Numerical Study of Glacial and Meltwater Global Ocean Thermohaline Conveyor
91
most of the sediment mass was spread over the abyssal valley in the Canary Basin (Fig. 2b). Note that although the sedimentation rate is far lower there than in
the Iceland Basin, the sediment mass is roughly the same because bottom area
in the latitude-longitude grid cells increases rapidly to the south. A relatively
high glacial accumulation rate is found in the Newfoundland Basin. However, we
do not see continuous southward sediment transport along the American coast,
a signature of all our experiments based on the modern ocean surface climatology. Instead, a noticeable southward sediment transport is found at the eastern
flank of the Mid-Atlantic Ridge.
Though an increased northward incursion of AABW at the LGM in the eastern North Atlantic is consistent with the contouring by Sarnthein et al. (1994),
the conclusions about an increased reverse abyssal gyre cannot be attributed
likewise to the western part of the basin. Indeed, the southward transport,
though noticeably curtailed, still existed in the western deep ocean. Analysis of
the velocity maps suggests (and trajectory analysis confirms; see below) that in
the west the northward flow of AABW at LGM was probably the same as or weaker than today's. Simultaneously, the eastern flank of the glacial AABW intrusion
(initially through the Vema Fracture Zone) was enhanced considerably. The exchange between the eastern and northern parts of the deep North Atlantic was
stronger at the LGM than today.
As the meltwater North Atlantic Current diverged from today's northeastern
path, the accumulation rate in the Iceland and Irminger Basins dropped and a
significant part of the sediment mass was spread over the abyssal valley in the
Canary Basin (Fig. 2c). Note that although the sedimentation rate is far lower
there than in the Iceland Basin, the sediment mass is roughly the same because
bottom area in the latitude/longitude grid cells increases rapidly to the south.
The sedimentation rate around Iceland decreased by over a factor of two as compared with its modern value (cf. Fig. 2a and b). This is mainly because of the absence of ventilating convection both in the NGS and in the Irminger Sea. At the
LGM, a relatively high glacial accumulation rate still emerges in the model in the
Newfoundland Basin (Fig. 2b). However, we do not see continuous southward
sediment transport along the North American coast, a signature of all our experiments based on the modern ocean surface climatology. Instead, a noticeable
southward sediment transport is found at the eastern flank of the Mid-Atlantic
Ridge. At the MWE this tendency is increased significantly. The accumulation
rate in the Newfoundland Basin decreased in comparison with the LGM run,
whereas deposition was stronger at the eastern flank of the Mid-Atlantic Ridge.
The area between Newfoundland and the Caribbean is almost totally free of sediment deposition.
5.3
Trajectory tracing
Although most of the features common to the three sediment transport patterns
(the HM, LGM and MWE) can be explained by comparing them with the circu-
91
most of the sediment mass was spread over the abyssal valley in the Canary Basin (Fig. 2b). Note that although the sedimentation rate is far lower there than in
the Iceland Basin, the sediment mass is roughly the same because bottom area
in the latitude-longitude grid cells increases rapidly to the south. A relatively
high glacial accumulation rate is found in the Newfoundland Basin. However, we
do not see continuous southward sediment transport along the American coast,
a signature of all our experiments based on the modern ocean surface climatology. Instead, a noticeable southward sediment transport is found at the eastern
flank of the Mid-Atlantic Ridge.
Though an increased northward incursion of AABW at the LGM in the eastern North Atlantic is consistent with the contouring by Sarnthein et al. (1994),
the conclusions about an increased reverse abyssal gyre cannot be attributed
likewise to the western part of the basin. Indeed, the southward transport,
though noticeably curtailed, still existed in the western deep ocean. Analysis of
the velocity maps suggests (and trajectory analysis confirms; see below) that in
the west the northward flow of AABW at LGM was probably the same as or weaker than today's. Simultaneously, the eastern flank of the glacial AABW intrusion
(initially through the Vema Fracture Zone) was enhanced considerably. The exchange between the eastern and northern parts of the deep North Atlantic was
stronger at the LGM than today.
As the meltwater North Atlantic Current diverged from today's northeastern
path, the accumulation rate in the Iceland and Irminger Basins dropped and a
significant part of the sediment mass was spread over the abyssal valley in the
Canary Basin (Fig. 2c). Note that although the sedimentation rate is far lower
there than in the Iceland Basin, the sediment mass is roughly the same because
bottom area in the latitude/longitude grid cells increases rapidly to the south.
The sedimentation rate around Iceland decreased by over a factor of two as compared with its modern value (cf. Fig. 2a and b). This is mainly because of the absence of ventilating convection both in the NGS and in the Irminger Sea. At the
LGM, a relatively high glacial accumulation rate still emerges in the model in the
Newfoundland Basin (Fig. 2b). However, we do not see continuous southward
sediment transport along the North American coast, a signature of all our experiments based on the modern ocean surface climatology. Instead, a noticeable
southward sediment transport is found at the eastern flank of the Mid-Atlantic
Ridge. At the MWE this tendency is increased significantly. The accumulation
rate in the Newfoundland Basin decreased in comparison with the LGM run,
whereas deposition was stronger at the eastern flank of the Mid-Atlantic Ridge.
The area between Newfoundland and the Caribbean is almost totally free of sediment deposition.
5.3
Trajectory tracing
Although most of the features common to the three sediment transport patterns
(the HM, LGM and MWE) can be explained by comparing them with the circu-