Benjamín Martínez-López

Barrier layers (BLs) reduce vertical mixing and limit the cold‐thermocline‐water entrainment into the mixed layer, influencing a wide range of air–sea interaction processes and ocean dynamics. They are conventionally characterized by their barrier layer thickness (BLT), but BLT cannot quantify either the density‐stratification intensity or the cold‐entrainment resistance. We introduce Barrier Layer Insulation (BLI), an energy‐based metric quantifying the BL's insulating capacity as the energy a water parcel at the BL's base must overcome to cross it against negative buoyancy. We also define the BLI density rate to quantify the degree of insulation concentration per unit depth. Using 2.8 million Argo profiles from 2005 to 2024, we constructed the first global seasonal climatologies of BLI and BLI density rate. Results reveal systematic decoupling between BLT and BLI across ocean basins and seasons: depending on the salinity‐stratification vertical structure, the thickest BLs are not necessarily the most insulating. The regions most dynamically consequential for cold entrainment reduction are not those where BLs are thickest or most spatially extensive, but those where their insulation is most vertically concentrated. The BLT–BLI decoupling is strongest in mid‐ to high‐latitude regions during boreal winter; tropical regions exhibit thin but highly insulating BLs. BLT is insufficient to characterize the dynamical importance of BLs, and BLI provides a physically grounded framework for assessing their insulation, with implications for processes in which cold entrainment is relevant, such as tropical cyclone intensification, El Niño–Southern Oscillation preconditioning, monsoon dynamics, Madden‐Julian Oscillation convection, and ocean heat content variability.

The year‐to‐year rate and acceleration of the changes in global sea surface temperatures (SSTs) for 1870–2022 are determined using non‐linear techniques. Our methodology identifies the non‐linear, long‐term tendencies of the warming, revealing subtle but essential features of the SST changes that are impossible to identify by linear techniques. Our analysis identifies inhomogeneous patterns of SST evolution. For instance, in most equatorial regions, including the western Pacific, the acceleration of the warming is positive, and sustained warming replaces the cooling at the beginning of the records. On the contrary, the warming acceleration in the central and eastern equatorial Pacific is negative, indicating a sustained warming at the beginning of the record that weakens over the years, resulting in a stagnated warming or even a cooling in recent years. We identify a strong warming with a negative acceleration for the North Atlantic. We hypothesize that this warming is part of the multidecadal variability of SST rather than a long‐term trend.

Climate simulations for the North Atlantic and Europe for recent and future conditions simulated with the regionally coupled ROM model are analyzed and compared to the results from the MPI‐ESM. The ROM simulations also include a biogeochemistry and ocean tides. For recent climate conditions, ROM generally improves the simulations compared to the driving model MPI‐ESM. Reduced oceanic biases in the Northern Atlantic are found, as well as a better simulation of the atmospheric circulation, notably storm tracks and blocking. Regarding future climate projections for the 21st century following the RCP 4.5 and 8.5 scenarios, MPI‐ESM and ROM largely agree qualitatively on the climate change signal over Europe. However, many important differences are identified. For example, ROM shows an SST cooling in the Subpolar Gyre, which is not present in MPI‐ESM. Under the RCP8.5 scenario, ROM Arctic sea ice cover is thinner and reaches the seasonally ice‐free state by 2055, well before MPI‐ESM. This shows the decisive importance of higher ocean resolution and regional coupling for determining the regional responses to global warming trends. Regarding biogeochemistry, both ROM and MPI‐ESM simulate a widespread decline in winter nutrient concentration in the North Atlantic of up to ~35%. On the other hand, the phytoplankton spring bloom in the Arctic and in the North‐Western Atlantic starts earlier, and the yearly primary production is enhanced in the Arctic in the late 21st century. These results clearly demonstrate the added value of ROM to determine more detailed and more reliable climate projections at the regional scale.

