Geothermal Heating in the Panama Basin: 1. Hydrography of the Basin

Abstract

The Panama Basin serves as a laboratory to investigate abyssal water upwelling. The basin has only a single abyssal water inflow pathway through the narrow Ecuador Trench. The estimated critical inflow through the Trench reaches 0.34 ± 0.07 m/s, resulting in an abyssal water volume inflow of 0.29 ± 0.07 Sv. The same trench carries the return flow of basin waters that starts just 200 m above the bottom and is approximately 400-m deeper than the depth of the next possible deep water exchange pathway at the Carnegie Ridge Saddle. The curvature of temperature-salinity diagrams is used to differentiate the effect of geothermal heating on the deep Panama Basin waters that was found to reach as high as 2,200-m depth, which is about 500 m above the upper boundary of the abyssal water layer.Believing that the deep Panama Basin waters can only escape from the basin through the shallow and broad Carnegie Ridge Saddle located at 86 ∘ W and 2,300-m depth, Detrick et al. (1974) compared the heat advected out of the basin with the total geothermal heat gain estimate. They raised the hypothesis of geothermal heating being the driver for abyssal overturning. However, current meter measurements showed no significant outflow at the Carnegie Ridge Saddle (Lonsdale, 1977). On the contrary, sediment ripple marks downstream of this passage indicated that deep waters could inflow into the basin, at least occasionally. However, the inflow Key Points: • The single abyssal water source for the Panama Basin is the flow through the Ecuador Trench • Critical flow theory suggests an abyssal water inflow of 0.29 ± 0.07 Sv • The effect of geothermal heating can reach as high as 2,200-m depth or 500 m above the abyssal water layerA 75-kHz upward looking acoustic Doppler current profiler (ADCP) was moored on the crest of the sill of the Ecuador Trench for 24 hr at a depth of 2,921 m. Another 75-kHz ADCP was moored on the central saddle of Carnegie Ridge for about 2 months at a depth of 2,300 m (Figure 1).

Geothermal Heating in the Panama Basin. Part II: Abyssal Water Mass Transformation

“…By contrast, in the Panama Basin, the wsBBL is hundreds to over a thousand meters thick at some places. Similarly, thick wsBBLs have been identified by Banyte, Morales Maqueda, et al () in the global ocean. We argue that oceanic basins have the bottom surfaces, which allow thick incrops to form.…”

“…The density and pressure, γ w s B B L and P w s B B L , at the upper boundary of the weakly stratified bottom waters are highly correlated with one another (top right panel of Figure ) and vary smoothly in space. This is a common property of abyssal waters observed over most of the global ocean basins (Banyte, Morales Maqueda, et al, ). Consequently, we use γ w s B B L to map bottom density and the linear relation between γ w s B B L and P w s B B L to outline shallow bathymetry (Figure ) with details given in Appendix .…”

“…However, the precision of CTD sensors is much greater than their accuracy, which allows us to accurately evaluate density gradients as small as 10 −5 kg/m 4 when defining the upper boundary of the wsBBL. The use of density gradient criteria to identify the wsBBL is discussed further in Banyte, Morales Maqueda, et al ().…”

Does intermediate spreading-rate oceanic crust result from episodic transition between magmatic and magma-dominated, faulting-enhanced spreading?—The Costa Rica Rift example

“…Each OBS was relocated to its actual position on the seabed by matching the observed travel times of the direct water wave arrival (P w ), with travel times calculated by forward ray-tracing using rayinvr (Zelt & Smith, 1992). The along-profile seabed depth was constructed using ship-acquired swath bathymetry data, and a water column model was constructed using the average sound velocity profile calculated from temperature and salinity measurements made during eight conductivity-temperature-depth (CTD) casts (Banyte et al, 2018). This water column model was used in, and remained fixed for, all subsequent sub-seabed modelling.…”

Application of a seismic network to baleen whale call detection and localization in the Panama basin–a Bryde's whale example

“…3. Sound velocity profile in the water column calculated by averaging CTD measurements obtained in the vicinity of the CRR (Banyte et al, 2018a(Banyte et al, , 2018b. This 1D profile was used to construct the 3D localization velocity model.…”