Auxiliary material for Paper 2008GL035918
                       
Wintertime observations of Subtropical Mode Water formation within the Gulf 
Stream

Terrence M. Joyce
Department of Physical Oceanography, Woods Hole Oceanographic Institution, Woods 
Hole, Massachusetts, USA
                                      
Leif N. Thomas
Department of Environmental Earth System Science, Stanford University, Stanford, 
California, USA
                                                
Frank Bahr
Department of Physical Oceanography, Woods Hole Oceanographic Institution, Woods 
Hole, Massachusetts, USA


Joyce, T. M., L. N. Thomas, and F. Bahr (2009), Wintertime observations of 
Subtropical Mode Water formation within the Gulf Stream, Geophys. Res. Lett., 
36, L02607, doi:10.1029/2008GL035918.

Introduction

This Supplemental Material is associated with a GRL paper 2008GL035918 entitled 
“Wintertime observations of SubTropical Mode Water formation within the Gulf 
Stream” by  Terrence M. Joyce, Leif  N. Thomas, and Frank Bahr. Here we show 
some additional figures dealing with the upstream and downstream structure of 
the Gulf Stream (GS) in the winter of 2007 when the CLIMODE data were collected 
(Figure S1), diagnosing the various terms in the Ertel Potential Vorticity (EPV) 
balance in regions of negative EPV (Fig. S2), and in the structure of the % 
oxygen saturation, fluorescence, potential density, and absolute momentum (Fig. 
S3) for the SeaSoar/ADCP section analyzed in the paper.  

Figure Captions

Figure S1. CTD stations for the Knorr 2007 winter cruise (upper panel) have been 
used to contrast the water mass structure for the CLIMODE study region in early 
February (section 1-1, lower left panel), and late March (section 2-2, lower 
right). In each we show, in stream coordinates, the potential temperature deg. 
C, upper left of each 4-panel group), salinity (psu, upper right), dissolved 
oxygen % saturation ( lower left) and downstream velocity (m/s, lower right) 
with potential density contours in white. The velocity contours (heavy black 
lines) are for 0, 0.5, 1, 1.5, and 2 m/s; a negative contour (dashed) of -0.2 
m/s is also shown. Note that the distance scale is different for the two 
sections. The GS core (xc=0) becomes weaker to the east as fluid detrains from 
either side of the current & re-circulates (violet colors, negative velocities). 
Eighteen Degree Water (EDW, sigmatheta=26.5) is not actively forming yet on the 
first, upstream section–-note that the seasonal thermocline to the south of the 
maximum flow is still covering an older vintage of EDW with only lighter waters 
having the oxygen saturation values typical of recent ventilation. On the final 
downstream section, newly formed EDW is found from xc=30:120 km. The SeaSoar 
section presented in the paper was taken in the Gulf Stream at 54W.

Figure S2. Histograms of regions of negative EPV (<-0.01E-8s-3) for the section 
under analysis. In the upper left, we show the potential density for the regions 
of active mixing, while in the upper right term T1 is given. Obviously, most of 
the negative EPV occurrences are not associated with statically unstable regions 
but require the inclusion of vertical shear (T1+T4, lower left), and lateral 
shear or relative vorticity (T1+T4+T2, lower right). Only a few negative EPV 
occurrences require that the northward Coriolis term (T3) to be included in the 
calculation; it is generally the least important term for the CLIMODE 
observations. By far the most dominant in over 90% of the EPV inversions on this 
section is the vertical shear term, T4.

Figure S3. SeaSoar/ADCP data from the cross-stream section discussed elsewhere 
are re-plotted showing % saturation for oxygen (upper) with regions of negative 
EPV (light contours), potential density contours (cyan lines), and absolute 
momentum Vd+fxc (black contours, Emanuel 1988). Fluorometer data (lower panel) 
are plotted with red lines for negative EPV and thin dashed black lines for 
potential density. Variations in Fluorometer and % oxygen saturation are similar 
here, although one can see that the water with high oxygen content in the upper 
200m at 35 km is nearly as saturated as that at -10 km, yet the latter region 
has higher chlorophyll giving substantially more fluorescence than the former. 
This is related to changes in phytoplankton across the Gulf Stream and not 
directly to wintertime ventilation.