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Lorraine Lisiecki & Maureen Raymo

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Lorraine Lisiecki & Maureen Raymo PP51B-0482 Age differences between Atlantic and Pacific benthic δ18O at terminations Lorraine Lisiecki & Maureen Raymo Boston University Abstract Methods Results Benthic δ18O is often used as a stratigraphic tool to place marine records on a common The age or duration of terminations (other than the most recent, T1) cannot be measured We create Atlantic and Pacific δ18O stacks for the last 5 terminations using F age model and as a proxy for the timing of ice volume/sea level change. However, directly. Instead we compare sedimentation rates during terminations to examine whether tie points only at the start and end of each termination and averaging data in 3.4 3.6 3.6 18 18 18 3.8 δ δ Pacic benthic Skinner & Shackleton [2005] found that the timing of benthic δ O change at the last the change in benthic O at terminations may be delayed or slower in the Pacific than 2-kyr intervals (Figure F). We also adjust the duration of Pacific O change O 3.8 18 T1 δ 18 18 4 termination differed by 4000 years between two sites in the Atlantic and Pacific. Do the Atlantic. Aligning Pacific δ O to Atlantic δ O should produce a spike in Pacific sedi- by assuming that the duration differences calculated in Figure D result solely 4 4.2 18 mentation rates if slow Pacific terminations are compressed to fit faster Atlantic termina- from lags in Pacific δ18O. Because the spikes in sed rate ratio all occur mid- 4.2 δ these results imply that benthic O change may not accurately record the timing of 4.4 δ 18 18 4.4 18 18 tions. We align the benthic δ O records of 20 Atlantic and 14 Pacific sites to the LR04 termination, δ O change appears to begin at nearly the same time in both O terminations? We compare benthic δ O records from 34 sites in the Atlantic and Pa- Atlantic benthic 4.6 18 18 4.6 18 benthic δ O stack [Lisiecki & Raymo, 2005] using an automated graphic correlation algo- oceans. Our sed rate results also suggest that Pacific δ O lags the Atlantic 4.8 cific to evaluate differences in the timing of terminations as recorded by benthic δ O. 4.8 18 rithm [Lisiecki & Lisiecki, 2002] (Figure B). Figure C shows the sedimentation rates of by less than 1.2 kyr at the end of terminations. δ 6 8 10 12 14 16 18 Statistical analysis of sedimentation rates derived from the alignment of benthic O Time (ka) 18 each site and their geometric mean. Because uncertainty in our age model affects abso- suggests an Atlantic lead over Pacific benthic δ O change during the last 6 termina- 18 lute sedimentation rates, we focus on the ratio of Pacific to Atlantic sedimentation rates Figure F shows the maximum lag between mean Pacific and Atlantic δ O to 3.2 tions. We estimate an average termination age difference of 1300 years between the 3.2 (Figure D), which is independent of age model. be 2 kyr in T1, 5 kyr in T2, 2 kyr in T3, 4 kyr in T4, and 4 kyr in T5. The mean 3.4 3.4 Atlantic and Pacific, approximately consistent with the delay expected due to ocean 3.6 T2 3.6 Pacic benthic lag for all five terminations is only 1.3 kyr. O 18 δ mixing rates, given that most glacial meltwater probably enters the North Atlantic. 3.8 3.8 4 4 However, we also find evidence of brief 4000 yr lags during the middle of several ter- LR04 4.2 B δ ODP 980 C 4.2 ODP 982 18 18 Discussion of Uncertainty 4.4 O ODP 983 minations, suggesting that termination mid-points may make poor δ O tie points. 1 4.4 ODP 984 10 Atlantic benthic ODP 552 Age model uncertainty is ~4 kyr, but uncertainty in Pacific-Atlantic age dif- 4.6 ODP 607 4.6 ODP 664 4.8 ODP 502 ODP 658 ferences should be only ~2 kyr. Our results describe average differences 4.8 ODP 659 122 124 126 128 130 132 134 136 ODP 925 Sed Rate (cm/kyr) 0 Time (ka) ODP 926 10 between ocean basins. Lags may vary depending on the specific hydro- ODP 927 ODP 928 ODP 929 5 logical setting of a particular site. ODP 1090 RC13-229 4.5 3.6 GeoB1041 3.5 ODP 1089 GeoB1214 4 ODP 677 Pacic benthic O T3 3.8 ODP 846 3.5 Our analysis is based on the assumption that sed rate changes during ter- 18 δ ODP 849 ODP 1012 ODP 1020 3 Atlantic Pacic minations are small or randomly distributed. This assumption clearly fails 4 