BAMOS
Dec 2018
Christina McCluskey and Jay Mace (University of Utah) on deck on the RV Investigator. Image: Grace Salgado
One of the goals of CAPRICORN was to provide the first
observations of INP composition and abundance over the
Southern Ocean in over four decades.
INP number concentrations (nINPs), aerosol composition, size
and number were measured in the boundary layer during
CAPRICORN. The results showed that nINPs were extremely low,
in fact two orders of magnitude lower than historical surveys.
The ocean-derived INPs observed in this study were organic in
nature, supporting a hypothesised link between ice nucleating
particles and organic particles associated with phytoplankton
blooms. Water samples were collected in collaboration with the
oceanography teams, revealing that the INP source potential
of Southern Ocean waters was lower compared to Northern
Hemisphere ocean waters. The data from this study provide a
desperately needed benchmark for constraining the number of
ice crystals that may form from heterogeneous ice nucleation
in the remote and poorly understood clouds occurring over the
Southern Ocean. Additional measurements were recently made
during a 2018 RV Investigator voyage that extend the nINP
survey closer to the ice edge. These observations have since
been used to demonstrate the ability to numerically represent
oceanic INPs and thus have enabled modelling studies to
determine the role of INPs in Southern Ocean clouds.
In addition to improving our understanding of aerosol-cloud
interactions, the combination of research groups on the ship led
to the development of new research ideas. The eddy group spent
almost a week each mapping the physics and biogeochemistry
of two contrasting mesoscale eddies, one cyclonic and one
anti-cyclonic. These eddies are of the order of 200km across
and, by virtue of their rotation, have either cool or warm sea
surface temperature anomalies as well as perturbations in
nutrient levels and productivity. The atmospheric observations
from the CAPRICORN group showed obvious impacts from the
ocean surface anomalies and this is something that will be
explored in more detail using large scale satellite observations
of eddy location, polarity and magnitude paired with satellite-
derived atmospheric composition. The Southern Ocean Time
Series mooring data also provide an important data set for air-
sea fluxes related to cloud formation, and validation data for
shortwave radiation. The combination of these three research
projects on RV Investigator was an efficient use of the Marine
National Facility and initiated previously unexpected research
directions.
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