Kinsley
Christopher W.
Kinsley
Christopher W.
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PreprintBarium-isotopic fractionation in seawater mediated by barite cycling and oceanic circulation( 2015-07-09) Horner, Tristan J. ; Kinsley, Christopher W. ; Nielsen, Sune G.The marine biogeochemical cycle of Ba is thought to be controlled by particulate BaSO4 (barite) precipitation associated with the microbial oxidation of organic carbon and its subsequent dissolution in the BaSO4-undersaturated water column. Despite many of these processes being largely unique to Ba cycling, concentrations of Ba and Si in seawater exhibit a strong linear correlation. The reasons for this correlation are ambiguous, as are the depth ranges corresponding to the most active BaSO4 cycling and the intermediate sources of Ba to particulate BaSO4. Stable isotopic analyses of dissolved Ba in seawater should help address these issues, as Ba-isotopic compositions are predicted to be sensitive to the physical and biogeochemical process that cycle Ba. We report a new methodology for the determination of dissolved Ba-isotopic compositions in seawater and results from a 4, 500 m depth profile in the South Atlantic at 39.99 S, 0.92 E that exhibit oceanographically-consistent variation with depth. These data reveal that water masses obtain their [Ba] and Ba-isotopic signatures when at or near the surface, which relates to the cycling of marine BaSO4. The shallow origin of these signatures requires that the substantial Ba-isotopic variations in the bathypelagic zone were inherited from when those deep waters were last ventilated. Indeed, the water column below 600 m is well explained by conservative mixing of water masses with distinct [Ba] and Ba-isotopic compositions. This leads us to conclude that large scale oceanic circulation is important for sustaining the similar oceanographic distributions of Ba and Si in the South Atlantic, and possibly elsewhere. These data demonstrate that the processes of organic carbon oxidation, BaSO4 cycling, and Ba-isotopic fractionation in seawater are closely coupled, such that Ba-isotopic analyses harbor great potential as a tracer of the carbon cycle in the modern and paleo-oceans.
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PreprintBarium isotopes reveal role of ocean circulation on barium cycling in the Atlantic( 2017-02-02) Bates, Stephanie L. ; Hendry, Katharine R. ; Pryer, Helena V. ; Kinsley, Christopher W. ; Pyle, Kimberley M. ; Woodward, E. Malcolm S. ; Horner, Tristan J.We diagnose the relative influences of local-scale biogeochemical cycling and regional-scale ocean circulation on Atlantic barium cycling by analyzing four new depth profiles of dissolved Ba concentrations and isotope compositions from the South and tropical North Atlantic. These new profiles exhibit systematic vertical, zonal, and meridional variations that reflect the influence of both local-scale barite cycling and large-scale ocean circulation. Previously reported epipelagic decoupling of Ba and Si in the tropics is also found to be associated with significant Ba isotope heterogeneity. We contend that this decoupling originates from the depth segregation of opal & barite formation but is exacerbated by weak vertical mixing, as in the tropics. Zonal influence from isotopically-‘heavy’ water masses in the western North Atlantic evidence the advective inflow of Ba-depleted Upper Labrador Sea Water, which is not seen in the eastern basin or the South Atlantic. Meridional variations in Atlantic Ba isotope systematics below 2,000 m appear entirely controlled by conservative mixing. Using an inverse isotopic mixing model, we calculate the Ba isotope composition of the Ba-poor northern end member as +0.45 ‰ and the Ba-rich southern end member +0.26 ‰, relative to NIST SRM 3104a. The near-conservative behaviour of Ba in the deep ocean indicates that Ba isotopes may serve as an independent tracer of the provenance of advected water masses in the Atlantic Ocean. The clearly resolved Ba-isotope signatures of northern- and southern-sourced waters may also prove useful in paleoceanographic studies, should appropriate sedimentary archives be identified. Overall, our results offer new insights into the controls on Ba cycling in seawater and thus the mechanisms that underpin the utility of Ba-based proxies in paleoceanography.
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ArticleOrbital- and millennial-scale variability in northwest African dust emissions over the past 67,000 years(American Geophysical Union, 2021-12-07) Kinsley, Christopher W. ; Bradtmiller, Louisa I. ; McGee, David ; Galgay, Michael ; Stuut, Jan-Berend W. ; Tjallingii, Rik ; Winckler, Gisela ; deMenocal, Peter B.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.
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ArticleGlacial to Holocene changes in trans-Atlantic Saharan dust transport and dust-climate feedbacks(American Association for the Advancement of Science, 2016-11-23) Williams, Ross H. ; McGee, David ; Kinsley, Christopher W. ; Ridley, David A. ; Hu, Shineng ; Fedorov, Alexey ; Tal, Irit ; Murray, Richard W. ; deMenocal, Peter B.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.
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ArticleClimatically driven changes in the supply of terrigenous sediment to the East China Sea(John Wiley & Sons, 2018-08-11) Anderson, Chloe H. ; Murray, Richard W. ; Dunlea, Ann G. ; Giosan, Liviu ; Kinsley, Christopher W. ; McGee, David ; Tada, RyujiWe 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.
