Marine heatwaves (MHWs) are discrete warm-water anomalies events occurring in both open ocean and coastal areas. These phenomena have drawn researchers’ attention since the beginning of the 2010s, as their frequency and intensity are severely increasing due to global warming. Their impacts on the oceans are wide, affecting the ecosystems thus having repercussions on the economy by decreasing fisheries and aquaculture production. Chilean Patagonia (41° S-56° S) is characterised by fjord ecosystems already experiencing the global change effects in the form of large-scale and local modifications. This study aimed to realise a global assessment of the MHWs that have occurred along Central and South Chile between 1982 and 2020. We found that the frequency of MHWs was particularly high during the last decade offshore Northern Patagonia and that the duration of the events is increasing. During austral winter and spring 2016, combination of advected warm waters coming from the extratropical South Pacific Ocean and persisting high pressure inducing reduced winds have together diminished the heat transfer from the ocean to the atmosphere, creating optimal condition for a long-lasting MHW. That MHW hit Patagonia during 5 months, from May to October 2016, and was the longest MHW recorded over the 1982-2020 period. In addition, a global context of positive phases of El Niño Southern Oscillation and Southern Annular Mode contributed to the MHW formation.

Abstract. The dissolved oxygen (DO) levels of oceanic-coastal waters has decreased over the last decade owing to the increase in surface water temperature caused by climate change. In addition, biological and human activity in coastal zones, bays, and estuaries has contributed to the acceleration of current deoxygenation. The Patagonian fjord and channel system is one world region where low DO water (LDOW, 30 %–60 % oxygen saturation) and hypoxia conditions (< 30 % oxygen saturation, 2 ml L−1 or 89.2 µmol L−1) is observed. An in-situ data set of hydrographic and biogeochemical parameters (2017 stations), collected from sporadic oceanographic cruises between 1970 and 2021, was used to quantify the mechanism involved in the presence of LDOW and hypoxic conditions in northern Patagonian fjords. Results denoted two main areas with LDOW (e.g., Puyuhuapi Fjord-Jacaf channel, Comau Fjord, and the Reloncaví estuarine system) extending from 25–400 m depth. Simultaneously, hypoxia was recorded in the Puyuhuapi Fjord, Jacaf Channel, and Quitralco Fjord. Quitralco registered the lowest values of DO (9.36 µmol L−1 and 1.6 % oxygen saturation) of the entire Patagonian fjord system. Areas of LDOW and hypoxia coincided with the accumulation of inorganic nutrients. Water mass analysis confirmed the contribution of equatorial subsurface water in the advection of the LDOW to only the Puyuhuapi Fjord and Jacaf Channel. In addition, in Puyuhuapi Fjord, hypoxic conditions occurred when the community respiration rate (6.6 g C m−2d−1) exceeded the gross primary production estimate (1.9 g C m−2d−1) possibly due to the increased consumption of DO during the use of both autochthonous and allochthonous organic matter. Biogeochemical processes and circulation regimens also contribute to deoxygenation and will be part of the discussion of the present research.

&lt;p&gt;Marine heatwaves (MHWs) are described as anomalously warm temperature events over a portion of the ocean during at least five consecutive days, developing in both coastal and open-ocean environments.&lt;/p&gt;&lt;p&gt;MHWs have been subject to numerous studies over the last years and it has been proved that their frequency and intensity is increasing through the decades in connection with human-induced global warming. Most of the studies are focusing on open-ocean MHW events and few in coastal environments, principally due to the lack of adequate data. Indeed, the detection of MHWs requires a long-term climatology of the ocean&amp;#8217;s surface temperature, generally made with satellite data. Nevertheless, the complexity of coastal environments makes the use of satellite data non-optimal because of insufficient temporal coverage with high resolution data and interferences with land systems.&lt;/p&gt;&lt;p&gt;The primary purpose of this study is to detect MHWs in a semi enclosed sea, with the study case of the Sea of Chilo&amp;#233;, North Chilean Patagonia. This sea is characterised by multiple fjords and channel systems, and has a cloudy and rainy climate; consequently, this kind of environment is not compatible with the use of satellite data to build the long-term climatology of the sea temperature at a high resolution required to detect the MHWs. Here, we use another way to calculate the climatology, using in situ data and interpolating them in order to have a continuous field. Indeed, the inner seas of North Patagonia have been quite well sampled across the years, with measurements realised since the 1950s, spatially scattered in all the regions at both surface and depth (including fjords and channels). To spatially interpolate these data, we used the tool DIVAnd (Data-Interpolating Variational Analysis) which allows to spatially interpolate in an optimal way discrete observations onto a regular grid, taking advantage of the information in the 4 dimensions. Doing this interpolation, we got a monthly climatology at 32 different depths, from the surface to 400m. MHWs were then detected by comparing the climatology to the local temperature in the Reloncav&amp;#237; Sound, in the Northern part of the Sea of Chilo&amp;#233;, where an anchored buoy recording the temperature of the sea surface since 2017 is present. We focused on MHWs that occurred during the last five years. Strong ones were detected during summers 2021 and 2022: two successive very intense and brief events occurred in January and February 2021, and several short successive events with increasing intensity from November 2021 to February 2022. We also realised the comparison between MHWs detected using in situ data and detected using satellite data.&lt;/p&gt;

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&lt;p&gt;In April 2019, a large anticyclonic Eddy has formed in Western Mediterranean Sea between Sardinia and Balearic Islands. This anticyclone was observable with Sentinel-3 SST satellite data for 7 months and its diameter was estimated to 150 km. Although mesoscale anticyclones are quite common in this part of the Mediterranean Sea, such large and long-live eddies remain exceptional and repercussions for ocean-atmospheric exchanges and for biodiversity might be consequent. However, due to the increase of temperatures during summer, the satellite SST track of the eddy has been lost during a few weeks in August and September. Indeed, the SST signature of the eddy was not distinguishable from surrounding waters anymore. In order to track the eddy during its entire life and have a better understanding of its characteristics, sea level anomaly derived from altimetric data will be analysed in this study with the Py Eddy Tracker toolbox to investigate the variation of its position, its altimetry and its size. The distribution of other remarkable eddies in this zone and period will also be considered. Moreover, a high-resolution SST field will be reconstructed with DINEOF method so the comparison between eddy&amp;#8217;s SST and altimetric characteristics will be assured.&lt;/p&gt;