Drilling on Antarctica’s continental shelf to uncover ice sheet history

We have finished drilling at our first site on the Ross Sea’s continental shelf, where we had overall excellent recovery for the method of drilling (rotary core barrel; RCB). The RCB is designed to cut through all types of sediment. Because we were targeting both hard diamictites (mixture of poorly-sorted clasts in a muddy/sandy matrix) and softer mudstones, the RCB method was the most appropriate for our site. The diamictites were likely deposited underneath or proximal to ice, and the mudstones which contain microfossils of phytoplankton (mainly diatoms in Antarctica) represent deposition in open marine conditions, far away from ice influence. We can use downcore changes in these sediment types to understand past advances and retreats of the West Antarctic Ice Sheet.

snnow drilling_kenny

Drilling in Antarctic conditions (Photo by Kim Kenny)

andrill graphic

Example of sediment core recovery from the Ross Sea from the ANDRILL program, and modeled ice sheet configuration as a result of this project (Gasson et al., 2016). When there are open water conditions, phytoplankton like diatoms thrive and are incorporated into the sedimentary record once they die, creating layers of diatomaceous sediment. At this time Antarctica’s ice sheets are retreated (bottom right model). As the ice sheet advances (top right model), rocks, mud, and sand carried by the ice sheet are deposited, creating layers of lithogenic sediment. Alternating layers of these two units through time tells us about the past environment used to infer ice sheet history.

excited_de zsantis

Some excited scientists: Imogen Browne, Tim van Peer, and Jeanine Ash (Photo by Laura de Santis)

Ice sheet models and paleoclimate data tell us that the Ross Sea is one of the last places on the continent to become glaciated, so drilling here helps us to constrain the biggest advances of the West Antarctic Ice Sheet over the past 20 million years or so. One of our main aims at this site is to constrain ice advance at a regional erosional surface, which we think happened around 16 million years ago during a period of Earth’s history called the Miocene. This surface represents regional advance and grounding of ice across the continental shelf of the Ross Sea, which only happens every few million years or so, and results in a fall in global sea level.

laure_muller

Co-chief Laura de Santis presenting an image of the sea floor during the middle Miocene (Photo by Jule Müller)

We rely on microfossils among other methods to tell us the age of erosional surfaces. Microfossils can be different types of phytoplankton, zooplankton, or pollen. In Antarctica, the dominant group of phytoplankton are called diatoms, which form discs and chains called ‘frustules’, composed of silica (glass). We know from regional studies of well-dated sedimentary sequences when different taxa of these groups appear and disappear through the geologic record due to evolution and extinction through time. These biological events are often associated with abrupt changes in the marine environment, such as initiation of new currents and warming or cooling of surface waters.

diatoms

Diatoms collected from surface waters south of 70S (Photos by Expedition 374 Paleontology team)

During the Miocene Climate Optimum (~17-15 million years ago), climate was warm enough for plants to grow around the edges of the continent. During this time, Antarctica’s ice sheets were generally reduced in extent and global sea level was much lower. However, recent studies from the Ross Sea and the ANDRILL project indicate that both the West and East Antarctic Ice Sheets were dynamic and capable of modulating global sea level, even during warmer climates of the middle Miocene. By studying past ice sheet behavior and response to warm climates like the middle Miocene, we can better model and predict how Antarctica will respond to ongoing anthropogenic warming.

