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2. A global synthesis of high-resolution stable isotope data from benthic foraminifera of the last deglaciation.

Author

Muglia, Juan, Mulitza, Stefan, Repschläger, Janne, Schmittner, Andreas, Lembke-Jene, Lester, Lisiecki, Lorraine, Mix, Alan, Saraswat, Rajeev, Sikes, Elizabeth, Waelbroeck, Claire, Gottschalk, Julia, Lippold, Jörg, Lund, David, Martinez-Mendez, Gema, Michel, Elisabeth, Muschitiello, Francesco, Naik, Sushant, Okazaki, Yusuke, Stott, Lowell, Voelker, Antje, and Zhao, Ning

Subjects
Seawater, Foraminifera, Carbon Isotopes, Carbon, Oxygen
Abstract

We present the first version of the Ocean Circulation and Carbon Cycling (OC3) working group database, of oxygen and carbon stable isotope ratios from benthic foraminifera in deep ocean sediment cores from the Last Glacial Maximum (LGM, 23-19 ky) to the Holocene (

Published
2023

3. Ice and ocean constraints on early human migrations into North America along the Pacific coast

Author

Praetorius, Summer K, Alder, Jay R, Condron, Alan, Mix, Alan C, Walczak, Maureen H, Caissie, Beth E, and Erlandson, Jon M

Subjects
Earth Sciences, Physical Geography and Environmental Geoscience, Geology, Life Below Water, Climate Action, Humans, North America, Ecosystem, Fresh Water, Human Migration, Oceans and Seas, Ice Cover, paleoceanography, sea ice, human migration, North Pacific, paleoclimate
Abstract

Founding populations of the first Americans likely occupied parts of Beringia during the Last Glacial Maximum (LGM). The timing, pathways, and modes of their southward transit remain unknown, but blockage of the interior route by North American ice sheets between ~26 and 14 cal kyr BP (ka) favors a coastal route during this period. Using models and paleoceanographic data from the North Pacific, we identify climatically favorable intervals when humans could have plausibly traversed the Cordilleran coastal corridor during the terminal Pleistocene. Model simulations suggest that northward coastal currents strengthened during the LGM and at times of enhanced freshwater input, making southward transit by boat more difficult. Repeated Cordilleran glacial-calving events would have further challenged coastal transit on land and at sea. Following these events, ice-free coastal areas opened and seasonal sea ice was present along the Alaskan margin until at least 15 ka. Given evidence for humans south of the ice sheets by 16 ka and possibly earlier, we posit that early people may have taken advantage of winter sea ice that connected islands and coastal refugia. Marine ice-edge habitats offer a rich food supply and traversing coastal sea ice could have mitigated the difficulty of traveling southward in watercraft or on land over glaciers. We identify 24.5 to 22 ka and 16.4 to 14.8 ka as environmentally favorable time periods for coastal migration, when climate conditions provided both winter sea ice and ice-free summer conditions that facilitated year-round marine resource diversity and multiple modes of mobility along the North Pacific coast.

Published
2023

5. Glacial isostatic adjustment directed incision of the Channeled Scabland by Ice Age megafloods

Author

Pico, Tamara, David, Scott R, Larsen, Isaac J, Mix, Alan C, Lehnigk, Karin, and Lamb, Michael P

Subjects
Channeled Scabland, glacial isostatic adjustment, erosional history
Abstract

During the last deglaciation, dozens of glacial outburst floods-among the largest known floods on Earth-scoured the Channeled Scabland landscape of eastern Washington. Over this same period, deformation of the Earth's crust in response to the growth and decay of ice sheets changed the topography by hundreds of meters. Here, we investigated whether glacial isostatic adjustment affected routing of the Missoula floods and incision of the Channeled Scabland from an impounded, glacial Lake Columbia. We used modern topography corrected for glacial isostatic adjustment as an input to flood models that solved the depth-averaged, shallow water equations and compared the results to erosion constraints. Results showed that floods could have traversed and eroded parts of two major tracts of the Channeled Scabland-Telford-Crab Creek and Cheney-Palouse-near 18 ka, whereas glacial isostatic adjustment limited flow into the Cheney-Palouse tract at 15.5 ka. Partitioning of flow between tracts was governed by tilting of the landscape, which affected the filling and overspill of glacial Lake Columbia directly upstream of the tracts. These results highlight the impact of glacial isostatic adjustment on megaflood routing and landscape evolution.

