Evolution of the large‐scale temperature field in the Greenland Sea during 1988–89 from tomographic measurements

Abstract

Moored thermistor, hydrographic, and tomographic measurements have been combined using least‐squares inverse methods to study the evolution of the 40 km and larger three‐dimensional temperature field in the Greenland Sea during winter 1988–89. In February, the sub‐surface temperature maximum at around 200‐m depth disappears over a large area. Upper waters warm around this time, while intermediate waters cool, consistent with vertical mixing. A chimney structure reaching depths in excess of 1000 m is observed to the southwest of the gyre center during March. The chimney has a spatial scale of about 50 km, a time scale of about 10 days, and breaks up in about 3–6 days. A one‐dimensional vertical heat balance adequately describes changes in total heat content in the chimney region from autumn 1988 until the time of chimney break‐up. A simple one‐dimensional mixed layer model is successful in reproducing fall to winter bulk temperature and salinity changes, as well as the observed evolution of the mixed layer. The estimated annual deep water production rate in the Greenland Sea for 1988–89 is about 0.1 Sverdrups, comparable to the decreased production rates since 1983 derived from tracer measurements. [Work supported by NSF and ONR.]