 

Advertisements

Crossing the Ross Sea Polynya and other antics

The JOIDES Resolution is now following RV/IB Nathaniel B Palmer into the Ross Sea Polynya, which is Earth’s largest ice making factory. Cool air temperatures encourage surface water freezing which creates sea ice. Strong winds then move this ice around, freeing up more space for sea ice formation. The Ross Sea is highly productive in the summer months, where sunlight, a stable water column, and abundant dissolved nutrients stimulate huge phytoplankton blooms. These blooms are consumed by krill, which are consumed by predators like penguins, seals, and whales.

iceberg

The first iceberg spotted on our way down to greeting the RV/IB Nathaniel Palmer. Photograph by Bill Crawford

escort

The JOIDES Resolution being escorted towards the Ross Sea polynya by the RV/IB Nathaniel Palmer. Photo by Gary Acton

penguins

First (Adélie) penguin spotting! Photo by Gary Acton

Before we arrive at our first site, all scientists need to adjust to their shift time. (day shift is from 12pm-12am and night shift is from 12am-12pm). Apparently, there is no ‘right’ way to do this, but some of us attempted to pull an all-nighter fueled with coffee and movie marathons. Others opted for short sleeps and an early start. Those of us night shifters who were bored yesterday decorated the conference room to celebrate Rob’s birthday (our co-chief) and the catering staff prepared a cake and cupcakes.

movie room

Some of the night shifters enjoyed the movie room (Molly Patterson; USA, Brian Romans; USA, Isabela de Sousa; Brazil, and Jeanine Ash; USA). Photo by Kim Kenny

DSC01902

Birthday celebrations for co-chief Rob McKay. Photo by Saki Ishino

During our transit, individual lab groups have practiced shipboard measurements and core descriptions on legacy cores recovered on previous Antarctic expeditions. The sedimentology team has discussed how to describe sediments from glaciomarine environments and practiced estimating grain size percentages and identifying minerals under the microscope. The physical properties group has reviewed methodologies for the required measurements. Kim Kenny, our on-board videographer has also been conducting short interviews with the science party- so stay tuned!

seds 2

Sedimentologists discuss legacy cores (Brian Romans; USA, Benjamin Kiesling; USA, Amelia Shevenell; USA, Saki Ishino; Japan, and Rob McKay; NZ). Photo by Mark Leckie

phys props

Physical properties night shift (Imogen Browne, USA; Francois Beny; France, Brian Romans; USA). Photo by Kim Kenny

 

Transit activities: drilling operations tour aboard the RV/DV Joides Resolution

The JOIDES Resolution is currently enroute to our rendezvous point with the U.S Antarctic Program’s RV/IB Nathaniel B Palmer, the icebreaker that will lead us through the sea ice and into the Ross Sea polynya. We will then proceed to our first drilling site on the continental shelf. Before we arrive on site, our job as scientists is to put together the methods sections of our reports within our individual science teams. Our science teams are made up of scientists from various countries and experience levels. Aside from working on the methods, touring labs, and listening to science talks related to what we expect to see in our shelf and rise sites, we have also been exploring the shipboard facilities including: the gym, computer room, and movie room. The first-timers are also trying to not get too lost in our new home.

double-cross.jpg

Our current ship track has us crossing both the Antarctic Circle and the dateline at the same time before we rendezvous with RV/IB N.B. Palmer

Yesterday, all scientists took a drilling operations tour of the ship, where we learned about the technology involved in obtaining the sediment sequences we will be recovering. Hard hats and safety glasses are required at all times in these areas, due to the inherent risks involved with drilling operations. We first had a look at the machinery on the drill floor where the bottom hole assemblies are prepared for drilling. The derrick is the tallest feature on the ship (147 ft), and the drawworks within the derrick make it possible for us to lower the drill string (pipe) to the sea floor. Inside the drill string are additional wirelines, which bring the sediment core barrels to and from the sea floor. This is a very noisy area, which is strictly off-limits, except for authorized personnel.

derrick

View of the derrick and drawworks from the drill floor. The drill string is lowered through the middle of the ship (moon pool) to the sea floor, where drilling begins, and the drill string advances ~10 meters at a time

pipes

Drill pipes aft of the rig floor awaiting the beginning of drilling operations

I am on the Physical Properties team with four other scientists from the U.S, South Korea, France, and the U.K. When our sediments first come into the laboratory, my group runs the cores through various instruments that measure the physical properties of the sediment. This includes density, magnetic susceptibility (related to sediment composition), and background radiation which helps in identification of clay minerals. These analyses allow us to establish first order sedimentological changes downcore and help us to make hole-to-hole correlations, when we drill multiple holes at one site. Dr. Amelia Shevenell is on the Sedimentology team, which includes eight scientists from the U.S, Norway, India, Japan, Brazil, and South Korea. The sedimentologists describe the core and make detailed notes about the lithology, color, sediment structures, biogenic components, and mineralogy. We will work in the core lab on 12-hour day and night shifts, and will be very busy once the first core arrives on deck!

