Radiocarbon and stable isotope constraints on Last Glacial Maximum and Younger Dryas ventilation in the western North Atlantic

TitleRadiocarbon and stable isotope constraints on Last Glacial Maximum and Younger Dryas ventilation in the western North Atlantic
Publication TypeJournal Article
Year of Publication2004
AuthorsKeigwin, LD
Date PublishedNov 3
ISBN Number0883-8305
Keywordsbenthic foraminifera, deep-sea sediments, ice-age, Ocean circulation, ocean ventilation, pacific-ocean, radiocarbon, SARGASSO SEA, southern-ocean, Thermohaline circulation, united-states, water circulation, western north atlantic

[1] Foraminiferal abundance, C-14 ventilation ages, and stable isotope ratios in cores from high deposition rate locations in the western subtropical North Atlantic are used to infer changes in ocean and climate during the Younger Dryas (YD) and Last Glacial Maximum (LGM). The delta(18)O of the surface dwelling planktonic foram Globigerinoides ruber records the present-day decrease in surface temperature (SST) of similar to 4 degreesC from Gulf Stream waters to the northeastern Bermuda Rise. If during the LGM the modern delta(18)O/salinity relationship was maintained, this SST contrast was reduced to 2 degreesC. With LGM to interglacial delta(18)O changes of at least 2.2parts per thousand, SSTs in the western subtropical gyre may have been as much as 5 degreesC colder. Above similar to 2.3 km, glacial delta(13)C was higher than today, consistent with nutrient-depleted ( younger) bottom waters, as identified previously. Below that, delta(13)C decreased continually to - 0.5parts per thousand, about equal to the lowest LGM delta(13)C in the North Pacific Ocean. Seven pairs of benthic and planktonic foraminiferal C-14 dates from cores > 2.5 km deep differ by 1100 +/- 340 years, with a maximum apparent ventilation age of similar to 1500 years at 4250 m and at similar to 4700 m. Apparent ventilation ages are presently unavailable for the LGM < 2.5 km because of problems with reworking on the continental slope when sea level was low. Because LGM δC-13 is about the same in the deep North Atlantic and the deep North Pacific, and because the oldest apparent ventilation ages in the LGM North Atlantic are the same as the North Pacific today, it is possible that the same water mass, probably of southern origin, flowed deep within each basin during the LGM. Very early in the YD, dated here at 11.25 +/- 0.25 ( n = 10) conventional C-14 kyr BP ( equal to 12.9 calendar kyr BP), apparent ventilation ages < 2.3 km water depth were about the same as North Atlantic Deep Water today. Below similar to 2.3 km, four YD pairs average 1030 +/- 400 years. The oldest apparent ventilation age for the YD is 1600 years at 4250 m. This strong contrast in ventilation, which indicates a front between water masses of very different origin, is similar to glacial profiles of nutrient-like proxies. This suggests that the LGM and YD modes of ocean circulation were the same.