I am copying here verbatim a post by the esteemed ASLR posted in another thread.
oren,
You (& others who are so inclined) should feel free to re-post any information that I provide in this thread to other threads where you feel that contrarians (and/or those who err on the side of least drama) are putting their collective thumbs on the scales.
For example, in the 'Hansen e al paper: 3+ meters SLR by 2100' thread, Reply #713 indicated that the findings of Polyak et al. (2018) that "Altogether, the data show that the MIS-5e highstand began by 126.6 ± 0.4 ka and ended no earlier than 116.0 ± 0.8 ka, representing 10.5 kyr of remarkable Western Mediterranean RSL stability between 1.4 and 2.9 m.a.p.s.l.", induced sidd to state:
"I find this striking because part of my concern for WAIS stability stems from the evidence for late Eemina sea level rise. If that did not actually happen, my concern is (slightly) diminished."
https://forum.arctic-sea-ice.net/index.php/topic,1327.700.htmlIn this regard, I note that the correct interpretation of paleo-SLR data is notoriously challenging and includes many uncertainties that could easily change Polyak et al. (2018)'s conclusions such as is illustrated by their own Fig. 3 (see the first attached image), including:
1. They show that their calculated RSL values (ranging from +1.4m to well over +14m) depend significantly on what GIA model and GIA assumptions that they utilize.
2. Their simplified GIA assumptions do not effectively consider phased ice mass loss scenarios from the NH and the SH.
See also:
Title: "Scientists find stable sea levels during last interglacial"
https://www.sciencedaily.com/releases/2018/09/180910111314.htmExtract: ""This is the most accurate, best resolved sea level record for MIS-5e of the last interglacial period," said Polyak. "It provides exceptionally accurate timing of the sea level history during the above mentioned period and shows that it rose to 6 meters above present sea level ~127,000 years ago, it would have gradually fell to 2 meters by 122,000 years ago, and would have stayed at that elevation for the remainder of the sea level highstand to 116,000 years ago," says Onac. "The results suggest that if the pre-industrial temperature will be surpassed by 1.5 to 2°C, sea level will respond and rise 2 to 6 meters (7 to 20 feet) above present sea level.""
& see:
Victor J. Polyak, Bogdan P. Onac, Joan J. Fornós, Carling Hay, Yemane Asmerom, Jeffrey A. Dorale, Joaquín Ginés, Paola Tuccimei, Angel Ginés. A highly resolved record of relative sea level in the western Mediterranean Sea during the last interglacial period. Nature Geoscience, 2018; DOI: 10.1038/s41561-018-0222-5
https://www.nature.com/articles/s41561-018-0222-5Abstract: "The magnitude and trajectory of sea-level change during marine isotope stage (MIS) 5e of the last interglacial period is uncertain. In general, sea level may have been 6–9 m above present sea level, with one or more oscillations of up to several metres superimposed. Here we present a well-dated relative sea-level record from the island of Mallorca in the western Mediterranean Sea for MIS-5e, based on the occurrence of phreatic overgrowths on speleothems forming near sea level. We find that relative sea-level in this region was within a range of 2.15 ± 0.75 m above present levels between 126,600 ± 400 and 116,000 ± 800 years ago, although centennial-scale excursions cannot be excluded due to some gaps in the speleothem record. We corrected our relative sea-level record for glacio-isostatic adjustment using nine different glacial isostatic models. Together, these models suggest that ice-equivalent sea-level in Mallorca peaked at the start of MIS-5e then gradually decreased and stabilized by 122,000 years ago, until the highstand termination 116,000 years ago. Our sea-level record does not support the hypothesis of rapid sea-level fluctuations within MIS-5e. Instead, we suggest that melting of the polar ice sheets occurred early in the interglacial period, followed by gradual ice-sheet growth."
Additional information Supplementary information is available for this paper at
https://doi.org/10.1038/ s41561-018-0222-5.
As further evidence that Polyak et al. (2018) may be erring on the side of least drama, Stocchi et al. (2018) find that: "Evidences of two MIS 5e RSL stands are found in Mallorca, northern Tyrrhenian coast of Italy, southeastern Sardinia and Tunisia."; which directly contradicts Polyak et al. (2018)'s conclusion.
