@article {2745, title = {Data Constraints on Glacial Atlantic Water Mass Geometry and Properties}, journal = {Paleoceanography and Paleoclimatology}, volume = {33}, year = {2018}, month = {Mar-09-2020}, pages = {1013 - 1034}, abstract = {The chemical composition of benthic foraminifera from marine sediment cores provides information on how glacial subsurface water properties differed from modern, but separating the influence of changes in the origin and end-member properties of subsurface water from changes in flows and mixing is challenging. Spatial gaps in coverage of glacial data add to the uncertainty. Here we present new data from cores collected from the Demerara Rise in the western tropical North Atlantic, including cores from the modern tropical phosphate maximum at Antarctic Intermediate Water (AAIW) depths. The results suggest lower phosphate concentration and higher carbonate saturation state within the phosphate maximum than modern despite similar carbon isotope values, consistent with less accumulation of respired nutrients and carbon, and reduced air-sea gas exchange in source waters to the region. An inversion of new and published glacial data confirms these inferences and further suggests that lower preformed nutrients in AAIW, and partial replacement of this still relatively high-nutrient AAIW with nutrient-depleted, carbonate-rich waters sourced from the region of the modern-day northern subtropics, also contributed to the observed changes. The results suggest that glacial preformed and remineralized phosphate were lower throughout the upper Atlantic, but deep phosphate concentration was higher. The inversion, which relies on the fidelity of the paleoceanographic data, suggests that the partial replacement of North Atlantic sourced deep water by Southern Ocean Water was largely responsible for the apparent deep North Atlantic phosphate increase, rather than greater remineralization.}, issn = {2572-4517}, doi = {10.1029/2018PA003408}, url = {https://onlinelibrary.wiley.com/doi/abs/10.1029/2018PA003408}, author = {Oppo, Delia W. and Gebbie, Geoffrey and Huang, Kuo-Fang and Curry, William B. and Marchitto, Thomas M. and Pietro, Kathryn R.} } @article {2584, title = {What do benthic ? 13 C and ? 18 O data tell us about Atlantic circulation during Heinrich Stadial 1?}, journal = {Paleoceanography}, volume = {30}, year = {2015}, month = {Jan-04-2015}, pages = {353 - 368}, abstract = {Approximately synchronous with the onset of Heinrich Stadial 1 (HS1), δ13C decreased throughout most of the upper (~1000{\textendash}2500 m) Atlantic, and at some deeper North Atlantic sites. This early deglacial δ13C decrease has been alternatively attributed to a reduced fraction of high-δ13C North Atlantic Deep Water (NADW) or to a decrease in the NADW δ13C source value. Here we present new benthic δ18O and δ13C records from three relatively shallow (~1450{\textendash}1650 m) subpolar Northeast Atlantic cores. With published data from other cores, these data form a depth transect (~1200{\textendash}3900 m) in the subpolar Northeast Atlantic. We compare Last Glacial Maximum (LGM) and HS1 data from this transect with data from a depth transect of cores from the Brazil Margin. The largest LGM-to-HS1 decreases in both benthic δ13C and δ18O occurred in upper waters containing the highest NADW fraction during the LGM. We show that the δ13C decrease can be explained entirely by a lower NADW δ13C source value, entirely by a decrease in the proportion of NADW relative to Southern Ocean Water, or by a combination of these mechanisms. However, building on insights from model simulations, we hypothesize that reduced ventilation due to a weakened but still active Atlantic Meridional Overturning Circulation also contributed to the low δ13C values in the upper North Atlantic. We suggest that the benthic δ18O gradients above ~2300 m at both core transects indicate the depth to which heat and North Atlantic deglacial freshwater had mixed into the subsurface ocean by early HS1.}, doi = {10.1002/2014PA002667}, url = {http://doi.wiley.com/10.1002/2014PA002667}, author = {Oppo, Delia W. and Curry, William B. and McManus, Jerry F.