Causes and effects of composition changes in the ocean

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Physical oceanographers consider "salinity", a measure of salt content (notionally composed of all seawater constituents with concentrations greater than about 0.001 g/kg), to be conservative - that is, modified only by advective transport, by mixing, and by the addition/removal of pure water at boundaries through evaporation, precipitation, and river inflows. However, these major constituents are not completely conservative, and they undergo a variety of processes in the ocean that result in small changes to the relative chemical composition of sea salt. Chemical oceanographers are well aware of the non-conservative nature of many of these major constituents, but although knowledge about virtually every element in seawater has increased dramatically over the past 50 years, studies of the spatial and temporal variations in the relative amounts of many non-conservative major constituents have been almost completely neglected since the 1960s. Thus, a knowledge gap exists.***Scientifically, studying such neglected composition variations, and the physical/chemical mechanisms that give rise to them, may therefore prove to be an exciting area of fundamental interest to global ocean circulation studies. This is because such mechanisms would have traceable consequences that may help oceanographers identify critical transport pathways in the ocean (analogous to the way in which carbon/nutrient changes from remineralization of organic matter track the global thermohaline conveyor). ***In addition, knowledge of these variations will also improve direct calculations of transport because more accurate knowledge of the density field will be possible. The development of the new TEOS-10 seawater standard has highlighted the fact that the errors in actual salinity estimates, and therefore also in derived parameters like density, which are incurred by ignoring these non-conservative variations, are one to two orders of magnitude larger than the precision with which we currently "measure" salinity. This is one of the two major problems with our current oceanographic definition of salinity when applied to climate science issues (the other is related to metrological aspects of the definition).*****The objectives of this proposed work are therefore to gain a better quantitative understanding of changes in the major constituent composition of the ocean, primarily by measuring the so-called "salinity anomaly" in different regions through combined conductance/density sampling, and to investigate in detail some of the mechanisms that may give rise to these anomalies, concentrating on double- and multi-diffusive processes that may be important in regions like the Arctic.**************