DOGEE-SOLAS and SEASAW: high wind, gas and aerosol fluxes in the North East Atlantic Ocean

RRS Discovery cruise D313 involved two distinct but inter-related UK SOLAS projects: DOGEE-SOLAS (The UK SOLAS Deep Ocean Gas Exchange Experiment), P.I. Rob Upstill-Goddard, University of Newcastle upon Tyne, and SEASAW (Sea Spray and Whitecaps), P.I. Ian Brooks, University of Leeds. Both projects were primarily concerned with physical exchange processes at the air-sea interface and the determination of gas transfer velocities.

Additionally, SEASAW aimed to quantify sea-salt aerosol source functions. The two projects thus had a common overall research goal - to parameterize air-sea gas and aerosol exchange processes, which is essential for effectively modelling climate. Current gas exchange parameterizations have uncertainties of at least a factor of 2 at intermediate wind speeds, and much larger uncertainties at high wind speeds. For aerosols, these uncertainties approach an order of magnitude. Significantly reducing them was a central goal of both the international and UK SOLAS programmes.

DOGEE:
-To make several estimates of the open ocean gas transfer velocity (kw) of CO2 at high wind speeds by means of a dual-tracer release (3He SF6) with subsequent sampling underway and via the CTD rosette system.
-To measure total gas tension, dissolved O2, and CO2 in underway mode using the ship's non toxic seawater supply, and throughout the mixed layer using drifting mixed layer Lagrangian Floats, and to thus obtain independent estimates of air-sea gas exchange.
-To routinely record 5 to 10 second means of key meteorological variables (wind speed and direction, air temperature and humidity, sea surface temperature, IR surface temperature, downwelling long- and short-wave radiation and air pressure).
-To measure directly air-sea fluxes of CO2, sensible heat, latent heat and momentum (by direct eddy covariance (EC) and inertial dissipation) using AUTOFLUX, an automated sensor array developed at NOC.
AUTOFLUX also routinely measures air-sea fluxes of CO2, sensible heat, latent heat and momentum. All four turbulent fluxes are measured by EC. The latter two are also obtained using the inertial dissipation (ID) method. The fluxes are derived using a sonic anemometer (momentum and heat) and a Licor-7500 (H2O and CO2), using sampling intervals of up to 55 minutes.
-To quantify flow distortion biases in the direct flux measurements through comparison of eddy correlation latent heat fluxes to the inertial dissipation latent heat fluxes after the latter have been corrected using Computational Fluid Dynamics, and to correct other direct fluxes by analogy.

SEASAW:
-To establish the impact of various forcing parameters on the kw values of CO2 and O3 and thus improve their parameterisation, and relate these kw values to those of other trace gases via the Schmidt number.
-To determine the sea spray source function via direct eddy-covariance methods using ultrasonic anemometers alongside fast-response optical particle counters and condensation particle counters.
-To investigate the production and fate of sea spray aerosol particles very close to the ocean surface by means of 10Hz optical particle counter observations with sub-surface bubble observations.
-To utilise a single particle aerosol mass spectrometer and associated instruments to study the composition of individual aerosol particles as a means of source apportionment and to investigate interactions between the sea spray aerosol and other aerosol and gaseous components.