Oceans and Climate
Climate change is happening now. In the oceans we see this in physical, chemical and biological changes. Time series observations reveal increasing ocean temperatures, ocean acidification and extinction of species. Several NIVA-projects aim to monitor and understand the past, current and future ocean biogeochemistry, trying to understand the effects of climate change using new technology and modelling.
Ocean temperatures are mainly determined by latitude (degrees North or South of the equator) because the incoming solar radiation decreases towards the poles. Tropical water has the highest temperatures while the temperatures in polar waters are very low. Temperature is also carried within currents of flowing seawater, which create anomalies of ocean temperatures in some regions. In the North Atlantic, there is a hot anomaly caused by the warm North-Atlantic current which flows from the tropical regions off the American East Coast to the Nordic Seas and Greenland.
(Photo: Marit Norli, NIVA)
Colder water is denser (heavier for a given volume) and thus sinks below warmer water. As the North Atlantic current flows from the Tropics it dissipates heat on its way, getting denser and denser until it sinks and forms deep water near Greenland and between Iceland and Svalbard (Spitsbergen). This drives the thermohaline ocean circulation. Salinity also affects seawater density and the thermohaline circulation, because saltier water is more dense. Seawater salinity varies with addition (rivers, rain, ice-melting) or removal of fresh water (evaporation, ice-formation).
Water masses with different temperatures or salinities form horizontal layers in the oceans with relatively sharp boundaries. In a vertical profile we often observe a rapid decline in temperature or a rapid increase in salinity with depth. These shifts are called a thermocline or halocline respectively (or pycnocline if referring to the density gradient). The layering of water masses is called stratification, and is dependent on both temperature and salinity. These parameters are usually measured together using a CTD, which measures Conductivity (from which salinity is derived), Temperature, and Depth (as pressure).
An important reason why we measure inorganic carbon in the ocean is because of the large use of fossil fuels that began during the Industrial Revolution. Humans are about one million times more efficient at finding and burning fossil fuels than the natural biological and geological processes that formed fossil fuels. Because of our industrious nature, CO2 is rising at a rate of ~2 ppm per year and, as of now, about 1/3 of fossil fuel carbon has been taken up by the ocean. At the rate of our current fossil fuel use, CO2 in the atmosphere is projected to approximately double by year 2100. The oceanic uptake of CO2, the subsequent equilibration with in the rest of the carbonate system, and the release of protons is termed ocean acidification.
Carbonate shells are getting thinner in many species
Carbon cycling in the oceans
Carbon is a basic building block of all organic matter (and therefore life). In the ocean, carbon can exist in many forms that include both organic and inorganic forms. Organic forms consist primarily of organisms, their byproducts and degradation products (including dissolved organic carbon). Carbon in the ocean cycles between the inorganic and organic forms - most notably, inorganic carbon is incorporated into organisms such as microalgae by photosynthesis, and inorganic carbon is used together with calcium to form calcium carbonate shells by calcifying organisms such as shellfish. It is important for us to measure and understand these processes as they play important roles in determining the path and cycling of carbon in the oceans.
Changing habitats provide new opportunities for some species, while other species are pushed to escape. This causes species to invade new areas and compete with native species for food and habitat. Invasive species also transfer diseases and parasites, cause alterations to the habitat, hybridize with native species, and may in some cases push the native species to become extinct or displaced.
The pacific oyster is an invasive species in Norway. (Photo: Eli Rinde, NIVA)
The threats from invasive species are expected to increase in the future as habitats are altered by climate change and local pollution.
Adaptation to change
The oceans and the atmosphere are closely linked. Heat from the sun warms both the atmosphere and oceans, in some places (equator) more than other places (poles). Sinking cold air and rising hot air cause winds that in turn drive ocean currents and mixing processes. The ocean absorbs about 83% of the solar radiation and has slowed down the global warming of the atmosphere. Events in marine ecosystems are often determined by physical processes, but are also greatly affected by chemical processes and by interactions between species or structures in the biological communities.
Marine organisms adapt slowly to changes, and their future depends on their tolerance to changes in individual species and the interactions between them. Understanding how species are affected and the future ecological consequenses is a difficult but important task. We use a combination of labaratory studies, field studies and modeling to predict the future climate and ecology of the oceans in response to local inputs and climatic drivers.
(Photo: Marit Norli, NIVA)