Laurentide Ice Sheet Meltwater and the Atlantic Meridional Overturning Circulation During the Last Glacial Cycle: A View From the Gulf of Mexico - Abrupt Climate Change: Mechanisms, Patterns, and Impacts - page 41

18 O minima
even within Orca Basin cores ( 3 ‰ to 4.2 ‰ ). However,
the range is even greater near DeSoto Canyon (

script, 2011). There is quite a range of deglacial δ

1.2 ‰ to

) as discussed earlier. These ranges may relate to
differential temporal resolution in the cores and/or different
numbers of specimens analyzed. Nevertheless, there is a
clear trend toward higher

3.5 ‰

18 O values with distance west of
the Mississippi Delta junction, in agreement with a previous
compilation [Williams, 1984]. East of the junction, the evi-
dence is equivocal. What is clear is that meltwater in

δ

uence
was less than at corresponding distances west of the junction.
But in light of con

icting data from three DeSoto Canyon
area cores, the contention that LIS meltwater did not in u-

ence the northeastern Gulf of Mexico [Nürnberg et al., 2008]
remains to be con rmed by additional data.

3. ORCA BASIN CLIMATE RECORDS

18 O plot comparing white Globigerinoides

Figure 4. Distance δ

Some of the most detailed records of the last glacial cycle
come from Orca Basin in the north central Gulf of Mexico.
Located ~300 km from the present-day Mississippi River
delta junction, Orca Basin is well-suited for high-resolution
paleoclimatology because of unusually high accumulation
rates (~30

18 O values for the Holocene (open squares) and peak deglacial
meltwater spike (solid circles) versus distance from the Mississippi
Delta junction. Deglacial Orca Basin values are circled. A best tline
is drawn to highlight the increased anomaly in meltwater spike δ

ruber δ

18 O
values with lesser distance. Core information is given in Table 1.

300 cm kyr 1 ) and a ~200 m thick brine layer
(salinity >250) that preserves sedimentary laminations
[Shokes et al., 1977; Pilcher and Blumstein, 2007]. Abun-
dant pteropods throughout the glacial to present section of
the core indicate minimal dissolution of carbonate material
[Leventer et al., 1983]. Orca Basin lies within the Western
Hemisphere Warm Pool, which develops in late summer with
SST reaching >28.5°C in the Caribbean and Gulf of Mexico.
Stable isotope data from Orca Basin cores are available for
most of MIS 3 through the last deglaciation [Leventer et al.,
1982; Flower and Kennett, 1990, 1995; Flower et al., 2004;

-

18 O values (open squares) are in the
1.2 ‰ to 1.8 ‰ range for each core, with only slightly
lower δ

Mean Holocene δ

18 O values at lesser distance from the Mississippi
Delta junction (Figure 4). In contrast, deglacial δ

18 O minima
exhibit a clear trend versus distance, with lowest values
found in Orca Basin core MD02-2550 (C. Williams et al.,
Abrupt climate change and Laurentide Ice Sheet meltwater
routing to the Gulf of Mexico, submitted to Geology, 2011,
hereinafter referred to as Williams et al., submitted manu-

Table 1. Selected Gulf of Mexico Core Sites
Core Latitude Longitude Water Depth (m) Reference

GS7102-07 29° 87°36 ′ 1569 Emiliani et al. [1978]

GS7102-09 29° 87° 695 Emiliani et al. [1975]

EN32-PC4 a 26°56.1 ′ 91°21.7 ′ 2260 Flower and Kennett [1990]

EN32-PC6 a 26°56.8 ′ 91°21.0 ′ 2280 Leventer et al. [1982]

K97 25°37 ′ 93°12 ′ 3408 Kennett and Shackleton [1975]

K120 23°17.8 ′ 96°10.8 2537 Kennett and Shackleton [1975]

K139 20°30 ′ 92°37 ′ 2462 Kennett and Shackleton [1975]

TR126-23 20.8° 95.5° 2200 Williams [1984]

MD02-2550 a 26°56.77 ′ 91°20.74 ′ 2248 Williams et al. [2010]

MD02-2551 a

26°56.78 ′ 91°20.75 ′ 2255 Hill et al. [2006]

MD02-2575 29°0.1 ′ 87°7.13 ′ 847 Nürnberg et al. [2008]

LOUIS 2023 27.76° 92.59° 401 Aharon [2003]

RC12-10 23° 95.53° 3054 Poore et al. [2003]

a Orca Basin cores.