Abstract. The influence of mesoscale eddies on the flow field and the water masses, especially the
oxygen distribution of the eastern tropical South Pacific, is investigated
from a mooring, float, and satellite data set. Two anticyclonic (ACE1/2), one
mode-water (MWE), and one cyclonic eddy (CE) are identified and followed in
detail with satellite data on their westward transition with velocities of
3.2 to 6.0 cm s−1 from their generation
region, the shelf of the Peruvian and Chilean upwelling regime, across the
Stratus Ocean Reference Station (ORS; ∼20∘ S, 85∘ W)
to their decaying region far west in the oligotrophic open ocean. The ORS is
located in the transition zone between the oxygen minimum zone and the well
oxygenated South Pacific subtropical gyre. Velocity, hydrographic, and oxygen
measurements at the mooring show the impact of eddies on the weak flow region
of the eastern tropical South Pacific. Strong anomalies are related to the
passage of eddies and are not associated with a seasonal signal in the open
ocean. The mass transport of the four observed eddies across 85∘ W
is between 1.1 and 1.8 Sv. The eddy type-dependent available heat, salt, and
oxygen anomalies are 8.1×1018 J (ACE2), 1.0×1018 J
(MWE), and -8.9×1018 J (CE) for heat; 25.2×1010 kg
(ACE2), -3.1×1010 kg (MWE), and -41.5×1010 kg (CE) for
salt; and -3.6×1016 µmol (ACE2),
-3.5×1016 µmol (MWE), and
-6.5×1016 µmol (CE) for oxygen showing a strong imbalance
between anticyclones and cyclones for salt transports probably due to
seasonal variability in water mass properties in the formation region of the
eddies. Heat, salt, and oxygen fluxes out of the coastal region across the
ORS region in the oligotrophic open South Pacific are estimated based on
these eddy anomalies and on eddy statistics (gained out of 23 years of
satellite data). Furthermore, four profiling floats were trapped in the ACE2
during its westward propagation between the formation region and the open
ocean, which allows for conclusions on lateral mixing of water mass
properties with time between the core of the eddy and the surrounding water.
The strongest lateral mixing was found between the seasonal thermocline and
the eddy core during the first half of the eddy lifetime.
Impact of mesoscale eddies on water mass and oxygen distribution in the eastern tropical South Pacific
