GSA Data Repository 2015295
Oxygen isotope mass-balance constraints on Pliocene sea level
and East Antarctic Ice Sheet stability
Matthew J. Winnick1,* and Jeremy K. Caves1
1
Department of Earth System Science, Stanford University, 473 Via Ortega, Rm. 140, Stanford,
CA 94305 USA
*
Email: [email protected]
1. Sensitivity to Enhanced Warming over GIS and WAIS
In the scenarios presented in the main text, we assume that warming occurs with equal
magnitude over EAIS, GIS, and WAIS. However, there is substantial evidence that Pliocene
warming was amplified in the Northern Hemisphere (Lunt et al., 2012; Haywood et al., 2013;
Brigham-Grette et al., 2013; Miller et al., 2010) relative to the Southern Hemisphere. There is
further evidence that warming was likely greater over WAIS than over EAIS (Bromwich et al.,
2012; Haywood et al., 2013). Therefore, in may be inappropriate to assume that the same
temperature increases occurred over all three of these ice-sheets.
For Scenario 1 (full deglaciation of GIS and WAIS), this greater amplification is irrelevant.
However, for Scenario 2, it may have further changed the 18Oi of GIS and WAIS. We tested this
by amplifying warming over GIS by a factor of 3 and over WAIS by a factor of 2 relative to
warming over EAIS.
As shown in Fig. DR2, this assumption makes no substantial difference in our estimates. It
slightly lowers total estimated sea level rise in Scenario 2 due primarily to the greater transfer of
18
O into the GIS, removing the need to add melt to account for the 0.3 18Ob shift.
2. Calculation of the Masses of the Marine-based and Non-marine-based WAIS sectors
First, we use Fretwell et al. (2013) to partition the WAIS into the marine-based and non-marinebased sectors. The marine-based sector accounts for 3.4 m of sea level rise, while the nonmarine-based sector accounts for 0.9 m of sea level rise (see Table 1). For the non-marine-based
sector, we assume that all melt is converted into sea-level rise. Second, based on the assumption
that all melt from Greenland is converted to sea level rise (~7.3 m SLE), we calculate an
effective ocean surface area of 3.9 x 1014 m2. We then use this ocean surface area to calculate the
mass of the non-marine-based sectors of WAIS needed to cause 0.9 m sea level rise (0.322 x 1018
kg). The remainder (2.43 x 1018 kg) comprises the marine-based portions of the WAIS, which we
assume is derived from meteoric precipitation.
3. Sensitivity to Pliocene Bottom Water Temperatures
Following the methods of Miller et al. (2012), we test our results to different assumptions of
Pliocene bottom water temperature changes on the 18Ob record. In the main text, we assume
temperature-controlled changes in the equilibrium fractionation of calcification accounts for
0.1‰ of the MPWP interglacial-modern offset (equivalent to 67:33 partitioning of the Δ18Osw:ΔT signal). Here, we show results assuming temperature changes account for 0.05‰ and
0.15‰ of the total 0.3‰ offset, corresponding to 80:20 and 50:50 end-member signal
partitioning ratios of Δ18Osw:ΔT, respectively.
Under the 80:20 signal partitioning case, melting ice sheets must account for a greater portion of
the 18Ob signal, causing both higher estimated MPWP global mean sea level (GMSL) and a
greater contribution from EAIS as shown in Fig. DR3. Under our Scenario 2, 10-19 ºC of
Antarctic warming is required to account for the 18Ob signal without invoking EAIS melting
(Fig. DR3a). We also note that even with no Antarctic temperature change, maximum eustatic
sea levels are still only 17.5 m above modern under Scenario 1 (Fig. DR3b). This is significantly
lower than the peak GMSL estimate of 23 m using the same signal partitioning ratio from Miller
et al. (2012), and results from our inclusion of low 18O values from EAIS and melting of
submarine WAIS ice as discussed in the main text. Under Scenario 2 and no Antarctic
temperature change, peak GMSL is 15.5 m, with 8.5 m contribution from EAIS (~16% mass
loss).
Under the 50:50 signal partitioning case, melting ice sheets must account for smaller portion of
the 18Ob signal. This results in lower peak GMSL, less contribution from EAIS, and lower
temperatures needed to invoke no EAIS melting (Fig. DR4). Under Scenario 1, full melting of
GIS and WAIS accounts for the entire 18Ob signal, and any Antarctic temperature change must
involve EAIS growth (i.e., de Boer et al., 2015). Under Scenario 2 and our 2.5-5 ºC estimated
range in Pliocene Antarctic temperature increase, minimum peak GMSL, calculated using the
Masson-Delmotte et al. (2008) 18Op-T, relationship is 5-8 m above modern (Fig DR4b).
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Table DR1. Published estimates of peak global mean sea level (GMSL) MPWP sea level. All measurements are in meters. GMSL =
Global Mean Sea Level. IPCC = Intergovernmental Panel on Climate Change. ISM = Ice Sheet Model.
Mean Upper Lower
Type
Height bound bound Description
Reference
Paleoshore
35
Orangeburg Scarp, NC/SC
Dowsett and Cronin (1990)
Paleoshore
17.5
20
15
Min Est - Moore House Fm., VA
Krantz (1991)
Paleoshore
22.5
25
20
Min Est - Enewetak Atoll, Pacific
Wardlaw and Quinn (1991)
Paleoshore
60
Nome coastal plain, AK
Kaufman and Brigham-Grette (1993)
Paleoshore
30
Roe Plain, W. Australia
James et al. (2006)
18
18
22
32
12
Miller et al. (2012)
 O
Benthic  O, multiple studies
18
18
30
Dwyer and Chandler (2009)
 O
Peak GMSL from Mg/Ca-corrected  O
50
Peak GMSL, ~3.17 Ma
Rohling et al. (2014)
18O
18
34
Peak GMSL 3-point running mean, ~2.8 Ma
Sosdian and Rosenthal (2009)
 O
18
34
Peak GMSL, from Elderfield et al. (2012) data
Rohling et al. (2014)
 O
18
18
70
Dwyer et al. (1995)
 O
Peak GMSL from Mg/Ca-corrected  O
43
Mudelsee and Raymo (2005)
18O
Statistical analysis of 18O
IPCC
20
IPCC Highly Likely
Masson-Delmotte et al. (2013)
Assemblage
50
75
25
Peak GMSL, Benthic Assemblages
Naish and Wilson (2009)
ISM
13.5
10
WAIS melt (~6.5m) plus GIS deglaciation (3.5-7m)
Pollard and DeConto (2009)
ISM
24
20.5 AIS melt (17m) plus GIS deglaciation (3.5-7m)
Pollard et al. (2015)
ISM
10
~0m EAIS contribution; ISM and 10Be
Yamane et al. (2015)
ISM
5
29
1
Range of orbital configurations
Dolan et al. (2011)
Figure DR1: Attribution of 18Ob changes under Scenario 1 with full melting of the GIS and
WAIS. Compare to Figure 1, main text.
Figure DR2: Total eustatic sea level rise calculated assuming GIS and WAIS warming
amplification factors of 3x and 2x, respectively, relative to warming over EAIS. Compare to
Figure 2, main text.
Figure DR3: Attribution of 18Ob signal for Scenario 2 (A), and total eustatic sea level
calculations (B) for 80:20 Δ18Osw:ΔT signal partitioning.
Figure DR4: Attribution of 18Ob signal for Scenario 2 (A), and Total Eustatic Sea Level
(GMSL) calculations (B) assuming 50:50 Δ18Osw:ΔT signal partitioning.