Now showing 1 - 5 of 35
- ItemA metamorphic origin for Europa's ocean(John Wiley & Sons, Inc, 2021) Daswani, Mohit Melwani; Vance, Steven D.; Mayne, Matthew J.; Glein, Christopher R.Europa likely contains an iron-rich metal core. For it to have formed, temperatures within Europa reached urn:x-wiley:00948276:media:grl62926:grl62926-math-00011250 K. Going up to that temperature, accreted chondritic minerals — for example, carbonates and phyllosilicates — would partially devolatilize. Here, we compute the amounts and compositions of exsolved volatiles. We find that volatiles released from the interior would have carried solutes, redox-sensitive species, and could have generated a carbonic ocean in excess of Europa's present-day hydrosphere, and potentially an early urn:x-wiley:00948276:media:grl62926:grl62926-math-0002 atmosphere. No late delivery of cometary water was necessary. Contrasting with prior work, urn:x-wiley:00948276:media:grl62926:grl62926-math-0003 could be the most abundant solute in the ocean, followed by urn:x-wiley:00948276:media:grl62926:grl62926-math-0004, urn:x-wiley:00948276:media:grl62926:grl62926-math-0005, and urn:x-wiley:00948276:media:grl62926:grl62926-math-0006. However, gypsum precipitation going from the seafloor to the ice shell decreases the dissolved S/Cl ratio, such that Clurn:x-wiley:00948276:media:grl62926:grl62926-math-0007S at the shallowest depths, consistent with recently inferred endogenous chlorides at Europa's surface. Gypsum would form a 3–10 km thick sedimentary layer at the seafloor.
- ItemTiming of Proterozoic magmatism in the Sunsas belt, Bolivian Precambrian Shield, SW Amazonian Craton(Elsevier B.V., 2021-06-05) Nedel, Ingrid M.; Fuck, Reinhardt A.; Ruiz, Amarildo S.; Matos-Salinas, Gerardo R.; Ferreira, Alanielson da C.D.We present new U–Pb zircon and monazite ages from the Sunsas belt granitic magmatism in Bolivia, SW Amazonian Craton. The geochronological results revealed four major magmatic events recorded along the Sunsas belt domains. The older igneous event formed a granitic basement coeval to the Rio Apa Terrane (1.95 – 1.85 Ga) in the southern domain. The second magmatic episode is represented by 1.68 Ga granites associated to the Paraguá Terrane (1.69–1.66 Ga) in the northern domain. The 1.37–1.34 Ga granites related to San Ignacio orogeny represent the third and more pervasive magmatic event, recorded throughout the Sunsas belt. Moreover, magmatic ages of ~1.42 Ga revealed that the granitogenesis associated to the Santa Helena orogeny also affected the Sunsas belt, indicating that it was not restricted to the Jauru Terrane. Lastly, the 1.10–1.04 Ga youngest magmatism was developed during the Sunsas orogeny and represents the final magmatic evolution related to Rodinia assembly. Likewise, the 1.95–1.85 and 1.68 Ga inherited zircon cores obtained in the ~1.3 Ga and 1.0 Ga granite samples suggest strong partial melting of the Paleoproterozoic sources. The 1079 ± 14 Ma and 1018 ± 6 Ma monazite crystallization ages can be correlated to the collisional tectono-thermal event of the Sunsas orogeny, associated to reactions of medium- to high-grade metamorphism. Thus, the Sunsas belt was built by heterogeneous 1.95– 1.85 Ga and 1.68 Ga crustal fragments that were reworked at 1.37–1.34 Ga and 1.10–1.04 Ga related to orogenic collages. Furthermore, the 1.01 Ga monazite age suggests that granites previously dated by zircon can bear evidence of a younger thermal history. Therefore, the geochronological evolution of the Sunsas belt may have been more complex than previously thought.