Journeying to the Ross Sea, Antarctica aboard the RV/DV Joides Resolution

My Ph.D. advisor (Dr. Amelia Shevenell) and I (Imogen Browne) are part of an international scientific team who will spend the next two months aboard the International Ocean Discovery Program’s (IODP) drilling vessel, the JOIDES Resolution. The JOIDES Resolution is a 470-foot long floating laboratory that recovers marine sediments from around the globe to investigate the evolution of Earth’s climate, tectonic, and biologic systems.

On January 8, 2018, IODP Expedition 374 left the port of Lyttleton, New Zealand and began our transit across the Southern Ocean towards the Ross Sea, Antarctica to investigate how Antarctica’s ice sheets have evolved over the last ~25 million years. Expedition 374 is led by co-chiefs Rob McKay from Victoria University in New Zealand and Laura De Santis from Trieste University in Italy, but is the result of a collective effort of a number of scientists over the past 15 years. Expedition 374 is the second IODP expedition to Antarctica in the last decade and only the ninth expedition to the seas around the southernmost continent in the 50-year history of scientific ocean drilling.

cochiefs

Expedition 374 co-chiefs Laura De Santis (Italy) and Rob McKay (NZ)

To investigate Antarctica’s ice sheet history, we will analyze marine sediments collected from the shallow continental shelf and deeper continental rise of the Ross Sea. These sediments document past environmental changes immediately adjacent to Antarctica. By examining physical, geochemical, and biological changes in these sediments, we can start to piece together how Antarctica’s ice sheets have evolved through time, in concert with changing oceanic and atmospheric temperatures. This is important because the amount of ice on Antarctica influences global sea levels and may be sensitive to changes in the concentrations of greenhouse gases, such as carbon dioxide, in the atmosphere. Understanding how Antarctic ice sheet evolution both influenced and responded to past climate change is required to predict the future response of the ice sheet and global sea levels to ongoing atmospheric and oceanic warming. Stay tuned to hear more about IODP Expedition 374 and learn more about life aboard the JOIDES Resolution over the next 60 days.

JR in lyttleton

The JOIDES Resolution in port, Lyttleton, New Zealand

3/1/2014 – Everything Antarctica

Michelle writes:

The past week has been full of quintessential Antarctic experiences. I want to highlight these in the blog today because I actually spend a lot of time in the lab rather than outside on deck, so these experiences have been very special.

1-P1010681

1. Penguins: we got up close to a pair of Emperor penguins the other day as a large piece of sea ice floated by. They stood by watching the boat, craning their necks every so often like they were trying to get a better look at the giant, orange thing in front of them. My favorite thing about Emperor penguins is how they walk: it’s a slow shuffle as they move an entire side of their body in one motion. By contrast, I always see the little Adelie penguins run in spurts. They usually hold their wings out behind them and run so far forward it looks like they are going to trip over their little feet.

