Mercator Ocean International
Ocean Temperature Bulletin

Ocean Temperature Bulletin
March 2026

Mercator Ocean International (MOi) oceanographers examine marine heatwaves across the global ocean. They analyse a variety of datasets from observation analyses
(satellite sea surface temperature maps) to model analyses
(assimilating satellite and in situ observations) and model forecasts.¹

All images in this article can be used freely and should be credited with the following information :
Image source: European Union, Copernicus Marine Service Data 2025 © Mercator Ocean .

Key takeaway

 

  • March 2026 was the second warmest March on record for the global ocean (between 60°S and 60°N) with a mean sea surface temperature (SST) of 21.04 ± 0.08°C.
  • In the Mediterranean Sea, March 2026 was the third warmest March month, with a mean SST of 16.13 ± 0.15°C, ranking behind 2024 and 2025.
  • In the North Atlantic (between 0°N and 60°N), March 2026 was the sixth warmest March of the past 34 years, with a mean SST of 20.22 ± 0.13°C. The record of 2024 reached 20.75 ± 0.14°C.
  • March 2026 average sea surface temperatures were above average for 69% of the global ocean and for almost the entire Mediterranean Sea (97%).
  • The eastern part of equatorial region SST anomalies are reaching 1.5 °C, and whilst cold anomalies remain in this region, positive anomalies show the continue decline of La Niña towards ENSO-neutral conditions.
  • Marine heatwave events in the Mediterranean Sea were the third most extreme for a March month with less intense and shorter events that in March 2024 and 2025.

sea Surface Temperature

Daily sea surface temperatures averaged for the global ocean (top), the Mediterranean Sea (centre) and the North Atlantic Ocean (bottom) between 1991-2020 using ESA’s Climate Change Initiative (grey shades), and between 2021-2026 (coloured shades) using Mercator Ocean International’s GLO12 analysis and forecast.

  • March 2026, at global level (between 60°S and 60°N), was the second warmest March on record, with a mean Sea Surface Temperature (SST) of 21.04 ± 0.08°C — behind only 2024 (21.14 ± 0.07 °C). 
  • In the Mediterranean Sea, March 2025 was the third warmest March month, with a mean SST of 16.13 ± 0.15°C, ranking behind 2024 (16.36 ± 0.18°C) and 2025 (16.44 ± 0.11°C).
  • In the North Atlantic (between 0°N and 60°N), March 2025 was the sixth warmest March of the past 34 years, with a mean SST of 20.22 ± 0.13°C. The record of 2024 reached 20.75 ± 0.14°C. 

Sea surface temperature anomalies

March 2026 Mean SST Anomaly relative to a 30-year climatology (1993-2022), calculated using daily data from Mercator Ocean International’s GLO12 analysis and forecasting system for 2026 and from the GLORYS12 reanalysis for the climatological mean.

March 2026 mean SSTs are above average for 69% of the global ocean (between 60°S and 60°N), with 15% exceeding the average by at least 1°C.

  • Almost the entire Mediterranean Sea (97%) showed above-average SSTs, with 38% of the basin reaching at least 1°C above average, mainly in the northern part.
  • The North Pacific Ocean showed widespread high SSTs at midlatitude spanning the entire width of the basin and reaching 3°C above average in the western part. The west coast of Mexico is also experiencing significant above average SST, exceeding 2°C. Above-average SSTs were also observed in the South Pacific the west coast of South America, reaching more than 2°C above average. Between 20°S and 40°S, a large band of warm anomalies covers the basin, with values exceeding 2°C. The eastern part of equatorial region is characterized by above-average sea surface temperatures  (SSTs), averaging around 1.5 °C but locally exceeding 2 °C. Whilst cold anomalies remain in the central equatorial regions, above-average SSTs are developing in the eastern part, averaging around 1.5 °C, showing the continuing decline of La Niña towards ENSO-neutral conditions  .
  • The North Atlantic recorded above-average SSTs over 63% of its area (between 0°N and 60°N), mainly in the subtropical part of the basin, with anomalies reaching more than 1.5°C. Northeastern Europe is also experiencing anomalies exceeding 1.5°C locally. In the South Atlantic, between 30°S and 50°S, SSTs exceeded 2°C above average, mainly off the coast of South Africa.
  • In the Indian Ocean, above average SSTs are found est of Madagascar, reaching up to 2°C above average.
  • Sea surface temperatures are approximately 1°C above average in the Southern Ocean, between 50°E and 120°E.

