By Renee Cho
During the first half of 2019, two different International Ocean Discovery Program (IODP) expeditions took international teams of scientists to the stormy Southern Ocean under the leadership of Lamont-Doherty Earth Observatory scientists.
Maureen Raymo and Gisela Winckler each spent two months doing stints as co-chief scientist aboard the research vessel JOIDES Resolution. Their expeditions involved gathering information that will enable the geoscience community to learn more about Earth’s climate history.
Raymo, a paleoceanographer and director of the Lamont Core Repository, was on IODP Expedition 382 from March to May in areas of the Southern Ocean near Antarctica. As co-chief scientists, Raymo and Michael Weber, a paleoclimatologist at the University of Bonn, co-led a team of 30 scientists from around the world who are investigating how Antarctica’s ice sheets responded to past global warming.
From May to July, Winckler, a climate scientist and Center for Climate and Life Fellow, served as co-chief scientist for IODP Expedition 383 in the Pacific sector of the Southern Ocean. She and co-chief scientist Frank Lamy, a geologist at the Alfred Wegener Institute for Polar and Marine Research, led a different group of 30 international scientists on an expedition to drill sediment cores along the Chilean Margin and in the Central South Pacific to study how the dynamics of the Southern Ocean affect the global climate system.
Sediment cores are records of Earth’s history: They contain the fossils of tiny organisms, mineral dust blown from the continents, and rocky material scraped by glaciers off the land and carried out to sea by icebergs. Specialized research vessels like the JOIDES Resolution enable the collection of these sediments in the form of long cores. By analyzing the composition and geochemical fingerprints of the material in each core, scientists can figure out past variations in temperature, wind patterns, current speeds, and where any icebergs have come from and when.
Both expeditions will use the information contained within their newly recovered cores to examine how the atmosphere, oceans, and ice sheets responded to past global warming. These research projects are still in the early stages and will unfold over many years. What the scientists uncover will help the geoscience community make more accurate predictions about Earth’s future and enable us to better understand and adapt to climate change.
Raymo’s expedition drilled sediment cores at five sites in an area in the Scotia Sea known as Iceberg Alley. It’s east of the Antarctic Peninsula and many icebergs that break off the continent pass through the area.
The drilling was surprisingly successful, said Raymo, “There was a very real possibility that there would be a lot of time lost getting out of the way of icebergs and bad weather and high seas. And while we did lose some time to those influences, most of the time we were drilling.”
Eighteen sediment cores totaling almost three kilometers in length were recovered. The oldest cores date to the middle Miocene epoch, between 12 and 16 million years ago. Raymo said she was surprised that the drilling produced cores with continuous sedimentation for millions of years. “Typically records near Antarctica have a lot of gaps in them, but ours are just beautiful continuous records of climate change,” she said, giving credit to her co-chief, Mike Weber for identifying the drilling sites.
Raymo said the debris in the cores varies with age. “That’s telling you that the dynamics of the Antarctic ice is changing dramatically through time,” she said. Raymo and her expedition colleagues don’t yet know what the changes indicate; they will discover that by investigating the sediment. But the changes show that the Antarctic ice sheet has not been as stable over millions of years as previously thought.
Now that the sediment core material is at Lamont, Raymo and her colleagues have begun quantitative analyses of the iceberg material in the cores. Raymo is focused on trying to understand the Antarctic ice sheet’s history for the time period between one and two million years ago, and establishing what conditions might cause the ice sheet to melt now.
“We have no idea how vulnerable the Antarctic ice sheet is to a modest amount of global warming,” said Raymo. “So we’re trying to figure out how the ice responded to warming in the past.”
Knowing how fast the ice melted in the past is critical to understanding how Antarctica might respond to increased warming. And that will help scientists predict future sea level rise.
This wasn’t Raymo’s first time serving as a co-chief scientist but she still feels it’s a privilege. “As chief scientist, you really get to be a part of every sector of the science,” she said. “You get to solve problems with everybody, and you get to interface with the captain and the drillers.”
