Temperature and conductivity measurements under Ice Island T-3

Abstract

Marked step‐like structure exists in vertical profiles of temperature and salinity obtained in the Arctic Ocean. This structure occurs between 200 and 500 meters depth, where both temperature and salinity increase with depth. Nominally, the structure consists of thin sheets (0.1 meter thick) separating adjacent homogeneous layers (3 meters thick) that differ in temperature by 0.02°C and in salinity by 0.01‰. While the step structure is quite persistent, its character varies markedly with depth. Intermediate layers have been observed, as well as noncoincident temperature and salinity gradient sheets. Analysis of the data lends support to the hypothesis that this type of layering arises from the double‐diffusive process.

The diffusive regime of double-diffusive convection

“…High-resolution sampling with towed thermistor chains (Marmorino, 1989(Marmorino, , 1991 reveals that the lateral features have lengthscales of k m. Similarly, Padman and Dillon (1988) found that station spacings of less than k m were required to track individual layers in a DL staircase in the Canadian Basin of the Arctic. This is in line with the observations of Neshyba et al (1971), an excerpt of whose observations is presented as Figure 8 here. Note in particular the occurrence of "split" layers in this diagram, whose variation in this graphical representation is probably the result of advection of horizontal variability, as opposed to temporal development (Kelley, 1987b).…”

“…This is reminiscent of the Melling et al (1984) observation that tides are very weak in the Canadian Basin of the Arctic, where DL signatures are prominent. Indeed, Arctic sampling has provided many illustrations of layering in the ocean (Neal et al, 1969;Neshyba et al, 1971;Padman andDillon, 1987, 1989;Rudels et al, 1999). As is the case for the Antarctic, Arctic staircase fluxes appear to be weak compared with mixing rates expected in the open ocean.…”

Acoustic Detection of Oceanic Double-Diffusive Convection: A Feasibility Study

“…This work was inspired by the acoustic observations of diffusive-convection interfaces migrating and merging in the laboratory (Ross and Lavery 2009), which resemble field data such as those in Neshyba et al (1971), which in turn may be showing interface heaving and splitting in the Arctic. If acoustic observation of diffusiveconvection interfaces in the field is possible, acoustic techniques will provide a tool for ''filling the gaps'' between sparse conductivity-temperature-depth (CTD) profiles and provide improved and continuous heat-flux estimates, perhaps leading to a better understanding of the underlying physics.…”

Estimation of Ice Shelf Melt Rate in the Presence of a Thermohaline Staircase

“…Diffusive convection is prevalent at high latitudes where the logistics of sampling is demanding. However, diffusive convectionfavorable thermohaline staircases have been observed both in the Arctic Ocean (e.g., Neal et al 1969;Neshyba et al 1971;Padman and Dillon 1987;Polyakov et al 2012) and in the Weddell Sea in Antarctica (e.g., Foster and Carmack 1976;Muench et al 1990;Robertson et al 1995). Diffusive convection leads to a set of growing oscillations at the interface between cool, fresh, and warm, salty water (e.g., Turner and Stommel 1964;Marmorino and Caldwell 1976;McDougall 1981;Linden and Shirtcliffe 1978;Fernando 1987).…”