replying to Y.Yokoyama et al. Nature Communications https://doi.org/10.1038/s41467-022-33952-z (2022)
Our recent ice sheet reconstruction, PaleoMIST 1.0, was created on the basis of using near-field (i.e., ice sheet proximal) geological constraints. This was done so that it would be independent of far-field relative sea level observations, that are subject to uncertainties in the global distribution of ice, and deep sea proxy based global mean sea level reconstructions, which have large uncertainties due to temperature and salinity effects. We do not disagree with the interpretation of the far-field data highlighted by Yokoyama et al., but emphasise that near-field constraints should be the starting point for reconstructing ice sheets.
We thank Yokoyama et al. for the opportunity to further discuss our ice sheet and paleotopography reconstruction, PaleoMIST 1.01 and acknowledge their extensive work acquiring sea level proxy data.
Yokoyama et al. state: community efforts have led to better understanding of the GMSL (e.g., PALSEA). We agree, and this is why we provided a comparison of our modelled sea level against scrutinised paleo relative sea level proxies for over 150 regions2, primarily taken from databases assembled by the HOLSEA project3. We focused on including datasets that we used to reduce the misfit with modelled near-field relative sea level in North America4,5 and Europe6,7,8. We included a far-field dataset from southeastern Asia9 and selected locations in tropical regions based on a database of coral relative sea level proxies10, including Tahiti and the Huon Peninsula. This model-data comparison was used to justify the Earth model used in our reconstruction.
No standardised database exists for the LGM, so we entered data from a few well known far-field areas to test if the ice sheet volume in our reconstruction was reasonable. This was neither claimed nor meant to be a comprehensive review, and we unintentionally missed adding some data from the Bonaparte Gulf11. We do dispute the interpretation of Yokoyama et al. that relative sea level lowstand was between −120.6 and −124.5 m at the location of core GC5 in the Bonaparte Gulf. Here, we have included this data, along with several other far-field sites (Fig. 1).
For the Great Barrier Reef, when converting the data from ref. 12 to index points, we made an error by subtracting half of the water depth range estimate instead of adding. As a result, the index points plotted below the depth of the sample, instead of above. We apologise to Yokoyama et al. for this error. We do not dispute their interpretations. The corrected plot is shown in Fig. 1.
Originally, we conservatively set proxies with large uncertainties (i.e., >10 m)10,13 to be marine limiting (i.e., sea level was above the elevation of the indicator). Such large uncertainties reduce the utility of these data to precisely define paleo sea level. Here, we plot them as sea level indicators (index points), using different colours for data with vertical uncertainties below and above 10 m.
The model-data comparison shown in Fig. 1 demonstrates that the calculated relative sea level from our ice sheet reconstruction is consistent with many of the available proxies that constrain far-field LGM sea level to be between −100 and −130 m. Specific to this comment, the calculated minimum relative sea level with our preferred Earth model is −117 m at the location of core GC5 in the Bonaparte Gulf (Yokoyama et al.’s estimate is −120 to −123 m), and −120 m off the coast of Cairns (Yokoyama et al.’s estimate is −118 m). The discrepancy between our modelled sea level and the Bonaparte Gulf proxy can plausibly be explained by the lack of ocean thermal expansion effects, groundwater storage changes, and the absence of smaller ice caps and glaciers in our reconstruction, estimated to be 3–4 m of sea level equivalent at the LGM14.
Figure 2 shows relative sea level at a number of locations between 57 and 27 kyr BP (covering Marine Isotope Stage (MIS) 3). Some of the data support the deep sea δ18O records, while some support sea level that is 10 s of metres higher. For Papua New Guinea, we have plotted the data as interpreted in three different studies10,15,16. Our calculated relative sea level during MIS 3 is higher than estimates presented by ref. 16, but is consistent with the revised estimates from ref. 10, and ref. 17. For Tahiti, our modelled relative sea level is consistent with the estimate pointed out by Yokoyama et al. (although the estimate in ref. 18 was −67 to −101 m, not −65 to −75 m). This proxy is from the final part of MIS 3 when the ice sheets were advancing, and does not represent the MIS 3 highstand period.
