Constraining Physical Gas Exchange Processes and Transient Tracer Saturations in the Arctic Ocean using Noble Gas
Authors: Scott Stanley , Arck Yannis , Engelhardt Edith , Gerke Lennart , Freundt Florian , Hubner Chiara , Negele Sophie , Tanhua Toste , Aeschbach Werner 
Published: March 2024

The formation of sea ice in the Arctic Ocean, as well as other physical
processes such as injection of air and rapid cooling, plays a crucial
role in determining the physical and chemical properties of its waters,
which in turn drive the circulation in the Arctic [1]. Such
processes can be constrained by conservative tracers which are
biologically and chemically nonreactive, such as the noble gases. The
full suite of stable noble gases (He, Ne, Ar, Kr and Xe) have been
measured for the first time in the Arctic Ocean—along with CFC-12,
SF, and other transient tracers—during the
Ventilation and Anthropogenic Carbon in the Arctic Ocean (VACAO) project
of the wider Synoptic Arctic Survey 2021 (SAS21) [2]. The noble gas
profiles indicate a water column strongly influenced by rapid cooling
and excess air injection, with a surface signature characteristic of
solute rejection by sea ice formation.

We have compared multiple Arctic Ocean gas exchange models (based on
similar models used in the Antarctic by Loose et al. [3] and in the
Labrador Sea by Hamme et al. [4]) to constrain the fractions of
Arctic water composed of Pacific, Atlantic and sea ice melt-derived
origin waters, as well as the amount of sea ice being formed and air
being injected into the water via bubbles. These parameters are
estimated using a χ-minimisation
procedure, where the misfit between fitted parameters and data is
minimised. Preliminary results indicate a non-negligible sea ice term in
the equations describing gas saturation anomalies in the Arctic.

Another key goal of VACAO is to use transient tracers to study the
ventilation timescales of the Arctic Ocean, with application towards the
study of the efficacy of its CO solubility
pump/storage. CFC-12/SF is one tracer pair with which
this is attempted; water dating with this pair requires knowledge of the
concentration history of the tracers in the surface water, for which
there are no direct measurements. Thus, the physical gas exchange
parameters modeled from the noble gas data can be used in conjunction
with observed atmospheric histories to more accurately describe the
surface water histories of CFC-12 and SF. This in turn
can be used to better constrain the Transit Time Distribution parameters
used when dating Arctic waters [5]. Comparisons with other VACAO age
tracer data (Ar and
I/U) may act as validation
tools to this “correction” to CFC-12/SF dating.

References for Abstract

[1] Rudels, B., and Carmack, E. 2022. Arctic ocean water mass
structure and circulation. Oceanography, 35(3–4), 52–65 pp.

[2] Snoeijs-Leijonmalm, P. and the SAS-Oden 2021 Scientific Party
(2022). Expedition Report SWEDARCTIC Synoptic Arctic Survey 2021 with
icebreaker Oden. Swedish Polar Research Secretariat. 300 pp.

[3] Loose, B., Stammerjohn, S., Sedwick, P., & Ackley, S. (2023).
Sea ice formation, glacial melt and the solubility pump boundary
conditions in the Ross Sea. Journal of Geophysical Research:
Oceans, 128, e2022JC019322.

[4] Hamme, R. C., Emerson, S. R., Severinghaus, J. P., Long, M. C.,
& Yashayaev, I. (2017). Using noble gas measurements to derive air-sea
process information and predict physical gas saturations.
Geophysical Research Letters, 44, 9901–9909 pp.

[5] Jeansson, E., Tanhua, T., Olsen, A., Smethie, W. M.,
Rajasakaren, B., Ólafsdóttir, S. R., & Ólafsson, J. (2023). Decadal
changes in ventilation and anthropogenic carbon in the Nordic Seas.
Journal of Geophysical Research: Oceans, 128, e2022JC019318.