Oscar Pizarro

The question of how energy is redistributed in the ocean has renewed the interest for the processes leading to midlatitude subthermocline variability at low frequency. Here we investigate a process that has been disregarded although potentially relevant for climatic studies dealing with the planetary energy budget. The focus is on the Southeastern Pacific where an efficient oceanic teleconnection takes place, linking the remote surface equatorial momentum forcing with the subthermocline through the vertical propagation of low‐frequency long‐wavelength extratropical Rossby waves (ETRW). A high‐resolution model is used to document the vertical energy flux associated with ETRW at interannual to decadal time scales. The analysis of a long‐term (1958–2008) simulation reveals that the vertical energy flux can be interpreted to a large extent as resulting from the coastally forced ETRW as far south as 35°S, so that heat content variability can be predicted along theoretical trajectories originating from the coast below the thermocline. It is shown that the vertical energy flux associated with the El Niño Southern Oscillation forms beams below the thermocline that account for a large fraction of the total vertical energy flux at interannual time scales. Extreme El Niño events are the dominant contributor to this flux, which is hardly impacted by mesoscale activity. The energy beams experience a dissipation processes in the ocean below 1000 m that is interpreted as resulting from vertical turbulent diffusion. Our results suggest that the ETRW at ENSO time scales are strongly dissipated at the surface but still can modulate the heat content in the deep ocean of the Southeastern Pacific.

<p>The meridional modes (MM) in the Pacific are the conduit by which mid to high-latitudes external forcing (NPO/SPO) can trigger or influence ENSO; While for the Northern Hemisphere the MM (NPMM) is considered a precursor of ENSO, the MM-ENSO relationship in the Southern Hemisphere (SH) is more uncertain. Here we show that, rather than acting as a precursor, strong MMs of the SH (SPMM) are dominantly (~66%) triggered by strong El Niño events in observations and the historical simulations of the Large Ensemble CESM (LENS-CESM). In the LENS-CESM simulations, strong ENSO-induced SPMMs are associated with a precursor signal (warm SST anomalies) of the coast off northern central Chile (20°S-35°S) resulting from the combined effect of the propagation of oceanic downwelling coastal Kelvin waves and the reduction in upwelling favorable winds due to an activated Pacific South American (PSA) pattern during the development of coincident ENSO cycle. The analysis of the simulations of the Coupled Intercomparison Project phases 5 and 6 (CMIP5/6) indicate a large diversity in terms of the ENSO-SPMM relationship, which can be interpreted as resulting from the spread in the meridional location of the center of action of the SPMM and of the seasonality of the SPO variance. We further discuss how ENSO-induced SPMM interferes with the coincident ENSO cycle and contributes to its asymmetry.</p>

Oxygen minimum zones (OMZs) are extended oceanic regions for which dissolved oxygen concentration is extremely low. They are suspected to be expanding in response to global warming. However, currently, the mechanisms by which OMZ varies in response to climate variability are still uncertain. Here, the variability of the subtropical OMZ off central Chile of a regional coupled physical–biogeochemical regional model simulation was analyzed for the period 2000–2008, noting that its fluctuations were significant despite the relatively weak amplitude of the El Niño/Southern Oscillation (ENSO). In particular, the interannual variability in the OMZ volume (OMZVOL, defined as the volume with dissolved oxygen concentration (DO) ≤ 45μM) was approximately 38% larger than that of the seasonal cycle, with maximum and minimum anomalies of OMZVOL taking place during two cold La Niña (LN) years (2001 and 2007). The model analyses further reveal that these anomalies resulted from a combined effect of...

While observations suggest a long-term expansion of the Oxygen Minimum Zone (OMZ) in the South Eastern Pacific (SEP), it also exhibits a large interannual to decadal variability in its upper and lower limits. The uncertainty of the fate of the SEP OMZ in a warmer climate as simulated by Earth system models also questions to which extent natural variability in the OMZ can obscure the detection of externally forced trends. Here we analyze long-term simulations from a hierarchy of models of the OMZ off Peru and Chile and show that a significant share of the variability is not linearly related to climate modes (including ENSO), suggesting that it originates from internal dynamics associated to both local non-linear physical and biogeochemical processes. Still the OMZ volume tends to shrink during strong Eastern Pacific El Nino while it expands during La Nina and Central Pacific El Nino events. It is shown in particular that La Nina and strong El Nino events significantly modulate the OM...

Off the coast of central Chile, subsurface anticyclonic eddies are a salient feature of the oceanic circulation, transporting a significant fraction of coastal water that is rich in nutrients and poor in dissolved oxygen offshore. In this study, the formation mechanism of these eddies is analyzed through a high‐resolution (~0.3 km) and low‐resolution (~3 km) oceanic model that realistically simulate the regional mean circulation, including the Peru‐Chile Undercurrent (PCUC). An analysis of the vorticity and eddy kinetic energy in both simulations indicated that the subsurface eddies can be triggered through a combination of processes that are associated with instabilities of the PCUC. In the high‐resolution simulation, we observed that the interaction between the PCUC and topographic slope generates anticyclonic vorticity and potential vorticity close to zero in the bottom boundary layer. The separation of the undercurrent from the slope favors the intensification of anticyclonic vo...

ABSTRACT: An integrated effort between researchers at Oregon State University, Universidad UUUConcepcion, Aarhus University, Massachusetts Institute of Technology, and the Penn State University has been established to study and compare the microbial response to spatial and temporal variability of the Oxygen Minimum Zones(OMZ) along both the Oregon-USA and the central coast off Chile by integrating metagenomics and metatranscriptomics in the context of physical, biogeochemical, and Paleo-oceanographic ...