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ArticleHigh-resolution and high-precision correlation of dark and light layers in the Quaternary hemipelagic sediments of the Japan Sea recovered during IODP Expedition 346(Springer, 2018-03-26) Tada, Ryuji ; Irino, Tomohisa ; Ikehara, Ken ; Karasuda, Akinori ; Sugisaki, Saiko ; Xuan, Chuang ; Sagawa, Takuya ; Itaki, Takuya ; Kubota, Yoshimi ; Lu, Song ; Seki, Arisa ; Murray, Richard W. ; Alvarez-Zarikian, Carlos A. ; Anderson, William T. ; Bassetti, Maria-Angela ; Brace, Bobbi J. ; Clemens, Steven C. ; da Costa Gurgel, Marcio H. ; Dickens, Gerald R. ; Dunlea, Ann G. ; Gallagher, Stephen J. ; Giosan, Liviu ; Henderson, Andrew C. G. ; Holbourn, Ann E. ; Kinsley, Christopher W. ; Lee, Gwang Soo ; Lee, Kyung Eun ; Lofi, Johanna ; Lopes, Christina I. C. D. ; Saavedra-Pellitero, Mariem ; Peterson, Larry C. ; Singh, Raj K. ; Toucanne, Samuel ; Wan, Shiming ; Zheng, Hongbo ; Ziegler, MartinThe Quaternary hemipelagic sediments of the Japan Sea are characterized by centimeter- to decimeter-scale alternation of dark and light clay to silty clay, which are bio-siliceous and/or bio-calcareous to a various degree. Each of the dark and light layers are considered as deposited synchronously throughout the deeper (> 500 m) part of the sea. However, attempts for correlation and age estimation of individual layers are limited to the upper few tens of meters. In addition, the exact timing of the depositional onset of these dark and light layers and its synchronicity throughout the deeper part of the sea have not been explored previously, although the onset timing was roughly estimated as ~ 1.5 Ma based on the result of Ocean Drilling Program legs 127/128. Consequently, it is not certain exactly when their deposition started, whether deposition of dark and light layers was synchronous and whether they are correlatable also in the earlier part of their depositional history. The Quaternary hemipelagic sediments of the Japan Sea were drilled at seven sites during Integrated Ocean Drilling Program Expedition 346 in 2013. Alternation of dark and light layers was recovered at six sites whose water depths are > ~ 900 m, and continuous composite columns were constructed at each site. Here, we report our effort to correlate individual dark layers and estimate their ages based on a newly constructed age model at Site U1424 using the best available paleomagnetic datum and marker tephras. The age model is further tuned to LR04 δ18O curve using gamma ray attenuation density (GRA) since it reflects diatom contents that are higher during interglacial high-stands. The constructed age model for Site U1424 is projected to other sites using correlation of dark layers to form a high-resolution and high-precision paleo-observatory network that allows to reconstruct changes in material fluxes with high spatio-temporal resolutions.
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ArticleChanges in biological productivity along the northwest African margin over the past 20,000 years(John Wiley & Sons, 2016-01-23) Bradtmiller, Louisa I. ; McGee, David ; Awalt, Mitchell ; Evers, Joseph ; Yerxa, Haley ; Kinsley, Christopher W. ; deMenocal, Peter B.The intertropical convergence zone and the African monsoon system are highly sensitive to climate forcing at orbital and millennial timescales. Both systems influence the strength and direction of the trade winds along northwest Africa and thus directly impact coastal upwelling. Sediment cores from the northwest African margin record upwelling-related changes in biological productivity connected to changes in regional and hemispheric climate. We present records of 230Th-normalized biogenic opal and Corg fluxes using a meridional transect of four cores from 19°N–31°N along the northwest African margin to examine changes in paleoproductivity since the last glacial maximum. We find large changes in biogenic fluxes synchronous with changes in eolian fluxes calculated using end-member modeling, suggesting that paleoproductivity and dust fluxes were strongly coupled, likely linked by changes in wind strength. Opal and Corg fluxes increase at all sites during Heinrich Stadial 1 and the Younger Dryas, consistent with an overall intensification of the trade winds, and changes in the meridional flux gradient indicate a southward wind shift at these times. Biogenic fluxes were lowest, and the meridional flux gradients were weakest during the African Humid Period when the monsoon was invigorated due to precessional changes, with greater rainfall and weaker trade winds over northwest Africa. These results expand the spatial coverage of previous paleoproxy studies showing similar changes, and they provide support for modeling studies showing changes in wind strength and direction consistent with increased upwelling during abrupt coolings and decreased upwelling during the African Humid Period.
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ThesisReconstructing atmospheric changes in Monsoon regions using eolian dust(Massachusetts Institute of Technology and Woods Hole Oceanographic Institution, 2019-09) Kinsley, Christopher W.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.