Ivan Perez - Academia.edu (original) (raw)

Papers by Ivan Perez

The Cuban Countercurrent (CCC), along with the Yucatan Current, forms part of the Yucatan Basin c... more The Cuban Countercurrent (CCC), along with the Yucatan Current, forms part of the Yucatan Basin circulation system, but it has
not been well described and its connection to the system of currents in the Caribbean Sea has not been studied. Based on altimetry data
(1993–2009) and the MERCATOR three-dimensional assimilation model (2007–2009), the CCC was observed flowing ~1000 km from the
eastern Yucatan Channel to Jamaica and to have a width of ~150 km. Off southern Cuba, the mean velocity was 0.20 m s–1 at the surface and
0.05 m s–1 at 1000 m depth. The CCC transported ~3.5 Sv when it passed through the Yucatan Channel towards the Caribbean Sea, where
~1.6 Sv was recorded south of Cuba. During its annual cycle, the CCC weakened from December to February (0–250 m) and in the summer its
magnitude intensified slightly, reaching 0.35 m s–1 in August, due to the increase in water temperature of the Atlantic warm pool. Consequently,
the sea level rose in the center of the Yucatan Basin and the pressure gradient increased along the Cuban coast, producing an increase in zonal
velocity (0.1 m s–1) and transport (2–3 Sv; r = 0.90). Its connection to the Caribbean current system demonstrated the importance of its study.

Double-diffusive convection (DDC) has been detected in the Martinez and Baker channels of central... more Double-diffusive convection (DDC) has been detected in the Martinez and Baker channels of
central Patagonia (Chile) by employing a Self Contained Autonomous Micro-Profiler (SCAMP). This profiler
measures temperature and salinity in the water column with a vertical resolution on the millimetre scale. The
expedition took place in December 2011 and included 19 vertical high-resolution profiles from surface to ∼55
m depth. The formation of thermohaline staircase patterns, resulting from the DDC process, could be
documented by the micro-profiler’s measurements. DDC events, below the shallow but strongly stratified
surface layer (7-10 m), were confirmed to occur in intermediate depths between 15 and 45 m by means of the
Turner angle. Most of these events were usually weak but several strong ones could also be detected between
15 and 40 m. DDC is initiated at the interface between sub-surface waters of estuarine origin (cold and less
salty) and intermediate waters of oceanic origin (warmer and saltier), with upward heat and salt fluxes. DDC
together with mixing caused by winds, tides, and internal waves, constitute an important mechanism for
mixing the water column with implications for small organisms therein.

Daily images collected with the MODIS sensor on the NASA Aqua satellite were used to describe chl... more Daily images collected with the MODIS sensor on the NASA Aqua satellite were used to describe chlorophyll-a (chl-a)
concentrations before, during, and after synoptic-scale meteorological pulses in the Yucatan Basin, Caribbean Sea. The relative influence of
vertical diffusive and vertical advective transport on mixing of the near surface layer was quantified with wind data from the QuikSCAT
satellite. Computation of vertical density eddy diffusivity and gradient Richardson numbers was done with data from the three-dimensional
MERCATOR model. The model evidenced the importance of vertical shear (i.e., vertical diffusive processes) in generating mixing during
autumn and winter (2007–2009). During moderate meteorological pulses (e.g., cold fronts, easterly tropical waves, and low-pressure systems
with wind speeds of 9–15 m s–1 sustained over 2 days), mixing caused by diffusive transport (eddy viscosity of 10  10–3 m2 s–1) was at least
one order of magnitude higher than upward advective mixing (0.3  10–3 m2 s–1). During the passage of hurricanes Ivan (September 2004) and
Wilma (October 2005), upward advective mixing (5–7 m2 s–1) dominated mixing of the upper water column and was nearly four orders of
magnitude higher than during moderate meteorological events. Background chl-a concentrations of 0.03–0.08 mg m–3 were observed during
the July–October period. During synoptic weather pulses, three different patterns in the chl-a concentrations were observed: first, chl-a
concentrations in the range of 0.05 to 0.12 mg m–3 followed moderate meteorological pulses; second, higher regional chl-a concentrations
(0.5–2.0 mg m–3) followed the passage of hurricanes; and third, the formation of filaments showing apparent high chl-a (0.3–1.5 mg m–3) south
of Cuba, possibly caused by freshwater discharge from land. The changes in chlorophyll patterns following meteorological events illustrate
typical patterns of connectivity among different parts of the Yucatan Basin.

Sea surface wind data from the QuikSCAT satellite and two meteorological stations collected over ... more Sea surface wind data from the QuikSCAT satellite and two meteorological stations
collected over 1 decade (1999–2008) were used to study the dominant time scales of
the wind regime in the Yucatan basin. Wind data were used to quantify its implications
on regional hydrodynamics by evaluating Ekman pumping and Ekman transport. The
annual cycle of surface wind revealed different features than the Caribbean wind regime
with a relative wind stress maximum observed in the Yucatan basin in June caused by
the Caribbean low‐level jet. The strongest wind stress occurred during November
presumably due to the collapse of the Atlantic warm pool. This feature provides new
evidence of the importance of local atmosphere‐ocean coupling. Synoptic scale variability
was detected during fall and winter, leaving spring and summer almost free from
these activities. Empirical orthogonal functions revealed three dominant time scales of
variability: an annual scale in mode 1 (46.3% of the total variance), a synoptic scale
in mode 2 (27.7%), and a semiannual scale in mode 3 (6.4%). The third mode featured
extreme pulses (six tropical storms and nine hurricanes). Ekman transport was found
to contribute the most (93%) to total transport, whereas Ekman pumping contributed
only 7%. However, upwelling induced by Ekman pumping persisted during some synoptic
pulses, underscoring the importance of tropical storms and hurricanes. Offshore Ekman
transport over the continental shelf north of the Yucatan Peninsula favored upwelling
all year long. Onshore transport toward the coasts of southern Cuba and the eastern
Yucatan Peninsula favored downwelling.