 

Ranking March 2026

Ranking of average monthly SSTs reached in March 2026, calculated using daily data from Mercator Ocean International’s GLO12 analysis and forecasting system for 2026 and from the GLORYS12 reanalysis for the climatological mean. The colours indicate the rank of March 2026 among all months of March since 1993.

The ranking of average monthly SSTs is monitored so to contextualise the current situation relative to previous Marchs. This ranking is based on March monthly averages from 1993 to 2026. Here, we look at the ranking of March 2026 among all months of March since 1993.

  • Around 8% of the global ocean (between 60°S and 60°N) ranked as the warmest March month on record, 24% of the ocean is within the 4 warmest (not shown).
  • Most of the Mediterranean recorded average sea surface temperatures that ranked among the 10 highest ever observed in March, reaching record levels or the second-highest levels ever recorded in the northern part of the basin.
  • In the North Atlantic, SSTs reached record levels in northern Europe and in the subtropical region, from the Caribbean to the middle of the basin.
  • In the North Pacific, March 2026 SSTs are approaching or reaching record levels, particularly between 30°N and 60°N, and off the coast of the Philippines, between 125°E and 160°W.
  • In the South Pacific, large areas off the coasts of Chile and Peru, as well as between 180°W and 120°W, saw record-high average sea surface temperatures (SST) in March.
  • The Southern Ocean also reached SST records for the month of March, particularly between 60°E and 120°E.

Ongoing Marine Heatwaves

Month of onset for the ongoing MHWs on the 31st of March 2026. The colours indicate the month during which the MHW started. For instance, ocean pixels in red correspond to an MHW that developed during March 2026 and are less than one month old, in orange MHW between 1 and 2 months old, etc.
  • On the 31st of March, 23% of the global ocean (between 60°S and 60°N) was affected by MHWs.
  • The majority of these MHWs developed recently, with 17% of the global Ocean (between 60°S and 60°N) affected by MHWs less than 1 month old and 4% by events between 1- and 2-month-old.
  • Widespread and persistent MHWs are found in the subtropical region of the North Atlantic, off Chili coast and in the North Pacific, at midlatitude, between 150°E and 160°W.

Total Surface Marine Heatwaves

Global Ocean 

Surface occupied by MHWs in the global ocean (between 60°S and 60°N) between April 2025 and March 2026 based on daily monitoring. The black solid line represents the total surface of MHW, while the colored lines represent the surface of each MHW category. The gray background highlights the month of March 2026.
  • In March 2026, the total surface area of MHW (black line) increased from 21% to 23% of the global ocean (between 60°S and 60°N). The majority of MHWs events were moderate categories (around 19% of the global ocean) and, to a lesser extent, strong categories (between 2 and 4% of the global ocean).

 

Mediterranean Sea 

Surface occupied by MHWs in the Mediterranean Sea between April 2025 and March 2026 based on daily monitoring. The black solid line represents the total surface of MHW, while the colored lines represent the surface of each MHW category. The gray background highlights the month of March 2026.

 

  • In the Mediterranean Sea, the total area covered by MHWs decreased during March 2026, falling from 56% at the beginning of the month to 5% by the end. These MHW were mainly moderate in category, with a noteworthy surface of strong events in the first half of the month (between 12% and 17%), however, this percentage dropped to 0% by the end of the month. For comparison, in 2025, the total surface area of MHW extent decreased from 74% to 48% during the month of March 2025 (not shown).

North Atlantic 

Surface occupied by MHWs in the North Atlantic (between 0°N and 60°N) between April 2025 and March 2026 based on daily monitoring. The black solid line represents the total surface of MHW, while the colored lines represent the surface of each MHW category. The gray background highlights the month of March 2026.

 

  • In the North Atlantic (between 0°N and 60°N), the total surface area of MHW decreased from 18% to 11%. These events consist mostly of moderate and strong categories (from 17% to 10% and between 1-2%, respectively). For comparison, in March 2025, MHW extent decreased from 30% to 20% of the North Atlantic (not shown).

