Carlson Anders E.

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Carlson
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Anders E.
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Preprint

Rapid early Holocene deglaciation of the Laurentide ice sheet

2008-07-24 , Carlson, Anders E. , LeGrande, Allegra N. , Oppo, Delia W. , Came, Rosemarie E. , Schmidt, Gavin A. , Anslow, Faron S. , Licciardi, Joseph M. , Obbink, Elizabeth A.

The early Holocene deglaciation of the Laurentide Ice Sheet (LIS) is the most recent and best constrained disappearance of a large Northern Hemisphere ice sheet. Its demise is a natural experiment for assessing rates of ice sheet decay and attendant contributions to sea level rise. Here we demonstrate with terrestrial and marine records that the final LIS demise occurred in two stages of rapid melting from ~9.0- 8.5 and 7.6-6.8 kyr BP with the LIS contributing ~1.3 and 0.7 cm yr-1 to sea level rise, respectively. Simulations using a fully coupled atmosphere-ocean general circulation model suggest that increased ablation from enhanced early Holocene boreal summer insolation may have been the predominant cause of the LIS contributions to sea level rise. Although the boreal summer surface radiative forcing of early Holocene LIS retreat is twice that of projections for 2100 C.E. greenhouse gas radiative forcing, the associated summer surface air temperature increase is the same. The geologic evidence for rapid LIS retreat under a comparable forcing provides a prehistoric precedent for a possible large negative mass balance response of the Greenland Ice Sheet by the end of the coming century.

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Preprint

Geochemical proxies of North American freshwater routing during the Younger Dryas cold event

2006-12-19 , Carlson, Anders E. , Clark, Peter U. , Haley, Brian A. , Klinkhammer, Gary P. , Simmons, Kathleen , Brook, Edward J. , Meissner, Katrin J.

The Younger Dryas cold interval represents a time when much of the Northern Hemisphere cooled from ~12.9 to 11.5 kiloyears before present. The cause of this event, which has long been viewed as the canonical example of abrupt climate change, was initially attributed to the routing of freshwater to the St. Lawrence River with an attendant reduction in Atlantic meridional overturning circulation. However, this mechanism has recently been questioned because current proxies and dating techniques have been unable to confirm that eastward routing with an increase in freshwater flux occurred during the Younger Dryas. Here we use new geochemical proxies (ΔMg/Ca, U/Ca & 87Sr/86Sr) measured in planktonic foraminifera at the mouth of the St. Lawrence Estuary as tracers of freshwater sources to further evaluate this question. Our proxies, combined with planktonic δ18Oseawater and δ13C, confirm that routing of runoff from western Canada to the St. Lawrence River occurred at the start of the Younger Dryas, with an attendant increase in freshwater flux of 0.06 ± 0.02 Sverdrup (1 Sverdrup (Sv) = 106 m3 s-1). This base discharge increase is sufficient to have reduced Atlantic meridional overturning circulation and caused the Younger Dryas cold interval. In addition, our data indicate subsequent fluctuations in the freshwater flux to the St. Lawrence River of ~0.06 to 0.12 Sv, thus explaining the variability in the overturning circulation and climate during the Younger Dryas.

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Article

Consistently dated Atlantic sediment cores over the last 40 thousand years

2019-09-02 , Waelbroeck, Claire , Lougheed, Bryan C. , Vazquez Riveiros, Natalia , Missiaen, Lise , Pedro, Joel , Dokken, Trond , Hajdas, Irka , Wacker, Lukas , Abbott, Peter , Dumoulin, Jean-Pascal , Thil, Francois , Eynaud, Frederique , Rossignol, Linda , Fersi, Wiem , Albuquerque, Ana Luiza , Arz, Helge W. , Austin, William E. N. , Came, Rosemarie E. , Carlson, Anders E. , Collins, James A. , Dennielou, Bernard , Desprat, Stéphanie , Dickson, Alex , Elliot, Mary , Farmer, Christa , Giraudeau, Jacques , Gottschalk, Julia , Henderiks, Jorijntje , Hughen, Konrad A. , Jung, Simon , Knutz, Paul , Lebreiro, Susana , Lund, David C. , Lynch-Stieglitz, Jean , Malaizé, Bruno , Marchitto, Thomas M. , Martínez-Méndez, Gema , Mollenhauer, Gesine , Naughton, Filipa , Nave, Silvia , Nürnberg, Dirk , Oppo, Delia W. , Peck, Vicky L. , Peeters, Frank J. C. , Penaud, Aurélie , Portilho-Ramos, Rodrigo da Costa , Repschläger, Janne , Roberts, Jenny , Ruhlemann, Carsten , Salgueiro, Emilia , Sanchez Goni, Maria Fernanda , Schönfeld, Joachim , Scussolini, Paolo , Skinner, Luke C. , Skonieczny, Charlotte , Thornalley, David J. R. , Toucanne, Samuel , Van Rooij, David , Vidal, Laurence , Voelker, Antje H. L. , Wary, Mélanie , Weldeab, Syee , Ziegler, Martin

Rapid changes in ocean circulation and climate have been observed in marine-sediment and ice cores over the last glacial period and deglaciation, highlighting the non-linear character of the climate system and underlining the possibility of rapid climate shifts in response to anthropogenic greenhouse gas forcing. To date, these rapid changes in climate and ocean circulation are still not fully explained. One obstacle hindering progress in our understanding of the interactions between past ocean circulation and climate changes is the difficulty of accurately dating marine cores. Here, we present a set of 92 marine sediment cores from the Atlantic Ocean for which we have established age-depth models that are consistent with the Greenland GICC05 ice core chronology, and computed the associated dating uncertainties, using a new deposition modeling technique. This is the first set of consistently dated marine sediment cores enabling paleoclimate scientists to evaluate leads/lags between circulation and climate changes over vast regions of the Atlantic Ocean. Moreover, this data set is of direct use in paleoclimate modeling studies.

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