Publications by authors named "S Aarons"

32 Publications

Titanium isotopes constrain a magmatic transition at the Hadean-Archean boundary in the Acasta Gneiss Complex.

Sci Adv 2020 Dec 9;6(50). Epub 2020 Dec 9.

Origins Laboratory, Department of the Geophysical Sciences and Enrico Fermi Institute, The University of Chicago, Chicago, IL 60637, USA.

Plate subduction greatly influences the physical and chemical characteristics of Earth's surface and deep interior, yet the timing of its initiation is debated because of the paucity of exposed rocks from Earth's early history. We show that the titanium isotopic composition of orthogneisses from the Acasta Gneiss Complex spanning the Hadean to Eoarchean transition falls on two distinct magmatic differentiation trends. Hadean tonalitic gneisses show titanium isotopic compositions comparable to modern evolved tholeiitic magmas, formed by differentiation of dry parental magmas in plume settings. Younger Eoarchean granitoid gneisses have titanium isotopic compositions comparable to modern calc-alkaline magmas produced in convergent arcs. Our data therefore document a shift from tholeiitic- to calc-alkaline-style magmatism between 4.02 and 3.75 billion years (Ga) in the Slave craton.
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http://dx.doi.org/10.1126/sciadv.abc9959DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7725461PMC
December 2020

Nutrient Intake, Excretion and Use Efficiency of Grazing Lactating Herds on Commercial Dairy Farms.

Animals (Basel) 2020 Feb 28;10(3). Epub 2020 Feb 28.

US Dairy Forage Research Center, USDA Agricultural Research Service, 1925 Linden Drive West, University of Wisconsin, Madison, WI 53706, USA.

Estimating excreted nutrients is important for farm nutrient management, but seldom occurs on commercial grazing system farms due to difficulties in quantifying pasture intake. Nitrogen (N), phosphorus (P), potassium (K), sulphur (S), calcium (Ca) and magnesium (Mg) intake, excretion and use efficiency of 43 commercial dairy herds grazing pasture were calculated to understand the range in nutrient intake and excretion in these systems. Milk production, feed (grazed and supplement), as well as farm and herd management data were collected quarterly on representative farms located in temperate, arid, subtropical and tropical regions of Australia. Lactating herd sizes on these farms averaged 267 (30 to 1350) cows, with an average daily milk yield of 22 (9 to 36) kg/cow per day and the herds walked from <0.01 to 4 km/day on a variety of terrains. The mean total metabolizable energy (ME) required by cows in the herds was estimated to be 195 (116 to 289) MJ/cow per day. Although these farms are considered grazing systems, feeding strategies ranged from total dependence on pasture to total mixed rations (TMRTMR) and consisted of a wide variety of nutrient and energy contents. Mean pasture dry matter intake (DMI) (9 kg/cow per day, from 0.1 to 22 kg/cow per day) was just over half of total DMI. Dietary concentration of crude protein, P, K, S, Ca and Mg concentrations were, on average, 19%, 0.45%, 2.1%, 0.29%, 0.65%, and 0.3%, respectively, for all herds and, except for N, supplement nutrient concentrations were always more variable than pasture. Approximately 72% and 88% of diets provided greater than recommended P and N intakes, respectively. Calculated mean N, P, K, S, Ca and Mg excretions were 433, 61, 341, 44, 92 and 52 g/cow per day, respectively. Of the farm characteristics examined, residual maximum likelihood (REML) analysis indicated that daily excreted N, P and S were significantly related to per ha milk production, and excreted P, K and Mg were related to percentage of herd DMI provided as supplement. Mean use efficiencies by cows of N, P, K, S, Ca and Mg were 21%, 25%, 9%, 16%, 23% and 4%, respectively. These estimates of nutrient excretion and feed nutrient use efficiencies can be used to improve nutrient management on grazing system commercial dairy farms.
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http://dx.doi.org/10.3390/ani10030390DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7143236PMC
February 2020

Spatially and temporally variable urinary N loads deposited by lactating cows on a grazing system dairy farm.

J Environ Manage 2018 Jun 20;215:166-176. Epub 2018 Mar 20.

