Download Physical Oceanographic Science Priorities for POLAR POD Sarah

Physical Oceanographic Science Priorities for POLAR POD
Sarah Gille
Matt Mazloff
Scripps Institution of Oceanography
The POLAR POD routing offers a valuable opportunity to obtain year-round, high-frequency
measurements of the upper ocean in a difficult to access location, the Antarctic Circumpolar
Current. This region is a prime place for air-sea interactions, which serve as a major mechanism
for bringing heat and CO2 from the atmosphere into the ocean. Existing measurement systems
include Argo floats, which measure temperature/salinity profiles in the ocean every 10 days, but
do not provide continuous measurements nor do they measure the atmosphere. We also
currently obtain measurements from a number of research vessels and supply ships that operate in
the Southern Ocean (such as the US Antarctic Support Vessel, L. M. Gould), but these
measurements are not continuous throughout the year. POLAR POD will be able to make
measurements continuously for the duration of its mission, which will allow it to measure diurnal
variability in upper ocean processes as well as seasonal variability.
Here is a summary of research priorities:
(1) At a minimum, POLAR POD should obtain upper ocean temperature and salinity
measurements using a thermosalinograph system and basic meteorological measurements
of air temperature, humidity, wind speed and direction, precipitation, and downward
shortwave and longwave radiation. These measurements together are sufficient to
estimate air-sea exchanges of momentum, heat, fresh water, and gases using so-called bulk
formulae parameterizations.
(2) It would be useful to obtain more detailed observations of the upper ocean. Upper ocean
currents can be measured automatically using a vessel-mounted (shipboard) Acoustic
Doppler Current Profiler (ADCP), which can provide estimates of ocean currents over the
top 1000 m of the ocean. Such a system would make it possible to characterize the velocity
structure of the upper ocean and to evaluate the ocean response to time-varying surface
properties.
(3) Upper ocean temperature and salinity profiles would also be useful measurements, and
these could be obtained using a conductivity-temperature-depth (CTD) instrument which
could be tow-yowed with a winch from the deck of the vessel, or from a fast-fish underway
CTD designed to be dropped down and reeled in while the vessel was in motion. These
might also be possible using an array of thermistors and conductivity sensors mounted
directly on the vessel, though anti-biofouling strategies would be essential to keep them
working reliably for the duration of the campaign. These measurements would allow
investigators to explore the upper ocean variability on time-scales ranging from hours to
months.
With additional funding, further research might be feasible, though expanded sampling programs
would perhaps require significant support from research funding agencies, which might not be
possible until the POLAR POD had established a proven track record as a research platform.
(4) Because the POLAR POD is to be occupied all of the time and because it is intended to be
stable, it would be an excellent platform from which to observe turbulent air-sea fluxes.
Thus automated turbulent flux sensors would be an excellent complement to the standard
meteorological sensors. These would allow direct determination of air-sea fluxes and
would provide means to validate bulk parameterizations, particularly in high-wind
conditions that prevail in the Southern Ocean.
(5) There is quite a bit of interest in understanding the full atmosphere response to Southern
Ocean sea surface temperature anomalies. Satellite data have provided some interesting
results suggesting that the atmosphere responds strongly to oceanic temperature
anomalies, but there remain lingering questions about the robustness of the satellite
observations. Radiosonde observations would offer a means to verify the full atmosphere
structure in the Southern Ocean. Radiosonde launching systems are fairly bulky (about the
size of a shipping container), and require a supply of helium as well as dedicated staff. Data
have the important advantage that they can be fed into the global data transmission system
(the GTS), meaning that they could have an impact on weather forecasts throughout the
region.
(6)The stability of the POLAR POD also potentially makes it a valuable platform for measuring
ocean turbulence using continuously-operated tethered instruments. Such instrumentation
would allow a firm estimate of background mixing rates, and would also allow investigators
to explore the impact of individual wind events on transmitting energy into the deep
ocean.