The Shevenell Lab Returns to the Ross Sea

Hello Expedition Antarctica! My name is Emily Kaiser and I am a 3rd year PhD student in Dr. Amelia Shevenell’s Antarctic Paleoclimate Lab. In my research, I am focusing on constraining when ice retreated in locations around Antarctica and what mechanisms forced ice retreat following the Last Glacial Maximum (LGM; ~25,000 years ago!). During the LGM, large ice sheets existed across North America (e.g., the Laurentide Ice Sheet) and were (we think, in some places) at their maximum extent around the Antarctic margins. I am interested in this time period because it is the most recent large-scale ice retreat event. Today, Antarctica’s ice sheets are continuing to lose mass at an accelerating pace, contributing to the observed global sea level rise. The two main factors driving ice retreat today are rising atmospheric temperatures and warmer water masses interacting with marine-terminating ice. Since the instrumental records of Antarctic ice mass loss and subsequent sea level rise are limited to the instrumental era, we turn to the geologic records to expand our view of how ice sheets responded to past climate changes. Our paleo data can then be incorporated into climate models to more accurately project the effects of future climate change.

I am a member of the scientific team on board the RV/IB (read: research vessel/ icebreaker) Nathaniel B. Palmer sailing down to the Ross Sea, Antarctica. Our expedition is supported by the U.S. Antarctic Program (USAP) that oversees and supports all US-funded scientific research in Antarctica. Specifically, this cruise is funded by a National Science Foundation grant awarded to geophysicist Dr. Phil Bart from Louisiana State University (LSU), who is the Chief Scientist on the cruise. Our cruise is scheduled to be 73 days long and split into two legs: NBP23-01 and NBP23-02. For the first leg, NBP23-01, we are sharing ship time with a group of microbiologists and environmental scientists. In mid-January, we are docking at McMurdo (the largest US base) where the group we are currently sailing with will disembark and a new set of scientists will join us for NBP23-02. I’m going spotlight NBP23-01 for now and will share info about the second leg when we’re docked at McMurdo. Here’s a hint: 🐧.

Our floating laboratory and home until March, the RVIB Nathaniel B. Palmer docked in Lyttleton, NZ.

Fun fact: In 2018, Dr. Shevenell and PhD student Imogen Browne sailed to the Ross Sea with the International Ocean Discovery Program (IODP) onboard the Joides Resolution. They were interested in recoveringsediments deposited in the Miocene (~23-5 million years ago!) to help us understand larger scale ice sheet evolution. Many paleoclimatologists think about the Miocene because atmospheric CO2 levels were similar to levels we are seeing today. You can read more about their cruise on this blog!

Where we’re heading! We started our journey in Lyttleton, NZ and are currently navigating around a storm in the Southern Ocean. Overnight, we experienced almost 30 ft waves as we approached 54°S.

Cruise Goals and Objectives

The goal of our research cruise is to explore the timing and mechanisms forcing retreat of the Ross Ice Shelf (RIS) following the Last Glacial Maximum. To achieve our research goal, we need to incorporate a suite of geologic tools: seafloor mapping, sub-bottom profiling, and sediment coring. I will spotlight each objective further as we begin science operations over the next week – but here is a quick look at what we’re aiming for!

Objective 1: Map the Gap

While we can use satellites to resolve the general seafloor beneath the Ross Sea, we need a finer scale resolution to see features either carved out by past ice flow or deposited during ice retreat. On this cruise, we are utilizing a multibeam echosounder to explore the seafloor geomorphology. This instrument emits sounds that bounce off the seafloor and return to a receiver on the boat. In the Electronics Lab on the Palmer, we will stitch these surveys together to compile a map of our survey site. In the bathymetric map shared here, the rainbow lines represent previous multibeam surveys while the grey shading represents satellite-derived. In addition to filling in gaps in our knowledge of Ross Sea bathymetry, our project will also contribute towards goals set by the Seabed 2030 Project – with a goal of mapping 100% of the sea floor by 2030.

Bathymetric map of the Ross Sea. The grey shading is bathymetry derived from satellite altimetry. The colored lines represent existing multibeam coverage on the shelf. Notice all the gaps in data? Our 1st cruise objective is to “map that gap!”. Figure courtesy of Matthew Danielson, LSU.

Objective 2: What lies below the seafloor?

Seismic surveys have an important scientific purpose: exploring what lies beneath the seabed. Unlike the multibeam echosounder that reflects sound waves off the seafloor, seismic surveys use a sound wave that reflects from subsurface horizons. Since each type of sediment has unique physical properties, we can use data coming back to the acoustic receiver to determine sediment type, layer thickness, and buried features we cannot see from the multibeam echosounder. 

 Seismic surveys require a special permit and follow mitigations to protect marine life. Thus, we are sailing with a group of trained Protected Species Observers (PSO for short), who are on watch 24 hours/day monitoring the presence/absence of local marine life. While transiting to the Ross Sea, we have had PSO briefings and trainings so we are ready to begin science operations when we arrive at our study site. We are following very strict protocols to require the PSOs conduct continuous visual monitoring of marine life around the ship.  Their observations inform us when we can safely conduct surveys survey and when we are required to stop operations.

Fun fact: Two of the PSOs onboard graduated from the University of South Florida! Go Bulls!

Schematic of the seismic survey set up. The ship tows the source and a long line of receivers. Illustration from NOPSEMA.

Objective 3: Sediment coring

Once we complete multibeam and seismic surveys, we use that data to decide where we want to sediment core. The idea behind sediment cores is to collect undisturbed packages of sediment in the order they were deposited. With that logic, the sediment at the top of the core is the youngest and oldest material at the bottom of the core. There are a few different tools that we use to obtain sediment cores such as benthic grab samples, gravity coring, and piston coring. While all three of these techniques recover sediments, each one has a specific purpose. For example, grab samples are a great tool to see what is living just above and just below the seafloor. If you want to get a longer sediment record, you would use a gravity corer or a piston corer.

Once we bring the cores up from the seafloor, we put most of them into cold storage for future sampling. However, some core types and analyses require that we sample some of the cores onboard. The first step to sampling a sediment core is the visual description. We document things such as: sediment color, sediment type, abundance of microfossils, presence of any large rocks, etc. Then, each scientist goes in to take samples from the core for their post-cruise research. For example, I am interested in sampling these cores for radiocarbon dating and paleotemperature reconstructions. Other folks are interested in sampling for microfossils, sediment redox chemistry, methane concentrations, and more! 

Types of Cores. The three examples shown here are some of the ways we are planning on coring. Figures from Project Oceanography.

Objective 4: Preserving cores for future generations! 

The final cruise objective begins once we reach the shore. At the end of our cruise, we will disembark, and the cores will be shipped to the Antarctic Core Collection at Oregon State University for other scientists – and the future generations of scientists – to use! If you’d like to hear more about the core repository, check out my post from our visit earlier this year!

What’s next for NBP23-01? As we sail further south and into the Southern Ocean, we expect the seas to be rough for a little bit. But there’s another obstacle we need to cross once we’re closer to the Antarctic – sea ice! I’ll write again once we begin ice breaking!


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