Unraveling Antarctic Ice Sheet Dynamics Viewed though a Marine Depth Transect near the South Orkney Microcontinent, Weddell Sea (Keck Focused Project)

What: Sea level rise is observed in many coastal areas from remote islands in the Pacific to naval bases in Richmond, VA. Critical to modeling and then adapting to this sea level rise is understanding how fast ice sheets are melting (water into the oceans) and oceans are warming (thermal expansion). The first five Intergovernmental Panel on Climate Change (IPCC) reports suggested < 1.5 m average rise by the end of the twenty-first century. Some (e.g. Instar, 2016, Oppenheimer and Alley, 2016) now consider a 1.5-2 m average rise* by the end of the 21st century a possibility. There are many reasons for this revision, but the largest change is in our understanding of Greenland (not discussed) and Antarctic Ice Sheet dynamics. Antarctica is separated by the Trans-Antarctic Mountains into West and East. In West Antarctica and the Antarctic Peninsula, the Pacific side of Antarctica substantial parts of the ice sheets are shelves that float in the ocean and are therefore particularly prone to disintegration and melting. In 2002, NASA (2002) recorded the collapse of the Larsen B Ice Shelf on West Antarctica. Since then ice streams have accelerated their flow into the Weddell Sea (Rignot et al., 2004). Looking back in time, Andrill drilling on the Ross Ice Shelf showed multiple Ross Ice Shelf collapses during the Pliocene (Andrill, 2009), when atmospheric CO2 levels where similar to today’s CO2 levels, about 400 ppm.

In contrast, in East Antarctica the majority of the ice rests on stable craton and thus was considered unlikely to contribute to sea level rise in the next few centuries, if not millennia. However, recent research suggests that this is not the case. East Antarctic ice sheets are more unstable and susceptible to melting than previously thought. Examination of International Ocean Discovery Program Drilling (IODP) cores from Wilkes Land and other areas of East Antarctica, also showed considerable and unpredicted Pliocene melting (e.g. Williams et al., 2010, Cook et al., 2014).

In this project we will look for evidence of ice sheet collapse and stability at three IODP Sites (695, 696, and 697) in the Jane Basin, south of the South Orkney Microcontinent. This area, also known as Ice Berg Alley, collects sediment from east and west Antarctica as currents and ice bergs exit the Weddell Sea and join the world’s oceans.

*NOTE; There’s no such condition as “average rise” Tamisiea and Mitrovica. 2011.

When:  June 18- July 2 – College Station, TX (IODP/TAMU)

July 2- July 15 – Middletown, CT (Wesleyan)

Where: 2 weeks in College Station, TX (International Ocean Discovery Program); 2 weeks in Middletown, CT (Wesleyan University)

Who: 4 students and two mentors, Dr. Suzanne OConnell (Wesleyan University) and Dr. Joseph Ortiz (Kent State University) (Ortiz will participate in Middletown during the third week of the program.)

Figure 1. Modern bathymetric and oceanographic features of the northeastern Weddell and Scotia Seas. Solid red arrows show Weddell Sea Deep Water (WSDW), dense water above 4000m and Weddell Sea Bottom Water (WSBW), dense water deeper than 4000 m, exiting the Weddell Sea, joining Antarctic Circumpolar Current (ACC) and forming Antarctic Bottom Water (AABW). Yellow box (JB = Jane Basin) shows location of transect of ODP cores, PB = Powell Basin. (from Maldonado et al., 2003).

Figure 1. Modern bathymetric and oceanographic features of the northeastern Weddell and Scotia Seas. Solid red arrows show Weddell Sea Deep Water (WSDW), dense water above 4000m and Weddell Sea Bottom Water (WSBW), dense water deeper than 4000 m, exiting the Weddell Sea, joining Antarctic Circumpolar Current (ACC) and forming Antarctic Bottom Water (AABW). Yellow box (JB = Jane Basin) shows location of transect of ODP cores, PB = Powell Basin. (from Maldonado et al., 2003).

 

 Project Overview: Students will spend the first two weeks of the project at the IODP core repository at Texas A&M University (TAMU) in College Station, TX. During the day they will prepare and measure split cores for non-destructive analyses (description, XRF, magnetic susceptibility, color imaging, spectrophometry). Students will be expected to learn the basis for and be able to describe at least two of the measurements. While at TAMU students will spend a day exploring opportunities for additional research and graduate school at the College of Geosciences (http://geosciences.tamu.edu/). The second two weeks (third and fourth) will be spent at Wesleyan University in CT.

