Publications

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2014
Seierstad, IK, Abbott PM, Bigler M, Blunier T, Bourne AJ, Brook E, Buchardt SL, Buizert C, Clausen HB, Cook E, Dahl-Jensen D, Davies SM, Guillevic M, Johnsen SJ, Pedersen DS, Popp TJ, Rasmussen SO, Severinghaus JP, Svensson A, Vinther BM.  2014.  Consistently dated records from the Greenland GRIP, GISP2 and NGRIP ice cores for the past 104 ka reveal regional millennial-scale delta O-18 gradients with possible Heinrich event imprint. Quaternary Science Reviews. 106:29-46.   10.1016/j.quascirev.2014.10.032   AbstractWebsite

We present a synchronization of the NGRIP, GRIP and GISP2 ice cores onto a master chronology extending back to 104 ka before present, providing a consistent chronological framework for these three Greenland records. The synchronization aligns distinct peaks in volcanic proxy records and other impurity records (chemo-stratigraphic matching) and assumes that these layers of elevated impurity content represent the same, instantaneous event in the past at all three sites. More than 900 marker horizons between the three cores have been identified and our matching is independently confirmed by 24 new and previously identified volcanic ash (tephra) tie-points. Using the reference horizons, we transfer the widely used Greenland ice-core chronology, GICC05modelext, to the two Summit cores, GRIP and GISP2. Furthermore, we provide gas chronologies for the Summit cores that are consistent with the GICC05modelext timescale by utilizing both existing and new gas data (CH4 concentration and delta N-15 of N-2). We infer that the accumulation contrast between the stadial and interstadial phases of the glacial period was -10% greater at Summit compared to at NGRIP. The delta O-18 temperature-proxy records from NGRIP, GRIP, and GISP2 are generally very similar and display synchronous behaviour at climate transitions. The 1180 differences between Summit and NGRIP, however, changed slowly over the Last Glacial Interglacial cycle and also underwent abrupt millennial-to-centennial-scale variations. We suggest that this observed latitudinal delta O-18 gradient in Greenland during the glacial period is the result of 1) relatively higher degree of precipitation with a Pacific signature at NGRIP, 2) increased summer bias in precipitation at Summit, and 3) enhanced Rayleigh distillation due to an increased source-to-site distance and a potentially larger source-to-site temperature gradient. We propose that these processes are governed by changes in the North American Ice Sheet (NAIS) volume and North Atlantic sea-ice extent and/or sea-surface temperatures (SST) on orbital timescales, and that changing sea-ice extent and SSTs are the driving mechanisms on shorter timescales. Finally, we observe that maxima in the Summit NGRIP delta O-18 difference are roughly coincident with prominent Heinrich events. This suggests that the climatic reorganization that takes place during stadials with Heinrich events, possibly driven by a southward expansion of sea ice and low SSTs in the North Atlantic, are recorded in the ice-core records. (C) 2014 Elsevier Ltd. All rights reserved.

2005
Brook, EJ, White JWC, Schilla ASM, Bender ML, Barnett B, Severinghaus JP, Taylor KC, Alley RB, Steig EJ.  2005.  Timing of millennial-scale climate change at Siple Dome, West Antarctica, during the last glacial period. Quaternary Science Reviews. 24:1333-1343.   10.1016/j.quascirev.2005.02.002   AbstractWebsite

Using atmospheric methane and the isotopic composition of O-2 as correlation tools, we place the 6D record of ice from the Siple Dome (West Antarctica) ice core on a precise common chronology with the GISP2 (Greenland) ice core for the period from 9 to 57 ka. The onset of major millennial warming events in Siple Dome preceded major abrupt warmings in Greenland, and the pattern of millennial change at Siple Dome was broadly similar, though not identical, to that previously observed for the Byrd ice core (also in West Antarctica). The addition of Siple Dome to the database of well-dated Antarctic paleoclimate records supports the case for a coherent regional pattern of millennial-scale climate change in Antarctica during much of the last ice age and glacial-interglacial transition.