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The Newfoundland Basin lies on the southeastern Grand Banks
of the Northwest Atlantic, a key area where the exchange between subpolar and
subtropical gyres takes place. Dramatic seasonal changes occur in the
sea-surface temperature, salinity, and freshwater input due to the interaction
between the cold and fresh Labrador Current and warm and salty North Atlantic
Current (NAC) on the southeast Grand Banks. Due to this interaction, the
biological productivity and seasonal stratification of the upper water masses
are intensified. Such changes must have been more drastic during glacial times,
due to the penetration of the Polar and Arctic fronts and the southward
migration of the Gulf Stream/NAC. However, the extent to which such changes
impacted the sea-surface characteristics in the Newfoundland Basin is poorly
known. This study reports changes in the sea-surface characteristics using a
sediment core (Hu9007-08) collected from the Milne seamount during the last
145,000 years. Sediment processing involved sample washing, ice-rafted debris
(IRD) counts, and planktonic foraminifer census, as well as determination of
oxygen and carbon isotopes, 14C-AMS dating, and age model construction. A total
of 19 control points were used to construct the age model, in which linear
sedimentation rates between the 14C-AMS date points were considered. Heinrich
layers H1, H2, H4, and H5, as well as H11, were identified within MIS 3 and at
the penultimate deglaciation by IRD and Neogloboquadrina pachyderma peaks,
along with lighter oxygen isotopes. The rapid turnover of foraminiferal species
with distinct depth habitats and ecological niches in the mixed layer and
thermocline suggests an interplay between the polar and subpolar water masses
during both Heinrich and non-Heinrich periods. Only two North Atlantic-wide
cooling events, C24 and C21, in which the latter event is linked to the minor
IRD peak during the marine isotope stage (MIS) 5 in Hu90-08, compared to eight
cooling events in the eastern subpolar gyre (e.g., ODP Site 984). Millennial-scale
N. pachyderma variability in the western subpolar gyre appears to be absent
compared to the eastern subpolar gyre during the MIS 3, suggesting the
occasional presence of the NAC-borne salty and warm water, implying a
contrasting climate state between the western and eastern subpolar gyre. T.
quinqueloba, a subpolar species, data are fragmentary; however, there are
differences between the western and eastern subpolar gyre in addition to the
differences within the western subpolar gyre during MIS 5 that imply a variable
influence by the subpolar water. This finding suggests that the NAC influence
outweighs the impact of cold and fresh polar water in the northern northwestern
Atlantic during the MIS 5. The anti-covariation between N. pachyderma and N.
incompta provides a proxy for sea-surface temperature, with the former thriving
at temperatures below 8°C and the latter near 12°C. Overall, the data reflect
rapid changes in sea-surface characteristics in the western subpolar gyre,
driven by a dynamic balance between the Labrador Current and the NAC.
Author(s) Details
Harunur Rashid
College of Oceanography and Ecological Science, Shanghai Ocean University,
Shanghai 201306, China and Department of Earth and Environmental Sciences,
University of Ottawa, Ottawa, ON K1N 6N5, Canada.
Tongzheng Zhang
College of Oceanography and Ecological Science, Shanghai Ocean University,
Shanghai 201306, China.
Qian Qian Lu
College of Oceanography and Ecological Science, Shanghai Ocean University,
Shanghai 201306, China.
Ming Zeng
College of Oceanography and Ecological Science, Shanghai Ocean University,
Shanghai 201306, China.
Please see the book here :- https://doi.org/10.9734/bpi/crgese/v3/6058
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