HR: 1340h
AN: PP13A-0591    [Abstracts]
TI: Extreme Cooling of Slopewaters East of the USA and Canada During the Holocene
AU: * Sachs, J P
EM: jsachs@mit.edu
AF: Department of Earth, Atmospheric and Planetary Sciences Massachusetts Institute of Technology, 77 Massachusetts Ave., Room E34-254, Cambridge, MA 02139 United States
AU: Keigwin, L D
EM: lkeigwin@whoi.edu
AF: Department of Marine Geology and Geophysics Woods Hole Oceanographic Institution, 360 Woods Hole Rd., McLean Laboratory, Woods Hole, MA 02543 United States
AB: Detailed sea surface temperature records from the slopewaters east of the USA and Canada indicate that substantial, near-monotonic cooling of 4-10 degC began ~10,000 years ago and continues unabated to the present. That SST records from the Northeast Atlantic and air temperature records from Central Greenland indicate only moderate (~1-3 degC) cooling during the Holocene suggests that ocean-atmosphere dynamics acted to magnify the cooling we observe on the western side of the Atlantic, where the slopewaters are characterized by the interaction between cold, fresh Labrador Current waters and warm, salty Gulf Stream waters. Several hypotheses are advanced to explain these observations. (i) Holocene cooling of the slopewater system was forced by decreasing summer and mean annual insolation at high northern latitudes, and increasing mean annual and winter meridional insolation gradients between 20-65 N. (ii) An equatorward shift occurred in the mean position of the Gulf Stream from 45-50 N (west of 45 W) 11 kyr ago to its present position at 40 N. (iii) The subpolar gyre strengthened in response to stronger westerlies forced by a larger meridional temperatue gradient. An invigorated subpolar gyre transported more cold, fresh arctic water southward in the Labrador Current, cooling the Mid-Atlantic region at least as far south as Cape Hatteras. (iv) Colder SSTs and stronger westerlies over the Labrador Sea increased convection and the production of LSW, amplifying cooling of NW Atlantic slopewaters and acting as a positive feedback (on additional cooling). (v) Positive sea ice anomalies in the Labrador Sea and negative sea ice anomalies in the Greenland Sea resulted from the invigorated subpolar gyre circulation (as observed during the positive phase of the NAO) and amplified cooling of NW Atlantic slopewaters relative to the NE Atlantic. Lastly, we speculate that North Atlantic climate evolution during the Holocene was analogous to an extended positive phase of the NAO and that cooling of the NW Atlantic slopewaters is an important prelude to the expansion of perennial ice in Northeastern Canada at the start of the next glacial period.
DE: 3344 Paleoclimatology
DE: 4267 Paleoceanography
DE: 1055 Organic geochemistry
DE: 1620 Climate dynamics (3309)
DE: 1635 Oceans (4203)
SC: Paleoceanography and Paleoclimatology [PP]
MN: 2004 AGU Fall Meeting