@article {2809, title = {Millennial-scale iron fertilization of the eastern equatorial Pacific over the past 100,000 years}, journal = {Nature Geoscience}, volume = {10}, year = {2017}, month = {Jan-10-2017}, pages = {760 - 764}, abstract = {The eastern equatorial Pacific Ocean plays a crucial role in global climate, as it is a substantial source of CO2 to the atmosphere and accounts for a significant portion of global new export productivity. Here we present a 100,000-year sediment core from the eastern equatorial Pacific, and reconstruct dust flux, export productivity and bottom-water oxygenation using excess-230Th-derived fluxes of 232Th and barium, and authigenic uranium concentrations, respectively. We find that during the last glacial period (71,000 to 41,000 years ago), increased delivery of dust to the eastern equatorial Pacific was coeval with North Atlantic Heinrich stadial events. Millennial-scale pulses of increased dust flux coincided with episodes of heightened biological productivity, suggesting that dissolution of dust released iron that promoted ocean fertilization. We also find that periods of low atmospheric CO2 concentrations were associated with suboxic conditions and increased storage of respired carbon in the deep eastern equatorial Pacific. Increases in CO2 concentrations during the deglaciation are coincident with increases in deep Pacific and Southern Ocean water oxygenation levels. We suggest that deep-ocean ventilation was a primary control on CO2 outgassing in this region, with superimposed pulses of high productivity providing a negative feedback.}, issn = {1752-0894}, doi = {10.1038/ngeo3024}, url = {http://www.nature.com/articles/ngeo3024}, author = {Loveley, Matthew R. and Marcantonio, Franco and Wisler, Marilyn M. and Hertzberg, Jennifer E. and Schmidt, Matthew~W. and Lyle, Mitchell} } @article {2569, title = {Glacial-interglacial changes in central tropical Pacific surface seawater property gradients}, journal = {Paleoceanography}, volume = {30}, year = {2015}, month = {Jan-05-2015}, pages = {423 - 438}, abstract = {Much uncertainty exists about the state of the oceanic and atmospheric circulation in the tropical Pacific over the last glacial cycle. Studies have been hampered by the fact that sediment cores suitable for study were concentrated in the western and eastern parts of the tropical Pacific, with little information from the central tropical Pacific. Here we present information from a suite of sediment cores collected from the Line Islands Ridge in the central tropical Pacific, which show sedimentation rates and stratigraphies suitable for paleoceanographic investigations. Based on the radiocarbon and oxygen isotope measurements on the planktonic foraminifera Globigerinoides ruber, we construct preliminary age models for selected cores and show that the gradient in the oxygen isotope ratio of G. ruber between the equator and 8{\textdegree}N is enhanced during glacial stages relative to interglacial stages. This stronger gradient could reflect enhanced equatorial cooling (perhaps reflecting a stronger Walker circulation) or an enhanced salinity gradient (perhaps reflecting increased rainfall in the central tropical Pacific).}, doi = {10.1002/2014PA002746}, url = {http://doi.wiley.com/10.1002/2014PA002746}, author = {Lynch-Stieglitz, Jean and Polissar, Pratigya J. and Jacobel, Allison W. and Hovan, Steven A. and Pockalny, Robert A. and Lyle, Mitchell and Murray, Richard W. and Ravelo, A. Christina and Bova, Samantha C. and Dunlea, Ann G. and Ford, Heather L. and Hertzberg, Jennifer E. and Wertman, Christina A. and Maloney, Ashley E. and Shackford, Julia K. and Wejnert, Katherine and Xie, Ruifang C.} } @article {2456, title = {Particle sorting during sediment redistribution processes and the effect on 230 Th-normalized mass accumulation rates}, journal = {Geophysical Research Letters}, volume = {41}, year = {2014}, month = {Apr-08-2015}, pages = {5547 - 5554}, abstract = {The 230Th method of determining mass accumulation rates (MARs) assumes that little to no fractionation occurs during sediment redistribution processes at the seafloor. We examine 230Th inventories in radiocarbon-dated multicore sediments from paired winnowed and focused sites at Cocos and Carnegie Ridges, Panama Basin. Radiocarbon-derived sand MARs, which likely represent the vertical rain of particles poorly transported by bottom currents, are similar at each of the paired sites but are different using 230Th normalization. 230Th-normalized MARs are about 60\% lower at focused sites and likely underestimate vertical MARs, while the reverse is true for winnowed sites. We hypothesize that size fractionation occurs most frequently at lower current velocities, resulting in the coarse fraction being left behind and primarily the fine 230Th-rich grains being transported downslope. 230Th-normalization works well for recording fine-grained (detrital and opal), but not coarse-grained (carbonate), fluxes in regions that have undergone sediment redistribution.}, doi = {10.1002/2014GL060477}, url = {http://doi.wiley.com/10.1002/2014GL060477https://api.wiley.com/onlinelibrary/tdm/v1/articles/10.1002\%2F2014GL060477}, author = {Marcantonio, Franco and Lyle, Mitchell and Ibrahim, Rami} }