Extracted nonstationary oscillations and nonlinear trends of precipitation and sea surface temperature (SST) data reveal that rainfall variability in Mexico City is mainly composed by a long‐term positive trend, a multidecadal oscillation highly correlated with the Atlantic Multidecadal Oscillation (AMO), and year‐to‐year variability. The precipitation trend, lasting for more than a century, cannot be attributed to global warming or urbanization alone; rather, it can be thought of as part of a natural oscillation composed of alternating wet‐dry anomalies with a period of a couple of centuries, as past evidence indicates. To further test the dependence of the AMO‐related component, yearly SST time series were derived from a simplified model of the atmosphere‐ocean system forced by white noise. The simulated SST time series exhibits AMO‐like variability entirely consistent with the observed one, implying that North Atlantic SST multidecadal variability can be seen as the integrated response of surface ocean layers to external stochastic atmospheric forcing.

Pollen allergies have a remarkable clinical impact all over world. Quercus pollen is the main allergen in many parts of world. Due to the health impacts caused by exposure to oak pollen, the objectives of this study are to characterise the aerobiological behaviour of Quercus pollen and to determine its potential sources as well as their transport through the atmosphere of Mexico City and surrounding areas between January 2012 and June 2015. Airborne Quercus pollen monitoring was carried out simultaneously in five zones of Mexico City. The percentage of Quercus pollen of the total pollen collected from the air showed that the highest concentration was recorded in 2014, followed by 2012. The annual seasonal variation indicated that flowering and pollen emission into the atmosphere began between February and March. The maximum concentration of Quercus pollen was reached at Cuajimalpa. In 2012, the amount of pollen grains was distributed in March and April uniformly, whilst in 2014, the largest amount of pollen was concentrated in March. In 2012 and 2014 (years with the highest pollen concentrations), corresponding intraday variations were quite similar, with a low relative maximum in the morning and the highest concentrations in the evening. The largest values were recorded in 2014, and two processes can explain these. In the afternoon, pollen from secondary forest is carried by southwesterly converging winds, increasing the pollen concentration in Cuajimalpa. In the evening, there is an additional pollen contribution from primary forest via transport by NW winds.

Analysis of the simulated global temperature using a simple energy balance stochastic model

The Loop Current and its shed eddies dominate the circulation and dynamics of the Gulf of Mexico (GoM) basin. Those eddies are strongly energetic and are the cause of intense currents that may penetrate several hundred meters deep. However, there are regions in the GoM and periods of time in which the local atmospheric forcing plays an important role in its dynamics and thermodynamics. The circulation on the shelves, and particularly on the inner shelf, is mainly wind-driven with seasonality, changing direction during the year with periods of favorable upwelling/downwelling conditions. The wind-driven circulation is associated with the transport of waters with different temperature and salinity characteristics from one region to another. The interannual variability of the circulation on the shelves is linked to the atmospheric variability. Intraseasonal variability of the wind patterns considerably affects the likelihood and magnitude of upwelling and downwelling. The geometry of the GoM is such that large-scale winds may drive opposing upcoast/downcoast currents along different parts of the curving coast, resulting in convergence or divergence zones. The width of the shelves in the GoM is variable;while the West Florida Shelf, the Texas-Louisiana shelf and the Campeche Bank are more than 200km wide, they are narrower near Veracruz and Tabasco. Another consequence of the GoM physiography and the wind forcing is the development of cross-shelf transports in the southern Bay of Campeche, the southern Texas shelf and southeast of the Mississippi river, which in turn vary during the year. During autumn-winter (from September to April), the GoM is affected by cold fronts coming from the northwest United States, which are associated with strong, dry, and cold winds that mix its waters and generate large sensible and latent heat fluxes from the ocean to the atmosphere. These frontal passages also cool the GoM surface waters due to mixing with lower temperature subsurface waters. During summer, tropical cyclones crossing the GoM can dramatically affect circulation and coastal upwelling