TY - JOUR
T1 - Glacial thermohaline circulation states of the northern Atlantic: The compatibility of modelling and observations
AU - Bigg, G. R.
AU - Wadley, M. R.
AU - Stevens, D. P.
AU - Johnson, J. A.
PY - 2000
Y1 - 2000
N2 - We present 3He data froma repeat section across Drake Passage, fromthree sections off the South American
continent in the Pacific, at 28?S, 35?S, and 43?S, and fromthree sections in the Atlantic, eastward of the Malvinas, close
to 35?W, and near the Greenwich Meridian. In Drake Passage, a distinct high-3He signal is observed that is centered
just above the boundary of the Lower and the Upper Circumpolar Deep Water (LCDW, UCDW), and is concentrated
towards the northern continental slope. 3He concentrations in the Antarctic Circumpolar Current (ACC) upstream of
Drake Passage (World Ocean Circulation Experiment section P19 at 88?W) are markedly lower than those found in
Drake Passage, and a regional source of primordial helium in the path of the ACC that might cause the high-3He
feature can be ruled out. We explain the feature by addition of high-3He waters present at the 43?S Pacific section. This
supports a previous, similar interpretation of a low-salinity anomaly in Drake Passage (Naveira Garabato et al., Deep-
Sea Research I 49 (2002) 681), that is strongly related to the high-3He feature. Employing multiparameter water mass
analysis (including 3He as a parameter), we find that deep waters as met at the 43?S Pacific section, flowing south along
the South American continental slope, contribute substantially to the ACC waters in Drake Passage (fractions exceed
50% locally). Lesser, but laterally more extended contributions are found east of the Malvinas, and still smaller ones are
present at 35?W and at the Greenwich Meridian. Using velocity measurements from one of the two Drake Passage
sections, we estimate the volume transport of these waters to be 7.071.2 Sv, but the average transport may be
somewhat lower as the other realization had a less pronounced signal. The enhanced 3He signature in Drake Passage is
essentially confined north of the Polar Front. Further downstreamthe signature crosses this front, to the extent that at
35?W the contributions south and north of it are of similar magnitude. At the same time, the 3He levels north of the
front are reduced due to a substantial admixture of low-3He North Atlantic Deep Water, such that 3He becomes highest
south of the front. The flow of Southeast Pacific deep slope waters entering the ACC constitutes the predominant exit
pathway of the primordial helium released in the deep Pacific, and represents a considerable fraction of the deep water
return flow fromthe Pacific into the ACC. Therefore and also because the density range of the added deep slope waters
is intermediate between those of UCDW and LCDW, they must be considered a distinct water mass.
r 2003 Elsevier Ltd. All rights reserved.
AB - We present 3He data froma repeat section across Drake Passage, fromthree sections off the South American
continent in the Pacific, at 28?S, 35?S, and 43?S, and fromthree sections in the Atlantic, eastward of the Malvinas, close
to 35?W, and near the Greenwich Meridian. In Drake Passage, a distinct high-3He signal is observed that is centered
just above the boundary of the Lower and the Upper Circumpolar Deep Water (LCDW, UCDW), and is concentrated
towards the northern continental slope. 3He concentrations in the Antarctic Circumpolar Current (ACC) upstream of
Drake Passage (World Ocean Circulation Experiment section P19 at 88?W) are markedly lower than those found in
Drake Passage, and a regional source of primordial helium in the path of the ACC that might cause the high-3He
feature can be ruled out. We explain the feature by addition of high-3He waters present at the 43?S Pacific section. This
supports a previous, similar interpretation of a low-salinity anomaly in Drake Passage (Naveira Garabato et al., Deep-
Sea Research I 49 (2002) 681), that is strongly related to the high-3He feature. Employing multiparameter water mass
analysis (including 3He as a parameter), we find that deep waters as met at the 43?S Pacific section, flowing south along
the South American continental slope, contribute substantially to the ACC waters in Drake Passage (fractions exceed
50% locally). Lesser, but laterally more extended contributions are found east of the Malvinas, and still smaller ones are
present at 35?W and at the Greenwich Meridian. Using velocity measurements from one of the two Drake Passage
sections, we estimate the volume transport of these waters to be 7.071.2 Sv, but the average transport may be
somewhat lower as the other realization had a less pronounced signal. The enhanced 3He signature in Drake Passage is
essentially confined north of the Polar Front. Further downstreamthe signature crosses this front, to the extent that at
35?W the contributions south and north of it are of similar magnitude. At the same time, the 3He levels north of the
front are reduced due to a substantial admixture of low-3He North Atlantic Deep Water, such that 3He becomes highest
south of the front. The flow of Southeast Pacific deep slope waters entering the ACC constitutes the predominant exit
pathway of the primordial helium released in the deep Pacific, and represents a considerable fraction of the deep water
return flow fromthe Pacific into the ACC. Therefore and also because the density range of the added deep slope waters
is intermediate between those of UCDW and LCDW, they must be considered a distinct water mass.
r 2003 Elsevier Ltd. All rights reserved.
U2 - 10.1144/jgs.157.3.655
DO - 10.1144/jgs.157.3.655
M3 - Article
VL - 157
SP - 655
EP - 665
JO - Journal of the Geological Society
JF - Journal of the Geological Society
SN - 0016-7649
IS - 3
ER -