Published
2022

11. Calibration of the carbon isotope composition (δ13C) of benthic foraminifera

Author

Schmittner, Andreas, Bostock, Helen C, Cartapanis, Olivier, Curry, William B, Filipsson, Helena L, Galbraith, Eric D, Gottschalk, Julia, Herguera, Juan Carlos, Hoogakker, Babette, Jaccard, Samuel L, Lisiecki, Lorraine E, Lund, David C, Martínez‐Méndez, Gema, Lynch‐Stieglitz, Jean, Mackensen, Andreas, Michel, Elisabeth, Mix, Alan C, Oppo, Delia W, Peterson, Carlye D, Repschläger, Janne, Sikes, Elisabeth L, Spero, Howard J, and Waelbroeck, Claire

Subjects
Life Below Water, carbon, isotopes, benthic, foraminifera, calibration
Abstract

The carbon isotope composition (δ13C) of seawater provides valuable insight on ocean circulation, air-sea exchange, the biological pump, and the global carbon cycle and is reflected by the δ13C of foraminifera tests. Here more than 1700 δ13C observations of the benthic foraminifera genus Cibicides from late Holocene sediments (δ13CCibnat) are compiled and compared with newly updated estimates of the natural (preindustrial) water column δ13C of dissolved inorganic carbon (δ13CDICnat) as part of the international Ocean Circulation and Carbon Cycling (OC3) project. Using selection criteria based on the spatial distance between samples, we find high correlation between δ13CCibnat and δ13CDICnat, confirming earlier work. Regression analyses indicate significant carbonate ion (−2.6 ± 0.4) × 10−3‰/(μmol kg−1) [CO32−] and pressure (−4.9 ± 1.7) × 10−5‰ m−1 (depth) effects, which we use to propose a new global calibration for predicting δ13CDICnat from δ13CCibnat. This calibration is shown to remove some systematic regional biases and decrease errors compared with the one-to-one relationship (δ13CDICnat = δ13CCibnat). However, these effects and the error reductions are relatively small, which suggests that most conclusions from previous studies using a one-to-one relationship remain robust. The remaining standard error of the regression is generally σ ≅ 0.25‰, with larger values found in the southeast Atlantic and Antarctic (σ ≅ 0.4‰) and for species other than Cibicides wuellerstorfi. Discussion of species effects and possible sources of the remaining errors may aid future attempts to improve the use of the benthic δ13C record.

Published
2017

16. Carbon isotopes characterize rapid changes in atmospheric carbon dioxide during the last deglaciation

Author

Bauska, Thomas K, Baggenstos, Daniel, Brook, Edward J, Mix, Alan C, Marcott, Shaun A, Petrenko, Vasilii V, Schaefer, Hinrich, Severinghaus, Jeffrey P, and Lee, James E

Subjects
Earth Sciences, Physical Geography and Environmental Geoscience, Geology, Climate Action, Life Below Water, ice cores, paleoclimate, carbon cycle, atmospheric CO2, last deglaciation
Abstract

An understanding of the mechanisms that control CO2 change during glacial-interglacial cycles remains elusive. Here we help to constrain changing sources with a high-precision, high-resolution deglacial record of the stable isotopic composition of carbon in CO2(δ(13)C-CO2) in air extracted from ice samples from Taylor Glacier, Antarctica. During the initial rise in atmospheric CO2 from 17.6 to 15.5 ka, these data demarcate a decrease in δ(13)C-CO2, likely due to a weakened oceanic biological pump. From 15.5 to 11.5 ka, the continued atmospheric CO2 rise of 40 ppm is associated with small changes in δ(13)C-CO2, consistent with a nearly equal contribution from a further weakening of the biological pump and rising ocean temperature. These two trends, related to marine sources, are punctuated at 16.3 and 12.9 ka with abrupt, century-scale perturbations in δ(13)C-CO2 that suggest rapid oxidation of organic land carbon or enhanced air-sea gas exchange in the Southern Ocean. Additional century-scale increases in atmospheric CO2 coincident with increases in atmospheric CH4 and Northern Hemisphere temperature at the onset of the Bølling (14.6-14.3 ka) and Holocene (11.6-11.4 ka) intervals are associated with small changes in δ(13)C-CO2, suggesting a combination of sources that included rising surface ocean temperature.

Published
2016

27. Ryder Glacier in northwest Greenland is shielded from warm Atlantic water by a bathymetric sill

Author

Jakobsson, Martin, Mayer, Larry A., Nilsson, Johan, Stranne, Christian, Calder, Brian, O’Regan, Matthew, Farrell, John W., Cronin, Thomas M., Brüchert, Volker, Chawarski, Julek, Eriksson, Björn, Fredriksson, Jonas, Gemery, Laura, Glueder, Anna, Holmes, Felicity A., Jerram, Kevin, Kirchner, Nina, Mix, Alan, Muchowski, Julia, Prakash, Abhay, Reilly, Brendan, Thornton, Brett, Ulfsbo, Adam, Weidner, Elizabeth, Åkesson, Henning, Handl, Tamara, Ståhl, Emelie, Boze, Lee-Gray, Reed, Sam, West, Gabriel, and Padman, June