Figure 2. Nishaila Porter selecting cores at IODP.

Figure 2. Nishaila Porter selecting cores at IODP.

During the third week, Dr. Joseph Ortiz (Kent State University) will teach students how to do statistical analyses on the data they collected. They will learn how to do principal component and wavelet analyses to interpret their data (e.g. Ortiz, 2011, Yurco et al., 2010). During the fourth week, these analyses will continue. In addition, students will prepare posters to share their findings at the 2017 Geological Society of America meeting in Seattle, WA. Students are encouraged to work with their advisors to find funds that will allow them to continue their research during the summer beyond the 4-week Keck program.

Figure 3. Group picture of Keck students at IODP during summer 2014.

Figure 3. Group picture of Keck students at IODP during summer 2014.

Potential student projects (These projects can be subdivided by site and by time interval (e.g. early/late Pliocene) depending upon sediment recovery, project focus and student’s plans for the academic year.)

  • What is the influence and expression of orbital cycles from the different sediment components (XRF, magnetic susceptibility, spectral reflectance, and color), from different depths and time intervals? What changes in mineralogy and sediment chemistry are creating the signal?

  • Satellite data shows increased chlorophyll (higher productivity) around areas with large melting icebergs attributed to increased nutrient supply from melting ice (Duprat et al., 2016). In the sediment is there a correlation with increased IRD, wt. % biosilica in the <63um fraction, Total Organic Carbon (TOC) and C/N ratio?

 

Figure 4A. Location of three ODP sites to be studied, Sites 695, 696 and 697.  SOM=South Orkney Microcontinent.

Figure 4A. Location of three ODP sites to be studied, Sites 695, 696 and 697. SOM=South Orkney Microcontinent.

 

 

Figure 4B. Relative depths of the three sites.

Figure 4B. Relative depths of the three sites.

 

Figure 4C. Simplified sediment lithologies with sediment recovery and age (old Pliocene/Pleistocene boundary). (From Leg 113 Preliminary Report).

Figure 4C. Simplified sediment lithologies with sediment recovery and age (old Pliocene/Pleistocene boundary). (From Leg 113 Preliminary Report).

  • Diatom identification. What species changes and preservation changes are observed during times of high and low diatom abundance? (e.g. Hambrey et al, 2003) Are different types of diatom species (e.g. ice dwelling, lower salinity, warmer water) found with higher abundances of coarse fraction (IRD). (We can help a student process the diatoms and prepare the slides, using the Harwood method (unpublished), but the student would need access to someone familiar with diatom identification.)
  • Do changes in the mean sortable silt grain size indicate changes in the strength of Weddell Sea Deep Water, one of the precursors of AABW? In the North Atlantic (e.g. Hall and McCave, 2000) and Scotia Sea (Drake Passage, McCave et al., 2014) mean grain size in the sortable silt (10-63 um) size fraction increases with increased current speed. No one has measured sortable silt grain size on the < 63-micron fraction from all three ODP sites in the Jane Basin. With a depth transect, we will be able to compare current strength at three different depths. Of these the most important is Site 697, through which Weddell Sea Deep Water passes before joining the ACC and from there moves as AABW to the rest of the oceans. Preparing sediments for this grain size analysis is a long process, requiring, separating the coarse (>63 um fraction) and fine (<63 um fraction), drying the <63 um fraction, removing biosilica and then measuring the grain size. The student choosing this project will need access to a particle size analyzer. (Wesleyan does not own a particle size analyzer, but does have access to one at Central Connecticut State University.)
  • How far can icebergs travel? What is the source area for the sediments based on ages of hornblende and biotite from the 150-500 um fraction (Williams et al., 2010) and/or the petrology of ice rafted rocks large enough to make a thin-section?
  • Can glass shards be used to date paleoceanographic changes and/or provide a higher resolution age model for Jane Basin sediments? If sufficient numbers of glass shards are identified, geochemistry (composition and isotopic dating) may be able to indicate the source area and the age of the event.

Recommended Courses/Prerequisites:  A positive answer to the question, do you want to provide information to the scientific community and modelers about ice sheet dynamics in a warming world?”

 

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