¹N. G. Rudraswami,¹M. Pandey,²M. J. Genge,¹D. Fernandes
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.13764]
¹CSIR-National Institute of Oceanography, Dona Paula, Goa, 403004 India
²Department of Earth Science and Engineering, Imperial College London, London, SW7 2AZ UK
Published by arrangement with John Wiley & Sons

Bioavailable Fe is an essential nutrient for phytoplankton that enables the organisms to flourish and draw down atmospheric CO2 thus affecting global climatic conditions. In marine locales, remote from the continents, extraterrestrial dust provides an important source of Fe and thus moderates primary productivity. Here, we provide constraints on partitioning of extraterrestrial Fe between seawater and sediments from the observations of dissolution and the alteration of cosmic spherules recovered from deep-sea sediments and Antarctica. Of the ∼3000–14,000 t a−1 extraterrestrial dust that reaches Earth’s surface, ∼2–5% material falling in the oceans survives in marine sediments while the remainder is liberated into seawater. Both processes contribute ∼(3–10) × 10−8 mol Fe m−2 yr−1. The Fe contribution of surviving particles due to etching is estimated to be ∼10% of Fe contribution of meteoric smoke. Changes in extraterrestrial dust flux over geological time scales not only vary Fe delivery to the oceans by up to three orders of magnitude but also the partitioning of Fe between surface and abyssal waters depending on entry velocity and evaporation.

^1,2Atsushi Takenouchi,³Hirochika Sumino,⁴Karin Shimodate,²Akira Yamaguchi
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.13768]
¹The Kyoto University Museum, Kyoto University, Yoshida-honmachi, Sakyo, Kyoto, 606-8501 Japan
²National Institute of Polar Research, 10-3 Midori-cho, Tachikawa, Tokyo, 190-8518 Japan
³General Systems Studies, Graduate School of Arts and Science, The University of Tokyo, 3-8-1 Komaba, Meguro-ku, Tokyo, 153-8902 Japan
⁴Department of Physics, Graduate School of Science, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo, 113-8654 Japan
Published by arrangement with John Wiley & Sons

LL chondrites have experienced multiple shock events; however, the relations of each shock event and their timing have rarely been investigated. To demonstrate the relations between each shock texture and shock chronological ages, we conducted both petrological and chronological (⁴⁰Ar/³⁹Ar and I-Xe ages) studies using aliquots subsampled from the same chip of the Northwest Africa (NWA) 2139 LL6 chondrite. Our ⁴⁰Ar/³⁹Ar studies and petrological observation reveal that NWA 2139 recorded at least three impact events before 4.17 ± 0.10 Ga, thus resulting in a complex brecciated texture, silicate darkening, and thick shock veins. An intense heating event occurred at 4.17 ± 0.10 Ga, which recrystallized the thick veins and healing cracks. Then, a weak shock event occurred at <3.9 Ga. Combined with ⁴⁰Ar/³⁹Ar data of other LL chondritic materials, this study supports that the LL chondrite parent body was possibly broken up by 1.7 Ga, and that most of the breakup likely occurred within 3.8–4.2 Ga.