Total Number Marine Heatwaves

March 2026 MHW days of strong and higher category. Number of days during which a MHW of category strong, severe or extreme occurred in March 2026. Blank areas mean that no MHW of strong or higher category happened during the month. Blue shaded areas in the polar regions represent the sea ice maximum from the climatological period (1993-2022). Monitoring SST extremes with the MHW categorization approach as used here is not best suited for such regions.
  • 12% of the surface of the ocean was impacted by strong-or-higher MHW conditions for at least 1 day during March 2026. This is the 4th widest extent of the last 34 years, after 2025, 2016 and 2024 (28%). The northwest Pacific (around 45°N) and the Southern Ocean, between 50°E and 120°E are strongly affected (Figure 7), with intense MHWs lasting throughout the month.
  • Regionally, 7% of the North Atlantic (between 0°N and 60°N) was impacted by strong, or higher, MHW conditions for at least 1 day. This corresponds to the 8th largest extent for a March month – behind 1998, 2005, 2023, 2020, 2025, 2010 and 2024 (42%).
  • For the Mediterranean Sea, 28% of the basin was affected by strong-or-higher MHW conditions for at least 1 day, which is the 3rd largest extent for a March month, after 2025 (57%) and 2024 (60%).

Statistics

Marine heatwave average duration, intensity, occupied surface and activity in February 2026

MHW Characteristics for March months from 1993 to 2026. Duration, intensity, extent and activity averaged for each March month between 1993 and 2026 for the global ocean (top), for the Mediterranean Sea (centre) and the North Atlantic Ocean (bottom). March 2026 is highlighted with a blue edge.

  • Globally, March 2026 was the third most extreme March month in terms of MHW intensity after 2023 and far from 2024, and the fifth March month with longest MHW events on average after 2025, 1998, 2016 and 2024.
  • In the Mediterranean Sea, March 2026 was the third most extreme March on average but not as intense and long as March 2024 and 2025.
  • In the North Atlantic, March 2026 was the sixth most extreme March in terms of MHW duration and intensity, far from the events of March 2010 and 2024.

About the Bulletin

Datasets and products

Sea Surface Temperature

The results are obtained using the Copernicus Marine Service global analysis and forecasting system together with observation-based products.

  • GLOBAL_ANALYSISFORECAST_PHY_001_024 Global Ocean Physics Analysis and Forecast sea surface temperature. U. Copernicus Marine Service Information (CMEMS). Marine Data Store (MDS). DOI: https://doi.org/10.48670/moi-00016
  • ESA SST CCI reprocessed sea surface temperature analyses. E.U. Copernicus Marine Service Information (CMEMS). Marine Data Store (MDS). DOI: https://doi.org/10.48670/moi-00169
  • NOAA OI SST V2 High Resolution Dataset data provided by the NOAA PSL, Boulder, Colorado, USA, from their website at https://psl.noaa.gov, Huang, B., C. Liu, V. Banzon, E. Freeman, G. Graham, B. Hankins, T. Smith, and H.-M. Zhang, 2021: Improvements of the Daily Optimum Interpolation Sea Surface Temperature (DOISST) Version 2.1, Journal of Climate, 34, 2923-2939. doi: 10.1175/JCLI-D-20-0166.1
  • Global Ocean OSTIA Sea Surface Temperature and Sea Ice Analysis. E.U. Copernicus Marine Service Information (CMEMS). Marine Data Store (MDS). DOI: https://doi.org/10.48670/moi-00165
  • ODYSSEA Global Sea Surface Temperature Gridded Level 4 Daily Multi-Sensor Observations. E.U. Copernicus Marine Service Information (CMEMS). Marine Data Store (MDS). DOI: https://doi.org/10.48670/moi-00016

Notes: The global analysis system was used to study the ocean surface temperature from 2021 and 2025. To study surface temperature for previous years (1991 to 2020), it was used the ESA CCI data. The other observation-based sea surface temperature products (OSTIA, OI SST and Odyssea) were used for calculating monthly mean and uncertainty values for March 2025.

 Marine Heatwaves

The results are obtained using the Copernicus Marine Service global systems including the analysis and forecasting system together with the reanalysis product.

  • GLOBAL_ANALYSISFORECAST_PHY_001_024 Global Ocean Physics Analysis and Forecast sea surface temperature. U. Copernicus Marine Service Information (CMEMS). Marine Data Store (MDS). DOI: https://doi.org/10.48670/moi-00016
  • GLOBAL_MULTIYEAR_PHY_001_030 Global Ocean Physics Reanalysis sea surface temperature. E.U. Copernicus Marine Service Information (CMEMS). Marine Data Store (MDS). DOI: https://doi.org/10.48670/moi-00021

Notes: The global analysis system was used to study MHWs for 2024 and 2025. To study MHWs for previous March (1993 to 2023), it was used the reanalysis system. The reanalysis product was used for generating a daily climatology using the 30-year period from 1993 to 2022.