HR: 15:10h
AN: OS12B-06    [PDF]
TI: The Hydrologic Cycle, Ocean Mixing and Abrupt Climate Change: What do we Need to Measure?
AU: * Schmitt, R W
EM: rschmitt@whoi.edu
AF: Woods Hole Oceanographic Institution, Dept. Physical Oceanography, MS 21, Woods Hole, MA 02543 United States
AB: The hydrologic cycle occurs mostly over the oceans, yet research programs purporting to address the global water cycle focus largely on the much smaller terrestrial water cycle. (E.g.: a mere one percent of Atlantic Ocean rainfall would double the discharge of the Mississippi river.) This is understandable in the context of societal concern for freshwater supplies, but there is now strong evidence that significant changes are underway in the oceanic water cycle that may have dramatic effects on climate. Specifically, evidence from paleoclimatic data indicates that high latitude freshening caused abrupt circulation and climate changes in the past, and model results suggest that the ongoing freshening of the Northern Atlantic could lead to regional cooling in the future. However, the threshold for abrupt change in the oceanic thermohaline circulation is crucially dependent on the relationship between the intensity of hydrologic forcing and the rate of interior ocean mixing. As both these variables are poorly known, concerted efforts to understand the oceanic hydrologic cycle and mixing processes are required. One approach to both tasks must be a better assessment of the variations in oceanic salinity. The upper ocean salt content reflects the history of air-sea water exchange and is thereby an integral measure of the difference between evaporation and precipitation. The salinity distribution also controls the density stratification at high latitudes and thus has large impacts on mixing rates, air-sea exchange and sea-ice formation. However, aside from a handful of time-series sites and diminishing numbers of research cruises, the database for salinity is sparse. An expanded program of systematic salinity measurements is called for, to provide the data necessary to discern variability in the global water cycle, and to assess the impact on oceanic mixing and dynamics. The salinity sensing capabilities of profiling floats along with developing technology for long-lived sensors for surface drifters can contribute to the formation of a robust in-situ salinity-monitoring network. Long-term maintenance of such a network is required to assess the salinity variations of consequence for climate and will also be an important ground-truth-provider during the period of the Aquarius satellite mission.
DE: 1836 Hydrologic budget (1655)
DE: 4203 Analytical modeling
DE: 4504 Air/sea interactions (0312)
DE: 4568 Turbulence, diffusion, and mixing processes
DE: 4594 Instruments and techniques
SC: Ocean Sciences [OS]
MN: 2003 Fall Meeting