See:
Stocchi et al. (2018), "MIS 5e relative sea-level changes in the Mediterranean Sea: Contribution of isostatic disequilibrium", Quaternary Science Reviews 185, 122-134,
https://doi.org/10.1016/j.quascirev.2018.01.004http://www.staff.science.uu.nl/~boer0160/docs/Stocchi_etal_QSR_2018.pdfAbstract: "Sea-level indicators dated to the Last Interglacial, or Marine Isotope Stage (MIS) 5e, have a twofold value. First, they can be used to constrain the melting of Greenland and Antarctic Ice Sheets in response to global warming scenarios. Second, they can be used to calculate the vertical crustal rates at active margins. For both applications, the contribution of glacio- and hydro-isostatic adjustment (GIA) to vertical displacement of sea-level indicators must be calculated. In this paper, we re-assess MIS 5e sea-level indicators at 11 Mediterranean sites that have been generally considered tectonically stable or affected by mild tectonics. These are found within a range of elevations of 2–10 m above modern mean sea level. Four sites are characterized by two separate sea-level stands, which suggest a two-step sea-level highstand during MIS 5e. Comparing field data with numerical modeling we show that (i) GIA is an important contributor to the spatial and temporal variability of the sea-level highstand during MIS 5e, (ii) the isostatic imbalance from the melting of the MIS 6 ice sheet can produce a >2.0 m sea-level highstand, and (iii) a two-step melting phase for the Greenland and Antarctic Ice Sheets reduces the differences between observations and predictions. Our results show that assumptions of tectonic stability on the basis of the MIS 5e records carry intrinsically large uncertainties, stemming either from uncertainties in field data and GIA models. The latter are propagated to either Holocene or Pleistocene sea-level reconstructions if tectonic rates are considered linear through time."
Extract: "Conclusions
1. The observed range of MIS 5e RSL highstand from 11 tectonically stable sites in the Mediterranean is comprised between 2 and 10m above present msl. The observed highstands are not necessarily coeval. Evidences of two MIS 5e RSL stands are found in Mallorca, northern Tyrrhenian coast of Italy, southeastern Sardinia and Tunisia.
2. The GIA-induced RSL changes across the Mediterranean are characterized by significant regional variability throughout the MIS 5e. The Earth is in isostatic imbalance and a generalized RSL above present sea level is predicted. …
3. According to GIA, the MIS 5e RSL highstand occurs at different times as a function of the geographical location in the Mediterranean.
4. To precisely quantify the GrIS and AIS retreat during MIS5e on the basis on RSL data, requires that the maximum extent, thickness and retreat of the MIS 6 ice sheets, and in particular of Fennoscandia, are constrained.
5. A two-step melting chronology where the GrIS and AIS retreat is out of phase is capable of reconciling predictions and observation provided that the GIA processes are included.
6. Neglecting the uncertainties that are related to RSL indicators and GIA may lead to over or underestimations of local crustal motions even at sites that are considered tectonically stable. As a consequence, we suggest that caution should be exercised when extrapolating long-term tectonic rates from MIS 5e shorelines."
Furthermore Barlow et al. (2018) find no evidence that RSL fell (note that it takes longer to form new ice sheets and it can take for them to collapse) significantly from the circa 127kya peak (see the second attached image) during the MIS 5e (Eemian).
Barlow NLM, McClymont EL, Whitehouse PL, Stokes CR, Jamieson SSR, Woodroffe SA, Bentley MJ, Callard SL, Ó Cofaigh C, Evans DJA, Horrocks JR, Lloyd JM, Long AJ, Margold M, Roberts DH & Sanchez-Montes ML (2018), "Lack of evidence for a substantial sea-level fluctuation within the Last Interglacial", Nature Geoscience, vol. 11, 627–634,
https://doi.org/10.1038/s41561-018-0195-4https://www.nature.com/articles/s41561-018-0195-4Abstract: "During the Last Interglacial, global mean sea level reached approximately 6 to 9 m above the present level. This period of high sea level may have been punctuated by a fall of more than 4 m, but a cause for such a widespread sea-level fall has been elusive. Reconstructions of global mean sea level account for solid Earth processes and so the rapid growth and decay of ice sheets is the most obvious explanation for the sea-level fluctuation. Here, we synthesize published geomorphological and stratigraphic indicators from the Last Interglacial, and find no evidence for ice-sheet regrowth within the warm interglacial climate. We also identify uncertainties in the interpretation of local relative sea-level data that underpin the reconstructions of global mean sea level. Given this uncertainty, and taking into account our inability to identify any plausible processes that would cause global sea level to fall by 4 m during warm climate conditions, we question the occurrence of a rapid sea-level fluctuation within the Last Interglacial. We therefore recommend caution in interpreting the high rates of global mean sea-level rise in excess of 3 to 7 m per 1,000 years that have been proposed for the period following the Last Interglacial sea-level lowstand."
