Argentine Sea warms 3.2°C in 40 years; report warns warming will cover all waters and depress fishery biomass

The Argentine Patagonian Marine Conservation Forum released a report in October 2026, "Climate Change: Trends and Projections for the Southwest Atlantic," written by experts from CIMA CONICET and WCS Argentina. Integrating satellite observations and climate projections, it identifies the specific areas and intensity of change underway in the Argentine Sea. The report's conclusion: climate change is no longer a long-term risk for Argentine fisheries; both observations and projections point to changes already happening.

Between 1982 and 2020, surface water temperature in the Argentine Sea rose by about 2.4°C along the Brazil Current and by about 3.2°C in the Brazil-Malvinas Confluence, equivalent to roughly 0.6°C and 0.8°C per decade. The northern Argentine Sea, Uruguay and southern Brazil are among the world's major ocean warming hotspots. The report notes that this area is where water masses converge, fronts form and the many processes that support regional fishery productivity are concentrated—not an abstract average.

Biological responses are not linear. Between 2002 and 2022, surface chlorophyll rose on the slope front, the central Patagonian shelf, the Río de la Plata estuary and a stretch of coastal waters between 48°S and 50°S. The report's authors caution that no single cause can yet be identified; in some areas, warming combined with a shallower mixed layer may prolong favorable conditions for phytoplankton. The report therefore notes that reducing this relationship to "higher temperature means lower productivity" is incorrect—the ocean is simultaneously changing its stratification, circulation, nutrient availability and seasonality.

Projections are more definitive. By the end of this century, under a very high emissions scenario, relative to 1994-2015, surface water temperature will rise by about 3.2°C on the northern shelf and in the Río de la Plata estuary, and by up to 4°C in the Brazil-Malvinas Confluence. Adding the already observed warming, cumulative warming in the confluence would be about 7.2°C. The report sums it up in one sentence: the areas observed to be cooling in recent decades will no longer exist, and warming will extend across the entire analyzed sea area.

The north is the most intense warming focus, but the south is not excluded. Warming of about 1.8°C is projected for Tierra del Fuego, Isla de los Estados and Burdwood Bank; these areas have had recent thermal variability below 1°C, so seemingly moderate changes could greatly exceed the conditions to which local biological communities are adapted. The report stresses that exposure depends not only on the magnitude of warming but also on the speed of change, historical variability and each species' ability to migrate or adjust.

A UN Food and Agriculture Organization report, "Climate Change Risks to Marine Ecosystems and Fisheries," provides a second analytical scale. Its FishMIP model ensemble estimates how exploitable marine biomass may change: relative to 2005-2014, average biomass in Argentine jurisdictional waters falls 5.2% by 2041-2050 under a low-emissions scenario and 6.5% under a high-emissions scenario; by 2091-2100, it falls 6.8% under the low-emissions scenario and 17.8% under the high-emissions scenario. In all four cases, most models agree on the direction of change.

The report also explains how to read this figure: the FAO did not predict Argentina's landings, nor allocate losses to any particular species; the models reflect ecosystem productive capacity in the absence of fishing and do not incorporate pollution, habitat degradation or future management decisions, nor can they replace stock assessments. Their role is to signal that if the unexploited biomass the environment can support declines, biological reference points and sustainable yields may also be revised downward; constant catch or fishing mortality calculated under pre-climate-change ocean conditions may no longer be consistent with the precautionary principle.

Moving from the climate picture to specific fisheries is the main scientific difficulty. A study of 28 exploited resources in southern Brazil, Uruguay and northern Argentina found that Argentine hake, anchovy and the striped smooth-hound shark have high potential for distributional change, and that the Argentine shortfin squid (Illex argentinus) has very high potential. This mobility can allow species to escape some thermal stress, but it may not shield the ports, fleets or jurisdictions they currently depend on from impacts.

Argentine hake is a cold-water-associated species; warming on the northern shelf may make some habitat unfavorable and prompt it to move south or to other depths. This could change the availability of survey cruises, relationships among populations, the location of spawning and nursery areas, and operating costs. The report notes that this does not mean the species will necessarily disappear, but if the distribution continues to shift, historical series, assessment areas and even survey schedules will need to be re-examined.

The Argentine shortfin squid requires more cautious judgement. Its life cycle is close to one year, it undertakes large-scale migrations, and its abundance responds rapidly to environmental conditions affecting spawning, hatching, growth and feeding. A study published in 2025 identified non-stationary relationships between climate and catches, with state shifts around 1990-1991 and 2015-2016. The report stresses that this does not mean a given temperature alone can predict the outcome of a fishing season, but that past relationships may no longer hold. For a resource shared among the exclusive economic zone, disputed waters and adjacent high seas, distributional shifts may also change who can access the stock and where effort concentrates.

For Patagonian shrimp, the available evidence is not yet sufficient to give a consistent direction. Temperature, salinity, plankton, circulation and fronts influence its early stages and the location of commercial aggregations. Climate change may alter survival, recruitment, fishing seasons and distribution, and may even produce temporary advantages in some areas. The report considers it premature to treat warming as either an automatic explanation for its expansion or a forecast of collapse; the priority is to link shrimp surveys with sufficiently long environmental series and with models able to distinguish climate, density, fishing and natural variability.

Benthic resources face a different set of problems. Bivalves and species closely attached to the seabed have a weaker ability to follow their preferred conditions and may also be exposed to acidification, heatwaves, changes in oxygen content and harmful algal blooms. By contrast, highly mobile species can quickly switch areas, shifting impacts from biology to economics: longer distances, more fuel, changes in catch composition, and gains or losses in port activity.

The report ends on a management proposition: how to manage an ocean that is no longer stable.