Tipping elements in the arctic marine ecosystem

As global temperatures rise, they can trigger tipping points in marine ecosystems.  A tipping point is defined for the purposes of this article as “the critical point in forcing at which the future state of the system is qualitatively altered.” (Duarte et al. 2012)  Basically, a tipping point is a set of conditions or change in conditions that decisively transform the marine ecosystem.  Arctic marine ecosystems are especially sensitive, and relatively small changes in conditions could effectively act as tipping points. Duarte et al. discuss how climate change could alter global temperatures enough that arctic water temperatures and ice formation cycles would be pushed past their tipping points.  Since both of these variables are interconnected with the marine ecosystem at large, this could lead to biological change and possibly biological tipping points.  If water temperature and ice formation change, it would put stress on Arctic top predators which would have “cascading” effects on other populations which may eventually affect processes like air-sea CO2 exchange.   Theoretical tipping points in permafrost levels, methane hydrates levels, ocean biogeochemistry, the Greenland ice sheet composition and formation, and in arctic terrestrial ecosystems are analyzed for their effects on arctic marine ecosystems, especially the abovementioned changes.  It is unknown when, or whether, any tipping points will actually occur but the best estimate would be within the next few decades.—Katherine Recinos
Duarte, C.M., Augusti, S., Wassmann, P. Arrieta, J.M., Alcaraz, M., Coello, A., Marba, N., Hendriks, I.E., Holding, J., Garcia-Zarandona, I., Kritzberg, E., Vaque, D., 2012. Tipping elements in the arctic marine ecosystem. AMBIO: A journal of the human environment 41, 44–55.

Duarte et al. use data from a series of other studies to discuss the possibility of tipping points in arctic marine ecosystems.  The environmental tipping points considered are: air and seawater temperature, sea ice, Greenland ice sheet and glaciers, permafrost, arctic ozone layer, human activity, boreal forest dieback, peat desiccation decomposition and burning, ocean acidification.  They have effects ranging from increasing CO2to sea level rise, to changes in albedo.  These are not predicted to happen for decades to centuries.  The biological tipping points considered are: increased primary production, shift from diatoms to picoautotrophs, enhanced community respiration relative to production, decline of calanus glaciaris, decline of apical consumers, decline in vulnerable calcifying species, and loss of sea-ice community.  They have effects ranging from structural changes in food webs to ocean acidification.  These are not predicted to happen for decades.  However, Duarte et al. admit that not enough is known to accurately date these effects or if they will take place for certain.  There are already noticeable changes taking place within these categories, but it is still unclear if tipping points or thresholds will be crossed.       
If either the environmental or biological tipping points are crossed, it could have significant effects on arctic marine ecosystems.   Duarte et al. cite multiple studies on the how changes in temperature difference and ice formation would affect primary production.  This in turn would change marine food webs and composition of species.   Loss of ice would also affect top predator populations which would have a trickle-down effect.  A drastic change in temperature, or even in many cases a more subtle one, would directly affect species at all places in the food web by causing “poleward displacement.” 
Duarte et al. state that changes in the marine ecosystem could then lead to changes in chemical and biological processes such as air-sea CO2exchange and presence of CO2in different strata of water.  As the Arctic warms, it will also be more appealing and available for human use.  A greater human presence poses all the usual risks to marine life including chemical and oil spills and overfishing.  The authors conclude by warning that even though the tipping point might not be imminent, climate change has already been reshaping arctic ecosystems.

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