| Summary: | We conducted a survey along the Beaufort margin to investigate the origin of the Younger Dryas cooling that began about 13,000 years ago. For decades this cold event has been associated with sea ice in the Arctic and North Atlantic Oceans, and the storage and release of fresh water from a large glacial lake in North America, yet its origin remains controversial. Radiocarbon dates, isotope data, acoustic character and grain size data have fingerprinted the potential catastrophic flood deposit along the Beaufort margin in the Arctic Ocean. The marine evidence is consistent with the onshore data and provides a much-improved age model for the catastrophic glacial lake draining. The origin of Younger Dryas (YD) cooling at ~13 ka, after 2 kyr of postglacial warming, is a century-old climate problem. The YD is thought to have resulted from a slow-down of the Atlantic meridional overturning circulation (AMOC) in response to a flood of Laurentide ice sheet meltwater from glacial Lake Agassiz in Canada. Although there is no oxygen isotopic (d18O) evidence in the western North Atlantic for a local source of meltwater where it was predicted, we report here that the eastern Beaufort Sea contains the long-sought d18O minimum at ~12.9 ka, suggesting that Lake Agassiz meltwater flowed down the Mackenzie River and into the Arctic Ocean. This fresh water would have traveled north along the Canadian Archipelago, and through Fram Strait to the Nordic Seas where surface freshening and freezing near sites of deep water formation would have suppressed convection and caused the YD by reducing the AMOC. During the Younger Dryas dramatic changes to regional climates occurred. Models of oceanographic circulation predict that freshwater from the glacier lakes made their way from the Arctic to the north Atlantic Ocean. There it disrupted a circulation pattern that stretches from Greenland to the Southern Ocean. In normal mode, the AMOC transports warm equatorial waters poleward and releases heat to the atmosphere. Such a disruption caused substantial cooling in Europe, The Younger Dryas in fact takes its name from a flower (Dryas octopetala) that flourished in the continent’s cold conditions at the time. The Younger Dryas cooling lasted only a short time in an overall warming period that lasted 20,000 years, but it’s an important example of how feedbacks affect the climate system. Overall trends of warming or cooling on Earth are not linear but are punctuated by reversals and accelerations such as this one. Such events help scientists interpret current trends, distinguishing global climate signals from regional signals. The findings from this study will stimulate more research on how much fresh water is really necessary to cause a change in the system and weakening of the AMOC. It certainly calls further attention to the warming we're observing in the Arctic today, and the accelerated melting of Greenland ice. Earlier in 2018, a paper published by researchers at the University College London and Woods Hole Oceanographic Institution found evidence that the AMOC hasn’t been running at peak strength since the mid-1800s and is currently at its weakest point in the past 1,600 years. Continued weakening could disrupt weather patterns from the U.S. and Europe to the African Sahel. In summary, it is important to study past rapid climate events because they may provide important clues regarding future events. Cruise data from the project, "Testing the Northern Route for Younger Dryas Meltwater". Includes all the raw shipboard data collected in late summer 2013 on the U.S. Coast Guard Cutter Healy: • ADCP → Multiplexed data collected using a Hawaii UHDAS instrument system. All data available as a tarball doi:10.7284/112637. • CTD → CTD (Conductivity, Temperature, Depth) data collected using a Sea-Bird SBE-911plus instrument system. All data available as a tarball doi:10.7284/118783. • Metstation → Unprocessed Meteorological Station data collected using a SIO MET-System instrument system. All data available as a tarball doi:10.7284/119525. • Multibeam → Raw Multibeam Echosounder data collected using a Kongsberg EM122 instrument system. All data files available in native format (.ALL) doi:10.7284/112642. • Knudsen Subbottom → Raw subbottom data collected using a Knudsen Chirp 3260. All data files available in native format (.kea, .keb, .sgy) doi:10.7284/113452. Towed Chirp data were also collected during parts of this cruise: Raw seismic reflection sub-bottom data collected with a towed Edgetech 512i CHIRP sub-bottom profiler from Scripps Institution of Oceanography. The data files are in SEG-Y format and contain real-time GPS navigation in the header. All data files are available in native format (.sgy) doi:10.1594/IEDA/324150. Shipboard data was collected throughout the entire cruise except the two subbottom systems. Either the Towed Chirp system or the Knudsen Chirp was used at any given time due to source frequency conflicts. The subbottom data was collected to identify coring targets. It was also collected during transits between potential coring locations. Potential coring locations were based on information from previous research and subbottom stratigraphy.
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