NSF GRFP Research Proposal:  2014

Multi-proxy dating and mapping of Plio-Pleistocene marine terrace sequences, with focus on interglacial Marine Isotope Stage (MIS) 31

 

Introduction:
Accurate dating and mapping of Plio-Pleistocene marine terraces during periods of warmth is important for correlating sea level estimates, determining Antarctic and Greenland ice sheet stability (through coupled sea level/ice volume models), and correcting local dynamic topography (and mantle viscosity) models [1]. I propose using a calibrated multi-proxy dating approach (87Sr/86Sr isotope, U-Pb series, and 26Al–10Be isochron burial dating techniques) to identify and precisely date fossil shorelines believed to reflect the interglacial event Marine Isotope Stage (MIS) 31, an extreme warm period that may possibly be a natural analogue to expected future climate
.

Background:
Reconstructing sea level (SL) during past interglacial periods is necessary if we are to test coupled ice sheet/sea level models used to predict future variations in SL around the world, as these models rely on previous knowledge of Antarctic and Greenland ice sheet volume during past interglacial and warm periods with similar atmospheric CO2 levels as today [1]. A major difficulty in determining past SL maxima is the number of corrections required to account for vertical changes in land relative to SL since formation of the marine terraces. Raymo et al. (2011) shows that accurate SL values relative to present are only possible after correcting for glacial isostatic adjustment (GIA), dynamic topography (DT) due to changes in mantle convection, local tectonic movement and sediment loading, and gravitational influences from ice sheet fluctuations [1]. Of these influences, DT is the hardest to constrain locally. I propose to map and date Plio-Pleistocene marine terrace sequences at four locations worldwide to correct for local dynamic topography (DT) and glacial isostatic adjustment (GIA), allowing better constraints on relative sea level elevations at these study sites and, thus, global eustatic sea level for Marine Isotope Stage (MIS) 31.


MIS 31 is an especially pronounced interglacial event occurring during the early Pleistocene (~1.08 - 1.06 Ma) that is characterized by the configuration of orbital parameters thought to have produced one of the strongest high-latitude summer insolation anomalies in the last few million years [2]. Although global warming of upper ocean temperatures (with reduced sea ice around Antarctica) is well documented at this time in marine sediment cores from the southern ocean [3], and 3-D ice sheet-shelf modeling indicates total collapse of the West Antarctic ice sheet (but the relative stability of the East Antarctic ice sheet remains an open question) [2], no studies exist documenting observed MIS 31 marine terraces. Thus, the magnitude of the volumetric loss of polar ice sheets is highly uncertain. I will address this problem through research at coastal areas thought to preserve MIS 31 terraces due to moderate DT uplift rates (such as Cape Range, Australia, and Puerto Deseado, Argentina), and use this data to evaluate the ice sheet model results of DeConto et al. (2012).

Figure 1: The LR04 benthic oxygen isotope stack over last 1.25 Myr (Lisiecki and Raymo, 2005), showing periods of warmth (shaded red) and cold (shaded blue), with the three interglacials examined in this paper outlined in yellow. Excursions above the red line (3.2‰), denote especially depleted δ18O values during the last 1.25 million years, and are defined here as extreme interglacial events. The purple line represents average δ18O over this time period.

Methodology/Research Plan:
Working in collaboration with Dr. Maureen Raymo at Lamont-Doherty Earth Observatory (LDEO) of Columbia University, I have already identified four coastlines along “passive” margins in central Argentina, western South Africa,  and two locations in western Australia that will serve as my focus research sites. These sites are also all being investigated as part of Raymo’s Pliomax Project, which aims to reconstruct sea level during the mid-Pliocene warm period.  In addition, I have begun training in geochemical dating techniques at the LDEO labs of Dr. Steve Goldstein and Dr. Jorge Schafer as part of Pliomax’s focus on older shoreline facies. Once multiple SL proxies have been collected, I will perform stringent screening procedures to check for alteration on aragonite and carbonate samples using methods I have previous experience with (including thin section, X-Ray Diffraction and SEM analysis on both acid leached and unleached samples). Samples for 87Sr/86Sr isotope and U-Pb series dating will be prepared in the LDEO PicoTrace laboratory (one of the cleanest academic laboratories in the country) with help from Dr. Goldstein to ensure the highest quality dates are achieved.  Cosmogenic isochron burial dating using 26Al–10Be nuclides is a relatively new technique that holds great promise for highly precise dating of marine terraces from 0.5 to 5 million years ago in areas where other dating proxies are inadequate [4]. Preparation of samples will occur in LDEO’s Cosmogenic laboratory with assistance from Dr. Schafer.

Broader Impacts:
With over 634 million people (or 10% of the global population) currently living in coastal areas less than 10 m above SL [5], predicting future sea level rise in the face of natural and anthropogenic forcing is crucial for mitigation efforts aimed at reducing risks to coastal communities. My project will address this need by providing critical information on polar ice sheet stability during MIS 31, an interval when the geologic record suggests extensive warming and total collapse of WAIS [2, 3]. In particular, my data will determine the stability of the EAIS during MIS 31, trying to confirm the findings of DeConto et al. (2012) 3-D ice sheet/shelf model [2] that suggest relative stability of the EAIS. As described in my personal goals essay, my findings will be made available to coastal communities, researchers and policy makers around the globe through online forums, websites, and outreach programs. I will
continuemy role as an educator to young scientists, focusing on mentoring youth from low-income areas, specifically aiding students from my local Spring Valley High School in Rockland County, N.Y.

Figure 2: Comparison of June 21st insolation at 65*N for each of the interglacials examined in this paper (including MIS 1). Notice the high summer insolation values for MIS 31 and 5e, and low insolation values for MIS 11 and MIS 1. Curves derived using Analyseries 2.0 software (Paillard et al. 1996) with Laskar et al. 2004 orbital inputs.

References:

[1] Raymo, M. E. Mitrovica, J.X., J. O'Leary, M., DeConto, R.M., Hearty, P.J. 2011. Departures from eustasy in Pliocene sea-level records. Nature Geoscience. 4: 328-332.

 

[2] DeConto, R., Pollard, D., and Kowalewski, D. (2012). Modeling Antarctic ice sheet and climate variations during Marine Isotope Stage 31. Global and Planetary Change. 96-97: 181-188.

 

[3] Villa, G., Persico, D., Wise, S., Gadaleta, A. (2012). Calcareous nannofossil evidence for marine Isotope Stage 31 (1 Ma) in core AND-1B, ANDRILL McMurdo Ice Shelf Project (Antarctica). Global and Planetary Change). 96-97: 75-86.

 

[4] Granger, D., Lifton, N., Willenbring, J. (2013). A cosmic trip: 25 years of cosmogenic nuclides in geology. Geological Society of America Bulletin. 125:1379-1402.

 

[5] McGranahan, G., Balk, D., Anderson, B. (2007). The rising tide: assessing the risks of climate change and human settlements in low elevation coastal zones. Environment and Urbanization. 19: 17-37.

 

[6] Lisiecki, L. and Raymo, M. E. (2005). A Pliocene-Pleistocene stack of 57 globally distributed benthic δ18O records. Paleoceanography.  20, PA1003.  http://dx.doi.org/10.1029/2004PA001071.

 

[7] Paillard, D., L. Labeyrie and P. Yiou (1996), Macintosh program performs time-series analysis, Eos Trans. AGU,  77:  379.