} } @article {2588, title = {Decreased influence of Antarctic intermediate water in the tropical Atlantic during North Atlantic cold events}, journal = {Earth and Planetary Science Letters}, volume = {389}, year = {2014}, month = {Jan-03-2014}, pages = {200 - 208}, abstract = {Antarctic Intermediate Water (AAIW) is a key player in the global ocean circulation, contributing to the upper limb of the Atlantic Meridional Overturning Circulation (AMOC), and influencing interhemispheric heat exchange and the distribution of salinity, nutrients and carbon. However, the deglacial history of AAIW flow into the North Atlantic is controversial. Here we present a multicore-top neodymium isotope calibration, which confirms the ability of unclean foraminifera to faithfully record bottom water neodymium isotopic composition () values in their authigenic coatings. We then present the first foraminifera-based reconstruction of from three sediment cores retrieved from within modern AAIW, in the western tropical North Atlantic. Our records reveal similar glacial and interglacial contributions of AAIW, and a pronounced decrease in the AAIW fraction during North Atlantic deglacial cold episodes, Heinrich Stadial 1 (HS1) and Younger Dryas (YD). Our results suggest two separate phases of reduced fraction of AAIW in the tropical Atlantic during HS1, with a greater reduction during early HS1. If a reduction in AAIW fraction also reflects reduced AMOC strength, this finding may explain why, in many regions, there are two phases of hydrologic change within HS1, and why atmospheric CO2 rose more rapidly during early than late HS1. Our result suggesting less flow of AAIW into the Atlantic during North Atlantic cold events contrasts with evidence from the Pacific, where intermediate-depth records may indicate increased flow of AAIW into the Pacific during the these same events. Antiphased behavior between intermediate depths of the North Atlantic and Pacific implies that the flow of AAIW into Atlantic and Pacific seesawed during the last deglaciation.}, keywords = {antarctic intermediate water, Atlantic meridional overturning circulation, deglacial variability, Nd isotopes, North Atlantic cold events}, issn = {0012821X}, doi = {10.1016/j.epsl.2013.12.037}, url = {https://doi.org/10.1016/j.epsl.2013.12.037}, author = {Huang, Kuo-Fang and Oppo, Delia W. and Curry, William B.} } @article {2545, title = {Persistent export of 231Pa from the deep central Arctic Ocean over the past 35,000 years}, journal = {Nature}, volume = {497}, year = {2013}, month = {May-05-2015}, pages = {603 - 606}, abstract = {The Arctic Ocean has an important role in Earth{\textquoteright}s climate, both through surface processes1 such as sea-ice formation and transport, and through the production and export of waters at depth that contribute to the global thermohaline circulation2, 3. Deciphering the deep Arctic Ocean{\textquoteright}s palaeo-oceanographic history is a crucial part of understanding its role in climatic change. Here we show that sedimentary ratios of the radionuclides thorium-230 (230Th) and protactinium-231 (231Pa), which are produced in sea water and removed by particle scavenging on timescales of decades to centuries, respectively4, record consistent evidence for the export of 231Pa from the deep Arctic and may indicate continuous deep-water exchange between the Arctic and Atlantic oceans throughout the past 35,000 years. Seven well-dated box-core records provide a comprehensive overview of 231Pa and 230Th burial in Arctic sediments during glacial, deglacial and interglacial conditions. Sedimentary 231Pa/230Th ratios decrease nearly linearly with increasing water depth above the core sites, indicating efficient particle scavenging in the upper water column and greater influence of removal by lateral transport at depth. Although the measured 230Th burial is in balance with its production in Arctic sea water, integrated depth profiles for all time intervals reveal a deficit in 231Pa burial that can be balanced only by lateral export in the water column. Because no enhanced sink for 231Pa has yet been found in the Arctic, our records suggest that deep-water exchange through the Fram strait may export 231Pa. Such export may have continued for the past 35,000 years, suggesting a century-scale replacement time for deep waters in the Arctic Ocean since the most recent glaciation and a persistent contribution of Arctic waters to the global ocean circulation.}, keywords = {Marine chemistry, Palaeoceanography, Palaeoclimate}, issn = {0028-0836}, doi = {10.1038/nature12145}, url = {http://www.nature.com/doifinder/10.1038/nature12145}, author = {Hoffmann, Sharon S. and McManus, Jerry F. and Curry, William B. and Brown-Leger, L. Susan} } @article {2504, title = {Reconstructing 7000 years of North Atlantic hurricane variability using deep-sea sediment cores from the western Great Bahama Bank}, journal = {Paleoceanography}, volume = {28}, year = {2013}, month = {Jan-03-2013}, pages = {31 - 41}, abstract = {[1] Available overwash records from coastal barrier systems document significant variability in North Atlantic hurricane activity during the late Holocene. The same climate forcings that may have controlled