Abstract
Abstract Pore fluid chlorinity/salinity data from deep-sea cores related to the salinity maximum of the last glacial maximum (LGM) are analyzed using estimation methods deriving from linear control theory. With conventional diffusion coefficient values and no vertical advection, results show a very strong dependence upon initial conditions at −100 ky. Earlier inferences that the abyssal Southern Ocean was strongly salt-stratified in the LGM with a relatively fresh North Atlantic Ocean are found to be consistent within uncertainties of the salinity determination, which remain of order ±1 g/kg. However, an LGM Southern Ocean abyss with an important relative excess of salt is an assumption, one not required by existing core data. None of the present results show statistically significant abyssal salinity values above the global average, and results remain consistent, apart from a general increase owing to diminished sea level, with a more conventional salinity distribution having deep values lower than the global mean. The Southern Ocean core does show a higher salinity than the North Atlantic one on the Bermuda Rise at different water depths. Although much more sophisticated models of the pore-fluid salinity can be used, they will only increase the resulting uncertainties, unless considerably more data can be obtained. Results are consistent with complex regional variations in abyssal salinity during deglaciation, but none are statistically significant.
Highlights
McDuff (1985) pointed out that pore-waters in deep-sea cores have a maximum chlorinity at about 30m depth owing to the sea level reduction during the last glacial period
In the last 20 ky does any structure appear, and it remains below the estimated last glacial maximum (LGM) mean
Approach used here, initial condition structures in a purely diffusive 100 m core can persist for more than 100 ky, greatly complicating the inference that the terminal data are controlled by the sea level changes of the past 20 ky alone
Summary
McDuff (1985) pointed out that pore-waters in deep-sea cores have a maximum chlorinity (salinity) at about 30m depth owing to the sea level reduction during the last glacial period. ( ) = 1 0 ≤ ≤ and zero initial condition, with result shown in Fig. 7 and the terminal state compared to the analytic solution. Using the Filter-Smoother consistency can be found within varying estimated errors between the model and the measured terminal state Those solutions, which minimize the square difference from a priori ( ) are not unique, and as in least-squares generally, an infinite number of solutions can exist, albeit with all others having a larger mean-square. Those data change x ( − ∆ ) and its uncertainty, leading to a change in its immediate predecessor, x ( − 2∆ ) etc., commonly with a loss of amplitude the further the estimate recedes in time from the terminal data
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