The fjords of central Chilean Patagonia (47S) receive fresh water from both precipitation and th... more The fjords of central Chilean Patagonia (47S) receive fresh water from both precipitation and the Baker
River. This buoyancy input generates a two layer hydrographic system characterized by strong salinity
stratification (30 g kg1 over a depth range of 7–15 m), which favors baroclinic conditions in the fjord.
Hourly current velocity profiles were collected with an acoustic Doppler current profiler (ADCP) moored
at a depth of 40 m during March–April 2009, and complemented by 11 CTD profiles and hourly sea level
time series. These data allowed the detection of semidiurnal internal tidal waves for the first time in this
region. Wavelength and horizontal phase speeds were determined by the dynamical mode 1 for internal
waves. Maximum wavelength was 52 km, travelling at a horizontal phase speed of 1.16 m s1.Wavelet,
spectral and empirical orthogonal function (EOF) analysis techniques applied to the echo anomaly signal
and to the baroclinic velocity showed largest semidiurnal amplitudes near the pycnocline. Out of three
modes obtained from the EOF analysis, two modes displayed a two- or three-layer flow structure with
flow direction reversing at the pycnocline. The semidiurnal internal waves were found as fluctuations
near the pycnocline in sporadic packets correlated to high discharge pulses of the Baker River
(r2 = 0.77). Additionally, internal Froude number calculations at the mouth of the Baker River indicated
critical flow conditions, which allowed for generation of internal waves at the plume front. These waves
are separated from the river plume after internal wave phase speeds surpassed frontal speeds. This suggests
that the internal waves were modulated by pulses in high river discharge rather than the interaction
of barotropic tide with bathymetry (a sill). An implication of these internal waves would be to
increase vertical mixing of nutrients toward the surface, through shear instabilities, which would favor
primary production.

This work describes the hydrographic conditions found in Puyuhuapi Channel (northern Chilean Pata... more This work describes the hydrographic conditions found in Puyuhuapi Channel (northern Chilean Patagonia)
during recent years on a seasonal scale. Puyuhuapi Channel was once a glacial valley, but the
retreating ice allowed the inflow of marine waters. Five surveys were conducted between 2008 and
2012; historical data from 1995 to 2007 were included. A meteorological/oceanographic buoy was also
installed in the northern section of Puyuhuapi Channel and was operational beginning on April 12th,
2011. Puyuhuapi Channel’s surface characteristics highlight a fresher northern part and a more haline
southern part except during winter when the pattern can reverse due to the intrusion of oceanic water
via Jacaf Channel. The channel exhibits a highly variable meridional and seasonal vertical stratification,
especially in its northern part where during spring and summer the water column is highly stratified
but partially mixed during winter. Puyuhuapi Channel is the only fjord/channel with severe hypoxic conditions
in all of Chilean Patagonia.

Double-diffusive layering was quantified for the first time in the Chilean Patagonian fjords regi... more Double-diffusive layering was quantified for the first time in the Chilean Patagonian fjords region
(41.5–56S). Approximately 600 temperature and salinity profiles collected during 1995–2012 were used
to study water masses, quantify diffusive layering and compute the vertical diffusivity of heat. Development
of ‘‘diffusive-layering’’ or simply ‘‘layering’’ was favored by relatively fresh–cold waters overlying
salty–warm waters. Fresh waters are frequently derived from glacial melting that influences the
fjord either directly or through rivers. Salty waters are associated with Modified Subantarctic (MSAAW)
and Subantarctic Water (SAAW). Double-diffusive convection occurred as layering in 40% of the yearround
data and as salt fingering in <1% of the time. The most vigorous layering, was found at depths
between 20 and 70 m, as quantified by (a) Turner angles, (b) density ratios, and (c) heat diffusivity (with
maximum values of 5 105 m2 s1). Diffusive-layering events presented a meridional gradient with less
layering within the 41–47S northern region, relative to the southern region between 47 and 56S.
Layering occupied, on average, 27% and 56% of the water column in the northern and southern regions,
respectively. Thermohaline staircases were detected with microprofile measurements in Martinez and
Baker channels (48S), showing homogeneous layers (2–4 m thick) below the pycnocline (10–40 m). Also
in this area, increased vertical mixing coincided with the increased layering events. High values of
Thorpe scale (LT 7 m), dissipation rate of TKE (e = 105–103Wkg1) and diapycnal eddy diffusivity
(Kq = 106–103 m2 s1) were associated with diffusive layering. Implications of these results are that
diffusive layering should be taken into account, together with other mixing processes such as shear
instabilities and wind-driven flows, in biological and geochemical studies.