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  • 1
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    Climatically driven changes in the supply of terrigenous sediment to the East China Sea (2018)
    John Wiley & Sons
    Details
    Publication Date: 2022-05-25
    Description: Author Posting. © American Geophysical Union, 2018. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Geochemistry, Geophysics, Geosystems 19 (2018): 2463-2477, doi:10.1029/2017GC007339.
    Description: We examine the paleoceanographic record over the last ∼400 kyr derived from major, trace, and rare earth elements in bulk sediment from two sites in the East China Sea drilled during Integrated Ocean Drilling Program Expedition 346. We use multivariate statistical partitioning techniques (Q‐mode factor analysis, multiple linear regression) to identify and quantify five crustal source components (Upper Continental Crust (UCC), Luochuan Loess, Xiashu Loess, Southern Japanese Islands, Kyushu Volcanics), and model their mass accumulation rates (MARs). UCC (35–79% of terrigenous contribution) and Luochuan Loess (16–55% contribution) are the most abundant end‐members through time, while Xiashu Loess, Southern Japanese Islands, and Kyushu Volcanics (1–22% contribution) are the lowest in abundance when present. Cycles in UCC and Luochuan Loess MARs may indicate continental and loess‐like material transported by major rivers into the Okinawa Trough. Increases in sea level and grain size proxy (e.g., SiO2/Al2O3) are coincident with increased flux of Southern Japanese Islands, indicating localized sediment supply from Japan. Increases in total terrigenous MAR precede minimum relative sea levels by several thousand years and may indicate remobilization of continental shelf material. Changes in the relative contribution of these end‐members are decoupled from total MAR, indicating compositional changes in the sediment are distinct from accumulation rate changes but may be linked to variations in sea level, riverine and eolian fluxes, and shelf‐bypass processes over glacial‐interglacials, complicating accurate monsoon reconstructions from fluvial dominated sediment.
    Description: U.S. National Science Foundation Grant Numbers: NSF‐EAR1434175, NSF‐EAR1433665, NSF‐EAR1434138
    Keywords: East China Sea ; Bulk sediment ; Provenance ; Multivariate statistics ; East Asian Monsoon ; Loess
    Repository Name: Woods Hole Open Access Server
    Type: Article
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  • 2
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    Orbital- and millennial-scale variability in northwest African dust emissions over the past 67,000 years (2022)
    American Geophysical Union
    Details
    Publication Date: 2022-10-19
    Description: Author Posting. © American Geophysical Union, 2022. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Paleoceanography and Paleoclimatology 37(1), (2022): e020PA004137, https://doi.org/10.1029/2020PA004137.
    Description: Reconstructions of aeolian dust flux to West African margin sediments can be used to explore changing atmospheric circulation and hydroclimate over North Africa on millennial to orbital timescales. Here, we extend West African margin dust flux records back to 37 ka in a transect of sites from 19° to 27°N, and back to 67 ka at Ocean Drilling Program (ODP) Hole 658C, in order to explore the interplay of orbital and high-latitude forcings on North African climate and make quantitative estimates of dust flux during the core of the Last Glacial Maximum (LGM). The ODP 658C record shows a Green Sahara interval from 60 to 50 ka during a time of high Northern Hemisphere summer insolation, with dust fluxes similar to levels during the early Holocene African Humid Period, and an abrupt peak in flux during Heinrich event 5a (H5a). Dust fluxes increase from 50 to 35 ka while the high-latitude Northern Hemisphere cools, with peaks in dust flux associated with North Atlantic cool events. From 35 ka through the LGM dust deposition decreases in all cores, and little response is observed to low-latitude insolation changes. Dust fluxes at sites from 21° to 27°N were near late Holocene levels during the LGM time slice, suggesting a more muted LGM response than observed from mid-latitude dust sources. Records along the northwest African margin suggest important differences in wind responses during different stadials, with maximum dust flux anomalies centered south of 20°N during H1 and north of 20°N during the Younger Dryas.
    Description: This research was supported by NSF #OCE-1103262 to L. Bradtmiller, NSF #OCE-1030784 to D. McGee, P. deMenocal, and G. Winckler, and by internal grants from Macalester College and MIT.
    Description: 2022-06-07
    Keywords: North Africa ; Dust flux ; Aeolian dust ; Green Sahara ; Stadials
    Repository Name: Woods Hole Open Access Server
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  • 3
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    Glacial to Holocene changes in trans-Atlantic Saharan dust transport and dust-climate feedbacks (2017)
    American Association for the Advancement of Science
    Details
    Publication Date: 2022-05-26
    Description: © The Author(s), 2016. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Science Advances 2 (2016): e1600445, doi:10.1126/sciadv.1600445.
