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Abstract We report the Earth's rate of radiogenic heat production and (anti)neutrino luminosity from geologically relevant short‐lived radionuclides (SLR) and long‐lived radionuclides (LLR) using decay constants from the geological community, updated nuclear physics parameters, and calculations of theβspectra. We track the time evolution of the radiogenic power and luminosity of the Earth over the last 4.57 billion years, assuming an absolute abundance for the refractory elements in the silicate Earth and key volatile/refractory element ratios (e.g., Fe/Al, K/U, and Rb/Sr) to set the abundance levels for the moderately volatile elements. The relevant decays for the present‐day heat production in the Earth (19.9 ± 3.0 TW) are from40K,87Rb,147Sm,232Th,235U, and238U. Given element concentrations in kg‐element/kg‐rock and densityρin kg/m3, a simplified equation to calculate the present‐day heat production in a rock isurn:x-wiley:ggge:media:ggge22244:ggge22244-math-0001 The radiogenic heating rate of Earth‐like material at solar system formation was some 103to 104times greater than present‐day values, largely due to decay of26Al in the silicate fraction, which was the dominant radiogenic heat source for the first∼10 Ma. Assuming instantaneous Earth formation, the upper bound on radiogenic energy supplied by the most powerful short‐lived radionuclide26Al (t1/2= 0.7 Ma) is 5.5×1031 J, which is comparable (within a factor of a few) to the planet's gravitational binding energy.
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Size‐specific grazing and competitive interactions between large salps and protistan grazers
Abstract We investigated competition betweenSalpa thompsoniand protistan grazers during Lagrangian experiments near the Subtropical Front in the southwest Pacific sector of the Southern Ocean. Over a month, the salp community shifted from dominance by large (> 100 mm) oozooids and small (< 20 mm) blastozooids to large (~ 60 mm) blastozooids. Phytoplankton biomass was consistently dominated by nano‐ and microphytoplankton (> 2 μm cells). Using bead‐calibrated flow‐cytometry light scatter to estimate phytoplankton size, we quantified size‐specific salp and protistan zooplankton grazing pressure. Salps were able to feed at a > 10,000 : 1 predator : prey size (linear‐dimension) ratio. Small blastozooids efficiently retained cells > 1.4μm (high end of picoplankton size, 0.6–2 μm cells) and also obtained substantial nutrition from smaller bacteria‐sized cells. Larger salps could only feed efficiently on > 5.9μm cells and were largely incapable of feeding on picoplankton. Due to the high biomass of nano‐ and microphytoplankton, however, all salps derived most of their (phytoplankton‐based) nutrition from these larger autotrophs. Phagotrophic protists were the dominant competitors for these prey items and consumed approximately 50% of the biomass of all phytoplankton size classes each day. Using a Bayesian statistical framework, we developed an allometric‐scaling equation for salp clearance rates as a function of salp and prey size:urn:x-wiley:00243590:media:lno11770:lno11770-math-0001where ESD is prey equivalent spherical diameter (µm), TL isS. thompsonitotal length,φ = 5.6 × 10−3 ± 3.6 × 10−4,ψ = 2.1 ± 0.13,θ = 0.58 ± 0.08, andγ = 0.46 ± 0.03 and clearance rate is L d‐1salp‐1. We discuss the biogeochemical and food‐web implications of competitive interactions among salps, krill, and protozoans.
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- PAR ID:
- 10443344
- Publisher / Repository:
- Wiley Blackwell (John Wiley & Sons)
- Date Published:
- Journal Name:
- Limnology and Oceanography
- Volume:
- 66
- Issue:
- 6
- ISSN:
- 0024-3590
- Format(s):
- Medium: X Size: p. 2521-2534
- Size(s):
- p. 2521-2534
- Sponsoring Org:
- National Science Foundation
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