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JimD

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Timing in sea level rise
« on: August 14, 2013, 02:00:54 AM »
If this has already been posted sorry.  But I figured this would be of some interest to those that spend a lot of time in the Antarctica section of the blog or are very interested in sea level rise.

http://www.nytimes.com/2013/08/13/science/timing-a-rise-in-sea-level.html?hpw&_r=0
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AbruptSLR

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Re: Timing in sea level rise
« Reply #1 on: August 14, 2013, 03:45:43 AM »
JimD,

Thanks.  This is news to me and it is rather disturbing to think of an abrupt 17-ft jump in SLR towards the end of the Eemian.  I post below the referenced abstract for ease of review (also see the attached supplemental material from the paper):

Ice sheet collapse following a prolonged period of stable sea level during the last interglacial;
by: Michael J. O’Leary, Paul J. Hearty, William G. Thompson, Maureen E. Raymo, Jerry X. Mitrovica & Jody M. Webster; Nature Geoscience; (2013); doi:10.1038/ngeo1890

Abstract:
"During the last interglacial period, 127–116 kyr ago, global mean sea level reached a peak of 5–9  m above present-day sea level. However, the exact timing and magnitude of ice sheet collapse that contributed to the sea-level highstand is unclear. Here we explore this timing using stratigraphic and geomorphic mapping and uranium-series geochronology of fossil coral reefs and geophysical modelling of sea-level records from Western Australia. We show that between 127 and 119 kyr ago, eustatic sea level remained relatively stable at about 3–4 m above present sea level. However, stratigraphically younger fossil corals with U-series ages of 118.1±1.4 kyr are observed at elevations of up to 9.5 m above present mean sea level. Accounting for glacial isostatic adjustment and localized tectonics, we conclude that eustatic sea level rose to about 9 m above present at the end of the last interglacial. We suggest that in the last few thousand years of the interglacial, a critical ice sheet stability threshold was crossed, resulting in the catastrophic collapse of polar ice sheets and substantial sea-level rise."
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AbruptSLR

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Re: Timing in sea level rise
« Reply #2 on: August 14, 2013, 12:33:09 PM »
I thought that I would re-post the attached figure from Grant et al 2012 (see the "Paleo-Evidence" thread), just to indicate how unexpected the O'Leary et al 2013 findings are.
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AbruptSLR

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Re: Timing in sea level rise
« Reply #3 on: August 15, 2013, 04:08:55 AM »
As noted in the web article linked by JimD, the O'Leary et al 2013 is possibly a vindication of Professor Paul J. Hearty who has been warning (controversially, as some researchers doubted his claims) for a long time about the possible upward spike in sea-level circa 118.1 kyr; as indicated in the following 2007 referenced paper and first attached figure (note that O'Leary is a co-author of the 2007 paper):

Hearty, P.J., Hollin, J.T., Neumann, A.C., O'Leary, M.J., McCulloch, M. 2007. Global sea-level fluctuations during the Last Interglaciation (MIS 5e). Quaternary Science Reviews, 26: 2090-2112.

Hearty discusses the first and second attached 2007 figures in the following 2012 reference:

The geological imprint of sea-level and climate changes during the last interglacial period (LIG, sensu lato, ~130 to 80 ka); by: P.J. Hearty; Proceedings of the National Science Foundation
Workshop; Sea level changes into MIS 5: from observations to predictions; Palma de Mallorca; April 10-14, 2012; Guest Editors: Bogdan P. Onac & Joan J. Fornós

"The record of sea-level changes based on field observations and geochronological data during MIS 5 has been the focus studies by Hearty and colleagues over the past 3 decades. Although considered by some to be “renegade science”, a few of these works may have helped to evolve our views of the events of MIS 5, along with stimulating much discussion and controversy. This presentation offers a synthesis of many of the key geological observations and relative sea level indicators (or RSLIs) during the LIG (Fig. 1).

A conspicuous feature on many relatively stable coastlines of the world is a broad morphological or constructional terrace, and in warmer latitudes, a reef terrace lying between +2.0 and +4.0 m attributed to the early half of MIS 5e. The RLSI#2 feature is considered the most reliable SL benchmark of MIS 5e. After several thousand years of relative stability, the broad terrace briefly became emergent (RSLI#3), and was subject to pedogenesis and erosion. The subaerial exposure of the terrace may have either been the result of a drop of RSL (a Younger Dryas type event?), a minor positive hydro-isostatic effect, or both. Subsequently, instability and shifting sea levels are manifest in the geomorphological and sedimentary imprint of late MIS 5e. Incised bioerosional notches, rubble benches, and coralgal veneers record this instability during a rise and fall of RSL to between +6 and +9 m (RSLI#4/5). Numerous workers have derived similar geologic records of SL changes during MIS 5e from a variety of intermediate and far field sites around the globe.


It is also apparent that the transition from late MIS 5e to MIS 5d (RSLI#6) was a tumultuous period in the oceans and along the coastlines. Near the close of MIS 5e, massive boulders were transported over exposed 20 m cliffs and some laterally over 500 m in North Eleuthera (Fig. 2), Bahamas. At approximately the same time, fenestrae-filled, oolitic chevron ridges several km-long were emplaced across the lowlands of the east-facing Bahamas. On older built-up coastlines, the same fenestrae-filled oolite bears evidence of wave runup (or rain-induced fenestrae?) up to elevations of +40 m. The mechanism for deposition of the giant boulders and the chevrons of North Eleuthera has been widely cited as the work of tsunami. However, if the boulders are genetically and temporally related to chevrons and runup features, as I suggest they are, it is more likely they were all formed contemporaneously by intense storms during a period of higher sea levels. This conclusion is based primarily on the complex internal sedimentary structure of the chevron ridges, which is not indicative of a multi-hour set of tsunami waves. As SL fell at the close of MIS 5e in the Bahamas, massive accumulations of dune sand reflect high-energy wave and wind conditions intersecting and transporting a large reservoir of oolitic shelf sediments onto land."


