Nav: Home

Century-scale deep-water circulation dynamics in the North Atlantic Ocean

May 15, 2019

Dr Moriaki Yasuhara, Dr Hisayo Okahashi, and Dr Huai-Hsuan May Huang from School of Biological Sciences and Swire Institute of Marine Science of the University of Hong Kong (HKU), in collaboration with scientists in Lamont-Doherty Earth Observatory of Columbia University, Duke University, and US Geological Survey have recently reported their discovery on a key driver of past and perhaps future abrupt climate change that is deep-water dynamics in the North Atlantic Ocean in the journal Geology.

Since the proposal of "conveyor belt" paradigm by Wallace S Broecker, in 1980s, the deep ocean circulation, now known as the Atlantic Meridional Overturning Circulation (AMOC), has been widely regarded as an important driver of global climate changes. The AMOC is a process that cold and salty surface water sinks into deep ocean in the high-latitude North Atlantic Ocean, the lower limb deep water (known as North Atlantic Deep Water: NADW) flows southward (Image 1), and eventually upwells to the surface in the North Pacific Ocean. The strength of this circulation is known to affect global heat flow and regional climates. To study this circulation dynamics, the North Atlantic Ocean is especially important, because it is the place that deep water is formed through cooling surface water in the high latitude.

The lower (deeper) part of NADW below 2,500 meters is well studied, but upper NADW (intermediate water) behavior is poorly understood for the last deglaciation, that is, the transitional period from the last ice age to the warmer contemporary interglacial climate state. Furthermore, NADW dynamics for the past ~11,700 years (known as the Holocene) remain equivocal. Dr Yasuhara and his collaborators showed that subtropical North Atlantic intermediate-water temperature varied significantly during both of these time periods, based on trace element geochemistry of calcified shells of deep-sea microcrustacean Ostracoda in a sediment core (Image 2). Their reconstructions reveal a series of multi-century-scale abrupt deep-water warming events likely caused by the reduction deep-water circulation. The authors also discovered that many of these weakening events of deep-water circulation can be widely recognized in the western North Atlantic. These deglacial-Holocene deep-water-circulation dynamics are important for understanding present and future trends in Earth's climatic system because warming and resulting polar-ice melt can change the deep-water circulation. Recent United Nations IPBES (The Intergovernmental Science-Policy Platform on Biodiversity and Ecosystem Services) report indicated that ~1 million species are now are threatened with extinction (, changes in Earth's climatic system is an important part of the reason of this.

Lead author of the study Dr Yasuhara said "Holocene deep-water circulation was more dynamic than previously thought. There is increasing evidence that this circulation change in the North Atlantic affects climates of remote places including East Asia and also marine and terrestrial ecosystems. As recently discovered by scientists including my HKU colleagues Drs Benoit Thibodeau and Christelle Not, this global deep-water circulation has substantially weakened during the last century1. If further weakening happened in the future, there may be unexpectedly broad implications not only on our atomospheric and ocean systems but also on Earth's ecological systems and our society".

"Quantifying the intensity of North Atlantic Circulation in the past is one of the grand challenge of our field. In order to better understand the magnitude and significance of the 20th century weakening trend in the circulation1 we need more reconstruction of its intensity in the past, like the one provided by the study of Dr Yasuhara and colleagues." mentioned Dr. Thibodeau in the Department of Earth Sciences, HKU.
About the Research Paper

Journal: Geology

Title: North Atlantic intermediate water variability over the past 20,000 years

Authors: Moriaki Yasuhara (The University of Hong Kong), Peter B. deMenocal (Lamont-Doherty Earth Observatory of Columbia University), Gary S. Dwyer (Duke University), Thomas M. Cronin (US Geological Survey), Hisayo Okahashi (The University of Hong Kong), and Huai-Hsuan May Huang (The University of Hong Kong)

Link of the research paper:

1Supplemental reading: Last century warming over the Canadian Atlantic shelves linked to weak Atlantic Meridional Overturning circulation. Thibodeau B, Not C, Zhu, J, A Schmittner, D Noone, C Tabor, J Zhang & Z Liu, Geophysical Research Letters, 45 (22), 12376-12385.

youtube movie:

Images download:

The University of Hong Kong

Related Biological Sciences Articles:

Social and behavioral sciences for the intelligence community
The social and behavioral sciences (SBS) offer an essential contribution to the mission of the U.S.
Preventing chemical weapons as sciences converge
Scientists from Bradford warn of increased chemical weapons risk during a period of very rapid scientific change.
Advancing life sciences research with the internet of things
The internet of things (IoT) is allowing scientists to optimize laboratory operations and combine instruments to measure and respond to complex experimental conditions.
When sciences come together
Kyoto University investigates how seemingly separate concepts in scientific fields fuse to become universal approaches by by developing a new methodology to analyze citations in papers that use similar concepts, and tracked the changes over time.
85 new species described by the California Academy of Sciences in 2017
In 2017, researchers at the California Academy of Sciences added 85 new plant and animal species to the family tree, enriching our understanding of Earth's complex web of life and strengthening our ability to make informed conservation decisions.
'Cyberbiosecurity' and protecting the life sciences
Biology and biotechnology have entered a digital age, but security policies around such activities have not kept pace.
When life sciences become data sciences
The University of Freiburg offers Europe-wide infrastructure and service in Bioinformatics.
MDI Biological Laboratory providing incubator space to Coagulation Sciences LLC
The MDI Biological Laboratory has announced that it is providing incubator space and associated scientific resources on its Bar Harbor, Maine, campus to Coagulation Sciences LLC a Riverdale, N.Y.- based development-stage medical device company.
National Academy of Sciences elects 2 members from UChicago
Two University of Chicago faculty members have been elected to the National Academy of Sciences.
Plant geneticist elected to National Academy of Sciences
Julia Bailey-Serres, a professor of genetics at the University of California, Riverside, has been elected a member of the National Academy of Sciences (NAS) for her excellence in original scientific research.
More Biological Sciences News and Biological Sciences Current Events

Top Science Podcasts

We have hand picked the top science podcasts of 2019.
Now Playing: TED Radio Hour

Why do we revere risk-takers, even when their actions terrify us? Why are some better at taking risks than others? This hour, TED speakers explore the alluring, dangerous, and calculated sides of risk. Guests include professional rock climber Alex Honnold, economist Mariana Mazzucato, psychology researcher Kashfia Rahman, structural engineer and bridge designer Ian Firth, and risk intelligence expert Dylan Evans.
Now Playing: Science for the People

#540 Specialize? Or Generalize?
Ever been called a "jack of all trades, master of none"? The world loves to elevate specialists, people who drill deep into a single topic. Those people are great. But there's a place for generalists too, argues David Epstein. Jacks of all trades are often more successful than specialists. And he's got science to back it up. We talk with Epstein about his latest book, "Range: Why Generalists Triumph in a Specialized World".
Now Playing: Radiolab

Dolly Parton's America: Neon Moss
Today on Radiolab, we're bringing you the fourth episode of Jad's special series, Dolly Parton's America. In this episode, Jad goes back up the mountain to visit Dolly's actual Tennessee mountain home, where she tells stories about her first trips out of the holler. Back on the mountaintop, standing under the rain by the Little Pigeon River, the trip triggers memories of Jad's first visit to his father's childhood home, and opens the gateway to dizzying stories of music and migration. Support Radiolab today at