We describe a seiche process in a Chilean fjord, based on current, temperature and sealevel data obtained from the Reloncavi fjord (41.6° S, 72.5° W) in southern Chile. We combined four months of ADCP data with sealevel, temperature and wind time series to analyze the dynamics of low-frequency (periods > 1 day) internal oscillations in the fjord. Additionally, seasonal CTD data from 19 along-fjord stations were used to characterize the seasonality of the density field. The density profiles were used to estimate the internal long-wave phase speed (c) using two approximations: (1) a simple reduced gravity model (RGM) and (2) a continuously stratified model (CSM). No major seasonal changes in c were observed using either approximation (e.g., the CSM yielded 0.73 < c < 0.87 m s−1 for mode 1). The natural internal periods (TN) were estimated using Merians’s formula for a simple fjord-like basin and the above phase speeds. Estimated values of TN varied between 2.9 and 3.5 d...

Seasonal information of temperature, salinity, dissolved oxygen (DO) and chlorophyll, combined with meteorological and river discharge time series were used to describe the oceanographic conditions in the Reloncavi fjord (41°35' S; 72°20' W). The winds in the fjord valley blow mainly down-fjord during winter, reinforcing the upper layer outflow, while in spring–summer winds have a predominant up-fjord direction contrary to upper layer outflow. The fjord, with a deep sill at the mouth, was well stratified year-round and showed a thin surface layer of brackish water with mean salinities between 10.4 ± 1.4 (spring) and 13.2 ± 2.5 (autumn). The depth of the upper layer changed slightly along the different studied seasons remaining at about 4.5 m near the mouth. This upper layer presented a mean outflow (<i>Q</i><sub>1</sub>) of 3185 ± 223 m<sup>3</sup> s<sup>−1</sup>, which imply a flushing time of about 3 days of this layer....

Gliders have become an efficient and reliable oceanographic platform for measuring physical and biogeochemical properties of the seawater, and the global glider fleet is rapidly expanding. In Chile, glider observations have been carried out in very different oceanographic environments, from the mild upwelling region of subtropical northern Chile to the channels of southern Patagonia. Herein, we briefly present observations and results obtained in the oxygen minimum zone off Concepcion (∼36°30′S). Many new features have been observed in this region thanks to the relatively high resolution of the glider measurements. Future plans for the glider program include an oceanic time series off central Chile that will contribute to the regional observing system of the ocean and allow evaluations of low-frequency changes like those associated with El Niño and La Niña events.

In addition to being one of the most productive upwelling systems, the oceanic region off Peru is embedded in one of the most extensive Oxygen Minimum Zones (OMZs) of the world ocean. The dynamics of the OMZ off Peru remain uncertain, partly due to the scarcity of data and to the ubiquitous role of mesoscale activity on the circulation and biogeochemistry. Here we use a high-resolution coupled physical/biogeochemical model simulation to investigate the seasonal variability of the OMZ off Peru. The focus is on characterizing the seasonal cycle in Dissolved…

In contrast to the legendary upwelling that is present along the Peruvian and northern Chilean coasts, the coastal ocean off central Chile presents a highly seasonal upwelling regime that extends from early spring to mid fall. This region is also affected by a strong subsurface poleward flow that transport low-oxygen water from the eastern equatorial Pacific. At the surface two main northward flow have been identified during the upwelling period. A coastal current, over the continental shelf, and a jet-like flow in the coastal transition zone. The structure and main scales of variability of these flows and of the upwelling are poorly understood. One of the main limitations has been the lack of direct information of currents and, in general, ocean time series. During the last years an observational program has been conducted over the wide continental shelf off Concepción (36°30' S). This program has included ship-based (monthly) time-series, glider observations and mooring time s...

The Reloncavi fjord (42.5°S, 72.3°W) is northernmost fjord of Chile. Inside of this fjord of 55 km of length and 1-3 km of width, several aquaculture activities mainly related with salmon farms occupied the fjord since the beginning of 80's. Studies has shown that in this deep fjord (of depths about 450 m near of its mouth) is characterized by a thin (5-8 m depth) brackish upper layer outflows and a below there is an inflow layer in a characteristic pattern of an estuarine circulation, recently findings also suggest the presence of a third layer outflow with velocities around 2 cms-1 probably controlled by inside/outside fjord's exchanges. At low-frequency (T > 1 day) the along-fjord currents spectra shows two relevant accumulations of energy centered at 3 and 15 days periods. The 3 days period were in agreement with the natural internal response of the fjord (internal seiche), probably forcing by changes in the local wind stress which perturb the pycnocline locate at 3-4...

PO14A-03 An intensive oceanographic study was conducted in the Reloncaví fjord, Chile (41o 23S, 72o 30W) during austral winter and spring of 2008, and summer of 2009. Inside the fjord, several CTD stations showed a clear develop of the estuarine circulation with a fresh water surface layer of ca. 8 m wide in the head which change of wide seasonally, specially near of the mouth. Measurements of currents of three ADCPs mooring arrays along the fjord showed maximum surface down-fjord flow (through the mouth of the fjord) of ca. 0.5 m s-1 below there is a deep up-fjord flow layer and the wide depend of the sub-basin depths. Residual currents obtained from on side-ship ADCP measurements (bottom track mode) were < 0.1 m s-1 and showed a marked transversal structure which typically registered a maximum at the left side of the flow, suggesting an important influence of the Coriolis effects in the sub-inertial dynamics of the fjord, effect which were 5 times greater than the centripetal a...

We investigate the variability in the Southeastern Pacific sector from altimetric and in situ data and simple model simulations for the 1995-2000 period. Whereas the low frequency variability near the coast of Chile is strongly modulated by coastal Kelvin waves remotely forced in the equatorial region, the off-shore region is characterized by coherent Rossby wave propagations at seasonal and interanual