9 Years of WAP (1993-2001) LTER Physical Oceanography: Water Mass Distributions

Douglas G. Martinson

Lamont-Doherty Earth Observatory of Columbia University

Palisades, NY, 10964

(dgm@ldeo.columbia.edu)

This presentation presents the results of a water mass analysis of the 1993-2001 Palmer LTER hydrography data base. The analysis is intended to provide a longer term and broader scale context for the recent S.O. GLOBEC surveys. The water mass distributions show the following: (1) the WAP region is characterized by typical circumpolar water masses, though their signature in T-S space is slightly different on the slope (sharp V shape) relative to that on the shelf (U-shape); (2) the rapid erosion of the winter water (WW) by mixing, but the sharp regularity (defining the V shape) of the WW in T-S plots indicates that the ACC waters regularly sweep the continental slope and episodically floods the shelf, replacing modified shelf and coastal waters with typical circumpolar waters, while flushing the modified waters back into the circumpolar current; (3) freshening of the shelf waters from summer sea ice melt sets the surface water conditions for the following winter; (4) the ACC water sweeping the slope and shelf seems most consistent historically with waters flowing in from approximately 66-70˚ S (80-100˚ W); (5) despite considerable interannual variability in the vertical placement of the key water masses, they show sub-regional consistency in T-S space over the years; (6) the seasonal evolution of the water column is evident through the quick seasonal evolution of the water mass properties, even as deep as in the CDW, suggesting strong vertical (and perhaps lateral) mixing, e.g., the WW warms and salinates quickly through winter along, and the entire slope of the permanent pycnocline waters in T-S space changes to accommodate this warming. This change in permanent pycnocline slope indicates how deep and intense the vertical mixing is — a volumetric heat and salt budget suggests that the differences can be achieved by vertical mixing with strong mixing coefficients as one might expect over the slope and shelf regions (consistent with Smith and Klinck, DSR, 2002).