Relationship Between Sea Level and Bottom Pressure on Climate Scales—Implications for Assessing Heat Content and Deep Variability

Type: Poster presentation

Venue: AGU Fall Meeting 2012


Christopher G. Piecuch; Katherine J. Quinn; Rui M. Ponte (2012) Relationship Between Sea Level and Bottom Pressure on Climate Scales—Implications for Assessing Heat Content and Deep Variability. AGU Fall Meeting, San Francisco, CA.

Understanding the relation between sea level (SL) and bottom pressure (BP) is important for a number of topics relating to ocean circulation and climate, and in particular for diagnosing steric height changes and ocean heat storage. Previous modeling work suggests that, in open ocean regions on interannual time scales, BP variations are small relative to SL changes and the two quantities are not significantly correlated. Yet observational knowledge of BP variations and their relation to changes in SL over such long time scales is lacking. To investigate the relationship between SL and BP on climate scales, we considered interannual time series from satellite observations and a general circulation model ranging over 2005-2010 and smoothed over scales of 750 km. In many extratropical regions, both model and data depict BP changes that are strongly related to SL variations in terms of both phase and magnitude. Broad areas are evident at middle latitudes in all basins wherein BP changes explain a majority of the SL variance. These results contradict the notion that oceanic variability is mostly baroclinic at interannual periods, regardless of location or spatial scale.
Given the implications for interpretation and application of satellite data, we used model output to gauge how well interannual changes in heat content (HC) can be inferred indirectly from other fields. Given BP, SL, and sea surface temperature fields, good estimates of full-column HC variations can be made at low and middle latitudes. At middle latitudes in particular, knowledge of BP makes for much more skillful HC estimates. This implies that overall regional climate variability in some places can be usefully constrained on the basis of satellite data alone. Knowledge of BP is also useful in estimating deep-ocean HC changes when upper-ocean temperature and salinity fields (e.g., from Argo floats) are available. Difficulties can, however, arise from lack of information on deep ocean stratification and salinity changes. Results provide insight into whether deep ocean climate variability can be inferred indirectly based on current monitoring systems, or whether good estimates of deep variability will have to await routine sampling of the deep ocean.