Abstracts Blue Carbon

Blue Carbon



Abstract 118

Coastal carbon sinks – more than just ‘Blue Carbon’

by Tim Jennerjahn


One focus in climate change mitigation research of the past decade was on quantifying the carbon sink potential of vegetated coastal ecosystems (mangrove forests, tidal marshes, seagrass beds), commonly subsummed under the term ‘Blue Carbon’. However, the definition of ‘Blue Carbon Ecosystems’ (BCE) and, hence, the total budget of the coastal carbon sink is in debate. There are other carbon sinks in the land – ocean transition which are not yet accounted for, like, for example, coastal lagoons and tidal flats.

A major criterion in defining a BCE is that direct management action is possible to maintain or enhance C stocks and reduce greenhouse gas emissions. However, other coastal carbon sinks not classified as BCE are also affected and therefore indirectly managed by the effects of land use and land cover change (LUCC) in the hinterland and by coastal development. These affect the productivity and long-term storage in sediments of autochthonous and allochthonous carbon in the coastal ocean.

Two examples from Indonesia illustrate the relevance of other carbon sinks and the indirect management effect. The estuarine Segara Anakan Lagoon in south central Java hosts a mangrove forest and receives inputs from an agriculture-dominated hinterland. The lagoon itself has a moderate CAR with varying contributions of mangrove, hinterland and marine carbon. The hydrology and the suspended sediment load of the Brantas River in eastern Java is strongly affected by eight large dams. More than half of the potential sediment and carbon flux into coastal waters is retained in reservoirs and not deposited in mangrove forests, tidal flats and the shallow shelf in the coastal zone. Accounting for the other coastal carbon sinks and indirect management effects would increase the political and socioeconomic dimension of the Blue Carbon budget.


Abstract xxx

Past changes in and present status of the coastal carbon cycle

Tim Rixen | Nils Moosdorf | Alexandra Nozik

Leibniz Centre for Tropical Marine Research (ZMT), 28359 Bremen, Germany, Institute for Geology University of Hamburg, 20146 Hamburg, Germany
 | Leibniz Centre for Tropical Marine Research (ZMT), 28359 Bremen, Germany  |  Leibniz Centre for Tropical Marine Research (ZMT), 28359 Bremen, Germany

Data were obtained from the literature to identify past changes in and the present status of the coastal carbon cycle. They indicate that marine coastal ecosystems driving the coastal carbon cycle cover, on average, 6.4% of the Earth’s surface and contribute 55.7% to carbon transport from the climate-active carbon cycle to the geological carbon cycle. The data suggest that humans not only increase the CO2 concentration in the atmosphere but also mitigate (and in the past even balanced) their CO2 emissions by increasing CO2 storage within marine coastal ecosystems and inland waters. Since the associated carbon sink might have represented 13% of the mean joint land and ocean carbon uptake between 2000 and 2019, the underlying processes are discussed despite the complied data revealing large error ranges. Soil degradation in response to the expansion and intensification of agriculture is assumed to be a key process driving CO2 storage in ecosystems because it increases the supply of lithogenic matter that is known to favour the burial of organic matter in sediments. However, the impact on climate is still difficult to quantify because associated effects on CH4 and N2O emissions have not been established. Addressing these uncertainties is one of the challenges faced by future research, as are related issues concerning estimates of carbon fluxes between the climate-active and the geological carbon cycle and the development of suitable methods to quantify changes in the CO2 uptake of pelagic coastal ecosystems.


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