Preparing for AGU 2018!

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I'm giving an exciting talk at the AGU Fall meeting in Washington, D.C. next month! Come check it out:

Duration of the maximum extent of the East Antarctic Ice Sheet grounding line in the Ross Sea, Antarctica, and subsequent complex retreat

1Lindsay O. Prothro, 2Wojciech Majewski, 3Yusuke Yokoyama, 4Lauren M. Simkins, 1John B. Anderson, 5Masako Yamane, 6Naohiko Ohkouchi

1Department of Earth, Environmental and Planetary Science, Rice University; 2Department of Environmental Paleobiology, Polish Academy of Sciences; 3Atmosphere and Ocean Research Institute, University of Tokyo; 4Department of Environmental Sciences, University of Virginia; 5Institute for Space-Earth Environmental Research, Nagoya University; 6Department of Biogeochemistry, Japan Agency for Marine-Earth Science and Technology

Paleoclimate records of ice sheet dynamics serve as important boundary conditions for models intended to predict future change. However, the development of accurate records of the most recent glacial cycle in Antarctica has been challenging due to difficulties in obtaining meaningful radiocarbon dates. Despite being the most heavily investigated region of the Antarctic continental shelf (through seismic and multibeam surveys, coring, and attempted radiocarbon dating), the record of marine-based ice sheet dynamics in the Ross Sea has remained largely elusive and at odds with terrestrial records of ice sheet thinning. Past issues stem primarily from poorly-preserved carbonate (due to elevated CCD), contamination by glacially-recycled carbon, and limited consideration for geomorphic context and detailed sedimentary facies analysis when interpreting radiocarbon dates. The western Ross Sea, formerly covered by the East Antarctic Ice Sheet (EAIS) during the Last Glacial Maximum, shows evidence of a highly complex retreat pattern, but the timing remains uncertain. We reassess over 300 previously published and over 70 newly acquired radiocarbon ages within the context of a consistent sedimentary facies framework, with attention to geomorphic indicators of grounding-line position, to interpret the extent and timing of the local glacial maximum and subsequent retreat of the EAIS. We find that the ice streams flowing through Pennell and JOIDES troughs held their maximum extent for approximately 10,000 years before retreating at 14 and 11 cal ka BP, respectively. Due to new marine constraints, we can now link the drawdown of terrestrial ice near Ross Island at approximately 7.8 cal ka BP to a major ice shelf collapse and subsequent small readvance of Transantarctic outlet glaciers through southern JOIDES Trough.

Time and location: Session PP022A, Tuesday, 11 December 2018, 12:05 – 12:20 pm, Washington, D.C., Walter E Washington Convention Center 102AB

 

Using radiocarbon data from sediment cores, we assign calendar ages to these relative timesteps of ice retreat interpreted in Halberstadt et al., 2016:

Relative retreat timesteps

Modified from Halberstadt et al., 2016

Encyclopedia of Ocean Sciences, 3rd edition

Geomorphology, ,

Over the past couple of months I’ve been working on a little side project. Elsevier’s Encyclopedia of Ocean Sciences is undergoing an update for its third edition, to be released in 2019, and I’ve written an article for the new version. My contribution, “Ice-induced Plowing of the Seafloor”, is a complete rewrite of an article that hasn’t been updated since 2001 and thus needed to reflect advances in both seafloor observational technology and scientific thinking over the past two decades. The article will also be included in the Elsevier Reference Module in Earth Systems and Environmental Sciences.

See a sneak peek to the right of a graphic of iceberg-plowing that I created for the new edition!

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.

JohnFest 2018!

