North Atlantic Ocean

Executive Summary (with an focus on the North Atlantic. For the whole summary, see the report).
Sustained ocean observations, including ships, autonomous platforms, and satellites, are critical for monitoring the health of our marine ecosystems and developing effective management strategies to ensure longterm provision of the marine ecosystem services upon which human societies depend. Ocean observations are also essential in the development and validation of ocean and climate models used to predict future conditions. Ship‐ based biogeochemical time series provide the high‐ quality biological, physical and chemical measurements that are needed to detect climate change‐ driven trends in the ocean, assess associated impacts on marine food webs, and to ultimately improve our understanding of changes in marine biodiversity and ecosystems. While the spatial ‘footprint’ of a single time series may be limited, coupling observations from multiple time series with synoptic satellite data can improve our understanding of critical processes such as ocean productivity, ecosystem variability, and carbon fluxes on a larger spatial scale.

The International Group for Marine Ecological Time Series (IGMETS) analyzed over 340 open ocean and coastal datasets, ranging in duration from five years to greater than 50 years. Their locations are displayed in a world map (Discover Ocean Time Series, http://igmets.net/discover) and in the IGMETS information database (http://igmets.net/metabase). These cross‐ time‐ series analyses yielded important insights on climate trends occurring both on a global and regional scale.

At a global level, a generalized warming trend is observed over the past thirty years, consistent with what has been published by the IPCC (2013) report as well as other research. There are regional differences in temperature trends, depending on the time window considered, which are driven by regional and temporal expressions of large‐ scale climatic forcing and atmospheric teleconnections. This warming is accompanied by shifts in the biology and biogeochemical cycling (i.e. oxygen, nutrient, carbon), which impact marine food webs and ecosystem services.

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The first comprehensive analysis of in situ time series provided for the North Atlantic Ocean revealed that, despite being the most studied region of the global ocean, there are large areas in this region still lacking multidisciplinary in situ observations. However, over the 25‐ and 30‐ year analysis periods, > 95% of the North Atlantic Ocean significantly warmed and the chlorophyll concentrations decreased (p < 0.05). At the same time, negative trends in salinity, oxygen and nutrients , as exemplified by nitrate, were noted.

The analysis of existing time series showed that even in adjacent areas that appear to be relatively homogenous, there is large variability in ecosystem behaviour over time, as observed in the continental shelves at both sides of the North Atlantic Ocean. In general, over the 5‐year period prior to 2012, ~70% of the area of the South Atlantic showed cooling and 66% decreasing chlorophyll concentrations. However, over the past 30 years, > 85% of the South Atlantic increased in temperature. The paucity of in situ time series in this region, and the striking changes
that have been reported in South Atlantic ecosystems over the past two decades, highlight the need to have a better observing system in place.

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The IGMETS effort highlights the value of biogeochemical time series as essential tools for assessing, and predicting, global and regional climate change and its impacts on ecosystem services. The capacity to identify and differentiate anthropogenic and natural climate variations and trends depends largely on the length of the time‐ series, as well as on the location. Most of the ship based ecological time series are concentrated in the coastal ocean. While coastal zones in North America and Europe are being monitored, there is a conspicuous lack of biogeochemical time‐ series in other coastal regions around the world, and an almost complete absence of such observational platforms in the open ocean, which limits the capacity of analyses such as this. A more globally distributed network of time‐ series observations over multiple decades will be needed to differentiate between natural and anthropogenic variability.