Agriculture Victoria Research, Department of Economic Development, Jobs, Transport and Resources, 1301 Hazeldean Road, Ellinbank, Victoria 3821, Australia. Electronic address:

Feed nitrogen (N) intakes in Australian grazing systems average 545 g cow day, indicating that urinary N is likely to be the dominant form excreted. Grazing animals spend disproportionate amounts of time in places on dairy farms where N accumulation is likely to occur. We attached to grazing cows sensors that measure urine volume and N concentration, as well as global positioning systems sensors used to monitor the times the cows spent in different places on a farm and the location of urination events. The cows were monitored for up to 72 h in each of two seasons. More urination events and greater urine volumes per event were recorded in spring 2014 (3.1 L) compared with winter 2015 (1.4 L), most likely influenced by environmental conditions and the greater spring rainfall observed. Mean (range) N concentration (0.71%; 0.02 to 1.52%) and N load (12.8 g cow event; 0.3 to 64.5 g cow event) did not differ over the two monitoring periods. However, mean (range) daily N load was greater in spring (277 g cow day; 200 to 346 g cow day) than in winter (90 g cow day; 44 to 116 g cow day) due to the influence of urine volume. Relatively greater time was spent in paddocks overnight (13.3 h) than in paddocks between morning and evening milking (6.4 h), compared with the mean numbers of urinations in these places (6.4 and 3.8 respectively). The mean N load deposited overnight in paddocks (89.6 g cow) was more than twice that deposited in paddocks during the day (43.8 g cow), due to the greater N load per event overnight, and was more closely linked to the relative difference in time spent in paddocks than in the number of urination events. These data suggest that routinely holding cows in the same paddocks overnight will lead to high urinary N depositions, increasing the potential for N losses from these places. Further research using this technology is required to acquire farm and environment specific urinary data to improve N management.
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http://dx.doi.org/10.1016/j.jenvman.2018.03.046DOI Listing
June 2018

Reassessment of the Upper Fremont Glacier Ice-Core Chronologies by Synchronizing of Ice-Core-Water Isotopes to a Nearby Tree-Ring Chronology.

Environ Sci Technol 2017 04 4;51(8):4230-4238. Epub 2017 Apr 4.

Department of Earth System Science, University of California , Irvine, California 92697, United States.

The Upper Fremont Glacier (UFG), Wyoming, is one of the few continental glaciers in the contiguous United States known to preserve environmental and climate records spanning recent centuries. A pair of ice cores taken from UFG have been studied extensively to document changes in climate and industrial pollution (most notably, mid-19th century increases in mercury pollution). Fundamental to these studies is the chronology used to map ice-core depth to age. Here, we present a revised chronology for the UFG ice cores based on new measurements and using a novel dating approach of synchronizing continuous water isotope measurements to a nearby tree-ring chronology. While consistent with the few unambiguous age controls underpinning the previous UFG chronologies, the new interpretation suggests a very different time scale for the UFG cores with changes of up to 80 years. Mercury increases previously associated with the mid-19th century Gold Rush now coincide with early-20th century industrial emissions, aligning the UFG record with other North American mercury records from ice and lake sediment cores. Additionally, new UFG records of industrial pollutants parallel changes documented in ice cores from southern Greenland, further validating the new UFG chronologies while documenting the extent of late 19th and early 20th century pollution in remote North America.
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http://dx.doi.org/10.1021/acs.est.6b06574DOI Listing
April 2017

Dust outpaces bedrock in nutrient supply to montane forest ecosystems.

Nat Commun 2017 03 28;8:14800. Epub 2017 Mar 28.

Department of Plant Pathology and Microbiology, University of California, Riverside, California 92521, USA.

Dust provides ecosystem-sustaining nutrients to landscapes underlain by intensively weathered soils. Here we show that dust may also be crucial in montane forest ecosystems, dominating nutrient budgets despite continuous replacement of depleted soils with fresh bedrock via erosion. Strontium and neodymium isotopes in modern dust show that Asian sources contribute 18-45% of dust deposition across our Sierra Nevada, California study sites. The remaining dust originates regionally from the nearby Central Valley. Measured dust fluxes are greater than or equal to modern erosional outputs from hillslopes to channels, and account for 10-20% of estimated millennial-average inputs of bedrock P. Our results demonstrate that exogenic dust can drive the evolution of nutrient budgets in montane ecosystems, with implications for predicting forest response to changes in climate and land use.
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http://dx.doi.org/10.1038/ncomms14800DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5379052PMC
March 2017
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