The geological constraints of limited ice sheet extent make it implausible for global average sea level to be −60 to −90 m during most of MIS 318, even when accounting for two different hypotheses for Laurentide Ice Sheet configuration19,20. It is possible to increase the ice volume in our model by increasing the basal shear stress. We increased the maximal scenario values by 20%, but this only lowered sea level by 5.2 m. The core region of the Laurentide Ice Sheet was likely warm-bedded through the glacial cycle21, so it is unlikely that this could be invoked to significantly increase ice volume.
Our reconstruction was based only on near-field constraints. One reason for this was so that it would be independent of deep sea foraminifera δ18O records. δ18Oforam reflects changes in ambient (deep water) temperature as well as the oxygen isotopic composition of seawater, which itself is a function of global ice volume and water mass mixing22,23,24. A second reason is that sea level proxies prior to about 12 kyr BP are rare and subject to uncertainties due to tectonics and sediment loading, and the ~40 kyr limit of the radiocarbon method. The third reason is that the available LGM (and MIS 3) records are ambiguous as to where the water is distributed between the ice sheets25. There are significant differences in the Earth structure between ice sheets and locations where far-field relative sea level records exist26. Therefore, it is questionable if sea level calculated using spherically symmetric Earth structures (used by us and by Yokoyama et al.) can precisely represent far-field sea level. Finally, our models do not include non-ice sheet and GIA sources of water volume changes, which will lead to an inherent uncertainty on sea level of several metres14. This is why we used these proxies qualitatively to test our ice sheet reconstruction, rather than as an absolute constraint.
We consider our model as preliminary and we expect different results in future reconstructions with different assumptions on Earth model and ice sheet margin configuration. This is demonstrated by the calculated sea level lowstand at the Bonaparte Gulf and GBR sites (Fig. 1), which is similar to Yokoyama et al’s despite having a different ice sheet configuration. This is what led us to conclude there is no LGM “missing ice problem”, and that the solution to global ice volume at the LGM may be non-unique given the current constraints.
Ultimately, the solution to reducing the uncertainties on past sea level and ice sheet configuration is to collect new data. Yokoyama et al are providing a great service to the community with their efforts to do this. However, though far-field sea level proxies are a valuable resource to deduce global ice volume through time, they should not be used in exclusion of glacial-geological and near-field sea level observations, which we believe are the fundamental starting point for ice sheet reconstruction.
Updated versions of the two reports comparing calculated sea level and sea level proxies at over 150 locations2, which includes a description of the evaluation methods, are available at https://doi.org/10.5281/zenodo.5647136. The scripts and paleo sea level proxy database used to create these reports are available at https://github.com/evangowan/paleo_sea_level. Source data are provided with this paper.
Gowan, E. J. et al. A new global ice sheet reconstruction for the past 80,000 years. Nat. Commun. 12, 1199 (2021).
Gowan, E. J.Comparison of the PaleoMIST 1.0 ice sheet margins, ice sheet and paleo-topography reconstruction with paleo sea level indicators (2020). https://doi.org/10.5281/zenodo.4061593.
Khan, N. S. et al. Inception of a global atlas of sea levels since the Last Glacial Maximum. Quat. Sci. Rev. 220, 359–371 (2019).
Engelhart, S. E. & Horton, B. P. Holocene sea level database for the Atlantic coast of the United States. Quat. Sci. Rev. 54, 12–25 (2012).
Vacchi, M. et al. Postglacial relative sea-level histories along the eastern Canadian coastline. Quat. Sci. Rev. 201, 124–146 (2018).
Hijma, M. P. & Cohen, K. M. Holocene sea-level database for the Rhine-Meuse Delta, The Netherlands: Implications for the pre-8.2 ka sea-level jump. Quat. Sci. Rev. 214, 68–86 (2019).
