In this study, we used stable isotopes of oxygen (δ¹⁸O), deuterium (δD), and dissolved inorganic carbon (δ¹³C_DIC) in combination with temperature, salinity, oxygen, and nutrient concentrations to characterize the coastal (71°–78°W) and an oceanic (82°–98°W) water masses (SAAW—Subantarctic Surface Water; STW—Subtropical Water; ESSW—Equatorial Subsurface water; AAIW—Antarctic Intermediate Water; PDW—Pacific Deep Water) of the Southeast Pacific (SEP). The results show that δ¹⁸O and δD can be used to differentiate between SAAW‐STW, SAAW‐ESSW, and ESSW‐AAIW. δ¹³C_DIC signatures can be used to differentiate between STW‐ESSW (oceanic section), SAAW‐ESSW, ESSW‐AAIW, and AAIW‐PDW. Compared with the oceanic section, our new coastal section highlights differences in both the chemistry and geometry of water masses above 1,000 m. Previous paleoceanographic studies using marine sediments from the SEP continental margin used the present‐day hydrological oceanic transect to compare against, as the coastal section was not sufficiently characterized. We suggest that our new results of the coastal section should be used for past characterizations of the SEP water masses that are usually based on continental margin sediment samples.

Methane (CH₄) is one of the most powerful greenhouse gases with the capacity to influence the Earth's radiative budget as well as contribute to atmospheric chemistry. Natural oceanic production makes up to ∼4% of the overall global CH₄ emissions, however, there is uncertainty around the accuracy of this value due to a lack of accurate measurements. Such is the case in the Subtropical Eastern South Pacific Ocean (SESP), a region with pronounced chlorophyll‐a and oxygen gradients, which in turn affect the microbial CH₄ cycling. This study was conducted during spring‐summer (2014–2016) in the SESP. The region (∼17°–37°S/71°–110°W) is separated into (i) eutrophic, (ii) mesotrophic, and (iii) oligotrophic areas, according to oceanographic and biogeochemical criteria. The SESP presents high CH₄ zonal variability with levels ranging from 0.63 to 33.4 nmol L⁻¹, corresponding to 29% and 1,423% saturation, respectively. High CH₄ concentrations (>1,000% saturation) are observed in the narrow eutrophic area subjected to coastal upwelling. These conditions clearly differ to those observed in the extended oligotrophic subtropical gyre (∼100% saturation). Furthermore, CH₄ also tends to accumulate in the mesotrophic area (with upto 1,423% saturation), where oceanographic conditions as stratification, mesoscale eddies and island mass effect could trigger the presence of a microbial biomass that may be able to induce CH₄ regeneration. The CH₄ efflux is estimated to be between 0.13 and 19.1 µmol m⁻² d⁻¹ (mean ± SD = 4.72 ± 4.67) and the SESP has an emission rate of ∼87.9 Gg CH₄ yr⁻¹.

Light variability is a key environmental stressor influencing the physiology and productivity of marine macroalgae. This study examined the ecophysiological and biochemical responses of Lessonia spicata (Ochrophyta) during a natural light deprivation event caused by a solar eclipse. We measured the in vivo chlorophyll a (Chla) fluorescence, photoinhibition, and photosynthetic capacity, along with the pigment content, phenolic compound accumulation, and antioxidant capacity, to evaluate short-term photosynthetic adjustments. Dark-adapted conditions during the eclipse peak led to reduced photosynthetic and biochemical activity, while post-eclipse recovery involved the increased accumulation of photosynthetic pigments and photoprotective compounds. Carotenoids showed high antioxidant potential under eclipse exposure, contrasting with declines in chlorophyll content and productivity under pre-eclipse high irradiance. This study provides valuable insights into the rapid acclimation mechanisms of Lessonia spicata to transient light stress, highlighting its sensitivity and resilience to sudden shifts in solar irradiance. These findings contribute to the broader field of marine macroalgal photobiology and stress physiology, enhancing our understanding of how intertidal brown algae adapt to dynamic environmental conditions.

Carbon dioxide (CO₂) emissions due to human activities are responsible for approximately 80% of the drivers of global warming, resulting in a 1.1 °C increase above pre-industrial temperatures. This study quantified the CO₂ assimilation and productivity of the brown macroalgae Lessonia spicata in the central Pacific coast of Chile, across seasonal and daily cycles, under different environmental stressors, such as temperature and solar irradiance. Measurements were performed using an infra-red gas analysis (IRGA) instrument which had a chamber allowing for precise quantification of CO₂ concentrations; additional photophysiological and biochemical responses were also measured. CO₂ assimilation, along with the productivity and biosynthesis of proteins and lipids, increased during the spring, coinciding with moderate temperatures (~14 °C) and high photosynthetically active radiation (PAR). Furthermore, the increased production of photoprotective and antioxidant compounds, including phenolic compounds, and carotenoids, along with the enhancement of non-photochemical quenching (NPQ), contribute to the effective photoacclimation strategies of L. spicata. Principal component analysis (PCA) revealed seasonal associations between productivity, reactive oxygen species (ROSs), and biochemical indicators, particularly during the spring and summer. These associations, further supported by Pearson correlation analyses, suggest a high but seasonally constrained photoacclimation capacity. In contrast, the reduced productivity and photoprotection observed in the summer suggest increased physiological vulnerability to heat and light stress. Overall, our findings position L. spicata as a promising nature-based solution for climate change mitigation.

The rapid expansion of seawater reverse osmosis (SWRO) desalination has raised concern about the effects of brine discharges on coastal marine ecosystems. This study evaluated stress biomarkers in two benthic species with contrasting physiological strategies, the red seaweed Rhodymenia corallina and the sea anemone Anthothoe chilensis, following field transplantation near a desalination brine discharge in northern Chile. Biomarkers of photosynthetic performance, oxidative stress, antioxidant defense, and osmoregulation were assessed after 24 h, 48 h, and 5 d of exposure. R. corallina showed limited photosynthetic changes, moderate oxidative damage, and reduced antioxidant reserves, whereas A. chilensis showed reduced oxidative damage and maintained antioxidant and osmotic homeostasis. The Biomarker Response Index (BRI) revealed moderate alteration at 24 h followed by lower scores at later times. These distinct response patterns reveal marked species-specific sensitivity to brine exposure and support the value of integrating multiple biomarkers to characterize physiological responses. Given their ecological relevance and suitability for field transplantation in desalination-impacted areas, these findings support the evaluation of R. corallina and A. chilensis as candidate biomonitors for desalination environmental monitoring.