The planet's most comprehensive physical exam is underway, and the patient is our global ocean.
A detailed assessment of the ocean's health based on the 7th edition of the Copernicus Ocean State Report
A vast, dynamic ocean shapes our climate, supports immense biodiversity, and sustains human economies. Yet, this vital system is undergoing rapid, often dramatic changes. The 7th edition of the Copernicus Ocean State Report (OSR7) serves as the planet's essential medical check-up, providing a detailed assessment of the ocean's health. This comprehensive report, a flagship of the European Union's Copernicus Marine Service, translates billions of data points into a clear and compelling story of a world in flux—from intensifying heatwaves and unusual plankton blooms to shifting currents and deepening oxygen loss 1 2 6 .
Significant increase in deep layers of the IBI region
More frequent and intense globally
Record low heat exchange in key Arctic systems
In 2021, the waters around Scotland turned a startling shade of turquoise, not once, but twice 2 . The OSR7 identified these events as massive blooms of coccolithophores, a type of marine plankton 1 .
The report found that the coldest April in 30 years delayed the usual spring bloom. A subsequent stormy May injected nutrients into the water, creating the perfect conditions for these unusual summer blooms that captured public attention and significantly influenced the marine carbon cycle 1 2 .
The same year, a prolonged cyclone named Storm Blas hit the Balearic Islands, causing a dramatic and unexpected oceanographic phenomenon 1 .
The storm triggered intense upwelling, pulling deep, cold water to the surface. This led to coastal surface temperatures up to 6°C colder than usual for several days, demonstrating how extreme weather can violently disrupt local marine environments and reverse regional current systems 1 2 .
Coldest April in 30 years delays usual spring plankton bloom around Scotland.
Stormy conditions inject nutrients into Scottish waters, setting stage for unusual summer blooms.
Massive coccolithophore blooms turn Scottish waters turquoise, influencing marine carbon cycle.
Storm Blas triggers intense upwelling around Balearic Islands, causing surface temperatures 6°C colder than usual.
While surface temperatures can be highly variable, the true signature of global warming is written in the deep ocean. The OSR7 details a critical study of the Iberia–Biscay–Ireland (IBI) region 5 . Researchers used a multi-product approach, combining data from various observations and ocean reanalysis systems to map ocean heat content (OHC) from 1993 to 2021 1 5 .
The study revealed that while the upper ocean layer (0–150 m) is dominated by natural variability, a significant long-term warming trend is emerging in the deeper layers 1 2 . This deep-ocean warming amounts to about 50% of the global average trend, a clear indicator of the ocean's role as the planet's primary heat sink 1 .
The research identified that more than half of this variability is linked to changes in two specific water masses: the Sub-Arctic Intermediate Water and the Mediterranean Outflow Water, showing how regional oceans are affected by remote processes 1 5 .
| Indicator | Region | Trend | Impact |
|---|---|---|---|
| Ocean Heat Content5 | Iberia-Biscay-Ireland (deep layers) | Significant increase (+0.40 W m⁻²) | Contributes to sea-level rise, impacts ecosystems |
| Marine Heatwaves2 | Global | More frequent and intense | Coral bleaching, species mortality, habitat loss |
| Marine Cold Spells2 | Global | Less frequent | Disruption to species adapted to cooler conditions |
| Salinity1 | Mediterranean Sea | Overall increase, especially in eastern basin | Alters ocean density, currents, and biodiversity |
| Freshwater Content1 | Baltic Sea | Steady decrease (not spatially uniform) | Affected by circulation, precipitation, and runoff |
To understand how scientists unravel the complex story of ocean heating, we can look at the in-depth analysis of the Iberia–Biscay–Ireland (IBI) region featured in the OSR7 5 .
This study did not rely on a single data source. Instead, it employed a multi-product approach to ensure robustness 1 5 . Scientists combined several Copernicus Marine reanalysis products and observational data to estimate Ocean Heat Content (OHC) anomalies. They calculated the heat stored in different layers of the water column: the upper ocean (0–150 m), intermediate layer (0–700 m), and full depth (0–2000 m) 5 .
