Analyzing Radiocarbon in Coral, Researchers Look Back On 400 Years of Monsoons
by AMNH on
Courtesy of N. Goodkin
In East Asia, summer and winter monsoons can have an outsized impact on local communities.
These seasonal storms can determine how much freshwater is available, whether farmlands flood or wither from drought, the level of air quality, and the potential of wind energy production. But how these major weather systems change over time, and how they interact with other climate factors, is still poorly understood.
Part of the gap in knowledge comes from the fact that standardized records about East Asian monsoons don’t go back farther than the 18th century, and much of the existing material focuses on land observations. But a new study from Museum Curator Nathalie Goodkin and colleagues published this week by the American Geophysical Union analyzes coral to peer back 400 years and evaluate how monsoons in East Asia have varied over time.
Coral like the stony Porites lutea are skeletons built by individual coral polyps over hundreds of years. As they grow, these skeletons carry clues about contemporaneous environmental conditions—such as surface temperature and water mixing—and lock in years of valuable data that scientists can use to reconstruct climate conditions of the past. In the work that Goodkin, an assistant curator in the Department of Earth and Planetary Sciences, and colleagues are conducting in Southeast Asia, corals are analyzed for changes in ocean circulation driven by winds.
"The coral sampled for this study, called To Nhât, or Vietnamese for 'the big one,' is one of the largest corals ever found in nature and has opened up a window that, from an ocean studies perspective, gives us a glimpse farther back in time," says Goodkin.
HOW CORALS HOLD CENTURIES OF OCEAN CLIMATE DATA
Published July 7, 2018.
[Camera flies over a small lighthouse to a wide shot of the ocean under a cloudy sky.]
NATHALIE GOODKIN (Associate Curator, Division of Physical Sciences):
You can look out at a calm ocean, and it looks like nothing’s happening,
[Camera dives under the ocean and swims over a coral reef.]
GOODKIN: But in reality, there are so many forces that are happening within that water.
[Timelapse of a sunset to night over a beach. Surfers race over a huge wave.]
GOODKIN: It’s going to change at night. It’s going to change depending on where you are on the planet.
[Seals lounge on a small ice floe.]
GOODKIN: You have ice that’s melting and forming.
[Moving through a swarm of small jellyfish. Close-up of a bleached coral.]
GOODKIN: The pH will change as you change how much CO2 gets absorbed.
[Nathalie Goodkin appears on screen in an office with dried corals arranged on a table behind her.]
GOODKIN: So, really, there’s nothing in the ocean that’s static. And that makes it even harder to study, because any point in time is only really reflective of that point in time.
[The Museum logo appears over a view of the ocean’s surface as seen from beneath the waves. Cut to two side-by-side videos, one of a sensor of some kind, the other of two people hoisting a drone into the air from the deck of a ship.]
GOODKIN: We’ve only been recording the environment in detail for the last, maybe, 20 years,
[Archival footage of waves crashing on a beach, a man with a pipe taking notes, and of an anchor sinking to a reef.]
GOODKIN: with some ship data from the past 120 years.
[Nathalie Goodkin reappears on screen. Lower third caption reads “Nathalie Goodkin, Assistant Curator, Division of Physical Sciences]
GOODKIN: We can go ahead and measure for hundreds of years in the future, but the imperative to understand how our climate system works is really now.
[A school of fish feeds on corals.]
GOODKIN: And so, we need to understand the system back through history.
[Corals and sponges collect on a shipwreck. Cut to towers of coral with fish swimming around them.]
GOODKIN: I think it would surprise people to know that there are natural instruments that we have in the ocean collecting this data for us.
[Timelapse of a many-branched coral growing.]
GOODKIN: Corals grow in these large formations, and they’re building skeleton as they grow.
[A cloud of white particles appears and disappears into a coral. This repeats with green and red particles.]
GOODKIN: As they secrete their skeletons, they will take in chemicals from the sea water based on the conditions they’re growing in.
[Scuba divers insert a drill into a huge boulder coral.]
GOODKIN: And so, we can go back and look at specific chemicals that tell us information about
[An x-ray of a coral appears. Motion graphic circles highlight different areas and text reads: “Boron – acidity, Strontium – temperature, Barium – freshwater runoff, Oxygen – salinity, temperature, Carbon – ocean mixing.”]
GOODKIN: temperature, pH, salinity, and reconstruct those environmental conditions over the past several hundred years.
[A coral reef brimming with fish. The camera focuses on fossilized polyps of fossil corals. Pan over a yellowing specimen tag reading “Stylastraea anna, Whitfield, Upper Helderberg Limestone Falls of the Ohio, Central Ohio.”]
GOODKIN: A living coral would go back 500 years, but we can also look at fossil corals that can go back through the last 10,000 years.
[Nathalie Goodkin reappears on screen.]
GOODKIN: At this point, humans are having a very large impact on the environment, a larger impact than we can understand what will happen as a result.
[Sushi rushes by on a conveyor belt. Traffic rushes over a bridge. A drain tunnel empties into a small stream.]
GOODKIN: Little changes can make such a large difference in how the ocean moves and circulates,
[Timelapse satellite images of the Deepwater Horizon oil spill. Cut to a sea turtle gliding through the water.]
GOODKIN: and what that means for the life that’s in it.
[Whales surface on a hazy grey ocean. A researcher takes notes in the back of a boat.]
GOODKIN: The only way that we can really improve our ability to make good management decisions
[Scuba divers swim towards corals. A diver holds up one bleached coral and one unbleached coral.]
GOODKIN: is to understand how the system worked before we were impacting it.
[Nathalie Goodkin reappears on screen.]
GOODKIN: Protecting corals is important for so many reasons.
[A ray hides among big flat corals. A school of long skinny fish feed on corals.]
GOODKIN: It’s really, really important for biodiversity.
[Waves break on rocks and reefs a little bit offshore.]
GOODKIN: They provide significant coastal protection in storms.
[Nathalie Goodkin reappears on screen.]
GOODKIN: And from my perspective, it would take us enormous numbers of years and financial dollars to instrument the earth as well as the reefs are.
[A colorful reef with fish swimming above it.]
GOODKIN: Being able to preserve these samples provides us with an enormous resource for understanding our climate system, both in the future and back in time.
[Title screen appears.
AMNH / L. Stevens & L. Rifkind
AMNH / A. Lenzo, H. Gentry, R. Miyamoto
AMNH / K. Corben
Konrad Hughen, Woods Hole Oceanographic Institute
NOAA Adopt a Drifter Program
Patrick Martin, Nanyang Technological University
Wildlife Conservation Society
Images / Archive
AMNH / Microscopy and Imaging Facility
NASA MODIS Rapid Response Team
“Ghost Within” by Jay Price (PRS) / Warner/Chappell Production Music]
By analyzing radiocarbon content in a 4.6-meter core of coral, Goodkin and team were able to look back about 400 years in history and point to links between East Asian Monsoons and other climate systems, including the Siberian High, a collection of cold dry air at high latitude, and El Nino-Southern Oscillation, a tropical climate system.
They also identified periods where monsoons varied greatly from year to year. Such periods included 1640 to 1660—a time during which the Ming Dynasty was destabilized by drought, floods, famine, and disease before collapsing.