Rosentau, A. et al. A Holocene relative sea-level database for the Baltic Sea. Quat. Sci. Rev. 266, 107071 (2021).
Baranskaya, A. V. et al. A postglacial relative sea-level database for the Russian Arctic coast. Quat. Sci. Rev. 199, 188–205 (2018).
Mann, T. et al. Holocene sea levels in Southeast Asia, Maldives, India and Sri Lanka: The SEAMIS database. Quat. Sci. Rev. 219, 112–125 (2019).
Hibbert, F. D. et al. Coral indicators of past sea-level change: A global repository of U-series dated benchmarks. Quat. Sci. Rev. 145, 1–56 (2016).
Yokoyama, Y., Lambeck, K., De Deckker, P., Johnston, P. & Fifield, L. K. Timing of the Last Glacial Maximum from observed sea-level minima. Nature 406, 713–716 (2000).
Yokoyama, Y. et al. Rapid glaciation and a two-step sea level plunge into the Last Glacial Maximum. Nature 559, 603 (2018).
Ishiwa, T. et al. A sea-level plateau preceding the Marine Isotope Stage 2 minima revealed by Australian sediments. Sci. Reports 9, 6449 (2019).
Simms, A. R., Lisiecki, L., Gebbie, G., Whitehouse, P. L. & Clark, J. F. Balancing the Last Glacial Maximum (LGM) sea-level budget. Quat. Sci. Rev. 205, 143–153 (2019).
Cutler, K. B. et al. Rapid sea-level fall and deep-ocean temperature change since the last interglacial period. Earth Planet. Sci. Lett. 206, 253–271 (2003).
de Gelder, G. et al. High interstadial sea levels over the past 420ka from Huon terraces (Papua New Guinea). Preprint posted on EarthArXiv (2021). https://doi.org/10.31223/X5C03Z.
Thomas, A. L. et al. Penultimate deglacial sea-level timing from uranium/thorium dating of Tahitian corals. Science 324, 1186–1189 (2009).
Dalton, A. S. et al. The marine δ18O record overestimates continental ice volume during Marine Isotope Stage 3. Glob. Planet. Change 212, 103814 (2022).
Dalton, A. S. et al. Was the Laurentide Ice Sheet significantly reduced during marine isotope stage 3? Geology 47, 111–114 (2019).
Miller, G. H. & Andrews, J. T. Hudson Bay was not deglaciated during MIS-3. Quat. Sci. Rev. 225, 105944 (2019).
Pickler, C., Beltrami, H. & Mareschal, J.-C. Laurentide Ice Sheet basal temperatures during the last glacial cycle as inferred from borehole data. Clim. Past 12, 115–127 (2016).
Waelbroeck, C. et al. Sea-level and deep water temperature changes derived from benthic foraminifera isotopic records. Quat. Sci. Rev. 21, 295–305 (2002).
de Boer, B., van de Wal, R. S. W., Bintanja, R., Lourens, L. J. & Tuenter, E. Cenozoic global ice-volume and temperature simulations with 1-d ice-sheet models forced by benthic δ18o records. Ann. Glaciol. 51, 23–33 (2010).
Elderfield, H. et al. Evolution of ocean temperature and ice volume through the Mid-Pleistocene climate transition. Science 337, 704–709 (2012).
Lambeck, K., Rouby, H., Purcell, A., Sun, Y. & Sambridge, M. Sea level and global ice volumes from the Last Glacial Maximum to the Holocene. Proc. Natl. Acad. Sci. 111, 15296–15303 (2014).
Austermann, J., Mitrovica, J. X., Latychev, K. & Milne, G. A. Barbados-based estimate of ice volume at Last Glacial Maximum affected by subducted plate. Nat. Geosci. 6, 553–557 (2013).