Uncategorized

Two days later, I’m still laughing. This past weekend Rice University threw an enormous retirement event for my PhD advisor, John Anderson. It spanned two days and included parties, fancy food, and even a full day of academic talks from colleagues and former students. People came from all over the US and as far as Stockholm and Tokyo to be here to celebrate John. I think I probably laughed for three hours straight during the Saturday night event, which was essentially a full roasting of John by over 40 years’ worth of students. The cherry on top was this rendition of an old Jimmy Dean song performed by the great Richard Alley, esteemed climate scientist and John’s longtime friend and colleague:

Richard’s version of the lyrics (as well as I can interpret them):

Every morning at Rice you can see him arrive,
Head over the crowd as he walks up the drive,
Kinda broad in the shoulder, narrow in the hip,
All the students know you don’t give no lip
To Big John.

Somebody said he studied at South Alabam,
Where they say “Please” and “Thank you ma’am”,
Then New Mexico, his Master’s great
And a PhD from Florida State,
Big John.

Three years up north, Michigan’s Hope College,
Where he taught and gained a useful knowledge,
It’s a long long way from there to the coast,
Which is where we needed John the most,
Big John.

So he headed back south to Houston’s Rice,
In seventy-five, and the fit was nice,
As he climbed the ranks to the Ewing chair,
Forty-three years he’s been happy there,
Big John…. [see more]

 

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!

Rice University freshmen dive into scientific research

Teaching

A sample of the feedback I provide for "scientific inquiry" assignments in which students investigate, using peer-reviewed research, the answer to a question with which they were inspired during assigned class readings

This semester, I have designed and am teaching a course exclusive to first-semester freshman entitled “Freshman introduction to local environmental science research”. The goal of the course is to introduce freshmen prospective environmental scientists to the world of scientific research. Special focus is given to work conducted by researchers at Rice University and the broader Houston area.

Everything that we take for granted about working in science can be revelatory for undergraduates. Most students have no idea about the sociology of science, so this course is designed not just to hone their skills in scientific thinking, but to introduce them to the daily lives of scientists in active laboratories. During the course, students explore three published, peer-reviewed articles by local teams of researchers. Research has shown that students learn and retain knowledge best when they are agents of their own learning, so the course involves lots of critical thinking, discussion, self-directed investigations, and writing. Students gain background information about the article subjects, investigate their own science questions, and learn about the techniques and methods by touring the labs and meeting the teams that produced the feature articles.

Thus far, we have discussed biochar’s impact on nitric oxide emissions and how this can influence regional air quality and associated health costs (Pourhashem et al., 2017) and how sequestration of organic carbon through subduction may have led to reduced atmospheric carbon dioxide and increased oxygen during the Great Oxidation Event (Duncan and Dasgupta, 2017). The visit to the high-pressure/high-temperature experimental petrology lab was particularly exciting. Next we are discussing Simkins et al., (2018), a study about how subglacial hydrological systems can destabilize ice sheets.

At the top left is a sample of the sort of personalized feedback students receive to improve their investigative skills and writing abilities.

Celebrating World Oceans Day 2017

Geomorphology, Sedimentology and Stratigraphy, Teaching, , ,

Over the past few weeks, some other Rice sedimentologists (Travis Swanson—post-doc, Lauren Simkins—post-doc, Tian Dong—Phd student) and I have been developing a demonstration to bring to World Oceans Day at the Houston Museum of Natural Science. Our demonstration, which we have titled “Texas Gulf Coast and its response to sea level rise”, allows students of all ages to learn about what processes cause eustatic and relative sea level rise and how barrier islands like Galveston Island and coastal communities like Houston are affected by higher sea levels and storm surge. We created a hands-on bathtub model demonstrating how land-based ice affects eustatic sea level as it melts, as well as a model of sediment compaction and land subsidence to demonstrate relative sea level rise. Travis Swanson built a wave tank that was modeled after Houston and Galveston Island to demonstrate how barrier islands protect the mainland from storm surge. The tank was built with features that allowed us to raise and lower the water level and choose different wave frequencies. The plastic shark toys that we placed in the water were very effective for demonstrating to small children that sharks would be in their backyards if the sea level rose too much!

See our informational pamphlet, a write-up on the Rice University website, and a video of the event produced by CW39.

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.