cyclone activity over this interval (e.g., the West African Monsoon, El Ni{\~n}o{\textendash}Southern Oscillation (ENSO)) show abrupt changes around 6000 yrs B.P., but most coastal sedimentary records do not span this time period. Establishing longer records is essential for understanding mid-Holocene patterns of storminess and their climatic drivers, which will lead to better forecasting of how climate change over the next century may affect tropical cyclone frequency and intensity. Storms are thought to be an important mechanism for transporting coarse sediment from shallow carbonate platforms to the deep-sea, and bank-edge sediments may offer an unexplored archive of long-term hurricane activity. Here, we develop this new approach, reconstructing more than 7000 years of North Atlantic hurricane variability using coarse-grained deposits in sediment cores from the leeward margin of the Great Bahama Bank. High energy event layers within the resulting archive are (1) broadly correlated throughout an offbank transect of multi-cores, (2) closely matched with historic hurricane events, and (3) synchronous with previous intervals of heightened North Atlantic hurricane activity in overwash reconstructions from Puerto Rico and elsewhere in the Bahamas. Lower storm frequency prior to 4400 yrs B.P. in our records suggests that precession and increased NH summer insolation may have greatly limited hurricane potential intensity, outweighing weakened ENSO and a stronger West African Monsoon{\textemdash}factors thought to be favorable for hurricane development.}, doi = {10.1002/palo.v28.110.1002/palo.20012}, url = {http://doi.wiley.com/10.1002/palo.v28.1http://doi.wiley.com/10.1002/palo.20012https://api.wiley.com/onlinelibrary/tdm/v1/articles/10.1002\%2Fpalo.20012}, author = {Toomey, Michael R. and Curry, William B. and Donnelly, Jeffrey P. and van Hengstum, Peter J.} } @article {2563, title = {Rates and Mechanisms of Mineral Carbonation in Peridotite: Natural Processes and Recipes for Enhanced, in situ CO 2 Capture and Storage}, journal = {Annual Review of Earth and Planetary Sciences}, volume = {39}, year = {2011}, month = {Jun-05-2013}, pages = {545 - 576}, abstract = {Near-surface reaction of CO2-bearing fluids with silicate minerals in peridotite and basalt forms solid carbonate minerals. Such processes form abundant veins and travertine deposits, particularly in association with tectonically exposed mantle peridotite. This is important in the global carbon cycle, in weathering, and in understanding physical-chemical interaction during retrograde metamorphism. Enhancing the rate of such reactions is a proposed method for geologic CO2 storage, and perhaps for direct capture of CO2 from near-surface fluids. We review, synthesize, and extend inferences from a variety of sources. We include data from studies on natural peridotite carbonation processes, carbonation kinetics, feedback between permeability and volume change via reaction-driven cracking, and proposed methods for enhancing the rate of natural mineral carbonation via in situ processes ("at the outcrop") rather than ex situ processes ("at the smokestack"). }, issn = {0084-6597}, doi = {10.1146/annurev-earth-092010-152509}, url = {http://www.annualreviews.org/doi/10.1146/annurev-earth-092010-152509}, author = {Kelemen, Peter B. and Matter, Juerg and Streit, Elisabeth E. and Rudge, John F. and Curry, William B. and Blusztajn, Jerzy} } @inbook {1390, title = {North Atlantic intermediate depth variability during the Younger Dryas; evidence from benthic foraminiferal Mg/Ca and the GFDL R30 coupled climate model}, booktitle = {Geophysical Monograph, vol. 173}, year = {2007}, note = {id: 857; American Geophysical Union 2005 fall meeting, San Francisco, CA, United States, Dec 5-9, 2005 NSF grants OCE-0096495, ATM-0502428, OCE-0096472, OCE-0220776 and ATM-0501351 References: 72; illus.; Y}, month = {2007}, pages = {247-263}, publisher = {American Geophysical Union}, organization = {American Geophysical Union}, address = {Washington}, keywords = {24, Quaternary geology, Atlantic Ocean, benthic environment, Cenozoic, chemical ratios, Foraminifera, Glaciation, Gulf of Mexico, ice cores, Invertebrata, isotope ratios, isotopes, Little Bahama Bank, Mg/Ca, microfossils, North Atlantic, O-18/O-16, oxygen, paleo-oceanography, paleobathymetry, paleosalinity, paleotemperature, Pleistocene, Protista, Quaternary, Stable isotopes, Straits of Florida, upper, upper Weichselian, Weichselian, Younger Dryas}, isbn = {9780875904382}, author = {Came, Rosemarie E. and Curry, William B. and Oppo, Delia W. and Broccoli, Anthony J. and Stouffer, Ronald J. and Lynch-Stieglitz, Jean}, editor = {Schmittner, Andreas} }