Wessel, P. et al. The generic mapping tools version 6. Geochem. Geophys. Geosyst. 20, 5556–5564 (2019).
Peltier, W. & Fairbanks, R. G. Global glacial ice volume and Last Glacial Maximum duration from an extended Barbados sea level record. Quat. Sci. Rev. 25, 3322–3337 (2006).
Abdul, N. A., Mortlock, R. A., Wright, J. D. & Fairbanks, R. G. Younger Dryas sea level and meltwater pulse 1B recorded in Barbados reef crest coral Acropora palmata. Paleoceanography 31, 330–344 (2016).
Hanebuth, T., Stattegger, K. & Grootes, P. M. Rapid flooding of the Sunda Shelf: a late-glacial sea-level record. Science 288, 1033–1035 (2000).
Hanebuth, T. J., Stattegger, K., Schimanski, A., Lüdmann, T. & Wong, H. K. Late Pleistocene forced-regressive deposits on the Sunda Shelf (Southeast Asia). Mar. Geol. 199, 139–157 (2003).
Hanebuth, T., Stattegger, K. & Bojanowski, A. Termination of the Last Glacial Maximum sea-level lowstand: The Sunda-Shelf data revisited. Glob. Planet. Change 66, 76–84 (2009).
Cabioch, G. et al. Continuous reef growth during the last 23 cal kyr BP in a tectonically active zone (Vanuatu, SouthWest Pacific). Quat. Sci. Rev. 22, 1771–1786 (2003).
Cutler, K. B. et al. Radiocarbon calibration and comparison to 50 kyr BP with paired 14 C and 230 Th dating of corals from Vanuatu and Papua New Guinea. Radiocarbon 46, 1127–1160 (2004).
Wiedicke, M., Kudrass, H.-R. & Hübscher, C. Oolitic beach barriers of the last Glacial sea-level lowstand at the outer Bengal shelf. Mar. Geol. 157, 7–18 (1999).
Sasaki, K. et al. 230Th/234U and 14C dating of a lowstand coral reef beneath the insular shelf off Irabu Island, Ryukyus, southwestern Japan. Isl. Arc 15, 455–467 (2006).
Park, S.-C., Yoo, D.-G., Lee, C.-W. & Lee, E.-I. Last glacial sea-level changes and paleogeography of the Korea (Tsushima) Strait. Geo-Mar. Lett. 20, 64–71 (2000).
Camoin, G. F., Ebren, P., Eisenhauer, A., Bard, E. & Faure, G. A 300 000-yr coral reef record of sea level changes, Mururoa atoll (Tuamotu archipelago, French Polynesia). Palaeogeogr. Palaeoclimatol. Palaeoecol. 175, 325–341 (2001).
Chappell, J. et al. Reconciliaion of late Quaternary sea levels derived from coral terraces at Huon Peninsula with deep sea oxygen isotope records. Earth Planet. Sci. Lett. 141, 227–236 (1996).
Yokoyama, Y., Esat, T. M. & Lambeck, K. Coupled climate and sea-level changes deduced from Huon Peninsula coral terraces of the last ice age. Earth Planet. Sci. Lett. 193, 579–587 (2001).
Cabioch, G. & Ayliffe, L. K. Raised coral terraces at Malakula, Vanuatu, Southwest Pacific, indicate high sea level during marine isotope stage 3. Quat. Res. 56, 357–365 (2001).
Steinke, S., Kienast, M. & Hanebuth, T. On the significance of sea-level variations and shelf paleo-morphology in governing sedimentation in the southern South China Sea during the last deglaciation. Mar. Geol. 201, 179–206 (2003).
Geyh, M., Streif, H. & Kudrass, H.-R. Sea-level changes during the late Pleistocene and Holocene in the Strait of Malacca. Nature 278, 441 (1979).
Tanabe, S. et al. Stratigraphy and Holocene evolution of the mud-dominated Chao Phraya delta, Thailand. Quat. Sci. Rev. 22, 789–807 (2003).