In the following reference, Thompson et al 2011 provide some limited background support evidence for both O'Leary et 2013's and Hearty 2012's, claims about how quickly the sea level changed during the Eemian peak (MIS 5e / MIS 5.5):

Sea-level oscillations during the last interglacial highstand recorded by Bahamas corals;
by: William G. Thompson, H. Allen Curran, Mark A.Wilson and Brian White; 2011; Nature Geoscience| DOI: 10.1038/NGEO1253

"Similar reef environments in the Bahamas are growing in approximately 3m of water, so this puts sea level at 4m at 123 kyr, 6m at 119.2 kyr and at 0m at some time in between." Also: "We therefore suggest that ice sheets during the last interglacial, which was warmer than today and has been proposed as an analogue for future warming, were less stable than during the mid-to-late Holocene."


The article that JimD links to has the following quote:

"The only possible explanation for such a large, rapid jump in sea level is the catastrophic collapse of a polar ice sheet, on either Greenland or Antarctica.

Dr. O’Leary is not prepared to say which; figuring that out is the group’s next project. But a 17-foot rise in less than a thousand years, a geologic instant, has to mean that one or both ice sheets contain some instability that can be set off by a warmer climate."

While I have repeated cited the limits to making parallels between the Eemian (MIS 5e) and the rest of this century (see the third attached figure from SkepticalScience.com with a very simple visual comparison); nevertheless, I will note the following:

(1) The 2013 findings of the North Greenland Eemian Ice Drilling (NEEM) program indicate that the GIS probably only contributed about 1.6m to sea level rise during the Eemian (this and all following referenced changes in sea level are relative to modern sea level); and may researchers have stated that they estimate that combination of mountain glaciers and ocean thermal expansion probably contributed an additional 1m of sea level rise during the Eemian.  Thus if O'Leary et al 2013's estimate that from 127 to 119 kyr ago eustatic sea level rose roughly between 3 to 4m; this would level the AIS (primarily the WAIS) to contribute between 0.4 to 1.4m to sea level rise during the Eemian (MIS 5e).  I note here that other researchers cite significantly different levels of sea level rise during this period (eg see Grant et al in previous post).

(2) If O'Leary et al 2013's claim that 118.1±1.4 kyr ago, in less than 1,000 years, that eustatic sea level rose an additional 5 to 6m to roughly 9m above modern sea level; raises the possibility that the AIS might have lost up to 9 -1.6 – 1 – 0.4 = 6m in less than one thousand years (however, it is also possible that the GIS might have contributed significantly to the 118.1 +/- 1.4 kyr ago spike.

(3) If Hearty 2012 is correct that at the end of MIS 5e (circa 118 to 115 kyr ago) the ocean was very stormy (enough to lift and translate megaboulders) then the atmosphere would also likely be highly disturbed during this period; and I wonder whether the normal three atmospheric circulatory cells could have collapsed to a single cell during the spike and then returned to the three cell configuration while the sea level dropped sharply after the 9m peak (see the first attached figure).

(4) The fourth attached figure shows a typical cross-sectional profile through the Thwaites Glacier and if it is true that this glacier would become inherently unstable to rapid calving when the calving face is about 1,000 m thick; this figure indicates that the rapid collapse TG and the adjoining portions of the WAIS might possibly have contributed to O'Leary et al 2013's spike; while the occurrence of a single atmospheric circulatory cell might destabilize significant portions of the GIS and more likely the EAIS via such events as: violent storms, atmospheric rivers, and temporary changes in upwelling patterns.
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AbruptSLR

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Re: Timing in sea level rise
« Reply #4 on: August 15, 2013, 05:07:41 AM »
In my immediately preceding post I raised the possibility that a single cell atmospheric circulatory might have happened at the beginning of the O'Leary et al 2013 sea level spike (circa 118.1 kyr ago), and then returned back to a three cell atmospheric circulatory pattern as sea level may have dropped rapidly after the peak.  This raises the question as to why these atmospheric circulatory patterns might change so abruptly at this time.  While I do not know the answer to this question (or even whether the spike actually occurred); I offer the following speculations:

The first attached figure (from SkepticalScience.com), not only compares the Eemian and Holocene solar insolation trends, this figure also shows why the MIS 5e (Eemian) ended at approximately 118 kyr ago.  This possibly due to a combination of slow ocean thermal inertia, and slow melting of the Arctic Sea Ice, ASI, through the MIS 5e (Eemian / MIS 5.5); finally by around 118 kyr the prior three cell pattern finally flipped to a single cell pattern; and then possibly due to the loss of solar insolation (in combination with other unknown factors, like increased snow fall and changes in albedo and recovery of the ASI) the single cell pattern changed quickly back to a three cell pattern.

Also, just for fun I attach the second image also from SkepticalScience.com; which highlights the uncertainties in Eemian sea level change per Kopp et al 2009.
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
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AbruptSLR

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Re: Timing in sea level rise
« Reply #5 on: August 23, 2013, 02:05:10 AM »
My replies #56 to 61 in the "Paleo-Evidence" thread indicate that the O'Leary et al 2013 sea level spike might be related to atmospheric conditions more similiar to the early Eocene than to the early Eemian conditions.
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
― Leon C. Megginson