phylum and members of the acI Nanopelagicales lineage were differentially more abundant. The proportion of the bacterial community that changed differed by season; spring and clearwater communities changed most following the spiny water flea invasion that lessened clearwater intensity, while summer communities changed least following the zebra mussel invasion despite the shifts in Cyanobacteria diversity and toxicity. A modeling framework identified the invasions as primary drivers of the observed phenological changes. These long-term invasion-mediated shifts in microbial phenology demonstrate the interconnectedness of microbes with the broader food web and their susceptibility to long-term environmental change. 

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