Revisiting the mid-Pleistocene transition ocean circulation crisis.

The mid-Pleistocene transition (MPT) [~1.25 to 0.85 million years ago (Ma)] marks a shift in the character of glacial-interglacial climate (, ).

Mafic slab melt contributions to Proterozoic massif-type anorthosites.

Massif-type anorthosites, enormous and enigmatic plagioclase-rich cumulate intrusions emplaced into Earth's crust, formed in large numbers only between 1 and 2 billion years ago. Conflicting hypotheses for massif-type anorthosite formation, including melting of upwelling mantle, lower crustal melting, and arc magmatism above subduction zones, have stymied consensus on what parental magmas crystallized the anorthosites and why the rocks are temporally restricted. Using B, O, Nd, and Sr isotope analyses, bulk chemistry, and petrogenetic modeling, we demonstrate that the magmas parental to the Marcy and Morin anorthosites, classic examples from North America's Grenville orogen, require large input from mafic melts derived from slab-top altered oceanic crust.

Patagonian dust, Agulhas Current, and Antarctic ice-rafted debris contributions to the South Atlantic Ocean over the past 150,000 years.

Disentangling inputs of aeolian dust, ice-rafted debris (IRD), and eroded continental detritus delivered by ocean currents to marine sediments provide important insights into Earth System processes and climate. This study uses Sr-Nd-Pb isotope ratios of the continent-derived (lithogenic) fraction in deep-sea core TN057-6 from the subantarctic Southern Ocean southwest of Africa over the past 150,000 y to identify source regions and quantify their relative contributions and fluxes utilizing a mixing model set in a Bayesian framework. The data are compared with proxies from parallel core Ocean Drilling Program Site 1090 and newly presented data from potential South America aeolian dust source areas (PSAs), allowing for an integrated investigation into atmospheric, oceanic, and cryospheric dynamics.

Widespread Pb contamination in urban backyard soils for >100 years identified in soil cores constrained by Pb and Cs.

Contaminated soil in urban residential areas is often overlooked as a source of childhood exposure to toxic levels of lead (Pb). We document mean Pb concentrations of 1200 ± 1000 mg/kg, three times the now outdated EPA soil hazard standard of 400 mg/kg, for 370 surface soils collected from 76 homes in the boroughs of Brooklyn and Manhattan of New York City. The mean Pb content of 250 ± 290 mg/kg Pb for 571 surface soils collected from tree pits and public parks was much lower.

Provenance of Anthropogenic Pb and Atmospheric Dust to Northwestern North America.

Industrial activities release aerosols containing toxic metals into the atmosphere, where they are transported far from their sources, impacting ecosystems and human health. Concomitantly, long-range-transported mineral dust aerosols play a role in Earth's radiative balance and supply micronutrients to iron-limited ecosystems. To evaluate the sources of dust and pollutant aerosols to Alaska following the 2001 phase-out of leaded gasoline in China, we measured Pb-Sr-Nd isotopic compositions of particles collected in 2016 from snow pits across an elevational transect (2180-5240 m-a.

Evidence for a Northern Hemispheric trigger of the 100,000-y glacial cyclicity.

The causes of the Mid-Pleistocene Transition, the shift from ∼41-ky to 100-ky interglacial-glacial cycles and more intense ice ages, remain intensely debated, as this fundamental change occurred between ∼1,250 and 650 ka without substantial changes in astronomical climate forcings. Recent studies disagree about the relative importance of events and processes in the Northern and Southern Hemispheres, as well as whether the shift occurred gradually over several interglacial-glacial cycles or abruptly at ∼900 ka. We address these issues using a north-to-south reconstruction of the Atlantic arm of the global meridional overturning ocean circulation, a primary means for distributing heat around the globe, using neodymium (Nd) isotopes.