    Description: Saharan mineral dust exported over the tropical North Atlantic is thought to have significant impacts on regional climate and ecosystems, but limited data exist documenting past changes in long-range dust transport. This data gap limits investigations of the role of Saharan dust in past climate change, in particular during the mid-Holocene, when climate models consistently underestimate the intensification of the West African monsoon documented by paleorecords. We present reconstructions of African dust deposition in sediments from the Bahamas and the tropical North Atlantic spanning the last 23,000 years. Both sites show early and mid-Holocene dust fluxes 40 to 50% lower than recent values and maximum dust fluxes during the deglaciation, demonstrating agreement with records from the northwest African margin. These quantitative estimates of trans-Atlantic dust transport offer important constraints on past changes in dust-related radiative and biogeochemical impacts. Using idealized climate model experiments to investigate the response to reductions in Saharan dust’s radiative forcing over the tropical North Atlantic, we find that small (0.15°C) dust-related increases in regional sea surface temperatures are sufficient to cause significant northward shifts in the Atlantic Intertropical Convergence Zone, increased precipitation in the western Sahel and Sahara, and reductions in easterly and northeasterly winds over dust source regions. Our results suggest that the amplifying feedback of dust on sea surface temperatures and regional climate may be significant and that accurate simulation of dust’s radiative effects is likely essential to improving model representations of past and future precipitation variations in North Africa.
    Description: This study was supported, in part, by NSF awards OCE-1030784 (to D.M. and P.B.d.) and OCE-09277247 (to P.B.d.); NASA grant NN14AP38G (to C. Heald, Massachusetts Institute of Technology), which supports D.A.R.; and the Columbia University Center for Climate and Life. A.F. is supported by the NSF grant AGS-1116885 and the National Oceanic and Atmospheric Administration (NOAA) grant NA14OAR4310277. S.H. is supported by the NASA Earth and Space Sciences Fellowship. We also acknowledge computational support from the NSF/NCAR Yellowstone Supercomputing Center and the Yale University High Performance Computing Center.
    Keywords: Mineral dust ; North Africa ; Paleoclimate ; African Humid Period
    Repository Name: Woods Hole Open Access Server
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  • 4
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    Reconstructing atmospheric changes in Monsoon regions using eolian dust (2019)
    Massachusetts Institute of Technology and Woods Hole Oceanographic Institution
    Details
    Publication Date: 2022-05-26
    Description: Submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy in Geochemistry at the Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution September 2019.
    Description: Mineral dust is generated in continental interiors and exported by winds to ocean basins, providing a sedimentary archive which is one of the few direct indicators we have of atmospheric circulation in the past. This archive can be utilized in regions of dust transport also affected by monsoons to examine how different climate forcing mechanisms impact the monsoon regions over glacialinterglacial, orbital, and millennial timescales. This thesis generates new eolian dust records from two monsoon regions to reconstruct changes in atmospheric circulation in response to forcing by high-latitude insolation and boundary condition change. In Chapters 2 and 3 I use 230Thxsnormalization to construct high-resolution eolian dust flux records from sedimentary archives downwind from the West African and East Asian Monsoon regions respectively. The West African margin dust records show variability associated with an interplay between Northern Hemisphere summer insolation forcing and North Atlantic cooling. The longest record at ODP Site 658, stretching back to 67 ka, shows evidence for a “Green Sahara” interval from 60-50 ka and a skipped precessional “beat” from 35-20 ka. This record also shows evidence for abrupt increases in dust flux associated with Greenland stadials. The Shatsky Rise record at ODP Site 1208, downwind of East Asian dust sources, shows variability associated with glacial-interglacial boundary conditions over the last 330 ka, exhibiting high dust during glacial times. The record also exhibits variability associated with a Northern Hemisphere summer insolation control at times overriding the glacialinterglacial signal. In Chapter 4 I demonstrate the feasibility of using radiogenic neodymium isotopes (143Nd/144Nd) at IODP Site U1430 in the Sea of Japan to fingerprint the provenance of eolian material at the core site from Asian dust sources. I then generate a 143Nd/144Nd record from isolated eolian material over the last 200 ka to examine Westerly Jet behavior in the Asian interior, which shows resolvable orbital-scale variability from 200 to 100 ka, and muted variability from 100 to 0 ka. The findings imply a quicker shift of the Westerly Jet to the north of the Tibetan Plateau during times of high Northern Hemisphere summer insolation and a strong Asian monsoon.
    Description: This thesis research was supported by the National Science Foundation under Grant Nos. OCE-1030784 and EAR-1434138 and a Post-expedition activity award through the U.S. Science Support Program, Integrated Ocean Drilling Program. Kinsley was supported by fellowships from the MIT Department of Earth, Atmospheric, and Planetary Sciences in his first year of graduate school and the WHOI Academic Programs Office in his sixth year of graduate school.
    Keywords: Minerals ; Sediment transport ; Atmospheric circulation ; Monsoons ; Marine geophysics
    Repository Name: Woods Hole Open Access Server
    Type: Thesis
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