Francois Colas

Benthic or epibenthic dinoflagellates (EDs) are a potential risk to the environment and human health due to the production of toxins by some species. This study explored for the first time the presence of EDs mainly associated with macrophytes (macroalgae and seagrass) at 2 sites influenced by upwellings: Estero de Urías Lagoon (EUL), at the entrance of the Gulf of California, and Paracas Bay (PB), on the southern Peruvian coast. Prorocentrum lima complex was present at low abundances: ≤ 25 cells g-1 wet weight in EUL and ≤ 867 cells g-1 wet weight in PB. It was recorded in a wide range of temperatures from 22.2 to 31.6 °C in EUL and from 18.0 to 22.2 °C in PB. Despite its low abundance, monitoring the EDs community is essential to detect changes in the distribution patterns of harmful species in the context of climate change.

Ocean mesoscale thermal feedback (TFB) is the influence of mesoscale sea surface temperature (SST) anomalies on the overlying atmosphere and its feedback to the ocean. Over the past few decades, TFB has been shown to affect the atmosphere by inducing low-level wind and surface stress anomalies and modulating ocean–atmosphere heat fluxes ubiquitously over the global oceans. These anomalies can alter the climate variability. However, it is not clear yet to what extent heat and momentum flux anomalies modulate the mesoscale ocean activity. Here, using coupled ocean–atmosphere mesoscale simulations over a realistic subtropical channel centered on the equator in which the TFB can be turned off by spatially smoothing the SST as seen by the atmosphere, we show that TFB can damp the mesoscale activity, with a more pronounced effect near the surface. This damping appears to be sensitive to the cutoff filter used: on average, the surface mesoscale activity is attenuated by 9% when smoothing the SST using an ∼1000-km cutoff but by only 2% when using an ∼350-km cutoff. We demonstrate that the mesoscale activity damping is primarily caused by a sink of available eddy potential energy that is controlled by the induced-anomalous heat fluxes, the surface stress anomalies having a negligible role. When TFB is neglected, the absence of sink of potential energy is partly compensated by a more negative eddy wind work. We illustrate that TFB filtering in a coupled model must be done carefully because it can also impact the large-scale meridional SST gradients and subsequently the mean large-scale wind stress curl and ocean dynamics.

Máximos de viento en niveles bajos de la atmósfera ocurren frecuentemente sobre el mar peruano frente a la costa, denominados chorros o jets costeros. Estos jets costeros tienen un papel importante en la dinámica oceánica e impactos significativos en el clima y la ecología regional, así como en una serie de actividades humanas, por lo que las investigaciones sobre ellos son de mucha importancia. Este estudio presenta las características (frecuencia de ocurrencia, altura, intensidad y dirección) de los jets costeros frente a la costa peruana, usando datos de simulación atmosférica a alta resolución (7 km) con el modelo regional WRF, para el periodo 1994-2003, siguiendo un conjunto de criterios basado en el análisis de perfiles verticales del viento y de temperatura. Los resultados del análisis muestran que los jets costeros sobre el mar peruano pueden ocurrir durante todos los meses del año, sin embargo, varían en frecuencia y localización espacial. Estos jets son más frecuentes en verano y se concentran muy cerca de la costa. Predominantemente, tienen intensidad entre 8 y 10 m.s-1 y se presentan entre 200 y 300 m.s.n.m. Por otro lado, en invierno los jets costeros son menos frecuentes y tienen mayor extensión espacial; mayormente tienen intensidad entre 9 y 11 m.s⁻¹ y altura entre 400 y 500 m.s.n.m. Además, la dirección de los jets costeros es predominantemente sursureste (paralelo a la línea de costa) para todas las estaciones de año, excepto en invierno cuando el jet presenta también altas ocurrencias desde la dirección sureste.

The influence of chlorophyll shading on ocean dynamics has been usually disregarded in eastern boundary upwelling systems modeling studies in spite of their very high primary productivity. Here, we study how this effect impacts on the Peru upwelling system using a regional mesoscale‐resolving physical biogeochemical coupled model. We show that the shading effect leads to a surface cooling of up to 1°C on the shelf due to subsurface cooling of the source waters during their transit toward the shelf. The shading effect leads to a more realistic subsurface stratification, a slowdown of the alongshore currents, and a shoaling of the oxycline. Impacts on the regional model biases show that the shading effect needs to be taken into account in both physical and coupled physical‐biogeochemical regional models of upwelling systems.

Ocean mesoscale eddies are characterized by rotating-like and meandering currents that imprint the low-level atmosphere. Such a current feedback (CFB) has been shown to induce a sink of energy from the ocean to the atmosphere, and consequently to damp the eddy kinetic energy (EKE), with an apparent regional disparity. In a context of increasing model resolution, the importance of this feedback and its dependence on oceanic and atmospheric model resolution arise. Using a hierarchy of quasi-global coupled models with spatial resolutions varying from 1/4° to 1/12°, the present study shows that the CFB induces a negative wind work at scales ranging from 100 to 1000 km, and a subsequent damping of the mesoscale activity by ~30% on average, independently of the model resolution. Regional variations of this damping range from ~20% in very rich eddying regions to ~40% in poor eddying regions. This regional modulation is associated with a different balance between the sink of energy by eddy wind work and the source of EKE by ocean intrinsic instabilities. The efficiency of the CFB is also shown to be a function of the surface wind magnitude: the larger the wind, the larger the sink of energy. The CFB impact is thus related to both wind and EKE. Its correct representation requires both an ocean model that resolves the mesoscale field adequately and an atmospheric model resolution that matches the ocean effective resolution and allows a realistic representation of wind patterns. These results are crucial for including adequately mesoscale ocean–atmosphere interactions in coupled general circulation models and have strong implications in climate research.

In the decades, the use of scatterometer data allowed to demonstrate the global ubiquity of the ocean mesoscale thermal feedback (TFB) and current feedback (CFB) effects on surface winds and stress. Understanding these air‐sea interactions is of uttermost importance as the induced atmospheric anomalies partly control the ocean circulation and thus can influence the Earth climate. Whether the TFB and CFB effects can be disentangled, and whether satellite scatterometers can properly reveal them, remain rather unclear. Here, using satellite observations and ocean‐atmosphere coupled mesoscale simulations over 45°S to 45°N, we show that the CFB effect can be properly characterized and unraveled from that due to the TFB. We demonstrate that the TFB can be unambiguously characterized by its effect on the stress (and wind) divergence and magnitude. However, its effect on the wind and stress curl is contaminated by the CFB and thus cannot be estimated from scatterometer data. Finally, because scatterometers provide equivalent neutral stability winds relative to the oceanic currents, they cannot characterize adequately the CFB wind response and overestimate the TFB wind response by ≈25%. Surface stress appears to be the more appropriate variable to consider from scatterometer data.