The core of the investigation involved:
The study confirmed that the long-term warming signal in the IBI region is not a surface phenomenon but is entrenched in the deeper ocean 1 . The high interannual variability of the subsurface water masses masks these trends, but statistical analysis confirms their significance 5 .
Crucially, the research quantified the role of specific water masses. It found that the SAIW and MOW explain more than 50% of the OHC variability in the region 1 5 . Since the variability of these two water masses is known to be influenced by the North Atlantic Oscillation (NAO), the study demonstrated the mechanism by which atmospheric forcing can drive changes in the deep ocean without leaving a clear, consistent signal at the surface 5 .
| Water Mass | Characteristics | Role in Ocean Heat Content |
|---|---|---|
| Sub-Arctic Intermediate Water (SAIW) | Subsurface salinity minimum | Explains a significant portion of OHC variability; linked to North Atlantic Oscillation |
| Mediterranean Outflow Water (MOW) | Salinity maximum at intermediate depths | Explains a significant portion of OHC variability; its interannual oscillation affects heat distribution |
| Labrador Sea Water (LSW) | Underlying salinity minimum | Contributes to OHC variability through mixing with overlying water masses |
The report's alarming findings extend beyond European seas. On a global scale, marine heatwaves have become more frequent and intense, with one additional event occurring every five to ten years 2 . Conversely, their counterpart, marine cold spells, are becoming rarer, with one fewer event every five years 2 . This shift in the distribution of extreme temperature events poses a severe threat to marine biodiversity and the economies that depend on it.
Increasing in frequency and intensity globally, with one additional event every 5-10 years.
Decreasing in frequency globally, with one fewer event every 5 years.
The OSR7 also sharpens the focus on global ocean circulation. It examined inter-basin transports around the Southern Ocean, a critical node for global currents, and found a surprising discrepancy between observations and model results—a finding that will guide future improvements in climate monitoring 2 . Furthermore, data revealed a record low heat exchange across the Greenland-Scotland Ridge around 2018, a key system for Arctic climate, which decreased by 4–9% compared to the 1993-2020 average 2 .
Producing a report as comprehensive as the OSR7 requires a fleet of advanced technologies and methodologies. The "value chain" of ocean monitoring involves multiple steps, from data collection to the creation of user-friendly indicators 1 .
| Tool or Data Stream | Function |
|---|---|
| Satellite Observations | Provides global, repeated measurements of sea level, sea surface temperature, salinity, ocean color, and waves. |
| In Situ Measurements | Includes autonomous platforms (Argo floats), moored buoys, and research expeditions to collect subsurface data. |
| Ocean Reanalysis | Combines observations with numerical models using data assimilation to create a consistent 4D view of the ocean's past and present. |
| High-Frequency Radar (HFR) | Monitors coastal ocean surface currents in real-time, used in new tools for tracking upwelling. |
| Ocean Colour Data | Measures light reflected from the ocean to derive Essential Ocean Variables (EOVs) like chlorophyll concentration, a proxy for phytoplankton. |
The OSR7 itself introduced several new tools. One is an innovative coastal upwelling index that uses data from High-Frequency Radar, buoys, and models to categorize upwelling and downwelling events, providing high-resolution 2D maps for better management of marine resources 1 2 . Another new tool tracks dissolved oxygen variations in the Mediterranean Sea, where a record low oxygen level was detected deep in the southern Adriatic Sea in 2021, highlighting concerns about ocean deoxygenation 2 .
The Copernicus Ocean State Report is more than a scientific publication; it is a testament to international collaboration. The OSR7 was steered by over 80 scientists from 30 institutions across 14 countries 3 6 . This diverse expertise is essential for tackling the complex, interconnected challenges facing the marine environment.
The report's findings are not just diagnostic; they are a call to action. By providing a clear, scientifically robust assessment of the ocean's state, the OSR7 equips policymakers, industries, and citizens with the knowledge needed to develop timely adaptation strategies, raise awareness, and encourage action to protect and conserve the ocean 1 . In an era of unprecedented environmental change, such rigorous monitoring and reporting are our best hope for transitioning toward a sustainable ocean stewardship 1 .