Science is theoretically objective, but biases and paradigms often originate from something as fundamental as field site accessibility, data density, or publication date. Such biases may be at the heart of an enduring paradigm in paleoceanography and paleoclimatology—that changes in cold dense water production in the North Atlantic Ocean forced millennial-scale (<1000 year) global climate changes during the past ∼50,000 years. These changes were first identified in Greenland ice cores >30 years ago ([ 1 ][1]). On page 716 of this issue, Walczak et al. ([ 2 ][2]) present compelling data from marine sediments collected in the Northeast Pacific Ocean that add to evidence indicating that the engine of Earth's climate system lies outside the North Atlantic.
![Figure][3]
Unraveling a chain of regional climate events 50,000 years ago
Paleoclimate records from places like the Hulu Cave in China record strong Asian monsoon periods preceding Cordilleran melting events by a few millennia. Recurrent changes in iceberg discharges from the Cordilleran Ice Sheet coincide with Sea of Okhotsk sinking water production and precede regional climate changes in Greenland found in North Greenland Ice Core Project (NGRIP) ice cores and produced Heinrich event icebergs. U1419, Integrated Ocean Drilling Program (IODP) Site U1419.
GRAPHIC: V. ALTOUNIAN/ SCIENCE ; (GLOBE) NOAA
The paradigm holds that the intensity of North Atlantic Deep Water (NADW) production controls the rate of the Atlantic Meridional Overturning Circulation (AMOC), a central component of Earth's climate system ([ 3 ][4]). A key supporting observation is the tenuous temporal link between abrupt North Atlantic climate transitions during the last glaciation, inferred from Greenland ice cores, and melting of marine-terminating ice sheets encircling the North Atlantic ([ 4 ][5]). Marine sediments deposited in the glacial North Atlantic contain discrete layers of detrital carbonaterich sands in muddy sediments ([ 5 ][6]). These coarse deposits, called Heinrich events, suggest melt-out from debris-rich icebergs calved from North America's Laurentide Ice Sheet. Iceberg “armadas” and associated low-salinity glacial meltwater likely disrupted NADW production, thereby slowing the AMOC and altering global ocean circulation ([ 4 ][5]). This cascade of events forms the working hypothesis for abrupt (
1. A. C. Mix et al
., in Mechanisms of Global Climate Change at Millennial Time Scales, P. U. Clark et al., Eds. (Geophys. Monogr. Ser., American Geophysical Union), vol. 112, pp. 127–148.
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