New paper! Nature Communications study highlights complex behavior of retreating Antarctic ice

Geomorphology, Research, , ,

How do grounding line fluctuations affect upstream ice? This is a fundamental question which we have attempted to illuminate using observations of geomorphology on the seafloor of the western Ross Sea. Subglacial and ice-marginal landforms tell us that East Antarctic ice flowed through the Transantarctic Mountains into the Ross Embayment during the Last Glacial Maximum (LGM) to occupy Drygalski, JOIDES, and Pennell troughs. Following the LGM, retreating ice unzipped through JOIDES and Pennell troughs to form a large embayment in the grounding line. This triggered drawdown and enhanced flux through the southern Drygalski outlet glaciers that drove a major reorganization of flow in Drygalski Trough from northward- to southward-flowing and caused ice to readvance about 50 kilometers through southern JOIDES Trough, delivering a significant volume of ice back to the ocean. Click on the image of the manuscript header to read more!

The images below show the configuration of the ice sheet embayment in JOIDES and Pennell Troughs, followed by the configuration of ice after the readvance of outlet glaciers through southern Drygalski Trough into southern JOIDES Trough.

Update on AGU 2017

Chronology, Geomorphology, Research, Sedimentology and Stratigraphy, , , , , , , ,

Last month I presented a poster at the AGU Fall Meeting that summarizes my work so far on reconstructing the post-LGM deglacial history of the Ross Sea (read abstract here). Click the image to the right to view a full-resolution jpg of the poster!

AGU prep is underway

Chronology, Geomorphology, Research, Sedimentology and Stratigraphy, , , , , , , ,

It’s that time of year again! Everyone is scrambling to get their posters completed and printed before leaving for AGU, resorting to begging the library staff to stay open just a few minutes later. Even though we know AGU happens at the same time every year, and have plenty of time to prepare, there is inevitably a throng of anxious geoscientists vying for a spot on the printing waiting list the night before getting on the plane.

Nevertheless, I am excited to present my work on the deglacial history of the Ross Sea!

 

 

Here is the abstract:

Marine evidence of a deconvolving Antarctic Ice Sheet during post-LGM retreat of the Ross Sea sector

1Lindsay O. Prothro, 2Yusuke Yokoyama, 1Lauren M. Simkins, 1John B. Anderson, 3Wojciech Majewski, 2Masako Yamane, 4Naohiko Ohkouchi

1Department of Earth, Environmental and Planetary Science, Rice University; 2Atmosphere and Ocean Research Institute, University of Tokyo; 3Department of Environmental Paleobiology, Polish Academy of Sciences; 4Department of Biogeochemistry, Japan Agency for Marine-Earth Science and Technology

Predictive models of ice sheet and sea level change are dependent on observational data of ice-sheet behavior for model testing and tuning. The geologic record contains a wealth of information about ice-sheet dynamics, with fewer logistical, spatial, and temporal limitations than are involved in data acquisition along contemporary ice margins. However, past ice-sheet behavior is still largely uncertain or contested due to issues with obtaining meaningful radiocarbon dates. We minimize bias from glacially-reworked carbon and limitations from unknown geomorphic context and uncertainty in sediment facies identification by using careful sedimentary analyses within a geomorphic framework, as well as selection of appropriate dating methods. Our study area, the Ross Sea sector of Antarctica, is the primary drainage outlet for ~25% of the continent’s grounded ice. During the Last Glacial Maximum, the low-profile, marine-based West Antarctic Ice Sheet (WAIS) and the steeper profile, largely land-based East Antarctic Ice Sheet (EAIS) converged in the Ross Sea to flow out to or near the continental shelf edge. Geomorphic and sedimentary data reveal that during their subsequent retreat to form the Ross Sea Embayment, the two ice sheets behaved differently, with the WAIS rapidly retreating tens of kilometers followed by extended pauses, while the EAIS retreated steadily, with shorter (decadal- to century-long) pauses. This behavior leads us to believe that the two ice sheets may have contributed diachronously to sea level. By acquiring accurate timing of grounding line retreat, we are able to calculate volumes of ice lost throughout deglaciation, as well as associated sea level contributions. In addition, we attempt to rectify the contradicting marine and terrestrial interpretations of retreat patterns from the Ross Sea continental shelf.

Time and location: Session C21E, Tuesday, 12 December 2017 08:00 – 12:20; New Orleans Ernest N. Memorial Convention Center – Poster Hall D-F, Poster #0319

Running a few more grain size samples

Research, Sedimentology and Stratigraphy,

Sometimes you have to get creative in order to speed up your workflow in the lab. Luckily sediment grain-size measurements aren’t really affected by rogue skin cells! Here I’m labeling beakers, getting ready to prep sediment samples to soak overnight in a solution of sodium metaphosphate in water. Glacial sediment from the Ross Sea is rich in fine silt and clay, leading to unwanted clumps that must be disaggregated before being measured. Sodium metaphosphate does that job!

Coastal erosion in Galveston, Texas

Research, Sedimentology and Stratigraphy, ,

Every now and then, my research group takes a trip down to the Gulf Coast to discuss barrier island stability and collect sediment cores. Galveston Island’s foundation was built over a timespan of about 4000 years during the Holocene by prograding, or building out in a seaward direction, as a result of sand being supplied to the barrier faster than sea level rise could remove it. However, over the past 2000 years, Galveston’s shoreline has been retreating landward, most significantly during this century. Right now, the shoreline is retreating at rates up to ~4 m/yr. Through seismic records, we know the location of Galveston’s maximum seaward extent at about 2000 years ago. If we take that shoreline and use the present-day retreat rate to estimate where the shoreline should be today, we find that the shoreline would be nearly 3 miles (4.7 km) inland to where it is now! This tells us that the modern retreat rate is unprecedented, and that retreat must have been much slower over the majority of the 2000 years than it is today.

Two years after the catastrophic Galveston Hurricane of 1900, the city began construction of a 17-foot high, 10-mile long seawall to protect the city from future storm surge. The west end of the Galveston Island seawall was completed in 1963 but does not span the whole island. In 55 years, the shoreline of the unprotected side has retreated substantially. See the GoogleMap below marking the sharp boundary between the east side of Galveston that is protected by the seawall and the west side that is unprotected. I took the photo below while standing at the location marked on the map, facing west.

 

 

Here are some publications related to this topic that have come out of our group over the last few years:

Odezulu, C.I., Lorenzo-Trueba, J., Wallace, D.J. and Anderson, J.B., 2018. Follets Island: a case of unprecedented change and transition from rollover to subaqueous shoals. In Barrier Dynamics and Response to Changing Climate (pp. 147-174). Springer, Cham.

Anderson, J.B., Wallace, D.J., Simms, A.R., Rodriguez, A.B. and Milliken, K.T., 2014. Variable response of coastal environments of the northwestern Gulf of Mexico to sea-level rise and climate change: Implications for future change. Marine Geology, 352, pp.348-366.

Wallace, D.J. and Anderson, J.B., 2013. Unprecedented erosion of the upper Texas coast: Response to accelerated sea-level rise and hurricane impacts. GSA Bulletin, 125(5-6), pp.728-740.