Extract: "In conclusion, reconstructions of GMSL during the LIG4,5 have raised the intriguing possibility that fluctuations in ice-sheet volume occurred within the interglacial, that is, ice sheets regrew and then decayed. We have considered several possible driving mechanisms, acting alone or in combination, for multimetre changes in GMSL during the LIG. We find that the current understanding of ice-sheet histories during MIS 6 is not adequate enough to rule out the possibility that limitations in the modelling of the solid Earth response could be contributing to the appearance of a GMSL fall during the LIG3,11. However, if the GMSL fall was driven by changes in ice-sheet mass balance, it would require 1.15–3.45 million km3 of ice to form in less than 1,000 years; we found little geomorphological or sedimentary evidence for such substantial ice-sheet regrowth during the LIG. It is also clear that large uncertainties associated with the interpretation of some local RSL data that underpin the reconstructed GMSL curve remain. Taken together, our analysis leads us to question the occurrence of a rapid GMSL fall within the LIG, which also raises important questions about the very high reconstructed rates of GMSL rise following the lowstand; reported to be approximately 3 to 7 m kyr–1 (ref. 5).
We conclude that it is critical that future reconstructions of GMSL during the LIG include a range of realistic ice-sheet scenarios from the preceding glacial (MIS 6); take into account the impact of dynamic topography on the reconstructed elevations of former RSLs; and assemble a geographically and temporally widespread dataset of local RSL, with careful interpretation of fossil sea-level indicators with respect to tidal datums and accurate chronologies. Until these issues are better resolved, we would urge caution in using rates of GMSL rise from the LIG to project future sea-level changes.
…
5. Kopp, R. E., Simons, F. J., Mitrovica, J. X., Maloof, A. C. & Oppenheimer, M. A probabilistic assessment of sea level variations within the last interglacial stage. Geophys. J. Int. 193, 711–716 (2013)."
Finally, the third attached image from Austermann et al. (2017) indicates that correctly paleo-SLR data to account for dynamic topography (DT) can increase calculated estimates of paleo-SLR by about a meter in the Western Mediterranean during MIS 5e (Eemian);
Austermann J, Mitrovica JX, Huybers P and Rovere A (2017), "Detection of a dynamic topography signal in last interglacial sea-level records", Science Advances, vol. 3(7), e1700457,
https://doi.org/10.1126/sciadv.1700457http://advances.sciencemag.org/content/3/7/e1700457Abstract: "Estimating minimum ice volume during the last interglacial based on local sea-level indicators requires that these indicators are corrected for processes that alter local sea level relative to the global average. Although glacial isostatic adjustment is generally accounted for, global scale dynamic changes in topography driven by convective mantle flow are generally not considered. We use numerical models of mantle flow to quantify vertical deflections caused by dynamic topography and compare predictions at passive margins to a globally distributed set of last interglacial sea-level markers. The deflections predicted as a result of dynamic topography are significantly correlated with marker elevations (>95% probability) and are consistent with construction and preservation attributes across marker types. We conclude that a dynamic topography signal is present in the elevation of last interglacial sea-level records and that the signal must be accounted for in any effort to determine peak global mean sea level during the last interglacial to within an accuracy of several meters."
Extract: "A complication in all these studies is that various geodynamic processes contribute to the present elevation of paleo sea level records (
. A notable example of these processes is tectonic uplift or subsidence at active plate boundaries [for example, see Zazo et al. (9)], which often leads to the exclusion of these sites in reconstructions of past GMSL. Another important deformational process is the response of the Earth system to changes in ice and ocean loading during ice age cycles (10, 11), or glacial isostatic adjustment (GIA), a process first studied in the context of the LIG by Lambeck and Nakada (12). The accuracy of model-derived corrections for this global process is subject to uncertainties in ice history and mantle viscoelastic structure [for example, see Lambeck et al. (13)]. Additionally, the redistribution of sediment can lead to sea level changes through the buildup of topography and loading-induced deformation of the solid Earth and gravity field (14, 15).
Earth’s surface is further deflected by viscous stresses associated with buoyancy variations and flow within Earth’s convective mantle that can alter the elevation of sea-level markers subsequent to their formation (16–22). Effects of this so-called dynamic topography (DT) on the current elevation of sea-level markers dating to the mid-Pliocene (~3 million years ago) have been documented (23–25) and imply meter-scale displacements for LIG sea-level markers (24). Kopp et al. (4) incorporated uncertainties due to vertical land movement and applied nonzero rates in several passive margin regions. Although this correction may implicitly include the DT process, effects of DT are generally not addressed in sea level studies of Pleistocene interglacials and have not previously been shown to be detectable during the LIG. Here, we quantify and analyze the effects of DT on globally distributed markers of local peak sea level during the LIG."
Best,
ASLR