RC13-110 4 Introduction V19-28 Mean Sed Rate (cm/kyr) V21-146 O 3 δ 18 PC-72 at some study sites. Widespread, termination-specific changes in sed 18 δ ODP 806 4.2 O ODP 1123 4 18 ODP 1143 rates (e.g., due to IRD deposition, abyssal currents, or carbonate dissolu- Atlantic benthic Because a large fraction of benthic δ O change is due to ODP 1146 5 PC-18 Benthic 4.4 18 0 100 200 300 400 500 600 700 global ice volume change, benthic δ O is often used as a 0 100 200 300 400 500 600 700 tion) would produce errors in our results. For example, IRD would tend to 4.5 Time (ka) Time (ka) lengthen termination stratigraphy in the North Atlantic and lead us to un- 238 240 242 244 246 248 250 252 stratigraphic tool to place marine records on a common Time (ka) derestimate Pacific lags. Excluding the 5 North Atlantic sites with highly A age model and as a proxy for the timing of ice volume/sea We must also address the fact that glacial cycles produce large sedimentation rate level change. These applications require the assumptions variable IRD content from our analyses results in changes in termination 3.4 changes at many sites. This is partially compensated by averaging the sedimentation 3.4 18 that δ O change is rapidly transmitted throughout the duration of only 0.2 kyr. 3.6 3.6 Pacic benthic rates of many globally distributed sites. However, glacial cyclicity remains in the ratio of O T4 18 δ deep ocean and that the effects of hydrographic changes 3.8 3.8 Pacific to Atlantic mean sedimentation rate (Figure D) due to basin-wide sedimentation 4 are in phase with ice volume. 4 changes. In addition to 100-kyr cyclicity, the sed rate ratio also clearly shows rapid, large 4.2 δ 4.2 18 4.4 O changes at some terminations (T1, T2, T4, and T5). Atlantic benthic Recently, Skinner & Shackleton [2005] found that the Conclusions 4.6 4.4 18 4.8 4.6 timing of benthic δ O change at the last termination dif- 18 To test the statistical significance of the termination changes, we calculate the deviation ● For the last 5 terminations, Pacific benthic δ O change lags the Atlantic 329 331 333 335 337 339 341 343 345 fered by ~4000 years between two sites in the Atlantic and of the sed rate ratio relative its 13-kyr running mean (Figure E). Over the last 550 kyr, by an average of 1.3 kyr. Time (ka) Pacific (Figure A). Based on Mg/Ca paleothermometry, deviations in the sed rate ratio above the 2-σ limit are uniquely associated with termina- 3.4 they argued that these age discrepancies resulted from a tions and the pseudo-termination preceding MIS 7c. Integrating the area under each ter- ● During some terminations this lag briefly increase to ~4 kyr, perhaps due 3.4 3.6 3.6 Pacic benthic O T5 late temperature increase in the Pacific and millennial- 18 3.8 δ mination spike relative to pre- and post-termination sed rates provides an estimate of the to the hydrographic changes described by Skinner & Shackleton [2005]. 3.8 18 4 scale circulation changes in the Atlantic. Such a large dis- average duration difference between Atlantic and Pacific δ O change (Figure D). 4 18 4.2 δ 4.2 crepancy in O change would produce significant age 4.4 δ ● Because we find no evidence for large age offsets at the beginning or 18 18 4.4 O model errors when the alignment of δ O stratigraphy is 18 Atlantic benthic 4.6 1.3 kyr end of terminations, these points make better δ O tie points than termi- 4.6 based on termination mid-points. Additionally, this suggest 0.9 kyr 4.8 1.1 0.7 kyr nation midpoints. 5 4.8 Skinner & Shackleton [2005] that benthic δ18O change may not always be a reliable in- 0.2 kyr 1 411 413 415 417 419 421 423 425 427 429 431 433 0.6 kyr Time (ka) dicator of the timing of sea level change. ● The timing of δ18O change at individual sites could vary significantly from 0.9 0.1 kyr D the basin-wide averages presented here. Atlantic δ18 0.8 Here we compare benthic O records from 34 sites in Pac:Atl Sed Rate Pacic the Atlantic and Pacific to evaluate differences in the 0.7 T1 T2 T3 T4 T5 T6 T7 T8 δ18 timing of terminations as recorded by benthic O. 0.1 References 0.05 +2σ Lisiecki, L. E., and P. A. Lisiecki (2002), Application of dynamic programming to the correlation of paleoclimate records, Paleoceanography, 17, 1049, doi:10.1029/2001PA000733.
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