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North Atlantic Deep Water (NADW) Formation During the Holocene
Oppo, D.W., McManus, J.F. and Cullen, J.L. 2003. Deepwater variability in the Holocene epoch. Nature 422: 277-278.

What was done
The authors studied changes in the carbon-isotope composition of benthic foraminifera in a sediment core taken from Ocean Drilling Project site 980 (55N, 15W) on the Feni Drift in the subpolar northeastern Atlantic Ocean.

What was learned
In the words of the authors, "the new North Atlantic benthic 13C record unambiguously demonstrates that NADW varied on centennial-millennial time scales during the Holocene."

What it means
The authors say that "low 13C values during the Little Ice Age, the most recent of the Holocene millennial cold events, and during an early Holocene event at ~10.3 kyr hint at a linkage between millennial climate and deep water" and that "downcore variations in sedimentological indicies also indicate this possibility." They additionally conclude that "significant variations in the relative NADW contribution can occur in the absence of forcing by large ice sheets." Hence, it is looking more and more likely that the natural millennial-scale variability of NADW formation and the associated natural millennial-scale variability of earth's climate are driven by a common external forcing factor that operates throughout glacial and interglacial periods alike. Furthermore, that observation alone strongly suggests that millennial-scale variability in solar activity may well be what drives each of these closely-linked phenomena, as a wealth of independent data equally strongly suggests [see Solar Effects (Millennial-Scale Cycles) in our Subject Index].

Reviewed 28 May 2003