1-emperor-1 2. Blizzards: Antarctic storms are world-renowned as ferocious white-outs with howling winds and temperatures many tens of degrees below 0°C. We have hit a few storms throughout our cruise, but a couple days ago, we stepped out on deck to flying snow that stung our faces and temperatures so cold we could only stand to be outside for a few minutes. Some sea ice was piled higher than the back deck and I couldn’t see more than about 50 yards in any direction. This particular storm was located north of the ship, but it had pushed much of the sea ice south toward us. We are still trying to break through into open water. It’s slow going, but the captain and mates are working hard to get us through and ship speed should pick up soon. Continue reading

2/24/2014 – Feast and Famine

Katy writes:

Chief Scientist and Chief Rock

Chief Scientist and Chief Rock

The past 48 hours (approximately) have been relatively calm as far as work goes since some bad weather (35-45 knot winds) has halted over-the-deck operations. However, we were able to maintain station long enough (3.5 hours) for a rosette CTD and Amelia’s water pumping, which allows her and her colleagues at USF and elsewhere to collect archaea in different water masses and compare their population genomics. The 48 hours before these last two shifts (and I mean the full 48 hours) were packed with core sampling and collection. So as Michelle recently blogged, those days when we all count sleep as our “fun activity” of the day definitely come after these busy, but incredibly rewarding and exciting days and nights.

Good coring weather

Good coring weather

When the night-shifters woke up on the 21st, we saw two 3-meter kasten cores open on the table, being sampled simultaneously by the sizeable group of day-shifters. They had already taken Amelia’s DNA samples, foraminfera and organic geochemistry samples via syringes, and almost completed the diatom sampling for Amy. They had also brought up our biggest JPC to date: 13 meters!  All of these cores were taken at the same station, which had a lot of interesting diatom-rich layers that we were able to see in the open kasten cores and via the magnetic susceptibility in the JPC that we ran on the 22nd. The day-shifters were still wide awake and active when we came to relieve them, and we were excited to dive in to these new samples. Continue reading

2/23/2014 – Palmer Fever

Michelle writes:

I have never been affected by island fever. When I was going to school in Hawaii, people used to ask me, “Don’t you get island fever?” when I got back from a semester at UH-Hilo. “No, although sometimes I do get Hilo fever,” I would respond, referring to the fact that it was hard for me to get out of Hilo due to school, work, and no car. I understand why people would feel trapped on an island but it just never phased me.

What could be more fun than recovering Eocene/Oligocene boundary rocks?

What could be more fun than recovering Eocene/Oligocene boundary rocks?

I think about that question now that I have been on a ship for close to a month. I guess one would call it Palmer Fever. And the answer is “No, I don’t get Palmer Fever.” I think the reason is we stay busy everyday. The last two days have been up-on-your-feet-for-12-hours kind of days. By the end, everyone is pretty exhausted. However, there are slow days and we have free time when we come off shift. So what do we do? We have found fun and quirky ways to keep busy, on and off shift.

While passing time on a slow shift, most people read, write papers, or help another group with their sampling. Occasionally, someone will post a crossword and passers-by will stop to fill out a word or phrase on their way between jobs. For the students, downtime during shift is a perfect time to write a blog, check email, or peruse papers that our PIs have assigned.

During our time off, there are a surprising number of activities to keep a person busy:

Game Face status: on

Game Face status: on

The natural evolution of the Seasickness Competition

The natural evolution of the Seasickness Competition

  • Sleeping: we are usually falling over by 3AM after a noon to midnight shift (for the day shifters). This counts as fun for a bunch of students.
  • Cornhole tournament: there has been a fair amount of smack-talk and off-hours practicing as people are starting to get competitive.
  • Movie night: each night after a day shift, a couple of the ship’s mates host a movie in the lounge, which they call Action Theater. Action Theater usually involves comedies/action flicks and high-tech Nerf guns.
  • Working out: In addition to individual workouts, we have a sign up sheet for pushups/sit ups. Every time an instrument goes into or comes out of the water, you have to do however many pushups/sit ups you signed up for. I signed up for 10 push ups, so if a core is deployed I have to do 20: 10 for in the water, 10 for out of the water. I think I have done about 450 pushups, with about 100 to catch up on.
  • Galley socializing: On a busy day, like today, dinner is a short affair. However, after shift is done, a group will often spend 45 minutes in the galley just hanging out and chatting.

We also love to celebrate: Continue reading