Synchronization of North Pacific and North Atlantic climates and abrupt warming during last deglaciation

For most of the past 18,000 years the temperature records in the North Pacific and the North Atlantic are anti-synchronous. Warm temperatures in the Pacific often correspond to cold temperatures in the North Atlantic and vice versa.  In this study it is shown that the occasional synchronicity in the North Pacific and North Atlantic climates corresponds to periods of abrupt Northern Hemisphere warming.  About 15,500 to 11,000 years ago the climate in the two regions synchronized, with similar temperatures in both basins, just prior to and during the most abrupt climate transition of the last 20,000 years (Bølling-Allerød) and just prior abrupt final temperature rise before the current Holocene warm period.

Background

The mechanism which leads to glacial and interglacial events with a period of about 100,000 years is poorly understood.  Various mechanisms involving small variations in Earth’s orbit and tilt, ice sheet dynamics, variations in the Atlantic overturning current, greenhouse gases, and dust have been proposed. It is well-known that Southern and Northern hemispheres are often anti-synchronous, warming events in the North Atlantic correspond to cooling in the south and vice versa.  In this research the climates of the North Atlantic and North Pacific are compared over the period of the last deglaciation 18,000 to 11,000 years ago.

Data

In this study ocean sediments from the Gulf of Alaska (GOA) corresponding to the past 18,000 years have been analyzed. The resolution of the cores is about 80 years from the present to 11,000 years ago, about 10 years from 11,000 to 14,600 years ago, and about 35 years from 14,700 to 18,000 years ago. Sediments were dated by radiocarbon dating and from a known volcanic event which left debris in the sediment record. The Gulf of Alaska sediment record tracks local temperature, salinity, and global ice volume. Other data collected in the North Pacific indicate that the sediment record there reflects upper-ocean temperature.

In the North Atlantic, the North Greenland Ice Core Project (NGRIP) has analyzed ice cores for the same period. NGRIP ice cores record local temperature, moisture transport, and global ice volume. The NGRIP temperature record correlates with the marine paleotemperature records from the subpolar North Atlantic sea surface.

Analysis

Comparison of Gulf of Alaska and Greenland surface temperature over last deglaciation
Comparison of Gulf of Alaska (black line) and Greenland (purple line) surface temperatures from 18,000 years ago to present. (A) Surface temperature averaged over 2000 years. (B) High resolution surface temperature from delta-oxygen-18. Cross correlation between Gulf of Alaska and Greenland is shown below in (A) and (B). The highlighted region corresponds to the last deglaciation. The two peaks in the cross correlation correspond to the Bølling-Allerød warming and the final Holocene warming.

By comparing temperature records in the North Pacific and the North Atlantic, it can be seen that over most of the past 18,000 years, the relationship between sea temperatures in the North Atlantic and North Pacific was anti-synchronous, often described as a see-saw.  But starting several hundred years before the abrupt BøllingAllerød warming period 14,700 to 14,100 years ago, the North Atlantic and North Pacific climate records become synchronized with similar temperatures in the two basins.  Then just before the second abrupt warming which initiated the present warm Holocene period, the North Atlantic and North Pacific temperature records again became highly synchronized.  Subsequently about 10,000 years ago the North Atlantic and North Pacific climate records became anti-synchronized, suggesting a return to the characteristic North Pacific-North Atlantic seesaw.

Praetorius and Mix, Science 25 July 2014: Vol. 345 no. 6195 pp. 444-448 DOI: 10.1126/science.1252000