- ItemAssessment of C, N, and Si Isotopes as tracers of past ocean nutrient and carbon cycling(John Wiley & Sons, Inc., 2021) Farmer, J. R.; Hertzberg, J. E.; Cardinal, D.; Fietz, S.; Hendry, K.; Jaccard, S. L.; Paytan, A.; Rafter, P. A.; Ren, H.; Somes, C. J.; Sutton, J. N.Biological productivity in the ocean directly influences the partitioning of carbon between the atmosphere and ocean interior. Through this carbon cycle feedback, changing ocean productivity has long been hypothesized as a key pathway for modulating past atmospheric carbon dioxide levels and hence global climate. Because phytoplankton preferentially assimilate the light isotopes of carbon and the major nutrients nitrate and silicic acid, stable isotopes of carbon (C), nitrogen (N), and silicon (Si) in seawater and marine sediments can inform on ocean carbon and nutrient cycling, and by extension the relationship with biological productivity and global climate. Here, we compile water column C, N, and Si stable isotopes from GEOTRACES-era data in four key ocean regions to review geochemical proxies of oceanic carbon and nutrient cycling based on the C, N, and Si isotopic composition of marine sediments. External sources and sinks as well as internal cycling (including assimilation, particulate matter export, and regeneration) are discussed as likely drivers of observed C, N, and Si isotope distributions in the ocean. The potential for C, N, and Si isotope measurements in sedimentary archives to record aspects of past ocean C and nutrient cycling is evaluated, along with key uncertainties and limitations associated with each proxy. Constraints on ocean C and nutrient cycling during late Quaternary glacial-interglacial cycles and over the Cenozoic are examined. This review highlights opportunities for future research using multielement stable isotope proxy applications and emphasizes the importance of such applications to reconstructing past changes in the oceans and climate system.
- ItemOceanographic anomalies coinciding with humpback whale super-group occurrences in the Southern Benguela(Nature, 2021-10-22) Dey, Subhra Prakash; Vichi, Marcello; Fearon, Giles; Seyboth, Elisa; Findlay, Ken P.; Meynecke, Jan-Olaf; De Bie, Jasper; Lee, Serena Blyth; Samanta, Saumik; Barraqueta, Jan-Lukas Menzel; Roychoudhury, Alakendra N.; Mackey, BrendanSeasonal feeding behaviour of humpback whales (Megaptera novaeangliae) has been observed in the coastal waters of the Southern Benguela where the species has been observed forming super-groups during the austral spring in recent years since 2011. Super-groups are unprecedented densely-packed aggregations of between 20 and 200 individuals in low-latitude waters and their occurrences indicate possible changes in feeding behaviour of the species. We accessed published data on super-groups occurrence in the study area in 2011, 2014 and 2015, and investigated oceanographic drivers that support prey availability in this region. We found that enhanced primary production is a necessary but not sufficient condition for super-groups to occur. Positive chlorophyll anomalies occurring one month prior to the super-group occurrences were identified, but only a concurrent significantly reduced water volume export from the region throughout October were conducive to the aggregations in the specific years. Hydrodynamic model results attributed the anomalous decreased volume export to the strength and orientation of the Goodhope Jet and associated eddy activity. The combination of random enhanced primary production typical of the region and emerging anomalous conditions of reduced water export in October since 2011 resulted in favourable food availability leading to the unique humpback whale aggregations. The novelty of this grouping behaviour is indicative of the lack of such oceanographic conditions in the past. Given the recency of the events, it is difficult to attribute this reduction in ocean transport to climatic regime shifts, and the origin should be likely investigated in the distant water mass interaction with the greater Agulhas system rather than in local intensifications of the upwelling conditions. A positive trend in the humpback whale population abundance points to the need to monitor the exposure of the species to the changing climate conditions.
- ItemDiminutive fleet-footed tyrannosauroid narrows the 70-million-year gap in the North American fossil record(Springer Nature, 2019-02-21) Zanno, Lindsay E.; Tucker, Ryan T.; Canoville, Aurore; Avrahami, Haviv M.; Gates, Terry A.; Makovicky, Peter J.To date, eco-evolutionary dynamics in the ascent of tyrannosauroids to top predator roles have been obscured by a 70-million-year gap in the North American (NA) record. Here we report discovery of the oldest Cretaceous NA tyrannosauroid, extending the lineage by ~15 million years. The new taxon-Moros intrepidus gen. et sp. nov.-is represented by a hind limb from an individual nearing skeletal maturity at 6-7 years. With a ~1.2-m limb length and 78-kg mass, M. intrepidus ranks among the smallest Cretaceous tyrannosauroids, restricting the window for rapid mass increases preceding the appearance of colossal eutyrannosaurs. Phylogenetic affinity with Asian taxa supports transcontinental interchange as the means by which iconic biotas of the terminal Cretaceous were established in NA. The unexpectedly diminutive and highly cursorial bauplan of NA's earliest Cretaceous tyrannosauroids reveals an evolutionary strategy reliant on speed and small size during their prolonged stint as marginal predators.