Published
2020
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34. Palaeoclimate constraints on the impact of 2 °C anthropogenic warming and beyond

Author

Fischer, Hubertus, Meissner, Katrin J., Mix, Alan C., Abram, Nerilie J., Austermann, Jacqueline, Brovkin, Victor, Capron, Emilie, Colombaroli, Daniele, Daniau, Anne-Laure, Dyez, Kelsey A., Felis, Thomas, Finkelstein, Sarah A., Jaccard, Samuel L., McClymont, Erin L., Rovere, Alessio, Sutter, Johannes, Wolff, Eric W., Affolter, Stéphane, Bakker, Pepijn, Ballesteros-Cánovas, Juan Antonio, Barbante, Carlo, Caley, Thibaut, Carlson, Anders E., Churakova (Sidorova), Olga, Cortese, Giuseppe, Cumming, Brian F., Davis, Basil A. S., de Vernal, Anne, Emile-Geay, Julien, Fritz, Sherilyn C., Gierz, Paul, Gottschalk, Julia, Holloway, Max D., Joos, Fortunat, Kucera, Michal, Loutre, Marie-France, Lunt, Daniel J., Marcisz, Katarzyna, Marlon, Jennifer R., Martinez, Philippe, Masson-Delmotte, Valerie, Nehrbass-Ahles, Christoph, Otto-Bliesner, Bette L., Raible, Christoph C., Risebrobakken, Bjørg, Sánchez Goñi, María F., Arrigo, Jennifer Saleem, Sarnthein, Michael, Sjolte, Jesper, Stocker, Thomas F., Velasquez Alvárez, Patricio A., Tinner, Willy, Valdes, Paul J., Vogel, Hendrik, Wanner, Heinz, Yan, Qing, Yu, Zicheng, Ziegler, Martin, and Zhou, Liping

Published
2018
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35. Mid-Pleistocene climate transition drives net mass loss from rapidly uplifting St. Elias Mountains, Alaska

Author

Gulick, Sean P. S., Jaeger, John M., Mix, Alan C., Asahi, Hirofumi, Bahlburg, Heinrich, Belanger, Christina L., Berbel, Glaucia B. B., Childress, Laurel, Cowan, Ellen, Drab, Laureen, Forwick, Matthias, Fukumura, Akemi, Ge, Shulan, Gupta, Shyam, Kioka, Arata, Konno, Susumu, LeVay, Leah J., März, Christian, Matsuzaki, Kenji M., McClymont, Erin L., Moy, Chris, Müller, Juliane, Nakamura, Atsunori, Ojima, Takanori, Ribeiro, Fabiana R., Ridgway, Kenneth D., Romero, Oscar E., Slagle, Angela L., Stoner, Joseph S., St-Onge, Guillaume, Suto, Itsuki, Walczak, Maureen D., Worthingtona, Lindsay L., Baileyb, Ian, Enkelmannc, Eva, Reeced, Robert, and Swartz, John M.

Published
2015

42. Global climate evolution during the last deglaciation

Author

Clark, Peter U., Shakun, Jeremy D., Baker, Paul A., Bartlein, Patrick J., Brewer, Simon, Brook, Ed, Carlson, Anders E., Cheng, Hai, Kaufman, Darrell S., Liu, Zhengyu, Marchitto, Thomas M., Mix, Alan C., Morrill, Carrie, Otto-Bliesner, Bette L., Pahnke, Katharina, Russell, James M., Whitlock, Cathy, Adkins, Jess F., Blois, Jessica L., Clark, Jorie, Colman, Steven M., Curry, William B., Flower, Ben P., He, Feng, Johnson, Thomas C., Lynch-Stieglitz, Jean, Markgraf, Vera, McManus, Jerry, Mitrovica, Jerry X., Moreno, Patricio I., and Williams, John W.

Published
2012

47. Isotopic Characterization of Water Masses in the Southeast Pacific Region: Paleoceanographic Implications

Author

Reyes‐Macaya, Dharma, primary, Hoogakker, Babette, additional, Martínez‐Méndez, Gema, additional, Llanillo, Pedro J., additional, Grasse, Patricia, additional, Mohtadi, Mahyar, additional, Mix, Alan, additional, Leng, Melanie J., additional, Struck, Ulrich, additional, McCorkle, Daniel C., additional, Troncoso, Macarena, additional, Gayo, Eugenia M., additional, Lange, Carina B., additional, Farias, Laura, additional, Carhuapoma, Wilson, additional, Graco, Michelle, additional, Cornejo‐D’Ottone, Marcela, additional, De Pol Holz, Ricardo, additional, Fernandez, Camila, additional, Narvaez, Diego, additional, Vargas, Cristian A., additional, García‐Araya, Francisco, additional, and Hebbeln, Dierk, additional

Published
2022
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