Raymo says the hardest part of the expedition was working the midnight to noon graveyard shift for two months. But she also loved being at sea for that long. “You can walk off the ship feeling like you have made lifelong friends with people that you didn’t know when you walked on the ship.”
The diverse team of expedition scientists, half women and half men, came from all over the world. Raymo says she found the environment less sexist and stressful with a crew that is comprised equally of women and men compared to life on a research vessel 30 years ago, when most participants where men.
The Pacific Sector of the Southern Ocean
Winckler’s expedition drilled sediment cores in the central South Pacific, halfway between Chile and New Zealand, “in the middle of nowhere,” she said, where no expedition had drilled before. (Read Winckler’s blog posts about the expedition here.)
Their science plan was to drill at four sites in the Central South Pacific, and three more sites at the Chilean Margin. The scientists hoped to obtain cores spanning the past five million years, including the Pliocene period, three to four million years ago. During the Pliocene, carbon dioxide levels were similar to what they are today, the planet was warmer, and global sea level was a good bit higher.
At two sites, the ship was able to drill even deeper in time, to the Upper Miocene period, about eight million years ago.
“Seeing that happen, core after core after core, drilling deeper and deeper into the sediments, hundreds of meters was fantastic,” said Winckler. “These beautiful, continuous sequences are ideal for interpreting the climate information in the sediments because it allows you to know where you are in terms of time.”
The scientists recovered almost three kilometers of sediment core and some contained surprises. Drop stones, or large pebbles transported by icebergs, provide evidence that icebergs of the past had traveled to the ship’s location 1,000 miles from Antarctica, where no icebergs exist today. The finding could advance the team‘s research on how the Southern Ocean works as an interface between what’s happening on Antarctica and the rest of the planet.
And at two sites, the team drilled into the basalt of the ocean crust much earlier than expected, illustrating how little is known about the ocean floor. Meanwhile, microfossil experts onboard found well-preserved microfossils of two brand new species of foraminifera, single-celled planktonic organisms.
Once the sediment cores were brought onto the ship and split open, the team saw color changes revealing distinct climates. Different types of microorganisms—the main ingredient of the sediments in the Southern Ocean—thrive under different conditions, so “you can see these time changes from warmer time periods into colder time periods or vice versa, just by looking at the color,” said Winckler. “It’s sort of the poetry of these sediments and how they tell you their story.”
Winckler is pleased with how well the expedition went, despite an unexpected change in schedule. In the middle of the expedition, a monster storm forced the ship to leave the region and travel about 1,500 miles north, where they ended up spending two weeks. Due to the storm, the expedition wasn’t able to recover sediment from their southernmost site in the Antarctic part of the Southern Ocean, a crucial piece of their research project.
“We never had a window of time with weather conditions long enough to work there successfully,” said Winckler. “That was the most difficult part of the expedition—giving that up.”
The cores from both expeditions will be archived at IODP’s Gulf Coast Repository in College Station, Texas, with samples distributed all over the world to the expedition participants. At Lamont, Winckler, together with Jenny Middleton and Julia Gottschalk, two Lamont postdocs who also participated in the expedition, will analyze the sediment records to determine how Earth got into stages warmer than what we are experiencing today. They will examine the dust in the cores and how it connects to the carbon cycle, carbon storage, and atmospheric carbon dioxide.
The international team of scientists will also analyze the different sizes of grains in the sediments which can reveal how fast the Arctic Circumpolar Current, the ocean’s fastest current, traveled in the past; the speed of the current influences the whole climate system.
Winckler says the Southern Ocean is one of the key regions that determine the planet’s climate, so scientists need to better understand how the entire system works and how fast it changes.
“We need to feed our climate models better information and better constraints to improve how well we can predict the future,” said Winckler.
“We need that information about the natural variability of the past to understand what we are doing by impacting the natural climate system with our outrageous fossil fuel emissions.”