Mr. Tom's Blog

T/S orientering...

In many ways my life in oceanography began in Bermuda. It was here, in January 1966, that I first met Doug Webb. This became the start of our journey to develop the SOFAR float to explore and map ocean currents. But that isn’t the reason I’m writing this. Instead, in becoming a frequent guest at the Bermuda Biological Station, I soon became aware of the time series of bi-weekly hydrographic casts, by then 10 years old and running (and thankfully still running today). My knowledge of oceanography at that time was limited; I knew little about hydrography and water mass analysis.

It was there that I became aware of the extraordinary Mediterranean Salt Tongue that spreads across the North Atlantic. And of the enormous pool of warm 18°C water that stretched from the Gulf Stream south to and beyond Bermuda. I became aware of the striking seasonal cycle of surface warming and cooling, and salinity changes due to evaporation and precipitation. After graduation when I started to have an income I bought the Sverdrup et al. (1942) book ‘The Oceans’. In it you’ll see schematic T/S diagrams for all ocean basins. You’ll learn that the Atlantic is saltier than the Pacific, that the deep waters are cold and fresher just about everywhere. Indeed, in those early years of our science oceanographers were busy mapping out the basic properties of water. Remember those beautiful composite plots of temperature, salinity and oxygen from the Antarctic to the Nordic Seas prepared by Georg Wüst? They showed the south-to-north spread of Antarctic Bottom Water and Antarctic Intermediate Water, and north to south spread of North Atlantic Deep Water. Not to mention how the deep thermoclines at mid-latitudes shoal close to the surface at the equator. Figures can be worth a thousand words!

When I began teaching Introductory Physical Oceanography at Yale, one of the quiz questions I might give the students was a set of T/S-diagrams asking them to identify what water in the world ocean they represent. Asking them to bone up on basic hydrography was a way of building up their intuition about the oceans. With very few exceptions all water properties are set at the surface. Hydrography was the key tool we had for understanding how stuff moves about in the ocean. That was certainly true then and remains true today. Water mass analysis will continue to be a fundamental tool in our studies of ocean circulation.