Crucial to our climate and harbouring unique ecosystems in its dark depths
The North Atlantic Ocean is crucial for moderating our climate and removing CO2 from the atmosphere. NIOZ performs research on subjects like global ocean circulation, deep-sea ecosystems and palaeoceanography.
Part of the global ocean, the North Atlantic intimately links the atmosphere and bio-geosphere, while playing a major role in climate, life and economy.
The ocean’s circulation is crucial in moderating Western Europe’s climate. It also facilitates global carbon cycling, as the formation of deep water in the North Atlantic is responsible for the removal of vast quantities of CO2 from the atmosphere. The ocean margins are home to thriving ecosystems.
Increasingly, however, the North Atlantic is threatened by human activities. This poses one of the main challenges our society faces in the coming decades.
Ocean circulation research
The North Atlantic provides a critical link in global ocean circulation, with local surface waters sinking and forming the deep ocean conveyor.
NIOZ hosts an observational ocean network to study deep water formation. This includes a series of moorings in the Irminger Sea between the southern tip of Greenland and Iceland.
In this area, winter convection of cooled surface water to deeper layers has been shown to help create vertical mixing and heat transport in the ocean. Changes in circulation also affect the dissolved constituents and indirectly the organisms living in these water masses.
Ocean surface productivity
In the North-East Atlantic, a South-North geographical gradient exists, from a strong and permanently stratified system in the (sub)tropics to a seasonally stratified system in the temperate regions. This gradient provides an ideal system to investigate how productivity and composition of microbial communities are affected.
Ocean climate models predict increased stratification, enhancing nutrient limitation and consequently a shifting phytoplankton community towards smaller species. Reduced primary productivity and changes in the shares of grazing by zooplankton and viral lysis to phytoplankton loss are expected. Whether grazing or viral lysis is the dominant loss factor will determine the flow of carbon and nutrients through the food web, to either the higher trophic levels (grazing), or to dissolved organic matter and increased activity of the microbial loop (viral lysis).
Preliminary results from NIOZ research show that in general viral lysis and grazing are about equally important. However, the share of viral lysis increased with stratification towards the subtropics, indicative of a more regenerative system. This situation is expected to expand to more northern latitudes when stratification increases due to warming of the ocean surface layer. In turn, this will also have consequences for deep water ecosystems.
In contrast to common belief, the deeper parts of the North Atlantic are home to unique, thriving ecosystems, including cold-water coral reefs, sponge grounds and hydrothermal vent communities.
NIOZ studies show these ecosystems thriving at great depths in the dark and cold ocean, where food supply is limited.
Deep-sea ecosystems are not only characterised by high biodiversity and biomass, providing habitats for a wide range of invertebrates and fish, but also form hotspots of carbon mineralisation. Cold-water corals and sponges build reef systems as large as tropical reefs. Uniquely, they live without light and depend for their food supply on primary productivity at the surface ocean.
Ocean circulation also determines the availability of nutrients at the surface layer, and hence biological productivity. Ocean life depends on the prevalence of nutrients and trace metals, which influences the functioning of entire ecosystems.
NIOZ participates in large projects in the North Atlantic like GEOTRACES, whose aim is to identify processes and quantify fluxes that control the distributions of key trace elements and isotopes in the ocean. The ultra-clean water sampling system PRISTINE was developed in close cooperation with our NMF department to enable scientists to measure the ultra-low concentrations of trace metals occurring in many areas of the oceans.
Rivers and melting sea ice can enrich the ocean with nutrients and trace metals. Sahara dust transported over large distances through the atmosphere with the offshore trade winds is a potential fertilizer of the ocean as well. NIOZ traces dust originating from the Sahara desert across the whole Atlantic Ocean, with a trans-Atlantic array of moored equipment.
NIOZ also works on the analysis of deep-sea sediment cores to reconstruct the geological past.
Today the deepest parts of our oceans contain enough oxygen to support a high diversity of large animals. But in the past this has been different, when conditions similar to the Black Sea prevailed, with a widespread anaerobic bottom water layer. What caused such tipping points and what consequences did this have for atmospheric CO2 levels and the climate?
On glacial-interglacial timescales the North Atlantic has played a major role as a modulator of climate change by differences in heat transport and deep water formation. Studies on high-resolution archives of the last glacial period have shown that rapid changes in North Atlantic circulation affected the climate globally.