Study of the Gulf Stream-Slopewater system

Date of Award




Degree Name

Doctor of Philosophy (Ph.D.)


Meteorology and Physical Oceanography

First Committee Member

Arthur J. Mariano - Committee Chair


A study of the Gulf Stream-Slopewater system from 4-year outputs of a high resolution numerical simulation of the North Atlantic is presented, with particular emphasis on the Slopewater Jet (SJ). The SJ is partly fed by a Gulf Stream bifurcation in the vicinity of the New England Seamount Chain (NESC). A stability analysis reveals that the NESC has a potential destabilizing effect on the Gulf Stream. However, the Taylor constraint of the NESC's spatial distribution explains most of the lower-layer mean flow, and deflection of the northern portion of the Stream into the Slopewater region shortly downstream of the seamount chain. The transport of the Slope Jet indeed doubles between the NESC and the Grand Banks (and is consistent with observations), from 7--9 Sv to 19 Sv, in agreement with the transport estimations of McLellan (1957). The increase in transport is due partly to Gulf Stream water rejections, and partly to the entrainment and mixing of waters from the shelf and from the Labrador Current (LC). A statistical analysis of the pycnocline depth above the NESC shows that the chain enhances the 9 month-1 meandering variability frequency of the Gulf Stream, which affects the shape of the upper layer streamline divergence. The Gulf Stream's meandering variability is the main source of SJ variability shortly downstream of the NESC, in terms of lateral oscillation of the Jet, while the main transport variability is related to the invasion of GS waters merging with the SJ on an annual basis. The seasonality of the Slopewater column manifests as an annual variation in the transports of both the SJ and the DWBC, reaching a maximum in the fall and a minimum in the spring. This apparent coupling seems to result however from independent factors, namely the proximity of the Gulf Stream's mean path and anticyclonic eddies in the slopewater in the fall, versus the seasonal deep water mass formation, also leading in this numerical simulation to a maximum transport in the Mid Atlantic Bight in the fall. South of the Grand Banks, the variability of the upper slopewater is related to an annual transport of the Labrador Current and SJ in phase, with a dominant annual time scale, although the upstream SJ variability is also present and may induce direct changes in the LC transport. There is also a seasonal signal in the water mass characteristics of the eastward flow.The analysis of the numerical model has shown remarkably similar results to the most recent observations on the Slopewater system. However, the statistical study revealed sub-annual to biannual variability timescales, rather than interannual time-scales.


Physical Oceanography

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