Liu, J. et al. Delta development and channel incision during Marine Isotope Stages 3 and 2 in the western South Yellow Sea. Mar. Geol. 278, 54–76 (2010).
Wang, Y., Li, G., Zhang, W. & Dong, P. Sedimentary environment and formation mechanism of the mud deposit in the central South Yellow Sea during the past 40kyr. Mar. Geol. 347, 123–135 (2014).
Pico, T., Mitrovica, J. X., Ferrier, K. L. & Braun, J. Global ice volume during MIS 3 inferred from a sea-level analysis of sedimentary core records in the Yellow River Delta. Quat. Sci. Rev. 152, 72–79 (2016).
Liu, J., Saito, Y., Wang, H., Zhou, L. & Yang, Z. Stratigraphic development during the Late Pleistocene and Holocene offshore of the Yellow River Delta, Bohai Sea. J. Asian Earth Sci. 36, 318–331 (2009).
Cronin, T. M., Szabo, B. J., Ager, T. A., Hazel, J. E. & Owens, J. P. Quaternary climates and sea levels of the U.S. Atlantic Coastal Plain. Science 211, 233–240 (1981).
Mixon, R. B., Szabo, B. J. & Owens, J. P. Uranium-series dating of mollusks and corals, and age of Pleistocene deposits, Chesapeake Bay area, Virginia and Maryland. Professional Paper 1067- E, United States Geological Survey (1982). https://doi.org/10.3133/pp1067E.
Scott, T. W. Correlating late Pleistocene deposits on the coastal plain of Virginia with the glacial-eustatic sea-level curve. Master’s thesis, Old Dominion University, Norfolk, VA, United States (2006).
Mallinson, D., Burdette, K., Mahan, S. & Brook, G. Optically stimulated luminescence age controls on late Pleistocene and Holocene coastal lithosomes, North Carolina, USA. Quat. Res. 69, 97–109 (2008).
Moore, C. Geoarchaeological investigations of stratified Holocene aeolian deposits along the Tar River in North Carolina. Ph.D. thesis, Coastal Resources Management, East Carolina University, Greenville, NC, United States (2009).
Best, K. M. Quaternary geologic evolution of the Croatan beach ridge complex, Bogue Sound, and Bogue Banks, Carteret County, NC. Master’s thesis, Department of Geological Sciences, East Carolina University, Greenville, NC, United States (2010).
Culver, S. J. et al. Micropaleontologic record of Quaternary paleoenvironments in the Central Albemarle Embayment, North Carolina, U.S.A. Palaeogeogr. Palaeoclimatol. Palaeoecol. 305, 227–249 (2011).
Parham, P. R. et al. Quaternary coastal lithofacies, sequence development and stratigraphy in a passive margin setting, North Carolina and Virginia, USA. Sedimentology 60, 503–547 (2013).
Pico, T., Creveling, J. & Mitrovica, J. Sea-level records from the US mid-Atlantic constrain Laurentide Ice Sheet extent during Marine Isotope Stage 3. Nat. Commun. 8, 15612 (2017).
E.J.G. is funded by an International Postdoctoral Fellowship of Japan Society for the Promotion of Science. Figures in this paper were plotted with the aid of Generic Mapping Tools27. The authors acknowledge PALSEA, a working group of the International Union for Quaternary Sciences (INQUA) and Past Global Changes (PAGES), which in turn received support from the Swiss Academy of Sciences and the Chinese Academy of Sciences.
The authors declare no competing interests.
Peer review information
Nature Communications thanks Peter Clark and the anonymous reviewer(s) for their contribution to the peer review of this work.
Publisher’s note Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.
About this article
Cite this article
Gowan, E.J., Zhang, X., Khosravi, S. et al. Reply to: Towards solving the missing ice problem and the importance of rigorous model data comparisons. Nat Commun 13, 6264 (2022). https://doi.org/10.1038/s41467-022-33954-x